Preparation and properties of sup(99m)Tc-labelled chelates for use in nuclear medicine

The available published data on methods of preparation and evaluation of sup(99m)Tc-labelled aminopolycarboxylic acids (iminodiacetic acid - IDA, nitrilotriacetic acid - NTA, ethylenediaminetetraacetic acid - EDTA, diethylenetriaminepentaacetic acid - DTPA) are rather incomplete and contradicting. Therefore, it can not be ruled out that in many cases identically named preparations may differ in composition, stability and in vivo behaviour. A critical comparison is made of hitherto published data and the authors' results. The evaluation was carried out with reo-ard to optimized reaction conditions when using redox systems based on Sn2+ and Fe2+ as well as to correlations of the behaviour of intravenously administered labelled compounds in laboratory animals. For Sn2+, best results were demonstrated in the case of sup(99m)Tc-DTPA. Labelling may be performed with the use of a kit containing the minimum amount of carrier components and undergoing no changes over a period of 42 months. In contrast to most commercial preparations with a reaction pH value between 4 and 5, it was possible to work in the more favourable range of pH between 7.2 and 7.4 with labelling yields higher than 97%. The addition of a stabilizer as emphasized by some authors and producers was not required with the authors' preparation. The advantage of a faster blood clearance of sup(99m)Tc-IDA as compared with other chelating agents is depreciated by increased incorporation in the liver. Sup(99m)Tc-NTA was the least suitable preparation. When using Fe2+, sup(99m)Tc-EDTA gave the best results. Labelling must be performed, however, at an elevated temperature with the use of a multicomponent kit. None of the tested sup(99m)Tc-labelled chelates reached the parameters of 131I-hippurate as to clearance kinetics. (author)