Geometric Distortion in Structural Magnetic Resonance Imaging

Geometric distortion, an undesirable image artifact, is an inferior aspect associated with magnetic resonance imaging (MRI). Although slight distortions in MR images often have no consequences in reaching clinical conclusions, geometric distortions can make significant differences in certain MR applications such as, for example, stereotactic localization in radio-surgery and MR image-guided biopsy. In this article, geometric distortion in structural MRI is reviewed. It begins with a brief discussion of various sources that can cause geometric distortion in structural MRI, followed by a review of the apparatus and methods that have been developed for the measurement and characterization of the geometric distortion in MRI. The paper will then focus on a novel phantom-based technique that has been developed recently by the authors. This technique can provide a comprehensive and complete measurement of the geometric distortion in 3-dimensions with unprecedented details and accuracy. The major outcomes of a comprehensive study on the geometric distortion in representative clinical MR scanners, carried out recently using this technique, will be discussed. The article will also include a discussion of various correction methods that have been developed for correcting geometric distortion in MRI.