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

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

• A. Decreases
• B. Increases
• C. Remains the same
• D. Becomes unpredictable

Answer: (A)

When you image deeper, the system has to wait longer for echoes to travel to the deepest point and back before sending the next pulse. Pulse repetition frequency is how many pulses you emit each second, which is basically the inverse of that listening time. Since the round-trip travel time increases with depth, the interval between pulses increases, so the PRF drops. In other words, deeper imaging lowers the pulse repetition frequency. For example, at a few centimeters depth the PRF might be on the order of tens of kilohertz, but at greater depths it falls to a few kilohertz because you must listen longer before each new pulse.

When you image deeper, the system has to wait longer for echoes to travel to the deepest point and back before sending the next pulse. Pulse repetition frequency is how many pulses you emit each second, which is basically the inverse of that listening time. Since the round-trip travel time increases with depth, the interval between pulses increases, so the PRF drops. In other words, deeper imaging lowers the pulse repetition frequency. For example, at a few centimeters depth the PRF might be on the order of tens of kilohertz, but at greater depths it falls to a few kilohertz because you must listen longer before each new pulse.