A radiograph is taken using 450 milliamperes (mA) for 0.1 seconds. What exposure time is needed to maintain receptor exposure if the radiograph is repeated at 300 mA?

To determine the correct exposure time required to maintain receptor exposure when switching from one milliampere (mA) setting to another, it is essential to understand the relationship between milliamperes, exposure time, and total exposure. The exposure is calculated as the product of the mA and the time in seconds.

Initially, the exposure at 450 mA for 0.1 seconds gives us:

Exposure = mA × time

= 450 mA × 0.1 s

= 45 mAs (milliampere-seconds).

When switching to 300 mA, we need to find the new exposure time that will yield the same total exposure of 45 mAs. Using the equation where the new exposure (X) must equal the previous exposure:

45 mAs = 300 mA × X s.

To find X, rearrange the equation:

X = 45 mAs / 300 mA

= 0.15 s.

This calculation shows that 0.15 seconds is the amount of time required at 300 mA to achieve the same receptor exposure as the initial exposure with 450 mA for 0.1 seconds. Thus, 0.15 s is the correct