If the first radiograph of a foot is done using 4 mAs at 40 inches, and a second radiograph is done using 50 inches, how much mAs should be used to maintain exposure to the IR?

Question

Quizplus · Accepted Answer

The distance from the tube to the IR has increased from 40 inches to 50 inches, a distance change of 1.25 (40/50). To maintain exposure to the IR, the mAs must be increased by a factor of 1.25 squared (1.25 x 1.25 = 1.56).

4 mAs x 1.56 = 6.24 mAs, which can be rounded up to 6 mAs. Therefore, the correct answer is C, 6 mAs.

If the First Radiograph of a Foot Is Done Using