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An iterative transmission algorithm incorporating cross‐talk correction for SPECT
Author(s) -
Narayanan Manoj V.,
King Michael A.,
Byrne Charles L.
Publication year - 2002
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1472500
Subject(s) - attenuation , correction for attenuation , iterative reconstruction , algorithm , transmission (telecommunications) , subtraction , single photon emission computed tomography , attenuator (electronics) , emission computed tomography , computer science , physics , projection (relational algebra) , optics , mathematics , computer vision , nuclear medicine , positron emission tomography , telecommunications , medicine , arithmetic
Simultaneous emission/transmission acquisitions in cardiac SPECT with a Tc 99 m/ Gd 153source combination offer the capability for nonuniform attenuation correction. However, cross‐talk of Tc 99 mphotons downscattered into the Gd 153energy window contaminates the reconstructed transmission map used for attenuation correction. The estimated cross‐talk contribution can be subtracted prior to transmission reconstruction or incorporated in the reconstruction algorithm itself. In this work, we propose an iterative transmission algorithm (MLTG‐S) based on the maximum‐likelihood gradient algorithm (MLTG) that explicitly accounts for this cross‐talk estimate. Clinical images were acquired on a three‐headed SPECT camera, acquiring Tc 99 memission and Gd 153transmission images simultaneously. Subtracting the cross‐talk estimate prior to transmission reconstruction can result in negative and zero values if the estimate is larger than or equal to the count in the transmission projection bin, especially with increased attenuator size or amount of cross‐talk. This results in inaccurate attenuation coefficients for MLTG reconstructions with cross‐talk subtraction. MLTG‐S reconstructions on the other hand, yield better estimates of attenuation maps, by avoiding the subtraction of the cross‐talk estimate. Comparison of emission slices corrected for nonuniform attenuation reveals that inaccuracies in the reconstructed attenuation map caused by cross‐talk can artificially enhance the extra‐cardiac activity, confounding the ability to visualize the left‐ventricular walls.