Radiographic processing is necessary for the 

production of the useful visible image.

It links exposure to interpretation and 

influences quality.

An understanding of basic sense saitama tree is necessary 

for subsequent lectures.

Sensei Tom a tree is defined and the anatomy of the 

sensitive metric curve is detailed 

density and contrast are discussed and 

methods of their calculations are presented.

When we look at the graze of 

a radiograph,

we're looking at the anatomy as portrayed in 

this picture,

this radiograph.

We're looking at bits of information and we're trying 

to understand from 

analyzing these shades of gray,

what's right or wrong with the patient.

Now,

as we look at the bits of anatomy as expressed as 

shades of gray or black or the absence of 

blackness,

then we really are judging the quality of the 

radiograph by many criteria.

One of course is positioning visualization 

of the anatomical part.

We also are judging the general shades of 

gray by a subjective means.

We are personally saying,

well I like this shade of gray or I like this level 

of density or this 

cleanliness in the areas where there should be no density.

So we need a way in which we can 

look at the radiograph,

the shades of gray,

the gray scale in a way that is not 

subjective but is more technically 

scientific or more technically 

correct.

And this method has provided us by the 

system or the word that 

describes a system called Sensei tom a tree,

sensitization or sensitizing means to 

expose.

And sensitive geometry is a measure 

of exposures.

So first of all,

let's consider some of the 

definitions that we're going to be dealing with and some of the components 

of Sensei tom a tree.

First of all,

density is a measure of the blackening 

on the film.

This is simply the amount of silver 

in a given area and basically what we 

talk about a radiograph as the whole film being 

exposed.

Some of the areas of course are non anatomical,

but wherever we have density,

we have blackening on the film.

We have piles of silver.

Now you can have a high density as we see here.

It's very black and we have a low density,

Usually in radiography,

we very seldom have a use for a density that is 

greater than 3.0 as a matter of fact,

the eye does not respond unaided to a 

density that is greater than 3.0 

On the other hand,

the lowest density that we might use or have 

available to us would be approximately .18.

When we talk about densities often times,

people will just say simply a density of 18,

but they mean 0.18.

The point here is that 

a density of .18 is the inherent 

fog and loss of density due to 

the structure of the film.

This is often said to be manufacturing base plus fog.

In reality we know that we have a very 

thick piece of bass on seven mils in thickness 

that is seven thousands of an inch thick.

That the gelatin layer is very,

very small relative to this.

Both gelatin layers together only accounting for 

approximately half a mil thickness.

The density this 0.18 density 

that we're talking about uh is 

primarily due to loss of density in the 

base.

The base,

of course,

is a plastic base.

As light passes through it,

it's attenuated,

it's absorbed,

it's deflected or refracted so that the 

light doesn't continue to pass through the base and out the 

other side.

That means that as we perceive light 

passing through this base,

some will appear to have been lost in 

an average film.

Fresh out of the out of the film been placed into a 

processor and developed fixed and washed,

in which there has been no exposure except 

manufacturing and hopefully the correct story.

So there's no added density.

We will find a base plus fog of .18 

Of this .18 Over 

75% will be due to the loss of light passing through the 

base or approximately .16.

The difference between .16 and 

.18 is .02.

And this is usually the maximum amount of 

manufacturing fog that is generated in the 

gelatinous or gelatin layers or 

recording media in the gelatin layers that which we normally 

call the emotions.

So you can see that the manufacturing fog is very,

very small.

And that most of this base plus fog 

density is due to the attenuation of 

flight or the non passing of light through the 

base material.

Of course,

the base also has a slight blue tint and this 

helps the radiologist in making his 

visualization of the information.

Let's look further at our scale of 

grays.

We know what the high limit is and the low limit,

but what would the entire scale look 

like if we had many levels here?

We see that we're going from a density of zero.

There is no silver at this level,

The density of zero.

And then we start to get more and more 

silver.

So therefore we get more and more blackening 

At the highest level.

You can see that it's very black.

Matter of fact,

it's so black that you probably cannot distinguish 

between a level of 2.5 and 

3.0,

so we have a full scale of densities.

How do we measure these densities?

Well,

when we have a piece of film,

whether it has anatomy or it has a sensitive 

metric shade of grays we see 

here,

we measure by having a light source 

and calibrated light source that will pass light 

through the film,

we can monitor how much light is 

going to pass through the film and how much light actually 

comes out the other side.

So the difference between the incident light and the 

light that actually comes out through the film,

the transmitted light allows us to 

calculate the amount of density.

We measure density in this case 

as you see here,

the light source as such and the measurement device 

are all contained in one and this is done 

on a density thomas.

A dense odometer measures density.

This is a very common one that's readily available.

I should hasten to point out that as you can see,

the individual here is monitoring this 

sensitive metric strip,

the shades of gray and we had the light 

table and a photo multiplier tube and then 

the sweet pan that when you have a unit with a 

sweet pan,

that you on occasion have to make an 

interpretation of of exactly where that needle 

lies insofar as between one point and the 

next point.

And that many times people 

assume unfortunately,

that when they buy themselves a dense odometer,

that this really is the key to quality 

quality control system.

This is not necessarily so because it's 

obvious that when you have a need to make an 

interpretation in the reading of a density,

that the difference between one person's method of reading and 

interpreting can lead to an error as compared with 

another persons.

So in general,

when you buy a density tom attar,

the biggest expense is the allocating of one 

person's time to do all of the sense of the metric and density 

metric reading of films and plotting 

interpretation and we'll get into this as we go along.

Now if we take these two 

skulls,

we can see that there's a 

very slight difference between the two skull 

densities.

At the point where the circle is of course there's a 

slightly greater density in the overall radiograph.

But at these two spots which 

are identical in the amount of exposure passing 

through this part of the anatomy,

We have a difference of density of .6,

so 2.55 

or a difference of .05.

That's a very small amount of difference.

But the I can see this small amount of 

difference between the two.

It's this ability to see the small 

amounts of differences that allows us to say that the 

I really is a very excellent density 

metric tools with training your eye can be a 

very critical tool.

It can help you to ascertain whether or not you have too much 

density,

too little density.

And this is really why we need to understand since optometry,

so that we can better judge the quality of the 

radiograph as to too much 

density or too little density and thereby relate to 

whether or not we're correctly visualizing the anatomy.

Now keep in mind that we talked about density is the 

amount of blackening on the film.

We measure density by the 

amount of light passing through the film.

And we see here that when we have 100% light 

transmitted,

we have zero density.

There is no density.

There is no silver,

there's nothing to block the light.

So all the light passes through.

And when we have 10% of the light being 

transmitted,

we have a density of one.

These numbers 012,

three are logarithmic numbers 

as a measure of the amount of 

light being transmitted.

There's a another way of expressing it as the log 

of the inverse of the transmit points of light 

through the film.

But basically we have this kind of a density scale 

012 and three.

This is our full range for medical radiography.

Industrial radiography sometimes 

uh has a tendency goes high as a level of 

density of five.

And of course as I mentioned,

this is beyond the capability of the eye.

So they need very hot,

bright lights,

hot lights to be able to read these very high densities.

Now let's consider the difference between 

densities.

The difference between densities is the definition of 

contrast contrast is a difference between 

two or more densities.

We've often heard the little 

statement that contrast 

contrast enhances the visibility of 

detail.

It enhances the visibility,

does not create detail,

does not create detailed sharpness.

It simply enhances the visibility of detail 

allows us to see differences if you will.

So if we have a large difference between two things,

then we can more easily see that there is this difference.

Another way of saying it is if we have two densities of equal 

values side by side,

if they appear equal Then we see no difference 

between the two.

But we know that the anatomy of a patient is 

made up of many anatomical 

differences.

And you've probably even heard the mhm.

The phrase anatomical contrast because of 

these differences between bone tissue,

air water and things of this nature within the 

physiological structure of the patient.

So contrast is a difference between two 

densities two or more densities.

Here we see two numbers and we can 

say that just these pure numbers.

1.26.

If we take away .26,

the difference is 1.00.

So this number,

1.00 is a difference.

These numbers are,

as I said,

just simply numbers but they could represent 

Densities to different densities.

And the 1.00 then would 

be our contrast number.

It would be the result of subtracting one from the other.

And this will tell us the difference the amount of 

density that is between these two 

extremes.

In this slide we see a more practical example in 

which there is 

in this particular scale,

really only two steps of density,

1.5 and 

3.0 Remember at zero we have 

all the light passing through 100% transmission.

And here where we have some density,

there's less light and at 3.0,

there's very little light passing through.

Look at this scale over here notice that 

there's a lot of shades of gray in between 

Now,

which scale would be a long scale of contrast,

which would be a short scale of contrast.

Well,

basically we can say that This is the more 

contrast e of the two gray 

scales of the two cents symmetric strips.

This is more contrasting.

It has higher contrast and we 

can see that there's less gray steps 

in this scale.

So it is a short scale of contrast.

So we have what seems to be conflicting terms.

We have a short scale of contrast and 

yet it's high contrast here.

We have a long scale of contrast but it's 

low contrast.

Notice the difference between the various steps 

here Between this step and the next one.

We have a difference of .5.

We take 1.0 we subtract .5 and the 

difference is .5 so we have a difference Or a 

contrast of .5 Over 

here.

If we take the difference between 1.5 and 

its next adjacent step,

we see that that's 3.0,

the difference is 1.5,

So it's 1.5 as a contrast number 

versus .5.

The contrast level here is approximately three times 

greater than is the contrast expressed by all of 

these shades of gray in this long scale 

of contrast example.

So we have short scale of contrast.

We have long scale contrast.

Most people just simply call it low 

contrast or high contrast.

Let's look more closely at how contrast might aid 

our interpretation of information.

We can see here that there is two 

slides.

We could say that one has high contrast and one is 

low.

You may not really like either 

radiograph,

but let's consider first of all that 

in this image is very bright.

There's blacks and whites.

This is a very high contrast image,

but notice the detail of this little 

unusual Q popular here.

We can see the railing.

We can see that it's attached to the building,

but also notice that we don't see any clouds 

and down on the side here,

it's very difficult to see the distinguishing piles 

of snow.

And yet we can very easily see this window 

and we can see some of the details around the windows,

the landscape.

Now,

let's go to the next radiograph and where we have a lot of 

densities,

a lot of shades of gray and there's 

very little white,

characteristically little black,

There's a lot of shades of darkness,

dark grays in this radiograph.

We see that you can't really tell that 

there's a post here connecting the cumulus.

It's very difficult to see and yet notice all the 

beautiful clouds in the sky that we missed before.

The other radiograph down here.

It's very difficult.

You may not be able to see that there's a window there or how the land 

slopes and yet in these 

formations of the snow on bushes,

we can more easily see all of the intricate shapes.

So this is to say that we may 

consider high contrast and radiography.

Most people do.

Most people are very concerned about high contrast,

but this does not mean that we use the highest contrast 

possible.

Nor does it mean that we have a system that of course would have no 

contrast.

We need contrast to see differences to see the subtle 

differences of the anatomy.

We do have a problem in selecting 

contrast and trying to come up with the best system.

We neither need low contrast nor the highest 

possible contrast,

but we do need contrast 

here.

We see a schematic,

if you will,

it's a uh phantom 

exposure in which we have a synth 

synthetic contrast media 

injected.

One is a low contrast exposure 

and the other is a high contrast exposure.

Can you tell?

Which is which keep in mind that these are 

phantom exposures,

wow.

In this case there's very little grays.

And over here there's a lot of grays here where there's a little 

grays.

We see no information in what might 

be the intestinal track 

in this case there is just the faint image of 

some information.

Some particles or something there.

Well,

really neither one is very acceptable.

But what if we balanced our contrast?

We came out with a system that gave us 

not maximum contrast nor minimal,

but just the right amount as here.

Now we can see the information very clearly 

we have some shades of gray but we have a 

difference between these shades of gray.

We have a contrast level here.

It's washed out and here is masked over 

by gray's.

So this is an excellent example 

of balancing to achieve the best 

contrast that we can.

All of this discussion on contrast is 

a difference between densities and the definition of 

density.

Just the amount of blackening on the film is the 

basis of sensitive geometry.

We might define basic sense optometry 

as the quantitative measure 

of the response of film to exposure 

and development.

Probably the thing that confuses most people is the fact 

that this statement is exposure 

and development,

not just exposure or not just development 

but the development along with the exposure,

each one influences the 

response of the film.

So sensitive geometry is the quantitative 

measure of the 

response of film too,

exposure and development.

And of course development means processing.

If we look at the basis of uh 

sense of geometry,

there is a system employed here,

There's four things we need to do to generate 

some information sense symmetrically or technically if 

you will,

we can say that we first of all have to expose,

we have an exposure factor development of course 

and then we measure,

we make a measurement such as with our eyes 

value judgment or we might use a dense 

odometer and then we interpret,

we make an interpretation,

we say,

well is this good or bad?

Let's look more closely at how we can use 

this up here,

We've made the exposure with an image quality device 

most usually called a stepped wedge and most 

step wedges are referred to as a square root of two step 

wedge,

although many seldom are of the less 

expensive type.

We have a series of steps so that with one exposure 

we get many little exposures and this 

just saves some work and time and it helps us to produce a more 

uniform film and symmetrically 

so this would be our exposure device.

And then we make an image on the film and this is 

processed.

And then we plot,

we measure and plot and then we interpret the shape 

of this curve,

notice that we're plotting the log relative 

exposure against the total density 

gannon log units.

And we need to look more closely at how this 

all works.

So let's continue.

And first of all consider this is our exposure 

device.

We have a basically a square root of two 

aluminum stepped wedge.

We of course have it very thick here,

so less exposure will pass through.

Down here is thinner and more will pass through and the image will 

be darker.

So this gives us a shade of grays.

We have a lead block here which will provide an area where there is 

no exposure.

So we may monitor the base plus fog density to 

see how this influences the entire shade of 

grays.

Of course,

of the baseball song is very high.

Then this will influence all of these steps equally.

Next,

after we made the exposure under controlled conditions 

and we process,

then we end up with a gray scale.

And using the density thermometer,

we can apply these numbers and we can 

find out how the densities 

increase.

Using these numbers.

Then you can see along here we have an exposure 

and we have densities and we plot now notice 

that this is not a nice straight line.

It has a change to it.

This light area down here we have a 

light slowly increasing area here.

Then it increases more uniformly up through this 

area and then it starts to drop 

off.

It decreases in its rate of 

density increments increasing.

So we can add some anatomy to this 

particular shape.

We can say that down here we have a toe.

This is a nonlinear portion.

It's constantly changing as you increase in exposure.

Specifically as you go up the relative M A s.

We see down here is we double R M a S 

Or a factor of two.

We see that the density doesn't go up equally.

It just goes up very slowly and then it starts to increase 

faster.

So this is nonlinear.

Then we reach a point where it straightens out.

And as you go up a unit in exposure.

This way you will go up a unit in 

density so that it becomes linear.

And this is called the straight line portion.

Then we have the shoulder which again is nonlinear.

The most useful portion will be just above base plus 

fog or approximately 

.25-2.0.

That's the most useful range of the densities that we find in 

radiology.

Top density will be something over 

3.0.

And of course the baseball baseball will be our low density level of 

about .18 

density.

Again too,

review is a measure of the blackening on the film.

We have many density levels to consider.

First of all,

we can talk about the density at the toe which would be minimum 

density or is often phrased 

demon as a photographic term.

We have the shoulder shoulder is 

maximum density or it's in the area of 

non linearity response which will eventually 

lead to the maximum density possible.

So that would be called D max.

We have the slope of the line or in this 

case as we see film a film A is more 

to the left as you view it.

So therefore it's faster.

That means simply that we get more density for one exposure 

than we would for the film be 

film be for an equal exposure gives 

us less density.

So it's said to be slower 

film A will give us a greater contrast 

level than be because between any two 

exposures we would have a greater difference of 

densities 

Contrast is a difference between two or more 

densities 

and we can measure contrast in several ways 

average gradient as you see it takes 

and draws a line between two specific points 

in the most useful range of the H.

And D.

Curve and it averages out all of the 

densities.

It averages out the changing slope of the curve.

This would be as opposed to gradients which is a 

line drawn tangential to any one point along this 

entire curve.

So let's look more closely at how we might 

calculate contrast.

First of all we need to consider these two 

curves.

In this case Film C.

Is more vertical and it would be said to have a 

greater contrast just by its basic shape.

This would be a part of the interpretation aspect of Sensei 

tom a tree film Di is laying down more 

so it is said to have a longer scale of contrast.

But let's look here we see two exposures 

notice that the difference of these exposures is expressed 

as a difference of density.

Notice the Delta D.

or difference of density on film.

Di is .18.

Whereas the same two exposures if we extend upwards 

Gives us a delta d.

or difference of density for film see of 

.64 so that we 

have a substantial increase in the 

difference of densities for equal 

exposures.

So film C would be said to have a 

higher level of contrast.

A difference of densities 

More precisely we might for instance calculate gamma.

Gamma is the contrast of the straight line portion and it 

negates the non insularity of the toe and the 

shoulder.

You see the line is extended along the straight line portion,

the straightest part of the curve.

It's just simply extended and we can take points any place 

along here.

One easy way of calculating gamma is to simply 

monitor the number of squares as it says 

here of the X and the 

Y axis in a triangular fashion.

And in this case it would be just 

20/13.

That gives us the number 1.5,

3 or a difference.

And we can see that no matter where we take this 

relationship will still maintain the same 

approximate number.

So that's gamma and it has a tendency to 

give us an overall level of 

contrast.

And overall number,

gradient goes just the other way.

It allows us to find the 

contrast at such at any one point 

along the entire curve.

And that generates many,

many numbers that may or may not be useful.

But notice along here we have a,

B and C.

And gradient at any one of these points is constantly 

changing.

Average gradient is the most useful.

And this is an averaging out of all these points along this 

scale.

You can see,

we have two exposures and we have to density 

levels and the basic formula would be 

the average gradient is equal to two point 

oh or density of 2.0 plus base plus 

fog.

From this,

we subtract 0.25 plus base plus 

fog and you see the base plus fog is influencing 

our exposure 

to summarize.

Then we can look at these radiographs and we can see a difference 

in contrast.

You can see the difference in the gray scale,

in the shape of the curves 

which one has more contrast.

Notice the shape of the curves,

the difference of densities in the two 

radiographs.

And again in this case,

according to the kurds,

we have equal contrast.

We only have a speed shift.

The film on the left is more dense,

has more density for an equal exposure than the film on the 

right.

But the difference is equal.

Here we see two films there was between these two 

films has a density of .05.

This simply means that if you can see this difference,

which I believe you can.

It says that your I can be as critical enough to 

see a difference of 

.05 density units 

and again back to our radiographs 

to see the subtle differences.

And finally we can summarize again by saying that we have these 

factors of image definition.

Density is the amount of blackening the amount of silver on the 

film,

demon or minimum density D max 

maximum density and speed contrast is a 

difference between density since calculated by gamma 

gradient or average gradient.

So when the technologist makes a controlled 

exposure,

they are using the device which is reproducible,

it eliminates the variables of the human anatomy 

and it allows for a scientific way in which a 

judgment can be made of the density on 

the films,

as well as the difference between densities or 

the contrast.

So we know in radiology that processing 

Is one aspect of the production of the 

visible image.

It's a part of a sense of commentary and 

sense of geometry is a way that we can evaluate the 

quality of our radiographs,

considering that we have constantly changing 

patients.