Anode Heel Effect

Overview

The anode heel effect refers to the phenomenon where there is decreased x-ray field intensity towards the anode side of an x-ray tube compared to the cathode side.
This occurs due to the varying emission of x-rays from the target material at different angles.

X-rays are generated beneath the surface of the target material.
X-rays emitted perpendicularly to the electron beam (closer to the anode) must pass through more material, resulting in higher absorption and lower field intensity.
Conversely, x-rays emitted more parallel to the electron beam (closer to the cathode) face less material, leading to less absorption and higher field intensity.

Anode Angle:
- Increasing the angle decreases the amount of target material perpendicular to the anode, reducing x-ray absorption.
Target-to-Film Distance:
- Increasing distance allows more beam divergence, which can reduce the heel effect, making the image more uniform.
Field Size:
- Smaller field sizes lead to a more uniform image due to peripheral variations being absorbed by the collimator.
Positioning:
- Aligning higher attenuating material towards the cathode and lower towards the anode can create a more uniform field.

The anode heel effect is used beneficially in x-ray imaging by aligning the anode-cathode axis with the patient's body thickness variations.
Particularly useful in imaging of kidneys, ureter, bladder (KUB), skull, chest, pelvis, abdomen, thoracic, lumbar areas.
In mammography, the effect is utilized by positioning the cathode near the thoracic wall and the anode near the nipple for better image quality.

The anode heel effect is discussed in the context of imaging technology and physics.

Curry TS, Dowdey JE, Murry RE, Christensen's Physics of Diagnostic Radiology, Lippincott Williams & Wilkins, 1990.
Mearon T & Brennan P, Anode Heel Effect in Thoracic Radiology: A Visual Grading Analysis, SPIE Proceedings, 2006.
Vockelmann C, Mammography: Basic Knowledge Radiology, 2023.