Beam Nonuniformity Ratio (BNR) is defined as what?

Beam Nonuniformity Ratio (BNR) is defined as what?

• A. The ratio of SAI to SPI
• B. The difference SPI minus SAI
• C. The ratio of SPI to SAI
• D. The sum SPI plus SAI

Answer: (C)

Beam nonuniformity is about how uneven the ultrasound beam delivers energy. It is defined as the ratio of the spatial peak intensity (SPI) to the spatial average intensity (SAI) across the beam. If the beam were perfectly uniform, SPI would equal SAI, giving a ratio of 1. In real devices, SPI exceeds SAI, so the ratio is greater than 1. A higher ratio means more pronounced hotspots and less uniform energy delivery, which can affect safety and treatment effectiveness. Therapeutic ultrasound devices typically have a BNR somewhere around 2:1 to 6:1, with lower values indicating better beam uniformity. This definition is not the inverse (SAI over SPI), nor a difference or a sum of the two intensities.

Beam nonuniformity is about how uneven the ultrasound beam delivers energy. It is defined as the ratio of the spatial peak intensity (SPI) to the spatial average intensity (SAI) across the beam. If the beam were perfectly uniform, SPI would equal SAI, giving a ratio of 1. In real devices, SPI exceeds SAI, so the ratio is greater than 1. A higher ratio means more pronounced hotspots and less uniform energy delivery, which can affect safety and treatment effectiveness. Therapeutic ultrasound devices typically have a BNR somewhere around 2:1 to 6:1, with lower values indicating better beam uniformity. This definition is not the inverse (SAI over SPI), nor a difference or a sum of the two intensities.