Grey and White Matter Magnetisation Transfer Ratio Measurements in the Lumbosacral Enlargement: A Pilot In Vivo Study at 3T

Chinyere O Ugorji,David H Miller,Claudia A M Wheeler-Kingshott,Martina D Liechti,Marios C Yiannakas,Jalesh N Panicker,Rebecca S Samson,Norbert Weidner

doi:10.1371/journal.pone.0134495

Abstract

Magnetisation transfer (MT) imaging of the central nervous system has provided further insight into the pathophysiology of neurological disease. However, the use of this method to study the lower spinal cord has been technically challenging, despite the important role of this region, not only for motor control of the lower limbs, but also for the neural control of lower urinary tract, sexual and bowel functions. In this study, the feasibility of obtaining reliable grey matter (GM) and white matter (WM) magnetisation transfer ratio (MTR) measurements within the lumbosacral enlargement (LSE) was investigated in ten healthy volunteers using a clinical 3T MRI system. The mean cross-sectional area of the LSE (LSE-CSA) and the mean GM area (LSE-GM-CSA) were first obtained by means of image segmentation and tissue-specific (i.e. WM and GM) MTR measurements within the LSE were subsequently obtained. The reproducibility of the segmentation method and MTR measurements was assessed from repeated measurements and their % coefficient of variation (%COV). Mean (± SD) LSE-CSA across 10 healthy subjects was 59.3 (± 8.4) mm2 and LSE-GM-CSA was 17.0 (± 3.1) mm2. The mean intra- and inter-rater % COV for measuring the LSE-CSA were 0.8% and 2.3%, respectively and for the LSE-GM-CSA were 3.8% and 5.4%, respectively. Mean (± SD) WM-MTR was 43.2 (± 4.4) and GM-MTR was 40.9 (± 4.3). The mean scan-rescan % COV for measuring WM-MTR was 4.6% and for GM-MTR was 3.8%. Using a paired t-test, a statistically significant difference was identified between WM-MTR and GM-MTR in the LSE (p<0.0001). This pilot study has shown that it is possible to obtain reliable tissue-specific MTR measurements within the LSE using a clinical MR system at 3T. The MTR acquisition and analysis protocol presented in this study can be used in future investigations of intrinsic spinal cord diseases that affect the LSE.

Highlights

Neurological disorders affecting the spinal cord (SC) can involve either the grey matter (GM), white matter (WM) or both
Magnetisation transfer (MT) imaging is a quantitative magnetic resonance imaging method, which can be used in the central nervous system to study the interaction between restricted protons and free protons [6,7,8]
The feasibility of obtaining tissue-specific (i.e. GM and WM) magnetisation transfer ratio (MTR) measurements within the lumbosacral enlargement (LSE) was investigated for the first time using a commercially available 3T MR system, software and hardware and by addressing a number of technical considerations

Summary

Introduction

Neurological disorders affecting the spinal cord (SC) can involve either the grey matter (GM), white matter (WM) or both. Conditions such as multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS) and neuromyelitis optica affect both tissue types [1,2,3], whereas certain leukodystrophies affect the WM tracts only [4, 5]. Ex vivo investigations have previously shown that the magnetisation transfer ratio (MTR) correlates with tissue myelin content and, less strongly, with axonal density in the brain [9] and spinal cord [10]. Significant reductions in MTR values, as compared to healthy controls, have been reported in the upper SC in cases of ALS [17], MS [18,19,20] and spinal cord injury (SCI) [21, 22], with significant correlations identified between the MTR measures and common measures of sensory and motor dysfunction

Methods

Results

Conclusion