Chemical properties

Sc-44 is a rare earth, usually in trivalent state. It can be radiolabelled with macrocyclic chelators, e.g. DOTA or other chelators such as NODAGA, AAZTA, pypa, mpatcn, etc. . The ionic radius is 74.5 pm.

Nuclear properties

Sc-44 decays by beta-plus emission (94.27(5)%) and electron capture (5.73%) with a half-life of 4.042(25) hours to stable Ca-44. It emits a medium energy positron spectrum with 632 keV average energy and 1474 keV maximum energy.

Moreover, Sc-44 emits a hard gamma-ray at 1157.0 keV (99.9%) in prompt coincidence (T_1/2=2.7 ps) with every emitted positron.

The mean electron energy emitted per decay is 596 keV, the mean photon energy per decay is 2136 keV .

Production

Sc-44 is produced by proton irradiation of enriched Ca-44 oxide (or carbonate targets) at: Injector 2 at PSI  or C30 cyclotron at NCBJ. ARRONAX uses instead deuteron irradiation .

Distribution

The radiochemical separations are performed at ARRONAX (ARRONAX, Nantes, France), PSI Radiochemistry Laboratory (PSI, Villigen, Switzerland) or POLATOM (NCBJ, Otwock-Swierk, Poland). Activity will be shipped from there to the users in form of ScCl₃ (or acetate) solution, ready for labelling of e.g. DOTA-compounds.

Examples of use

• Sc-44 has been evaluated preclinically with peptides, PSMA ligands, affibodies and monoclonal antibodies .
• Settings of commercial activity meters have been evaluated with Sc-44 .
• The preclinical PET imaging performance of Sc-44 has been compared to other positron emitters .
• The impact of the prompt gamma ray emission on quantification with preclinical and clinical scanners has been evaluated .
• First-in-human applications of Sc-44-DOTATOC and Sc-44-PSMA respectively have been reported with clinical PET/CT imaging up to 23.5 h post injection .
• Sc-44-PSMA PET/CT imaging is considered useful to evaluate maximum permissible activity in Lu-177-PSMA therapy .
• Sc-44 is considered the prime candidate for 3γ-imaging, also called γ-PET .
• Sc-44 is also considered the prime candidate for ortho-positronium mean lifetime imaging .