AxCaliber: An MRI Method to Measure the Diameter Distribution and Density of Axons in Neuronal Tissue

and Density of Axons in Neuronal Tissue P.J. Basser, T. Blumenfeld , G. Levin, Y. Yovel, Y. Assaf, STBB/LIMB/NICHD, NIH; Department of Neurobiochemistry, Tel Aviv University Discussion The experimental determination of the diameter distribution, p(d), of emulsions and droplets has long been studied using NMR methods (see (1,2)). In these experiments, p(d) is estimated from PFG data by assuming a model of restricted diffusion within spheres. We have adapted this approach to estimate the diameter distribution within cylindrical nerve fascicles—a pack or array of nerve axons—by assuming that axons contain a restricted pool of water within their intracellular spaces. A composite hindered and restricted model of diffusion (CHARMED) within axons was first elaborated and tested in (3), and then applied clinically in (4).