Infographics / CT Physics

Patient dose vs mAs, kV and pitch

A graph of relative patient dose against relative mAs (tube current times rotation time). The dose against mAs relationship is a straight line through the origin: doubling mAs doubles the dose. For contrast, a second dashed curve shows tube output rising steeply with kVp (about kVp squared to cubed), which is non-linear. A side note states noise falls as one over the square root of mAs, so doubling mAs reduces noise only to about 0.71, not half.

Patient dose is directly proportional to mAs A graph of relative patient dose against relative mAs (tube current times rotation time). The dose against mAs relationship is a straight line through the origin: doubling mAs doubles the dose. For contrast, a second dashed curve shows tube output rising steeply with kVp (about kVp squared to cubed), which is non-linear. A side note states noise falls as one over the square root of mAs, so doubling mAs reduces noise only to about 0.71, not half. 0 1 2 4 1 2 relative mAs (mA × rotation time) relative dose / tube output patient dose ∝ mAs straight line through origin tube output ∝ kVp²–kVp³ steeper, non-linear key relationships 2× mAs → 2× dose ½ rotation time → ½ dose noise ∝ 1/√mAs 2× mAs → noise ×0.71, not halved
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