研究目的
To provide a method to retrieve the intrinsic spatial resolution of a gamma-ray detector block based on monolithic crystals within an assembled PET scanner, using software collimation and comparing it with a distant detector approach.
研究成果
The proposed software collimation method effectively measures the intrinsic spatial resolution of monolithic crystal-based PET detectors within an assembled system, showing results comparable to the traditional distant detector approach. The method is efficient, requiring only one measurement, and the derived model accurately fits experimental data. Intrinsic resolution values range from 0.64 mm to 1.29 mm depending on crystal thickness and position, with thicker crystals showing worse resolution due to light truncation. This approach can be integrated into reconstruction algorithms to improve image quality in PET systems.
研究不足
The method neglects multiple gamma interactions within the crystal, which may affect accuracy near edges. The model is not fully valid for large collimation angles (≥0.1 rad) and may overestimate effects at crystal edges. Simulations assume specific source energy distributions and may not capture all real-world variations.
1：Experimental Design and Method Selection:
The study involves comparing two methods for measuring intrinsic spatial resolution: a software collimation method and a distant detector method. A theoretical model is developed to fit light distribution profiles, assuming Gaussian detector resolution and Lorentzian source profile modified by collimation.
2：Sample Selection and Data Sources:
Three LYSO monolithic crystal blocks of different thicknesses (10 mm, 15 mm, 20 mm) with dimensions 50 mm × 50 mm are used. A 22Na radioactive source with 0.25 mm diameter and low activity (7.4 kBq) is employed. Data is acquired in coincidence mode using custom SiPM arrays.
3：25 mm diameter and low activity (4 kBq) is employed. Data is acquired in coincidence mode using custom SiPM arrays.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Monolithic LYSO crystals, custom 16×16 SiPM arrays (SensL), readout electronics, 22Na source, PMMA encapsulation, retroreflector layers, temperature sensors, and data acquisition system.
4：Experimental Procedures and Operational Workflow:
For the distant detector method, one detector is moved from 115 mm to 1780 mm away to vary collimation angles, with acquisition times adjusted for similar counts. For the software collimation method, detectors are fixed at 115 mm apart, and events are filtered based on LOR angles. Data is binned and analyzed using center of gravity algorithms for position estimation and energy windows applied. Simulations using GATE based on Geant4 are performed to model source profiles.
5：Data Analysis Methods:
Measured profiles are fitted using the developed theoretical model in Wolfram Mathematica to extract intrinsic resolution. Gaussian fits are used for FWHM calculation, and statistical deviations are considered for error estimation.
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