Challenges in nuclear medicine: innovative theranostic tools for personalized medicine

Nanomaterial Probes for Nuclear Imaging

Nuclear imaging is a powerful non-invasive imaging technique that is rapidly developing in medical theranostics. Nuclear imaging requires radiolabeling isotopes for non-invasive imaging through the radioactive decay emission of the radionuclide. Nuclear imaging probes, commonly known as radiotracers, are radioisotope-labeled small molecules. Nanomaterials have shown potential as nuclear imaging probes for theranostic applications. By modifying the surface of nanomaterials, multifunctional radio-labeled nanomaterials can be obtained for in vivo biodistribution and targeting in initial animal imaging studies. Various surface modification strategies have been developed, and targeting moieties have been attached to the nanomaterials to render biocompatibility and enable specific targeting. Through integration of complementary imaging probes to a single nanoparticulate, multimodal molecular imaging can be performed as images with high sensitivity, resolution, and specificity. In this review, nanomaterial nuclear imaging probes including inorganic nanomaterials such as quantum dots (QDs), organic nanomaterials such as liposomes, and exosomes are summarized. These new developments in nanomaterials are expected to introduce a paradigm shift in nuclear imaging, thereby creating new opportunities for theranostic medical imaging tools.

47Sc as useful β--emitter for the radiotheragnostic paradigm: a comparative study of feasible production routes

Background

Radiotheragnostics makes use of the same molecular targeting vectors, labeled either with a diagnostic or therapeutic radionuclide, ideally of the same chemical element. The matched pair of scandium radionuclides, ⁴⁴Sc and ⁴⁷Sc, satisfies the desired physical aspects for PET imaging and radionuclide therapy, respectively. While the production and application of ⁴⁴Sc was extensively studied, ⁴⁷Sc is still in its infancy. The aim of the present study was, therefore, to investigate and compare two different methods of ⁴⁷Sc production, based on the neutron irradiation of enriched ⁴⁶Ca and ⁴⁷Ti targets, respectively.

Methods

⁴⁷Sc was produced by thermal neutron irradiation of enriched ⁴⁶Ca targets via the ⁴⁶Ca(n,γ)⁴⁷Ca → ⁴⁷Sc nuclear reaction and by fast neutron irradiation of ⁴⁷Ti targets via the ⁴⁷Ti(n,p)⁴⁷Sc nuclear reaction, respectively. The product was compared with regard to yield and radionuclidic purity. The chemical separation of ⁴⁷Sc was optimized in order to obtain a product of sufficient quality determined by labeling experiments using DOTANOC. Finally, preclinical SPECT/CT experiments were performed in tumor-bearing mice and compared with the PET image of the ⁴⁴Sc labeled counterpart.

Results

Up to 2 GBq ⁴⁷Sc was produced by thermal neutron irradiation of enriched ⁴⁶Ca targets. The optimized chemical isolation of ⁴⁷Sc from the target material allowed formulation of up to 1.5 GBq ⁴⁷Sc with high radionuclidic purity (>99.99%) in a small volume (~700 μL) useful for labeling purposes. Three consecutive separations were possible by isolating the in-grown ⁴⁷Sc from the ^46/47Ca-containing fraction. ⁴⁷Sc produced by fast neutron irradiated ⁴⁷Ti targets resulted in a reduced radionuclidic purity (99.95–88.5%). The chemical purity of the separated ⁴⁷Sc was determined by radiolabeling experiments using DOTANOC achievable at specific activities of 10 MBq/nmol. In vivo the ⁴⁷Sc-DOTANOC performed equal to ⁴⁴Sc-DOTANOC as determined by nuclear imaging.

Conclusion

The production of ⁴⁷Sc via the ⁴⁶Ca(n,γ)⁴⁷Ca nuclear reaction demonstrated significant advantages over the ⁴⁷Ti production route, as it provided higher quantities of a radionuclidically pure product. The subsequent decay of ⁴⁷Ca enabled the repeated separation of the ⁴⁷Sc daughter nuclide from the ⁴⁷Ca parent nuclide. Based on the results obtained from this work, ⁴⁷Sc shows potential to be produced in suitable quality for clinical application.

Electronic supplementary material

The online version of this article (doi:10.1186/s41181-017-0024-x) contains supplementary material, which is available to authorized users.

State-Of-The-Art and Recent Advances in Quantification for Therapeutic Follow-Up in Oncology Using PET

¹⁸F-fluoro-2-deoxyglucose (¹⁸F-FDG) positron emission tomography (PET) is an important tool in oncology. Its use has greatly progressed from initial diagnosis to staging and patient monitoring. The information derived from ¹⁸F-FDG-PET allowed the development of a wide range of PET quantitative analysis techniques ranging from simple semi-quantitative methods like the standardized uptake value (SUV) to “high order metrics” that require a segmentation step and additional image processing. In this review, these methods are discussed, focusing particularly on the available methodologies that can be used in clinical trials as well as their current applications in international consensus for PET interpretation in lymphoma and solid tumors.