Technetium-99m Citrate for Imaging Inflammation: An Experimental Study

Citric acid was labeled with 99mTc by the Sn++ reduction method with an efficiency of >98%. The biodistribution of 99mTc-citrate was determined in mice with abscesses in their right thigh muscles and compared to 67Ga-citrate. The maximum abscesses/muscle ratios for 99mTc-citrate were 4.00±1.39 and 4.47±1.76 at 1 h for the turpentine- and Staphylococcus-induced abscesses, respectively. Corresponding values for 67Ga-citrate were 4.76±2.04 and 3.97±1.99 at 4 h. Arthritis was induced in 10 rabbits with intra articular injection of ovalbumin. Scintigraphic images obtained as a function of age up to 21 days showed increased activity involving the synovium. The maximum arthritic/contralateral knee ratio was 3.56±2.42 at 21 days. The blood clearance curve of 99mTc-citrate in rabbits was biexponential with a fast (T1/2=51 min) and a slow (T1/2=22 h) components. Analysis of urine samples indicated that most of the excreted radioactivity was due to intact 99mTccitrate (>95%), as determined by ITLC and electrophoresis. Our results demonstrated that 99mTc-citrate is a potential radio pharmaceutical for the visualization of inflammatory lesions.