Multi-Parametric Phase-Cycled Balanced Steady-State Free Precession Brain Tissue Characterization in...

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).

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.

Prospective and retrospective, observational.

Twenty RRMS patients (34.5 ± 5.9 years, female 15/20) and 10 HC subjects (33.4 ± 6.9 years, female 5/10).

3 T; T₁-weighted magnetization-prepared rapid gradient-echo, T₂-weighted fluid-attenuated inversion recovery, pc-bSSFP, B₁ ⁺ mapping, single-shot spin-echo echo-planar-imaging diffusion tensor imaging (DTI).

R₁, R₂, 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.

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.

Significant group, ROI, and group-by-ROI effects were found for R₁ (β = -0.16) and R₂ (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 [R₁, R₂, AI]). Fourteen of 16 ROIs showed significantly lower R₁ and R₂ (d = -4.25 to -0.85) in RRMS than HC. All ROIs remained non-significant for AI. R₂ (p_corr ≥ 0.055) and AI (p_corr ≥ 0.108) anisotropy comparison between RRMS and HC groups did not reach significance.

Phase-cycled bSSFP relaxometry showed WM-predominant differences in RRMS, with additional whole-brain assessment including gray matter.

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Stage 1.