A comparison of PET imaging characteristics of various copper radioisotopes

Purpose: PET radiotracers which incorporate longer-lived radionuclides enable biological processes to be studied over many hours, at centres remote from a cyclotron. This paper examines the radioisotope characteristics, imaging performance, radiation dosimetry and production modes of the four copper radioisotopes, Cu-60, Cu-61, Cu-62 and Cu-64, to assess their merits for different PET imaging applications. Methods: Spatial resolution, sensitivity, scatter fraction and noise-equivalent count rate (NEC) are predicted for Cu-60, Cu-61, Cu-62 and Cu-64 using a model incorporating radionuclide decay properties and scanner parameters for the GE Advance scanner. Dosimetry for Cu-60, Cu-61 and Cu-64 is performed using the MIRD model and published biodistribution data for copper(II) pyruvaldehyde bis(N-4-methyl) thiosemicarbazone (Cu-PTSM). Results: Cu-60 and Cu-62 are characterised by shorter half-lives and higher sensitivity and NEC, making them more suitable for studying the faster kinetics of small molecules, such as Cu-PTSM. Cu-61 and Cu-64 have longer half-lives, enabling studies of the slower kinetics of cells and peptides and prolonged imaging to compensate for lower sensitivity, together with better spatial resolution, which partially compensates for loss of image contrast. Cu-61-PTSM and Cu-64-PTSM are associated with radiation doses similar to [F-18]-fluorodeoxyglucose, whilst the doses for Cu-60-PTSM and Cu-62- PTSM are lower and more comparable with (H2O)-O-15. Conclusion: The physical and radiochemical characteristics of the four copper isotopes make each more suited to some imaging tasks than others. The results presented here assist in selecting the preferred radioisotope for a given imaging application, and illustrate a strategy which can be extended to the majority of novel PET tracers.