A pulse restoration circuit minimizing performance degradation of PET detector caused by using long cable

Recently, we have reported the approach of transmitting photo-sensor charge signal to preamplifier using long cable for development of hybrid PET-MRI. However, pulse distortions degrading the performance of PET detector might occur in this approach. The purpose of this study is to develop a pulse restoration circuit (PRC) compensating the performance degradations caused by using the long cable from Gaige-mode avalanche photodiode (GAPD) to PET electronics. The effect of the cable length on the PET detector performance was examined using different lengths of flexible flat cable (FFC) ranging from 0 to 21 m. Rise time, fall time and amplitude of the GAPD output were measured as a function of the cable length. Photopeak position, energy resolution and time resolution were also measured using a 100 MS/s data acquisition unit. The PRC based on the filtering and shaping networks was consisted of amplitude, rise time-fall time restoration parts. The amplitude restoration part was designed using op-amp and resistors and the rise time-fall time restoration parts were designed using RC shaping filter. There were changes in the PET detector performance as a function of the FFC lengths ranging from 0 to 21m. The amplitude and the photopeak position decreased from 169 mV to 100 mV and from 400 ch to 300 ch, respectively. The rise time, fall time and the time resolution increased from 35 ns to 61 ns, from 210 ns to 450 ns and from 1.1 ns to 2.2 ns, respectively. No considerable changes were observed in the energy resolution of 16%. These performance changes was improved by employing the PRC. The measured pulse shapes passing through the long cable with PRC, were identical to the GAPD output with the cable length of 0 m, and the photopeak position was restored. The time resolution was also improved from 2.2 ns to 1.3 ns. This study demonstrated that the PRC could improve the performance degradations caused by using long cable.