Pulse repetition period is generally about _______ than pulse duration.

• A. Longer
• B. Shorter
• C. 100 to 1000 times longer
• D. 0.5 times longer

Answer: (C)

Pulse repetition period is the time from the start of one ultrasound burst to the start of the next, and it includes both the emitted pulse and the listening time after the burst during which echoes are received. The pulse itself is brief—only a few nanoseconds to a few microseconds—whereas the listening window is determined by imaging depth and the need to wait for echoes from deeper targets. Because that listening time is much longer than the actual pulse, the repetition period ends up being hundreds of microseconds to milliseconds, which is roughly 100 to 1000 times longer than the pulse duration. This large difference explains why deeper imaging, which lengthens the listening interval, also lengthens the pulse repetition period and reduces frame rate.