Which mechanism primarily underlies the anode heel effect?

• A. X-ray absorption within the anode
• B. Scattering within the patient
• C. Grid misalignment
• D. Filament evaporation

Answer: (A)

The heel effect comes from self-absorption of X-rays in the anode due to its angled geometry. When the electron beam strikes the tilted target, X-ray photons are produced throughout the focal spot, but those traveling toward the anode side must pass through more of the anode material than those heading toward the cathode side. That extra material absorbs more photons, reducing intensity on the anode side, while the cathode side has a shorter path through the anode and higher intensity. So the primary mechanism is X-ray absorption within the anode itself.

Scattering in the patient, grid misalignment, or filament evaporation don’t set this intrinsic intensity gradient across the beam; they affect other aspects of image quality or tube operation, not the fundamental cause of the anode heel effect.