44Sc

Scandium-44 (44Sc) is a radioactive isotope of scandium (atomic number 21) with a mass number of 44. It is used in nuclear medicine as a positron emitter for PET imaging. The isotope is produced either directly in cyclotrons by irradiating calcium targets with protons (for example via the 44Ca(p,n)44Sc reaction) or, more commonly for clinical use, as the daughter product from a 44Ti/44Sc generator. The parent 44Ti has a long half-life of about 60 years, enabling long-term, shelf-stable sources of 44Sc for radiolabeling procedures.

The decay of 44Sc is primarily via positron emission to 44Ca, with the emitted positrons annihilating to produce pairs of 511 keV photons that can be detected by PET cameras. This makes 44Sc useful for imaging biological processes when bound to radiopharmaceuticals and targeting molecules. In medical imaging, 44Sc is explored as an alternative to other PET radionuclides because its half-life of roughly 4 hours offers a compromise between image quality and practical logistics, allowing centralized production and distribution while still enabling high-contrast, patient-specific imaging.

Chemically, 44Sc behaves similarly to other scandium isotopes, forming stable chelate complexes with common chelators such as DOTA and NOTA. These chelates enable the attachment of 44Sc to peptides and other targeting vectors, producing radiopharmaceuticals for receptor- or enzyme-targeted PET imaging. Safety and regulatory considerations apply, as with all radioactive tracers, and production and use are subject to appropriate radiopharmaceutical guidelines.