TC-99M CITRATE VERSUS GA-67-CITRATE FOR THE SCINTIGRAPHIC VISUALIZATION OF INFLAMMATORY LESIONS

Citric acid was labeled with Tc-99m with an efficiency of > 99%. The biodistribution of Tc-99m-citrate was studied in mice with turpentine-induced abscesses in comparison to Ga-67-citrate. The max. abscess/muscle concentration ratios were 4.61 +/- 1.92 (3 h) for Tc-99m-citrate and 4.76 +/- 2.04 (4 h) for Ga-67-citrate. Arthritis was induced in 10 rabbits by intra-articular injection of ovalbumin Scintigrams obtained 4 days later and at 3 h post-injection of Tc-99m-citrate showed increased activity involving the synovium. The max. arthritic/contralateral knee ratio was 3.19 +/- 1.29 (3 h) and 6.47 +/- 3.71 (24 h) for Tc-99m- and Ga-67-citrate, respectively. The blood clearance curve of Tc-99m-citrate in rabbits was biexponential with a fast (T1/2 = 36 min) and a slow (T1/2 = 18 h) component, compared to mono-exponential clearance of Ga-67-citrate (T1/2 = 23 h). In 10 patients with rheumatoid arthritis whole-body scintigrams and spot images of involved joints, indicated localization of the tracer in inflamed tissues. The mean target-to-soft tissue ratios were 3.04 +/- 0.81 and 4.95 +/- 2.56 for Tc-9mm-citrate and Tc-99m-MDP, respectively. Renal clearance of radioactivity was evident from the scintigrams. Our results demonstrated that Tc-99m-citrate is effective as a radiopharmaceutical for the visualization of inflammatory lesions and may be preferred to Ga-67-citrate due to the ideal physical characteristics of the radionuclide, easy preparation, low cost, early accumulation and the preference for the renal route of excretion.