CeBr3 for Time-of-Flight PET

In this paper we report on our investigation of the CeBr₃ timing properties for Time-of-Flight (TOF) Positron Emission Tomography (PET). The TOF detection can significantly improve the signal-to-noise ratio in a reconstructed PET image and reduce the number of events necessary to do the reconstruction. In order to achieve TOF PET, a scintillator must have good timing resolution and good light output. We have investigated seven CeBr₃ samples of different height, ranging from 3 mm to 37 mm. Two Hamamatsu R4998 fast photomultipliers were used for most experiments. Each sample was measured against a common standard (LaBr₃:5%Ce) and the average timing resolution was found to be about 166 ps (fwhm). The two reference (LaBr₃:5%Ce) crystals measured against each other gave the timing resolution of 170 ps. The best time resolution of 108 ps (fwhm) was measured for two CeBr₃ samples (3 and 12 mm height). The longest sample (37 mm) provided 215 ps (fwhm). Two such samples working in coincidence would give about 252 ps timing resolution (fwhm, calculated). We have also measured TOF, where the source was moved between the two detectors and the change in a timing peak position was registered. The results show that a shift of 5 cm could be easily resolved by such a system.