Final answer:
The exception to what milliamperage control regulates is the quality of x-ray photons; it does affect the quantity and density but not the quality or contrast of an X-ray image.
Step-by-step explanation:
The milliamperage control on an X-ray machine regulates the quantity of x-ray photons and the density of the x-ray image, but not the quality of the x-ray photons nor the contrast of the x-ray image. The correct answer to which one is the exception is (a) Quality of x-ray photons. Milliamperage directly affects the tube current in an X-ray tube and, consequently, the number of electrons hitting the target. As the number of electrons increases, more x-ray photons are produced, thus increasing the image density. However, the quality, which pertains to the energy level of the x-ray photons, is primarily controlled by the kilovoltage peak (kVp) settings, not the milliamperage. Similarly, the contrast of an X-ray image is mainly influenced by the kVp and patient factors, not the milliamperage.