Optimised production of technetium-94m for PET imaging by proton-irradiation of phosphomolybdic acid in cyclotron liquid target

Natural-abundance phosphomolybdic acid (H₃(Mo₁₂PO₄₀) ‧12H₂O, 0.181–0.552 g Mo/mL) solutions were irradiated with 12.9 MeV protons on a GE PETtrace cyclotron using an adapted standard liquid target. Technetium-94m (^94mTc) was produced through the ⁹⁴Mo(p,n)^94mTc nuclear reaction with saturation yields of up to 53 ± 6 MBq/μA. End of bombardment activities of 161 ± 17 MBq and 157 ± 7 MBq were achieved for the 0.552 g Mo/mL solution (10 μA for 30 min) and 0.181 g Mo/mL solution (15 μA for 60 min), respectively. No visible degradation of the niobium target body and foil were seen during the irradiations of up to 15 μA for 60 min. The produced ^94mTc was separated from the target phosphomolybdic acid solution with >98% recovery using an aqueous biphasic extraction resin. Compared to previous reported liquid target methods for ^94mTc production, the better production yield, in-target solution stability during irradiation and ^94mTc separation recovery of phosphomolybdic acid makes it a very promising target material for routine clinical ^94mTc production at medical facilities with liquid targets already installed for ¹⁸F production.