A radiograph is acquired using 200 milliamperes (mA) and an exposure time of 200 milliseconds (ms). What new exposure time must be used to obtain the same receptor exposure if the radiograph is repeated with 300 mA?

To maintain the same receptor exposure when changing the milliamperage (mA), you can apply the inverse relationship between mA and exposure time. When the mA is increased, the exposure time must be decreased to keep the total milliampere-seconds (mAs) constant, which is crucial for achieving consistent receptor exposure.

In this case, the initial exposure is calculated using:

[

\text{mAs} = \text{mA} \times \text{time in seconds}

]

First, convert milliseconds to seconds:

200 milliseconds = 0.2 seconds

Now, calculate the initial mAs:

[

\text{Initial mAs} = 200 , \text{mA} \times 0.2 , \text{s} = 40 , \text{mAs}

]

Now, if the mA is increased to 300, you need to find the new exposure time that will yield the same mAs of 40 mAs. The equation can be rearranged to solve for time:

[

\text{time} = \frac{\text{mAs}}{\text{mA}}

]

Substituting in the known