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Film Optical Density

Film Optical Density. Film screen. Radiographic Density Overall blackening of the radiographic image as a result of the energy deposited inthe film emulsion. Film screen. Radiographic Contrast / Grayscale The difference between two adjacent radiographic densities in the image.

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Film Optical Density

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  1. Film Optical Density

  2. Film screen • Radiographic Density • Overall blackening of the radiographic • image as a result of the energy deposited • inthe film emulsion.

  3. 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.

  4. Densitometer

  5. .25 TO -2.5 The straight line of the H&D curve Density

  6. 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

  7. 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 3 1 = 0 100 1 = 1 1011 = 2 1021 = 3 103 1 10 100 1000

  8. 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%

  9. An unexposed and processed film will have a density of about? • zero • 0.1 • 1.0 • 2.5

  10. If the quantity of black on the film allows 1% of light to pass through, that film has a density of • 0.01 • 0.1 • 1.0 • 2.0

  11. If the quantity of black on the film allows 10% of light to pass through, that film has a density of • 0.01 • 0.1 • 1.0 • 2.0

  12. 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? • Radiographic contrast • Radiographic density • Recorded detail • Radiographic filtration

  13. 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.

  14. Optical Density • Controlling factor: mAs • mAs determines the quantity of x-rays • What is the formula to determine quantity of x-rays?

  15. How is OD measured on a monitor

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