The 15% kVp Rule
FormulaIncreasing the kVp by 15% raises the penetrating power of the beam, allowing the mAs to be halved with equivalent optical density. Reducing the kVp by 15% has the opposite effect.
+15% kVp → mAs ÷ 2
−15% kVp → mAs × 2
Practical use: prefer high kVp and low mAs to optimise dose while maintaining acceptable contrast (ALARA principle). Changing the kVp also modifies image contrast.
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