Which projection would NOT benefit from the heel effect when the cathode end is directed toward the head?

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

Answer: (C)

The heel effect creates more x-ray intensity on the cathode side of the beam. When you position the cathode end toward the head, the side of the anatomy closest to the head gets more exposure, which helps compensate for parts that are thicker toward that end.

In an AP projection of the thoracic spine, the thicker portion of the anatomy tends to be toward the caudal (lower) end, near the feet. That thicker region would fall toward the anode side in this setup, so the extra intensity from the cathode toward the head wouldn’t help where it’s most needed. That’s why this projection wouldn’t benefit from this cathode orientation.

The other projections generally have their greater thickness toward the head end in this setup, so placing the cathode toward the head provides better exposure where needed and helps even out the image.