Chemical properties

Copper-61 (⁶¹Cu) is an emerging, high-efficiency positron-emitting diagnostic radionuclide engineered for Positron Emission Tomography (PET). Featuring a 3.33-hour half-life, ⁶¹Cu acts as a prominent logical alternative to short-lived clinic standards like Gallium-68 (⁶⁸Ga, t_1/2 = 68min) and a highly sensitive counterpart to Copper-64. It is increasingly integrated into precision imaging protocols for peptides and small-molecule tracers. In solution, Cu-61 is usually in divalent state, as copper chloride. It can be radiolabelled with highly robust macrocyclic copper specific chelators, such as Me-COSar, DiAmSar or CB-TE2A, CB-DO2A REF,REF.

Nuclear properties

Cu-61 decays with a half-life of 3.33 hours via β⁺ (61.5%) and EC decay (38.5%) to stable Ni-61. The emitted positrons have 500 keV average energy and 1216 keV maximum energy REF.

Cu-61 emits 19 ????-ray transitions ranging in energy from 67 to 2120 keV.

The total energy emitted per decay (Q value) is 2.238 keV REF.

Production

At IFIN-HH (TR19), Cu-61 is produced by proton irradiation of enriched solid Ni-61 targets via the ⁶¹Ni(p,n)⁶¹Cu reaction, resulting in high-specific activity (>500 GBq/mg). This reaction has a high cross-section and avoids co-production of Cu-60 at proton energies below 15 MeV.

At HZDR, Cu-61 can also be produced via the Ni-62(p,2n)Cu-61 reaction, which uses more affordable and more widely available Ni-62 target material and can give higher saturation yields. REF

Distribution

The radiochemical separation will be performed at IFIN-HH (Măgurele, Romania), or at the Institute of the Radiopharmaceutical Cancer Research (HZDR, Dresden, Germany) and the activity will be shipped from there to the users in the form of a CuCl₂ solution in dilute HCl.

Examples of use

• Cu-61 forms the theranostic “radiocopper trio” together with Cu-64 and Cu-67, offering a PET imaging option whose physical half-life is better matched than Cu-64 to the pharmacokinetics of fast-clearing tracers such as peptides REF.
• Cu-61-labelled small molecules have been evaluated preclinically for PET imaging of hypoxic tissue in tumour, brain and heart REF.
• Together with Cu-64 and Cu-67, Cu-61 is highlighted as offering two PET imaging partners of distinct half-lives (3.34 h and 12.7 h) that can be matched to the pharmacokinetics of different targeting vectors, a flexibility not available with other theranostic radiometal sets such as Sc-43/44/47 or Tb-152/155/161 .