The coefficient of variation of exposures shall not be greater than what percentage on 4-6 consecutive exposures?

• A. 3%
• B. 5%
• C. 7%
• D. 10%

Answer: (B)

Consistency in exposure across a short series of radiographs is tested here. The coefficient of variation measures how spread out the exposure values are relative to their mean, calculated as the standard deviation divided by the mean and expressed as a percentage. Keeping this CV at or below 5% over four to six consecutive exposures means the exposures are tightly clustered, so image density and patient dose remain nearly the same from one image to the next. If the CV were higher, there would be noticeable differences in density between images, potentially requiring repeats and increasing overall dose or compromising diagnostic quality. A 5% threshold strikes a balance between practicality and precision, whereas tighter limits (like 3%) would be harder to achieve, and looser limits (7% or 10%) would allow too much variability.