Accumulation of some small molecular weight complexes of 99mTc in experimental abscesses

Abstract

The purpose of the present investigation was to evaluate the feasibility of imaging inflammatory lesions with some small molecular weight complexes of 99mTc with renal excretion in comparison to 99mTc-dextran (D), 99mTc-HIG and 67Ga-citrate. The biodistributions of pertechnetate (P), 99mTc-citrate (Cit), -gluconate (G), -glucoheptonate (GH), -DTPA, -glucose phosphate (GP), -D, -HIG and 67Ga-Cit were determined in mice with turpentine-induced abscesses at 1, 3, 6 and 24 h after i.v. injection of 15 MBq. % uptake/g tissues and abscess/muscle ( A M ), blood ( A B ), liver ( A L ), intestine ( A I ) and kidney ( A K ) concentration ratios were calculated. The scintigraphic images of all mice were obtained by a γ-camera. The abscesses were well visualized with all the radiopharmaceuticals (RPs). The excretion was mainly via the kidneys except for 99mTc-D, 99mTc-HIG and 67Ga-Cit. They showed variable amounts of liver and kidney uptake. Similar A M ratios were obtained with all the RPs, reaching max. at 3 h with pertechnetate, 99mTc-Cit and 99mTc-GP, at 6 h with 99mTc-DTPA and at 24 h with 99mTc-G, 99mTc-GH, 99mTc-D and 99mTc-HIG. The max. A M ratios were 3.61 ± 1.63, 4.61 ± 3.92, 5.21 ± 1.24, 3.60 ± 0.52, 3.43 ± 0.92, 5.37 ± 0.67, 5.98 ± 1.17 and 4.76 ± 2.03 for 99mTc-P, -Cit, -G, -GH, -DTPA, -D, -HIG and 67Ga-Cit, respectively. Our results indicated that small molecular weight complexes of 99mTc can be used in imaging inflammation as well as high molecular weight complexes such as 99mTc-D, 99mTc-HIG and 67Ga-Cit. However, the first group is preferred, because of rapid blood clearance and excretion predominantly via the kidneys, which is an advantage for the identification of abdominal abscesses. The main mechanism of accumulation of all the RPs might be a simple diffusion process through the injured capillaries. An additional mechanism of binding to proteins was considered in view of the increasing concentration ratios with 99mTc-G, -GH, -D and -HIG as time progressed.