What describes the line-focus principle regarding target angle?

• A. Smaller target angle yields a larger effective focal spot.
• B. Smaller target angle yields a smaller effective focal spot but heel heat concentration increases.
• C. Target angle has no effect on heat distribution.
• D. Smaller target angle increases exposure time.

Answer: (B)

The line-focus principle is about using an angled target to control both the apparent focal spot size and how heat is distributed in the anode. When the target is tilted more steeply (a smaller angle), the projection of the actual focal spot onto the plane perpendicular to the beam becomes smaller, so the effective focal spot is reduced. At the same time, that same tilt causes heat to be deposited more intensely in a smaller area of the anode—the heel effect becomes more pronounced—so heat concentration increases toward the anode side. This combination—smaller effective focal spot with increased heel heat concentration—matches the described behavior. The other options contradict either the change in focal spot size, the impact on heat distribution, or the relationship to exposure time.