MR imaging artifacts that simulate disease: how to recognize and eliminate them.
Occasionally, artifacts may simulate pathologic conditions on magnetic resonance (MR) images. Motion artifacts especially affect images of the chest and abdomen. There are a number of techniques for reducing motion artifacts, including respiratory and cardiac gating, k-space phase reordering, gradient moment nulling, even echo rephasing, and physical restraints. Aliasing occurs when the field of view does not include all of the anatomic structures present in the imaged section. Aliasing artifacts can be eliminated by increasing the field of view, oversampling, and use of saturation pulses or surface coils. Truncation artifacts represent the difference between the original and the reconstructed image and can be reduced with data extrapolation algorithms or image filtering. Chemical shift artifacts and magnetic susceptibility artifacts are due to a local deformity of the magnetic field, resulting in spatial misregistration. Chemical shift artifacts are more severe in images acquired with a narrow-bandwidth technique; magnetic susceptibility artifacts are more severe in images acquired with a long echo time. Pitfalls in the interpretation of MR images can be avoided by becoming familiar with the appearances and causes of common MR imaging artifacts.