A hardware projector/backprojector pair for 3D PET reconstruction

Abstract

Forward and Backward projections are two computational costly stepsin tomography image reconstruction such as Positron Emission Tomography(PET). To speed-up reconstruction time, a hardware projection/backprojectionpair has been built following algorithm architecture adequacy principles.Thanks to an original memory access strategy based on an 3D adaptiveand predictive memory cache, the external memory wall has been overcome.Thus, for both projector architectures several units run efficiently.Each unit reaches a computational throughput close to 1 operationper cycle.In this paper, we present how from our hardware projection/backprojectionpair, an analytic (3D-RP) and an iterative (3D-EM) reconstructionalgorithms can be implemented on a System on Programmable Chip (SoPC).First, an hardware/software partitioning is done based on the differentsteps of each algorithm. Then the reconstruction system is composedof two hardware configurations of the programmable logic resources(FPGA). Each one corresponds mainly to the projection and backprojectionstep.Our projector/backprojector has been validated with a software 3D-RPand 3D-EM reconstruction on simulated PET-SORTEO data. A reconstructiontime evaluation of these reconstruction systems are done based onthe measured performances of our projectors IPs and the estimatedperformances of the additional simple hardware IPs. The expectedreconstruction time is compared with the software tomography distributionSTIR. A speed-up of 7 can be expected for the 3D-RP algorithm anda speed-up of 3.5 for the 3D-EM algorithm. For both algorithms, thearchitecture cycle efficiency expected is largely greater than thesoftware implementation : 120 times for 3D-RP and 60 times for 3D-EM.