Signal Transmission With Long Cable for Design of PET Detector for Hybrid PET-MRI

Recently, we reported a hybrid positron emission tomography-magnetic resonance imaging (PET-MRI) approach involving the transmission of a photo-sensor charge signal to a preamplifier using a long cable. However, in this application, pulse distortions may degrade the performance of the PET detector. The purpose of this study is to further extend the charge signal transmission (CST) approach and to design a PET detector module capable of transmitting the photo-sensor charge signal to PET electronics remotely located outside the MRI room for the hybrid PET-MRI. To achieve this, we developed a pulse restoration circuit (PRC) compensating the performance degradations caused by using the long cable from Geiger-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 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. PRC based on the filtering and shaping networks consisted of amplitude, and rise and fall restorations. The amplitude restoration was designed using op-amp and resistors. The rise time-fall time restoration was designed using RC shaping filter. The measured pulse shapes passing through the long cable with PRC were similar to the output of GAPD with the cable length of 0 m (amplitude 169 mV, rise time 35 ns and fall time 210 ns), and the degrading PET detector performance caused by long cable were restored (energy resolution 16%, photopeak position 400 ch and time resolution 1.3 ns). There were no significant changes in the PET detector module performance using the CST approach with PRC as a function of the cable length, both outside and inside the MRI room. There were no obvious artifacts or changes in the MR phantom images. These results show that the proposed approach using extended charge signal transmission method with long cable and simple pulse restoration circuit is reliable and useful for the development of a hybrid PET-MRI system.