ARDMS Ultrasound Physics & Instrumentation Practice Exam

The Nyquist limit in Doppler ultrasound defines the threshold to avoid aliasing of frequency shifts. It represents the maximum frequency that can be accurately measured without confusion, specifically related to the sampling rate of the ultrasound system. According to the Nyquist theorem, to prevent aliasing, the sampling frequency must be at least double the highest frequency present in the signal being measured. Therefore, the Nyquist limit is typically calculated as half of the pulse repetition frequency (PRF) of the Doppler ultrasound system. If the frequency shift of the reflected ultrasound waves exceeds this limit, aliasing will occur, which can lead to incorrect interpretations of blood flow directions and velocities. Understanding the Nyquist limit is crucial for accurate Doppler measurements in clinical practice.