Hybrid Diffusion Imaging (HYDI)

Hybrid diffusion imaging (HYDI) is a new diffusion MRI method for characterizing complex diffusion. Diffusion-weighted measurements are obtained on multiple `shells' of constant diffusion weighting. This diffusion encoding approach is amenable to multiple types of diffusion imaging analysis. The inner shells may be used to estimate the diffusion tensor and generate maps of the diffusion anisotropy and mean diffusivity. The outer shell, which has high angular resolution, may be used to estimate the distribution of white matter fiber tracts in a voxel. Finally, all of the data may be used to estimate the diffusion displacement spectrum for characterizing the full diffusion behavior in a voxel. HYDI experiments were performed on the brains of healthy volunteers and the results are presented. Overall, HYDI is an efficient and promising method for characterizing complex diffusion in the human brain and potentially other tissues.