The variation of x-ray intensity along the longitudinal axis describes which phenomenon?

• A. Beam collimation
• B. Positive beam limitation
• C. Anode heel effect
• D. X-ray emission spectrum

Answer: (C)

Anode heel effect explains the variation in x-ray intensity along the longitudinal axis. Because the anode is angled, photons produced toward the anode side must pass through more of the tungsten target and are more likely to be absorbed, reducing intensity on that side. Photons toward the cathode side pass through less material and are less attenuated, increasing intensity there. The net result is a gradient of beam intensity from the cathode side to the anode side. In practice, this is why the thicker part of the anatomy is often positioned toward the cathode side to even out exposure, or filters may be used to compensate.