How to Keep a Vital Diagnostic Isotope in Stock

The Science

Using high-intensity proton beams, researchers made significant quantities of titanium-44 (⁴⁴Ti), which is particularly useful to the astrophysics research community in their studies of supernovae. In pursuit of alternative uses for this isotope, the researchers also designed a system that fixes this isotope on a surface. There, it decays into the much shorter-lived scandium-44g (^44gSc). The scandium is vital to positron emission tomography (PET) scans of activities in the brain, heart and elsewhere.

The Impact

The challenge is in producing enough ⁴⁴Ti to satisfy the needs of the astrophysics and medical research communities such that keeping ^44gSc (half-life of ~4 hours) “in stock” at hospitals is not impacted by competing research usage of the “parent” ⁴⁴Ti material. In the team’s new device, the ⁴⁴Ti becomes a “generator” of the ^44gSc. The scandium can be used in PET imaging to study metabolic processes in the body. Properly maintained, such a radionuclide generator could last for decades, providing an onsite supply of the needed isotope.

Summary

Positron emission tomography (PET) typically relies on relatively short-lived positron emitters, i.e., radioisotopes that decay with the emission of “antimatter” electrons and possess half-lives on the order of 10 to 110 minutes. Longer-lived positron emitters such as ⁴⁴Sc in its energetic ground state (^44gSc) enable imaging of slower biological processes. Titanium-44 (half-life 60 years), which functions as a source for ^44gSc, is also of interest to astrophysicists who study the origin of matter in supernovae: the isotope is produced in silicon burning in the innermost regions of the material ejected in core-collapse supernovae in the same processes that produce iron and ⁵⁶Ni. Reference samples of ⁴⁴Ti are thus used as standards for detector calibrations.

While hundreds of micrograms do not sound impressive to some, such masses can represent the world’s stock of a precious isotope. Researchers from Los Alamos and Brookhaven National Laboratories have demonstrated a method to make quantities of ⁴⁴Ti that are sufficient to support important developmental research into the medical application of scandium. They also designed a technique to fix the radioactivity on a solid support so that it can continuously be washed with an appropriate solution to recover its daughter isotope ^44gSc for medical research. The long-lived parent yields ^44gSc on a daily “as needed’’ basis for PET imaging purposes directly available at hospitals and other facilities.

Funding

This research was funded by the U.S. Department of Energy, Office of Science via funding from the Isotope Development and Production for Research and Applications subprogram in the Office of Nuclear Physics.

Publications

V. Radchenko, C.A.L. Meyer, J.W. Engle, C.M. Naranjo, G.A. Unc, T. Mastren, M. Brugh, E.R. Birnbaum, K.D. John, F.M. Nortier, and M.E. Fassbender,“Separation of ⁴⁴Ti from proton irradiated scandium by using solid-phase extraction chromatography and design of ⁴⁴Ti/⁴⁴Sc generator system.” Journal of Chromatography A 1477, 39-46 (2016). [DOI: 10.1016/j.chroma.2016.11.047]

V. Radchenko, J.W. Engle, D.G. Medvedev, J.M. Maassen, C.M. Naranjo, G.A. Unc, C.A.L. Meyer, T. Mastren, M. Brugh, L. Mausner, C.S. Cutler, E.R. Birnbaum, K.D. John, F.M. Nortier, and M.E. Fassbender, “Proton-induced production and radiochemical isolation of ⁴⁴Ti from scandium metal targets for ⁴⁴Ti/⁴⁴Sc generator development.” Nuclear Medicine and Biology 50, 25-32 (2017). [DOI: 10.1016/j.nucmedbio.2017.03.006]