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

Abstract

Background Magnetic resonance images can be afected in a number of ways by magnetic feld inhomogeneity. The study aimed to optimize the main magnetic feld homogeneity (MFH) by assessing how magnetic feld inho mogeneity afects 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 feld of view with the application of shim. However, for all the phantom positions, geomet rical distortion in images acquired at 200 mm feld of view was generally better and worse at 400 mm feld 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 signifcant diferences (p>0.05) in the MFH, SNR, and geometrical distortion values. Compared to fndings at higher feld strengths, it was observed that MRI systems of higher feld strengths (greater than 1.5 T) could ofer superior magnetic feld homogeneity and SNR without causing observable geometri cal distortion. Conclusions The optimal feld of view for the fast feld echo (FFE) sequence required to maximize MFH, SNR, and reduce distortion during image acquisition may vary across MRI systems of diferent feld strengths. To determine the appropriate feld 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.