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Automatic compensation of motion artifacts in MRI

Patient motion during the acquisition of a magnetic resonance image can cause blurring and ghosting artifacts in the image. This paper presents a new post‐processing strategy that can reduce artifacts due to in‐plane, rigid‐body motion in times comparable to that required to re‐scan a patient. The algorithm iteratively determines unknown patient motion such that corrections for this motion provide the best image quality, as measured by an entropy‐related focus criterion. The new optimization strategy features a multi‐resolution approach in the phase‐encode direction, separate successive one‐dimensional searches for rotations and translations, and a novel method requiring only one re‐gridding calculation for each rotation angle considered. Applicability to general rigid‐body in‐plane rotational and translational motion and to a range of differently weighted images and k‐space trajectories is demonstrated. Motion artifact reduction is observed for data from a phantom, volunteers, and patients. Magn Reson Med 41:163‐170, 1999. © 1999 Wiley‐Liss, Inc.