A satisfactory radiograph is made using 20 mAs at 40 inches SID. How much mAs is needed to produce a similar radiograph at 60 inches SID?

Question

Quizplus · Accepted Answer

The exposure is adjusted according to the inverse square law of radiation, which states that the intensity of radiation is inversely proportional to the square of the distance from the source. When the SID increases from 40 inches to 60 inches, the square of the distance increases by a factor of (60/40)^2 = 2.25. Therefore, to maintain the same exposure, the mAs must also be increased by this factor: 20 mAs * 2.25 = 45 mAs.

A Satisfactory Radiograph Is Made Using 20 MAs at 40