TY - JOUR T1 - <strong>Hybrid charge division multiplexing: a feasibility study for the time-based readout of SiPM-based PET detectors</strong> JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1334 LP - 1334 VL - 58 IS - supplement 1 AU - Haewook Park AU - Guen Bae Ko AU - Jae Sung Lee Y1 - 2017/05/01 UR - http://jnm.snmjournals.org/content/58/supplement_1/1334.abstract N2 - 1334Objectives: Time-based readout (i.e., time-over-threshold (TOT)) of output signals from the charge division network is technically challenging because the imperfect calibration of TOT data significantly degrades the energy performance of detector and the quality of flood histogram. Therefore, it is important for PET detectors to yield homogeneous output signals so that the TOT data strongly correlates to the energy of the detected photons. In our previous work, we proposed and validated the concept of hybrid charge division method using discretized positioning circuit (DPC), showing the good performance of detector and the excellent pulse uniformity. In this study, we digitally implemented a simple TOT readout to further demonstrate the feasibility of the time-based readout of the hybrid charge division method as compared with the conventional resistive and capacitive charge division methods.Methods: A feasibility study was conducted using a one-to-one coupled detector that consists of a 16-channel Hamamatsu multi-pixel photon counter (MPPC; S11064-050P) and a 4 × 4 array of 3 × 3 × 20 mm3 lutetium gadolinium oxyorthosilicate (LGSO) crystal block. The output signals from the multiplexing network (i.e., A, B, C and D) were digitized using a waveform digitizer (DT5742) and the TOT data of each output signal were encoded by a digital leading edge discriminator (LED) with the fixed threshold of 35 mV. Nonlinear least-squares curve fitting was performed using a logarithmic regression model and the best-fit curve was used for the calibration of the TOT data. The energy-calibrated TOT data were subsequently used to generate flood histogram. Because of the symmetry structure of the DPC network, only a single output signal (i.e., D signal) discharged along the diagonal direction of SiPM array was used for the graphical visualization of the TOT data against the integrated charge of the output signal.Results: In the resistive DPC, the TOT data and the integrated charge exhibited a good correlation, yielding a coefficient of determination (R2) of 0.9530 and a root mean square error (RMSE) of 23.1, but the correlation had become weak as the amount of integrated charge increased. In the capacitive DPC, the TOT data yielded a poor correlation to the integrated charge with an R2 of 0.7121 and an RMSE of 133.4, showing the need of position-dependent TOT calibration. The hybrid DPC, however, exhibited the strongest logarithmic correlation with the highest R2 of 0.9629 and the lowest RMSE of 9.8 among the three charge division methods, even when a large amount of charge was integrated. The individual 16 crystals were well-identified in the flood histograms; the hybrid DPC yielded the best quality of flood histogram, showing the smallest pixel size; whereas both the resistive and the capacitive DPCs resulted in the significant blurring on the periphery of crystal block.Conclusion: Hybrid charge division method exhibited outstanding feasibility of the time-based readout, yielding the strongest logarithmic correlation between the TOT data and the integrated charge of the output signal, and better quality of flood histogram as compared with the conventional resistive and capacitive charge division methods. Therefore, the proposed method can be useful for enhancing the performance of time-based readout in terms of energy linearity and calibration simplicity. Research Support: This work was supported by grants from the National Research Foundation of Korea (NRF) funded by the Korean Ministry of Science, ICT and Future Planning (grant no. NRF-2014M3C7034000 and NRF-2016R1A2B3014645). ER -