MR imaging of intrarenal macrophage infiltration in an experimental model of nephrotic syndrome

The objective of this study was to use MR imaging to detect macrophage infi ltration of the kidney after injection of ultrasmall superparamagnetic iron oxide (USPIO) particles in a rat model of experimental nephropathy. Ninety pmol of USPIO were injected intravenously in 10 rats with nephropathy seco ndary to intravenous injection of 5 mg of puromycin aminonucleoside (PAN), and in 10 control rats. The signal intensity was measured in each kidney co mpartment before and 24 h after injection of the contrast agent. FLASH sequ ences were performed on a spectrometer operating at 4.7 T. MR findings were compared with histological data. Twenty-four hours after injection of USPI O, a significant decrease (P < 0.0001) was observed in signal intensity in each kidney compartment in the PAN group. There was no variation in the con trol group. In the diseased kidneys, histological data revealed the presenc e of macrophages with iron oxide particles within their cytoplasm and lysos omes. Using USPIO, MR imaging can evidence infiltration of the rat kidney b y macrophages. Magn Reson Med 41:156-162, 1999. (C) 1999 Wiley-Liss, Inc.