Improvements in Between-Vendor MRI Harmonization of Renal T₂ Mapping using Stimulated Echo Compensation

Background: T-2 mapping is valuable to evaluate pathophysiology in kidney disease. However, variations in T-2 relaxation time measurements across MR scanners and vendors may occur requiring additional correction. Purpose: To harmonize renal T-2 measurements between MR vendor platforms, and use an extended-phase-graph-based fitting method ("StimFit") to correct stimulated echoes and reduce between-vendor variations. Study Type: Prospective. Subjects: 8 healthy "travelling" volunteers (37.5% female, 32 +/- 6 years) imaged on four MRI systems across three vendors at four sites, 10 healthy volunteers (50% female, 32 +/- 8 years) scanned multiple times on a given MR scanner for repeatability evaluation. ISMRM/NIST system phantom scanned for evaluation of T2 accuracy. Field Strength/Sequence: 3T, multiecho spin-echo sequence. Assessment: T-2 images fit using conventional monoexponential fitting and "StimFit." Mean absolute percentage error (MAPE) of phantom measurements with reference T-2 values. Average cortex and medulla T-2 values compared between MR vendors, with masks obtained from T-2-weighted images and T-1 maps. Full-width-at-half-maximum (FWHM) T-2 distributions to evaluate local homogeneity of measurements. Statistical Tests: Coefficient of variation (CV), linear mixed-effects model, analysis of variance, student's t -tests, Bland-Altman plots, P-value <0.05 considered statistically significant. Results: In the ISMRM/NIST phantom, "StimFit" reduced the MAPE from 4.9%, 9.1%, 24.4%, and 18.1% for the four sites (three vendors) to 3.3%, 3.0%, 6.6%, and 4.1%, respectively. In vivo, there was a significant difference in kidney T-2 measurements between vendors using a monoexponential fit, but not with "StimFit" (P = 0.86 and 0.92, cortex and medulla, respectively). The intervendor CVs of T-2 measures were reduced from 8.0% to 2.6% (cortex) and 7.1% to 2.8% (medulla) with StimFit, resulting in no significant differences for the CVs of intravendor repeat acquisitions (P = 0.13 and 0.05). "StimFit" significantly reduced the FWHM of T-2 distributions in the cortex and whole kidney. Data Conclusion: Stimulated-echo correction reduces renal T-2 variation across MR vendor platforms.