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

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

Answer: (C)

Heel effect means the X-ray beam is more intense on the cathode side, so you gain better exposure by placing the thicker part of the anatomy toward the cathode end. With the cathode aimed toward the head, you’d want the portion of the limb that’s thickest along the beam path to be toward the head to take advantage of that increased intensity.

The projection that would not benefit from this arrangement is the AP tibia/fibula view. In this view the beam travels along the length of the bone from front to back, and the region of greatest cross-sectional thickness of the tibia/fibula isn’t consistently aligned toward the head end. Because the thickest part isn’t reliably toward the cathode in this orientation, the heel effect wouldn’t provide the intended exposure boost.

The other projections involve positions where the thicker part of the limb can be aligned toward the cathode end (toward the head) to capitalize on the heel effect, which is why they would be more likely to take advantage of it.