Analysis of partial volume effects in diffusion-tensor MRI

The diffusion tenser is currently the accepted model of diffusion in biological tissues. The measured diffusion behavior may be more complex when two or more distinct tissues with different diffusion tensors occupy the same voxel, In this study, a partial volume model of MRI signal behavior for two diffusion-tenser compartments is presented. Simulations using this model demonstrate that the conventional single diffusion tenser model could lead to highly variable and inaccurate measurements of diffusion behavior. The differences between the single and two-tensor models depend on the orientations, fractions, and exchange between the two diffusion tenser compartments, as well as the diffusion-tenser encoding technique and diffusion-weighting that is used in the measurements. The current single compartment model's inaccuracies could cause diffusion-based characterization of cerebral ischemia and white matter connectivity to be incorrect. A diffusion-tenser MRI imaging experiment on a normal human brain revealed significant partial volume effects between oblique white matter regions when using very large voxels and large diffusion-weighting (b similar to 2.69 x 10(3) sec/mm(2)). However, the apparent partial volume effects in white matter decreased significantly when smaller voxel dimensions were used. For diffusion tenser studies obtained using typical diffusion-weighting values (b similar to 1 x 103 sec/mm(2)) partial volume effects are much more difficult to detect and resolve. More accurate measurements of multiple diffusion compartments may lead to improved confidence in diffusion measurements for clinical applications. (C) 2001 Wiley-Liss, Inc.