WEBVTT 00:00.000 --> 00:30.000 position:50% align:top line:0% *This machine-generated transcript may have errors. If remediation or a manually-generated transcript is needed, please contact NLM Support at https://support.nlm.nih.gov.* 00:32.740 --> 00:35.450 Radiographic processing is necessary for the 00:35.450 --> 00:38.050 production of the useful visible image. 00:38.240 --> 00:40.910 It links exposure to interpretation and 00:40.910 --> 00:42.160 influences quality. 00:42.740 --> 00:45.730 An understanding of basic sense saitama tree is necessary 00:45.730 --> 00:47.060 for subsequent lectures. 00:47.440 --> 00:50.420 Sensei Tom a tree is defined and the anatomy of the 00:50.420 --> 00:52.360 sensitive metric curve is detailed 00:52.820 --> 00:55.410 density and contrast are discussed and 00:55.410 --> 00:57.860 methods of their calculations are presented. 01:03.540 --> 01:06.510 When we look at the graze of 01:06.520 --> 01:07.650 a radiograph, 01:07.660 --> 01:10.520 we're looking at the anatomy as portrayed in 01:10.520 --> 01:11.720 this picture, 01:11.720 --> 01:12.750 this radiograph. 01:13.140 --> 01:15.910 We're looking at bits of information and we're trying 01:15.910 --> 01:18.230 to understand from 01:18.290 --> 01:20.160 analyzing these shades of gray, 01:20.540 --> 01:22.660 what's right or wrong with the patient. 01:23.240 --> 01:23.500 Now, 01:23.500 --> 01:26.490 as we look at the bits of anatomy as expressed as 01:26.500 --> 01:28.760 shades of gray or black or the absence of 01:29.440 --> 01:30.160 blackness, 01:30.610 --> 01:33.610 then we really are judging the quality of the 01:33.610 --> 01:35.860 radiograph by many criteria. 01:35.950 --> 01:38.830 One of course is positioning visualization 01:38.830 --> 01:40.260 of the anatomical part. 01:40.640 --> 01:42.990 We also are judging the general shades of 01:42.990 --> 01:45.990 gray by a subjective means. 01:45.990 --> 01:47.360 We are personally saying, 01:47.360 --> 01:50.200 well I like this shade of gray or I like this level 01:50.200 --> 01:52.570 of density or this 01:52.580 --> 01:55.250 cleanliness in the areas where there should be no density. 01:56.040 --> 01:58.520 So we need a way in which we can 01:58.790 --> 02:00.400 look at the radiograph, 02:00.410 --> 02:01.330 the shades of gray, 02:01.330 --> 02:04.050 the gray scale in a way that is not 02:04.050 --> 02:06.020 subjective but is more technically 02:06.360 --> 02:08.950 scientific or more technically 02:08.960 --> 02:09.710 correct. 02:09.820 --> 02:12.260 And this method has provided us by the 02:12.260 --> 02:15.030 system or the word that 02:15.030 --> 02:17.460 describes a system called Sensei tom a tree, 02:17.940 --> 02:20.790 sensitization or sensitizing means to 02:20.790 --> 02:21.650 expose. 02:21.660 --> 02:24.420 And sensitive geometry is a measure 02:24.650 --> 02:26.080 of exposures. 02:27.040 --> 02:28.220 So first of all, 02:28.230 --> 02:29.700 let's consider some of the 02:30.940 --> 02:33.870 definitions that we're going to be dealing with and some of the components 02:34.140 --> 02:36.220 of Sensei tom a tree. 02:36.630 --> 02:37.340 First of all, 02:37.350 --> 02:40.300 density is a measure of the blackening 02:40.320 --> 02:41.460 on the film. 02:42.940 --> 02:45.740 This is simply the amount of silver 02:45.860 --> 02:48.620 in a given area and basically what we 02:48.620 --> 02:51.200 talk about a radiograph as the whole film being 02:51.200 --> 02:51.960 exposed. 02:52.530 --> 02:54.940 Some of the areas of course are non anatomical, 02:55.230 --> 02:57.560 but wherever we have density, 02:58.040 --> 02:59.830 we have blackening on the film. 02:59.830 --> 03:01.160 We have piles of silver. 03:01.740 --> 03:04.660 Now you can have a high density as we see here. 03:04.660 --> 03:07.650 It's very black and we have a low density, 03:08.340 --> 03:09.790 Usually in radiography, 03:09.790 --> 03:12.570 we very seldom have a use for a density that is 03:12.570 --> 03:15.090 greater than 3.0 as a matter of fact, 03:15.100 --> 03:18.050 the eye does not respond unaided to a 03:18.050 --> 03:20.460 density that is greater than 3.0 03:21.540 --> 03:22.390 On the other hand, 03:22.400 --> 03:25.230 the lowest density that we might use or have 03:25.230 --> 03:28.110 available to us would be approximately .18. 03:28.940 --> 03:31.200 When we talk about densities often times, 03:31.200 --> 03:33.830 people will just say simply a density of 18, 03:34.020 --> 03:36.160 but they mean 0.18. 03:37.140 --> 03:40.000 The point here is that 03:40.010 --> 03:42.890 a density of .18 is the inherent 03:42.900 --> 03:45.720 fog and loss of density due to 03:45.730 --> 03:47.160 the structure of the film. 03:47.540 --> 03:50.350 This is often said to be manufacturing base plus fog. 03:50.740 --> 03:53.670 In reality we know that we have a very 03:53.670 --> 03:56.650 thick piece of bass on seven mils in thickness 03:56.660 --> 03:59.160 that is seven thousands of an inch thick. 03:59.540 --> 04:00.820 That the gelatin layer is very, 04:00.820 --> 04:02.750 very small relative to this. 04:03.140 --> 04:05.660 Both gelatin layers together only accounting for 04:05.670 --> 04:07.930 approximately half a mil thickness. 04:08.440 --> 04:11.370 The density this 0.18 density 04:11.610 --> 04:14.270 that we're talking about uh is 04:14.280 --> 04:16.930 primarily due to loss of density in the 04:16.930 --> 04:17.300 base. 04:17.300 --> 04:17.680 The base, 04:17.680 --> 04:18.080 of course, 04:18.080 --> 04:19.430 is a plastic base. 04:19.490 --> 04:21.210 As light passes through it, 04:21.230 --> 04:22.440 it's attenuated, 04:22.440 --> 04:23.290 it's absorbed, 04:23.300 --> 04:26.260 it's deflected or refracted so that the 04:26.260 --> 04:29.230 light doesn't continue to pass through the base and out the 04:29.230 --> 04:29.850 other side. 04:30.430 --> 04:33.040 That means that as we perceive light 04:33.050 --> 04:34.440 passing through this base, 04:34.560 --> 04:37.510 some will appear to have been lost in 04:37.510 --> 04:38.600 an average film. 04:38.610 --> 04:41.320 Fresh out of the out of the film been placed into a 04:41.320 --> 04:43.860 processor and developed fixed and washed, 04:44.340 --> 04:46.540 in which there has been no exposure except 04:46.540 --> 04:49.410 manufacturing and hopefully the correct story. 04:49.410 --> 04:50.650 So there's no added density. 04:51.340 --> 04:54.250 We will find a base plus fog of .18 04:54.740 --> 04:57.570 Of this .18 Over 04:57.570 --> 05:00.530 75% will be due to the loss of light passing through the 05:00.530 --> 05:03.100 base or approximately .16. 05:03.740 --> 05:06.480 The difference between .16 and 05:06.570 --> 05:08.770 .18 is .02. 05:09.000 --> 05:11.270 And this is usually the maximum amount of 05:11.280 --> 05:14.030 manufacturing fog that is generated in the 05:14.030 --> 05:16.630 gelatinous or gelatin layers or 05:16.870 --> 05:19.770 recording media in the gelatin layers that which we normally 05:19.770 --> 05:20.750 call the emotions. 05:21.440 --> 05:23.950 So you can see that the manufacturing fog is very, 05:23.950 --> 05:24.720 very small. 05:24.950 --> 05:27.390 And that most of this base plus fog 05:27.390 --> 05:30.310 density is due to the attenuation of 05:30.400 --> 05:33.370 flight or the non passing of light through the 05:33.370 --> 05:34.300 base material. 05:34.520 --> 05:34.850 Of course, 05:34.850 --> 05:37.710 the base also has a slight blue tint and this 05:37.710 --> 05:40.280 helps the radiologist in making his 05:40.290 --> 05:42.160 visualization of the information. 05:43.240 --> 05:45.790 Let's look further at our scale of 05:45.790 --> 05:46.440 grays. 05:46.440 --> 05:48.960 We know what the high limit is and the low limit, 05:49.190 --> 05:52.170 but what would the entire scale look 05:52.170 --> 05:54.840 like if we had many levels here? 05:54.840 --> 05:57.440 We see that we're going from a density of zero. 05:57.580 --> 06:00.060 There is no silver at this level, 06:00.690 --> 06:02.160 The density of zero. 06:02.540 --> 06:04.970 And then we start to get more and more 06:04.980 --> 06:05.600 silver. 06:05.610 --> 06:08.150 So therefore we get more and more blackening 06:08.640 --> 06:09.940 At the highest level. 06:09.950 --> 06:12.110 You can see that it's very black. 06:12.120 --> 06:12.610 Matter of fact, 06:12.610 --> 06:15.400 it's so black that you probably cannot distinguish 06:15.400 --> 06:17.480 between a level of 2.5 and 06:17.490 --> 06:18.730 3.0, 06:18.860 --> 06:21.860 so we have a full scale of densities. 06:22.340 --> 06:24.220 How do we measure these densities? 06:24.550 --> 06:25.010 Well, 06:25.020 --> 06:26.700 when we have a piece of film, 06:26.710 --> 06:29.510 whether it has anatomy or it has a sensitive 06:29.510 --> 06:32.490 metric shade of grays we see 06:32.490 --> 06:32.960 here, 06:33.540 --> 06:36.330 we measure by having a light source 06:36.630 --> 06:39.250 and calibrated light source that will pass light 06:39.260 --> 06:40.260 through the film, 06:41.040 --> 06:43.130 we can monitor how much light is 06:43.740 --> 06:46.630 going to pass through the film and how much light actually 06:46.630 --> 06:47.660 comes out the other side. 06:48.440 --> 06:51.220 So the difference between the incident light and the 06:51.220 --> 06:54.170 light that actually comes out through the film, 06:54.170 --> 06:56.970 the transmitted light allows us to 06:56.970 --> 06:59.110 calculate the amount of density. 06:59.940 --> 07:02.500 We measure density in this case 07:02.600 --> 07:03.800 as you see here, 07:03.800 --> 07:06.670 the light source as such and the measurement device 07:06.680 --> 07:09.120 are all contained in one and this is done 07:09.130 --> 07:10.670 on a density thomas. 07:11.340 --> 07:13.720 A dense odometer measures density. 07:14.140 --> 07:17.100 This is a very common one that's readily available. 07:17.490 --> 07:19.940 I should hasten to point out that as you can see, 07:19.940 --> 07:22.790 the individual here is monitoring this 07:22.800 --> 07:23.950 sensitive metric strip, 07:24.540 --> 07:27.450 the shades of gray and we had the light 07:27.940 --> 07:30.710 table and a photo multiplier tube and then 07:30.720 --> 07:33.610 the sweet pan that when you have a unit with a 07:33.610 --> 07:34.360 sweet pan, 07:34.660 --> 07:37.240 that you on occasion have to make an 07:37.240 --> 07:40.080 interpretation of of exactly where that needle 07:40.090 --> 07:43.070 lies insofar as between one point and the 07:43.070 --> 07:43.660 next point. 07:44.240 --> 07:46.910 And that many times people 07:46.910 --> 07:49.190 assume unfortunately, 07:49.190 --> 07:51.470 that when they buy themselves a dense odometer, 07:51.670 --> 07:54.400 that this really is the key to quality 07:54.840 --> 07:55.860 quality control system. 07:56.340 --> 07:59.060 This is not necessarily so because it's 07:59.060 --> 08:01.400 obvious that when you have a need to make an 08:01.400 --> 08:04.100 interpretation in the reading of a density, 08:04.460 --> 08:07.460 that the difference between one person's method of reading and 08:07.460 --> 08:10.420 interpreting can lead to an error as compared with 08:10.420 --> 08:11.210 another persons. 08:11.450 --> 08:12.490 So in general, 08:12.830 --> 08:14.320 when you buy a density tom attar, 08:14.330 --> 08:17.130 the biggest expense is the allocating of one 08:17.130 --> 08:19.960 person's time to do all of the sense of the metric and density 08:19.960 --> 08:22.890 metric reading of films and plotting 08:22.890 --> 08:25.850 interpretation and we'll get into this as we go along. 08:27.240 --> 08:29.440 Now if we take these two 08:29.450 --> 08:30.390 skulls, 08:30.680 --> 08:33.410 we can see that there's a 08:33.410 --> 08:35.840 very slight difference between the two skull 08:35.840 --> 08:36.500 densities. 08:36.510 --> 08:39.420 At the point where the circle is of course there's a 08:39.430 --> 08:42.260 slightly greater density in the overall radiograph. 08:42.940 --> 08:45.810 But at these two spots which 08:45.810 --> 08:48.810 are identical in the amount of exposure passing 08:48.810 --> 08:50.760 through this part of the anatomy, 08:51.240 --> 08:53.820 We have a difference of density of .6, 08:53.820 --> 08:56.820 so 2.55 08:56.830 --> 08:59.360 or a difference of .05. 09:00.100 --> 09:01.680 That's a very small amount of difference. 09:02.080 --> 09:04.740 But the I can see this small amount of 09:04.740 --> 09:06.860 difference between the two. 09:08.340 --> 09:11.100 It's this ability to see the small 09:11.110 --> 09:14.000 amounts of differences that allows us to say that the 09:14.000 --> 09:16.880 I really is a very excellent density 09:16.880 --> 09:19.670 metric tools with training your eye can be a 09:19.670 --> 09:20.930 very critical tool. 09:20.940 --> 09:23.890 It can help you to ascertain whether or not you have too much 09:23.890 --> 09:24.420 density, 09:24.590 --> 09:25.490 too little density. 09:25.760 --> 09:28.190 And this is really why we need to understand since optometry, 09:28.250 --> 09:30.720 so that we can better judge the quality of the 09:30.720 --> 09:33.280 radiograph as to too much 09:33.280 --> 09:36.180 density or too little density and thereby relate to 09:36.180 --> 09:38.860 whether or not we're correctly visualizing the anatomy. 09:39.440 --> 09:42.440 Now keep in mind that we talked about density is the 09:42.440 --> 09:43.850 amount of blackening on the film. 09:44.240 --> 09:47.150 We measure density by the 09:47.540 --> 09:49.660 amount of light passing through the film. 09:50.740 --> 09:53.650 And we see here that when we have 100% light 09:53.650 --> 09:54.390 transmitted, 09:54.840 --> 09:55.930 we have zero density. 09:56.220 --> 09:57.420 There is no density. 09:57.420 --> 09:58.380 There is no silver, 09:58.390 --> 09:59.850 there's nothing to block the light. 09:59.850 --> 10:01.260 So all the light passes through. 10:01.910 --> 10:04.590 And when we have 10% of the light being 10:04.590 --> 10:05.190 transmitted, 10:05.190 --> 10:06.960 we have a density of one. 10:07.340 --> 10:09.200 These numbers 012, 10:09.200 --> 10:11.750 three are logarithmic numbers 10:14.390 --> 10:17.370 as a measure of the amount of 10:17.370 --> 10:18.690 light being transmitted. 10:19.340 --> 10:22.230 There's a another way of expressing it as the log 10:22.230 --> 10:25.160 of the inverse of the transmit points of light 10:25.400 --> 10:26.150 through the film. 10:26.940 --> 10:29.660 But basically we have this kind of a density scale 10:31.340 --> 10:33.650 012 and three. 10:33.960 --> 10:36.910 This is our full range for medical radiography. 10:37.440 --> 10:40.170 Industrial radiography sometimes 10:40.180 --> 10:42.980 uh has a tendency goes high as a level of 10:42.980 --> 10:44.070 density of five. 10:44.150 --> 10:45.190 And of course as I mentioned, 10:45.190 --> 10:46.970 this is beyond the capability of the eye. 10:46.970 --> 10:48.060 So they need very hot, 10:48.440 --> 10:49.210 bright lights, 10:49.220 --> 10:52.170 hot lights to be able to read these very high densities. 10:53.640 --> 10:56.270 Now let's consider the difference between 10:56.270 --> 10:56.990 densities. 10:57.500 --> 10:59.950 The difference between densities is the definition of 10:59.950 --> 11:02.830 contrast contrast is a difference between 11:02.830 --> 11:04.140 two or more densities. 11:04.840 --> 11:07.620 We've often heard the little 11:07.620 --> 11:09.350 statement that contrast 11:10.240 --> 11:12.880 contrast enhances the visibility of 11:12.890 --> 11:13.490 detail. 11:14.040 --> 11:15.470 It enhances the visibility, 11:15.480 --> 11:16.770 does not create detail, 11:16.770 --> 11:18.440 does not create detailed sharpness. 11:18.810 --> 11:21.530 It simply enhances the visibility of detail 11:21.530 --> 11:23.690 allows us to see differences if you will. 11:23.800 --> 11:26.770 So if we have a large difference between two things, 11:26.990 --> 11:29.960 then we can more easily see that there is this difference. 11:30.340 --> 11:32.840 Another way of saying it is if we have two densities of equal 11:32.840 --> 11:34.410 values side by side, 11:35.140 --> 11:37.860 if they appear equal Then we see no difference 11:37.860 --> 11:38.650 between the two. 11:39.240 --> 11:42.240 But we know that the anatomy of a patient is 11:42.240 --> 11:44.270 made up of many anatomical 11:44.530 --> 11:45.280 differences. 11:45.730 --> 11:47.850 And you've probably even heard the mhm. 11:48.740 --> 11:51.550 The phrase anatomical contrast because of 11:51.550 --> 11:54.550 these differences between bone tissue, 11:54.740 --> 11:57.650 air water and things of this nature within the 11:57.760 --> 12:00.250 physiological structure of the patient. 12:01.440 --> 12:04.350 So contrast is a difference between two 12:04.360 --> 12:05.940 densities two or more densities. 12:05.950 --> 12:08.660 Here we see two numbers and we can 12:08.660 --> 12:11.140 say that just these pure numbers. 12:11.150 --> 12:12.480 1.26. 12:12.480 --> 12:15.020 If we take away .26, 12:15.030 --> 12:17.660 the difference is 1.00. 12:18.040 --> 12:19.320 So this number, 12:19.330 --> 12:22.210 1.00 is a difference. 12:22.720 --> 12:24.250 These numbers are, 12:24.250 --> 12:24.670 as I said, 12:24.670 --> 12:27.160 just simply numbers but they could represent 12:27.540 --> 12:29.370 Densities to different densities. 12:29.670 --> 12:32.590 And the 1.00 then would 12:32.600 --> 12:34.350 be our contrast number. 12:34.640 --> 12:37.130 It would be the result of subtracting one from the other. 12:37.130 --> 12:39.360 And this will tell us the difference the amount of 12:39.510 --> 12:42.420 density that is between these two 12:42.500 --> 12:43.260 extremes. 12:45.390 --> 12:47.990 In this slide we see a more practical example in 12:47.990 --> 12:50.220 which there is 12:51.190 --> 12:52.760 in this particular scale, 12:53.640 --> 12:56.250 really only two steps of density, 12:56.840 --> 12:59.130 1.5 and 12:59.130 --> 13:01.700 3.0 Remember at zero we have 13:01.870 --> 13:04.450 all the light passing through 100% transmission. 13:04.840 --> 13:06.970 And here where we have some density, 13:07.310 --> 13:09.430 there's less light and at 3.0, 13:09.660 --> 13:11.760 there's very little light passing through. 13:12.710 --> 13:15.680 Look at this scale over here notice that 13:15.680 --> 13:17.760 there's a lot of shades of gray in between 13:18.740 --> 13:18.880 Now, 13:18.880 --> 13:21.730 which scale would be a long scale of contrast, 13:22.110 --> 13:24.480 which would be a short scale of contrast. 13:24.810 --> 13:25.140 Well, 13:25.150 --> 13:28.150 basically we can say that This is the more 13:28.150 --> 13:30.650 contrast e of the two gray 13:30.650 --> 13:33.230 scales of the two cents symmetric strips. 13:33.500 --> 13:34.800 This is more contrasting. 13:34.810 --> 13:37.710 It has higher contrast and we 13:37.710 --> 13:40.670 can see that there's less gray steps 13:40.740 --> 13:41.650 in this scale. 13:41.660 --> 13:44.320 So it is a short scale of contrast. 13:44.560 --> 13:47.540 So we have what seems to be conflicting terms. 13:47.690 --> 13:50.480 We have a short scale of contrast and 13:50.490 --> 13:52.320 yet it's high contrast here. 13:52.320 --> 13:55.060 We have a long scale of contrast but it's 13:55.070 --> 13:56.820 low contrast. 13:57.120 --> 13:59.950 Notice the difference between the various steps 13:59.950 --> 14:02.720 here Between this step and the next one. 14:02.720 --> 14:05.350 We have a difference of .5. 14:05.740 --> 14:08.640 We take 1.0 we subtract .5 and the 14:08.640 --> 14:11.600 difference is .5 so we have a difference Or a 14:11.600 --> 14:14.100 contrast of .5 Over 14:14.100 --> 14:14.640 here. 14:14.650 --> 14:17.560 If we take the difference between 1.5 and 14:17.560 --> 14:18.760 its next adjacent step, 14:18.770 --> 14:20.110 we see that that's 3.0, 14:20.110 --> 14:22.060 the difference is 1.5, 14:22.640 --> 14:25.430 So it's 1.5 as a contrast number 14:25.530 --> 14:26.960 versus .5. 14:27.840 --> 14:30.700 The contrast level here is approximately three times 14:30.710 --> 14:33.500 greater than is the contrast expressed by all of 14:33.500 --> 14:36.380 these shades of gray in this long scale 14:36.390 --> 14:38.490 of contrast example. 14:39.440 --> 14:41.700 So we have short scale of contrast. 14:41.700 --> 14:44.380 We have long scale contrast. 14:44.420 --> 14:46.910 Most people just simply call it low 14:46.910 --> 14:49.350 contrast or high contrast. 14:49.570 --> 14:52.330 Let's look more closely at how contrast might aid 14:52.340 --> 14:54.050 our interpretation of information. 14:54.440 --> 14:56.960 We can see here that there is two 14:56.960 --> 14:57.660 slides. 14:57.670 --> 15:00.410 We could say that one has high contrast and one is 15:00.410 --> 15:00.910 low. 15:01.160 --> 15:03.490 You may not really like either 15:03.490 --> 15:04.180 radiograph, 15:04.190 --> 15:06.910 but let's consider first of all that 15:07.040 --> 15:09.910 in this image is very bright. 15:09.920 --> 15:11.330 There's blacks and whites. 15:11.480 --> 15:13.860 This is a very high contrast image, 15:14.540 --> 15:16.630 but notice the detail of this little 15:17.040 --> 15:18.560 unusual Q popular here. 15:19.640 --> 15:20.960 We can see the railing. 15:20.960 --> 15:23.060 We can see that it's attached to the building, 15:24.940 --> 15:27.800 but also notice that we don't see any clouds 15:28.180 --> 15:29.750 and down on the side here, 15:29.800 --> 15:32.720 it's very difficult to see the distinguishing piles 15:32.810 --> 15:34.140 of snow. 15:34.150 --> 15:36.250 And yet we can very easily see this window 15:37.210 --> 15:39.380 and we can see some of the details around the windows, 15:39.380 --> 15:40.160 the landscape. 15:40.540 --> 15:40.650 Now, 15:40.650 --> 15:43.600 let's go to the next radiograph and where we have a lot of 15:43.990 --> 15:44.780 densities, 15:44.790 --> 15:47.680 a lot of shades of gray and there's 15:47.680 --> 15:48.520 very little white, 15:49.940 --> 15:51.300 characteristically little black, 15:51.300 --> 15:53.980 There's a lot of shades of darkness, 15:54.020 --> 15:56.340 dark grays in this radiograph. 15:56.340 --> 15:59.260 We see that you can't really tell that 15:59.260 --> 16:01.480 there's a post here connecting the cumulus. 16:01.480 --> 16:04.180 It's very difficult to see and yet notice all the 16:04.180 --> 16:06.710 beautiful clouds in the sky that we missed before. 16:06.710 --> 16:09.000 The other radiograph down here. 16:09.000 --> 16:09.930 It's very difficult. 16:10.150 --> 16:13.050 You may not be able to see that there's a window there or how the land 16:13.050 --> 16:15.510 slopes and yet in these 16:16.140 --> 16:18.170 formations of the snow on bushes, 16:18.170 --> 16:21.030 we can more easily see all of the intricate shapes. 16:21.640 --> 16:24.060 So this is to say that we may 16:24.820 --> 16:27.210 consider high contrast and radiography. 16:27.220 --> 16:28.130 Most people do. 16:28.140 --> 16:30.730 Most people are very concerned about high contrast, 16:31.240 --> 16:33.990 but this does not mean that we use the highest contrast 16:33.990 --> 16:34.570 possible. 16:34.950 --> 16:37.840 Nor does it mean that we have a system that of course would have no 16:37.840 --> 16:38.490 contrast. 16:38.490 --> 16:41.450 We need contrast to see differences to see the subtle 16:41.450 --> 16:42.760 differences of the anatomy. 16:43.840 --> 16:46.140 We do have a problem in selecting 16:46.140 --> 16:48.770 contrast and trying to come up with the best system. 16:48.780 --> 16:51.600 We neither need low contrast nor the highest 16:51.600 --> 16:52.830 possible contrast, 16:52.840 --> 16:54.850 but we do need contrast 16:56.040 --> 16:56.230 here. 16:56.230 --> 16:58.140 We see a schematic, 16:58.260 --> 16:58.880 if you will, 16:58.880 --> 17:00.900 it's a uh phantom 17:01.070 --> 17:04.020 exposure in which we have a synth 17:04.030 --> 17:07.010 synthetic contrast media 17:07.010 --> 17:07.660 injected. 17:08.640 --> 17:11.560 One is a low contrast exposure 17:11.560 --> 17:13.300 and the other is a high contrast exposure. 17:13.310 --> 17:13.960 Can you tell? 17:13.970 --> 17:16.780 Which is which keep in mind that these are 17:16.780 --> 17:17.930 phantom exposures, 17:18.640 --> 17:19.060 wow. 17:19.440 --> 17:21.860 In this case there's very little grays. 17:21.870 --> 17:24.820 And over here there's a lot of grays here where there's a little 17:24.820 --> 17:25.240 grays. 17:25.240 --> 17:27.870 We see no information in what might 17:27.870 --> 17:30.270 be the intestinal track 17:30.840 --> 17:33.800 in this case there is just the faint image of 17:33.810 --> 17:34.820 some information. 17:34.830 --> 17:37.170 Some particles or something there. 17:38.240 --> 17:38.600 Well, 17:38.610 --> 17:40.550 really neither one is very acceptable. 17:40.940 --> 17:43.280 But what if we balanced our contrast? 17:43.280 --> 17:45.830 We came out with a system that gave us 17:45.930 --> 17:48.150 not maximum contrast nor minimal, 17:48.150 --> 17:50.360 but just the right amount as here. 17:51.120 --> 17:53.350 Now we can see the information very clearly 17:53.940 --> 17:56.540 we have some shades of gray but we have a 17:56.540 --> 17:58.140 difference between these shades of gray. 17:58.140 --> 18:00.490 We have a contrast level here. 18:00.500 --> 18:03.340 It's washed out and here is masked over 18:03.340 --> 18:04.650 by gray's. 18:04.720 --> 18:07.720 So this is an excellent example 18:07.730 --> 18:10.270 of balancing to achieve the best 18:10.270 --> 18:11.770 contrast that we can. 18:13.340 --> 18:16.320 All of this discussion on contrast is 18:16.320 --> 18:19.310 a difference between densities and the definition of 18:19.310 --> 18:19.730 density. 18:19.730 --> 18:22.450 Just the amount of blackening on the film is the 18:22.450 --> 18:24.630 basis of sensitive geometry. 18:24.900 --> 18:27.140 We might define basic sense optometry 18:27.440 --> 18:30.320 as the quantitative measure 18:30.330 --> 18:33.070 of the response of film to exposure 18:33.070 --> 18:33.950 and development. 18:34.540 --> 18:37.540 Probably the thing that confuses most people is the fact 18:37.540 --> 18:40.060 that this statement is exposure 18:40.440 --> 18:41.510 and development, 18:41.710 --> 18:44.510 not just exposure or not just development 18:44.730 --> 18:47.410 but the development along with the exposure, 18:47.430 --> 18:50.000 each one influences the 18:50.010 --> 18:51.170 response of the film. 18:51.840 --> 18:54.770 So sensitive geometry is the quantitative 18:55.070 --> 18:57.650 measure of the 18:57.650 --> 18:59.350 response of film too, 18:59.740 --> 19:01.960 exposure and development. 19:02.540 --> 19:04.760 And of course development means processing. 19:05.540 --> 19:08.310 If we look at the basis of uh 19:08.320 --> 19:09.240 sense of geometry, 19:09.240 --> 19:11.090 there is a system employed here, 19:11.110 --> 19:14.080 There's four things we need to do to generate 19:14.080 --> 19:17.040 some information sense symmetrically or technically if 19:17.040 --> 19:17.450 you will, 19:18.140 --> 19:20.730 we can say that we first of all have to expose, 19:20.740 --> 19:23.660 we have an exposure factor development of course 19:24.240 --> 19:25.620 and then we measure, 19:25.630 --> 19:28.570 we make a measurement such as with our eyes 19:28.580 --> 19:31.010 value judgment or we might use a dense 19:31.010 --> 19:32.830 odometer and then we interpret, 19:32.830 --> 19:34.030 we make an interpretation, 19:34.030 --> 19:34.700 we say, 19:34.700 --> 19:36.660 well is this good or bad? 19:37.140 --> 19:40.110 Let's look more closely at how we can use 19:40.110 --> 19:41.210 this up here, 19:41.210 --> 19:43.830 We've made the exposure with an image quality device 19:44.440 --> 19:47.320 most usually called a stepped wedge and most 19:47.320 --> 19:50.080 step wedges are referred to as a square root of two step 19:50.080 --> 19:50.480 wedge, 19:50.490 --> 19:53.480 although many seldom are of the less 19:53.480 --> 19:54.270 expensive type. 19:55.540 --> 19:58.480 We have a series of steps so that with one exposure 19:58.490 --> 20:01.430 we get many little exposures and this 20:01.430 --> 20:04.200 just saves some work and time and it helps us to produce a more 20:04.200 --> 20:07.170 uniform film and symmetrically 20:07.740 --> 20:09.910 so this would be our exposure device. 20:10.050 --> 20:12.710 And then we make an image on the film and this is 20:12.710 --> 20:13.380 processed. 20:13.730 --> 20:14.760 And then we plot, 20:15.340 --> 20:18.330 we measure and plot and then we interpret the shape 20:18.330 --> 20:19.060 of this curve, 20:19.950 --> 20:22.870 notice that we're plotting the log relative 20:22.870 --> 20:25.460 exposure against the total density 20:25.650 --> 20:26.740 gannon log units. 20:27.840 --> 20:30.680 And we need to look more closely at how this 20:30.680 --> 20:31.410 all works. 20:31.940 --> 20:33.060 So let's continue. 20:33.060 --> 20:35.850 And first of all consider this is our exposure 20:35.850 --> 20:36.460 device. 20:37.040 --> 20:39.790 We have a basically a square root of two 20:39.800 --> 20:41.160 aluminum stepped wedge. 20:41.540 --> 20:43.580 We of course have it very thick here, 20:43.580 --> 20:45.670 so less exposure will pass through. 20:45.780 --> 20:48.750 Down here is thinner and more will pass through and the image will 20:48.750 --> 20:49.280 be darker. 20:49.280 --> 20:51.060 So this gives us a shade of grays. 20:51.310 --> 20:54.210 We have a lead block here which will provide an area where there is 20:54.210 --> 20:54.790 no exposure. 20:54.790 --> 20:57.700 So we may monitor the base plus fog density to 20:57.700 --> 21:00.580 see how this influences the entire shade of 21:00.580 --> 21:01.140 grays. 21:01.140 --> 21:01.500 Of course, 21:01.500 --> 21:03.390 of the baseball song is very high. 21:03.390 --> 21:06.100 Then this will influence all of these steps equally. 21:07.120 --> 21:07.570 Next, 21:07.570 --> 21:10.500 after we made the exposure under controlled conditions 21:10.500 --> 21:11.500 and we process, 21:12.040 --> 21:14.800 then we end up with a gray scale. 21:15.090 --> 21:16.550 And using the density thermometer, 21:16.760 --> 21:19.690 we can apply these numbers and we can 21:19.690 --> 21:21.880 find out how the densities 21:22.040 --> 21:22.710 increase. 21:24.140 --> 21:25.840 Using these numbers. 21:25.840 --> 21:28.700 Then you can see along here we have an exposure 21:29.240 --> 21:32.060 and we have densities and we plot now notice 21:32.060 --> 21:34.390 that this is not a nice straight line. 21:34.600 --> 21:37.360 It has a change to it. 21:37.930 --> 21:40.770 This light area down here we have a 21:40.770 --> 21:43.690 light slowly increasing area here. 21:43.700 --> 21:46.690 Then it increases more uniformly up through this 21:46.690 --> 21:49.560 area and then it starts to drop 21:49.560 --> 21:50.060 off. 21:50.070 --> 21:52.430 It decreases in its rate of 21:52.440 --> 21:54.560 density increments increasing. 21:55.540 --> 21:58.420 So we can add some anatomy to this 21:58.660 --> 21:59.670 particular shape. 22:00.440 --> 22:02.780 We can say that down here we have a toe. 22:02.790 --> 22:04.410 This is a nonlinear portion. 22:04.940 --> 22:07.660 It's constantly changing as you increase in exposure. 22:07.670 --> 22:10.450 Specifically as you go up the relative M A s. 22:10.450 --> 22:13.070 We see down here is we double R M a S 22:13.940 --> 22:14.960 Or a factor of two. 22:15.440 --> 22:17.460 We see that the density doesn't go up equally. 22:17.460 --> 22:20.270 It just goes up very slowly and then it starts to increase 22:20.270 --> 22:20.840 faster. 22:21.200 --> 22:22.550 So this is nonlinear. 22:23.340 --> 22:25.650 Then we reach a point where it straightens out. 22:25.660 --> 22:28.380 And as you go up a unit in exposure. 22:28.620 --> 22:31.390 This way you will go up a unit in 22:31.390 --> 22:33.990 density so that it becomes linear. 22:34.070 --> 22:36.260 And this is called the straight line portion. 22:37.000 --> 22:39.010 Then we have the shoulder which again is nonlinear. 22:39.940 --> 22:42.680 The most useful portion will be just above base plus 22:42.680 --> 22:44.070 fog or approximately 22:44.070 --> 22:45.860 .25-2.0. 22:45.860 --> 22:48.840 That's the most useful range of the densities that we find in 22:48.840 --> 22:49.560 radiology. 22:50.320 --> 22:52.720 Top density will be something over 22:52.730 --> 22:53.660 3.0. 22:55.140 --> 22:58.070 And of course the baseball baseball will be our low density level of 22:58.070 --> 22:59.550 about .18 23:02.540 --> 23:03.310 density. 23:03.320 --> 23:04.670 Again too, 23:06.130 --> 23:09.120 review is a measure of the blackening on the film. 23:09.330 --> 23:11.790 We have many density levels to consider. 23:13.240 --> 23:13.900 First of all, 23:13.900 --> 23:16.890 we can talk about the density at the toe which would be minimum 23:16.890 --> 23:19.570 density or is often phrased 23:19.580 --> 23:22.510 demon as a photographic term. 23:22.750 --> 23:25.240 We have the shoulder shoulder is 23:25.250 --> 23:28.190 maximum density or it's in the area of 23:28.330 --> 23:31.320 non linearity response which will eventually 23:31.320 --> 23:33.270 lead to the maximum density possible. 23:33.640 --> 23:35.690 So that would be called D max. 23:36.140 --> 23:39.040 We have the slope of the line or in this 23:39.040 --> 23:42.030 case as we see film a film A is more 23:42.140 --> 23:43.950 to the left as you view it. 23:43.960 --> 23:45.160 So therefore it's faster. 23:45.160 --> 23:47.990 That means simply that we get more density for one exposure 23:48.320 --> 23:50.920 than we would for the film be 23:51.060 --> 23:54.060 film be for an equal exposure gives 23:54.060 --> 23:54.960 us less density. 23:54.960 --> 23:56.460 So it's said to be slower 23:57.740 --> 24:00.660 film A will give us a greater contrast 24:00.660 --> 24:03.000 level than be because between any two 24:03.000 --> 24:05.490 exposures we would have a greater difference of 24:05.490 --> 24:06.350 densities 24:09.420 --> 24:11.820 Contrast is a difference between two or more 24:11.820 --> 24:12.450 densities 24:14.840 --> 24:17.650 and we can measure contrast in several ways 24:17.690 --> 24:20.440 average gradient as you see it takes 24:20.520 --> 24:23.200 and draws a line between two specific points 24:23.480 --> 24:26.000 in the most useful range of the H. 24:26.000 --> 24:26.240 And D. 24:26.240 --> 24:28.780 Curve and it averages out all of the 24:28.780 --> 24:29.360 densities. 24:29.360 --> 24:32.060 It averages out the changing slope of the curve. 24:32.540 --> 24:35.250 This would be as opposed to gradients which is a 24:35.250 --> 24:38.030 line drawn tangential to any one point along this 24:38.030 --> 24:38.960 entire curve. 24:39.340 --> 24:41.630 So let's look more closely at how we might 24:41.640 --> 24:43.360 calculate contrast. 24:47.140 --> 24:49.860 First of all we need to consider these two 24:49.860 --> 24:50.440 curves. 24:50.680 --> 24:52.210 In this case Film C. 24:52.220 --> 24:54.990 Is more vertical and it would be said to have a 24:54.990 --> 24:57.410 greater contrast just by its basic shape. 24:57.420 --> 25:00.310 This would be a part of the interpretation aspect of Sensei 25:00.310 --> 25:03.270 tom a tree film Di is laying down more 25:03.270 --> 25:05.800 so it is said to have a longer scale of contrast. 25:05.870 --> 25:08.380 But let's look here we see two exposures 25:08.940 --> 25:11.920 notice that the difference of these exposures is expressed 25:11.920 --> 25:13.170 as a difference of density. 25:13.540 --> 25:14.990 Notice the Delta D. 25:14.990 --> 25:16.600 or difference of density on film. 25:16.600 --> 25:18.030 Di is .18. 25:18.740 --> 25:21.610 Whereas the same two exposures if we extend upwards 25:22.540 --> 25:23.630 Gives us a delta d. 25:23.630 --> 25:25.700 or difference of density for film see of 25:25.700 --> 25:28.560 .64 so that we 25:28.560 --> 25:31.200 have a substantial increase in the 25:31.210 --> 25:34.080 difference of densities for equal 25:34.080 --> 25:34.730 exposures. 25:34.740 --> 25:37.470 So film C would be said to have a 25:37.470 --> 25:39.610 higher level of contrast. 25:39.620 --> 25:41.050 A difference of densities 25:43.540 --> 25:46.450 More precisely we might for instance calculate gamma. 25:46.940 --> 25:49.910 Gamma is the contrast of the straight line portion and it 25:49.910 --> 25:52.860 negates the non insularity of the toe and the 25:52.860 --> 25:53.360 shoulder. 25:53.740 --> 25:56.680 You see the line is extended along the straight line portion, 25:56.690 --> 25:57.940 the straightest part of the curve. 25:57.940 --> 26:00.580 It's just simply extended and we can take points any place 26:00.580 --> 26:01.360 along here. 26:01.740 --> 26:04.640 One easy way of calculating gamma is to simply 26:04.640 --> 26:07.350 monitor the number of squares as it says 26:07.350 --> 26:09.850 here of the X and the 26:09.850 --> 26:12.510 Y axis in a triangular fashion. 26:13.440 --> 26:14.860 And in this case it would be just 26:14.930 --> 26:16.540 20/13. 26:16.560 --> 26:18.180 That gives us the number 1.5, 26:18.180 --> 26:19.380 3 or a difference. 26:20.040 --> 26:22.770 And we can see that no matter where we take this 26:23.740 --> 26:26.620 relationship will still maintain the same 26:27.380 --> 26:28.360 approximate number. 26:30.040 --> 26:32.470 So that's gamma and it has a tendency to 26:32.780 --> 26:35.710 give us an overall level of 26:35.910 --> 26:36.480 contrast. 26:36.480 --> 26:37.350 And overall number, 26:37.740 --> 26:39.250 gradient goes just the other way. 26:39.250 --> 26:40.760 It allows us to find the 26:42.940 --> 26:45.860 contrast at such at any one point 26:45.870 --> 26:47.260 along the entire curve. 26:47.260 --> 26:48.540 And that generates many, 26:48.540 --> 26:50.540 many numbers that may or may not be useful. 26:50.750 --> 26:52.590 But notice along here we have a, 26:52.600 --> 26:53.770 B and C. 26:54.230 --> 26:57.010 And gradient at any one of these points is constantly 26:57.250 --> 26:57.950 changing. 27:04.640 --> 27:06.300 Average gradient is the most useful. 27:06.720 --> 27:09.630 And this is an averaging out of all these points along this 27:09.640 --> 27:10.270 scale. 27:10.730 --> 27:11.060 You can see, 27:11.060 --> 27:13.730 we have two exposures and we have to density 27:13.730 --> 27:16.660 levels and the basic formula would be 27:16.660 --> 27:19.500 the average gradient is equal to two point 27:19.510 --> 27:22.480 oh or density of 2.0 plus base plus 27:22.480 --> 27:23.060 fog. 27:23.070 --> 27:23.410 From this, 27:23.410 --> 27:26.360 we subtract 0.25 plus base plus 27:26.360 --> 27:29.100 fog and you see the base plus fog is influencing 27:29.110 --> 27:30.260 our exposure 27:33.100 --> 27:33.890 to summarize. 27:33.890 --> 27:36.640 Then we can look at these radiographs and we can see a difference 27:36.930 --> 27:38.070 in contrast. 27:38.080 --> 27:39.580 You can see the difference in the gray scale, 27:39.590 --> 27:40.860 in the shape of the curves 27:43.840 --> 27:45.950 which one has more contrast. 27:45.960 --> 27:47.350 Notice the shape of the curves, 27:47.360 --> 27:49.860 the difference of densities in the two 27:49.870 --> 27:50.760 radiographs. 27:54.240 --> 27:56.170 And again in this case, 27:56.310 --> 27:57.360 according to the kurds, 27:57.360 --> 27:58.840 we have equal contrast. 27:58.850 --> 28:00.770 We only have a speed shift. 28:01.340 --> 28:04.300 The film on the left is more dense, 28:04.310 --> 28:07.260 has more density for an equal exposure than the film on the 28:07.260 --> 28:07.670 right. 28:08.640 --> 28:10.190 But the difference is equal. 28:10.510 --> 28:13.440 Here we see two films there was between these two 28:13.440 --> 28:15.450 films has a density of .05. 28:15.840 --> 28:18.550 This simply means that if you can see this difference, 28:18.550 --> 28:19.650 which I believe you can. 28:19.660 --> 28:22.440 It says that your I can be as critical enough to 28:22.440 --> 28:24.260 see a difference of 28:24.270 --> 28:26.670 .05 density units 28:30.640 --> 28:32.390 and again back to our radiographs 28:34.440 --> 28:35.990 to see the subtle differences. 28:37.240 --> 28:40.190 And finally we can summarize again by saying that we have these 28:40.190 --> 28:41.570 factors of image definition. 28:41.580 --> 28:44.390 Density is the amount of blackening the amount of silver on the 28:44.400 --> 28:44.860 film, 28:45.540 --> 28:48.350 demon or minimum density D max 28:48.350 --> 28:51.350 maximum density and speed contrast is a 28:51.350 --> 28:54.030 difference between density since calculated by gamma 28:54.050 --> 28:56.270 gradient or average gradient. 28:58.540 --> 29:01.470 So when the technologist makes a controlled 29:01.470 --> 29:02.290 exposure, 29:02.450 --> 29:05.030 they are using the device which is reproducible, 29:05.040 --> 29:07.560 it eliminates the variables of the human anatomy 29:07.940 --> 29:10.610 and it allows for a scientific way in which a 29:10.620 --> 29:13.560 judgment can be made of the density on 29:13.560 --> 29:14.560 the films, 29:15.040 --> 29:17.750 as well as the difference between densities or 29:17.930 --> 29:18.850 the contrast. 29:19.740 --> 29:22.350 So we know in radiology that processing 29:22.800 --> 29:25.550 Is one aspect of the production of the 29:25.550 --> 29:26.360 visible image. 29:26.840 --> 29:29.770 It's a part of a sense of commentary and 29:29.850 --> 29:32.840 sense of geometry is a way that we can evaluate the 29:32.840 --> 29:34.420 quality of our radiographs, 29:34.470 --> 29:36.840 considering that we have constantly changing 29:36.840 --> 29:37.550 patients.