When the cathode end is directed toward the head, which projection would NOT take advantage of the heel effect?

• A. Lateral Femur
• B. AP Lower Leg
• C. AP T/S
• D. Lateral T/S

Answer: (C)

Heel effect means the beam is more intense on the cathode side and less on the anode side. When the cathode end is directed toward the head, the head end gets more exposure. Projections in which the beam travels along the length of a long, thick part—so thickness varies significantly along the beam path—benefit from placing the thicker portion toward the cathode. A view where the X-ray beam passes through the body from front to back with only a relatively small anteroposterior path through the chest doesn’t present a substantial thickness variation along the beam direction, so shifting the cathode toward the head doesn’t meaningfully change exposure across the image. In that case, the heel effect wouldn’t be a practical advantage for optimizing this projection.