Film Optical Density Film screen Radiographic Density Overall

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 • The straight line of the H&D curve

To see changes in optical density • In order to see changes in optical density on a radiograph you must increase you m. As 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 = # of photons hitting film OD= 1 =0 1 1 100 1 = 1 10 OD # 2 3 1 = 2 102 1 = 3 100 1000

• 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%

• 1. 2. 3. 4. 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 1. 0. 01 2. 0. 1 3. 1. 0 4. 2. 0

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

• 1. 2. 3. 4. 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: m. As • m. As determines the quantity of xrays • What is the formula to determine quantity of x-rays?

How is OD measured on a monitor