For a fixed actual focal spot size, what is the general effect of decreasing the anode angle on spatial resolution?

• A. Increases spatial resolution
• B. Decreases spatial resolution
• C. No change
• D. Increases heat capacity

Answer: (A)

The key idea is the line-focus principle: the apparent size of the focal spot on the image is determined by the actual focal spot size and the angle of the anode. When the anode angle is small while the actual focal spot remains the same, the projection of that spot becomes larger. That means more geometric unsharpness or blur in the image, which degrades the ability to distinguish fine details. So, decreasing the anode angle increases the effective focal spot size and lowers spatial resolution. Heat capacity isn’t the factor being tested here, since the question is about sharpness rather than how much heat the anode can store.