Whole Brain Adiabatic T1rho and Relaxation Along a Fictitious Field Imaging in Healthy Volunteers and Patients With Multiple Sclerosis: Initial Findings

Abstract

Background: In preclinical models of multiple sclerosis (MS), both adiabatic T_1rho (T_1ρadiab ) and relaxation along a fictitious field (RAFF) imaging have demonstrated potential to noninvasively characterize MS.

Purpose: To evaluate the feasibility of whole brain T_1ρadiab and RAFF imaging in healthy volunteers and patients with MS.

Study type: Single institutional clinical trial.

Subjects: 38 healthy volunteers (24-69 years) and 21 patients (26-59 years) with MS. Five healthy volunteers underwent a second MR examination performed within 8 days. Clinical disease severity (The Expanded Disability Status Scale [EDSS] and The Multiple Sclerosis Severity Score [MSSS]) was evaluated at baseline and 1-year follow-up (FU).

Field strength/sequence: RAFF in second rotating frame of reference (RAFF2) was performed at 3 T using 3D-fast-field echo with magnetization preparation, RF amplitude of 11.74 μT while the corresponding value for T_1ρadiab was 13.50 μT. T₁ -, T₂ -, and FLAIR-weighted images were acquired with reconstruction voxel size 1.0 × 1.0 × 1.0 mm³ .

Assessment: The parametric maps of T_1ρadiab and RAFF2 (T_RAFF2 ) were calculated using a monoexponential model. Semi-automatic segmentation of MS lesions, white matter (WM), and gray matter (GM), and WM tracks was performed using T₁ -, T₂ -, and FLAIR-weighted images.

Statistical tests: Regression analysis was used to evaluate correlation of T_1ρadiab and T_RAFF2 with age and disease severity while a Friedman test followed by Wilcoxon Signed Rank test for differences between tissue types. Short-term repeatability was evaluated on voxel level.

Results: Both T_1ρadiab and T_RAFF2 demonstrated good short-term repeatability with relative differences on voxel level in the range of 6.1%-11.9%. Differences in T_1ρadiab and T_RAFF2 between the tissue types in MS patients were significant (P < 0.05). T_1ρadiab and T_RAFF2 correlated (P < 0.001) with baseline EDSS/MSSM and disease progression at FU (P < 0.001).

Data conclusion: Whole brain T_1ρadiab and T_RAFF2 at 3 T was feasible with significant differences in T_1ρadiab and T_RAFF2 values between tissues types and correlation with disease severity.

Evidence level: 1 TECHNICAL EFFICACY: Stage 1.

Keywords: healthy volunteers; multiple sclerosis; relaxation along a fictitious field; spin-lock imaging.