Three-dimensional whole-brain simultaneous T1, T2, and T1ρ quantification using MR Multitasking: Method and initial clinical experience in tissue characterization of multiple sclerosis

Purpose To develop a 3D whole-brain simultaneous T1/T2/T1 rho quantification method with MR Multitasking that provides high quality, co-registered multiparametric maps in 9 min. Methods MR Multitasking conceptualizes T1/T2/T1 rho relaxations as different time dimensions, simultaneously resolving all three dimensions with a low-rank tensor image model. The proposed method was validated on a phantom and in healthy volunteers, comparing quantitative measurements against corresponding reference methods and evaluating the scan-rescan repeatability. Initial clinical validation was performed in age-matched relapsing-remitting multiple sclerosis (RRMS) patients to examine the feasibility of quantitative tissue characterization and to compare with the healthy control cohort. The feasibility of synthesizing six contrast-weighted images was also examined. Results Our framework produced high quality, co-registered T1/T2/T1 rho maps that closely resemble the reference maps. Multitasking T1/T2/T1 rho measurements showed substantial agreement with reference measurements on the phantom and in healthy controls. Bland-Altman analysis indicated good in vivo repeatability of all three parameters. In RRMS patients, lesions were conspicuously delineated on all three maps and on four synthetic weighted images (T2-weighted, T2-FLAIR, double inversion recovery, and a novel "T1 rho-FLAIR" contrast). T1 and T2 showed significant differences for normal appearing white matter between patients and controls, while T1 rho showed significant differences for normal appearing white matter, cortical gray matter, and deep gray matter. The combination of three parameters significantly improved the differentiation between RRMS patients and healthy controls, compared to using any single parameter alone. Conclusion MR Multitasking simultaneously quantifies whole-brain T1/T2/T1 rho and is clinically promising for quantitative tissue characterization of neurological diseases, such as MS.