Beam non-uniformity ratio (BNR) is defined as which of the following?

• A. The ratio of the intensity of the highest peak to the average intensity of all peaks
• B. The ratio of average intensity to the highest peak
• C. The ratio of energy to time
• D. The ratio of peak intensity to frequency

Answer: (A)

Beam non-uniformity ratio measures how uneven the ultrasound beam is across its cross-section. It is defined as the ratio of the maximum (highest peak) intensity within the beam to the average intensity across the beam. A higher BN ratio indicates more pronounced hot spots and less uniformity, which can affect image quality and the precision of dose distribution. This concept isn’t about energy divided by time or peak intensity divided by frequency; those pairings describe different physical quantities. The BN ratio specifically characterizes how the brightest part of the beam compares to its overall average, highlighting nonuniformity in the beam profile.