Almeida Silva Salvado, DS; (2017) SPECT System Design Optimisation for a Simultaneous SPECT/MRI Clinical Scanner. Doctoral thesis , UCL (University College London).

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Abstract

The aim of this project was to optimize the design of a Single Photon Emission Computed Tomography (SPECT) insert based on high-resolution detectors and a high-sensitivity collimator, for a Magnetic Resonance Imaging (MRI) scanner, in order to perform simultaneous human brain SPECT/MRI and improve radionuclide-based therapies for glioma patients. The radionuclides of interest are 99mTc, 111In and 123I. Specific emphasis was given to the collimator and overall system design, data simulation and performance assessment, which would feed directly into the European-funded INSERT project. The SPECT insert was to consist of a stationary system with SiPM-based photodetectors, insensitive to magnetic fields. Regarding the design, a number of system and collimator geometries were evaluated considering the restricted space in the MRI bore and the limited angular sampling. High sensitivity was prioritised over high spatial resolution, because of the clinical application. Gamma shielding design was also addressed. Analytical calculations of system sensitivity and resolution, in addition to Monte Carlo simulations, were performed to compare various slit-slat and pinhole collimator designs. A new collimator design was proposed: multi-mini-slit slit-slat (MSS) collimator. The MSS has multiple mini-slits, some of which are shared between adjacent detectors, and they are embedded in the slat component, allowing for longer slats in comparison to a standard slit-slat collimator. The MSS design demonstrated to have the best overall performance, and the final system design consisted of a partial ring with 20 detectors. A framework for geometrical calibration of the system was developed and assessed, utilising a single prototype detector equipped with a prototype collimator. This framework takes advantage of the specific collimator design to estimate geometrical parameters from independent measurements of calibration phantoms. Experimental evaluation with tomographic acquisition of phantoms demonstrated the applicability of the new collimation concept, confirming the superiority of the MSS design over equivalent pinhole collimation.

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