• Nuclear imaging
• Positron Emission Tomography
• Cherenkov detector

With new developments in the field of medical imaging, the time-of-flight method has gained increasing popularity in positron emission tomography (TOF-PET). Clinical TOF-PET systems using L(Y)SO:Ce have proven the benefits of the TOF-method which is now a widely accepted method. The Cherenkov effect is an optical phenomenon which provides an almost instantaneous response to the photoelectric absorption of 511 keV annihilation photons. However, the Cherenkov yield is mostly in the blue and UV- region of the light spectrum (300 -500 nm) and is extremely low (about 20 photons per photoelectric absorption of an annihilation photon). This complicates energy discrimination and is unfavorable for clinical PET.
BGO crystals have been state-of-the-art in PET systems until about a decade ago. In addition to lower price, BGO offers superior physical properties required for detection of annihilation photons. After the introduction of L(Y)SO:Ce, BGO was replaced due to inferior scintillation properties. However, the optical properties of BGO crystals, especially its high refractive index and transparency to blue-UV light make it a good Cherenkov radiator. Previous studies have proven the feasibility of applying BGO crystals as hybrid scintillator/Cherenkov radiator in TOF-PET in lab-scale coincidence experiments.
In this work we try to prove these results for prototype detector modules. Therefore, BGO arrays with various optical reflector materials have been examined and are being compared in terms of coincidence resolving time (CRT), photon detection yield and energy resolution.