Final answer:
In adapting x-ray exposure factors for an image with an 8:1 grid, the milliampere-seconds (mAs) needs to be adjusted to compensate for the grid's absorption. For an 8:1 grid, the conversion factor is typically 4, and the appropriate factor combination of 400 mA, 12 ms, and 90 kV maintains the necessary mAs.
Step-by-step explanation:
The exposure factors used for a particular nongrid x-ray image were 300 mA, 4 ms, and 90 kV. When using an 8:1 grid for another image, the amount of radiation required increases due to the absorption and scatter reduction capabilities of the grid. Grids require an increase in exposure to maintain image quality, often referred to as a grid conversion factor. For an 8:1 grid, the typical conversion factor is around 4. Therefore, the new exposure factors must be multiplied by this factor to compensate for the grid's absorption.
In the given particular case, if we multiply the original milliampere-seconds (mAs) by the grid conversion factor (300 mA × 4 ms = 1.2 mAs; 1.2 mAs × 4 = 4.8 mAs), you would adjust the exposure to either increase the time or the milliamperes accordingly to reach that new mAs. One possible adjustment could be increasing the milliamperes to 400 mA and lengthening the time to 12 ms (400 mA × 12 ms = 4.8 mAs), at the same voltage of 90 kV. Therefore, the choice of 400 mA, 12 ms, and 90 kV does appear appropriate in maintaining the necessary mAs while using the 8:1 grid.