Studies On Positioning And Energy Performance Optimization Of Advanced Detector For Nuclear Medicine Imaging Systems

Nuclear medicine imaging is one of the main techniques for disease diagnosis in modern medicine and the dominant imaging tools are Positron Emission Tomography(PET)and Single Photon Emission Computed Tomography(SPECT).Gamma ray detector is the core component of PET and SPECT systems and optimizing detector performance is of significant importance for the overall performance as well as clinical diagnosis value improvements for PET and SPECT.The objective of this dissertation is to optimize the energy and positioning performance of gamma ray detector based on the clinical application requirements for PET and SPECT systems.Energy resolution is of important value for dual-radionuclide SPECT imaging.CZT detector is utilized in SPECT system for its high enegy resolution.This dissertation focuses on studying the correction method for the low energy tail effect of CZT detector induced by its incomplete charge collection process.Based on a commercial CZT SPECT system,a tailing model was proposed to describe the projection of the low energy tail counts.With the tailing model,a projection count model-based scatter and crosstalk correction method was developed and implemented in simultaneous 99mTc/123 I dual-radionuclide imaging and the quantitative accuracy of the images were effectively improved.In anthropomorphic torso phantom experiment with cardiac component insert,the nontransmural and transmural defect constrast of 99 mTc image were respectively improved from 0.39 to 0.51 and from 0.62 to 0.73.In patient study,the myocardium-to-blood pool ratio was improved from 7.0 to 63.6.Measuring depth of interaction(DOI)information is one of the important directions for PET detector technology development.Based on dual-ended readout technique,this dissertation studied the 3D positioning capability and energy performance optimization of crystal array-based detector.DOI positioning capability of the detector under different crystal surface finishing types and DOI positioning algorithms was intensively studied.The DOI-dependency of total output signal of the photodetectors at the two crystal ends was studied and the energy performance of the detector was quantified by considering the DOI-dependent total output signal of the detector.The best crystal surface finishing type is the combination of corundum-grinded crystal surface and diffuse reflecting film(under this crystal surface finishing type,a DOI resolution better than 2 mm can be achieved with balanced energy performance).Both linear and logarithm positioning algorithms can effectively extract the DOI information and the achieved DOI resolution is comparable between the two algorithms.Compared to the crystal array-based detector,continuous crystal-based fully 3D positioning technology is one of the hot research topics of detector design for nuclear medicine imaging systems in recent years.This dissertation studied the detector design with fully 3D positioning capability based on continuous LYSO crystal and SiPM.Two 3D positioning algorithms including statistical-based positioning(SBP)and artificial neural network(ANN)were investigated and a positioning resolution of about 2.0 mm and 4.0 mm was achieved for x/y and DOI direction,respectively.Two output channel number compression strategies respectively based on Anger and principal component analysis(PCA)were proposed to reduce the output channels of the detector.Based on SBP,the positioning resolution in x/y and DOI direction was respectively about 2.6 mm and 5.0 mm under either compression strategies,which is comparable with that without any compression,and this substantially improves the engineering application value of continuous crystal-based detector design.The dissertation comprehensively studied the optimization method of positioning and energy performance of advanced gamma ray detector for nuclear medicine imaging systems,which is of great importance for the quantitative accuracy improvement of dual-radionuclide SPECT imaging and the spatial resolution improvement of both PET and SPECT systems.