Question

If I make an exposure at 80 kVp 8 mAs 72 inches, what technique would I need at 36 inches?

1) 60 kVp at 4 mAs
2) 80 kVp at 2 mAs
3) 80 kVp at 4 mAs
4) 60 kVp at 16 mAs

Answer 1

The technique you would need at 36 inches is option 2) 80 kVp at 2 mAs.

Step-by-step explanation:

The technique you would need at 36 inches is option 2) 80 kVp at 2 mAs.

The exposure at 80 kVp, 8 mAs, 72 inches is equivalent to an exposure at 80 kVp, 2 mAs, 36 inches. The exposure factors needed to maintain the same density are inversely proportional to the distance squared (Inverse Square Law). So, since the distance is halved (36 inches instead of 72 inches), the mAs should also be halved to maintain the same density.

Remember that kVp controls the quality or penetrating power of the x-ray beam, while mAs controls the quantity or number of x-ray photons produced. Changing the mAs will affect the image brightness, while changing the kVp will affect the image contrast.