3-D MAXIMUM A POSTERIORI ESTIMATION FOR SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY ON MASSIVELY-PARALLEL COMPUTERS

Since the introduction by Shepp and Vardi [1] of the expectation-maximization (EM) algorithm for generating maximum likelihood (ML) and maximum a posteriori (MAP) estimates in emission tomography, there have been many investigators applying the ML method. However, almost all of the previous work has been restricted to 2-dimensional reconstructions. The major focus and contribution of this paper is to demonstrate a fully 3-dimensional implementation of the MAP method for single photon emission computed tomography (SPECT). The 3-dimensional reconstruction exhibits a major increase in resolution when compared to the generation of the series of separate 2-dimensional slice reconstructions. As has been noted, the iterative EM algorithm for 2-dimensional reconstruction is highly computational; the 3-dimensional algorithm is far worse. To accommodate the computational complexity, we have extended our previous work in the 2-dimensional arena [2]-[4] and demonstrate an implementation on the class of massively parallel processors of the 3-dimensional algorithm. Using a 16 000 (4000) processor MasPar/DECmpp-Sx machine, the algorithm is demonstrated to execute at 2.5 (7.8) sec/EM-iteration for the entire 64x64x64 cube of % planar measurements obtained from the Siemens Orbiter rotating camera operating in the high resolution mode.