Introduction: Currently there is no noninvasive method to determine spinal cord integrity after a SCI and thus a patient’s potential for recovery. This is despite 253,000 people in the United States living with a SCI. DTI measurement of spinal cord injury is significantly confounded by inflammation and tissue loss manifested in diffusion MRI signal modeling as a spectrum of isotropic diffusion tensor components1. To overcome these factors we have developed a novel data-driven model-selection diffusion basis spectrum imaging (DBSI)2 to more accurately delineate anisotropic signal sources. We hypothesized that DBSI acting as an axonal injury biomarker more accurately correlated with neurological disabilities in humans following an acute SCI and/or a chronic SCI than the current standard DTI biomarker

Methods: A prospective non-randomized cohort of 27 spinal cord injury patients underwent imaging over a 2 year period. DBSI derived fractional anisotropy (FA ), axial diffusivity (AD), radial diffusivity (RD), edema fraction and axonal density were correlated with clinically utilized grading scales including American Spinal Injury Association (ASIA) Score.

Results: Patients showed a decline in cross-sectional spinal cord area compared with a stable cord area in controls. Higher International Standards for Neurological Classification of SCI (ISNCSCI) scores at 12 months post-injury were associated with a reduced loss in cross-sectional spinal cord area and higher corticospinal FA encompassing the corticospinal tract at the cerebral peduncle. Compared with recovered ASIA-E patients, severely injured ASIA-A patients showed increased DTI radial (A: 0.32 E: 0.20, p<0.05) and axial diffusivity (A: 1.1 E: 0.91 , p<0.05), increased DBSI water fraction (A: 0.11 E: 0.05 , p<0.05), decreased DTI (A: 0.84 E: 0.89 , p<0.05) and DBSI FA (A: 0.66 E: 0.74 , p<0.05), and decreased DBSI fiber ratio (A: 0.059 E: 0.071 ,p<0.05)

Conclusions: DBSI can delineate extensive upstream atrophic and microstructural changes of corticospinal axons occur due to Wallerian degeneration as indicated by reduced FA and axonal density after spinal cord injury, with greater reductions in axonal density relating to poorer recovery.

Patient Care: We believe that DBSI can become a biomarker of axonal integrity with which to guide therapy and quantify its effectiveness.

Learning Objectives: Diffusion Basis Spectrum Imaging (DBSI)can overcome the confounding factors that effect DTI and shows promise as a biomarker of axonal integrity.

References: 1 Kim, J. H. et al. Noninvasive diffusion tensor imaging of evolving white matter pathology in a mouse model of acute spinal cord injury. Magnetic Resonance in Medicine 58, 253-260, doi:10.1002/mrm.21316 (2007). 2 Wang, Y. et al. Quantification of increased cellularity during inflammatory demyelination. Brain 134, 3590-3601 (2011).