Background and objective： It has been shown that macrophages play an important role in the development of severe acute pancreatitis （SAP）, and eventually lead to multiple organ failure （MOF）. Clodronate-liposome selectively depleted macrophages. This study was to investigate the role of renal macrophage infiltration in acute renal injury in rats with SAP and to evaluate the potential of superparamagnetic iron oxide （SPIO）-enhanced magnetic resonance imaging （MRI） for diagnosis. Methods： Superparamagnetic Fe3O4 nanoparticles were prepared by chemical coprecipitation. SPIO-liposomes and SPIO-clodronate-liposomes were prepared by the thin film method. SAP models were prepared by injection of sodium taurocholate into the subcapsular space of rat pancreas. Sprague-Dawley rats were randomly divided into a control group, SAP plus SPIO-liposome （P） group, and SAP plus SPIO-clodronatecontaining liposome （T） group. Kidney injury was evaluated by T2-weighted MRI scan. The levels of serum amylase （SAM）, blood urea nitrogen （BUN）, and serum creatinine （SCr） were measured by an automated enzymatic method. Serum tumor necrosis factor-α （TNF-α） was measured by enzyme-linked immunosorbent assay （ELISA）. Pathological changes in the pancreas and kidney were observed using hematoxylin and eosin （H＆E） staining, while cell apoptosis was detected with terminal deoxynucleotidyl transferase dUTP nick end labeling （TUNEL） staining. In addition, the macrophage markers （CD68） of the renal tissue were detected with immunohistochemistry. Results： The pathological changes in the pancreas and kidneys of rats in the T group were milder than those in the P group. The MRI signal intensity of the kidneys in the P and T groups was significantly lower than that in the control group. There were significant changes in the two experimental groups （P〈0.01）. The levels of SAM, Bun, SCr, and TNF-α in rats in the P group were higher than those in the control group （P〈0.01） and in
