Dependency on Tissue Anisotropy and White Matter Fiber Orientation of Phase-Cycled bSSFP Relaxometry at 3 Tesla

Motivation: Magnetic resonance relaxation anisotropy in tissue has been reported previously for both T1 and T2, with implications to assess the integrity of tissue microstructure. Goal(s): To evaluate the dependency on brain tissue anisotropy and white matter fiber orientation of relaxometry metrics (T1, T2) and asymmetry index (AI), derived from phase-cycled bSSFP (pc-bSSFP), in a large cohort of healthy subjects. Approach: 80 healthy subjects were scanned at 3T using pc-bSSFP and diffusion tensor imaging. T1 and T2 were quantified using MIRACLE - an SSFP configuration-based approach. Results: All metrics (T1, T2, AI) showed a distinct sensitivity to white matter fiber orientation and fractional anisotropy. Impact: Relaxation parameters and frequency profile asymmetries derived from pc-bSSFP demonstrated a distinct sensitivity to brain tissue microstructure, with a dependency on white matter fiber orientation and fractional anisotropy.