Duty cycle in ultrasound describes what?

• A. The amplitude of the sound wave.
• B. Total duration of the ultrasound session.
• C. The amount of time sound waves are penetrating tissue; expressed in on/off cycle of time.
• D. The size of the transducer head.

Answer: (C)

Duty cycle describes the proportion of time the ultrasound is actually emitting during each cycle. It is the on-time divided by the total cycle time (on plus off), usually expressed as a percentage. This isn’t about the wave’s amplitude (intensity), nor the overall session length, nor the transducer size. In practice, a low duty cycle means short pulses with longer pauses, delivering less energy and causing less heating (more non-thermal effects), while a higher duty cycle delivers more energy and increases heating (used for thermal effects). For example, a short pulse of 2 ms with 8 ms off yields a 20% duty cycle, whereas continuous ultrasound is effectively a 100% duty cycle.