Only the ______ portion of the pulse repetition period is changed when the sonographer alters imaging depth.

• A. Echo time
• B. Transmit (send) time
• C. Processing time
• D. Listening (receive) time

Answer: (D)

Pulse repetition period is the time from the start of one ultrasound pulse to the start of the next. It includes the time to emit the pulse (transmit time), the time spent listening for echoes (receive time), and any processing time before the next pulse.

When you change imaging depth, you’re changing how long you must listen for echoes. Deeper imaging means echoes take longer to return, so the receive time lengthens. The emitted pulse duration is fixed by the transducer and the pulser, and processing time remains essentially constant, so they don’t change with depth. Therefore, the portion of the period that changes with imaging depth is the listening (receive) time. As depth increases, the receive time grows, lengthening the PRP and reducing the frame rate.