What mode of operation is typically used to achieve nonthermal effects in ultrasound?

• A. Pulsed mode
• B. Continuous wave mode
• C. Intermittent random mode
• D. Steady-state mode

Answer: (A)

Nonthermal effects come from the mechanical actions of ultrasound, such as cavitation and microstreaming, rather than from heating tissue. Achieving these mechanical effects relies on delivering energy in short bursts with rest periods between them. This pulsed delivery lets peak pressures act on tissues while giving time for heat to dissipate, so overall temperature rise stays low. In contrast, continuous wave energy keeps delivering energy without breaks, which tends to accumulate heat and produce thermal effects rather than the mechanical, nonthermal ones. The other modes aren’t used to promote these nonthermal mechanical interactions because they don’t provide the same balance of burst delivery and cooling time.