Cobalt-55 positron emission tomography in symptomatic atherosclerotic carotid artery disease: borderzone versus territorial infarcts

Expanding the PET radioisotope universe utilizing solid targets on small medical cyclotrons

Molecular imaging with medical radioisotopes enables the minimally-invasive monitoring of aberrant biochemical, cellular and tissue-level processes in living subjects. The approach requires the administration of radiotracers composed of radioisotopes attached to bioactive molecules, the pairing of which considers several aspects of the radioisotope in addition to the biological behavior of the targeting molecule to which it is attached. With the advent of modern cellular and biochemical techniques, there has been a virtual explosion in potential disease recognition antigens as well as targeting moieties, which has subsequently opened new applications for a host of emerging radioisotopes with well-matched properties. Additionally, the global radioisotope production landscape has changed rapidly, with reactor-based production and its long-defined, large-scale centralized manufacturing and distribution paradigm shifting to include the manufacture and distribution of many radioisotopes via a worldwide fleet of cyclotrons now in operation. Cyclotron-based radioisotope production has become more prevalent given the commercial availability of instruments, coupled with the introduction of new target hardware, process automation and target manufacturing methods. These advances enable sustained, higher-power irradiation of solid targets that allow hospital-based radiopharmacies to produce a suite of radioisotopes that drive research, clinical trials, and ultimately clinical care. Over the years, several different radioisotopes have been investigated and/or selected for radiolabeling due to favorable decay characteristics (i.e. a suitable half-life, high probability of positron decay, etc.), well-elucidated chemistry, and a feasible production framework. However, longer-lived radioisotopes have surged in popularity given recent regulatory approvals and incorporation of radiopharmaceuticals into patient management within the medical community. This review focuses on the applications, nuclear properties, and production and purification methods for some of the most frequently used/emerging positron-emitting, solid-target-produced radioisotopes that can be manufactured using small-to-medium size cyclotrons (≤24 MeV).

Radiometals for imaging and theranostics, current production, and future perspectives

The aim of this review is to make the reader familiar with currently available radiometals, their production modes, capacities, and quality concerns related to their medical use, as well as new emerging radiometals and irradiation technologies from the perspective of their diagnostic and theranostic applications. Production methods of ¹⁷⁷ Lu serve as an example of various issues related to the production yield, specific activity, radionuclidic and chemical purity, and production economy. Other radiometals that are currently used or explored for potential medical applications, with particular focus on their theranostic value, are discussed. Using radiometals for diagnostic imaging and therapy is on the rise. The high demand for radiometals for medical use prompts investigations towards using alternative irradiation reactions, while using existing nuclear reactors and accelerator facilities. This review discusses these production capacities and what is necessary to cover the growing demand for theranostic nuclides.

Cyclotron production and radiochemical separation of 55Co and 58mCo from 54Fe, 58Ni and 57Fe targets

This work presents the production with a cyclotron of the positron emitter ⁵⁵Co via the ⁵⁴Fe(d,n) and ⁵⁸Ni(p,α) reactions and the Auger electron emitter ^58mCo via the ⁵⁷Fe(d,n) reaction after high current (40μA p and 60μA d) irradiation on electroplated targets. High specific activity radionuclides (up to 55.6 GBq/μmol ⁵⁵Co and 31.8GBq/μmol ^58mCo) with high radionuclidic purity (99.995% ⁵⁵Co from ⁵⁴Fe, 98.8% ⁵⁵Co from ⁵⁸Ni, and 98.7% ^58mCo from ⁵⁷Fe at end of bombardment, EoB), in high activity concentration (final separated radionuclide in < 0.6mL) and with almost quantitative overall activity separation yield (> 92%) were obtained after processing of the irradiated targets with novel radiochemical separation methods based on HCl dissolution and the resin N,N,N',N'-tetrakis-2-ethylhexyldiglycolamide (DGA, branched). One hour long irradiations using 38-65, 110-214 and 59-78mg of enriched ⁵⁴Fe (99.93%), ⁵⁸Ni (99.48%) and ⁵⁷Fe (95.06%), respectively, electroplated over a 1.0cm² surface, yielded 58² ± 66MBq ⁵⁵Co, 372 ± 14MBq ⁵⁵Co and 810 ± 186MBq ^58mCo, respectively, decay corrected to EoB. The separation methods allow for the recovery of the costly enriched target materials, which were reconstituted into metallic targets after novel electroplating methods, with an overall recycling efficiency of 93 ± 4% for iron. The produced radionuclides were used to radiolabel the angiogenesis marker antibody TRC105 conjugated to the chelator NOTA as a demonstration of their quality.

Evaluation of nuclear reaction cross sections for optimization of production of the emerging diagnostic radionuclide ⁵⁵Co

The excitation functions of the (54)Fe(d,n)(55)Co, (56)Fe(p,2n)(55)Co and (58)Ni(p,α)(55)Co reactions were analyzed with relevance to the production of the β(+)-emitter (55)Co (T½=17.53 h), a promising cobalt radionuclide for PET imaging. The nuclear model codes ALICE-IPPE, EMPIRE and TALYS were used to check the consistency of the experimental data. The statistically fitted excitation function was employed to calculate the integral yield of the product. The amounts of the radioactive impurities (56)Co and (57)Co were assessed. A comparison of the three investigated production routes is given.

Mapping biological behaviors by application of longer-lived positron emitting radionuclides

With the technological development of positron emission tomography (PET) and the advent of novel antibody-directed drug delivery systems, longer-lived positron-emitting radionuclides are moving to the forefront to take important roles in tracking the distribution of biotherapeutics such as antibodies, and for monitoring biological processes and responses. Longer half-life radionuclides possess advantages of convenient on-site preparation procedures for both clinical and non-clinical applications. The suitability of the long half-life radionuclides for imaging intact monoclonal antibodies (mAbs) and their respective fragments, which have inherently long biological half-lives, has attracted increased interest in recent years. In this review, we provide a survey of the recent literature as it applies to the development of nine-selected longer-lived positron emitters with half-lives of 9-140h (e.g., (124)I, (64)Cu, (86)Y and (89)Zr), and describe the biological behaviors of radionuclide-labeled mAbs with respect to distribution and targeting characteristics, potential toxicities, biological applications, and clinical translation potentials.

55Cobalt complexes with pendant carbohydrates as potential PET imaging agents

Bis-ligand cobalt(II) complexes of four 3-hydroxy-4-pyridinone ligands with pendant carbohydrates were synthesized and examined for their potential as radiopharmaceuticals. Non-radioactive complexes were prepared on the macroscopic scale and characterized by elemental analysis, mass spectrometry, IR and UV/visible spectroscopy. Facile radiolabeling produced the 55Co complexes in high radiochemical yields (>95%). Identification of the radiolabeled compounds was accomplished by HPLC comparison with the corresponding non-radioactive complexes.