TM 8-340 1 TECHNICAL MANUAL No. 8-240 WAR DEPARTMENT, Washington, July 3, 1941. ROENTGENOGRAPHIC TECHNICIANS Prepared under direction of tThei Surgeon General Cj Section I. General 1 II. X-rays; their nature and origin 2-1 III. The electron; its relation to the atom, to magne- tism, and to electrical currents 5-7 IY. X-ray machines; functioning principles, funda- mental component parts, and typical wiring ar- rangements 8-25 V. Calibrations 26-34 VI. Trouble analyses; maintenance and repair of X-ray equipment 85-36 VII. Protective measures 37-39 VIII. Auxiliary radiographic equipment 40-42 IX. Darkroom equipment 43-46 X. Radiographic quality 47 XI. Technical procedure 48-50 Page XII. Roentgenograms (figs. 38 to 109, inch) 74 Index 219 Paragraphs Section I GENERAL Paragraph Purpose and scope 1 1. Purpose and scope.—This manual is intended to serve a two- fold purpose: a general outline for a course of instruction of student X-ray technicians; and a reference text for the technician, particularly with respect to exposure factors and reminders of the gamut of pre- cautionary measures which should lead to perfection of their practice of roentgenography. Necessarily the descriptions and explanations have been limited to fundamentals. Detailed descriptions as to the construction features of various auxiliary parts which might be found on the equipment of one or another manufacturer have been avoided. It is believed that inclusion of such details would have led to too much 1 TM 8-240 1-3 confusion. Variations in designs and construction features of X-ray apparatus are today so numerous that for these aspects it is necessary to refer to descriptive literature as issued by the manufacturers and to texts which deal essentially with X-ray physics. MEDICAL DEPARTMENT Section II X-RAYS; THEIR NATURE AND ORIGIN Nature 2 ()rigin 3 Types 4 Paragraph 2. Nature.—X-rays are radiant energy. They simulate light rays, ultraviolet rays, heat rays, and even radio waves. Like them, X-rays travel at the rate of 186,000 miles per second. Names have been applied to these several types of radiant energy, from time to time, as man has become somewhat familiar with the effects of one or another group. Intricate physical testings indicate that there should be no sharp demarcation separating one band of wave lengths from another that precedes or follows it. There is an actual merging or gradation of the wave lengths and frequencies, and one type is to be distinguished from another merely in an arbitary manner. The range of wave lengths which have been assigned to the several ar- bitrary band limits is indicated in figure 1. The shortest wave lengths shown in figure 1 are designated “gamma5' rays. Some scientists believe that “cosmic rays55 are similar to these gamma rays but even shorter. Gamma rays are emitted from radium. As indicated in figure 1 some of the gamma rays are identical with some of the waves included in the X-ray band. The longer gamma rays are identical with the shortest X-rays. With the development of apparatus capable of performing at higher and higher kilovoltages, shorter and shorter wave lengths of X-ray energy are being produced, and more and more of this gamma band is being duplicated by the artificial accomplishments of man—versus the natural physical effects which occur in the element radium and other radioactive substances. 3. Origin.—When using the term “X-ray55 (i. e., roentgen ray), we are inclined to consider those rays which are produced by the bom- bardment of a stream of electrons upon a metal target in an evacuated tube. The stream of electrons constitute what was formerly described as cathode rays. It was thought that these cathode rays were actu- ally reflected from the target and that they constitute the X-ray energy. This was a misconception. Electrons are not ordinarily reflected from the face of the target nor are they changed into X-ray 2 TM 8-240 ROENTGENOGRAPHIC TECHNICIANS 3 FRta. Uld9 CM5. .01 AHSS. —i * &ETA PARTICLE EXPULSIONS AND BOMBARDMENTS OF INNER ELECTRONS 1.4'IO'SCM5yin'* i 1.4 1 1 f-6AIWA RMS-> SPONTANEOUSLY EMITTED BY RAD 1UM VALENCE INTERNED- INNER ELECTRONS ELECTRONS I ATE OR CATHODE RAT ELECTRONS IMPACTS X-RAYS 1.2 HO** 1019 120 —t 1 “ULTRA VIOLET .00008CM .00002CM 8000 4000 I THERAPEUTIC ZONE i VISIBLE SPECTRUM «- SOLAR RAYS - REACHING EARTH •3 .. -l O 2 5 CC >- > -I INFRA-RED - OR HEAT RAYS CHARGED ATOMS IN MOLECULES Figure 1.—Wave spectra, .04 CM OlCM 4 * lO" MO6 1 1 SHORT METALLIC OSCILLATORS WITH CURRENTS OF VERY HIGH FREQUENCY 300 MC IN I* 10'° 1 oo LU < 2 < NJ t— QC UJ . ZT USED IN RADIO COMMUNICATION I . . i ULTRA SHORT WAVES 30.000 I0M l< 10" 1 SHORT RADIO WAVES OSCILLATORY CURRENTS RADIO OR LIGHTNING 10 KC 550 1500 30.000 M 545 M 200M 5x10'* 5.5x10'* 2*10'* •*-h F h— COMMERCIAL BROADCAST BAND LONG RADIO WAVES 3 TM 8-240 3-4 MEDICAL DEPARTMENT energy. They produce the X-ray energy simply because of their deceleration of movement or impact upon the target. The electrons continue to move on through the target to complete an electrical cir- cuit. X-rays are energy, whereas electrons which produce them constitute a form of matter. The production of X-ray energy might be considered analogous to the production of heat which is developed because of friction when two surfaces are rubbed together. As a matter of fact, a very great deal of heat is produced simultaneously with the production of X-rays. Heat is also a form of energy. It is a form of radiant energy, and actually its wave lengths are those described in the infrared band as shown in figure 1. When generat- ing X-ray energy within an evacuated tube, much heat is produced. In fact, when operating X-ray apparatus, besides generating radiant waves of the X-ray band and of the infrared band, there are also generated the various gradations of wave lengths which constitute ultraviolet rays and even light rays. A gamut of rays is produced. 4. Types.—a. There are three general types of X-rays to be considered: Primary. Stray. Secondary (scattered). (1) Primary X-rays are those X-rays which are produced by the impact of primary electrons within the area of the focal spot of the target of the X-ray tube. Primary electrons are those electrons which are driven from the filament of the X-ray tube to the target. (2) Stray X-rays are distinguished as those X-rays which are pro- duced by the impact of primary electrons upon other than the focal spot of the X-ray tube. (3) Secondary X-rays are those X-rays which are produced be- cause of the release of, and the bombardment by, electrons which belong to atoms of a substance affected either by the primary electrons, secondary electrons, or X-rays. With this consideration, secondary X-rays might be produced in the target of the X-ray tube; they might be produced in other portions of the X-ray tube; but of much greater importance than either of these two possibilities is the third possible location of their development—within substance outside of the X-ray tube, including the tissues of the body. b. These three types of X-rays are more graphically distinguished in the section concerned with the discussion of grids. 4 TM 8-240 5 ROENTGENOGRAPHIC TECHNICIANS Section III THE ELECTRON; ITS RELATION TO THE ATOM, TO MAGNETISM, AND TO ELECTRICAL CURRENTS Paragraph General 5 Magnetism 6 Electricity 7 5. General.—a. Electrons are minute particles of matter (in contradistinction to energy). When flowing in very great quan- tities, the path of electrons can be seen, but the single electron is so infinitesimally small that it cannot be seen even by the most powerful ultra microscopes that man has been able to construct. However, on the basis of tangible physical and chemical phenomena, scientists recognize the electron to be an actual particle of matter. b. Its relationship to matter can best be understood by reviewing several basic definitions. Matter must be considered to include gases, liquids, and solids. It might be defined as anything that occupies space (and has weight). Any type of matter might be subdivided by physical means until there is uniformity in the characteristics throughout all portions of it. Such would be a break-down into a “pure substance.” It is conceivable that division upon division of any such pure substance might be made until there would be left the very smallest particle of that pure substance which still maintained all the characteristics of it. This small particle would be called a molecule. A pure substance or a molecule might be composed of a single element such as hydrogen (H2), or it might be composed of a stable combination of two or more components such as hydrogen and oxygen, as in the case of water. Thus, when pure substances are compounds, their molecules contain more than one element. Com- pounds may be broken down into their constituent elements. Today it is difficult to define an element. Chemists are inclined to consider only those pure substances which maintain their characteristics re- gardless of mechanical or chemical influences. They recognize sub- stances which are relatively stable, describing 96 elements. Physi- cists include in their considerations many transient or unstable simple- pure substances and they describe well over 300 of them. This con- fusion has led to such terms as “isotopes,” “isomers,” etc. However, if one were to consider dividing any simple pure substance into its very smallest particles, eventually there would be obtained a unit which would be the smallest possible division of the element still maintain- ing all the characteristics of that element. This unit would be an atom. To distinguish further these two units, we might consider a 5 TM 8-240 5-6 MEDICAL DEPARTMENT .-molecule of hydrogen (H2) versus an atom of hydrogen (H). A molecule of water (H20) contains two atoms of hydrogen and one atom of oxygen. An intact atom is an electrically neutral particle. However, with the gain or loss of one or more electrons, an atom devolps an electrical charge, and it is then called an “ion.” This relationship is more graphically demonstrated in the section con- cerned with electricity. c. All atoms are composed of a nucleus and one or more circulating electrons. The nucleus may be composed of a single proton (as in the case of an atom of hydrogen), or it may contain one or more neutrons plus one or more protons. No atom is large enough to be PkOTON ELECTION NEUTRON HYDROGEN ATOM ALUMI N U AA ATOM HtLIUAA ATOM BORON ATOM Figure 2.—Atomic structures, seen by any means, and yet physicists tell us that a proton has a mass which is 1,800 times the mass of an electron. We might think of a proton as being analogous to our sun, while an electron might be considered analogous to our earth, revolving about it. Following such a theme, a neutron consists of a proton and an electron (the latter being fixed in relation to the former). All electrons are identical, one with another. All protons are identical, one with another. All neutrons are identical, one with another. One ele- ment differs in characteristics from another element merely because of the number and arrangement of the protons, electrons, and (per- haps) neutrons contained in their respective individual atoms. Thus all elements are composed of the same essential “building blocks.” 6. Magnetism.—a. The exact nature of magnetism is unknown. It is believed to be due to an arrangement of the individual atoms 6 TM 8-240 ROENTGENOGRAPHIC TECHNICIANS 6 whereby their circulating electrons become fixed into uniform posi- tions with relation to their respective nuclei. Each atom might ha- considered as an individual magnet having two poles (extremities) ; its nucleus versus its electrons bearing potentials opposite, one to the other. The magnet as a whole is considered to be a composite of literally millions of these atomic magnets as shown in figure 3. b. The earth itself is a very large magnet, having a magnetic north pole and a magnetic south pole. The magnetic field of force extending between these poles explains the positioning and alinements NON-MAGNETIZED fcAIk MAGNETIZED BA*. Figure 3. of the floating needle of a compass (the latter being a very small permanent magnet). Certain substances such as loadstone (iron oxide) possess magnetic properties even as they are found in nature. When these properties of magnetism are not lost by ordinary degrees of impact or the application of moderate temperatures of heat, these substances are called permanent magnets. There are combinations, such as aluminum, nickel, and cobalt, which by themselves do not possess magnetic properties, but which after being influenced by a magnetic field of force develop into very powerful magnets. This combination (trade name “alnica”) maintains magnetic properties indefinitely after becoming magnetized. It is an artificial magnet but one which is also a permanent magnet. There are other sub- 7 TM 8-240 6-7 MEDICAL DEPARTMENT stances, such as soft iron, which do not possess the properties of magnetism, as they are found in nature, but which develop mag- netism when influenced by a strong magnetic field. Such substances are called temporary magnets. Silicon steel is another example of such a substance. It may transiently develop the characteristics of a magnet but lose those qualities when not influenced by a field of force. When the properties of magnetism are maintained by a tem- porary magnet for some length of time following the influence of a field of force, there is considered to be a lag of magnetic effect. For A FIELD OF FOP-CE >S bU I IT UP AbOUT A CONDUCTOR. WHEN ELECTIONS FLOW THRU THAT CONDUCTOR* THE FIELD Of FORCE IS INTENSIFIED bY CON CENT RAT I NO THE PATH OF THE ELECTRONS BY MEANS OF LOOPS* AN ELtCROAAAONtT CONTAINS A CORE, SURROUNDED bY A SERIES OF LOOPS Figure 4.—Electromagnet. certain performances, such as those of a core of a transformer, this Lag is detrimental. It is called “hysteresis.” c. When electrons move through a conductor, there is developed about that conductor a magnetic field of force. The magnetic field of force might be intensified by concentrating the path of the current of electrons. This can be accomplished by making a series of loops in the conductor and approximating the loops. This concentration of the magnetic field of force might further be intensified by inserting a substance, such as soft iron or silicon steel, into the field. There is developed thereby an electromagnet, as shown in figure 4. 7. Electricity.—a. The term “electricity” should connote electron mobilization. In this broad sense, there would be included the ac- tivities of photoelectrons, recoil electrons, the electron rearrangements 8 TM 8-240 ROENTGENOGRAPHIC TECHNICIANS 7 concerned with fluorescence, phosphorescence, magnetism, and ioniza- tion. However, the term usually implies the activity of an electric current. An electric current is simply the flow of electrons from one location to another. Usually, an electric current flows through a metal conductor. In such conductor, it should be considered that the electrons actually move out beyond the limits of one atomic structure and into an adjoining atom; that there is a constant re- lease of one or more electrons from individual atoms; but an almost immediate reinstatement of them from succeeding atoms. It is be- Figure 5.—Chemical battery. lieved that only the most peripherally located circulating electrons are concerned in this excitation movement. Because of replace- ments of the mobilized electrons (except in instances such as the chemical battery described below), ionization and disintegration of the conductor itself does not result. This result is counteracted when the electrons move in true circuits, as they usually do. h. An understanding of the relationship of the electron to the development of X-rays requires a consideration of the excitations and movement of electrons when actuated by a magnetic field of force. Just as it is true that when certain substances, such as soft iron or silicon steel, are subjected to the influence of a magnetic field of force, there results a rearrangement of the electrons concerned with the individual atoms to the extent of the development of mag- netic properties in that substance itself, so also it is true that when a 9 TM 8-340 7-8 MEDICAL DEPARTMENT metallic conductor, such as copper, is placed within the sphere of influence of a magnetic field of force, there result an agitation and movement of the electrons concerned with individual atoms. If a circuit of such a conductor is provided, the electrons will move through such a circuit, but they will do so only provided there be movements either of the field of force or of the conductor. Section IV X-RAY MACHINES; FUNCTIONING PRINCIPLES, FUNDA- MENTAL COMPONENT PARTS, AND TYPICAL WIRING ARRANGEMENTS Dynamos and motors 8 Types of electrical currents 9 Electrical cycle 10 Electrical phase 11 Circuits 12 Electrical units 13 Measuring instruments 14 Wave form 15 Line requirements 16 Solenoids 17 Choke coils ' 18 Rheostat 19 Transformers 20 Autotransformer 21 X-ray tubes 22 Self-rectification 23 Valve tube rectification 24 Inverse suppressor 25 Paragraph 8. Dynamos and motors.—a. The factor of movement, either of the magnetic field of force or of the electrons, is particularly well demonstrated by the functioning of a dynamo (electrical generator) or the principles of a motor. h. One might consider a dynamo as a device designed to convert mechanical energy into electrical energy. Such a definition is of course fallacious for today we do not think of electrical energy, but instead we realize that actual particles of matter, the electrons, are induced to flow. The mechanical energy referred to in this widely used definition is the energy which causes the armature of the dynamo to revolve. Falling water, steam, or even electrical devices may be utilized. The essential consideration is that a portion of a metallic conductor, forming an open loop (the armature) and a small seg- ment of a complete circuit, is mechanically revolved in a magnetic 10 TM 8-340 ROENTGENOGRAPHIC TECHNICIANS 8 field. This open loop is positioned so that with revolution of it there results the maximum cutting across the lines of force concerned with the magnetic poles. Having movement and the field of force, elec- trons contained in the individual atoms of the armature are excited to move, and with the provision of completion of a circuit, they travel through the commutator to the community line. AAECHAHICAL PoWEk MA6NET INTENSIFIED BY COILS COMMUTATOR RINGi WLUSH SHAFT 'ARMATURE COMAM/'MlTV LINE DYNAMO ® Half-ring commutator suitable for pulsat- © Two-ring commutator suitable for alter- ing direct current. nating current. Figure 6.—Dynamo. As indicated in figure 6, either alternating current or pulsating direct current might be generated by a dynamo, depending upon the design of its commutator. When one pole of the magnet constantly influences one terminal of the external circuit, while the other pole of the magnet constantly influences the other terminal of the external circuit (as shown in fig 6®), there will result a pulsating direct type of electron flow in the external circuit. If each terminal is influenced first by one pole and then by the other pole of the magnet (as indicated with the type of construction of the commutator shown in fig. 6@), there will result an alternating type of electron flow in the external circuit. c. In contrast to the principles concerned with the functioning of a dynamo, a motor might be considered as a device designed to con- vert electrical energy into mechanical energy. More definitely, be- cause of movements of electrons, there is developed a field of force; and because of alternations in the direction of movements of elec- trons, there is an expansion and collapse of this field of force. Thus, 11 TM 8-240 8-9 MEDICAL DEPARTMENT in the case of a motor, the movement of the electrons produces move- ment of the field of force; and the movement of the field of force produces revolution of the armature—which in the case of the motor consists of magnetic poles. d. Just as dynamos may develop either alternating or pulsating direct types of current flow, depending upon the construction features of their commutators, so also motors may be designed for operation on either alternating or pulsating direct types of current flow, depending upon the construction features of their commutators. 9. Types of electrical currents.—Four types of electrical cur- rents might be considered: a. A continuous direct current is one in which the electrons travel steadily in one direction. This type of current has been called a galvanic current. It is the type of current produced by batteries. h. A pulsating direct current is one in which the electrons move in one direction but not quite as steadily, as in the case of a continuous direct current. Instead, in the case of a pulsating direct current, some electrons begin to move and very quickly more and more of them are moving but then, after reaching a peak (considering the number of electrons moving), less continue in motion, and then there follows a repetition of this acceleration and deceleration. This is the type of electrical current produced by a dynamo having a commutator of the design shown in figure 6(T). c. An alternating current is one in which the electrons move first in one direction and then in the opposite direction. There are incre- ment and reduction as to the number of electrons flowing, as considered in the case of pulsating direct current. However, in the case of alternating current, the accelerations and decelerations of electron movements extend all the way from and to the base line; and moreover these waves are directed first in one direction and then the opposite, changing with every alternation. d. The term “unidirectional’' is applied to those currents where there is conversion of an alternating current (rectification) so that all pulsations of electron flow move in the same direction—full wave, or there may be an inhibition of every other pulsation (i. e., alterna- tion)—half wave. With the use of valve tubes (thermionic rectifica- tion), full wave rectification is productive of wave forms which extend practically from the base line to peak levels, comparable to those of pulsating direct current. Prior to the use of valve tubes, this rectifi- cation was accomplished by the use of a rotating disk or cross arm terminals, in which instances only a portion of each wave became effective. These comparisons are shown in figure 7. 12 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 10 10. Electrical cycle.—The design of the dynamo and the speed of rotation of its armature govern its cycle performance. A cycle might be considered as the electron movement induced by the full elfect of each of two magnetic poles (of opposite potential). The term is usually applicable to alternating current, in which case one cycle is equal to two alternations. With the same considerations, in the case of pulsating direct current, one cycle is equal to two pulsa- tions. Today most communities are supplied with 60-cycle current. With such, there are 60 cycles per second; 60 episodes wherein the CONTINUOUS direct current PULSATINC7 DIRECT CU^ENT ALTfc(LNATINO CURRENT » rvi/ia MECHANICAL THERMION! C fUU. WAVE UNIDIRECTIONAL CURRENT HALT WAVE UNIDIRECTIONAL CURRENT Figure 7.—Electrical currents. electrons are excited to movement by the full effects of each of two magnetic poles, and therefore 120 alternations. Some communities are supplied with 50-cycle current, in which case there would be 50 episodes of magnetic pole influences or 100 alternations per second. A few communities in the United States still utilize 30-cycle current while in such places as the Canal Zone 25-cycle current is used. Trans- formers and other component parts of X-ray equipment are designed and constructed to function on a particular cycle. Usually, when equipment is designed to function on a relatively low cycle current, it will also function with current of higher cycle, though not as ef- ficiently. When equipment is designed to function with a relatively high cycle (i. e., 60-cycle), and it is connected into a line of relatively 13 TM 8-240 10-13 MEDICAL DEPARTMENT low cycle (i e., 25-cycle), it is likely to burn out, particularly because the impedance in the cores of the transformers is insufficient. It is therefore important that the cycle of the electrical supply be known and that the design of the X-ray equipment be proper. 11. Electrical phase.—The design of the dynamo also controls the phase performance. The term “phase” is used to signify the relative number of magnetic pole effects "with relation to each cycle. It might be considered as a particular electrical time degree of a segment of a cycle. For most X-ray equipment single phase current is used. It is produced when the entire electron movement over the period of a cycle can be accounted for on the basis of only two I CYCLE - SINGLE PHASE •“ =SINGL€ -PHASE WAVES -TWO PHASE WAVES Figure 8.—Three phase alternator waves. arotirr+.;=r rTHP.EE PHASE WAVES magnetic pole effects. During this same time interval it is pos- sible that other pairs of magnetic pole effects may be superimposed as shown in figure 8. 12. Circuits.—The term “circuit” really refers to a complete path of electron movement from and to the site where the excitation of movement developed. When devices are connected into a circuit so that they constitute a portion of this path, they are said to be con- nected in series. When these devices are connected as a bridging across a portion of this path, they are said to be connected in parallel. This latter relationship must necessarily be relative to other compo- nents in the circuit. 13. Electrical units.—a. The term “ampere” as used in roent- genography might be considered as the unit of quantity of electron movement. Actually it is the unit of intensity; it signifies quantity of current per unit of time. For instance, it is that quantity of current which will deposit silver from a silver nitrate solution at the rate of 0.0011182 gram per second. The actual unit of quantity 14 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 13 is the coulomb, but this term is not used in roentgenographic par- lance, ampere being generally used synonymously for it. h. A milliampere is 1/1000 of an ampere. The current of the high tension circuit of roentgenographic equipment is measured in terms of milliamperes. c. The volt is the unit of electrical pressure. It is the unit of force which causes electrons to move against resistance. Actually, it is that amount of potential (energy) required to overcome a resistance of 1 ohm in a conductor carrying 1 ampere of current. oi u d 3 o VA t- Z LU d cL 3 O ® Series. UJ O cL 3 o \s\ i- z ui d d 3 U ® Parallel. Figure 9.—Circuits. d. A kilovolt is equal to 1,000 volts. The potential of the high tension circuit of roentgenographic equipment is measured in terms of kilovolts. The values are commonly described in terms of Kv. P. (kilovolts peak) or P.Kv. (peak kilo voltage), since these high poten- tials are usually measured with sphere gaps, and the peak values are the ones considered. For a more complete discussion of these ex- pressions, see the descriptions of average, effective, and peak values (par. 156), 15 TM 8-240 13-14 MEDICAL DEPARTMENT e. The ohm is the unit of electrical resistance. It is the resistance provided by a column of mercury 106.3 cm. long and having a mass of 14.4521 grams at 0°C. /. A megohm is equal to 1,000,000 ohms. The intratubal resistance of a valve tube is in the order of megohms. g. The watt is the unit of electrical power. Watts measure the product of the volts times the amperes; 746 watts are equivalent to a horsepower. h. A kilowatt is equal to 1,000 watts. It is equal to l1 horse- power. 14. Measuring instruments.—a. Most instruments for measur- ing electrical units are constructed on the basic principles of a galvanometer. A galvanometer consists of a freely rotating coil of wire, mounted on a pivot and encircling a pointer. The movement of the pointer depends upon the intensity of a field of force which is developed because of the flow of electrons within the coil. h. An ammeter is designed and calibrated to measure amperes. It is constructed with very little internal resistance, and it must be connected in series relationship to the circuit as a whole. c. A milliammeter is of design and construction very similar to that of an ammeter but calibrated for the measurement of milliamperes. It also must be connected in series. d. A voltmeter differs from an ammeter or a milliammeter by having constructed into it a high internal resistance and being calibrated to record volts. Since it is designed to measure pressure or the difference in potential, it must be connected “across the line.” This explains why a high internal resistance must be incorporated into it. Figure 10 is intended to distinguish these differences in construction features. e. A meter is used to measure watts. To connect it into a circuit, four connections are required for it is actually a combination ammeter and voltmeter. It is very important that the ammeter binding posts be connected in series relationship, while the volt- meter binding posts be connected across the line. /. A ballistic meter is an instrument designed to measure ampere values in terms of duration of time (to extent of 1 second or less). The principle of operation of ballistic meters invokes inertia and momentum. g. Sphere gaps are used to measure kilovolts peak. Kilovolt- meters are used for this same purpose in some experimental labora- tories, but the internal resistance required in such meters is so large they are not practical for use with radiographic equipment in the 16 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 14 Calibrated SCALE ' PeR-MANEMT Maonet 'Eearjnjc? Rotating x COIL Scale y LOAD., SHUNT D. C. AMMETEk A.C. AAAAAETEk, IRON COKE'’ COIL' Figukh 10.—Measuring instruments. 3Dnnos j.N3mjro LOAD A - C • VOLTMETER D. C. VOLTMETER Ol -I U VA RESISTANCE IKON CORE COIL CALI &RATED SCALE _ RESISTANCE " MAGNET — -I 5 O 0 z 1 o c£ source CURJLENT 318009°—41 2 17 TM 8-240 14-15 MEDICAL DEPARTMENT average laboratory. Oftentimes the voltmeter which is mounted on the control stand is referred to as a kilovoltmeter, but it is not. It is connected across the primary circuit of the high tension trans- former; it actually measures volts though it may be calibrated in terms of kilovolts, 15. Wave form.—a. Various types of electrical currents have been discussed. Continuous direct current has been distinguished from pulsating direct, and each of these has been compared with alternating and unidirectional types. h. The plotting of a continuous direct current indicates constancy of current flow and therefore a single measurement value. In con- trast to this, the plottings of each of the other three types indicate variations in current flow from moment to moment. They are pul- sating currents and for them the question arises as to what value MAXIMUM on PEAK .707 E FFECT1VE. .kVo AVERAGE. Figure 11.—Pure sine wave showing projection from segments of a circle and relative planes representing measurement values. should be measured. One might consider the maximum or peak value—representing the value at the peak of the pulsation. This is actually the value measured with proper use of sphere gaps. However, since this value does not represent the total summation, taking into consideration all moments of the cycle or half cycle, another measurement may be preferred. This is called the effective value and is described as the root mean square value. It is the value recorded by meter readings. Still another value is to be considered— the average value or continuous direct current equivalent. These three measurement values are indicated in the plotting of a sine wave. (See fig. 11.) (1) Knowing one of these values, in the case of a pure sine wave, it is possible to compute either of the other two. The maximum value is equal to 1.41 times the effective or 1.57 times the average. The effective is equal to 0.71 times the maximum or 1.11 times the average. The average is equal to 0.64 times the maximum or 0.90 times the effective. 18 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 15-19 (2) These wave forms apply both to the amperage and to the voltage. It is only under ideal conditions that the actual function- ing wave (the combination of the amperage wave and the voltage wave) is a true sine wave. Considerable distortion of wave form is likely to prevail in the wave form of circuits having an inductive type of load, such as produced by transformers. Because of such loads, in the case of X-ray apparatus, the voltage wTave may not coincide either as to time or shape with the amperage wave, in which case there would result distortion of wave form. Each unit might be considered to have its own particular wave form. This explains some of the variations in radiographic performances. As much as 30 to 40 percent difference has been found in comparing the X-radia- tion performance of one unit with that of another, using identical technical factors and correcting for meter variations, etc. 16. Line requirements.—One of the first considerations should concern the line supply and wiring into the building. High capacity equipments have been purchased without the realization that their loads would be more than could be tolerated either by the pole transformer or by the dimensions of wfire used for leads into the building. These requirements will vary according to the particular efficiencies of transformer designs, but average requirements are as indicated in table I. 17. Solenoids.—In order to understand the functioning of vari- ous essential parts of an X-ray machine, it is necessary to consider the principles involved in a solenoid or helix. As mentioned elsewhere in this text, when electrons flow through a conductor, because of their movement there is built up about that conductor a magnetic field of force. This magnetic field of force can be concentrated by making a series of loops. This constitutes a solenoid. 18. Choke coils.—The magnetic field of force which is developed about a conductor when electrons flow through it tends to restrain the movement of the electrons. There is actually the paradoxical effect of a force tending to inhibit the very cause of its origin. If this field of force is sufficiently intensified—by means of concentrated loops and a core, there may be accomplished almost complete inhibition of elec- tron flow. This arrangement of utilizing an adjustable core (tem- porary magnet) within the magnetic field of force provided by a solenoid is called a choke coil. Choke coils are used particularly in the primary circuit of the filament transformers. There they serve as filament regulators. 19. Rheostat.—Oftentimes a rheostat is used as a substitute for a choke coil. A rheostat, essentially, is nothing more or less than a poor 19 TM 8-240 19 MEDICAL DEPARTMENT (1) Machine capacity (milliamperes) (2) Peak kilo- volt- age (3) Nominal line volt- age (4) Trans- former load (Kv.- A.) (5) Wire size (B.&S.), trans- former to switch (6) Wire size (B. & s.), switch to con- trol (7) Ground wire (8) Fuse capac- ity (am- peres) (9) Line switch capacity (amperes) Self-rectified; 10 85 100-130 1. 5 8 8 15 Base reception. 30 85 100-130 5. 0 6 8 40 60. 100 85 208-240 15. 0 4 6 8 70 100. Full wave: 200 85 208-240 15. 0 4 6 8 70 100. 500 85 208-240 25. 0 00 3 6 180 200. 1,000 85 208-240 50. 0 300, 000 0 4 350 400. Three phase: 500 85 208-240 3-15 3 4 8 100 200. 1,000 85 208-240 3-25 00 3 6 200 200. Table I.—Power supply requirements NOTES 1. The above specifications are the minimum requirements for a single X-ray machine of the rating specified. 2. They are based on a normal line regulation of 2 percent when the X-ray machine is not in operation. 3. The wire sizes in column (5) are based on a run of 100 feet. If the run is 200 feet, double the wire size. 4. The wire sizes in column (6) are based on a maximum run of 10 feet. 5. If more than one X-ray machine is to be used, or additional load is contemplated for the future, larger wire and transformer sizes must be specified for satisfactory operation. WIILE LINES of fORCt Figure 12.—Solenoid. IRON CORE I SCREW I lAQjUSTMtMd Figure 13.—Variable choke coil. 20 TM 8-240 19-20 ROENTGENOGRAPHIC TECHNICIANS conductor of electricity. It offers resistance to the flow of electrons. Ordinarily some means of adjustment is provided so that more or less of this resistant conductor can be introduced into the circuit. In this respect a rheostat differs from a true resistor. Rheostats may be used as filament regulators in either the primary or the secondary filament circuits. For roentgenotherapeutic equipment they are usually in- corporated into the primary circuit of the high tension transformer. 20. Transformers.—a. General.—The physical effects described in the case of the choke coil are utilized in the functioning of trans- formers. A transformer serves as a functional connecting link between two entirely independent electrical circuits. Actually there is no elec- trical connection provided between these two circuits. The design of a transformer is very much as if a choke coil connected into one PWfAAW WINDING? SECONDARY WINDING SfcCONDAW 5 WINDING PRIMARY WINDING ® Step-up. Figuke 14.—Transformers. ® Step-down. circuit were approximated to a choke coil connected into another cir- cuit. The approximation of these two choke coil arrangements must be such that the field of force produced by the electrons moving in the one circuit will excite the movement of electrons in the second circuit. The strength and influence of the field of force of the primary circuit are intensified by utilizing a closed core—a temporary magnet such as soft iron or silicon steel which is constructed not as a bar but, instead, usually of thin strips arranged in laminations in the form of a rectangle or doughnut. b. /Step-up.—When the number of turns in the secondary winding is greater than the number of turns in the primary winding, the trans- former is described as being a step-up transformer. This term refers to the increase in voltage. The voltage of the secondary circuit bears a relationship to the voltage of the primary circuit approximately as the number of turns in the secondary winding bears a ratio to the number of turns in the primary winding. c. Step-down.—When the number of turns in the secondary circuit is less than the number of turns in the primary circuit, the result 21 TM 8-240 20 MEDICAL DEPARTMENT is the opposite. There are then fewer turns of conductor (i. e., actually less length of it) in the secondary circuit to be influenced by the fluctuating field of force of the primary, and as a consequence there is a reduction in voltage. This is the arrangement in a step- down transformer. The term refers to a decrease in voltage. d. Windings.—In the case of a step-up transformer, the primary winding consists of relatively large copper wire because it must ac- commodate relatively large current capacities. The secondary wind- ing is constructed of very small gage copper wire because it is intended to accommodate much less current. The very opposite re- lations as to gage of copper wire used for the primary and for the secondary windings, respectively, in the case of a step-down trans- former hold true; namely, the primary winding ordinarily consists of relatively small gage wire, while the secondary winding consists of relatively large gage. e. Perfornumce.—The design and construction of transformers are very complicated engineering problems. There are numerous factors which govern their efficiency of performance. By efficiency is meant the current consumption (in terms of wattage) of the pri- mary circuit as compared with the total current induced (i. e., avail- able) in the secondary circuit. Most transformers designed for func- tioning with X-ray apparatus are of relatively low efficiency; they show an efficiency or power factor from as low as 38 percent to barely more than 48 percent. The efficiency of transformer function might be gaged in terms of wave form. Transformers incur induc- tive types of loads which tend to alter the wave form of the current. With roentgenographic equipment these alterations (distortion of wave form) are directly concerned with X-radiation performance. Though P.Kv. (peak kilovoltage) values be controlled, for the very same milliampere second values, the X-radiation performance of one unit may differ considerably from the X-radiation performance of another unit. Moreover, in the case of a poorly designed trans- former the wave form is likely to be altered when it is operated at a high milliamperage setting as compared with operation on a low milliamperage setting. A load which exceeds the ideal capacity of the transformer will cause distortion of the wave form so that even though identical milliamperage-second values may be imposed, and even though the peak kilovoltage values may be the same, the X-radiation performance will be less than that obtained at a lower milliamperage setting—one that is easily accommodated without dis- tortion of the wave form. However, even though the load (milli- amperage setting) is well within reasonable capacity limits, there will 22 TM 8-240 20-21 ROENTGENOGRAPHIC TECHNICIANS occur some voltage drop for an increase in the load (i. e., milliam- perage) of the secondary circuit. This fact makes it important that kilovoltage calibrations be accomplished in terms of the useful milliamperages. 21. Autotransformer.—a. An autotransformer consists of a single winding or series of loops of copper wire which provide a com- mon path for two independent circuits. Usually this copper wire is of large gage in order to eliminate the production of heat which would otherwise result from resistance to the flow of an appreciable quantity V-3 V-l .V-2 PR.IMARY CIRCUIT SECONDARY CIRCUIT (Line Voltage Compensator Side) (Volt Selector Side) Figure 15.-—Autotransformer. of electrons in it. Autotransformers are connected across the line, and if it were not for the intense field of force provided by their large core there would result an actual short circuiting. The field of force is so great that electrons concerned with atoms of the copper winding itself are excited to flow in a direction opposite to that of the electrons of the primary current. All that is necessary for actual current flow of these secondary electron mobilizations is that leads be provided and that a secondary circuit be completed. The voltage of this latter cir- cuit bears a relationship to the voltage of the primary circuit as the number of turns utilized in the secondary circuit bears a ratio to the total number of turns incorporated in the entire autotransformer. b. It has been said that an autotransformer is always a step-down transformer in effect. This is not necessarily true, for as shown in figure 15, it is possible to utilize in the primary circuit less than the total number of turns incorporated in the autotransformer. It will be noted that this figure takes into consideration 3 voltmeters, VI, V2, and V3. When the control at A is adjusted as indicated so that less turns are utilized in the primary than are incorporated in the 23 TM 8-340 21-22 MEDICAL DEPARTMENT entire autotransformer, the voltage across the entire number of turns, as indicated on voltmeter 2, will be greater than the voltage recorded on voltmeter 1, and the relationship will be approximately a propor- tion consistent with the number of turns utilized in each instance. If the controls B and C should be adjusted so as to utilize the entire num- ber of turns of the autotransformer, the end result would be a step-up in voltage. It will be noted that the control B is such as to utilize steps of a single winding or loop, whereas the control C is such as to utilize steps of a number of windings or loops. In this way, the con- trol B represents the minor control of the autotransformer, whereas the control G represents the major control. It is practical to consider the secondary circuit of an autotransformer as the volt selector side of it, for by making adjustments in this circuit by means of controls such as B and C, there can actually be selected the desired voltage value for application to another component part of the equipment, such as to the primary winding of the step-up transformer. When adjustments are provided in the primary circuit of an autotransformer, as indicated with the use of the control A, this instrument will also function as a line voltage compensator. The voltmeter V2 then becomes a line voltage indicator. 22. X-ray tubes.—a. General.—X-rays have been produced with tubes of various designs and with various types of generating appa- ratus. The discovery of X-rays in 1895 by Wilhelm Conrad Rontgen CATHODE ACTUAL TAHOE T PARTIAL VACUUM ANODE Figure 16.—Roentgen’s tube. was accomplished with the use of a Hittorf tube which was a modifica- tion of a Crookes tube. Such tubes contained a partial vacuum. Partially evacuated tubes were in common usage for several decades fol- lowing the discovery of the X-rays. The main objection to these par- tially evacuated tubes was that they were not consistent in performance. This was due to the fact that the resistance which existed between the terminals within the tube varied according to the degree of ioniza- tion of the gas contained. Conduction of the electrons (cathode rays) 24 ROENTGENOGRAPHIC TECHNICIANS TM 8-340 22 took place as soon as ionization was produced because of the potentials (negative, at the cathode; positive at the anode) developed at the two terminals. The ease of this conduction increased as ionization pro- gressed, and since ionization of the gases progressed with continued usage of the tube, the resistance between the terminals (i. e., the intra- tubal resistance) progressively decreased and thereby the degree of impact of the electrons became less and less. As a consequence the production of X-radiation varied both as to quantity and quality. Some of these tubes had one degree of vacuum; some another. It was necessary to have a collection of tubes in an X-ray laboratory; tubes of various degrees of hardness (referring to the shortness of wave length of the X-rays produced in relation to one or another degree of vacuum). One tube was used for one thickness of the body, another tube for another. Unfavorable as this might seem, it was even more annoying that the performance of any one tube was not steady. h. Modem.—In 1912, Coolidge invoked two important principles which even today are used in the construction of an X-ray tube. These principles include a complete vacuum and provision for thermionic control of current flow. A perfect vacuum offers complete resistance to the flow of electrons. Modern X-ray tubes are therefore as com- pletely evacuated as man can accomplish. Even the metal parts which are to be contained within the tube are degassed. When using these tubes the resistance of this vacuum is reduced by heating one of the terminals, the cathode, for with a certain quantity of heat applied to a conductor (approximately 500° C. in the case of tungsten), mobilized electrons will move out beyond the limits of the conductor. Coolidge selected tungsten for this purpose because of its very high melting point. To provide for its heating, the tungsten was drawn to wire- like dimensions, as in the case of modern electric lamps, and a separate heating circuit was supplied. This is called the filament circuit. It is completed through the filament itself without involving the target or anode terminal of the tube at all. These relations are indicated in figure 17. It is important to realize that the quantity of electrons per- mitted to flow across the gap and between the cathode to the anode ter- minals of this X-ray tube is dependent upon the degree of heating of the filament of the cathode. Thus, regulation of the filament circuit actually controls the quantity of electrons flowing across the tube— the high tension circuit. To this extent, the filament regulator might be said to control the quantity of X-ray production. c. Capacities.—(1) However, even with the support of valve tubes, there is a limit to the amount of heat that can be tolerated. This limit is described as the tube capacity. In general, the larger the 25 TM 8-240 22 MEDICAL DEPARTMENT dimensions of the actual focal spot of the tube, the greater will be its heat unit capacity per unit of time, and the greater will be its milliamperage tolerance. With a smaller actual focal spot dimen- sion, this same tube will tolerate the same total number of heat units, but it will not tolerate as high a milliamperage setting. As men- tioned in describing the types of X-rays, the focal spot of an X-ray tube is that limited portion of the target designed to receive the impact of the primary electrons (the cathode rays). The relation- ship between the actual focal spot and the effective focal spot is LINE SOURCE RHEOSTAT STEP - DOWN trans- former X-lkAY TUBE ■FILAMENT CIICUIT Figure 17. circuit. shown in figure 18. Many radiographic tubes contain a double focus arrangement whereby one or the other focal spot dimensions may be utilized. The dimension of the effective focal spot is an important factor in relation to the detail which can be obtained on the roentgenogram, as discussed in the section concerned with technical factors which govern quality. (2) (a) For diagnostic tubes, there are two kinds of capacity: 1. The maximum load (i. e, milliamperage) for any one individual exposure. 2. The summation of heat units—represented by all the ex- posures made by a tube during a given working period. (6) The individual exposure load ratings are determined largely by the size of the focal spot of the tube regardless of other fea- tures of the design of the target. Rotating anode tubes are excep- tions. They have much higher ratings for a given focal spot size than do stationary anode tubes. However, within their own cate- gory, the individual load ratings of rotating anode tubes are also determined largely by focal spot size. It is customary to establish 26 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 22 technique factors for exposures of any given part of the body in terms of a fixed milliamperage and time. For certain cases, notably chest exposures, it is desired to make the milliamperage as high as possible so that the time may be as short as possible. For most other exposures, a greater amount of X-ray energy is required, and a longer time factor is usually employed with a lower milliamperage factor. In tables II and III, milliamperage tolerances for each focal size TUNGSTEN BUTTON \ COPPER 'ANODE' FILAMENT TARGET ACTUAL FOCAL SpOT ' EFFECTIVE fOCAL SpOT - Figure 18.—Heat storage capacity. are indicated. Four different figures are given in each case; two for cases requiring very short exposures, as for chests; and two for the routine requirements of the longer exposures, as with the use of grids. Under each heading the figures in column (A) represent the maximum milliamperage that it would be safe to employ rou- tinely where it is desired to cut exposure times as much as possible, and exceptional care should be taken to set the currents accurately, etc. The figures in column (B) represent normal working values to insure good tube life and allow a certain amount of leeway for errors. Since these tolerances differ when half wave (including self-rectification) is utilized rather than full wave, two tables are given, one for full-wave rectified generators and one for half-wave generators. These values might serve as a general guide in the selection of focal spot size. However, in actual operation, the tech- nique factors to be employed should always be checked against the 27 TM 8-340 22 MEDICAL DEPARTMENT rating charts supplied with the tube to make sure that the tube ratings are never exceeded. Focal spot size—mm.2 Chest exposures Bucky exposures (A) (B) • (A) (B) Stationary anode: 1.5 Milliamperes 25 Milliamperes 20 Milliamperes 20 Milliamperes 15 2.3 _ 75 60 40 30 3.2 120 100 60 40 3.8 200 150 75 50 4.2 250 200 80 60 5.0 350 250 100 60 Rotating anode: 1.0 200 150 75 50 2.0 500 400 100 60 Table II.—Full-wave generator, milliamperage vs. focal spot size Table III.—Self-rectified generator, milliamperage vs. focal spot size Focal spot size—mm.1 Chest exposures Bucky exposures (A) (B) (A) (B) 1.5 __ Milliamperes Milliamperes Milliamperes 15 Milliampert 10 2.3 40 30 30 25 3.2 60 50 40 30 3.8 100 75 50 40 4.2 100 80 60 50 5.0 100 100 60 60 Courtesy Machlett Laboratories, Inc., Springdale, Conn. (c) The heat which is generated by an X-ray exposure is almost immediately removed from the focal area by conduction into the body of the anode structure, where it is stored while being gradually dis- sipated. This dissipation of heat is by means of radiation into the surrounding medium and by conduction in air, water, or oil which may be used as a cooling medium. The anode structure of the tube may become overheated if a number of exposures are made which repre- sent a total amount of heat in excess of the heat storage capacity of the anode. To avoid this condition, it is necessary to know the heat storage capacity of the anode and the heat-dissipation characteristics of the tube. These properties of the tube are usually published by 28 TM 8-240 22-23 ROENTGENOGRAPHIC TECHNICIANS the manufacturer. The amount of heat involved in an exposure is usually expressed in terms of arbitrary units described as heat units (the product of the peak kilovoltage times the milliamperage times the time in seconds). If the total number of heat units involved in a series of exposures to be made in rapid succession exceed the heat storage capacity of the anode, it will be overheated unless sufficient cooling intervals are allowed between exposures to allow for the dis- sipation of the excess amount of heat. A study of the heat-dissipation characteristics is necessary to indicate the length of cooling intervals required. 23. Self-rectification.—With this arrangement, as long as the target of the tube remains relatively cool (i. e., less than 500° C.), and when alternating current is supplied to the terminals of this tube, only RESISTANCE (VA R, I /». & I- E ) ■STEP-DOWN X-KAV TU&E STEP-UP PRIMARY i RADIATOR Figure 19.—Simple self-rectified X-ray circuit (with combination transformer) those alternations which are directed to the filament terminal are able to get across the gap. Those alternations which are directed to the target terminal are inhibited. The result is self-rectification. A half-wave unidirectional current is produced. With provision for this type of function on the part of the X-ray tube, an X-ray machine unit may consist of no more than a main switch, a combination (step-up and step-down) transformer, a resistance wire (serving as a rheostat), and the X-ray tube. This is the design of the mobile unit used in the World War, When self-rectification is imposed upon an X-ray tube, special construction features are ordinarily provided for dissipation of heat which is pro- duced in the target. Even though various construction features are incorporated into X-ray tubes, such as radiator fins, water or oil cir- culation, etc., nevertheless because of this danger of excessive heat accumulating in the target, the capacity of any tube must necessarily 29 TM 8-340 23-25 MEDICAL DEPARTMENT be less when self-rectification is imposed upon that tube. Unfor- tunately, when electrons bombard a target, not only X-rays are pro- duced but there is a great production of heat rays (it is estimated that only about 0.4 percent of the energy is of the nature of X-rays, while more than 99 percent of the energy is converted into heat). The re- sult is that before very long sufficient heat accumulates in the target of the tube to force electrons into space beyond the limits of the target structure, and thereby the resistance of the vacuum is counter- acted in both directions. The filament of the tube cannot tolerate the bombardment by the electron stream. It is rather delicate and quickly destroyed. 24. Valve tube rectification.—That portion of the target nor- mally receiving the impact of the electron stream is usually con- structed of tungsten. In the case of some X-ray tubes the entire target is constructed of tungsten. Since tungsten is not as efficient in conducting heat as copper, the latter is used by several of the manufacturers for the construction of much of the target (i. e., anode) terminal. The accumulation of heat is detrimental regard- less of whether or not the X-ray tube is required to provide for its own rectification. In some equipment, as shown in figure 20, addi- tional tubes called valve tubes are inserted into the circuit to incur the action of rectification. These tubes are not constructed exactly as are X-ray tubes, but they are designed on thermionic principles, and thereby serve to protect the X-ray tube. 25. Inverse suppressor.—In the case of certain relatively low milliamperage capacity units (10 to 30 milliamperes), instead of incorporating valve tubes in the high tension circuit for the pur- pose of rectification, an inverse suppressor may be connected into the primary circuit (concerned with the high tension transformer). The purpose of inverse suppressors is to limit partially the ampli- tude of voltage effective upon the target terminal of the X-ray tube. Inverse suppressors may be constructed on the principle of a thermionic tube or on the principle of crystal rectification. In either instance, there is provided a shunt resistance in a position parallel to the rectifying component. This shunt resistance pro- vides for the flow of a small quantity of current in the unfavorable direction so as to provide for demagnetizing the core of the high tension transformer (i. e., offsetting transformer lag), and thereby increasing the amplitude movement of the magnetic field of force and the efficiency of the transformer over that which would be obtained in case a true half-wave pulsating unidirectional current were supplied in the primary circuit. This performance is indi- 30 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 25 FILAMENT TRANS. X-RAY \TUBE > AUTO TRANS. POWER TRANS. (motor.) RECTIFYING OlSR. ® MECHANICAL FULL-WAVE RECTIFIED UNIT flLAMENT TRANS. HIGH TENSION TRANS., XRAY TU&E 1 VALVE TUBE AUTO TRANS. VALVE TUBE TRANS. @ SINGLE-VALVE HALF-WAVE RECTIFIED UNIT FILAMENT TRANS. VALVE TUBES X-RAY TUBE AUTO TRANS. POWER. TRANS. (D fOUk-VALVt fULL-WAVE RECTIFIED UNIT VALVE TUbE TRANS. Figure 20.—Valve tube rectification 31 TM 8-240 25 MEDICAL DEPARTMENT WAVE EFFECT (ON PRIMARY Of HIGH TENSION TRANSFORMER) EFFECTIVE ALTERNATION demagnetizing alternation RESISTANCE SHUNT PLATE-CRYSTAL TYPE Figure 21.—Inverse suppressor function. COPPER OXIDE crystals METALLIC COPPER Direction of current flow FOR DEMAGNETIZING ALTERNATION THERMIONIC TYPE HOT FILAMENT VAPOR MERCUPA direction of current flow for MAGNETIZING ALTERNATION 32 TM 8-240 25-26 ROENTGENOGRAPH1C TECHNICIANS cated in figure 21. Inverse suppressors are usually used when it is necessary to reduce the bulk and weight of the high tension trans- former to a minimum, as for instance when the high tension trans- former is contained with the X-ray tube. Small transformers necessarily have relatively poor regulation. In performance, the difference between the voltage for the alternations carrying the load versus the voltage developed by those alternations not carrying the load may be as great as 15 to 20 P.Kv. for load considerations of 25 to 30 milliamperes. The construction features in the tube head (i. e., spacing, oil content, etc.) may not tolerate such no-load potentials. It is to compensate for these construction features or to protect shockproof cables that inverse suppressors are utilized. Section V CALIBRATIONS Paragraph General 26 Kilovoltage calibrations 27 Milliamperage 28 Timer 29 Distance 30 Dimensions of the effective focal spot 31 Quantity of X-radiation 32 Grids 33 Cassettes 34 26. General.—There are certain performance characteristics which must be considered individual to any one unit. The design and construction features of high tension transformers are not consistent. To a lesser degree, this also holds true for filament transformers and for autotransformers. Even when constructed by any one company and regardless of large scale line production, these variations prevail. Of course the differences in performances are considerably greater when the product of one manufacturer is compared with that of an- other. There are, therefore, a number of questions to which even an expert X-ray technician is entitled when faced with strange equip- ment. Certain questions would indicate intelligence on his part rather than ignorance. For instance, he should inquire as to calibrated set- tings concerned with kilovoltage values in relation to usable milli- amperage loads; he is entitled to know the radius of the particular grid; what its ratio is and therefore what milliamperage-second re- quirement is necessary when using the grid as compared with roent- genographic factors without the use of it; and he is entitled to know the sensitizing speed of the particular intensifying screens (contained in one or another cassette). 313009°—41 3 33 TM 8-240 27 MEDICAL DEPARTMENT 27. Kilovoltage calibrations.—a. When a certain voltage is ap- plied through the primary of the high tension transformer, the voltage in the secondary winding is amplified in accordance with the ratio of the number of turns of the secondary to the number of turns in the primary, as previously described. However, the actual voltages concerned with both the secondary circuit and the primary circuit depend not only upon the voltage selection in the primary but also upon the current load in the secondary circuit. Even though there is no actual load, as long as the primary winding is energized, a certain potential is developed in the secondary winding. This potential is described as the no-load potential. In relation to any given setting which might pertain to one or another useful voltage, this no-load potential is called the inverse voltage. It is especially important with consideration of half-wave performance (either self-rectification or where valve tubes are used in the secondary circuit). Kegardless of in- hibiting unfavorably directed alternations of current flow by means of valve tubes, no-load or inverse potentials become effective. If these potentials are excessive, there may result a break-down with short circuiting to the housing (if a tube unit) or through the insulation of shockproof cables. These dangers are less likely in the case of full-wave rectified units. In either case, though, with heating of the filament whereby a certain milliamperage of current is allowed to flow through the X-ray tube, there will result a certain reduction in the intratubal (X-ray tube) resistance, and because of this there will be a reduction in the kilovoltage of the circuit. This reduced kilovoltage is called the “useful.” With every increase in heating of the filament of the X-ray tube, and resultant increase in the milliamperage load, the useful voltage will be reduced, regardless of the no-load potential remaining constant. It is the useful kilovoltage that is concerned with the production of X-rays, their quality, and the resultant radi- ographic density; hence the importance of knowing the useful kilo- voltage values in relation to milliamperage settings. These values are usually recorded on the meters of modern X-ray equipment. However, with certain machines, arbitrary numbers or letters are used to desig- nate the button settings, particularly of the autotransformer, and for them, especially, sphere gap calibration may be necessary. For this, leads must be extended from the high tension terminals and connections provided so that the spheres are placed in a circuit and parallel with the X-ray tube itself. In the case of half-wave performance, a valve tube should be connected into this parallel circuit. When this valve tube is positioned as indicated in figure 22 (T), the sphere gap calibration will measure the useful voltage; whereas when the valve tube is posi- 84 TM 8-240 27-28 ROENTGENOGRAPHIC TECHNICIANS tioned as indicated in figure 22 (2), there will be measured the no-load voltage. h. A slight error is incurred by this method because of the resist- ance through the valve tube itself. This error is usually in the order of 1 to 2 kilovolts, but as far as the relationship between the useful kilovoltage and the no-load kilovoltage is concerned, this error is can- celed as long as the valve tube is used in both instances and the con- nections to it merely changed. With full-wave rectification it is not necessary to include a valve tube in the sphere gap circuit. The useful kilovoltage is measured with the filament of the X-ray tube heated VALVE TUBE Filament trans i X-RAY TU6E 'FILAMENT TRANS, VALVE TU&E / HIGH TENSION TRANS. CURRENT TENDS I TO FLOW IN < EITHER direction' *-RAY, TUBE alternation INHIBITED ALTERNATION ADMITTED ACROSS SPHERES ® Measuring useful voltage. @ Measuring inverse voltage. Figure 22.—Wiring diagram for calibration of half-wave (including self-rectified) equipment. sufficiently to provide for the particular milliamperage load, while the no-load value is measured with the filament circuit open so that the filament is not heated. Useful kilovoltage values should be de- termined for at least three zones for each of the milliamperage loads. For radiographic equipment, it is practical that these three zones be in the neighborhood of 40, 60, and 80 P.Kv. Each of these settings should be carefully checked at least three times. Having obtained trustworthy values in this manner, it is then possible to plot them on coordinate paper so as to obtain information as to all other intervening values, as indicated by a calibration chart (fig. 23). 28. Milliamperage.—Today the values indicated on the scale of a standard milliammeter are usually reliable to within 5 percent of their full-scale deflexion. In case the recording by any one milliammeter should be doubted, it is usually practical to connect in series with it a second milliammeter of known trust. It is not unusual to depend upon two milliammeters (twin milliammeters) when using apparatus for 35 TM 8-240 28-29 MEDICAL DEPARTMENT X- ray therapy, but this is not practical in the case of roentgenographic equipment. As described in the discussion pertaining to wave form, the radiographic performance of any one piece of equipment may not be proportional to the milliamperage merely because of distortion of the wave form, particularly under conditions of high capacity loads. Moreover, due to inherent filtration factors, the X-radiation perform- ance by one tube may differ markedly from that of another, and for this reason radiographic calibrations (using penetrometers, aluminum Figure 23.—Primary voltmeter reading. ladders, etc.) of milliamperage and/or of kilovoltage values, as oftentimes recommended, are not truly indicative. 29. Timer.—Prolonged exposure times may be checked with the use of a reliable stop watch. Exposure of less than 1 second might be checked with the use of a spinning top. This device is simply an X-ray opaque top containing a perforation or notch so that when the top is made to spin, the perforation or notch will rotate through a plane parallel to the film over which it is positioned. If an exposure is made, the X-ray tube being positioned above the top, provided the top be truly X-ray opaque, there will be projected a series of outlines of the perforation or notching. These should indicate the number of pulsations of X-radiation coincident with the pulsations of the high 36 TM 8-240 29-30 ROENTGENOGRAPHIC TECHNICIANS tension current. In the case of full-wave rectification, with a 60-cycle current, there are 120 pulsations per second. In such a case, the num- ber of clots of radiographic density indicated by the top test, divided by 120, will indicate the fraction of a second exposure. In the case of half-wave currents, provided the cycle be 60, the divisor should be 60 rather than 120. 62. IMPULSES .52 SECOND 27 /i IMPULSES .23 SECOND i*'/z IMPULSES .12 SECONDS SPINNING TOP TESTS FOIL. TIMtik (f Olkf FACTION of SEGJ, fOP. fULL WAVE PvECflFlED UNIT 120 IMPULSES" I SECOND Figure 24.-—Spinning top tests for timer (for fraction of second) for full-wave rectified unit. 30. Distance.—Occasionally it may be necessary to measure the position of the focal spot of the X-ray tube in relation to the plane of the exit portal of the primary bean. This may be indicated when dealing with foreign body localizations or when troubled by a cut-off in the area of coverage by the primary beam. With modern equip- ment the entire tube is likely to be concealed either within a tube unit or a tube housing. Should it be necessary to determine the exact location of the focal spot, a simple procedure is to place an 8- by 10-inch film (contained in a cardboard holder) on its side, the 37 TM 8-240 30-32 MEDICAL DEPARTMENT middle of it positioned across the exit portal and approximately at right angles to it. After making an exposure, such as 60 Kv.P. for 40 Ma.S., this film should be processed in the usual manner and then laid upon a white background. By projecting the converging borders of the semitriangular density on the film, there will be obtained a fairly accurate measurement of the position of the focal spot beneath the plane of the exit portal. It should be realized that a slight error will be incurred because of “penumbra.” This error will be greater when a large focal spot is used rather than a small one. The penumbra can be identified and eliminated to a consider- able extent provided the radiographic density is proper. FILM (INCAW)BOA(U) HOLDER) PRjOCtSSfcO FI LAA FOCAL SPOT PWMAPY E.EAM TU&E HOUSING WHITE PAPEP-. DISTANCE1 OF FOCAL SPOT BENEATH PORTAL OF EXIT FROM TU&E. Figure 25.—Determination of focal spot level 31. Dimensions of the effective focal spot.—When the roent- genographic detail is consistently hazy and lacking in sharpness, it may be desirable to measure the dimensions of the focal spot. This can be done with the use of a lead diaphragm having an 0.5 mm. pin point opening. After placing this diaphragm beneath the portal of the X-ray tube, and at one-third the distance between it and a dental film, make an exposure sufficient to produce a density on the film (if the focal film distance be 30 centimeters, 60 Kv.P. for 40 Ma.S. should suffice). Using calipers, measure across the area of uniform density (ignoring the peripheral lesser densities—produced by penumbra). With this measurement apply the following formula: projected dimension 8 X aperture dimension „ _ g =effective focal spot dimension 32. Quantity of X-radiation.—The quantity of X-radiation de- livered may be measured with the use of an r-meter (Victoreen dosimeter). This calibration is seldom indicated for roentgeno- graphic equipment, though very important with therapy equipment. 38 TM 8-240 32-33 ROENTGENOGRAPH1C TECHNICIANS When the ordinary r-meter is used for calibration of radiation per- formances, at the relatively low kilovoltage values used for roent- genography, a certain error is incurred. However, such an error is canceled when the calibrations are made to obtain comparative data, as for instance in the testing of constancy of radiation performance at high versus low milliamperage settings. Provided the kilovoltage values be controlled, for the same milliampere-second values, in the case of a good transformer, the quantity of X-radiation delivered ACTUAL FOCAL SPOT PIN POINT DIAPHKA0M (.5mm- IN DIAMETEIL) IOCMS. 'SHEET LEAD 20cms. PROJECTED fOCAL SPOT (MEASUWNO "EFFECTIVE" FOCAL / SPOT) penumbaa Figure 26.—Measuring focal spot. at a low mil Hamper age setting will coincide (within 5 to 6 percent) with that delivered at a high milliamperage setting. This will not be true in case the milliamperage load exceeds ideal limits of capacity of the transformer. In the case of the latter, the r-performance will be reduced at the high milliamperage settings. Such evidence is indicative of distortion of wave form. 33. Grids.—Well-constructed grids (Bucky diaphragms) are de- signed with a definite radius and grid ratio. Depending upon its radius, the X-ray tube should be positioned within a certain limited range of distance from it. Depending upon its ratio, appropriate compensation in the X-radiation exposure will be required. These re- quirements are described in the paragraph devoted to the description of grids (par. 42). 39 TM 8-240 34-36 MEDICAL DEPARTMENT 34. Cassettes.—Until individually understood, the characteristics of any one cassette (mainly because of the characteristics of its inten- sifying screens) should be considered as unknown and yet as impor- tant as any of the performance factors described above. It is essential to realize that the fluorescence by intensifying screens varies with the kilovoltage and that their sensitizing speeds vary accordingly. Hence, the importance of calibrating each individual cassette as de- scribed in the paragraph pertaining to cassettes (or at least allowing an approximate speed factor consistent with the kilovoltage range). Section VI TROUBLE ANALYSES; MAINTENANCE AND REPAIR OF X-RAY EQUIPMENT Paragraph General 35 Manifestations of trouble 36 35. General.—Before attempting to remedy X-ray equipment diffi- culties, the approach to the trouble must be systematic and analytical. The wiring diagram should be studied and above all else, common sense must be utilized to the highest degree. Consider the trouble possibilities in relation to each circuit. In most instances the diffi- culty is of minor nature. Hesitate before proceeding to dismantle intricate and expensive components. Practically all electrical troubles are caused by open circuits or short circuits (including grounded circuits). 36. Manifestations of trouble.—a. Inconstancy of 'perform- ance.—In fluctuations of milliamperage, consider the possibilities of a gassy X-ray tube, or if valve tubes are used, this same condition with respect to one or more of them. These fluctuations may be indi- cated by repeated opening of the circuit breaker. If sputtering is concurrently noted, test the performance at lower kilovoltage set- tings—consistent performances at lower kilovoltage settings may indicate an intermittent shorting about the X-ray tube due to a low oil level. b. Partially dead equipment.—A range of possibilities is to be considered: (1) In case the filament of the X-ray tube is not lighted (con- sidering that it is visible by means of a transparent window), or in case X-rays are not produced, even though the prereading volt- meter indicates energization of the high tension transformer, con- sider the possibility of a short circuit in the filament circuit or a burned-out filament in the X-ray tube. If the X-ray tube is of double 40 TM 8-240 36 ROENTGENOGRAPHIC TECHNICIANS focus design, change the adjustment to the other focal spot and test an exposure. If no milliamperage is recorded by the milliammeter with either setting;, and if there is no evidence of X-radiation with either setting, test the several circuits concerned with the filament. Check rheostat for broken or burned-out sections. (2) Failure of X-ray production with or without registration of milliamperage but associated with sputtering in the high tension transformer during operation. Consider a shorting either around the X-ray tube or through the case of the transformer—due to low oil level; perhaps there is a content of air admixed with the oil; or perhaps the high tension leads have become detached. (3) Lack of registration of prereading voltage and of milliam- perage, regardless of evidence that filament circuits are intact. Con- sider dead button setting on autotransformer or detached leads con- cerned with it. (Never vary settings when high tension switch is closed.) Check potential across the voltmeter. Connections or com- ponents on it may have been burned out. Check all external con- nections; consider short circuiting possibilities which might result from dust or accumulation. c. Completely dead equipment.—This evidence is likely to indicate bumed-out fuses. Use a test lamp (220-volt lamp or 110-volt lamp, depending upon the voltage of the incoming line used), checking across the line, ahead of the fuses, and beyond them, and then elim- inating one or another fuse. Replace burned-out fuses with new ones. They may have been burnt out because of an overload due to careless adjustment of controls; therefore before proceeding with subsequent trial exposures, it is important to set all controls at low values and then to readjust to higher settings. In case the new fuses are immediately burned out, even at low settings, it is likely that short circuiting exists (due either to wear or abuse of the apparatus). Disconnections might then be accomplished, separating first the high tension transformer and opening the primary circuit concerned with it. Using the test lamp, check the several low tension circuits. d. Precautionary measures.—Repair problems naturally prompt precautionary measures. Some of these include— (1) Routine cleaning and dusting of equipment. This should be practised at least weekly with particular care of all exposed high tension leads. (2) Routine checking of all external connections. (3) Prompt repair of all minor defects. (4) Strict adherence to calibrated values and capacity limits. 41 TM 8-240 37-38 MEDICAL DEPARTMENT Section VII PROTECTIVE MEASURES Paragraph General _ 37 Electrical dangers- 38 X-radiation hazards 39 37. General.—In dealing with X-ray equipment, two types of hazards must be respected: electrical dangers and X-radiation dangers. 38. Electrical dangers.—a. The use of shockproof equipment is now so prevalent that electrical dangers have been almost eliminated. However, the safety provided by this type equipment is of itself a danger because it is likely to relieve too completely the mind of the operator. After handling trustworthy shockproof equipment, there is considerable likelihood that our younger X-ray technicians may fail to recognize the electrical hazards which exist as far as the operation of nonshockproof equipment is concerned. Moreover, ev- eryone should realize that regardless of self-contained tube heads (i. e., when the X-ray tube is immersed in oil and contained in the same tank which accommodates the high tension transformer), or with the use of shockproof cables, one is still handling currents of excep- tionally high voltage which under certain conditions might resist the protective provisions. Therefore, even with modern shockproof equip- ments, the possibilities of electrical hazards should be respected. h. Death may result from any one of four physiological effects; (1) The ventricles of the heart may be thrown into fibrillation from which, in the human, they seldom or never recover. (2) Tetanic convulsion of the respiratory apparatus may result, with resultant fixation of the muscles of the thorax and the dia- phragm into the phase of deep inspiration. (3) The brain centers concerned with constriction of blood vessels may be so stimulated as suddenly to produce extreme blood pressure with resultant hemorrhages. (4) The resistance on the part of the tissues to the flow of the electrical current may be so great as to produce extreme accumula- tions of heat with the result of actual charring. c. Contrary to general belief, voltage is not the factor directly responsible for any of these effects. It is amperage that causes fatalities, and of greatest importance is the volume of current which is effective upon the heart. It has been estimated that for the fre- quencies of current utilized with most roentgenographic equipment (60-cycle), the human heart will tolerate no more than 6 to 15 milli- 42 TM 8-240 38 ROENTGENOGRAPHIC TECHNICIANS amperes. The heart is involved to the greatest extent when the elec- trical contacts include one upper extremity and the opposite lower extremity, for with such a contact, approximately 10 percent of the total current involves the heart. Interpreted as total current flowing through the body, by such a route, a minimal lethal value would amount to between 60 and 150 milliamperes. Some individuals have idiosyncrasies (either because of defects in their heart or because of an overly excitable nervous mechanism), and they cannot tolerate even the lower of these values. It is estimated that approximately 90 percent of maleffects incident to electrical shock are those con- cerned with the heart—hence the importance of these considerations. With high voltage and very low amperage (i. e., milliamperage), there is a tendency for an individual to be thrown for a distance. With lesser voltage and sufficient current to stimulate muscle con- traction, a complete gripping contact is likely. A certain amount of voltage is required to overcome the resistance of the skin and superficial tissues. This value varies, depending upon the dryness of the skin, the thickness of it, and the amount of fat contained in the subcutaneous tissues. With very moist skin and a thin individual, it has been estimated that only 65 volts are required to overcome all body resistance. d. Regardless of the unfavorable possibilities, every effort should be made to restore a victim from electrical shock. However, one should never directly grasp the individual, because by so doing the result will most likely be suicide with the accomplishment of no aid whatsoever to the first victim. Instead of plunging to one’s own death, the first objective should be to break the electrical circuit by opening a switch. Perhaps the victim might be disentangled by throwing over him, a sheet or rope or some other nonconductor and then forcibly removing him from his contacts. Thereafter he should be treated as a victim of shock. He should be placed in the lying posi- tion, prone, with his face turned to one side and chin resting on the back of one of his hands—to provide for freedom of breathing. His collar and other clothing should be loosened and then the Schaeffer method of resuscitation (as used for the semidrowned) should be instituted. The chest manipulations should be continued at a rate of about 12 to 15 times per minute, without despair, for as long as 2 to 4 hours—awaiting the arrival of a doctor. e. This treatment is effective in only a small percentage of cases. However, one should not despair in attempting to revive a victim of this sort. The poor results of treatment should emphasize the im- portance of avoiding the possibilities of electrical shock. Conspicu- 43 TM 8-240 38-39 MEDICAL DEPARTMENT ous warnings should be posted wherever dangers exist. With roentgenographic equipment, exposed condensers are examples of such dangers. It should be realized that these condensers may dis- charge even though the machine is not in operation. They may discharge hours and even days later. Figure 27.—Schaeffer method of resuscitation. 39. X-radiation hazards.—X-radiation hazards are to be con- sidered both in relation to the technician and to the patient. Ordi- narily, the technician receives only a minimum of primary X-radia- tion at any one time, though he may receive considerable secondary X-radiation—from the patient as well as from adjoining materials (such as the examining table, chair, etc.). Even small dosages, if repeated often, become injurious. The maleffects are mainly con- cerned with the blood cells and those tissues which produce them. Ultimately an anemia may result. The blood cells become so reduced in numbers that the individual may not only become pale and weak, actually lacking in vitality, but he may succumb easily to all types of infections because of his lack of resistance. Occasionally, the blood- forming tissues become overly stimulated in reaction to these deple- tions, and as a consequence there may result a wild growth of these cells in the form of one or another type of leukemia. This is actually a form of cancer which is usually fatal within a period of 3 to 6 years. The importance of precautions cannot be overemphasized. These precautions should include protective measures necessary to avoid un- necessary X-radiation exposures; they should include proper hygienic care, regularity of exercise in the open, proper dietary, and periodic blood examinations. The recommendations of the Advisory Com- mittee on X-ray and Radium Protection, as published in the National Bureau of Standards Handbook HB20, should be observed. In addi- 44 TM 8-240 39-40 ROENTGENOGRAPHIC TECHNICIANS tion to the general systematic effects, as produced by repeated small dosages of X-radiation, injury to the skin (of either the technician or the patient) is to be considered. A single prolonged exposure Is sufficient to do this. Hair follicles may be injured and the hair thereby caused to fall out or the skin may actually be burned—though these effects may not become evident for as long as 10 days to more than 2 weeks later. The intensity of effects is the greatest when short dis- tances (focal-skin distances) are used; 12 inches should be the mini- mum. Though the inherent filtrations of X-ray tube arrangements vary, table IY should serve as a rough guide as to maximum safe tolerances. Table IV.—Filtrations with voltages oj 90 Kv.P. and less Focal-skin distance Tolerance limits (summation values) Inches Milliampere- seconds 15 1, 200 16 1, 365 17 1, 541 18 1, 728 19 1, 925 20 2, 133 21 2, 352 22 2, 581 23 2, 821 24 3, 072 25 3, 333 26 3, 605 27 3, 888 28 4, 181 29 4, 485 30 4, 800 72 27, 648 These values are based upon an inherent filtration in the X-ray tube unit, or added filter to the equivalence of at least 1-mm aluminum. For roentgenography about the head, reduce the milliampere-second allow- ances to half those listed. Section VIII AUXILIARY RADIOGRAPHIC EQUIPMENT Paragraph General 40 Diaphragms, cones, and cylinders 41 Grids 42 40. General.—a. With the passage of a beam of X-rays through a substance, a large percentage of the rays traverse the substance 45 TM 8-240 40-42 MEDICAL DEPARTMENT while some of them become absorbed. Absorption occurs when an X-ray directly strikes the nucleus of an atom. There results a mobilization of electrons (atomic). Mobilization of the electrons, per se, as well as subsequent bombardments by them, are productive of a new order of X-ray energy. The X-ray energy produced in this manner is called secondary radiation. The secondary rays are gen- erated from any point source within the substance pervaded. The result is very much as if there were not merely the one X-ray tube functioning but, instead, numerous X-ray tubes and these located at various levels and positions. Since the X-radiation is generated from numerous point sources, there results a multiplication in the projection of any one density which might be positioned between the X-ray tube and a film. The primary beam of X-rays serves to pro- ject such a density onto one position of the film, while the secondary rays serve to project it onto other locations. The effect of the sec- ondary rays is much more feeble than that of the primary beam but sufficient to result in blurring of outlines. This blurring is described as secondary fog. h. The degree of secondary fog is proportional to the mass of tissue affected by the primary beam or other X-radiation, and it is increased with increases in kilovoltage. These effects are decreased by reduc- tion in kilovoltage; reduction in the mass of substance traversed by the primary beam—as accomplished with the use of diaphragms or cones; and absorption of tangentially directed rays—by the use of grids. 41. Diaphragms, cones, and cylinders.—Limitation in the de- velopment of secondary radiation with the use of a diaphragm, cone, or cylinder is illustrated in figure 28. It should be emphasized that when using a diaphragm it must be placed either beneath the X-ray tube or upon the part that is being studied. It should serve to limit the diameter of the primary beam. A diaphragm positioned be- tween the part and the film serves merely as a mask. It does not serve to reduce the amount of secondary radiation produced in the part. Grids, though, are positioned between the part and the film. They serve to absorb rather than to limit the production of secondary rays. 42. Grids.—a. A moving grid is called a Bucky diaphragm or a Potter-Bucky diaphragm. It was Dr. G. Bucky who developed the idea of utilizing strips of lead, arranged in parallel positions, to absorb the tangentially directed rays. The thickness of the lead strips of the earliest types of grids was such that the densities of these strips as projected onto the films were annoying to the roentgen- 46 TM 8-240 42 ROENTGENOGRAPHIC TECHNICIANS ologist. For this reason Dr. Hollis Potter invoked the principle of moving the strips of lead. If the exposure time is coordinated pro- perly in relation to the grid travel time, the individual strips of lead are not visualized on the film. The lead strips serve the pur- pose of filtration but at the expense of some radiation absorption. Therefore when using grids it is necessary to increase the milliam- ® UN ktSTPJCTED PRIMARY RADIATION ® USE of DIAPHtLAOM @ USE of CONE 0 USE of EXTENSION CYLINDER. Figure 28.—Development of radiation. pere-seconds or kilovoltage. The construction features of the curved type of grid as compared with the flat type are shown in figure 29. h. Grids possess individual characteristics which should be under- stood in order to provide for proper handling. Some grids are constructed with approximately 20 lead strips per inch width; others with approximately 30; while others contain 40 to 55 lead strips. The greater the number of lead strips per inch, naturally, the less is the thickness of each individual lead strip. The less the thickness of each individual lead strip, the less tendency there is to produce grid marks or wooliness on the roentgenogram. c. Grids also differ as to ratio. The grid ratio might be defined as the proportion between the width of each individual lead strip 47 TM 8-240 42 MEDICAL DEPARTMENT (i. e., thickness of the grid itself) in relation to the spacing between the lead strips. A common grid ratio is 5 to 1, but grids are con- structed with a 3 to 1 ratio, 6 to 1, 8 to 1, and occasionally even 12 to 1 ratio. The higher the ratio the greater is the efficiency of ab- sorption of the secondary rays, but at the same time the greater is the milliampere-second compensation requirement. d. Grids also differ as to radius. The grid radius might be defined as that distance at which the X-ray tube should be positioned so as to obtain to the greatest extent a parallel relationship of the rays CATHODE MY5 TARGET PR.IMAR.Y B€A/n substance: traversed by X-RAYS SECONDARY / RAYS ,GWO CASSETTE-"^ ® Flat. ® Curved. Figure 29.—Grids, of the primary beam to the lead strips. With consideration of a curved grid, the grid radius is actually the radius of a circle of which the grid itself would constitute an arc. It is important to use grids with the X-ray tube properly positioned, otherwise there results absorption of primary X-rays as well as of the secondary. On the film this is evidenced by sections of underexposure. It is described as cut-off. Most grids are constructed with a radius of 30 inches, but some are constructed with a 25-inch radius while others have a 36-inch, 48-inch, or even a 72-inch radius. With some the radius would be infinity, for the lead strips are exactly parallel to one another. e. The radius of a grid is usually described on the side of its hous- ing, but it can be determined by positioning the grid beneath the 48 TM 8-340 42 ROENTGENOGRAPHIC TECHNICIANS X-ray tube and making a number of exposures at different distances. That distance which serves to project each individual lead strip uniformly (i. e., as of uniform thickness) upon the film can be considered to be the grid radius. The grid ratio might be de- termined by positioning the X-ray tube off center to the extent of the geometric base as considered in relation to the similar triangles showing in figure 30. For example, if it is thought that the ratio is 5 to 1 and the radius is 30 inches, the geometric relationship would be—5:1 :: 30: x—indicating that a shift of the X-ray tube to the extent of 6 inches should result in a complete cut-off (of radiation effect). A-E. =WlDTd of LEAD STWP Q-C =5PACE BETWEEN LEAD SIMPS F-F’=TUb£ SHIFT FOIL. COMPLETE "CUT OFF” AABC AAff’ .*. Ab:BC::AF:FF‘ CblUD . RADIUS CUlWfcO r ORJD Figure 39.—Relation between cut-off and grid ratio. /. Grid lines or wooliness may result even with the use of moving grids. The following possibilities are to be considered: (1) Failure of the grid to move. (2) The exposure occurring ahead of the time of initiation of grid movement (or pretravel time being too short to provide for smooth movement of the grid at the time when the exposure begins). (3) The exposure time continuing beyond the period of grid move- ment (or the post-travel time being too short and allowing jerky movement of the grid before termination of the exposure). (4) Jerky movements of the grid during the ideal travel period. (5) Uneven thickness of grid strips. (6) The composite travel (i. e., pretravel, effective travel, and post-travel) being more than twice the exposure time. (7) The X-ray tube being positioned off center, laterally or ver- tically in relation to the proper radius centering. 49 TM 8-240 42-43 MEDICAL DEPARTMENT (8) The exposure time being so short as to produce synchroniza- tion—i. e., exposures of Vio of a second or less, where self-rectification is utilized and the exposure is dependent upon as few as six impulses. g. Grid lines must be expected when using stationary types of grids. With modern construction, having very thin lead strips and as many as 50 or more lead strips per inch, these lines are so thin as to result in very little annoyance. The advantages of a stationary grid of this sort are two fold: they provide for minimal part-film distance, thereby lessening the degree of distortion; and the milliampere- second compensation requirement by them is not great. Section IX DARKROOM EQUIPMENT Paragraph Processing room 43 Films 44 Film handling 45 Chemical processing 46 43. Processing room.—The first essential of a processing room is that it should be sufficiently light and X-ray proof so that films contained therein will not become fogged. The temperature of the room should not exceed 90°F. This fact emphasizes the importance of not having too great an area of heating surfaces and seeing that these are not located in close proximity to the sites of film storage. The darkroom should be located on a side of the building where, during the summertime, the heat of the sun will not become too intense. Thus an eastern exposure is to be preferred or a side of the building protected by shade, particularly during the afternoon. Cer- tain construction features are desirable. For instance, a film bypass should be constructed in a convenient location into an inside wall. Rather than use a door, a labyrinth or maze should be provided for ingress and egress. The walls of this labyrinth should be painted a dull black, and its design and dimensions (i. e., width of the pas- sageway in relation to total length) should be such as to inhibit the entrance of light into the room in amounts which would cause fog- ging of uncovered films. It is practical to have an air circulating fan. This might be constructed into an outside wall so as to provide either for ingress or egress of the air. It should be of lightproof construction. Properly filtered lighting sources should be provided, preferably mounted onto the ceiling. Since the filtering character- istics provided by these may not be sufficient to protect the particular emulsions of the X-ray films, it is important to make the film tests 50 TM 8-340 43-44 ROENTGENOGRAPHIC TECHNICIANS mentioned above under actual working conditions. It should not be necessary that the ceiling and walls of a processing room be painted black. They may be of a relatively light color, a peagreen, for instance, provided other protective measures prevail, as described. It is practical to have the film loading bin and loading bench on one side of the room and the processing tanks within handy reach of them, but at a sufficient distance to counteract splashing of chemicals onto sites where films or intensifying screens might be exposed or later come in contact. Racks for film hangers should be provided and located within handy reach of the loading bench. (See fig. 31.) 14 FT. - SHE LVE.S LIGHT-PROOF FLUE FOR FAN VENTILATOR. WINDOW WITH LIGHT-PROOF SHUTTER SINK- 26 in. PEY WASH- FIX WAS r) -26.«r -26i*r 10 ft. 30im. STORAGE COMBINATION FILM BIN/IPAPINO BENCH 6, DRYER. BY- PASS Figure 31.—Processing room. 44. Films.—a. The appearance of an X-ray film is well known. Standard dimensions, as used for medical purposes, include 35-milli- meter film (in roll), dental, 4- by 5-inch, 4- by 10-inch, 5- by 7-inch, 61/2- by 81/2-inch, 8- by 10-inch, 10- by 12-inch, 7- by 17-inch, 11- by 14-inch, 14- by 17-inch, and 14- by 36-inch. h. All of these films are composed of a light transparent base covered on one or both sides with a gelatinous emulsion containing a suspension of a silver halide. Double coatings are found on all except the 35-mm roll film and some of the dental films. The base of modem X-ray films contains less than 3 percent nitrocellulose. It 51 TM 8-240 44 MEDICAL DEPARTMENT is mainly composed of cellulose acetate. Nitrocellulose is still used in small percentages to provide for pliability and to improve the light transparency. It is an unfavorable constituent because of its avidity for combustion. The burning rate of the cellulose acetate base is much less than that of the nitrate. It is compared to the burning rate of paper, but some of the modern bases are even less ignitible than paper. Though they will burn, unless the flame is repeatedly renewed it becomes self-extinguished. These slow burn- ing characteristics have developed for this film the name of safety film. Safety film may be distinguished by one or more small rec- tangular notches cut into one border of each individual film. c. Film emulsions vary markedly not only with consideration of differences in composition, as produced by one manufacturer versus another, but also as far as any one manufacturer is concerned. For instance, among X-ray films produced by any one manufacturer there are two types: a screen film which is especially sensitive to the fluorescent light of intensifying screens and not so sensitive to the direct action of X-rays; and a direct exposure film, which is sensitive to the action of X-rays and not so sensitive to the wave lengths of fluorescent lighting as emitted from intensifying screens. This latter film emulsion may be identified by a double rectangular notch cut into one of its borders, as distinguished from the screen film containing a single notch. These notches provide for identi- fication while handling the films in the darkroom, but they are further identified by printed information which is readable after processing. The screen film is the one most commonly used. d. Film emulsion becomes sensitized when subjected to energies such as ordinary light, ultraviolet light, or X-rays. Unfortunately, sensitization also occurs to some extent by the effects of heat, static discharges, and rough handling. The result of any of these is an intermediary stage of oxidation of the silver salts contained in the emulsion. When subjected to the chemicals contained in the devel- oper, those granules of the silver salts which have been so affected are first changed from the salt combinations into metallic silver. With further oxidation, these particles of metallic silver develop a black color. When a part is interposed between the X-ray tube and the film, there results a varying degree of sensitization because of varying quantities of X-ray energies becoming effective upon one or another portion of the film. With proper control of such an exposure there results an inverted shadowgraph (a negative) which is actually a positive (photographically speaking). 52 TM 8-240 44 ROENTGENOGRAPH1C TECHNICIANS e. Film emulsions differ as to size of grain (of the silver salts) as well as to the degree of their sensitization. Ordinarily the smallest possible grain size is desirable since sharper detail is obtainable with it. It is generally true that the faster the sensitizing characteristics, the larger is the grain size. The steeper the slope of sensitization (i. e., the shorter the gradation of it), the greater will be the contrast on the roentgenogram for any set of technical factors. y\--High Contrast Emulsion 5-Low Contrast Emulsion Figure 32,—Sensitization curves. /. The steps of gradation might be demonstrated with the use of an aluminum ladder. This may be of 1 to 3 or more millimeters in thickness (aluminum) per step, each step having area dimensions of approximately iy2 by 3 inches. Such a ladder might be placed over a film (contained in a cardboard holder) and subjected to a slight X-ray exposure, depending upon the thickness of the steps (using factors such as 60 K.v.P. 10 Ma.S. at a distance of 30 inches). In order to obtain more complete information in this regard, it is advisa- ble to repeat this test, having the film contained between intensifying screens in a cassette (for this testing, the Ma.S. factors should be re- 53 TM 8-340 44 MEDICAL DEPARTMENT cluced in accordance with the speed of the intensifying screens). It must be remembered that the speed of intensifying screens varies with the kilovoltage. It is desirable to obtain testings of the film at 40 Kv.P Using * Carob A 40 Kv.P Using 80 Kv.P Casset re Figure 33.—Ladder tests. kilovoltages of 40 as well as at 80. The comparative scale of grad- ation is shown in figure 33. g. Many roentgenologists insist upon high degrees of contrast while others favor considerably less. The amount of contrast obtained with roentgenography can be controlled to a large degree by heeding 54 TM 8-240 44-45 ROENTGENOGRAPHIC TECHNICIANS the relationships of the technical factors discussed in the succeeding1 paragraphs. However, it should be realized that the inherent quality of the emulsion is a very important factor. 45. Film handling.—a. Films should be stored on end and in a cool, dry place. It is important to protect all unexposed films not only against the effects of light but also from heat and X-radiation. The cardboard cartons in which they are supplied are protective merely against light. The possibilities of X-radiation coming from an ad- joining room or from rooms above or below the site of storage should be considered. The use of sheet lead may be necessary. It might be used to line one or more walls of the film bin. To protect against the wave lengths utilized in roentgenography, 1.5-mm thickness of lead should suffice. h. Unexposed films should be removed from their cartons only in a darkened room. With the use of proper light filters, complete dark- ness is not required. The emulsion of X-ray films is sensitive to the blue violet portions of the light spectrum. The wave lengths of light concerned with the red, orange, and amber portions of the light spec- trum are not injurious to the emulsion, and since they provide for con- siderable visual accommodation, it is favorable that the processing room be provided with lighting filtered accordingly. However, light filters should not be trusted without testing, and for this it is sug- gested that an exposed film covered by an object of some sort be placed in one or another working position and left there for a period of time, such as 5 minutes, and then processed. Sensitization of the emulsion will of course indicate escape of sensitizing wave lengths of light or the admission of X-radiation into the room. c. For the making of exposures, films might be carried in a card- board holder or in a cassette. Cardboard holders function in much the same manner as do ordinary envelopes. In loading a film into either of the latter, the protective black paper should be left about the film. In the case of a cardboard holder, it is important to fold the apron portion of the flaps first, then the sides, and finally the end, as shown in figure 34. The top cover of these holders is impreg- nated with small amounts of lead (to filter secondary radiation which would otherwise provide back-scattering and fogging of the film), and for this reason the base portion of this holder should be placed up toward the X-ray tube during the exposure. Cassettes usually contain intensifying screens, though for nonscreen films cassettes are available which serve the same purpose as provided by cardboard holders. Actually, a very small percentage of the X-radiation which traverses a part becomes absorbed by or is effective upon the film 55 TM 8-240 45 MEDICAL DEPARTMENT emulsion. It has been estimated that less than 1 percent of the X-radiation which passes through a film actually sensitizes the emul- sion. It is to increase the efficiency of the X-rays that intensifying screens are used. d. Intensifying screens are composed of a special cardboard base having a coating of calcium tungstate crystals held together in a binder. X-radiation produces fluorescence when striking calcium tungstate. This fluorescence is used to sensitize the emulsion in con- junction with the X-radiation itself, and therefore the black separat- ing paper used in packing should be removed before placing films in cassettes which contain intensifying screens. Ordinarily, two in- tensifying screens are contained in a cassette, and the calcium tungs- tate surfaces of these are positioned in immediate contact with the Figure 34.—Proper folding of cardboard holder. film, one screen being above and one below. Intensifying screens may vary markedly as to their degree of fluorescence. Some screens con- tain one thickness of calcium tungstate crystals, some another. More- over, the crystals of the calcium tungstate may be of one diameter or another. The larger the diameter of the crystal and/or the thicker the layering of the calcium tungstate crystals, the faster (i. e., the more intensely fluorescent) the screen. Intensifying screens are produced by several manufacturers in the United States. They are identified as to relative speeds by means of trade names. In general, there are three grades: slow, medium, and fast. However, the speed of any intensifying screen varies, depending upon the wave length of the X-ray energy. The shorter the wave length of X-rays, the greater is the fluorescence produced by them upon the screens. Expressed in terms of kilovoltage, this relationship might 56 TM 8-240 45 ROENTGENOGRAPHIC TECHNICIANS be indicated by curves. (See fig. 35.) Since no one speed factor can be considered to apply to any one type of screen or even to any one screen (because of this relationship to kilovoltage), it is practical to calibrate each individual cassette. This calibration curve should be recorded on the back of the cassette and consulted before making an exposure, KILOVOLTA6E PEAK A Slow Screen (Sharpest Detail) 5 Medium Cf*5T (l€A5T txP03URf KtQUIRfOj RELATIVE SPEEDS Figure 35. referring to the particular kilovoltage effect in each instance. The procedure of calibration might be outlined as follows: (1) Equipment and items necessary; Cassette to be calibrated. Unexposed (14- by 17-inch) X-ray film. 14- by 17-inch cardboard holder. Scissors to cut film. Lead letters and numbers for identification of film strips. Lead sheets sufficiently large to cover a 14- by 17-inch cardboard holder. 57 TM 8-240 45 MEDICAL DEPARTMENT One X-ray unit. Graph paper (square). (2) The focal-film distance for all exposures is 10 feet. A 1-mm aluminum filter should be used throughout. The actual steps of procedure are as follows: (a) Cut an unexposed 14- by 17-inch film lengthwise into four strips as shown in figure 36. (h) Place strip A-l in one corner of the cassette to be calibrated; make the first exposure using factors listed in A-l, after placing lead numbers A-l in a position appropriate for identification. (c) Unload the cassette in the darkroom; reload with strip A-2 and make the second exposure using factors listed in A-2, after pro- viding lead numbers for identification. (d) Again unload the cassette (in the darkroom) ; reload with strip A-3; make third exposure using factors in A-3, again identify- ing by lead numbers. (e) Load strip B into cardboard holder (maintaining black paper about film). Delineate 8 block divisions on the exposure side of this cardboard holder and number these 1, 2, 3, etc., as indicated in figure 36. Place lead figure B in the position of block 8. Make an over-all exposure using 40 Kv.P. for 80 Ma.S. Place sheet of lead (1.5-mm in thickness) so as to cover all except block 1. Repeat exposure of 40 Kv.P. and 40 Ma.S. Then move lead sheet so as to expose blocks 1 and 2 and repeat this same exposure. Thereafter, expose one block at a time, repeating the exposures so that finally each block will have received the Ma.S. exposure listed in figure 36. (/) Repeat this same procedure for strips C and D using the factors listed. Be sure to identify each strip by placing letters C or D in the respective positions for block 8. iff) Process all portions of strips A, B, C, and D at the same time. (h) After drying films compare densities of A-l with various blocks of strip A, densities of A-2 with various blocks of strip B, and the densities of A-3 with various blocks of D. (i) With consideration of the relative requirements of Ma.S., plot relative speeds in terms of the three kilovoltage values and extend curve. e. This relationship of speed factor to kilovoltage is very com- monly ignored. If for some reason calibration of individual cas- settes cannot be accomplished, at least factors should be considered for each of several ranges of kilovoltage. For instance, with con- 58 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 45 Block ffQ 40 KyP, 80 MaS. Blook #8 60 KyP. 150 MaS. ia_ Block if 6 80 KyP. 140 MaS. Block ff7 40 KyP. 12p MaS. Block #7 60 KyP.j 210 MaS, 32: Blook #7 80 KyP, 180 MaS. Block if6 40 KyP. 160 MaS. Blook #6 60 KyP, 270 MaS. 22 Block #6 60 KyP. 220 MaS. Relative Speed Block #5 40 KyP. 200 MaS, Relative Speeds Blook #5 60 KyP. 330 MaS. Relative Speeds, Strip "C" 26' Blook ff5 80 KyP. 260 MaS. Figure 36.—Calibration of cassettes—technical factors and relative speed values. Strip "D"' Strip "B" Block f4 40 KyP. 240 Ma£. Blook #4 60 KyP, 390 MaS, 30 Block f4 80 KyP, 300 MaS • Block #3 40 KyP. 280 MaS. Blook ffZ 60 Kv.P, 450 MaS. 34 Block #3 80 KyP, 340 MaS. Block #2 40 KyP. 320 MaS. Blook ff2 60 KyP. 510 Mas. 38 ■ Blook jfZ 80 KyP. 380 WaS. [Block #1 40 KyP. 360 Ma.". Block #1 60 KyP, 570 MaS. 42 Block § 1 80 KyP, 420 MaS. For card- board ex- posures at 80 KyP. D. For card- board ex- posures at 60 KyP. C. For card- board ex- posures at 40 KyP, B. (Strip A-l) For screen exposure (Strip A-2) For screen exposure 60 KyP. 5 Ma. 3 Seo. (Strip A-3) For screen exposure A. 40 KyP. 5 Ma. 4 Seo. 80 KyP, 5 Ma. 3 Seo. 59 TM 8-240 45-46 MEDICAL DEPARTMENT sideration of medium speed intensifying screens, a number of indi- vidual calibrations have indicated the following averages: Kv.P: 30-40 40-50 50-60 60-70 70-80 80-90 Average speed: 4 10 14 18 21 25 /. Intensifying screens may be purchased separately and subse- quently mounted into cassettes. Not infrequently the mountings are defective. Sometimes slightly X-ray opaque bindings are used. Re- peated visualizations of such binders may be seen upon the roentgen- ograms. Moreover, foreign substances might fall behind the screens or even between them and upon the film, and because of them “arte- facts” may result. In case a certain portion of roentgenograms re- peatedly show a fuzziness—an nnsharpness of detail—there is to be considered the possibility of irregularities in the contact surfaces of the intensifying screens in apposition to the film surfaces. Test- ing as to this possibility might be accomplished by making a roentgenogram of a wire mesh. 46. Chemical processing.—a. This should be accomplished on the basis of time and control of temperatures. Repeated viewing of the film during its development is too likely to result in streaked development—due to the close proximity of the film to viewing lights which might be used, and also to uneven contact between the chemicals and the emulsion. Temperature control for the developer is especially important. The ideal temperature is 65°F. With most developers, insufficient reduction is accomplished when the tempera- ture is below 60°F., while the process is too rapid and uneven, with the result of chemical fog, when the temperature is above 70°F. At greater temperatures swelling of the emulsion is likely to occur. The essential constituents include elon (metol, or pictol, etc.) and hydroquinone. These are the reducing agents which, under proper conditions, select those granules of the silver halide which have been sensitized by the X-rays (or other factors), and they convert these granules into metallic silver. The elon is not very penetrating. It acts on the superficial layers of the emulsion while the hydroquinone, though acting more slowly, is more penetrating. Other constituents include sodium sulphite, which serves to counteract oxidation of these agents; bromids, which serve to restrain the reducing agents and thereby provide for more uniform effects, lessening the likelihood of chemical fog; and an alkalizing agent, such as sodium carbonate, which serves as a catalyst for the reducing agents. h. Having a fresh developer, the ordinary time requirement for development is 4 to 6 minutes, provided the temperature is within a few degrees of 65°F. With old developer, a longer time should 60 TM 8-340 ROENTGENOGRAPH1C TECHNICIANS 46 be allowed. Following this, the film should be washed for 10 or 15 seconds in circulating water and then placed into the hypo or fixing bath. There are two reasons for this intermediary washing: ® Good intensifying screen contact. @ Poor intensifying screen contact. Figure 37.—Roentgenogram of wire screen. (1) The developer is of alkaline reaction while the fixing bath is acid. Rapid changeover, in the case of fresh solutions, is likely to produce surface heating (and fogging) of the emulsion. 61 TM 8-240 46 MEDICAL DEPARTMENT (2) A large film may carry over as much as one ounce of solution. Repeated admixtures of the developer into the fixing bath will not only result in diluting the latter but also directly weakening it. c. When leaving the developer the gelatinous emulsion of the film is soft, both because of effects of the water and because of the alkalinity. The purposes of the fixing bath are to— (1) Remove those granules of the silver halide which were not sensitized and therefore not acted upon by the developer. (2) Harden the emulsion. The first of these functions is accomplished by sodium thiosulphate, while the second function is performed by the alum contained. In addition, the fixing bath also contains sodium sulphite—again serving to counteract oxidation, and an acid (such as glacial acetic or sul- phuric) which serves to stop all further development. d. Ordinarily, films should be left in the fixing bath for as long as 10 to 20 minutes. They should then be placed in a bath of cir- culating water. Usually, 15 minutes or more are required for ade- quate washing. With incomplete washing, the film when dry will show either a thin coating of white crystalline material or it will appear foggy. Drying may be facilitated with the use of a fan and a draft of warm air (as provided with the aid of a heater). Should the air be too hot, the emulsion will become crinkled. e. The importance of the film processing room is too seldom appre- ciated. It has been estimated that 80 to 90 percent of the trouble which occurs in an X-ray department can be found there. It is there that intensifying screens are frequently rendered defective because of foreign materials falling upon their surfaces, improper fixations, or because of nicks imposed upon their surfaces, etc. With frequent replacements they become a most expensive item in the department. Other troubles which might be attributed to the film processing room are given in table V. 62 TM 8-340 ROENTGENOGRAPHIC TECHNICIANS 46 Table V Defect in roent- Factors attributable to— genogram Processing room Storage room Exposure room Localized blur- ring of detail. Repeated outlines of hairs, dust particles, etc.— decreased ra- diographic den- sities. Warping of the sur- face of intensify- ing screens—care- less mounting or handling. Accumulations of such on the sur- faces of the screens — failure in routine clean- ing. Pitted or torn sur- faces of intensify- ing screen. Mottled areas of Light leak into Careless opening Careless handling blackness, usu- film loading bin. of film carton of cardboard ally extending Light leak through in lighted room. holder or cas- centrally from worn edges of Prolonged storage sette with light borders. cardboard holder in flat position admission into or cassette. with sensitiza- tions of emul- sion due to im- pacts. either. Widespread fog- Leakage of X-ra- Films stored too Minimal X-radia- ging. diation into proc- close to radiator t i o n exposure essing room. or hot pipes; before or after Sight development. excessive heat in the roentgeno- Hot chemicals. storage room. graphic proce- Excessive heat in X-radiation leak- dure. storage bin. age in the stor- age room (also possibility of gamma ray ex- posure from nearby radium). Excessive second- ary radiation —need for grid, cone, or dia- phragm. “Christmas tree- Static discharges Impacts; rough Impacts; rough like,” or circu- (especially inci- handling. handling of lar densities dent to rough cardboard hold- with feathery removal of film ers and cas- margins. from protective black paper). Impacts. settes. 63 TM 8-240 46 MEDICAL DEPARTMENT Table V—Continued Defect in roent- genogram Factors attributable to— Processing room Storage room Exposure room Moon-shaped or Bending of film in- V-shaped areas cident to finger- of decreased nail pressure or density. creasing of the film. Fusiform areas of Close contact of decreased den- buckled portions sity. of two films in developer. Transfer of image Slight contact of from one film emulsion surfaces to another. of two films in developer. Streaky densities. Sight development. Hot solutions. Insufficient den- Old (oxidized) de- Underexposure. sities. veloper. Cold developer. Strip of trans- Level of developer parent base at too low—not cov- one end of film ering entire film. with sharp de- marcation or bubble outline. Greyish yellowish Level of hypo too strip at one low—not cover- end of film. ing entire film. Y ellowish dis- Old (oxidized) hypo. coloration throughout ro- entgenogram. Fusiform area of Close contact of grayish yellow emulsion sur- or yellow. faces because of buckling of films in hypo. Rough, whitish, Inadequate wash- or crystalline ing of film after surface—noted hypo fixation of after drying. it. Crinkled surface. Excessive heating of wet emulsion— likely during pro- cessive drying. 64 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 46 Table V—Continued Defect in roent- Factors attributable to— genogram Processing room Storage room Exposure room Bubble or track Dropping of water bucklings. or chemicals onto dried film. TJnsharpness of Defective intensify- Movement of pa- detail. ing screens; fast screens with large fluorescent crys- tals. • tient or of film or of tube dur- ing exposure. Use of large focal spot of tube. Distortion—asso- ciated with short focal film distance in rela- tion to large part film dis- tance. Excessive density throughout Hot developer Overexposure. film. Wooliness of ac- Improper action of grid (see under tual grid mark- ings. description of grid function). Gray ness—long Use of cardboard High kilo voltage. scale of grada- holders instead of Secondary fog— tions of den- cassette with in- need for grid, sity—lack of tensifying screens. cone, or dia- contrast. Shortening of de- velopment time because of hot developer. phragm. Excessive con- Use of fast intensi- Low kilovoltage. trast—short fying screen— scale gradation. rather than me- dium or slow screens or card- board holders. Prolonged develop- ment in cold de- veloper. 65 TM 8-240 47 MEDICAL DEPARTMENT Section X RADIOGRAPHIC QUALITY Photoroentgenographic quality 47 Paragraph 47. Photoroentgenographic quality.—This quality might be analyzed in terms of four main characteristics: a. Distortion.—The perversion of true shape of the part of the object studied. Roentgenographically speaking, distortion may be of two types: (1) Magnified.—The equal magnification of all portions of a plane of the part. This type of distortion results when the part film distance (i. e., the distance between a plane of the part under consideration and the film) is great in proportion to the focal film distance (i. e., the dis- tance between the focal spot of the X-ray tube and the film). (2) True.—The unequal magnification of various portions of a plane of the part under consideration. This type of distortion may be produced because of malalinement of the tube in relation to the film and/or the part. h. Detail.—The sharpness of contour and structural lines. Detail is decreased by— (1) Distortion. (2) Movement of the part, the film, or the tube. (3) Use of large effective focal spot. (4) Use of an intensifying screen—the larger the crystal of the fluorescent substance or the thicker the layer of it, the less sharp is the detail obtainable. (5) Poor intensifying screen-film contact. c. Contrast.—The relative degree of blackness of the black portions of the film as compared with whiteness of the white portions, that is, the abruptness of change in the gradation of densities. Contrast is decreased by— (1) Use of a film of which the emulsion has a long scale gradation. (2) Increasing the kilovoltage. (3) Using slow types of intensifying screens or cardboard holders rather than screens. (4) Secondary radiation, which is increased in proportion to the thickness of the part and increases in kilovoltage. The maleffects of secondary radiation might be reduced by the use of grids, cones, or diaphragms. (5) Overexposure and shortening in the time of development or the use of cold developer. d. Radio graphic density.—The generalized blackness of the exposed portions of the film. 66 ROENTGENOGRAPHIC TECHNICIANS TM 8-240 47-48 (1) Radiographic density is increased by— (a) Time and milliamperage—which bear an almost direct propor- tion to the density. Therefore, time and milliamperage are inter- changeable (provided the wave form is not changed). (b) Kilovoltage—in proportion approximately as the squares of the relative kilovoltages. (c) Excessive developing time or hot developer. (2) Radiographic density is decreased by— (a) Distance—in proportion approximately as the squares of the relative distances. (b) The use of grids, cones or diaphragms—unless milliamperage, time, or kilovoltage is increased. Section XI TECHNICAL PROCEDURE Paragraph Preparation 48 Roentgenographic technique 49 Roentgenographic procedure 50 48. Preparation.—Before actually making a roentgenqgraphic exposure, the following factors should be considered: a. Film size.—This should be no larger than required to cover the field for study; yet a reasonable expanse of tissues should be visualized beyond the actual site where pathology is suspected. Two or more views might be accommodated on one film by protecting certain por- tions of the film with lead while making one or another exposure. b. Film container.—A cardboard holder, nonscreen cassette, or a cassette. The use of a cardboard holder or nonscreen cassette is recom- mended when the thickness of the part is 10 cm or less and when the sharpest of detail is required. It is also recommended when reduc- tion of contrast is desired. It provides for a wide latitude of accept- able exposures. With modern film emulsions, the milliampere-second factor may be as much as 50 percent plus or minus from the ideal and still obtain a readable roentgenogram. This same latitude pertains to the use of cassettes with intensifying screens provided the individual cassette has been calibrated for speed factors in relation to' kilovoltage, as described in paragraph When the exposure time must be re- duced to the minimum, particularly with consideration of the pos- sibilities of movement, the use of intensifying screens is recommended. They are recommended for all parts of thickness greater than 10 cm because of the large amount of secondary radiation (and secondary fog) which would be developed in case of utilizing the increased mil- liampere-seconds or higher kilovoltage required for the use of cardboard holders. 67 TM 8-240 48 MEDICAL DEPARTMENT c. Positions.—At least two positions are ordinarily indicated, pro- viding1 for visualizations of planes at right angles one to the other. Oblique views should be considered. Stereoscopic pairs may be in- dicated. More elaborate procedures such as planigraphy, serialscopy, kymography, etc., are ordinarily special studies, either specifically re- quested or accomplished at a reexamination. Particularly when con- cerned with infants and children, it is advisable to include studies of the opposite side as well as that of the part requested. d. Use of ai cone, diaphragm, or grid.—This should be considered for any part the tissues of which are solid and not air-contained, or where there is edema or accumulation of fluids, and particularly when the thickness of the part is 12 cm or greater. e. Captioning.—This should include identification of the patient and the date of the examination. It is also advisable to identify the side as to R or L and give the name of the hospital or clinic. /. Technical factors.—These factors are milliamperage, time, dis- tance, and kilovoltage. (1) Milliamperage must necessarily depend upon the capacity of the unit (including the tube capacity) and the requirements of focal spot dimensions. High milliamperage imposes the require- ment of relatively large focal spot dimensions which detract from the sharpness of detail. Generalities pertaining to this relationship are described in paragraph 22. The tube rating charts supplied by the manufacturer should be consulted. Ordinarily, it is said that there is a direct ratio relationship between radiographic density and the milliamperage which is used (other factors being constant). This is generally true, provided the performance capacity of the transformer be not taxed. The design of some X-ray transformers is such that the wave form is distorted when operating at high milliamperage settings. In such cases, the radiographic density can- not be expected to be proportionate to the milliamperage. This may pxplain the reason why a certain technique may be unsatisfactory when used with one unit even though that same technique was found to have been ideal when used with another unit. Moreover, with some X ray apparatus, a. c. milliammeters are used whereas with others d. c. meters are used; a. c. meters are calibrated in terms of effec- tive values whereas d. c. meters are calibrated in terms of average values. This difference, too, may account for difficulties in duplica- tion of results. A number of other factors might also be mentioned, such as differences in the inherent filtration of X-ray tubes, changes in the performance of any one tube because of pittings of its target and the resultant filtrations by the substance of the target itself, 68 TM 8-240 ROENTGENOGRAPHIC TECHNICIANS 48 as well as by tungsten which may have become impregnated into the glass wall of the tube. Such factors as these account for the statement that “the milliamperage of one unit may not be identi- cal with the milliamperage of another unit.” However, a large percentage of these variations in performance can be overcome by the use of an ideal technique, invoking compensation factors which might concern a particular cassette, a particular grid, cone, or other auxiliary device. (2) Time of exposure should be reduced to the minimum to coun- teract the effects of motion. For all practical considerations, the time of the exposure and the milliamperage are interchangeable. The greater the milliamperage the less will be the time of exposure required and vice versa. Two types of motion are to be considered: voluntary and involuntary. Voluntary motion includes the movement of mus- cles which ordinarily would be controlled (even though these move- ments may not have been intentional). Involuntary motion includes the pulsation of arteries and movements of veins as well as of the heart. For roentgenography of the chest, the exposure time should be no greater than %() second (if these pulsation movements are to be counteracted for the majority of cases). (3) Distance, with reference to roentgenography, usually implies the focal-film distance, which is the distance between the focal spot of the tube and the film. The focal-skin distance is to be distinguished as the distance between the focal spot of the tube and the skin of the patient. It is to be considered when calculating the summation dosage of X-radiation received by the patient. A third type of distance re- ferred to is part-film distance, which is the distance between any level of the part being studied and the film. This last type of distance is of importance with respect to distortion as already described. Be- cause of the thickness of certain parts, such as the chest, their part- film distance must be compensated by using a relatively long focal-film distance. When possible, the focal-film distance for chest roent- genography should be 72 inches or longer. This distance may be neces- sary for roentgenography where measurements are to be made on the roentgenogram, as for instance, in the case of the “sella turcica.” Such work is called teleroentgenography. For most requirements, the com- monly used focal-film distance is 30 inches. This latter distance has been chosen because for many parts the thickness is not such as to incur an appreciable amount of distortion at this distance, and the milliamperage requirements in relation to the exposure time are ordi- narily easily accommodated by the capacities of the X-ray machine and the X-ray tube. For this reason, the majority of grids have been 69 TM 8-240 48 MEDICAL DEPARTMENT constructed to a 30- or a 36-inch radius. When using a grid (i. e., Bucky), it is necessary to be guided by the grid radius. However, there is some latitude as to the adaptation of modern grids to distances greater and also to distances less than their radius. When having to use a tube with a large focal spot, it is advisable to use a relatively long focal-film distance if sharp detail is essential. Occasionally it is de- sirable to shorten the focal-film distance to less than that for which a certain technique has been developed. In either instance, it may be convenient to convert the milliampere-second values of the calcu- lated technique as indicated in table VI. Known distance (inches) -t vr 05 05 Ox O. 4^ 4* 4- CO CO to to o Ox o Ox o 00 Ox O Ox o on k—4 to Ox k—4 to to to co CO Ox 05 to CO Ox -J k—4 Ox -4 I—4 CD CD CD k-4 k—4 CO • o k—4 k—4 to to CO CO oo 4- Ox —4 4- M 00 k—4 Ox o 05 CD 4* 05 4- 4^ k—4 I—4 k—4 CO Ox to to to CO 4^ 4- Ox 05 -4 CO CD 4^ Ox CO 4- O CD CO k—4 -4 05 05 H—4 I—4 k—4 to 4- O CO co CO 4- On 05 05 -1 CO -1 OX •—4 CO 00 4>- CO 4^ CD CD k—4 —4 05 g k-4 k—4 k—4 to CO 45- p Ox co 4- 4* Ox 05 00 00 to 05 to Ox CD k—4 00 05 k—4 00 00 Ox 4^ 05 CD Pj k—4 H-i k—4 to co 4- CD GO 4- Ox 05 -I CO 4- 00 OX 05 & 4- -J Ox 4- 05 to 4- 4- oo 05 00 c k-4 h-4 V—4 k—4 to to 4^ 50 5 0 cr 4- On On 05 00 o to Ox o -1 00 i—1 CD CD CO 00 co 4* 00 k—4 k—4 to CO 4^ Ox Ox On 05 -