If kVp is increased by 15% with the mAs unchanged, receptor exposure will approximately:

If kVp is increased by 15% with the mAs unchanged, receptor exposure will approximately:

• A. Remain the same
• B. Increase by about 25%
• C. Double
• D. Decrease

Answer: (C)

The key idea is how changing kVp affects the number of photons reaching the image receptor when mAs is held constant. Receptor exposure depends on how many photons actually make it through the patient and reach the detector, not just how many are produced by the tube. Increasing kVp by about 15% raises the average photon energy and makes the beam more penetrating, so a larger fraction of photons passes through the patient to the receptor. In the diagnostic range, this increase in transmitted photons is enough to roughly double the receptor exposure even though the number of photons produced (mAs) hasn’t changed. It’s an approximate rule of thumb, so exact results can vary with filtration, patient size, and geometry, but the idea is that modest kVp boosts can significantly boost receptor exposure when mAs stays the same.

The key idea is how changing kVp affects the number of photons reaching the image receptor when mAs is held constant. Receptor exposure depends on how many photons actually make it through the patient and reach the detector, not just how many are produced by the tube. Increasing kVp by about 15% raises the average photon energy and makes the beam more penetrating, so a larger fraction of photons passes through the patient to the receptor. In the diagnostic range, this increase in transmitted photons is enough to roughly double the receptor exposure even though the number of photons produced (mAs) hasn’t changed. It’s an approximate rule of thumb, so exact results can vary with filtration, patient size, and geometry, but the idea is that modest kVp boosts can significantly boost receptor exposure when mAs stays the same.