What are the three controls on the x-ray machine?

• A. kVp, mA, time
• B. kVp, mA, distance
• C. mA, time, distance
• D. kVp, exposure time, angle

Answer: (A)

Controlling an X-ray exposure relies on three adjustable factors that determine beam quality, quantity, and duration. The energy and penetrating power of the beam are set with kilovoltage peak (kVp). Higher kVp increases penetration and reduces image contrast, while lower kVp produces less penetration and higher contrast. The number of photons produced—affecting image brightness or density—is governed by the tube current, milliamperage (mA). More current means more electrons hitting the target per second and thus more photons. The total exposure also depends on how long the tube is energized, the exposure time; longer duration increases the total number of photons. When you multiply mA by exposure time, you get mAs, a measure of the overall photon quantity.

Distance and angle influence the image geometry and patient dose, but they are not the primary exposure controls on the generator. Distance changes intensity by the inverse square law, and angle affects projection, not the machine’s exposure factors. So the three controls you adjust on the X-ray machine to manage exposure are kVp, mA, and exposure time.