Correction of Artifacts Induced by B₀ Inhomogeneities in Breast MRI using Reduced Field-of-View Echo-Planar Imaging and Enhanced Reverse Polarity Gradient Method

Abstract

Purpose: Diffusion weighted (DW) echo-planar imaging (EPI) is prone to geometric and intensity distortions due to B0 inhomogeneities. Pulse sequences that excite spins within a reduced field-of-view (FOV) in the phase encoding (PE) direction have been developed to decrease such distortions. In addition, use of the reverse polarity gradient (RPG) method, a retrospective approach to correct distortion artifacts, has been shown to improve the localization of tumor lesions. The purpose of this work was to evaluate the performance of reduced-FOV acquisition and RPG in decreasing distortion artifacts for breast imaging. Methods: EPI data were acquired with full and reduced-FOV in a breast phantom and in a group of 170 women at 3T. The performance of RPG in correcting distortion artifacts in EPI data was evaluated using the mutual information (MI) metric between EPI and anatomical low-distortion images before and after distortion correction. Results: RPG corrected distortions by 61% in full-FOV EPI and 48% in reduced-FOV EPI in a breast phantom. In patients, MI increased on average 13+/-8% and 8+/-6% for both full and reduced-FOV EPI data after distortion correction, respectively. The 95th percentile and maximum displacement between uncorrected and corrected full-FOV EPI datasets were 0.8+/-0.3cm and 1.9+/-0.3cm, and for reduced-FOV were 0.4+/-0.2cm and 1.3+/-0.3cm. Conclusion: Minimal distortion was achieved with RPG applied to reduced-FOV EPI data. RPG improved distortions for full-FOV, but with more modest improvements and limited correction near the nipple.

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

“…A salient question, however, is whether this correction actually produces images that more accurately reflect anatomy. The consistent increases in MI between DWI b=0 and T2 images after DisCo is in line with prior work that performed MI-based analyses in other organs (17, 20). We further showed that applying RPG can lead to reduction in error between anatomic landmarks annotated on diffusion and structural images (Figure 5).…”

“…Prior studies have demonstrated that B0 inhomogeneities affect organ or lesion localization in the prostate and breast (16, 17, 20). The extent of B0 inhomogeneities and their consequent artifacts depend, in part, on the anatomic environment of a lesion (e.g.…”

Diffusion Breast MRI: Current Standard and Emerging Techniques

“…Reduced field of view (rFOV) improves spatial resolution and decreases artifacts by limiting the field of view and number of k-space lines in the phase-encoding direction ( 99 , 100 ). Improved image quality with rFOV compared to standard DWI techniques has been shown to enhance lesion conspicuity and morphologic assessment in the breast ( 101 – 104 ).…”

“…T 2 -weighted, conventional DWI (b=0 s/mm 2 ), full FOV EPI (b=0 s/mm 2 ), and reduced FOV EPI (50% phase field of view) (b=0 s/mm 2 acquired at 3T) images are shown. Reduction of percent phase encoding direction to 50% reduces geometric distortions caused by B 0 -inhomogeneity, especially in the nipple region ( 100 ).…”

Tri-Compartmental Restriction Spectrum Imaging Breast Model Distinguishes Malignant Lesions from Benign Lesions and Healthy Tissue on Diffusion-Weighted Imaging

“…In addition to T 1 -and T 2 -weighted images, axial reduced field-of-view (FOV) echo-planar imaging DW-MRI was performed with the following parameters: spectral attenuated inversion recovery (SPAIR) fat suppression, echo time (TE) = 82 ms, repetition time (TR) = 9000 ms, b-values (number of diffusion directions) = 0, 500 (6), 1500 (6), and 4000 (15) s/mm 2 , gradient pulse duration (δ) = 29.34 ms, gradient pulse time interval (∆) = 37.67 ms, FOV = 160 × 320 mm 2 , acquisition matrix = 48 × 96, reconstruction matrix = 128 × 128, voxel size = 2.5 × 2.5 × 5.0 mm 3 , phase-encoding (PE) direction anterior-posterior (A/P), and no parallel imaging. The b = 0 s/mm 2 volumes were collected in the A/P and posterior-anterior (P/A) PE directions to correct DW-MRI data for geometric and intensity distortions due to B 0 inhomogeneities using the reverse polarity gradient (RPG) method [26,27]. For the diffusion sequence, δ and ∆ time constants were fixed, while the gradient magnitude was manipulated to produce different b-values.…”