A chemical method for the labeling of fibrinogen with 99mTc

A new method allowing the labelling of fibrinogen with 99mTcO4- is described. The 99mTcO4- is reduced by stannous chloride in an alkaline medium. After 1 h incubation with fibrinogen, the pH was brought down to 7.1. The study of (1) the pH of the solution, (2) the quantity of the reducer, and (3) the time of incubation allowed us to specify optimal conditions for labeling. The labeling yield varied from 91.68% plus or minus 6.05% to 95.18% plus or minus 2.13% according to the method of control used: the precipitation of fibrinogen by (NH4)2SO4 25% or thin-layer chromatography with methylethylketone as solvent. Clottable radioactivity averaged 72% plus or minus 4.43%. Column chromatography separated the tracer into two radioactive peaks. The first peak corresponded to the fibrinogen and carried 73.36% plus or minus 5.8% of the total radioactivity. The total recovered radioactivity amounted to 89.86% plus or minus 8.07%. Spectroscopic clottability was 88.23% plus or minus 2.42%. The in vivo stability of the labeling and the molecule was followed for 24 h after intravenous injection. If the radioactivity measured in the 5 min sample was considered to equal 100%, the 24 h sample averaged 32.71% plus or minus 3.25%, of which 85.68% plus or minus 2.92% was recovered in the clot. In conclusion, this method enabled us to obtain a stable tracer that we used for routine investigations in man.