Isotopes for New Modalities of PET/SPECT Imaging: Experimentation and Evaluation

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The conventional medical imaging by PET and SPECT relies on back projection techniques and it has drawbacks of artifacts due to scattering and absorption of gamma rays, contributing to false negative and/or false positive diagnostics. Dual energy imaging with separate isotopes has been suggested as possible means of improving the image qualities. They invariably involve additional equipment, higher doses and longer exposures etc. We attempt a novel approach of combining PET/SPECT imaging with single isotopes which emit positrons and gamma rays within less than a few nano second time lags. When implemented, we can employ standard 3D- vertex reconstruction technique of nuclear and particle physics experiments. In addition to enhanced contrast, this method provides multiple images based on different software cuts with conventional back projection to evaluate the image artifacts critically and minimize false diagnostics. In identifying candidate isotopes, we focussed on biological compatibility of isotopes to humans, dual energy requirement for attenuation corrections, economic viability and ease of production, stability of materials etc. The candidate isotopes are 43-Sc, 73-Se, 123-Xe, 85-Y, 77-Kr and 75-Br, the elements of which are already in medical use and ingestion. ***I am the principal investigator of an international collaboration with members from Canada, Japan, Korea, India and Vietnam. We will perform experiments at Osaka university-Japan, TRIUMF- laboratory on UBC campus and at the cyclotron laboratory of the University of Saskatchewan with proton and alpha beams to determine the optimum beam energies and irradiation times to maximize the production of isotope of choice, while keeping the interfering activities to a minimum. The next phase of this research is radiochemical separation procedures to develop clinically usable isotope production and separation methods and pass on this knowledge to the end users in health organizations. ***Some of the isotopes are to be made at sufficiently low energies such that small cyclotrons of several MeV proton beams of high intensities, which will avoid huge real estate or long distance transportations. The modality of combined PET/SPECT can be retrofitted to existing PET***machines with minor changes of hardware/software of imaging. We will perform imaging tests with a prototype detector assembly in laboratory setting. ***This project, when completed, will consolidate the position of Canada as a leader of nuclear medial imaging research and development. Canadian society will benefit as the patients will get improved imaging with less radiation doses and less ambiguities. Radiologists will have multiple images of human organs, all obtained in one setting with a single isotope and be able to critically evaluate them and make better assessment of a patient condition. ******