Labelling of manganese-based magnetic resonance imaging (MRI) contrast agents with the positron emitter 51Mn, as exemplified by manganese-tetraphenyl-porphin-sulfonate (MnTPPS4)

The potential tumor seeking MRI contrast agent MnTPPS4 was labelled with the positron emitting nuclide 51Mn in no-carrier-added (n.c.a.) form. The complex formation kinetics were investigated and the apparent rate constants were determined under pseudo-first-order conditions. The derived bimolecular rate constants gave the Arrhenius parameters EA=84 kJ mol−1 and A=2×1012 s−1 M−1. Optimum labelling conditions were derived (radiochemical yields>99% possible, effective yields about 32%). Separation and purification of n.c.a. 51MnTPPS4 were performed for potential human use. All impurities were<1%.