A digital architecture for routinely storing and buffering the entire 64-bit event stream at maximum bandwidth for every acquisition in clinical real-time 3-D PET: Embedding a 400 Mbyte/sec SATA RAID 0 using a set of four solid-state drives

A new “Stream Buffer” data acquisition architecture is proposed for positron emission tomography (PET). This new architecture significantly improves performance in high-count-rate (e.g. Rubidium-82) clinical 3-D PET. This Stream Buffer concept improves PET by removing several long-running limitations found in current data acquisition architectures. Stream buffering ensures the non-volatile storage of the entire, raw 64-bit PET coincidence event stream. In addition, this buffering benefits on-line, downstream processing - e.g. LOR-to-bin rebinning and histogramming, processing which remains critical to an effective clinical environment. Primarily this new architecture makes use of multiple high-performance solid-state drives (SSD) to form a single, very-high-speed (400 Mbyte/sec) buffer for coincidence event (list-mode) data. For reference, SSD make use of NAND flash chips for storage instead of rotating media. Today, an SSD may readily exceed 100 Mbyte/sec for read/write throughput. Here a set of 4 SATA SSD are configured as an embedded 64-Gbyte RAID 0. A single FPGA implements the striping RAID controller. The resulting 4-channel RAID is expected to have a sustainable, aggregate bandwidth of at least 400 Mbyte/sec. The Stream Buffer concept requires high-speed, time-shared write/read access into/from this RAID. With both read and write accesses each available for sustainable 200 Mbyte/sec throughput, stream buffering improves PET data acquisition in several ways. Once the PET event stream is delivered to the FPGA which controls the embedded RAID - e.g. via 2 Gbps Fibre Channel, none of the event stream data need be lost because of insufficient bandwidth. A non-volatile copy of the raw 64-bit PET event stream data can always be preserved for optional post-acquisition processing whether on-line downstream processing is selected or not. The RAID (read) output proceeds only at the available downstream throughput rate - i.e. fully eliminating the critica- - lity of higher downstream throughput needed to prevent event loss. On-line cardiac and respiratory gating should also benefit.