Stackable electronics architecture for densely packed PET detectors

We are developing a 1 mm3 resolution, high sensitivity clinical PET system, comprising two detector panels. Each panel contains 9 cartridges, each of which has eight layers of 1mm high detectors, requiring 768 readout signals per cartridge. A single layer comprising 16 data acquisition (DAQ) modules digitizes the readout information for 1 cartridge. A digital interface board (DIB) provides communication and interconnects to all of the DAQ modules in a cartridge. The DIB can transmit data through a gigabit Ethernet link or through a daisy chain to another DIB. In a clinical setting, with 10 mCi injected dose, the cartridge data rate is expected to be 146 Mbps (38 kHz event rate per DAQ module [1] and 240 bits per event). To minimize cabling in our system, three cartridges are daisy chained together and the maximum data rate remains well below the Ethernet link capability. The DIB provides a synchronous clock signal to the entire system. One cartridge is selected to provide the master clock. This signal is routed across the daisy chain flexes within a panel and across an inter-panel cable to the other panel. The DIB transmits the clock signal to the DAQ modules. To minimize jitter, the clock tree only contains two levels of buffering. Along with the clock signal, a coincidence signal is routed between the panels. This signal is routed similarly to the clock signal such that all DAQ modules know if the opposing panel has an event. The DAQ module can gate data to transmit only during coincidence events. System testing with randomly generated events demonstrates a singles count rate capability of 52 kcps per DAQ module, or 832 kcps per cartridge. The DAQ module was shown to be the limiting factor of the cartridge count rate.