An EM algorithm for estimating SPECT emission and transmission parameters from emission data only

• Published in: IEEE transactions on medical imaging Vol. 20; no. 3; pp. 218 - 232
• Main Authors: Krol, A., Bowsher, J.E., Manglos, S.H., Feiglin, D.H., Tornai, M.P., Thomas, F.D.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.03.2001; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Attenuation; Biological and medical sciences; Computer simulation; Emission; Estimates; Estimating; Humans; Image reconstruction; Imaging phantoms; Investigative techniques, diagnostic techniques (general aspects); Mathematical models; Maximum likelihood estimation; Medical sciences; Miscellaneous. Technology; Parameter estimation; Performance evaluation; Photons; Physics computing; Radionuclide investigations; Reconstruction; Single photon emission computed tomography; Studies; Testing; Thorax; Radionuclide study; Parameter estimation; Computer simulation; Emission; Photon; Image reconstruction; Attenuation coefficient; Statistical model; Simultaneous measurement; Maximum likelihood; EM algorithm; Test object; Emission tomography
• ISSN: 0278-0062; 1558-254X
• DOI: 10.1109/42.918472

A maximum-likelihood (ML) expectation-maximization (EM) algorithm (called EM-IntraSPECT) is presented for simultaneously estimating single photon emission computed tomography (SPECT) emission and attenuation parameters from emission data alone. The algorithm uses the activity within the patient as transmission tomography sources, with which attenuation coefficients can he estimated. For this initial study, EM-IntraSPECT was tested on computer-simulated attenuation and emission maps representing a simplified human thorax as well as on SPECT data obtained from a physical phantom. Two evaluations were performed. First, to corroborate the idea of reconstructing attenuation parameters from emission data, attenuation parameters (/spl mu/) were estimated with the emission intensities (/spl lambda/) fixed at their true values. Accurate reconstructions of attenuation parameters were obtained. Second, emission parameters /spl lambda/ and attenuation parameters Cl were simultaneously estimated from the emission data alone. In this case there was crosstalk between estimates of /spl lambda/ and /spl mu/ and final estimates of /spl lambda/ and /spl mu/ depended on initial values. Estimates degraded significantly as the support extended out farther from the body, and an explanation for this is proposed. In the EM-IntraSPECT reconstructed attenuation images, the lungs, spine, and soft tissue were readily distinguished and had approximately correct shapes and sizes. As compared with standard EM reconstruction assuming a fix uniform attenuation map, EM-IntraSPECT-provided more uniform estimates of cardiac activity in the physical phantom study and in the simulation study with tight support, but less uniform estimates with a broad support. The new EM algorithm derived here has additional applications, including reconstructing emission and transmission projection data under a unified statistical model.