Geometric distortion correction in prostate diffusion‐weighted MRI and its effect on quantitative apparent diffusion coefficient analysis

Purpose To evaluate the effect of correction for B0 inhomogeneity‐induced geometric distortion in echo‐planar diffusion‐weighted imaging on quantitative apparent diffusion coefficient (ADC) analysis in multiparametric prostate MRI. Methods Geometric distortion correction was performed in echo‐planar diffusion‐weighted images (b = 0, 50, 400, 800 s/mm2) of 28 patients, using two b0 scans with opposing phase‐encoding polarities. Histology‐matched tumor and healthy tissue volumes of interest delineated on T2‐weighted images were mapped to the nondistortion‐corrected and distortion‐corrected data sets by resampling with and without spatial coregistration. The ADC values were calculated on the volume and voxel level. The effect of distortion correction on ADC quantification and tissue classification was evaluated using linear‐mixed models and logistic regression, respectively. Results Without coregistration, the absolute differences in tumor ADC (range: 0.0002–0.189 mm2/s×10−3 (volume level); 0.014–0.493 mm2/s×10−3 (voxel level)) between the nondistortion‐corrected and distortion‐corrected were significantly associated (P < 0.05) with distortion distance (mean: 1.4 ± 1.3 mm; range: 0.3–5.3 mm). No significant associations were found upon coregistration; however, in patients with high rectal gas residue, distortion correction resulted in improved spatial representation and significantly better classification of healthy versus tumor voxels (P < 0.05). Conclusions Geometric distortion correction in DWI could improve quantitative ADC analysis in multiparametric prostate MRI. Magn Reson Med 79:2524–2532, 2018.