Which projection would take advantage of the heel effect if the cathode was toward the head?

• A. AP Lumbar Spine
• B. Lateral FEMUR
• C. AP Thoracic Spine
• D. Lateral Lumbar Spine

Answer: (B)

Heel effect means the X-ray beam is slightly more intense on the cathode side, so the thicker part of a long structure should be placed toward the cathode end to compensate for greater attenuation there. If the cathode is toward the head, the thicker, proximal portion of the femur (near the hip) should be toward the head to take advantage of that increased exposure. A lateral projection of the femur lines up along the long axis of the bone and best positions the proximal, thicker region toward the cathode end, giving more uniform exposure along the length. Other projections don’t align the thicker part toward the cathode end in the same way, so they don’t benefit as much from the heel effect.