During pulsed-wave Doppler, which parameter affects acoustic exposure?

During pulsed-wave Doppler, which parameter affects acoustic exposure?

• A. Doppler gain
• B. High pass filter
• C. Pulse repetition frequency
• D. Baseline position

Answer: (C)

Acoustic exposure is driven by how much energy is emitted over time. In pulsed-wave Doppler, energy is sent in short pulses, so the amount of energy delivered per second depends on the duty cycle of those pulses. The duty cycle equals pulse duration multiplied by the pulse repetition frequency (PRF). The pulse duration is fixed by the transducer, but changing the PRF changes how often those pulses are emitted. Increasing the PRF increases the duty cycle and therefore the average energy delivered to tissue (more acoustic exposure); lowering PRF reduces exposure. The other controls affect signal processing or display—Doppler gain changes amplification of echoes, high pass filter alters which frequencies are passed, and baseline position is a display setting—without changing the emitted energy.

Acoustic exposure is driven by how much energy is emitted over time. In pulsed-wave Doppler, energy is sent in short pulses, so the amount of energy delivered per second depends on the duty cycle of those pulses. The duty cycle equals pulse duration multiplied by the pulse repetition frequency (PRF). The pulse duration is fixed by the transducer, but changing the PRF changes how often those pulses are emitted. Increasing the PRF increases the duty cycle and therefore the average energy delivered to tissue (more acoustic exposure); lowering PRF reduces exposure. The other controls affect signal processing or display—Doppler gain changes amplification of echoes, high pass filter alters which frequencies are passed, and baseline position is a display setting—without changing the emitted energy.