As the duty cycle of ultrasound approaches 100 percent, the thermal effects tend to which of the following?

As the duty cycle of ultrasound approaches 100 percent, the thermal effects tend to which of the following?

• A. It becomes more thermal.
• B. It becomes more mechanical.
• C. There is no change in tissue effects.
• D. It reduces heat generation.

Answer: (A)

Duty cycle tells us how much of the time the ultrasound is actually on. When it’s nearly continuous, energy is delivered almost all the time and there’s little time for tissue to cool between exposures. That ongoing energy input causes a temperature rise, so thermal effects become more pronounced. Mechanical effects rely more on the instantaneous pressure and pulsed delivery, which is not the dominant factor when the exposure is effectively continuous. So, as the duty cycle approaches 100 percent, heating increases rather than decreases.

Duty cycle tells us how much of the time the ultrasound is actually on. When it’s nearly continuous, energy is delivered almost all the time and there’s little time for tissue to cool between exposures. That ongoing energy input causes a temperature rise, so thermal effects become more pronounced. Mechanical effects rely more on the instantaneous pressure and pulsed delivery, which is not the dominant factor when the exposure is effectively continuous. So, as the duty cycle approaches 100 percent, heating increases rather than decreases.