“A new imaging modality to non-invasively assess multiple sclerosis pathology”

- A novel diffusion imaging called Diffusion Basis Spectrum Imaging (DBSI) is reviewed.
- Inflammation exerts unpredictable and often contradictory effects on diffusion tensor imaging metrics complicating result interpretations.
- DBSI distinguishes and quantifies inflammation from axonal and myelin injury in CNS white matter tracts.

We describe a novel imaging method to assess central nervous system pathology called “Diffusion Basis Spectrum Imaging” (DBSI). Diffusion tensor imaging (DTI) has been widely used to estimate axonpathology and demyelination. However, in the settings of acute inflammation and chronic tissue loss asare common in multiple sclerosis, DTI signals can lead to false interpretations. DBSI is a computationallynovel method that separates isotropic from anisotropic components in imaging voxels. Isotropicdiffusion is believed to reflect inflammatory components (cells, edema), as well as intrinsic cells andextracellular space. DBSI enables the measurement of axial and radial diffusivities within the anisotropiccomponents of imaging voxels, which reflect the integrity of axon fibers and myelin, respectively.

We report on a non-invasive imaging technique that can discern inflammation from axon fibers within the human CNS white matter. The healthy CNS is complex, with glial and neuronal cells, myelinated and unmyelinated axonal fibers that are typically bundled into tracts (which often cross each other), and regions of extracellular space, including cerebrospinal fluid. In pathological conditions, invading inflammatory cells and edema are also often present. Diffusion basis spectrum imaging (DBSI, a data-driven multi-tensor model) was developed at Washington University to identify and quantify these various elements within an imaging voxel. Diffusion tensor imaging (left) provides a single averaged tensor for an imaging voxel of co-existing crossing-fibers, infiltrating inflammatory cells, and extracellular space. DBSI (right) describes these components of normal anatomy and pathology using multiple tensors: free water (as in a ventricle) is represented by free isotropic diffusion tensors; cells are represented by restricted isotropic diffusion tensors; edema water is represented by hindered isotropic diffusion tensors; crossing-axons are represented by anisotropic diffusion tensors with increased radial diffusivity representing demyelination and reduced axial diffusivity reflecting axonal injury.216