Animal and human studies of a new 99mTc labelled phosphine-isocyanide complex with possible applications to radionuclide ventriculography

A new 99mTc-phosphine-isocyanide complex with the general structure [99mTc (DEPE)2 (CNR)2]+ has been synthesised and tested in animals and one human. In three animal species (rat, rabbit, dog), the complex is an efficient myocardial imaging agent, while in humans it remains in the blood pool. The complex is 100% protein bound in animals and humans, but whereas in humans it is attached to a 51.5 kdalton protein (probably prealbumin), in rabbits it appears to be bound to a larger macromolecule (M.W.> 100 kdalton). The efficiency of the complex for blood pool labelling was tested in a human volunteer and compared with the standard in vivo red cell labelling technique with stannous pyrophosphate. A satisfactory radionuclide angiogram could be performed with less than 370 MBq of the complex. The count rate for the complex (cps/MBq) was 15% higher than that obtained with the labelled red cells and the absence of splenic activity was notable. In humans this complex appears to be an efficient blood pool labelling agent which might be useful for radionuclide ventriculography.