For 1 MHz ultrasound, which combination of intensities is typical for pulsed versus continuous modes?

• A. Pulsed 0.5-1.0; Continuous 1.5-2.0
• B. Pulsed 1.5-2.0; Continuous 0.5-1.0
• C. Pulsed 2.0-3.0; Continuous 3.0-4.0
• D. Pulsed 0.2-0.4; Continuous 0.6-0.8

Answer: (A)

In therapeutic ultrasound, how energy is delivered changes what the tissue experiences. Pulsed mode applies energy in on and off cycles, so the average energy delivered is reduced, which helps limit heating while still providing mechanical effects. Continuous mode sends energy without interruption, so more energy accumulates in the tissue, producing more heating and a stronger mechanical effect.

For a treatment at 1 MHz, the common practical ranges are about 0.5–1.0 W/cm^2 in pulsed mode to keep heating in check, and about 1.5–2.0 W/cm^2 in continuous mode to achieve the desired effects with ongoing exposure. This combination reflects the safety and efficacy balance clinicians aim for: pulsed mode lowers average energy, while continuous mode delivers higher energy consistently. Other ranges would either underdeliver in continuous mode or risk excessive heating in pulsed mode, so this pairing is the typical practice.