An automatic exposure control radiograph is taken at 200 mA and 60 kVp. If initial receptor exposure is 20 microgray and kVp is increased to 69 while keeping other parameters, the receptor exposure will be which value?

• A. 10 Gy
• B. 25 Gy
• C. 20 Gy
• D. 17.5 Gy

Answer: (C)

Automatic exposure control aims to keep the receptor exposure at a set target. When you raise kVp, the beam becomes more penetrating, so to hit the same receptor dose, the system automatically reduces the exposure (mA or exposure time). With the kVp increased from 60 to 69 and the AEC still controlling the exposure, the receptor exposure is adjusted back to the original target level. In other words, the exposure to the image receptor should remain essentially the same as before (20 microgray). The numbers shown in Gy in the answer options don’t reflect typical receptor-exposure units (microgray), so the key idea is that AEC maintains constant receptor exposure despite the kVp change.