Neurite orientation dispersion and density imaging of the healthy cervical spinal cord in vivo

Hui Zhang,Torben Schneider,Francesco Grussu,Claudia A.M Wheeler–Kingshott,Daniel C Alexander

doi:10.1016/j.neuroimage.2015.01.045

Abstract

Here we present the application of neurite orientation dispersion and density imaging (NODDI) to the healthy spinal cord in vivo. NODDI provides maps such as the intra-neurite tissue volume fraction (vin), the orientation dispersion index (ODI) and the isotropic volume fraction (viso), and here we investigate their potential for spinal cord imaging. We scanned five healthy volunteers, four of whom twice, on a 3T MRI system with a ZOOM-EPI sequence. In accordance to the published NODDI protocol, multiple b-shells were acquired at cervical level and both NODDI and diffusion tensor imaging (DTI) metrics were obtained and analysed to: i) characterise differences in grey and white matter (GM/WM); ii) assess the scan–rescan reproducibility of NODDI; iii) investigate the relationship between NODDI and DTI; and iv) compare the quality of fit of NODDI and DTI. Our results demonstrated that: i) anatomical features can be identified in NODDI maps, such as clear contrast between GM and WM in ODI; ii) the variabilities of vin and ODI are comparable to that of DTI and are driven by biological differences between subjects for ODI, have similar contribution from measurement errors and biological variation for vin, whereas viso shows higher variability, driven by measurement errors; iii) NODDI identifies potential sources contributing to DTI indices, as in the brain; and iv) NODDI outperforms DTI in terms of quality of fit. In conclusion, this work shows that NODDI is a useful model for in vivo diffusion MRI of the spinal cord, providing metrics closely related to tissue microstructure, in line with findings in the brain.

Highlights

Neurite orientation dispersion and density imaging (NODDI) (Zhang et al, 2012) is a model-based diffusion-weighted (DW) MRI technique that allows the quantification of specific microstructural features directly related to neuronal morphology
Results from simulations at a SNR level of 10 are reported in the central plots of Fig. 4. They represent the relationship between diffusion tensor imaging (DTI) indices and metrics vin and orientation dispersion index (ODI) that could be observed if the imaged tissue matched exactly the NODDI model assumptions and the parameters employed to run the simulations, for a SNR level plausible in the spinal cord in vivo
Here we have studied for the first time multi-shell DW MRI data of the healthy cervical cord in vivo with NODDI, and related the results to those provided by routine DTI

Summary

Introduction

Neurite orientation dispersion and density imaging (NODDI) (Zhang et al, 2012) is a model-based diffusion-weighted (DW) MRI technique that allows the quantification of specific microstructural features directly related to neuronal morphology. Unlike model-free techniques, such as diffusion spectrum imaging (DSI) (Wedeen et al, 2005) or diffusion propagator imaging (Descoteaux et al, 2011), which do not make any particular assumption about the local tissue microstructure, NODDI relies on the formulation of a geometric model that aims to capture the salient features of neuronal microarchitecture. This formulation tries to overcome the main limitation of phenomenological models, such as diffusion tensor imaging (DTI) (Basser et al, 1994), which are sensitive to changes in the local microstructure but only provide unspecific, surrogate information. Grussu et al / NeuroImage 111 (2015) 590–601 neurofibromatosis (Billiet et al, 2014), neonatal encephalopathy (Lally et al, 2014) and healthy newborn brain (Kunz et al, 2014)

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