Reduced Field-of-View Diffusion-Weighted Imaging of the Lumbosacral Enlargement: A Pilot In Vivo Study of the Healthy Spinal Cord at 3T.

Marios C Yiannakas,Ferran Prados,Daniel R Altmann,Claudia A M Gandini Wheeler-Kingshott,David H Miller,Rebecca S Samson,Sebastien Ourselin,Francesco Grussu,Polymnia Louka,Marco Battiston,Gernot Reishofer

doi:10.1371/journal.pone.0164890

Abstract

Diffusion tensor imaging (DTI) has recently started to be adopted into clinical investigations of spinal cord (SC) diseases. However, DTI applications to the lower SC are limited due to a number of technical challenges, related mainly to the even smaller size of the SC structure at this level, its position relative to the receiver coil elements and the effects of motion during data acquisition. Developing methods to overcome these problems would offer new means to gain further insights into microstructural changes of neurological conditions involving the lower SC, and in turn could help explain symptoms such as bladder and sexual dysfunction. In this work, the feasibility of obtaining grey and white matter (GM/WM) DTI indices such as axial/radial/mean diffusivity (AD/RD/MD) and fractional anisotropy (FA) within the lumbosacral enlargement (LSE) was investigated using a reduced field-of-view (rFOV) single-shot echo-planar imaging (ss-EPI) acquisition in 14 healthy participants using a clinical 3T MR system. The scan-rescan reproducibility of the measurements was assessed by calculating the percentage coefficient of variation (%COV). Mean FA was higher in WM compared to GM (0.58 and 0.4 in WM and GM respectively), AD and MD were higher in WM compared to GM (1.66 μm2ms-1 and 0.94 μm2ms-1 in WM and 1.2 μm2ms-1 and 0.82 μm2ms-1 in GM for AD and MD respectively) and RD was lower in WM compared to GM (0.58 μm2ms-1 and 0.63 μm2ms-1 respectively). The scan-rescan %COV was lower than 10% in all cases with the highest values observed for FA and the lowest for MD. This pilot study demonstrates that it is possible to obtain reliable tissue-specific estimation of DTI indices within the LSE using a rFOV ss-EPI acquisition. The DTI acquisition and analysis protocol presented here is clinically feasible and may be used in future investigations of neurological conditions implicating the lower SC.

Highlights

Diffusion-weighted imaging (DWI) can be used to study the diffusion of water molecules in neural tissue [1]
Mean fractional anisotropy (FA) was higher in white matter (WM) compared to grey matter (GM) (0.58 and 0.4 in WM and GM respectively), AD and mean amount of diffusion (MD) were higher in WM compared to GM (1.66 μm2ms-1 and 0.94 μm2ms-1 in WM and 1.2 μm2ms-1 and 0.82 μm2ms-1 in GM for AD and MD respectively) and RD was lower in WM compared to GM (0.58 μm2ms-1 and 0.63 μm2ms-1 respectively)
The scan-rescan %COV was lower than 10% in all cases with the highest values observed for FA and the lowest for MD

Summary

Introduction

Diffusion-weighted imaging (DWI) can be used to study the diffusion of water molecules in neural tissue [1]. Reliable DTI acquisition and analysis protocols to study the lower SC could provide new insights into the pathophysiology of symptoms such as bladder and sexual dysfunction, which are often associated with neurological conditions such as MS [28, 29], SC injury (SCI) [30, 31] and multiple system atrophy (MSA) [32, 33] In this pilot study, the feasibility of obtaining tissue-specific (i.e. GM and WM) DTI indices within the lower SC was investigated in a number of healthy volunteers using DTI with rFOV [15, 26] on a clinical 3T MRI system. The DTI acquisition and analysis protocol presented here addresses key methodological considerations such as: i) the positional variation of the lower SC through the use of the lumbosacral enlargement (LSE) as previously suggested [34]; ii) the scan-rescan reproducibility of the DTI indices; iii) the influence of the diffusion encoding protocol on the quality and reproducibility of the DTI indices

Study Participants

Results

Discussion