Concerning quality assurance in film-screen radiography: a. The testi

1.	Concerning quality assurance in film-screen radiography: a. The testing of filtration within the system is not routinely performed b. Total filtration should be equivalent to at least 1.5 mm of aluminium c. Assessment of optical density is the main measure of correct automatic exposure control (AEC) functioning d. Focal spot size may be estimated using the pinhole method e. A lower-than-expected output dose measurement is unrelated to exposure time
Answer» a. False. The amount of filtration is most important when the diagnostic information depends on fine contrast being demonstrated between the tissues being imaged (e.g. in mammography). This contrast may be lost if there is beam hardening if filtration is too great. b. False. It should be equivalent to 2.5 mm of aluminium. c. True. The AEC functions by terminating the exposure once a film has a received dose sufficient to produce an adequate film. Therefore, the optical density of test films can be monitored as the level at which the AEC is set and then varied while monitoring the dose. Test subject thickness (usually Perspex) may also be altered at the same time. d. True. This technique produces a magnified image of the focal spot. The focal spot size can then be calculated by determining the magnification by knowing the focus-to-film and pinhole-to-film distances. e. False. Along with changing the tube potential and tube current, a shorter exposure time may also reduce the output.

Concerning quality assurance in film-screen radiography: a. The testing of filtration within the system is not routinely performed b. Total filtration should be equivalent to at least 1.5 mm of aluminium c. Assessment of optical density is the main measure of correct automatic exposure control (AEC) functioning d. Focal spot size may be estimated using the pinhole method e. A lower-than-expected output dose measurement is unrelated to exposure time

Answer»

a. False. The amount of filtration is most important when the diagnostic information depends on fine contrast being demonstrated between the tissues being imaged (e.g. in mammography). This contrast may be lost if there is beam hardening if filtration is too great.

b. False. It should be equivalent to 2.5 mm of aluminium.

c. True. The AEC functions by terminating the exposure once a film has a received dose sufficient to produce an adequate film. Therefore, the optical density of test films can be monitored as the level at which the AEC is set and then varied while monitoring the dose. Test subject thickness (usually Perspex) may also be altered at the same time.

d. True. This technique produces a magnified image of the focal spot. The focal spot size can then be calculated by determining the magnification by knowing the focus-to-film and pinhole-to-film distances.

e. False. Along with changing the tube potential and tube current, a shorter exposure time may also reduce the output.

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