If the Spatial Peak Intensity equals the Spatial Average Intensity, what is the Beam Nonuniformity Ratio (BNR)?

If the Spatial Peak Intensity equals the Spatial Average Intensity, what is the Beam Nonuniformity Ratio (BNR)?

• A. 2
• B. 0
• C. 1
• D. Undefined

Answer: (C)

BNR is the ratio of the brightest point in the beam to the average intensity across the beam cross-section, defined as SPI divided by SAI. When the Spatial Peak Intensity equals the Spatial Average Intensity, the ratio becomes 1, meaning the beam is perfectly uniform in intensity across its cross-section. For example, if every point across the beam has the same intensity, say 2 W/cm^2, then SPI is 2 and SAI is 2, giving BNR = 1. In real ultrasound beams, some nonuniformity usually exists, so SPI is greater than SAI and BNR is greater than 1.

BNR is the ratio of the brightest point in the beam to the average intensity across the beam cross-section, defined as SPI divided by SAI. When the Spatial Peak Intensity equals the Spatial Average Intensity, the ratio becomes 1, meaning the beam is perfectly uniform in intensity across its cross-section. For example, if every point across the beam has the same intensity, say 2 W/cm^2, then SPI is 2 and SAI is 2, giving BNR = 1. In real ultrasound beams, some nonuniformity usually exists, so SPI is greater than SAI and BNR is greater than 1.