Tests on scalability of a strip-line based TOF PET signal readout method

We have investigated the strip-line based SiPM signal readout method for TOF PET application; output of multiple SiPMs are connected on a single transmission-line, and signal waveforms from SiPMs are acquired at both ends of the strip-line by using high speed waveform sampler. This approach enables to decode the position of interaction along the transmission-line by using arrival time difference, and thus could reduce the number of readout electronics channels efficiently while keeping the fast time response of SiPMs. The scalability is one of the features of the strip-line readout method; the length of strip-line and the number of SiPMs connected on the strip can be easily extendable without increasing electronics channels. Previously we have built a prototype board with four strip-lines each with eight SiPMs (5.2mm pitch) installed on it, and demonstrated that the strip-line readout method is applicable for TOF PET. To check the scalability of the readout method, we modified the prototype board to connect two separate strip-lines into one single strip-line. From the laser test bench, the electronic time resolution along the strip is measured to be ~36ps fwhm (equivalent to 1.7mm fwhm in position) and found that the time resolution is not degraded by doubling SiPMs on a strip.