ARDMS Ultrasound Physics & Instrumentation Practice Exam

As imaging depth increases, what happens to the pulse repetition period?

1. Decreases

2. Remains the same

3. Increases

4. Fluctuates

The correct answer is: Increases

As imaging depth increases, the pulse repetition period increases. This is because the pulse repetition period is the amount of time it takes for the ultrasound machine to send out a pulse and then listen for the echo returning from the tissue. When imaging at greater depths, the sound waves must travel further to reach the tissue and return. Since the speed of sound in tissue is constant, a longer travel distance necessitates a longer time interval for both the transmission of the pulse and the reception of the echo, thereby increasing the pulse repetition period. In scenarios where the imaging depth is shallow, the ultrasound system can send and receive pulses in a shorter time frame, resulting in a decreased pulse repetition period. Thus, as the depth of the imaging increases, the expectation is for a corresponding increase in the pulse repetition period to accommodate the longer time needed for the sound waves to make the round trip to the deeper tissues and back to the transducer.