Film Optical Density Spectral Matching & sensitometry.
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Transcript of Film Optical Density Spectral Matching & sensitometry.
![Page 1: Film Optical Density Spectral Matching & sensitometry.](https://reader036.fdocuments.net/reader036/viewer/2022081420/5697bf8a1a28abf838c8a4a5/html5/thumbnails/1.jpg)
Film Optical Density
Spectral Matching &
sensitometry
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Film screen
• Radiographic Density
• Overall blackening of the radiographic
• image as a result of the energy deposited
• inthe film emulsion.
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Film screen
Radiographic Contrast / Grayscale
• The difference between two adjacent
• radiographic densities in the image.
• The overall number of density shades
• present in the image.
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Densitometer
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Density
• .25 TO -2.5
• The straight line of the H&D curve
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To see changes in optical density
• In order to see changes in optical density on a radiograph you must increase you mAs by at least 20 – 30%
• To double the density on a radiograph you must double your density
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Optical Density• A numerical value indicating the degree of blackening on
the film. (average OD seen on a radiograph = 1.2 Range is 0.21 –
2.5)
# of photons coming through film = OD # # of photons hitting film
OD= 1 2 31 = 0 100 1 = 1 101 1 = 2 102 1 = 3 103
1 10 100 1000
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• Carltons – CH 21 (pg 307) – increments of optical density • • Density log = incident light intensity • transmitted light intensity• • OD # % of light photons transmitted• 0 100 %• 1 10 %• 2 1 %• 3 0.1 %• If the quantity of black metallic silver on a radiograph• is such that it allow• 1 % of the light to pass through – what is the OD?• 10%• 100%
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• An unexposed and processed film will have a density of about?
1. zero
2. 0.1
3. 1.0
4. 2.5
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If the quantity of black on the film allows 1% of light to pass through, that film has a density of
1. 0.01
2. 0.1
3. 1.0
4. 2.0
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If the quantity of black on the film allows 10% of light to pass through, that film has a density of
1. 0.01
2. 0.1
3. 1.0
4. 2.0
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• The relationship between the intensity of light striking a film and the intensity of
light transmitted through the film is an expression of which of the following?
1. Radiographic contrast
2. Radiographic density
3. Recorded detail
4. Radiographic filtration
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Image-forming x-rays
• Two kinds of photons are responsible for the OD and contrast on an image: Photons that pass through without interacting and those that are scattered though Compton.
• X-rays that exit the patient are remnant and those that interact with the IR are image-forming.
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Optical Density
• Controlling factor: mAs • mAs determines the quantity of x-
rays
• What is the formula to determine quantity of x-rays?
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How is OD measured on a monitor
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Optical Denisty H & D curveSpectral Matching
RT 244
Week 13/14
Rev 11/09
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Log denisty H & D curve
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• If the exposure of the film results in optical densities (OD) that lie in the toe or shoulder regions, where the slope of the curve is less, contrast is reduced.
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• Slope of the straight-line portion of the characteristic curve is greater for image receptor A than for image receptor B. Image receptor A has higher contrast.
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• How does the slope affect
• Latitude?• Contrast?
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Spectral Matching (F/S)
• What does it mean?
• Name the two types of screen phosphors
• What light spectrum do they emit?
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Spectral Matching (F/S systems)
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Spectral Matching (F/S systems)
Red safe light
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Safe lights
• What wattage bulb?
• Distance from counter top?
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Sensitometry
• What is the purpose?• What does it measure?• Why is it important?
More on this in RT 255 QA/QC
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Sensitometric curve
• Developer temp• Can effect• Slope of curve• Less exposure is
needed for higher• Dev temps
• What is the ave temp? for a 90 sec processor?
100º90º
Log of relative exposure
DE
NS
ITY
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