aliasing(redirected from Foldover frequencies)
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1. introduction of an artifact or error in sampling of a periodic signal when the sampling frequency is too low to capture the signal properly.
2. in pulsed Doppler ultrasonography, an artifact occurring when the velocity of the sampled object is too great for the Doppler frequency to be determined by the system.
3. an artifact occurring in magnetic resonance imaging when a part being examined is larger than the field of view; an image of the area outside the field of view appears as an artifact inside the field of view.
an artifact that is caused by undersampling of signal data in diagnostic imaging.
aliasingA phenomenon that occurs when digitising less than two samples per period in a periodic function, where the anatomy being imaged by magnetic resonance extends beyond the field of view (FOV). Areas extending beyond the FOV boundaries are aliased back into the image to appear at artefactual locations.
Magnetic resonance imaging artifact produced when anatomy outside the field of view is mismapped inside it.
an imaging artefact in Doppler ultrasound, governed by the Nyquist limit, in which the blood flow direction appears to be reversed. An experienced operator can readily distinguish the aliased image from the true image.