Pulse repetition period is the inverse of which quantity?

• A. Duty factor
• B. Frame rate
• C. Pulse repetition frequency
• D. Pulse duration

Answer: (C)

Pulse repetition period is determined by the rate at which pulses are emitted. In ultrasound, the pulse repetition frequency counts how many pulses start each second, while the pulse repetition period measures the time between the starts of successive pulses. These are exact reciprocals: PRP = 1 / PRF. So if the system emits 1000 pulses per second, the time between starts is 0.001 seconds (1 ms).

Understanding the other terms helps see why they aren’t the inverse. Duty factor is the fraction of time the system is actively transmitting within one PRP (pulse duration divided by PRP). Frame rate refers to how many image frames are produced per second, which doesn’t map directly to the time between pulses. Pulse duration is the length of each transmitted pulse itself, not the interval between pulses.