Chapter 9 Fosbinder
Quiz yourself by thinking what should be in
each of the black spaces below before clicking
on it to display the answer.
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| What is sensitometry? | The study of the relationship between from the amount of intensity from tube and amount of density on the film
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| What 3 things can sensitometry measure? | 1. Speed
2. Exposure Latitude
3. Contrast
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| What will always be on the film? | Chemical Fog
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| Equipment is needed for sensitometry? (2) | Penetrometer or Sensitometer
Densitometer
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| What is a penetrometer? (Step wedge) | Piece of aluminum with varying densities in the shape of a step wedge.
Step 1- black (X-rays pass through, thinest step)
Step 11- white
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| What is a Sensitometer? | A device that is designed to expose a reproducible, uniform, optical step wedge onto a film.
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| Which is more effective, a penetrometer or Sensitometer? | Sensitometer
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| What is a densitometer? | A device used to numerically measure the amount of blackness on the film after processing.
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| What is the light transmit formula? | The amount of light that is actually transmitted through the film.
it x 100
io
***only have to recognize formula***
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| What Optical Density? | The numerical calculation of transmitted light through a film to incident light originally striking the film.
Log10 (io)
(it)
OD ranges 0-4
0 = white part of the image 4 = black part of an image
**only have to recognize formula **
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| What is the relationship between optical density and light transmittance? | Increased optical density (more black) = decreased light transmittance
Decreased optical density (more white) = increased light transmittance
OD increases by .3 and decreases light by 1/2
OD decreased by .3 and increases light by double
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| What is a sensitometric curve? | A graph demonstrating how a film respond to a series's of increasing exposures.
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| 5 Parts of the sensitometric curve? | 1. Toe
2. Threshold
3. Straight-line region/ slope/ gamma
4. Average gradient
5. Shoulder
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| What is the toe of the curve? | Bottom of curve, low density/underexposed, never at zero because of base + fog
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| What is base + fog? | Film has a tint added to the base, fog is present due to processing chemicals.
Acceptable range of B+F is between 0.1-0.2 optical density
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| Where do you find base + fog on a film? | On any blank unexposed part of the film.
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| What is the threshold of the curve? | Area where the curve begins to turn upward.
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| What is the straight line region (slop/gamma)? | Area of the diagnostic and useful ranges in density. Found between the threshold and the shoulder.
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| What is the optical density range on a graph? | 0-4
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| What is the useful range of optical density on a graph? | 0.25-2.5
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| What is the diagnostic range of optical density on a graph? | 0.5-2.0
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| What is the shoulder of the curve? | The point on the curve where the maximum density have be produced. Most amount of black. (Dmax)
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| What is average gradient? | A line drawn on the slope representing the densities found within the image.
Normal average gradient diagnostic range = 0.25-2.0 about the B+F measurement
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| What is solarization? | The point on the curve beyond where the maximum density had been produced (Dmax)
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| What are the 3 film characteristics determined by the curve? | 1. Film Speed
2. Film Contrast
3. Exposure Latitude
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| What is film speed? | The films sensitivity to radiation, and indicated the amount of optical density produced for a given radiation exposure.
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| What is a speed point? | The point on hype sensitometric curve that corresponds to the optical density of 1.0 + B + F
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| What is the speed exposure point? | The point in the x-axis that corresponds to the speed point on the y-axis which indicated the intensity of the exposure needed to produce a density of 1.0 + B + F regardless of the shape of the curve.
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| What is film contrast controlled by? | The design and manufacturing of the film components and effects of processing.
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| If the graph has a high contrast, what will the slope look like? | More vertical.
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| If the graph has a more horizontal slope what type of contrast will the film have? | Low
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| How do you find the slop of a curve? | Rise Or Y2-Y1
Run X2-X1
High number = steep slope = high contrast
Low number = long slope = low contrast
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| What is exposure latitude? | Refers to the range of exposures that produces optical density within the straight line region of the curve
Horizontal slope = wide latitude = low contrast, lots of grays
Vertical slope = narrow latitude = high contrast! more black and white
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| What is optimal density? | It is achieved when radiographic densities are produced that lie within the straight-line region of the curve thus maximizing the amount of information visible.
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