The increased metabolic rate during ultrasound heating is a direct consequence of which factor?

• A. Mechanical energy
• B. Acoustic streaming
• C. Cavitation
• D. Thermal heating

Answer: (D)

The main idea is that metabolic rate rises when tissue temperature goes up. Biochemical reactions proceed faster at higher temperatures because enzymes and substrates collide more energetically, often described by the Q10 effect (roughly doubling or tripling every 10°C). In ultrasound heating, the energy delivered by the beam is absorbed and converted into heat in the tissue, raising its temperature. That temperature rise directly speeds up metabolic processes, so the increased metabolic rate is a direct consequence of thermal heating. Other ultrasound phenomena—mechanical energy effects, acoustic streaming, and cavitation—are different effects of ultrasound; they don’t directly cause the metabolic rate to increase in the way temperature does.