Sc-43 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.
Sc-43 decays by β+ decay (88.1(8)%) or electron capture (11.9(8)%) with a half-life of 3.891(12) hours to stable Ca-43. It emits a medium energy positron spectrum with 476 keV average energy and 1199 keV maximum energy.
Moreover, Sc-43 emits a γ-ray at 372.9 keV (22.5%).
The mean electron energy emitted per decay is 419 keV, the mean photon energy per decay is 981 keV +.
Sc-43 and Sc-44 have very close half-lives and similar positron intensities. However, Sc-43 is lacking the intense hard γ-ray emission of Sc-44. This makes Sc-43 a more favorable alternative to Sc-44, except for specific applications where the prompt 1157 keV γ-ray in the Sc-44 decay is used. In particular, the recovery coefficient in PET imaging is higher for Sc-43 and the γ dose rate is about twice lower.
Sc-43 is produced by proton irradiation of enriched Ca-44 oxide targets at Injector 2 at PSI. This production route leads to a coproduction of Sc-43 and some fraction of Sc-44.
The radiochemical separations are performed at PSI Radiochemistry Laboratory (PSI, Villigen, Switzerland). Activity will be shipped from there to the users in form of ScCl3 (or NaCl/HCl) solution, ready for labelling of e.g. DOTA-compounds.
Examples of use
|Decay||Decays to stable Ca-43: 88% β+, 12% EC|
|Processing||2-step column separation|
|Primary Container||2.5 mL borosilicate glass V-vial with silicon rubber screw cap|
|Chemical form||In 0.05 M HCl or 4.85 M NaCl/0.13 M HCl|
|Radioactive Concentration (gamma spectrometry)||n.a.|
|Appearance||Clear colourless solution|
|Radionuclide Identification (gamma spectrometry)||373 keV gamma line present|
|Radionuclidic purity (gamma spectrometry)||99.9% (thereof 65-70% Sc-43 and 30-35% Sc-44g) and 0.1% Sc-44m|
|Chemical purity (ICP-OES)||n.a.|
|Molar activity (ICP-OES)||>100 GBq/µmol at calibration time (>0.3% of theoretical maximum)|
|Apparent Molar Activity||Labelling up to 25 MBq/nmol DOTANOC or DOTATATE|
|pH (pH strips)||Depends on chemical form|
|Activity available||Up to 1 GBq|
|Activity limit for UN2910 (excepted package) shipment||20 MBq in dry state or 2 MBq in liquid form|
|Other information||Due to the chemically identical behavior and the very similar nuclear properties of Sc-43 and Sc-44, indeed any mixture ratio of both Sc radioisotopes is useful and safe for PET imaging. Thus, in this specific case, the definition of “radionuclidic purity” should be considered as “(Sc-43 plus Sc-44)/(all RN activities)”|