Impact of Magnetic Field Inhomogeneity on the Quality of Magnetic Resonance Images and Compensation Techniques: A Review

Abstract

Background: Magnetic field inhomogeneity in magnetic resonance imaging (MRI) is caused by the inherent properties of the main magnet, external ferromagnetic components surrounding the magnet, and the patient itself. Significant deviations from magnetic field inhomogeneity can create artifacts in MRI images, thereby compromising image quality. Optimizing magnetic field homogeneity improves image quality and helps to reduce artifacts. The goal of this article therefore is to help radiographers and operators of MRI understand the clinical basis of magnetic field inhomogeneity and its effects on MR images. This would assist them to appreciate the trade-offs between sequence parameters and image quality metrics towards optimizing magnetic field inhomogeneity. Methods: A narrative literature review was conducted from relevant databases using search terms such as MRI, magnetic field inhomogeneity, optimization, magnetic field inhomogeneity artifacts, and MRI shimming. Results: Minimizing field inhomogeneities in MRI is not straightforward but involves a multitude of factors and steps. Magnetic field homogeneity could be optimized to improve MR image quality by choosing the most appropriate pulse sequence/imaging parameters that could best minimize distortion and increase SNR based on the anatomical region of interest (or tissue types) while complementing it with shimming and use of dielectric pads. Conclusion: Future works to investigate the association between the MRI pulse sequence parameters and measurements of MR image quality metrics, based on individual tissue densities, could provide a new window for reducing magnetic field inhomogeneity due to susceptibility and chemical shift effects.