Controlled saturation magnetization transfer for reproducible multivendor variable flip angle T and T mapping.

Purpose: The widespread clinical application of quantitative MRI has been hindered by a lack of reproducibility across sites and vendors. Previous work has attributed this to incorrect B mapping or insufficient spoiling conditions. We recently proposed the controlled saturation magnetization transfer (CSMT) framework and hypothesized that the lack of reproducibility can also be attributed to magnetization transfer effects. This work seeks to validate this hypothesis and demonstrate that reproducible multivendor single-pool relaxometry can be achieved with the CSMT approach.

Methods: Three healthy volunteers were scanned on scanners from 3 vendors (GE Healthcare, Philips, Siemens). An extensive set of images necessary for joint T and T estimation were acquired with (1) each vendor default RF pulses and spoiling conditions; (2) harmonized RF spoiling; and (3) harmonized RF spoiling and CSMT pulses. Different subsets of images were used to generate 6 different T and T maps for each subject's data from each vendor. Cross-protocol, cross-vendor, and test/retest variability were estimated.

Results: Harmonized RF spoiling conditions are insufficient to ensure good cross-vendor reproducibility. Controlled saturation magnetization transfer allows cross-protocol variability to be reduced from 18.3% to 4.0%. Whole-brain variability using the same protocol was reduced from a maximum of 19% to 4.5% across sites. Both CSMT and native vendor RF conditions have a reported variability of less than 5% for repeat measures on the same vendor.

Conclusion: Magnetization transfer effects are a major contributor to intersite/intrasite variability of T and T estimation. Controlled saturation magnetization transfer stabilizes these effects, paving the way for the use of single-pool T and T as a reliable source for clinical diagnosis across sites.