Sunday, November 2, 2008

What is the function of kV, mA & time?

This image is too contrasty. A slight increase in kV will do the trick!

a. kV is for penetration & contrast

b. mA is the amount of current thus the blackening of the film

c. time is the how long the exposure is

kV is for penetration: Thus, when doing chest x-rays at 100cm instead of 180cm (such as AP view), the kV has to be reduced by about 20%.

kV determines contrast: The higher the kV, the lower the contrast. Thus, penetrated film would have a much lower contrast relative to less penetrated film.

mA is for blackening of film: The thicker the tissue, the higher should be the mA. Thus, if you normally use 6mAs for normal size individual, you will need to reduce this to 4 for skinny individual or increase to 8 for obese individual.

Similarly, if for chest radiograph you use 6mAs, but for finger, it should be reduced to just 1 because of thinner tissue.

Time is how long the exposure is: Use shorter time for chest x-rays but longer time for extremity x-rays.

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