Which statement best defines mA in radiography?

• A. The quantity of electrons crossing the tube during exposure
• B. The voltage across the tube during exposure
• C. The duration of exposure
• D. The distance to the film

Answer: (A)

mA is the tube current—the rate at which electrons flow from the cathode to the anode in the X-ray tube. This current determines how many X-ray photons are produced, because more electrons crossing the tube each second means more interactions at the anode and more photons. The energy of those photons (beam quality) is set by the kilovoltage across the tube, not by mA. The exposure time tells you how long the tube is producing electrons, and the distance to the film affects intensity via the inverse square law. So the statement describing the quantity of electrons crossing the tube during exposure best defines mA. The total exposure quantity is mA multiplied by time (mAs).