Fully automated segmentation of the cervical cord from T1-weighted MRI using PropSeg: Application to multiple sclerosis

Abstract

Spinal cord (SC) atrophy, i.e. a reduction in the SC cross-sectional area (CSA) over time, can be measured by means of image segmentation using magnetic resonance imaging (MRI). However, segmentation methods have been limited by factors relating to reproducibility or sensitivity to change. The purpose of this study was to evaluate a fully automated SC segmentation method (PropSeg), and compare this to a semi-automated active surface (AS) method, in healthy controls (HC) and people with multiple sclerosis (MS). MRI data from 120 people were retrospectively analysed; 26 HC, 21 with clinically isolated syndrome, 26 relapsing remitting MS, 26 primary and 21 secondary progressive MS. MRI data from 40 people returning after one year were also analysed. CSA measurements were obtained within the cervical SC. Reproducibility of the measurements was assessed using the intraclass correlation coefficient (ICC). A comparison between mean CSA changes obtained with the two methods over time was performed using multivariate structural equation regression models. Associations between CSA measures and clinical scores were investigated using linear regression models. Compared to the AS method, the reproducibility of CSA measurements obtained with PropSeg was high, both in patients and in HC, with ICC > 0.98 in all cases. There was no significant difference between PropSeg and AS in terms of detecting change over time. Furthermore, PropSeg provided measures that correlated with physical disability, similar to the AS method. PropSeg is a time-efficient and reliable segmentation method, which requires no manual intervention, and may facilitate large multi-centre neuroprotective trials in progressive MS.

Keywords: Cord cross-sectional area; Grey matter; Image segmentation; Magnetic resonance imaging; White matter.

Fig. 1

(A–C) Segmentation of the cervical cord using the active surface (AS) method; seed points are manually positioned in the centre of the cord to cover the C2/C5 level; also shown is an example of a single axial reformatted slice through the C2/C3 intervertebral disc showing the cord contour identified using the AS method (contour shown in red). (D–F) Segmentation of the cervical cord using the PropSeg method with the sagittal volume (contour shown in cyan); also shown is the same axial reformatted slice through the C2/C3 intervertebral disc showing the cord contour identified using both the PropSeg (contour shown in cyan) and AS methods (contour shown in red) for comparison. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

A) The cervical cord in the sagittal plane showing a multiple sclerosis (MS) lesion (hypointense) at the C2 level in a case of secondary progressive MS (SPMS), B) axial slice through the level of the lesion at the C2 level, C) the cord contour identified using the AS method (contour shown in red) and D) the same axial slice through the MS lesion at C2 showing the cord contour identified using both the PropSeg (contour shown in cyan) and AS methods (contour shown in red) for comparison. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)