A Prototype high resolution SiPM-based PET system for small volume imaging

Positron Emission Tomography (PET) is a molecular imaging technique which measures the distribution of positron-emitting radio-pharmaceuticals in a living subject by the detecting the γ-rays produced by positron-electron annihilations. Depending on the biological and chemical characteristics of the compound, many different functional processes within the living subject can be studied. Apart from the clinical applications of PET as a “routine imaging modality” in nuclear medicine, small-animal PET has become an important tool for preclinical studies, such as for the evaluation of new radiotracers and related therapies. The main requirements for small-animal PET are a uniform high spatial resolution, which is needed to resolve small structures in the reconstructed tracer distribution within the full field of view (FoV) and a high sensitivity, which allows the detection of small physiological changes and with the smallest levels of radiotracer uptake. The scintillator, detector, detector module, gantry, data acquisition systems and image analysis and reconstruction algorithms are all critical factors in the success of PET systems. In this Thesis, each of these aspects of system design are investigated, and an advanced low-cost small-animal PET system is designed and prototyped based on the results. The final imaging system, Compact Millimetre Resolution Positron Emission Tomography (CMRPET) is a high spatial resolution positron emission tomography (PET) scanner with full depth of interaction capability. Its pixellated scintillator and detector architecture allows the depth of interaction (DoI) of each 511 keV gamma ray event to be localised to a 3 x 3 x 3 mm3 scintillator voxel. The detector module configuration houses an edgeon 4 x 4 array of voxels, which ensures the high gamma ray detection sensitivity is not compromised. The incorporation of DoI in the design results in minimal degradation of spatial resolution in the reconstructed PET image across the field of view (FoV) of the scanner. The average spatial resolution measured is 2.0 mm with a standard deviation of 0.3 mm, measured using a 1 mm diameter source placed at different radial displacements inside the FoV. The prototype was validated by comparing simulation results with experimental results.