3-Tissue Constrained Spherical Deconvolution as a novel means of assessing free water and cellular microstructure across the brain and lifespan

This project aims to use an advanced mathematical representation of diffusion to generate voxel-wise quantitative estimates of brain cellular microstructure, and then demonstrate the utility of these estimates in a range of subjects across the lifespan. Rather than relying on DTI, which has only 6 free terms to describe the diffusion signal, estimates of cellular microstructure will be derived from constrained spherical deconvolution (CSD). CSD is a more recently developed method that uses spherical harmonics with a theoretically unlimited number of terms available for describing the diffusion signal. CSD will allow for more advanced and anatomically accurate estimates of 3 underlying tissue components, each of which predominates in specific brain areas: intracellular anisotropic signal (ICA) which is primarily located in myelinated axonal areas, intracellular isotropic signal (ICI) which is highest in GM areas such as the cortex, and extracellular isotropic signal (ECI) which predominates outside brain tissue but also represents freely diffusing water within the brain. Changes in these tissue compartments may be important biomarkers for various disorders or may occur throughout the lifespan as a component of healthy development and aging.