Feasibility of single-shot multi-level multi-angle diffusion tensor imaging of the human cervical spinal cord at 7T.

Abstract

PurposeDiffusion tensor imaging (DTI), which is frequently used to characterize microstructure impairments in many spinal cord diseases at clinical fields, may benefit from 7T investigations. Yet, it presents specific technical challenges, such as increased magnetic susceptibility‐induced image distortions.MethodsEight healthy volunteers were scanned at 7T using a prototype diffusion multi‐slice multi‐angle (MSMA) single‐shot spin‐echo echo planar imaging (EPI) sequence developed to explore the whole cervical spinal cord while limiting the partial volume effects related to the cord curvature. To mitigate the increased susceptibility‐induced distortions encountered at 7T, a reverse phase‐encoding strategy was also used. Images acquired from C1‐to‐C7 were registered to the AMU40 template to automatically extract DTI metrics in gray matter/white matter regions of interest. Effects of inhomogeneities on the DTI metrics and repeatability of the measurements were also investigated. Lastly, a DTI acquisition with a 400‐µm in‐plane resolution was acquired on one volunteer to push forward 7T potentialities.ResultsThe MSMA sequence allowed accessing to high‐resolution axial diffusion images sampling the whole cord within a single acquisition. DTI metrics were found in agreement with literature at lower field, stable along a 50–120% relative variation range, with a mean inter‐scan coefficient of variation of 8%. The two‐‐fold spatial‐resolution increase of the additional DTI acquisition enabled main white matter tracts visualization on a single‐subject basis.ConclusionAlthough C7‐level imaging needs some improvement, this preliminary study shows that transverse 7T DTI of the whole cervical spinal cord is feasible, laying the groundwork for improved multi‐parametric MR investigations and microstructure characterization of the spinal cord. Magn Reson Med 80:947–957, 2018. © 2018 International Society for Magnetic Resonance in Medicine.