OPTIMUM  kV RANGES

Exposure technique charts should be constructed with a constant kV for each body region, gradually raising the mAs as the patient's size increases.  The kV needs to be held constant in order to control the gray scale.  Larger patients need more mAs.

These are guidelines for optimum kV ranges.  Slight variations are possible.  Higher kV (with attendant lower mAs values) would create a wider gray scale; lower kV (with attendant higher mAs values) would create more contrast.  

For a high frequency generator, 5 to 10 lower kV may be necessary to avoid too wide a gray scale.  (Single phase kVs are inherently lower because they have an oscillating wave with dips below the peak [kVp], whereas kV is true with high-frequency generators, making these two sets of ranges approximately equal.)