ARDMS Ultrasound Physics & Instrumentation Practice Exam

If pulse repetition frequency increases, what happens to the duty factor?

1. Decreases

2. Increases

3. Remains the same

4. Becomes negligible

The correct answer is: Increases

When pulse repetition frequency (PRF) increases, the duty factor also increases. The duty factor is the ratio of the pulse duration (the time the ultrasound system is actively sending pulses) to the total time of the pulse cycle (which includes both the duration of the pulse and the listening time). As PRF increases, this means that more pulses are being transmitted in a given time period. If the pulse duration remains constant while PRF increases, the fraction of time that the system is actively transmitting (the duty factor) also increases. This results in a higher duty factor, indicating a more significant portion of time spent transmitting compared to receiving. Understanding this relationship is critical in ultrasound imaging, as it affects various aspects like image quality, heating, and penetration depth. A higher duty factor may also lead to increased tissue heating, which is an important consideration in patient safety.