Which projection would NOT take advantage of the heel effect if the cathode was toward the feet?

Which projection would NOT take advantage of the heel effect if the cathode was toward the feet?

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

Answer: (B)

The heel effect creates a brightness gradient along the direction from the cathode toward the anode, so you get more exposure on the cathode side of the image. When the cathode end is toward the feet, the part that is thickest toward the feet would benefit because that thick region would be on the higher-intensity side. Projections of the trunk (AP lumbar, AP thoracic, and lateral lumbar) involve thickness variations along the length of the anatomy, so positioning the thicker portion toward the feet (the cathode side) can help even out exposure. The lateral view of the femur, however, has the beam traveling from front to back through the thigh, and the major attenuation is across the cross-section rather than along the head-to-toe axis. In this orientation, the cathode-foot gradient does not align with the part’s thickness variation, so the heel effect would not be useful.

The heel effect creates a brightness gradient along the direction from the cathode toward the anode, so you get more exposure on the cathode side of the image. When the cathode end is toward the feet, the part that is thickest toward the feet would benefit because that thick region would be on the higher-intensity side. Projections of the trunk (AP lumbar, AP thoracic, and lateral lumbar) involve thickness variations along the length of the anatomy, so positioning the thicker portion toward the feet (the cathode side) can help even out exposure. The lateral view of the femur, however, has the beam traveling from front to back through the thigh, and the major attenuation is across the cross-section rather than along the head-to-toe axis. In this orientation, the cathode-foot gradient does not align with the part’s thickness variation, so the heel effect would not be useful.