RTBC X-ray Tube and Components Practice Test 2026 - Free X-ray Components Practice Questions and Study Guide

The anode heel effect is a gradient in beam intensity across the image field caused by the angle of the anode; photons emitted toward the anode side must pass through more of the anode material and are attenuated more, whereas photons toward the cathode side have less attenuation and produce a brighter area. This effect becomes more pronounced when the geometry exaggerates differences in path length, especially with a shorter source-to-image distance. Decreasing SID makes the beam diverge more and increases the variation in path length across the field, so the heel effect is stronger. Increasing SID reduces this gradient, and altering mA or kVp changes overall exposure or energy but not the geometric intensity distribution across the field. Hence, the exposure modification that increases the anode heel effect is decreasing SID.