MRI quantification of non-Gaussian water diffusion in normal human kidney: a diffusional kurtosis imaging study.

Our aim was to prospectively evaluate the feasibility of diffusional kurtosis imaging (DKI) in normal human kidney and to report preliminary DKI measurements. Institutional review board approval and informed consent were obtained. Forty-two healthy volunteers underwent diffusion-weighted imaging (DWI) scans with a 3-T MR scanner. b values of 0, 500 and 1000 s/mm(2) were adopted. Maps of fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (D⊥), axial diffusivity (D||), mean kurtosis (MK), radial kurtosis (K⊥) and axial kurtosis (K||) were produced. Three representative axial slices in the upper pole, mid-zone and lower pole were selected in the left and right kidney. On each selected slice, three regions of interest were drawn on the renal cortex and another three on the medulla. Statistical comparison was performed with t-test and analysis of variance. Thirty-seven volunteers successfully completed the scans. No statistically significant differences were observed between the left and right kidney for all metrics (p values in the cortex: FA, 0.114; MD, 0.531; D⊥, 0.576; D||, 0.691; MK, 0.934; K⊥, 0.722; K||, 0.891; p values in the medulla: FA, 0.348; MD, 0.732; D⊥, 0.470; D||, 0.289; MK, 0.959; K⊥, 0.780; K||, 0.287). Kurtosis metrics (MK, K||, K⊥) obtained in the renal medulla were significantly (p <0.001) higher than those in the cortex (0.552 ± 0.04, 0.637 ± 0.07 and 0.530 ± 0.08 in the medulla and 0.373 ± 0.04, 0.492 ± 0.06 and 0.295 ± 0.06 in the cortex, respectively). For the diffusivity measures, FA of the medulla (0.356 ± 0.03) was higher than that of the cortex (0.179 ± 0.03), whereas MD, D⊥ and D|| (mm(2) /ms) were lower in the medulla than in the cortex (3.88 ± 0.09, 3.50 ± 0.23 and 4.65 ± 0.29 in the cortex and 2.88 ± 0.11, 2.32 ± 0.20 and 3.47 ± 0.31 in the medulla, respectively). Our results indicate that DKI is feasible in the human kidney. We have reported the preliminary DKI measurements of normal human kidney that demonstrate well the non-Gaussian behavior of water diffusion, especially in the renal medulla.