Investigation of diffusion time dependence of apparent diffusion coefficient and intravoxel incoherent motion parameters in the human kidney

Purpose To characterize the diffusion time (Δ eff ) dependence of apparent diffusion coefficient (ADC) and intravoxel incoherent motion (IVIM)-related parameters in the human kidney at 3T. Methods Sixteen healthy volunteers underwent an MRI examination at 3T including DWI at different Δ eff ranging from 24.1 ms to 104.1 ms. The extended mono-exponential ADC, and IVIM models were fitted to the data for each Δ eff , and medullary and cortical ADC, (pseudo-) diffusion coefficients (D* and D) and flow-related signal fraction (f) were calculated. Results When all the data was used for fitting, a trend toward higher ADC with increasing Δ eff was observed between 24.1 and 104.1 ms ([median and interquartile range]: 2.10 [1.94 2.26] to 2.36 [2.09 2.69] x10 −3 mm 2 /s for cortex, and 2.24 [2.10 2.36] to 2.64 [2.49 2.78] x10 −3 mm 2 /s for medulla). In contrast, no significant differences in ADC were found when only the data acquired at b-values higher than 200 s/mm 2 was used for fitting. When the IVIM model was applied, cortical and medullary f increased significantly (cortex: 0.24 [0.22 0.30] to 0.54 [0.43 0.63] x10 −3 mm 2 /s; medulla: 0.26 [0.23 0.38] to 0.50 [0.39 0.62] x10 −3 mm 2 /s) and cortical D (cortex: 1.66 [1.59 1.71] to 1.24 [1.10 1.47] x10 −3 mm 2 /s) and cortical D* (cortex: 9.10 [5.50 12.9] to 4.19 [3.84 5.73] x10 −3 mm 2 /s) decreased significantly between 24.1 and 104.1 ms. Conclusion Renal perfusion and tubular flow substantially contribute to the observed increase in ADC over a wide range of Δ eff between 24 and 104 ms.