What pulse parameters change with imaging depth?

The correct answer highlights a fundamental aspect of ultrasound imaging related to how certain pulse parameters are dependent on the imaging depth. As ultrasound waves travel through tissue, the time taken for these waves to travel to a target structure and return is impacted by the distance they must cover.

Pulse repetition period (PRP) changes with imaging depth because PRP is the total time it takes for one pulse to be sent out and for the echo to return. When the depth of the imaging target increases, the PRP lengthens as it takes longer for the sound to travel to the target and back. Consequently, the pulse repetition frequency (PRF), which is the inverse of PRP, decreases because fewer pulses are emitted per second when the imaging depth is increased.

Duty factor, which is the ratio of the pulse duration to the PRP, also changes with imaging depth. As depth increases and PRP increases, the duty factor generally decreases because the time the pulse is actively being transmitted (pulse duration) does not increase substantially compared to the longer PRP.

This understanding is crucial for sonographers because manipulating these parameters can influence image quality and the ability to visualize structures at different depths.