Effect of crystal-photodetector interface extraction efficiency on Cerenkov photons' detection time

Area of Science:

• Nuclear Instrumentation and Medical Imaging
• Positron Emission Tomography (PET)
• Photonics and Optical Physics

Background:

• Cerenkov photons offer potential for improved timing resolution in time-of-flight positron emission tomography (TOF-PET) due to their prompt emission.
• Challenges include low yield and complex optical transport, necessitating optimization of light extraction and detector geometry.
• Monte Carlo simulations are vital for understanding Cerenkov photon behavior beyond benchtop limitations.

Purpose of the Study:

• To investigate the impact of crystal aspect ratio and refractive index at the crystal-photodetector interface on optical photon extraction and detection time.
• To analyze the mean detection time of early optical and Cerenkov photons as a function of detected Cerenkov photons per event.
• To determine strategies for enhancing the detection efficiency of prompt Cerenkov photons for improved TOF-PET timing resolution.

Main Methods:

• Optical simulations using the GATE Monte Carlo platform were performed on bismuth germanium oxide crystals.
• Simulations varied crystal aspect ratio and refractive index at the crystal-photodetector interface.
• Mean detection times for the first, second, and third detected optical and Cerenkov photons were calculated and analyzed.

Main Results:

• Thinner crystals resulted in lower mean detection times due to reduced electron transit time.
• Decreasing the refractive index discontinuity at the interface improved optical photon detection efficiency and the probability of detecting the fastest photons.
• Cerenkov photons were identified as the first detected optical photons in most configurations, highlighting the importance of their detection efficiency.

Conclusions:

• Optimizing crystal geometry (thinner crystals) and optical coupling (reduced refractive index mismatch) significantly reduces mean photon detection times.
• Enhanced detection of early Cerenkov photons directly improves timing resolution by mitigating signal loss and transit time spread.
• These findings are crucial for advancing TOF-PET scanner performance through improved detector design and optical photon management.