An 1152 channel singles list-mode data acquisition system for MADPET-II

A data acquisition system has been developed to read out signals from the MADPET-II small animal LSO-AFD PET scanner. The scanner consists of 36 independent detector modules arranged in a dual-radial layer ring (Φ 71 mm). Each module contains a 4×8 array of optically isolated, 2×2 mm LSO crystals, coupled one-to-one to a 32 channel APD. To take full advantage of the detector geometry, signals from each crystal are individually processed without any data reduction. This is realised using custom designed mixed-signal ASICs for analogue signal processing, and KPGAs to control the digitisation of analogue signals and subsequent multiplexing. A DCs digitise the signal peak height, TDCs time stamp each event relative to a system clock, and two 32 bit words containing the energy, time and position information for each event are multiplexed through three FIFO stages before being written to disk via gigabit Ethernet. Even´ singles event is processed and stored in list mode format, and coincidences are sorted post-acquisition in software. A 128-channel prototype system is currently in operation. System pulse height linearity and count rate performance were measured by supplying test inputs to the pre-amplifier. All channels responded linearly with R²>0.9988 over a 6:1 input dynamic range, and input pulses were transmitted to disk with 0% data loss up to 45,000 cps/channel. The timing resolution of the TDC was measured to be 1 ns FWHM.