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

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

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

Answer: (B)

Heel effect means the X-ray beam is more intense on the cathode side of the tube. When the cathode end is toward the head, you want the thicker portion of the anatomy along the beam’s path to lie toward the head so those tissues receive the higher exposure. The AP thoracic spine is a tall, lengthwise structure, so orienting the patient with the cathode toward the head allows the upper, thicker part of the chest/shoulder region to benefit from the increased intensity, helping produce more uniform exposure along the long column of the spine. Lateral projections don’t align with this head-to-foot variation in thickness, and the other options either involve different projection directions or shorter axes, where the heel effect contributes less.

Heel effect means the X-ray beam is more intense on the cathode side of the tube. When the cathode end is toward the head, you want the thicker portion of the anatomy along the beam’s path to lie toward the head so those tissues receive the higher exposure. The AP thoracic spine is a tall, lengthwise structure, so orienting the patient with the cathode toward the head allows the upper, thicker part of the chest/shoulder region to benefit from the increased intensity, helping produce more uniform exposure along the long column of the spine. Lateral projections don’t align with this head-to-foot variation in thickness, and the other options either involve different projection directions or shorter axes, where the heel effect contributes less.