A BNR of 1:1 indicates which of the following about the ultrasound beam?

• A. A perfect, hotspot-free beam
• B. High hotspot risk
• C. No beam propagation
• D. Unstable intensity

Answer: (A)

The concept here is how the ultrasound beam’s uniformity is measured by Beam Nonuniformity Ratio (BNR). BNR compares the peak intensity in the beam to the average intensity across the beam. A BNR of 1:1 means the peak intensity equals the average intensity everywhere in the beam, which is a perfectly uniform, hotspot-free beam.

So the best description is that it indicates a perfect, hotspot-free beam. In practice, real ultrasound beams have BNR values greater than 1, meaning there are some hotspots; lower is better for safety and image quality. A higher BNR would imply more pronounced hotspots and higher risk of localized heating. The other statements—no beam propagation or unstable intensity—don’t reflect what BNR measures.