Characterization of DTI Indices in the Cervical, Thoracic, and Lumbar Spinal Cord in Healthy Humans
Figure 1
(a) Sagittal view of the spinal cord indicating the cervical, thoracic, and lumbar regions acquired in the diffusion-weighted data. (b) An example of a map and the same map with an ROI manually drawn on the image to indicate the boundaries of the spinal cord. (c) An example of a 3D-surface representation of the density of voxels along the FA versus MD distribution from the cervical cord of one subject. The height of the surface () reflects the number of voxels with overlapping MD () and FA () values on the plot. From this example, it is apparent that voxels cluster in three distinct groups, the highest density of voxels with high FA and low MD values, the middle cluster with low FA and low MD values, and a small third cluster with low FA and high MD values. (d) An example of the FA versus MD voxel distribution in the cord from one subject in the cervical region of the spinal cord. All voxels were plotted (red) and a k-means clustering method partitioned the data into three distinct clusters. The center of the cluster (or “centroid”) is shown in blue and is the mean FA and MD of each cluster. Clusters were further restricted to include only voxels which fell within a threshold distance from the centroid (green), thereby, excluding the voxels with the greatest amount of partial volume effects. Clusters with high FA values and low MD values are assigned to white matter (WM), clusters with low FA values and low MD values are assigned to grey matter (GM), and clusters with low FA values and very high MD values are assigned to cerebral spinal fluid (CSF) and noise. (e) Two examples of the spatial location of the centroid mapping back. The green voxels indicate where the grey matter cluster mapped back to, while the red indicates white matter voxels and the blue is CSF. Grey matter voxels (green) were located in the center regions of the cord and extended outwards towards the dorsal and ventral horns while white matter clusters (red) were located to areas outside of the grey matter regions. CSF clusters (blue) consistently mapped to the outer boundaries of the cord.
