99Tcm-dextran: a potential inflammation-seeking radiopharmaceutical.

The aim of this study was to test whether 99Tcm-dextran can be used for imaging inflammation. An in vivo inflammation model was prepared by intramuscular (i.m.) injection of Freund's complete adjuvant to the thigh of five rabbits. Serial imaging of the animals was done with 99Tcm-dextran for 2 weeks following the onset of inflammation. The radiotracer was seen to concentrate selectively in the lesion, with a mean target-to-nontarget ratio of 3.01 (range 2.74-3.15) from day 4 onwards. The area of scintiscan abnormality increased with time and was more marked than the physical appearance of the lesion. In two rabbits, the tracer was also seen to localize at the site of injection of the anaesthesia in the normal thigh. The best time to image was found to be 2-4 h after 99Tcm-dextran administration. It would appear that abnormally increased capillary permeability in the inflamed area results in enhanced uptake of the macromolecule. We conclude that 99Tcm-dextran is a potential inflammation-seeking radiotracer, though it needs to be evaluated further.