Imaging osteomyelitis with streptavidin and Indium-111-labeled biotin

Animal studies of infection imaging by a two-step protocol have shown that important improvements in target to nontarget ratios are possible. In this protocol, unlabeled streptavidin is administered and allowed sufficient time to accumulate in the lesion, probably by nonspecific processes, and to clear elsewhere. Thereafter, 111In-biotin is administered. A fraction of the labeled biotin may be retained in the lesion because of biotin's high affinity for streptavidin while most of the activity is cleared through the kidneys. Methods: Radioscintigraphy with unlabeled streptavidin followed with 111In-labeled biotin was performed in 15 patients with chronic osteomyelitis. As controls, each patients received either 111In-labeled biotin without the preadministration of streptavidin or 111In-labeled non- specific IgG. Results: Regions of focal uptake were identified in all patients receiving streptavidin followed by radiolabeled biotin as early as 10 min postadministration of radioactivity, and retention of label was evident through 24 hr. Coincident regions of abnormal accumulation were apparent with 111In-IgG, but only in delayed images. Moreover, with 111In-biotin alone, without the preadministration of streptavidin, focal accumulations were detected in areas similar to that identified with the two- step protocol. Although, these observations were only in the earliest images. Conclusion: The results of this preliminary clinical investigation suggest that a two-step protocol with unlabeled streptavidin and radiolabeled biotin may be an alternative for the detection of infection.