Optimisation of analog and digital Silicon Photomultipliers for the Positron Emission Tomography

The research is focusing on the development of medical imaging devices based on particle detectors, in particular in the field of positron emission tomography (PET). The aim of the EndoTOFPET-US project is to develop a multi-modal imaging tool combining ultrasound with time-of-flight PET into an endoscopic imaging device. One of the objectives is to reach a coincidence time resolution of 200 ps full width at half maximum (FWHM). Firstly I developed an experimental setup to evaluate 256 MPPC arrays for the second external plate of the EndoTOFPET-US project to ensure the performance of each component of the detector. A full study of the breakdown voltage, dark count rate, single photon time resolution (SPTR) for the MPPC array (S12642-0404PB-50(X)) was performed and shows the MPPC array is a low noise photon detection device and has good timing performance of SPTR. An average CTR value of 222 ps FWHM has been measured by NINO ASIC and HPTDC for the 256 MPPC arrays coupling with 3×3×15mm3 Lutetium-yttrium oxyorthosil- icate (LYSO) 4 × 4 crystal matrices. Single LYSO crystal coupled to the MPPC array reached CTR of 170 ps better than the value of 222 ps measured. With the study of the coupling between crystal and SiPM I found that thickness of glue and alignment will affect the timing performance. Additionally, I also found that the crosstalk in the HPTDC will degrade the timing performance. So I can conclude that optimizing the coupling between crystal and SiPM and better performance of electronics can improve the timing performance of PET detector. I have also studied the energy resolution of the multiple channel digital SiPM (MDSiPM) device designed by TU Delft for the endoscopic probe for the EndoTOFPET US project. The energy measurement using the MDSiPM coupled to the LYSO fiber crystal matrices with each cell size of 0.75×0.75×10mm3. 511 keV photon peak can be identified for each channel and 18.26% energy resolution (FWHM) for 511 keV has been achieved. In parallel I performed different measurements on the Philips digital SiPM to characterize this newly developed device and investigate the possibility of improving the timing perfor- mance of PET detector. Taking the advantage of possibility to enable the cells individually of Philips digital SiPM, a group of different dimensions of LYSO crystals coupled to the Philips digital SiPM has been used to study the influence of using different active area of digital SiPM on the number of photons detected, energy resolution and coincidence time resolution (CTR). From the study I performed, I conclude that optimizing the coupling between crystal and SiPM to extra more scintillating photons can improve the energy resolution and CTR.