Spinal cord atrophy is a common feature of multiple sclerosis (MS), can be detected in vivo using MRI, and is one of the main substrates of disease progression. In our previous studies, we have adapted the boundary shift integral (BSI) technique developed for the brain, to be applied to the spinal cord, obtaining the first registration-based method for longitudinal assessment of spinal cord atrophy.
We aim to 1) compare spinal cord atrophy measurements using segmentation- and registration-based methods, with possible implications for clinical trial design (e.g., measurement variability, image noise floor); 2) compare spinal cord atrophy measurements obtained from routine brain (C1-2) and dedicated spinal cord MRI (C1-2 and C2-5), using segmentation- and registration-based methods; 3) explore possible clinical correlates, also in relation to conventional brain MRI measures; and 4) explore possible treatment effect.
We included 220 primary-progressive multiple sclerosis patients from a phase 2 clinical trial, with baseline and week-48 3DT1-weighted MRI of the brain and spinal cord (1x1x1mm3), acquired separately. We obtained segmentation-based cross-sectional spinal cord area (CSA) at C1-2 (from both brain and spinal cord MRI) and C2-5 levels (from spinal cord MRI) using DeepSeg, and, then, we computed corresponding GBSI.
Depending on the spinal cord segment, we included 67.4-98.1% patients for CSA measurements, and 66.9-84.2% for GBSI. Spinal cord atrophy measurements obtained with GBSI had lower measurement variability, than corresponding CSA. Looking at image noise floor, the lowest median standard deviation of the MRI signal within the cerebrospinal fluid surrounding the spinal cord was found on brain MRI at C1-2 level. Spinal cord atrophy derived from brain MRI was related to corresponding measures from dedicated spinal cord MRI, more strongly for GBSI than CSA. Spinal cord atrophy measurements using GBSI, but not CSA, were associated with upper and lower limb motor progression. No treatment effect was detected for any spinal cord atrophy measurements.
Notwithstanding reduced measurement variability, clinical correlates, and possibility of using brain acquisitions, spinal cord atrophy using GBSI should remain a secondary outcome measure in MS studies, until further advancements increase the quality of acquisition and reliability of processing.