According to the line-focus principle, decreasing the target angle results in what change to the effective focal spot?

According to the line-focus principle, decreasing the target angle results in what change to the effective focal spot?

• A. Increases
• B. Becomes unpredictable
• C. Decreases
• D. Stays the same

Answer: (C)

Line focus work hinges on the fact that the apparent focal spot is the projection of the actual focal spot onto the beam’s path, made smaller by the angle of the anode. When you lower the target angle, the projection along the beam becomes more foreshortened, so the effective focal spot size decreases. This gives better sharpness in the image because the beam’s origin is more compact, though it shifts heat loading more onto a smaller area of the anode and strengthens the heel effect.

Line focus work hinges on the fact that the apparent focal spot is the projection of the actual focal spot onto the beam’s path, made smaller by the angle of the anode. When you lower the target angle, the projection along the beam becomes more foreshortened, so the effective focal spot size decreases. This gives better sharpness in the image because the beam’s origin is more compact, though it shifts heat loading more onto a smaller area of the anode and strengthens the heel effect.