Optical simulation study on the spatial resolution of a thick monolithic PET detector.

Area of Science:

• Medical Imaging Physics
• Nuclear Instrumentation
• Scintillation Detector Technology

Background:

• Current clinical positron emission tomography (PET) detectors have intrinsic spatial resolution limitations of approximately 3-4 mm.
• Improving resolution with traditional pixelated detectors leads to increased cost and degraded performance in timing, energy resolution, and sensitivity.
• Continuous monolithic scintillation detectors offer a promising alternative for next-generation high-resolution PET systems.

Purpose of the Study:

• To investigate the influence of silicon photomultiplier (SiPM) pixel size, photon detection efficiency (PDE), and readout channel configuration on the spatial resolution of monolithic PET detectors.
• To determine the ultimate spatial resolution achievable with monolithic detectors through advanced optical simulations.
• To assess the feasibility of channel combination for reducing readout complexity without compromising resolution.

Main Methods:

• Optical simulations incorporating an advanced surface reflection model were performed.
• A 50 x 50 x 16 mm³ lutetium-yttrium oxyorthosilicate (LYSO) crystal coupled to an SiPM array was simulated.
• A nearest neighbor (NN) algorithm was used for event positioning, analyzing parameters like SiPM pixel size, PDE, and channel readout strategy.

Main Results:

• Simulated spatial resolution ranged from 0.40-0.66 mm full width at half maximum (FWHM), significantly exceeding current clinical PET capabilities.
• Optimal resolution was achieved with smaller SiPM pixels, higher PDE, and individual channel readout.
• Combining readout channels demonstrated minimal impact on resolution while substantially reducing the number of required channels; mean depth of interaction (DOI) estimation error was 1.6 mm.

Conclusions:

• Monolithic PET detectors, optimized through parameters like SiPM characteristics and readout strategy, can achieve unprecedented spatial resolution.
• Channel combination presents a viable method for simplifying readout electronics without sacrificing resolution.
• These optical simulations provide a precise and efficient tool for calibrating future monolithic PET detectors.