Cavitation in ultrasound refers to gas bubble formation as a result of which effects?

• A. Nonthermal effects
• B. Thermal effects
• C. Mechanical friction
• D. Electrical stimulation

Answer: (A)

Cavitation is driven by the acoustic pressure changes produced by the ultrasound wave. During the rarefaction phase, pressure drops and dissolved gases come out of solution to form microbubbles. These bubbles can then oscillate or violently collapse, creating mechanical effects like microstreaming and local shear forces that interact with surrounding tissues. This bubble dynamics is a mechanical process, not a heat-driven one, so it falls under nonthermal effects. Heating from energy absorption is a separate phenomenon and not what causes the bubble formation itself. Electrical stimulation and mechanical friction aren’t the mechanisms behind cavitation.