10:30 AM - 10:45 AM
▲ [11a-N324-6] Depth of Interaction Double Side Readout of GAGG Array Crystal for Compton and PET Detector
Keywords:Depth of Interaction (DOI), GAGG Array Crystal, Double Side Readout
Detector with Depth of Interaction (DOI) capability becomes an important part to achieve high spatial resolution and sensitivity as in Positron Emission Tomography (PET) system. For this purpose, double side readout is often the preferred method. In double side readout system, two detectors are coupled to both ends of the crystal to produce the pulse height which is required for DOI determination. In this study, we used GAGG array crystal with 20 cm thickness consisting of 8 x 8 pixels as shown in Fig.1a. Two MPPCs each having 8 x 8 pixels were used as detectors to be coupled to each end of the GAGG crystal. High-energy gamma photons from 137Cs (662 keV) were focused through the lead collimator in the region between the two ends of the crystal pixel. The incident radiation is converted to the light at the point of interaction which is read by the MPPC to produce signals. The amplitude of the signal at each end of the crystal depends on the location of the interaction point. The DOI from the end of a pixel was estimated as the ratio of the signal amplitude at the end point to the total signal amplitudes at the pixel. In addition, the sum of the signal amplitudes at the ends of the same pixels was used to determine the energy spectrum of the 137Cs. DOI resolution and energy resolution were observed by moving collimated radiation 1 mm to 10 mm with 1 mm interval from the end of a crystal pixel as shown in Fig. 1b. Each spectrum measurement is carried out using an oscilloscope. Coincidence event was maintained by using the 'AND' logic setting on the oscilloscope trigger for each measurement. Trigger levels for the signals from each end of the pixel were set to obtain the optimum spectrum. The number of events for each measurement was 10000 events.