RTBC X-ray Tube and Components Practice Test

The concept in play is the line-focus principle. The anode angle determines how the actual focal spot on the anode is projected into the image plane. When the anode angle is smaller, the effective focal spot size becomes smaller, so the source appears more point-like in the direction of the beam, which improves spatial resolution. At the same time, heat is generated in the actual focal spot but is spread over a smaller heated area on the anode surface as the angle decreases, which reduces the anode’s ability to dissipate that heat (lower heat capacity). So using a small anode angle with the same actual focal spot enhances resolution while decreasing heat capacity.