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VIDEO INFO! How do we calculate the exposure time given mAs and mA? #xray #xraytech
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Thanks for the video. Another pro tip would be multiplying the kVp by 0.85 to get your answer without the subtraction step!
xxMurmaiderxx
Thank you, I was a bit confused and thought I was doing too many steps. This was very helpful.
isabelmedrano
Hi Benjamin, I have a math question this time. I can’t figure out why I’m getting the wrong answer on this problem. The quiz question asks me to determine which of these two groups of exposure factors will deliver the smallest patient dose:
(A.) 50 mAs, 70 kVp
(B.) 25 mAs, 90 kVp
My thought was that (A) would deliver a lower patient dose, and here’s why. 90 kVp is roughly equivalent to two 15% increases of 70 kVp. So using the 15% rule, it would seem that the mAs for (A) (which is 50) would need to be cut in half TWICE (to 12.5) in order to maintain exposure. But when we look at the mAs for (B) we see that it’s not ¼ of 50, it’s only ½ of 50. Therefore, it appears as though (B) would deliver a larger dose than (A), since the mAs for (B) is about 12.5 higher than what it would need to be for (A) and (B) to be equivalent. But according to Boardvitals that's not correct. It says that (B) would deliver a smaller dose than (A), and it doesn’t really explain why. Can you help me understand?
