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Kilovoltage affects both
contrast and density. If it is too low the resulting film will have a "soot and
whitewash" appearance, i.e. high contrast. When the kilovoltage is too high,
contrast will be reduced because the shorter wavelength.
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The kilovoltage
potential (kVp) determines the quality of the x-ray beam and thus its ability
to penetrate tissue. Higher kVp settings produce more penetrating
beams, with a higher percentage of radiation
reaching the film. Some units do not have a
control for changing kVp and employ what is referred to as a "constant
kVp" setting.
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A KVp
setting of 75 to 85 is adequate for penetrating most distal portions of a mature
horse's leg. Lower kVp settings can be of value when radiographing immature
horses and for soft-tissue techniques.
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A higher kVp
setting allows for use of a lower mas setting. This would generally mean a short
time of exposure.
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The inverse relationship
between kVp and mas can be seen in the following settings, all of which will
produce comparable radiographs if other factors are unchanged.
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60 kVp
and 4.0 mas (10 ma x 0.4 sec)
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70 kVp
and 2.0 mas (10 ma x 0.2 sec)
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80 kVp
and 1.0 mas (10 ma x 0.1 sec)
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90 kVp
and 0.5 mas ( 5 ma x 0.1 sec)
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In the range of
kVp settings normally used, adding 10 kVp
and dividing the mas in half will produce a comparable radiograph.
Conversely, subtracting 10 kVp and doubling the mas maintains
radiographic density at a similar level.
