Investigating the timing behavior of compton scattering in BGO for time-of-flight PET

Area of Science:

• Medical Physics
• Detector Physics
• Positron Emission Tomography

Background:

• Bismuth germanate (BGO) is a promising material for hybrid Cherenkov/scintillation time-of-flight positron emission tomography (TOF-PET).
• Pixelated BGO detectors can suffer from inter-crystal scattering (InterCS), degrading timing accuracy.
• Prompt Cherenkov photons offer excellent timing but are affected by scattering events.

Purpose of the Study:

• To experimentally investigate the impact of InterCS on Cherenkov timing in pixelated BGO detectors.
• To identify optimal timestamp selection strategies for BGO TOF-PET.
• To quantify the reduction in prompt photon statistics due to InterCS.

Main Methods:

• Constructed a dual-pixel BGO detector with segmented SiPM readout.
• Classified events into full-energy deposition (FED), InterCS, and penetration using energy-weighted positioning.
• Validated event classification with GATE simulations.
• Evaluated multiple timestamp selection strategies and quantified prompt photon statistics.

Main Results:

• InterCS events showed a coincidence timing resolution of 221 ps FWHM, compared to 184 ps FWHM for FED events.
• Energy-based timestamp selection was suboptimal.
• InterCS events had reduced prompt photon yield (4.73 photons/ns) compared to FED events (5.76 photons/ns).

Conclusions:

• Inter-crystal scattering systematically degrades timing performance in pixelated BGO Cherenkov TOF-PET detectors.
• Energy redistribution and reduced prompt photon statistics contribute to timing degradation.
• Time-aware, per-pixel timestamp selection is necessary for optimal performance in BGO TOF-PET systems.