Multi‐Parametric Phase‐Cycled Balanced Steady‐State Free Precession Brain Tissue Characterization in Relapsing‐Remitting Multiple Sclerosis

Background Time‐efficient phase‐cycled balanced steady‐state free precession (pc‐bSSFP) imaging is a novel microstructure‐ and myelin‐sensitive approach for multi‐parametric brain tissue characterization not yet evaluated in demyelinating diseases such as multiple sclerosis (MS). Purpose To evaluate quantitative relaxometry metrics in white matter (WM) and gray matter (GM) of relapsing‐remitting multiple sclerosis (RRMS) and healthy control (HC) cohorts using a multi‐parametric pc‐bSSFP framework. Study Type Prospective and retrospective, observational. Population Twenty RRMS patients (34.5 ± 5.9 years, female 15/20) and 10 HC subjects (33.4 ± 6.9 years, female 5/10). Field Strength/Sequence 3 T; T 1 ‐weighted magnetization‐prepared rapid gradient‐echo, T 2 ‐weighted fluid‐attenuated inversion recovery, pc‐bSSFP, B 1 + mapping, single‐shot spin‐echo echo‐planar‐imaging diffusion tensor imaging (DTI). Assessment R 1 , R 2 , and the bSSFP asymmetry index (AI) were compared between RRMS and HC across selected WM and GM regions of interest (ROIs). DTI‐derived fiber‐to‐field angle, number of fiber orientations, and fractional anisotropy were used for parameter anisotropy analysis. Statistical Tests Linear mixed‐effects models tested group, ROI, and group‐by‐ROI effects for each metric. Anisotropy differences between cohorts were assessed with two‐sided t ‐tests. ROI and anisotropy tests employed false discovery rate correction with significance set at p corr < 0.05. Results Significant group, ROI, and group‐by‐ROI effects were found for R 1 ( β = −0.16) and R 2 ( β = −2.84). The ROI effect was significant for AI while the group ( p = 0.450) and group‐by‐ROI ( p = 0.747) effects were non‐significant. Age and sex covariates did not reach significance (Age: p = [0.563, 0.705, 0.591], Gender: p = [0.839, 0.822, 0.179], for [ R 1 , R 2 , AI]). Fourteen of 16 ROIs showed significantly lower R 1 and R 2 ( d = −4.25 to −0.85) in RRMS than HC. All ROIs remained non‐significant for AI. R 2 ( p corr ≥ 0.055) and AI ( p corr ≥ 0.108) anisotropy comparison between RRMS and HC groups did not reach significance. Data Conclusion Phase‐cycled bSSFP relaxometry showed WM‐predominant differences in RRMS, with additional whole‐brain assessment including gray matter. Evidence Level 2. Technical Efficacy Stage 1.