High pulse repetition frequency (PRF) helps reduce aliasing in Doppler imaging but may introduce what trade-off?

High pulse repetition frequency (PRF) helps reduce aliasing in Doppler imaging but may introduce what trade-off?

• A. It completely eliminates aliasing
• B. Reduces aliasing but increases range ambiguity
• C. It has no effect on aliasing
• D. It increases aliasing

Answer: (B)

PRF sets the sampling rate for Doppler frequency shifts, so it directly controls two different kinds of ambiguity. Raising PRF increases the Nyquist limit, allowing higher Doppler frequencies to be measured without wrapping around, which reduces velocity aliasing. But a higher PRF also shortens the time between pulses, so echoes from deeper tissues can arrive just as a new pulse is being emitted. That makes it harder to assign echoes to the correct depth, creating range ambiguity. In short, you gain better velocity unambiguity at higher speeds but lose depth (range) unambiguity. That’s why higher PRF reduces aliasing but increases range ambiguity.

PRF sets the sampling rate for Doppler frequency shifts, so it directly controls two different kinds of ambiguity. Raising PRF increases the Nyquist limit, allowing higher Doppler frequencies to be measured without wrapping around, which reduces velocity aliasing. But a higher PRF also shortens the time between pulses, so echoes from deeper tissues can arrive just as a new pulse is being emitted. That makes it harder to assign echoes to the correct depth, creating range ambiguity. In short, you gain better velocity unambiguity at higher speeds but lose depth (range) unambiguity. That’s why higher PRF reduces aliasing but increases range ambiguity.