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A High Resolution PET Readout Method Using Time over Threshold and Center-of-Gravity Algorithm

초록/요약

The importance of developing a high-resolution positron emission tomography (PET) that can study the function of the organ is increasing. Therefore, the appropriate readout electronics and PET detector for high resolution should be composed. In this paper, Center-of-gravity (COG) - time over threshold (TOT) readout method was developed by applying data of each channel obtained using TOT-based analog/digital processing method to COG algorithm. A PET detector was formed by an 8 × 8 array of 1.52 × 1.52 × 6 mm3 coupled to a 4 × 4 array of 3 × 3 mm2 SiPM (silicon photo-multiplier). Also, 0.7 mm light guide was coupled between 8 × 8 array of lutetium yttrium oxyorthosilicate (LYSO) and 4 × 4 array of SiPM. COG-TOT readout circuit consisted of analog signal processing circuit composed of OP-AMP, RC-shaper and comparator and digital signal processing circuit composed of 16 counters and time-to-digital converter (TDC) implemented using field programmable gate array (FPGA). The acquired counter values were used to estimate the position of gamma interacted pixel by using COG algorithm. The flood histogram was obtained using Na22 point source to evaluate the capability of discrimination of 64 crystal pixels. An acquired flood histogram showed that all 64 crystals from the detector could be resolved clearly. The average energy resolution was 10.8 ± 2.5% full-width-at-half-maximum (FWHM). The coincidence resolving time was measured as 1.1 ns FWHM. The results of this study indicated that COG-TOT method would be useful for achieving high resolution less than the pixel size of photosensor with simplifying readout electronics.

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