What is a common technique used to avoid aliasing in ultrasound?

Moving the baseline up or down to fit the spectral display is a common technique used to avoid aliasing in ultrasound, particularly in Doppler imaging. Aliasing occurs when the frequency of the returning echoes exceeds the Nyquist limit, which is half of the sampling rate. By adjusting the baseline, the sonographer can effectively reposition the spectral display such that it aligns better with the expected frequency shifts caused by blood flow. This can help to avoid the misrepresentation of velocities, making it easier to accurately assess blood flow and identify any abnormalities.

In Doppler ultrasound, if the baseline is set too low, higher velocities can wrap around the display and cause confusion regarding true flow direction and velocity. By moving the baseline, the sonographer can accommodate higher velocities within the display range and enhance the clarity of the analysis. This technique is essential for obtaining accurate and interpretable Doppler waveforms, thus supporting reliable clinical assessments.