a. False. For larger breasts, the doses are much higher than for average breasts, as there is a greater thickness of material for the radiation to penetrate and so more is absorbed. Also, loss of reciprocity in the film means even larger doses are needed to achieve the right film density. However, the dose is not linear and rises more steeply after about 6 cm.
b. True. A back screen means that, as most interactions still take place at the edge of the screen nearest to the radiation source, the film is nearer the interaction, i.e. light source, and the light does not spread out as much, giving a better resolution. By using single-sided film, the emulsion is in direct contact with the screen and the resolution is therefore as good as possible. However, use of a single screen and single-sided emulsion means than a higher dose is required than if doubled-sided film with two screens were used.
c. False. Due to beam hardening, the amount of radiation dose reaching the detector varies with ** thickness and composition. If the AEC worked by detecting a fixed dose, film density would vary with ** variation.
d. False. By varying the kV, you can reduce the dose and exposure time. However, by changing the target–filter combination, a greater dose saving can be made for the same loss in contrast, or a lower loss in contrast can be achieved for the same dose decrease.
e. False. Increasing the kV does increase the output of the X-ray tube and the ESD, but output at mammographic energies is roughly proportional to kV3 . In general radiography, output is approximately proportional to kV2 .
