What type of ultrasound artifact is referred to as aliasing?

Aliasing is a specific type of ultrasound artifact that occurs in Doppler ultrasound imaging when the frequency of the reflected sound waves exceeds the Nyquist limit. This limit is calculated as half of the pulse repetition frequency (PRF). When this happens, the system misinterprets the high-frequency signals as being lower frequencies, which leads to an incorrect representation in the Doppler spectrum. This results in a visual pattern that appears to "wrap around," making it look like velocities are going from high to low, instead of showing the true higher velocities.

Identifying aliasing is crucial in clinical practice, especially when evaluating blood flow in veins and arteries, as it can impact the interpretation of patient conditions related to venous or arterial disease. Recognizing this artifact allows a sonographer to adjust the Doppler settings—such as increasing the PRF or lowering the frequency to prevent misinterpretation of blood flow dynamics. Understanding aliasing ultimately helps provide more accurate diagnostic information.