Concerning the properties of radio graphic film: a. Optical density i

1.	Concerning the properties of radio graphic film: a. Optical density is a measure of film blackening based on the degree of transmission of incident light on the film b. Using double-sided emulsion has no effect on optical density c. The greater the optical density of a film, the lower the intensity of the transmitted light beam d. A useful range of optical densities is approximately 0.25–4 e. Different optical densities in areas within the same film are what produce image contrast when viewing the image
Answer» a. True. Optical density = log₁₀ Io/In, where Io is the intensity of incident light and In is the intensity of transmitted light. b. False. The optical densities for each layer are cumulative so that, for the same level of exposure, the densities are increased compared with using a single layer. c. True. Referring back to the equation in (a), if the optical density = 1, then only 10% of light is transmitted, as log₁₀ 10 =1. Likewise, if optical density = 2, then only 1% of light is transmitted (log₁₀ 100 = 2). d. False. Optical densities of around 2 may be seen with normal illumination; however, an optical density of 3 appears very dark and requires the use of a focal bright light to see through it. An optical density of 4 means that only 1/10,000 of the incident light has been transmitted, so the film will appear black. e. True. Contrast may be measured as the difference in optical densities: OD₁ – OD₂. This difference will be produced by the nature of the tissue being imaged.

Concerning the properties of radio graphic film: a. Optical density is a measure of film blackening based on the degree of transmission of incident light on the film b. Using double-sided emulsion has no effect on optical density c. The greater the optical density of a film, the lower the intensity of the transmitted light beam d. A useful range of optical densities is approximately 0.25–4 e. Different optical densities in areas within the same film are what produce image contrast when viewing the image

Answer»

a. True. Optical density = log₁₀ Io/In, where Io is the intensity of incident light and In is the intensity of transmitted light.

b. False. The optical densities for each layer are cumulative so that, for the same level of exposure, the densities are increased compared with using a single layer.

c. True. Referring back to the equation in (a), if the optical density = 1, then only 10% of light is transmitted, as log₁₀ 10 =1. Likewise, if optical density = 2, then only 1% of light is transmitted (log₁₀ 100 = 2).

d. False. Optical densities of around 2 may be seen with normal illumination; however, an optical density of 3 appears very dark and requires the use of a focal bright light to see through it. An optical density of 4 means that only 1/10,000 of the incident light has been transmitted, so the film will appear black.

e. True. Contrast may be measured as the difference in optical densities: OD₁ – OD₂. This difference will be produced by the nature of the tissue being imaged.

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