← X-ray subtopic / Sim: kVp / mAs Explorer
kVp / mAs Explorer
Drag the kVp and mAs sliders. Watch beam quality (average energy), beam quantity (photons), patient entrance skin dose, and subject contrast respond. The 15% rule becomes intuitive fast.
80
20
Detector exposure
—
Entrance skin dose
—
Subject contrast
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Relative signal (bone, muscle, fat, air)
Bone—
Muscle—
Fat—
Air—
Appearance on image
Bone
Muscle
Fat
Air
Try the 15% rule: raise kVp by 15% (80→92). Exposure should roughly double and contrast should fall — classic trade-off.
The physics
Detector exposure scales approximately with mAs × kVp². Entrance skin dose also rises with mAs (linear) and kVp (steeper than squared at the skin entry). Subject contrast is proxied here by the ratio of photoelectric (Z³/E³) to Compton (nearly flat) interaction, which falls with kVp. This is a schematic teaching model — not a dosimetry calculator — but the trends are real.