Imaging experimental intraabdominal abscesses with Tc-99m-PEG liposomes and Tc-99m-HYNIC IgG

Objective To evaluate the accuracy of technetium-99m-labeled polyethylene g lycol-coated liposomes (Tc-99m-PEG liposomes) and technetium-99m-labeled no nspecific human immunoglobulin G (Tc-99m-HYNIC IgG) for the scintigraphic d etection of experimental intraabdominal abscesses in comparison with that o f a standard agent, gallium-67 citrate. Background Scintigraphic imaging techniques can be very useful for the rapi d and accurate localization of intraabdominal abscesses. Two newly develope d radiolabeled agents, Tc-99m-PEG, liposomes and 99mTc-HYNIC IgG, have show n to be excellent agents for imaging experimental focal infection, but have not yet been studied in the detection of abdominal abscesses. Methods Intraabdominal abscesses were induced in 42 rats using the cecal li gation and puncture technique. Seven days later, randomized groups of rats received Tc-99m-PEG, liposomes, Tc-99m-HYNIC IgG, or Ga-67 citrate intraven ously. The rats were imaged up to 24 hours after the injection. The biodist ribution of the radiolabel was determined by counting dissected tissues ex vivo. Macroscopic intraabdominal abnormalities and focal uptake on the imag es were independently scored on a semiquantitative scale. Results Tc-99m-PEG liposomes provided the earliest scintigraphic visualizat ion of the abscess (as soon as 2 hours after the injection vs. 4 hours for the other two agents). Liposomes, IgG, and gallium all showed similarly hig h absolute uptake in the abscess. Focal uptake of liposomes and gallium cor related best with the extent of the macroscopic abnormalities. Conclusions Tc-99m-PEG liposomes and (TC)-T-99m-HYNIC IgG performed at leas t as well as the standard agent, 67Ga citrate, in the detection of experime ntal intraabdominal abscesses, with obvious advantages such as lower radiat ion exposure and more favorable physical properties. Of the two technetium agents, the liposomes seemed to be superior, providing the earliest diagnos tic image and the best correlation with the inflammatory abnormalities. In addition, the preferential localization of radiolabeled PEG liposomes holds promise for targeted delivery of liposome-encapsulated drugs.