  In magnetic resonance imaging (MRI), inhomogeneity in the main magnetic field
used for imaging, referred to as off-resonance, can lead to image artifacts
ranging from mild to severe depending on the application. Off-resonance
artifacts, such as signal loss, geometric distortions, and blurring, can
compromise the clinical and scientific utility of MR images. In this review, we
describe sources of off-resonance in MRI, how off-resonance affects images, and
strategies to prevent and correct for off-resonance. Given recent advances and
the great potential of low field and/or portable MRI, we also highlight the
advantages and challenges of imaging at low field with respect to
off-resonance.
