The biodistribution and
infection imaging properties of a 99mTc labeled
hydrazino nicotinamide (HYNIC) derivatized chemotactic
peptide analog (For-
Met-Leu-Phe-Lys-HYNIC) and 111In-DTPA-IgG were compared in rabbits with
Escherichia coli infection. Six New Zealand white rabbits were injected in the left posterior thigh with a
suspension of E. coli. Twenty four hours later, the animals were injected with: 1.0 mCi of 99mTc labeled
peptide plus 0.1 mCi of 111In-DTPA-IgG. At 2-3 and 16-18 h, dual photon scintigrams were acquired and the images were corrected for crossover between the two windows. After recording the final images, the animals were sacrificed and biodistribution was determined. At both imaging times the biodistributions of the two
reagents were markedly different. The highest concentrations of 111In-DTPA-IgG were detected in blood pool structures, liver and kidney. In contrast localization of 99mTc labeled
peptide was greatest in spleen, lung and liver (consistent with binding to leukocytes). In general, the sites of
infection were better visualized with the radiolabeled
peptide and T/B ratios increased with time (P < 0.01). At both times, the T/Bs for 99mTc-peptide were higher (P < 0.01); 3.54 +/- 0.47 vs 2.52 +/- 0.38 at 2-3 h and 6.88 +/- 0.79 vs 3.78 +/- 0.36 at 16-18 h. These results indicate that although both
radiopharmaceuticals localize at sites of
infection, the radiolabeled
peptide are superior
reagents for the rapid detection of focal sites of
infection. However, since the mechanisms of localization are different the combined use of both agents could have value in the general evaluation of
infection/
inflammation.