Pulse repetition frequency is determined by which of the following?

• A. Sound source
• B. Depth of view of a scan
• C. Frequency
• D. Maximum imaging depth of the system

Answer: (D)

Pulse repetition frequency is all about how quickly the system can send a new pulse and still wait long enough to receive echoes from the deepest point being imaged. The time between pulses is governed by the round-trip travel time to the farthest depth in view, so the deeper the maximum depth, the longer the return time the system must wait, and thus the lower the PRF. In other words, PRF is tied to the maximum imaging depth the system can handle, because that depth sets the required listening window after each pulse. The deeper you image, the longer you must listen, which reduces how often you can fire new pulses.

The speed of sound and the actual viewing depth used can influence some details, but the hardware-imposed maximum imaging depth is the factor that fixes the possible PRF range. Frequency mainly affects resolution and penetration, not how often pulses can be sent.