Phase-encoded Motion Artifacts

Phase-encoded motion artifacts appear as bright noise or repeating densities oriented in the phase direction, occurring as the results of motion during acquisition of a sequence. These artifacts may be seen from arterial pulsations, swallowing, breathing, peristalsis, and physical movement of a patient. They can be distinguished from Gibbs or truncation artifacts because they extend across the entire FOV, unlike truncation artifacts that diminish quickly away from the boundary causing them. Phase-encoded artifacts can be reduced by various techniques depending on their cause and location. Arterial pulsation artifacts can be reduced by spatial presaturation pulses prior to entry of the vessel into the slices. Spatial presaturation can also reduce some swallowing and breathing artifacts. Surface coil localization can reduce artifacts generated at a distance from the area of interest. Pulse sequences can be shortened, and respiratory and/or cardiac or peripheral gaiting techniques may also help. The following axial image of the head shows a phase-encoded motion artifact running transversely across the back of the head (posterior fossa) as a result of venous flow in the transverse sinuses.