Repetitive electrical activity produces microstructural alteration in myelinated axons. These transient microstructural changes can be non-invasively visualized via two different magnetic-resonance-based approaches: diffusion fMRI and dynamic T2 spectroscopy in the ex vivo perfused bullfrog sciatic nerves. Non-invasive diffusion fMRI, based on standard diffusion tensor imaging (DTI), clearly localized the sites of axonal conduction blockage as might be encountered in neurotrauma or other lesion types. Diffusion fMRI response was graded in proportion to the total number of electrical impulses carried through a given locus. Diffusion basis spectrum imaging (DBSI) method revealed a reversible shift of tissue water into a restricted isotropic diffusion signal component, consistent with sub-myelinic vacuole formation.
IMAGING NERVE FUNCTION AND PATHOLOGIES