Ordered subset expectation maximization
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Ordered subset expectation maximization (OSEM) is an expectation maximization (EM) algorithm widely used in medical imaging for positron emission tomography, single photon emission computed tomography and less frequently for X-ray computed tomography.
It improves upon the speed of previous EM techniques and improves upon the quality of previous FBP (filtered back projection) techniques.
References
Hudson, H.M., Larkin, R.S. (1994) "Accelerated image reconstruction using ordered subsets of projection data", IEEE Trans. Medical Imaging, XX, 100–108