A process for the preparation of a radionuclide imaging agent includes providing an imaging agent including a chelated place-holder metal； loading the imaging agent onto an acid stable stationary phase； replacing the chelated place-holder metal of the imaging agent loaded on the stationary phase with a replacement radioactive metal under mild reaction conditions； and eluting the imaging agent including the chelated replacement radioactive metal from the stationary phase to provide a radionuclide imaging agent suitable for positron emission tomography (PET) or single-photon emission computed tomography (SPECT). The imaging agent can include a targeting agent that is directly conjugated to the imaging agent or by means of a linker. The process may also apply to other metals that are non-radioactive but used as diluent metals or other metals that are strongly bound to DOTA.
