Which of the following would reduce receptor exposure by one-half if it was not possible for the technologist to adjust the mAs?

The choice that effectively reduces receptor exposure by one-half, when adjusting the milliampere-seconds (mAs) is not an option, involves a specific decrease in kilovoltage (kV). A decrease of approximately 15% in kV is known to halve the receptor exposure for a given radiographic technique.

When considering the relationship between kV and receptor exposure, it's important to recognize that kV impacts the penetration ability of the x-ray beam. Lowering the kV reduces the overall energy of the x-ray photons, which in turn decreases the intensity of the beam reaching the receptor. The 15% threshold has been empirically determined through practical experience and studies in radiography, making it a standard rule of thumb in practice.

If you decrease the kV by less than this threshold (like 10%), the reduction may not be sufficient to halve the receptor exposure. On the other hand, decreasing kV by more than 15% can result in underexposure, leading to increased image noise and reduced diagnostic quality. Therefore, the 15% decrease is the optimal choice to achieve the desired effect of halving the receptor exposure.