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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.

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film screen
Film screen
  • Radiographic Density
  • Overall blackening of the radiographic
  • image as a result of the energy deposited
  • inthe film emulsion.
film screen3
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.
density
.25 TO -2.5

The straight line of the H&D curve

Density
to see changes in optical density
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
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

slide8
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%
if the quantity of black on the film allows 1 of light to pass through that film has a density of
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
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
slide12
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
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 density15
Optical Density
  • Controlling factor: mAs
  • mAs determines the quantity of x-rays
  • What is the formula to determine quantity of x-rays?