What produces a hot spot in the ultrasound beam?

• A. Prolonged exposure to low energy levels
• B. Consistent energy distribution across the beam
• C. Very high-frequency focusing at the skin surface
• D. Uneven intensity producing a high level of energy in the center of the US beam relative to surrounding areas

Answer: (D)

A hot spot happens when the ultrasound beam deposits energy unevenly, creating a localized peak in energy at the center of the beam. The transducer’s beam naturally has more energy along the central axis, and focusing elements further concentrate energy into a focal region. This higher energy density in the center compared with the surrounding areas can raise tissue temperature in that small area, producing a hot spot. If energy were distributed evenly, there would be no hotspot. If energy were merely concentrated at the surface or spread uniformly, you wouldn’t see that localized center peak.