EVALUATION OF INTRARENAL DISTRIBUTION OF ULTRASMALL SUPERPARAMAGNETICIRON-OXIDE PARTICLES BY MAGNETIC-RESONANCE-IMAGING AND MODIFICATION BY FUROSEMIDE AND WATER RESTRICTION

RATIONALE AND, OBJECTIVES. The steady-state intrarenal distribution of ultrasmall superparamagnetic iron oxide (USPIO) particles in the cort ex, the outer medulla (OM), and the inner medulla (IM) was investigate d using magnetic resonance imaging in the normal rabbit kidney and in situations that modify the corticopapillary osmotic gradient. METHODS. Experiments were performed on rabbit kidneys with T2-weighted spin-ec ho sequence and T2-weighted gradient-recalled-echo sequence. The intra venous dose was 27 mu mole/kg of iron in all rabbits. Three groups wer e studied: normally hydrated rabbits (n = 5), after water restriction (n = 5) to increase the osmotic gradient, and after furosemide injecti on (n = 5) to decrease the osmotic gradient. The signal intensity (SI) was quantified by region of interest placed on the cortex, the OM and the IM. RESULTS. In normally hydrated rabbits, a maximal decrease of the SI after USPIO was noted in the medulla, without significant diffe rence between the OM and the IM on spin-echo sequences. The decrease o f the SI was maximal in the IM on gradient-recalled echo sequences. In dehydrated animals, the maximum SI loss was in the OM. The furosemide -induced transient enhancement of the IM lasted a few minutes. CONCLUS IONS. The observed SI changes due to the distribution of the USPIO bet ween OM and IM were not based on modifications of the osmotic gradient . The authors suggest that these SI changes were mostly dependent on t he vascular density.