Question

an x - ray is taken using 200 milliamperes (ma) at 0.50 seconds and results in 0.10 milligray (mgy) of patient exposure. assuming that all other factors remain constant, which ma settings would result in a patient exposure of 0.20 mgy?
20 ma
200 ma
300 ma
400 ma

Explanation:

Step1: Identify the relationship

The patient - exposure is directly proportional to the product of mA and time. Since time is constant here, patient - exposure is directly proportional to mA.

Step2: Set up the proportion

Let the initial mA be $mA_1 = 200$, initial exposure $E_1=0.10$ mGy, and the new exposure $E_2 = 0.20$ mGy. Let the new mA be $mA_2$. The proportion is $\frac{mA_1}{E_1}=\frac{mA_2}{E_2}$.

Step3: Solve for $mA_2$

Cross - multiply the proportion: $mA_1\times E_2=mA_2\times E_1$. Then $mA_2=\frac{mA_1\times E_2}{E_1}$. Substitute $mA_1 = 200$, $E_1 = 0.10$, and $E_2=0.20$ into the formula: $mA_2=\frac{200\times0.20}{0.10}=400$ mA.

Answer:

D. 400 mA