Tesi di dottorato di ricerca
Modeling of pixelated and continuous crystals for high-resolution small animal positron emission tomography
Settore scientifico disciplinare
Corso di studi
Relatore Prof. Del Guerra, Alberto
- Monte Carlo
- tomographic image reconstruction
Data inizio appello
Data di rilascio
Positron Emission Tomography (PET) is a metabolic imaging modality which measures the distribution of a radiotracer (a compound labeled with a positron emitting radionuclide) in a living subject by the detection of gamma-rays, which are emitted due to the positron-electron annihilations. Depending on the biological and chemical characteristics of the compound, various functional processes within the living subject can be studied. Apart from clinical PET, as a "routine imaging modality" in nuclear medicine, small-animal PET has become an important tool for preclinical studies, e.g. for the evaluation of new radiotracers and therapies or to study receptor bindings, gene expressions, ecc.<br>However, sophisticated PET scanners are necessary to scan small animals, such as a 30-g mouse, appropriately. The main requirements are a high spatial resolution, to resolve small structures in the reconstructed tracer distribution and a high sensitivity, to discriminate small changes and to be able to detect low doses of the radiotracer.<br><br>An integral part of all PET scanners is a reconstruction algorithm, which reconstructs the three dimensional radiotracer distribution from the measured gamma-rays. One purpose of this thesis was the implementation of such a reconstruction algorithm for the YAP-(S)PET scanner. Since an iterative reconstruction algorithm was implemented (maximum likelihood - expectation maximisation), a focus was set on setting up the system model, which is used for the forward- and backprojection during the reconstruction. The model is calculated efficiently and accurately with the newly formulated multi-ray integration method and the results are compared to other integration methods such as Monte Carlo.<br><br>Moreover, as the pixelated scintillation crystals of the YAP-(S)PET detectors limit the performance of the scanner, a new design is proposed which is based on slabs of continuous scintillation crystals which are coupled to silicon photomultipliers. First, a single detector head is optimised to improve the intrinsic detector spatial resolution. Afterwards, hit estimation methods are derived to estimate the gamma-ray interaction within the continuous crystal. Finally, the performance of the new design is studied by reconstructing coincidence events from a point source which is simulated with a Geant4 based Monte Carlo simulation.
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