Microvascular blood flow plays an important role in regulating renal perfusion. Intravoxel incoherent motion (IVIM) and arterial spin labeling (ASL) are two MRI techniques to measure the blood perfusion without contrast injection. The purpose of this study was to compare cortical perfusion indices, pseudo-diffusion coefficient (ADCfast) and perfusion fraction (PF) derived from IVIM with renal blood flow (RBF) derived from ASL in native and transplanted kidneys. The study was approved by the local ethics committee, and written informed consent was obtained from all participants. 20 volunteers and 62 renal allograft recipients 2-4 weeks after kidney transplantation underwent IVIM and ASL MRI on a 3T MRI (MAGNETOM Trio, a Tim system, Siemens Healthcare, Erlangen, Germany). IVIM was acquired using a prototype single-shot echo planar imaging (ss-EPI) sequence with 11 b values of 0, 10, 20, 40, 60, 100, 150, 200, 300, 500 and 700 s/mm2 on 3 gradient directions, TE/TR of 72.4/1600 ms, voxel size of 1.8´1.8´5 mm3, and a full bi-exponential fitting was used to calculate true diffusion coefficient (ADCslow), ADCfast, and PF. ASL was performed using a prototype flow-sensitive alternating inversion recovery (FAIR) trueFISP sequence with a TI of 1200 ms for perfusion images and a TI of 4000 ms for M0 images with TE/TR of 2.24/4.48 ms, FA of 70 degrees and voxel size of 2.3´2.3´5 mm3. T1 maps were acquired using a modified look-locker inversion-recovery (MOLLI) sequence with corresponding slice parameters to calculate the RBF. The correlation between cortical ADCfast, PF with RBF, and their correlation with estimated glomerular filtration rate (eGFR) were estimated by Pearson correlation analysis in the native and transplanted kidneys. P <0.05 was considered statistically significant.Color maps of ADCfast, PF and RBF for a native kidney (A) and a transplanted kidney (B) are shown in Figure 1. Mean cortical RBF exhibited a significant correlation with PF (R =0.50, P <0.05), but not with ADCfast in the native kidneys (Figure 2.A). Both ADCfast (R =0.26, P <0.05, Figure 2.B) and PF (R =0.32, P <0.05, Figure 2.C) exhibited a correlation with RBF in renal allografts. Cortical ADCfast, PF and RBF showed a positive correlation with eGFR for recipients (R=0.36, 0.45 and 0.60 respectively, P <0.01 for all).IVIM DWI estimates the tissue perfusion and diffusion at the same time. ADCfast provides a macroscopic description of the incoherent movement of blood in the microvasculature compartment, and PF describes the fraction of incoherent signal that arises from the vascular compartment in each voxel over the total incoherent signal. Theoretically, ADCfast might be considered as a measure of mean transit time, and PF as the flow volume in terms of the classical perfusion parameters [1]. Further experiments indicated that the ADCfast might reflect the true flow better. As shown in this study, PF has a strong correlation with RBF in both native and transplanted kidneys, while ADCfast has a strong correlation with RBF only in transplanted kidneys. ADCfast, PF and RBF all had a significant correlation with eGFR, showing the potential to detect differences in renal function for allografts.ADCfast and PF derived from IVIM are effective indices for monitoring renal perfusion, as well as RBF derived from ASL.