Which beam nonuniformity ratio (BNR) is generally considered better for ultrasound therapy?

• A. Lower BNR
• B. BNR does not affect hotspots
• C. Higher BNR
• D. BNR must be 2:1 for safety

Answer: (A)

Lower BNR means the ultrasound beam is more uniform. When the energy distribution is even, there are fewer hot spots, so the tissue heating is more predictable and safer. That makes therapy more reliable and reduces the risk of local overheating or burns.

If the beam is less uniform (higher BNR), the energy peaks can create hotspots, making heating less predictable and increasing the chance of tissue damage.

The statement that BNR doesn’t affect hotspots isn’t correct because hotspot formation is a direct result of beam nonuniformity. A higher BNR would worsen hotspots, not improve them. As for needing a specific ratio like 2:1 for safety, there isn’t a universal requirement; lower BNR is generally preferable, whatever the device allows.