In radiography, increasing mAs for an exposure does what?

• A. Increases kilovoltage
• B. Increases number of x-rays produced
• C. Increases focal spot size
• D. Decreases exposure time

Answer: (B)

The main idea is that mAs controls how many X-ray photons the tube emits. Increasing mAs raises the number of photons produced, so more reach the image receptor and the exposure (and patient dose) increases correspondingly. The energy of the X-ray beam, which determines penetration, is set by kVp, not mAs, so simply increasing mAs does not raise kilovoltage. The focal spot size is a physical property of the tube that affects sharpness, not the quantity of X-rays. Exposure time can change as a result of adjusting mA or time, but the direct effect of changing mAs is the increase in photon quantity.