When is pulsed ultrasound preferred over continuous ultrasound?

• A. When continuous heating is desired.
• B. When non-thermal effects are desired or when there is a need to minimize heating.
• C. For maximum thermal heating.
• D. When tissue depth exceeds 5 cm.

Answer: (B)

Pulsed ultrasound is used when the aim is to produce mechanical, non-thermal effects or to minimize heating. By delivering energy in bursts with rest intervals, the average energy the tissue absorbs drops, so temperature rise is limited. The peak intensity during the on-time can be higher, which enhances mechanical phenomena like microstreaming and cavitation that can stimulate tissue repair and cellular signaling without relying on heat. If the goal is to heat tissue for thermal effects, continuous ultrasound is more appropriate because it delivers energy steadily, promoting heating. The depth criterion isn’t the deciding factor for choosing pulsed over continuous; pulsed mode is about controlling heating and emphasizing non-thermal, mechanical effects.