Correction of Artifacts Induced by B 0 Inhomogeneities in Breast MRI Using Reduced-Field-of-View Echo-Planar Imaging and Enhanced Reversed Polarity Gradient Method.

Background: Diffusion-weighted (DW) echo-planar imaging (EPI) is prone to geometric distortions due to B ₀ inhomogeneities. Both prospective and retrospective approaches have been developed to decrease and correct such distortions.
Purpose: The purpose of this work was to evaluate the performance of reduced-field-of-view (FOV) acquisition and retrospective distortion correction methods in decreasing distortion artifacts for breast imaging. Coverage of the axilla in reduced-FOV DW magnetic resonance imaging (MRI) and residual distortion were also assessed.
Study Type: Retrospective.
Population/phantom: Breast phantom and 169 women (52.4 ± 13.4 years old) undergoing clinical breast MRI.
Field Strength/sequence: A 3.0 T/ full- and reduced-FOV DW gradient-echo EPI sequence.
Assessment: Performance of reversed polarity gradient (RPG) and FSL topup in correcting breast full- and reduced-FOV EPI data was evaluated using the mutual information (MI) metric between EPI and anatomical images. Two independent breast radiologists determined if coverage on both EPI data sets was adequate to evaluate axillary nodes and identified residual nipple distortion artifacts.
Statistical Tests: Two-way repeated-measures analyses of variance and post hoc tests were used to identify differences between EPI modality and distortion correction method. Generalized linear mixed effects models were used to evaluate differences in axillary coverage and residual nipple distortion.
Results: In a breast phantom, residual distortions were 0.16 ± 0.07 cm and 0.22 ± 0.13 cm in reduced- and full-FOV EPI with both methods, respectively. In patients, MI significantly increased after distortion correction of full-FOV (11 ± 5% and 18 ± 9%, RPG and topup) and reduced-FOV (8 ± 4% both) EPI data. Axillary nodes were observed in 99% and 69% of the cases in full- and reduced-FOV EPI images. Residual distortion was observed in 93% and 0% of the cases in full- and reduced-FOV images.
Data Conclusion: Minimal distortion was achieved with RPG applied to reduced-FOV EPI data. RPG improved distortions for full-FOV images but with more modest improvements and limited correction near the nipple.
Evidence Level: 3 TECHNICAL EFFICACY: Stage 1.
(© 2021 International Society for Magnetic Resonance in Medicine.)