A duty cycle of pulsed ultrasound is typically:

• A. Greater than 50%
• B. Exactly 60%
• C. Less than or equal to 50%
• D. 70%

Answer: (C)

Duty cycle in pulsed ultrasound describes how long the transducer is actively emitting during each cycle. It’s the ratio of the on-time (pulse duration) to the total cycle time (on-time plus off-time). In diagnostic imaging, the transducer sends short bursts and then waits for echoes, so the on-time is brief and the off-time is much longer. That keeps the duty cycle well under 50%, which helps keep average energy low to minimize tissue heating and mechanical effects. While the exact value varies with pulse duration and repetition interval, typical duty cycles are only a few percent. If the ultrasound were continuous, the duty cycle would be 100%, which isn’t how diagnostic devices operate.