Histopathological studies have shown that spinal cord WM and GM are affected by demyelination and neuronal loss in patients with MS. Advanced MRI techniques such as diffusion-weighted and diffusion tensor imaging (DWI and DTI) allow the detection and quantification of lesional and diffuse tissue injury. Although spinal cord DWI/DTI is technically challenging, a few DTI studies in patients with MS have demonstrated a significant decrease in fractional anisotropy (FA) that reflects the degree of integrity and alignment of fiber tracts. While the anisotropic sensitivity of DTI is useful for the study of highly organized anisotropic tissue such as WM tracts, it provides less useful information in highly isotropic organized tissue such as GM.
Diffusional kurtosis imaging (DKI) is an MR imaging technique developed by our coauthors Jens Jensen, Joseph Helpern, and Eric Sigmund to assess the degree of non-Gaussian diffusion.1 The mean kurtosis (MK) is a DKI-derived metric that provides a measure of the deviation of the diffusion probability distribution from a Gaussian form. MK has been shown to be sensitive to structural changes in both anisotropic tissue, such as WM, and isotropic tissue, such as GM, and therefore may provide information on tissue microarchitecture complementary to that given by FA and mean diffusivity (MD). DKI has already been used to study traumatic brain injury2 (featured in the March 2014 issue of the AJNR News Digest), brain tumors, and the spinal cord in patients with cervical myelopathy.
We hypothesized that studying the spinal cord using a non-Gaussian diffusion modality may be more sensitive to subtle pathologic changes because diffusional non-Gaussianity is a direct consequence of diffusion barriers and compartments and, therefore, a measurement of tissue complexity, regardless of the presence of microstructural anisotropy.3