Artifact Correction of Clinical Diffusion Weighted Imaging in Acute Ischemic Stroke.

BACKGROUND: Susceptibility-induced geometric distortions and non-physiologic hyperintensities confound acute ischemic stroke diagnosis on diffusion weighted imaging (DWI). Reverse phase-encoded imaging needed for artifact correction is rarely acquired acutely. Structural imaging-based correction is validated in healthy subjects, but its efficacy in acute stroke remains unclear. PURPOSE: To investigate whether structural imaging-based artifact correction reduces DWI distortions and non-physiologic hyperintensities in clinical acute stroke imaging. STUDY TYPE: Retrospective. POPULATION: 214 patients with acute ischemic stroke and clinical MRI from two centers. FIELD STRENGTH/SEQUENCES: 1.5 T/3 T; single-shot echo planar DWI; 3D MP-RAGE and 2D spin echo, gradient echo, turbo spin echo, and turbo inversion recovery T1-weighted sequences; 2D turbo spin echo and BLADE FLAIR sequences. ASSESSMENT: DWI distortions were corrected using the Synb0-DisCo and TOPUP algorithms with b0 and T1-weighted images. Mutual information evaluated geometric agreement against FLAIR and T1-weighted images before and after correction. The diagnostic value of hyperintense DWI lesions for apparent diffusion coefficient (ADC)-defined reference infarct was assessed. STATISTICAL TESTS: Wilcoxon sign rank or rank sum tests of mutual information, sensitivity, specificity, and positive and negative predictive value; Bland-Altman plots; and linear regression with coefficients of determination (R2) in linear and log space. Bonferroni-adjusted p < 0.05 was significant. RESULTS: After correction, DWI demonstrated significantly increased mutual information against FLAIR images [0.31 (IQR, 0.25-0.38) versus 0.30 (0.24-0.35)] and T1-weighted images [0.32 (IQR, 0.29-0.36) versus 0.29 (0.24-0.33)]. ADC-defined infarct volumes before and after correction correlated strongly (R2 0.998, log 0.541) with a negative bias of 0.51 (95% CI, 0.18-0.85) mL. DWI hyperintensities before and after correction correlated strongly (R2 0.996, log 0.360) but demonstrated a negative bias of 2.47 (95% CI, 1.95-3.00) mL. After correction, DWI hyperintensities demonstrated significantly improved specificity [0.998 (IQR, 0.994-1.000) versus 0.997 (0.992-0.999)] and positive predictive value [0.53 (IQR, 0.31-0.77) versus 0.39 (0.16-0.63)] for ADC-defined infarct. DATA CONCLUSION: Structural imaging-based distortion correction of routinely acquired clinical DWI in acute ischemic stroke improves anatomic geometry and reduces false positive hyperintensities. EVIDENCE LEVEL: 3. STAGE OF TECHNICAL EFFICACY: 3.