Nephrotoxic nephritis and obstructive nephropathy: Evaluation with MR imaging enhanced with ultrasmall superparamagnetic iron oxide - Preliminary findings in a rat model

PURPOSE: To evaluate the role of magnetic resonance (MR) imaging enhanced w ith ultrasmall superparamagnetic iron oxide (USPIO) in the evaluation and d ifferentiation of different types of nephropathies. MATERIALS AND METHODS: Two experimental rat models of nephropathies were st udied: a model of nephrotoxic nephritis induced by means of intravenous inj ection of sheep anti-rat glomerular basement membrane serum (n = 43) and a model of obstructive nephropathy (n = 6). Imaging sessions were performed w ith a spectrometer operating at 4.7 T with fast low-angle shot, or FLASH, s equences. Signal intensity was measured in each kidney compartment before a nd 24 hours after intravenous injection of USPIO (90 mu mol of iron per kil ogram of body weight). MR findings were compared with histologic data and u rine protein levels. RESULTS: In the nephrotoxic nephritis model 24 hours after injection of USP IO, a significant signal intensity decrease (P < .05) was present only in t he cortex where the glomerular lesions were located. In the obstructive nep hropathy model, the signal intensity decrease (P < .05) was located in all kidney compartments in response to diffuse interstitial lesions. The decrea se in signal intensity was due to iron uptake by either macrophages or mesa ngial cells gaining endocytic activity and was correlated, in the nephrotox ic nephritis model, to the degree of proteinuria. CONCLUSION: Twenty-four-hour delayed USPIO-enhanced MR imaging may help ide ntify and differentiate various types of nephropathies.