EM‐ML PET reconstruction on multiple processors with reduced communications

Positron emission tomography (PET) reconstruction by the EM algorithm is an iterative computation of Poisson emission rates to maximize a likelihood function. The method is time consuming and, for real scanner data, requires large numerical arrays. To speed up the computation on multiple processors which have their own local memory and communicate by passing messages on a network, a parallel method has been implemented in which processors compute several iterations before exchanging their latest data with other processors. This method is convenient for iterative reconstruction using a relatively small number of interconnected, standard processors such as workstations on a local‐area network. Computational aspects of the method are explained and illustrated with two‐dimensional reconstructions from a simulation and from sinograms produced by a PET scanner. Five hundred twelve (512) iterations are computed on a local‐area network of workstations and, for reference, on a distributed‐memory multiprocessor computer. The method is capable of producing high‐quality reconstructions with significant speed‐up. © 1996 John Wiley & Sons, Inc.