An optimized DOI decoding method for a PET detector with nine-crystal-to-one-photodetector coupling.

Area of Science:

• Medical Imaging
• Nuclear Physics
• Detector Technology

Background:

• Positron Emission Tomography (PET) requires depth-of-interaction (DOI) information to correct parallax errors from thick scintillators.
• Conventional light-sharing window (LSW) readout struggles with DOI decoding in high coupling ratio configurations (e.g., nine-to-one).
• Edge-of-field DOI effects are particularly significant in dedicated brain PET systems.

Purpose of the Study:

• To propose and evaluate a novel PET detector architecture for consistent DOI decoding across all crystals.
• To overcome the limitations of conventional LSW readout in high crystal-to-photodetector coupling scenarios.
• To enhance spatial resolution and positioning accuracy for improved PET imaging.

Main Methods:

• Designed a LYSO scintillator array (12x15 matrix) coupled to a 4x5 Hamamatsu MPPC array using transparent-interface LSWs.
• Implemented a nine-to-one coupling configuration and developed a transfer function linking DOI to the MPPC signal ratio (ROM).
• Evaluated detector performance using floodmaps, energy spectrum, and collimation experiments to calculate DOI Mean Absolute Error (MAE).

Main Results:

• Achieved an energy resolution of 11.8% and an average DOI MAE of 3.54 mm across interaction depths.
• Successfully decoded DOI for all crystals, including centrally coupled ones, with MAEs ranging from 2.34 mm to 5.37 mm.
• Demonstrated over a 1.5-fold improvement in spatial resolution compared to conventional LSW configurations.

Conclusions:

• The transparent-interface LSW design enables consistent DOI decoding at elevated coupling ratios.
• The novel architecture provides superior positioning accuracy and spatial resolution, suitable for small animal and dedicated brain PET.
• This advancement facilitates full-array DOI extraction, enhancing overall PET system performance.