A flexible advancedTCA based sampling ADC system for multimodality positron emission tomography

Multimodality imaging allows to combine the advantages of different imaging techniques within nuclear medicine. The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) has also to ensure that both modalities do not interfere with each other. The PET data acquisition system (DAQ) has to handle in particular the strong RF signals which occur during MR operation. Therefore, a DAQ system based on sampling ADCs and field programmable gate arrays (FPGAs) for online data processing is presented. The changeable FPGA firmware implements special trigger and noise suppression algorithms which allow the operation of silicon photomultiplier based PET detectors inside a MR system without additional shielding. In a second step, the FPGAs determine also the precise time information for each detected photon event from the pulse form data. The basic building block is an easy exchangeable mezzanine card with a size of 70 mm times 130 mm, which includes up to 32 ADC channels with 70 MHz sampling rate at 12 bit. To integrate the required amount of ADC channels for a complete PET system, four mezzanine cards are combined on an Advanced TCA (ATCA) carrier module, which equals 128 ADC channels. A complete Advanced TCA crate can then house up to 1536 analog channels. The resolution of the time reconstruction algorithm was verified with coincidence measurements. Additionally, data was acquired inside a running MR tomograph, to test the behavior of the trigger algorithms.