The Effects of Intra-voxel Fiber Architecture on the Diffusion Tensor Parameters
Fobel R, Stanisz G
University of Toronto
This study uses numerical simulations to model the effects that various axonal fiber architecture have on the measurable diffusion tensor parameters. As expected, small SNR is a major contributor to measured differences in the DTI eigen values, λ2 and λ3. However, for DTI data with sufficiently high SNR, differences between λ2 and λ3 indicate non-uniform fiber architecture within the voxel. In this case, the assumption of axially symmetric diffusion is no longer valid and results in under/overestimation of the minor eigenvalues. A reduced fractional anisotropy, FA and increased axial asymmetry in non-uniform fiber architecture demonstrates the inability of the diffusion tensor methodology to resolve differences in intra-voxel fiber structures. Any hope of differentiating between fiber architectures on a sub-voxel level will require both an increase in measured gradient orientations and a framework beyond the diffusion tensor methodology.