Which projection would NOT take advantage of the heel effect if the cathode end is aimed toward the head?

• A. AP Thoracic Spine
• B. Lateral Thoracic Spine
• C. AP Lower Leg
• D. Lateral Femur

Answer: (D)

The heel effect creates a brighter beam on the cathode side and a dimmer beam on the anode side, so you can use it to compensate for tissue that is thicker along the direction the beam travels by placing that thicker part toward the cathode end (toward the head in this scenario). Projections where the anatomy’s greatest thickness lies along the craniocaudal (head-to-toe) direction can be helped by this, because the beam’s intensity variation along that axis can offset attenuation.

A lateral projection of the femur, however, has the beam traveling side-to-side (medial to lateral) rather than along the head-to-foot axis. The major thickness variation along the beam path isn’t in the craniocaudal direction, so the heel effect won’t provide the same compensating benefit. Therefore, this projection would not take advantage of the heel effect when the cathode end is aimed toward the head.