BNR stands for Beam Non Uniformity Ratio. What does it measure?

• A. Ratio of average intensity to peak intensity.
• B. Ratio of lowest peak intensity to average intensity.
• C. Ratio of highest peak intensity to the average intensity.
• D. Ratio of peak intensity to background noise.

Answer: (C)

Beam Non-Uniformity Ratio measures how uneven the beam’s brightness is across its cross-section. It is defined as the highest intensity within the beam divided by the average intensity across the beam. This captures how pronounced the hot spots are: a perfectly uniform beam would have the peak intensity close to the average, giving a ratio near 1. In practice, the ratio is greater than 1, with lower values indicating a more uniform beam and better image quality, and higher values showing more nonuniformity and potential artifacts. The description described here matches the ratio of the highest peak intensity to the average intensity. It’s not the inverse ratio (average to peak), not the lowest peak to average, and not related to background noise.