What is the anode heel effect caused by?

The anode heel effect arises from the absorption of X-rays as they pass through the anode material. In an X-ray tube, the anode is typically made of a dense metal such as tungsten, which efficiently converts the incident electrons into X-rays. However, not all X-rays generated make it out to the patient; some are absorbed within the anode itself.

As the X-rays produced are emitted at different angles due to the target's geometry, those produced closer to the 'heel' side of the anode (which is inclined) have a longer path through the anode material before exiting the tube. Consequently, these X-rays are more likely to be absorbed, resulting in a decreased intensity of X-rays on the side of the beam that corresponds to the heel of the anode. This effect leads to differences in exposure across the radiographic image, with the beam being more intense on the side of the X-ray tube that is opposite the anode's heel (the cathode side).

Understanding this phenomenon helps radiographers optimize image quality by positioning denser anatomical structures on the cathode side where the X-ray intensity is higher. This not only improves the overall diagnostic quality of the images but also aids in patient safety by ensuring adequate exposure