What is the usual range of diagnostic x-ray tube anode angles?

• A. 2-10 degrees
• B. 12-20 degrees
• C. 15-30 degrees
• D. 30-45 degrees

Answer: (B)

The question tests how the anode angle influences the focused spot and beam distribution using the line-focus principle. By tilting the anode, the apparent (effective) focal spot size seen from the patient becomes smaller than the actual focal spot, which improves sharpness, while the angle also introduces the heel effect, causing varying intensity across the field.

In diagnostic tubes, a balance is sought: a small enough effective focal spot for good spatial resolution, but not so large a heel effect or uneven exposure. The typical range that achieves this balance is about twelve to twenty degrees. Angles smaller than this tend to yield a less favorable balance for sharpness, while angles larger than this increase the heel effect and exposure nonuniformity across the image. Thus, twelve to twenty degrees is the usual, practical range.