Regional T-1 mapping of the whole cervical spinal cord using an optimized MP2RAGE sequence

While T1 measurements present multiple challenges (robustness, acquisition time), the recently proposed MP2RAGE sequence (magnetization-prepared two rapid acquisition gradient echoes) has opened new perspectives to characterize tissue microstructure changes occurring in a pathological or developmental context. Extensively used for brain studies, it was herein adapted to investigate the cervical spinal cord (SC) at 3 T. By integrating Bloch equations, the MP2RAGE sequence parameters were chosen to optimize SC gray matter/white matter (GM/WM) T1 contrast with sub-millimetric resolution, a scan time less than 10 min and a reliable T1 determination with minimal B1 + variation effect, within a range of values compatible with different pathologies and surrounding structures. The residual B1 + effect on T1 values was corrected using a look-up-table approach and B1 + mapping. The accuracy of B1 +-corrected T1 measurements was assessed on a phantom with respect to conventional inversion recovery. In vivo MP2RAGE acquisitions were performed on five young (28.8 +/- 4.3 years old) and five elderly (60.2 +/- 2.9 years old) volunteers and analyzed using a template-based approach. Phantom experiments led to high agreements between inversion-recovery spin-echo and MP2RAGE-based T1 values (R2 = 0.997). In vivo T1 values for cervical WM, anterior GM (aGM), posterior sensory tracts (PSTs) and lateral motor tracts (LMTs) were 917 +/- 29 s, 934 +/- 33 ms, 920 +/- 37 ms and 877 +/- 35 ms, respectively, with all subjects and cervical levels considered. Significant differences were observed between aGM and LMTs, and between LMTs and PSTs, in agreement with the literature. Repeated T1 measurements demonstrated high reproducibility of the MP2RAGE in the SC (variation coefficient < 5% in all regions of interest). Finally, preliminary assessment of age-related SC tissue microstructure variation additionally showed evidence of SC atrophy and slight trends of T1 decrease with age in all regions. Overall, this study shows that fast, robust and accurate sub-millimetric resolution T1 mapping in the cervical SC using the MP2RAGE sequence is possible, paving the way for future multi-centric and longitudinal clinical studies investigating the pathological cord.