Evaluation of the impact of magnetic field homogeneity on image quality in magnetic resonance imaging: a baseline quantitative study at 1.5 T

Abstract

Background Magnetic resonance images can be affected in a number of ways by magnetic field inhomogeneity. The study aimed to optimize the main magnetic field homogeneity (MFH) by assessing how magnetic field inhomogeneity affects the signal-to-noise ratio (SNR) and geometric distortion of images acquired along the diameter of a spherical volume phantom from the isocenter of the MRI scanner. Results The MFH ranged between 0.10 and 0.60 ppm. The best MFH and the maximum SNR were determined in the isocenter at 400 mm field of view with the application of shim. However, for all the phantom positions, geometrical distortion in images acquired at 200 mm field of view was generally better and worse at 400 mm field of view. MFH could be optimized to reduce geometrical distortion and increase SNR by increasing the receiver bandwidth and the number of excitations whiles complementing it with shimming during image acquisition. According to Chi-square independent test, there were no significant differences (p > 0.05) in the MFH, SNR, and geometrical distortion values. Compared to findings at higher field strengths, it was observed that MRI systems of higher field strengths (greater than 1.5 T) could offer superior magnetic field homogeneity and SNR without causing observable geometrical distortion. Conclusions The optimal field of view for the fast field echo (FFE) sequence required to maximize MFH, SNR, and reduce distortion during image acquisition may vary across MRI systems of different field strengths. To determine the appropriate field of view, the method and results of this study could serve as a guide for medical physicists as part of their routine quality assurance test procedures.