Segmentation of CSF and nerve roots in separate VOIs at each vertebral level. CSF and nerve root VOIs corresponding to the different vertebral levels may be delimited as shown in axial (a), sagittal (b), coronal (c), and 3D model views (d), from 10th thoracic vertebra (upper) to first sacral vertebra (lower). The volume of these segmented VOIs then is calculated by multiplying the number of voxels of the analyzed tissue by the voxel size of the images

Three-dimensional CSF and cauda equina roots per vertebral level and color-coded vulnerability. Dorsal (a–c) and lateral (d–f) views, including (a, d) or not including illustrative MR axial planes with or without (c, f) CSF. Rostral thoracolumbar vertebral levels (T10–L1) may include the conus medullaris (red–dark orange), and a higher proportion of the spinal canal is occupied by cauda equina nerve roots in L2–L4 (orange–yellow) than in L5 sacral levels (green–white)

Intervertebral zones. Once the CSF and nerve root VOIs within the dural sac are obtained, volumes and ratios between these two tissues may be calculated exclusively in the intervertebral zones, where punctures may be performed in patients. Here, small blocks of 11 axial slices (7.15 mm high) were analyzed

Axial MR planes at the middle zone of the different intervertebral levels in different illustrative cases. There is high variability among cases (Table 37.1)