Question

A lateral radiograph of the cervical spine was made at 40 in. using 300 mA and 0.03 second exposure. If it is desired to increase the distance to 72 in., what should be the new milliampere (mA) setting, all other factors remaining constant?

1000 mA

Answer 1

The milliamperes (mA) setting should be adjusted to approximately 92.6 mA after increasing the distance from 40 inches to 72 inches for an X-ray exposure, according to the inverse square law of radiation.

Step-by-step explanation:

The student is asking about the adjustment of exposure parameters in radiographic imaging when the distance from the X-ray tube to the image receptor is changed, known as the inverse square law of radiation. Initially, the settings were at 40 inches using 300 mA for 0.03 seconds. The desired increase in distance is to 72 inches. According to the inverse square law, the intensity of radiation is inversely proportional to the square of the distance from the source. Therefore, the new mA setting can be calculated using the formula:
(mA1 x D1^2) / D2^2 = mA2
Here,
mA1 = initial milliamperes (300 mA),
D1 = initial distance (40 inches),
D2 = new distance (72 inches).
Plugging in the values, we get:
(300 mA x 40^2) / 72^2 = mA2
(300 mA x 1600) / 5184 = mA2
480000 / 5184 = mA2
mA2 ≈ 92.6 mA
Hence, the new mA setting should be approximately 92.6 mA to maintain the same level of exposure.