KVP and mAs problems

tgibbons · Joined: 19 Dec 2008 Posts: 2

Hello,
This is my first semester in Radiology and I am having a hard time in the physics math part, especially with the Kvp and mAs. Does anyone have any ideas to help me out or any web sites that I can go to that will explain it better.

Thanks for all your help

papa · Posted: Mon Jan 05, 2009 2:59 pm Post subject:

chicken truck.... definately chicken truck Mr. Green

http://www.radiologyworkers.com/radiologyforums/viewtopic.php?t=4583&postdays=0&postorder=asc&start=0
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tgibbons · Joined: 19 Dec 2008 Posts: 2

Thanks for the analogy, but my problems is the math portion of the kvp & mAs relationship. I am having trouble on the formula portion and figuring the problems of increasing kvp the mAs and maintaining the density etc.
Any websites that will help me out would be great.

Thanks

wvaio · Joined: 22 Sep 2007 Posts: 82

If you are refering to the 15% rule, the formula simply states: in order to maintain density when adjusting kVp, if you increase kVp 15 % then you halve the mAs. If you decreace your kVp 15% then you double the mAs.

Example: You take a radiograph at 80 kVp and 40 mAs. What change in technique will produce a radiograph with lower contrast while maintaining density?

Answer: Since you want to lower contrast you will need to increase kVp. You would multiply the 80 kvp by 1.15. Essntially increasing it by 15 %. Then you would divide the mAs by 2.

80x1.15=92
40/2=20

The answer would be 92 kVp and 20 mAs

Example 2: You take a radiograph at 80 kVp and 40 mAs. What technique would you use to increase contrast while maintaining density?

Answer: Since you want to increase contrast, you will need to decrease kVp by 15% and increase the mAs by 2 times. You multiple the kVp by .85. Essentially decreasing it by 15%. Then you would multiple the mAs by 2.

80x.85=68
40x2=80

The answer would be 68 kVp and 80 mAs.

I always use the C/\ K\/ M/\ process. Contrast up kV down mAs up
and C\/ K/\ M\/ Contrast down kV up mAs down

Hope that helps.