With deeper imaging, the listening time and the pulse repetition period ______.

With deeper imaging, the listening time and the pulse repetition period ______.

• A. Shorten
• B. Remain the same
• C. Vary unpredictably
• D. Lengthen

Answer: (D)

Deeper imaging requires a longer time for sound to travel to the deepest target and back. Since the speed of sound in tissue is essentially constant, increasing depth directly increases the round-trip travel time. To capture echoes from those deeper regions without interference from echoes of the previous pulse, you must extend the listening window after each pulse. You also need to increase the interval between pulses—the pulse repetition period—so the next pulse isn’t emitted before all echoes from the prior pulse have returned. In short, as imaging depth increases, both the listening time and the pulse repetition period lengthen.

Deeper imaging requires a longer time for sound to travel to the deepest target and back. Since the speed of sound in tissue is essentially constant, increasing depth directly increases the round-trip travel time. To capture echoes from those deeper regions without interference from echoes of the previous pulse, you must extend the listening window after each pulse. You also need to increase the interval between pulses—the pulse repetition period—so the next pulse isn’t emitted before all echoes from the prior pulse have returned. In short, as imaging depth increases, both the listening time and the pulse repetition period lengthen.