If the anode angle is decreased, what is the combined effect on the focal spot and heel effect?

If the anode angle is decreased, what is the combined effect on the focal spot and heel effect?

• A. Decreased focal spot size and Increased heel effect
• B. Increased focal spot size and Decreased heel effect
• C. Decreased both
• D. Increased both

Answer: (A)

Lowering the anode angle tightens the projection of the focal spot through the line-focus principle, so the effective focal spot on the image becomes smaller (better spatial resolution). At the same time, a smaller angle increases the path length through the anode material for photons exiting toward the anode side, raising self-absorption and causing a greater variation in beam intensity across the field—the heel effect. So the combined result is a decreased focal spot size and an increased heel effect.

Lowering the anode angle tightens the projection of the focal spot through the line-focus principle, so the effective focal spot on the image becomes smaller (better spatial resolution). At the same time, a smaller angle increases the path length through the anode material for photons exiting toward the anode side, raising self-absorption and causing a greater variation in beam intensity across the field—the heel effect. So the combined result is a decreased focal spot size and an increased heel effect.