Correction of Artifacts Induced by B₀ Inhomogeneities in Breast MRI Using Reduced‐Field‐of‐View Echo‐Planar Imaging and Enhanced Reversed Polarity Gradient Method

Abstract

Background Diffusion‐weighted (DW) echo‐planar imaging (EPI) is prone to geometric distortions due to B0 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

Correcting B0 inhomogeneity-induced distortions in whole-body diffusion MRI of bone

“…We demonstrated consistent reductions in mean error across subjects, as well as the increases in MI between DWI b = 0 and T 2 images after correcting for distortion. This is in line with prior work that demonstrated improved similarity of DWI with T 2 anatomic imaging after RPG 17 , 18 . Inspection of data revealed some instances of increases in measured error after the application of RPG.…”

“…Prior studies have demonstrated that B 0 inhomogeneities affect organ or lesion localization in the prostate and breast 16 , 17 , 18 . The extent of B 0 inhomogeneities and their consequent artifacts depend, in part, on the anatomic environment of a region of interest or lesion (e.g., how close the lesion is to an air-tissue interface).…”

“…Both FSL’s topup and the reverse polarity gradient (RPG) technique are specific implementations of this approach 11 , 12 , 15 . The latter, RPG 12 , has been applied to DWI of prostate 16 , breast tissue 17 , 18 , and brain 12 , 19 , and has been shown to improve anatomic localization.…”

Correcting B0 inhomogeneity-induced distortions in whole-body diffusion MRI of bone

“…We demonstrated consistent reductions in mean error across subjects, as well as the increases in MI between DWI b=0 and T2 images after correcting for distortion. This is in line with prior work that demonstrated improved similarity of DWI with T2 anatomic imaging after RPG [8,10].…”

“…Prior studies have demonstrated that B0 inhomogeneities affect organ or lesion localization in the prostate and breast [7,8,10]. The extent of B0 inhomogeneities and their consequent artifacts depend, in part, on the anatomic environment of a region of interest or lesion (e.g., how close the lesion is to an air-tissue interface).…”