The biodistribution of a nanometer-sized colloid was tested in three groups of rats, one with a turpentine-induced abscess and one with a histamine-induced oedema in the musculature of a hind leg. The third group served as a control. A 99Tcm-labelled colloid with a mean particle size of 30 nm was administered to each group intravenously. The biodistribution of the tracer, studied l h after injection, demonstrated that the colloid accumulated to a very limited extent in oedematous tissue, whereas the uptake in inflamed muscle was high. The colloid was subsequently administered to patients with arthritis, osteitis and osteomyelitis. All sites of inflammation accumulated the radiopharmaceutical and could be visualized scintigraphically 45 min after its administration. The results were in agreement with 87Ga-citrate or 111In-leukocyte scintigraphy, and/or other diagnostic modalities. Hyperaemia alone was not sufficient to cause uptake. We conclude that the mechanism of uptake is regional spilling of the tracer into the extravascular space through gaps in the damaged basement membrane, and that nanometer-sized 99Tcm-labelled colloid may constitute a convenient radiopharmaceutical for detecting inflammation in the extremities.
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