During an ultrasound treatment to the low back, the patient reports hot spots directly under the transducer. Which ultrasound parameters are MOST likely responsible?

• A. Stationary technique, high beam nonuniformity ratio
• B. Dynamic technique, low beam nonuniformity ratio
• C. Stationary technique, low beam nonuniformity ratio
• D. Dynamic technique, high beam nonuniformity ratio

Answer: (A)

Hot spots under the transducer come from concentrated energy in a single location. When the ultrasound head is kept stationary, the tissue in that spot repeatedly absorbs energy, raising local temperature. If the beam has a high beam nonuniformity ratio, there are larger peaks in intensity across the beam, so those localized peaks become even more pronounced. The combination of not moving the head (stationary technique) and a beam with large intensity fluctuations (high BNR) creates the most pronounced hotspots directly under the transducer.

In contrast, moving the transducer (dynamic technique) distributes energy over a larger area, reducing peak temperatures, and using a low BNR beam yields a more uniform energy distribution with fewer hotspots.