  Diffusion MRI is a neuroimaging technique measuring the anatomical structure
of tissues. Using diffusion MRI to construct the connections of tissues, known
as fiber tracking, is one of the most important uses of diffusion MRI. Many
techniques are available recently but few properly quantify statistical
uncertainties. In this paper, we propose a directed acyclic graph
auto-regressive model of positive definite matrices and apply a probabilistic
fiber tracking algorithm. We use both real data analysis and numerical studies
to demonstrate our proposal.
