Combined Intravoxel Incoherent Motion and Diffusion Tensor Imaging of Renal Diffusion and Flow Anisotropy

PurposeWe used a combined intravoxel incoherent motion-diffusion tensor imaging (IVIM-DTI) methodology to distinguish structural from flow effects on renal diffusion anisotropy. MethodsEight volunteers were examined with IVIM-DTI at 3T with 20 diffusion directions and 10 b-values. Mean diffusivity (MD) and fractional anisotropy (FA) from DTI analysis were calculated for low (b 200 s/mm(2)), high (b > 200 s/mm(2)), and full b-value ranges. IVIM-parameters perfusion-fraction f(P), pseudo-diffusivity D-p, and tissue-diffusivity D-t were first calculated independently on a voxelwise basis for all directions. After estimating a fixed isotropic f(p) from these data, global anisotropies of D-t and D-p in the cortex and medulla were determined in a constrained cylindrical description and visualized using polar plots and cosine scatterplots. ResultsFor all b-value ranges, medullary FA was significantly higher than that of the cortex. The corticomedullary difference was smaller for the high b-value range. Significantly higher f(p) and D-t were determined for the cortex and showed a significantly higher directional variance in the medulla. Polar plot analysis displayed nearly isotropic D-p and D-t in the cortex and anisotropy in the medulla. ConclusionBoth flow and microstructure apparently contribute to the medullary diffusion anisotropy. The described novel method may be useful in separating decreased tubular flow from irreversible structural tubular damage, for example, in diabetic nephropathy or during allograft rejection. Magn Reson Med 73:1526-1532, 2015. (c) 2014 Wiley Periodicals, Inc.