The quantity of X-rays produced is primarily controlled by the

• A. Kilovoltage peak
• B. Milliamperage
• C. Exposure time
• D. Focal spot size

Answer: (B)

The main factor determining how many X-ray photons are produced is the current through the filament, measured in milliamperes. This filament current controls how many electrons are emitted per second; more electrons hitting the anode mean more X-ray photons generated, so increasing milliamperage increases the photon yield and thus image density. Kilovoltage peak, on the other hand, sets the energy of the photons (their penetrating power) rather than how many are produced. Focal spot size mainly affects image sharpness, not quantity. The total number of photons also depends on exposure time (the product mA × time, called mAs), but the rate at which photons are produced is governed primarily by milliamperage.