Film Optical Density Film screen Radiographic Density



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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.

  • The overall number of density shades

  • present in the image.



Densitometer



Density

  • .25 TO -2.5



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



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 = 1 101 1 = 2 102 1 = 3 103

  • 1 10 100 1000



Carltons – CH 21 (pg 307) – increments of optical density

  • 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%



  • An unexposed and processed film will have a density of about?

  • zero

  • 0.1

  • 1.0

  • 2.5



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



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



  • 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





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.



Optical Density

  • Controlling factor: mAs

  • mAs determines the quantity of x-rays

  • What is the formula to determine quantity of x-rays?



How is OD measured on a monitor





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