Extra- and intracellular accumulation of ultrasmall superparamagnetic ironoxides (USPIO) in experimentally induced abscesses of the peripheral soft tissues and their effects on magnetic resonance imaging

The effects of ultrasmall superparamagnetic iron oxide (USPIO) particles on magnetic resonance imaging (MRI) were studied in an animal abscess model a nd the findings compared with microscopic sections of the abscesses, Staphy logenic abscesses of the right hind leg were induced in six Sprague-Dawley rats. The USPIO particles consisted of polyethylene-glycol-coated Fe3O4 wit h a mean size of 26 nm and were injected intravenously (i.v.), with three a nimals receiving a dose of 50 mu mol/kg and three animals a dose of 150 mu mol/kg. Before and immediately after i.v. administration of the particles, MR data were acquired with fast gradient-echo technique FLASH sequences app lied over a period of 60 min. The Fe3O4-induced signal changes were registe red in regions of interest (ROIs) placed over the margin and center of the abscess, over the perifocal granulation tissue and over corresponding sites of the contralateral healthy muscle. Microscopic sections were prepared us ing the conventional paraffin technique and, in part, a kryohistologic meth od before staining of the specimen with hematoxylin and Berlin-blue reactio n. In addition to the mostly perfusion dependent loss of signal intensity w ithin 8 s after injection, a signal reduction, which could be rather pronou nced, was observed in the abscess margin and perifocal granulation tissue, with the underlying mechanism mainly attributed to extravasation and predom inantly extracellular deposition of Fe3O4, Conclusion: The USPIO particles used in this study lead to a prolonged demarcation of abscesses in the peri pheral soft tissues due to particle extravasation and accumulation in the p eriphery of the abscesses. Besides the known accumulation of already charac terized USPIO in the RES of liver, spleen and lymph nodes the study could d emonstrate ultrasmall iron oxide deposition (BY 818) in abscesses of the pe ripheral soft tissue, (C) 1999 Elsevier Science Inc.