Simple, rapid production of Tc-94m

Objectives With the increasing availability of PET cameras and the recent disruption of the supply of Mo-99 the positron emitting isotope of technetium (Tc-94m) may serve as an alternative to Tc-99m containing radiotracers. To this end a rapid and simple method for the production and isolation of Tc-94m has been developed that minimizes chemical manipulation and can be performed rapidly due to the short (53 min) half-life of Tc-94m.

Methods Production of Tc-94m from MoO3 solid targets, via the Mo-94(p,n) reaction, has already been demonstrated. However rather than use a solid target a concentrated solution of ammonium molybdate, containing hydrogen peroxide, was prepared and loaded into a standard water target before irradiation with 13 MeV protons at 1-4 μA for up to one hour. After irradiation the solution was withdrawn from the target, and mixed with concentrated NaOH before it was passed over an ion exchange resin, which selectively immobilized the pertechnetate. Upon elution of the resin the chemical and radionuclidic content of the pertechnetate eluent was assessed.

Results Using a non-isotopically enriched source of ammonium molybdate in the target solution three isotopes of technetium were identified after irradiation, Tc-94, Tc-95 and Tc-96 with the desired Tc-94m being the predominate product. By passing this solution through an ABEC ion-exchange resin the pertechnetate isotopes were cleanly separated from the bulk molybdate and all other radionuclides, with the process taking less than 20 minutes. The major by product in the irradiated solution was the short lived N-13 from the O-16(p,α) reaction.

Conclusions We have developed a rapid and simple method for the production of the short-lived Tc-94m that provides a chemically pure sample for the development of Tc-94m based radiotracers. Using enriched Mo-94 would produce Tc-94m in high radionuclidic purity.

Research Support Canadian funding agencies: NSERC & CIH