Objectives: To combine the intravoxel incoherent motion (IVIM) imaging and blood oxygen level-dependent MR imaging (BOLD) for assessment of the renal allograft pathological process and differentia between acute rejection (AR) and acute tubular necrosis (ATN) at the early stage after renal transplantation in rat model.

Materials and Methods: AR was induced by transplantation of Dark Agouti (DA) donor kidneys into Lewis recipients (allogenic ktx) (n=12). Lewis rat that received Lewis kidneys (isogenic ktx) (n=12) served as controls. ATN rat model was caused by ischemia/reperfusion injury (IRI) in Lewis rats (n=12). Six rats of each group were imaged longitudinally at postoperative day (POD) 1, 4 and 7, respectively; two rats were randomly chosen from the rest for histological studies. The apparent diffusion coefficient (ADC), the diffusion coefficient of microcirculation or perfusion (D*), the diffusion coefficient of pure molecular diffusion (D), and perfusion fraction (f) were calculated from IVIM, and R2* was obtained from BOLD. R2* is a measure of the rate of signal loss in a specific region and is related to the amount of deoxyhemoglobin present. Histological changes in the kidney were evaluated according to Banff criteria. Immunofluorescence was used to quantify cell infiltrates and fibrosis in kidney.

Results: After allogenic transplantation, animals developed acute allograft rejection which was confirmed by histological analysis and the severity of AR increased progressively over time. D, f value of the acute rejection group was significantly lower (p<0.05) than that in the native kidney and other groups at POD 1, 4, 7 while a progressive reduction in D* was observed at POD 4, 7 in renal cortex. Mean medullary R2* values in AR group were lower than in the isogenic ktx group and ATN group (p<0.05) at POD 7. In addition, f and D* were strongly correlated with R2*. Conclusions: IVIM imaging coupled with BOLD MR imaging is an effective tool for monitoring progress of AR and differentiating AR from ATN in rat models. Otherwise,it may help elucidate the underlying mechanisms of acute rejection and ATN.