Development of a Position Decoder Circuit to Recover Inter-Crystal Scattered Events

A new position decoder circuit (PDC) capable of both reducing the number of readout channels and recovering the inter-crystal scattered events was developed based on the fastest and second fastest signal identification method. The channel reduction ratio of the PDC was 32:2. A positron emission tomography (PET) detector block, composed of a 4 × 4 array of lutetium-yttrium oxyorthosilicate (LYSO) crystals and a 4 × 4 array of 3 × 3 mm2 silicon photomultipliers (SiPMs) was used to evaluate the performance of the PDC by measuring the energy resolution, coincidence resolving time (CRT), and recovery count maps of the inter-crystal scattered events. The entire energy spectra of the two detector blocks were successfully acquired using the PDC. The average increase in photopeak counts of all the pixels was 16.9 ± 5.0%. The average energy resolutions at 511 keV before and after the recovery of inter-crystal scattered events were 17.1 ± 1.1% and 17.8 ± 1.3%, respectively. The CRTs were 3.4 ns full width at half maximum (FWHM) and 3.6 ns FWHM before and after the recovery, respectively. The results of this study demonstrate the effectiveness of the developed PDC in improving the sensitivity of the PET detector block by recovering the inter-crystal scattered events while providing high channel reduction ratio. The PDC will be useful in reducing the scan time or radiation-dose by increasing the sensitivity of the PET system.