As a result of the anode heel effect, which side of the x-ray field demonstrates lower intensity?

• A. Anode side
• B. Cathode side
• C. Center
• D. Edge

Answer: (A)

An important idea here is that the x‑ray beam across the field isn’t perfectly uniform because of the anode heel effect. The anode target is angled, so photons emitted toward the anode side must pass through more of the anode material (the heel) and are absorbed more. That extra attenuation reduces the number of photons exiting toward that side, producing lower intensity there. Conversely, photons toward the cathode side traverse less material, suffer less attenuation, and yield higher intensity. So the side facing the anode has the lower intensity, while the cathode side is brighter. In practice, this gradient is used to advantage by placing thicker anatomy toward the cathode side to compensate for the higher intensity there, since center and edge are not fixed points of equal exposure.