High-Precision Three-Dimensional Positioning In Positron Emission Tomography Detectors

Positron Emission Tomography(PET),as one of the important technical modalities of nuclear medicine diagnosis,can image from the physiological and biochemical levels,and plays an important role in brain science research,clinical diagnosis and treatment,drug development and other research fields.As the key component of PET system,gamma photon front-end detector directly determines the core indexes of PET system,such as spatial resolution and sensitivity.However,limited by the technical difficulties of PET detector such as light output efficiency,depth of interaction measurement,small size crystal design and decoding,the functional imaging capability of the current PET system is not fully utilized.Therefore,it is of great research significance and application needs to develop PET systems with higher spatial resolution and sensitivity.Focusing on the high-precision three-dimensional positioning of the front-end detector,this dissertation explored the key elements of the GATE Monte-Carlo and Trace Pro method for the modeling and simulation of optical photon transmission,and proposed the best simulation tool selection and model construction methods under different application environments in terms of the detector configuration design,crystal selection and surface treatment,photoelectric sensor design and other model settings.The application of the simulation model was tested and verified in the optimization of light-sharing window crystal and light guide thickness.Therefore,the proposed simulation methods provide a new approach to discover the mechanism of optical photon propagation inside the PET detector and other innovative designs.The photonic microstructure processing method based on femtosecond laser was established,and the Trace Pro photon transport modeling and theory were applied to reveal the relation between different photonic crystal microstructures and the light output.The comparison of the influence of structure shape,such as hole,column and groove,on light output performance was completed,and the experimental manufacturing system and evaluation method of photonic crystal processing and optical output based on femtosecond laser were established and validated,on the segmented crystal level and crystal array level.High optical output enhancement effect has been obtained.A high-precision depth of interaction measurement method based on a rectangular light-sharing window detector was proposed.The simulation and optimization of continuous depth of interaction measurement was realized using GATE photon transport modeling and theory.The continuous relationship between depth of interaction and decoding spot shift was revealed based on the homogenous radiation method.To fulfill different application requirements,the simulation,optimization,design,assembly and decoding verification method of 4-to-1 and 9-to-1 coupling configurations were established and continuous high-precision depth of interaction measurement was completed.The optimization of the positioning algorithm of small-size detectors was explored,and the positioning of gamma photons of dual-layer offset detectors and 0.25 mm crystal detectors was successfully realized.Overall,the assembly and decoding of detectors of 1mm,0.5 mm,and 0.25 mm size were systematically completed,and technical solutions consisting of detector assembly,readout electronic circuit,and experimental setup were established and improved.Evaluation and analysis were conducted in terms of decoding map,energy resolution,time resolution,and so on.The decoding algorithms such as the noise suppression method and the second peak Compton screening method,and the new detector assembly technique of the combined reflections were proposed,which provides potential for building an ultra-high resolution PET system with spatial resolution better than0.5 mm.In summary,the research,focusing on photon transport model,depth of interaction and gamma photon positioning of small size array in PET detector,were applied to reveal the relationship model between light guide thickness and the peak-to-valley ratio,spot distance,full with at half maximum,noise ratio.Based on the Compton screening algorithm and timestamped sorted calibration method,the high resolution PET scanner of 0.5 mm spatial resolution was built and evaluated,which provides new ideas and imagination for future ultra-high resolution PET system development,whole-body PET system and multimodal molecular imaging system.