Which statement about the 15% rule is true?

Which statement about the 15% rule is true?

• A. It states that increasing kVp by 15% will double receptor exposure if mAs is not changed.
• B. It states that increasing kVp by 15% allows a decrease in mAs by half to maintain density.
• C. It states that kVp changes have no effect on density.
• D. It states that kVp changes require adjusting SID.

Answer: (B)

The 15% rule describes how small changes in kVp affect image receptor exposure and how you compensate with mAs to keep the same density on the radiograph. When you raise kVp by about 15%, the beam becomes more penetrating and more photons reach the detector. To keep the image density the same, you can reduce the total photon output by roughly half, so cutting mAs by about 50% maintains the same receptor exposure. This balance lets you lower patient dose (via reduced mAs) while preserving image quality when increasing kVp. If kVp is increased but mAs is left unchanged, receptor exposure tends to rise rather than stay the same, because there are more photons reaching the detector overall. Density is influenced by both kVp and mAs, not by kVp alone. The rule specifically does not involve changing the source-to-image distance; SID changes alter exposure through distance, not the kVp/mAs adjustment described by this rule.

The 15% rule describes how small changes in kVp affect image receptor exposure and how you compensate with mAs to keep the same density on the radiograph. When you raise kVp by about 15%, the beam becomes more penetrating and more photons reach the detector. To keep the image density the same, you can reduce the total photon output by roughly half, so cutting mAs by about 50% maintains the same receptor exposure. This balance lets you lower patient dose (via reduced mAs) while preserving image quality when increasing kVp.

If kVp is increased but mAs is left unchanged, receptor exposure tends to rise rather than stay the same, because there are more photons reaching the detector overall. Density is influenced by both kVp and mAs, not by kVp alone. The rule specifically does not involve changing the source-to-image distance; SID changes alter exposure through distance, not the kVp/mAs adjustment described by this rule.