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Comparing Filtered Backprojection and Ordered-Subsets Expectation Maximization for Small-Lesion Detection and Localization in ⁶⁷Ga SPECT

University of Massachusetts Medical Center, Worcester
Brigham and Women's Hospital, Boston
Lahey Clinic Medical Center, Burlington, Massachusetts

Correspondence: For correspondence or reprints contact: R. Glenn Wells, PhD, Division of Nuclear Medicine, University of Massachusetts Medical Center, Worcester, MA 01655.

ABSTRACT

Iterative reconstruction of SPECT images has recently become clinically available as an alternative to filtered backprojection (FBP). However, there is conflicting evidence on whether iterative reconstruction, such as with the ordered-subsets expectation maximization (OSEM) algorithm, improves diagnostic performance over FBP. The study objective was to determine if the detection and localization of small lesions in simulated thoracic gallium SPECT images are better with OSEM reconstruction than with FBP, both with and without attenuation correction (AC). Methods: Images were simulated using an analytic projector acting on the mathematic cardiac torso computer phantom. Perfect scatter rejection was assumed. Lesion detection accuracy was assessed using localization receiver operating characteristic methodology. The images were read by 5 nuclear medicine physicians. For each reconstruction strategy and for each observer, data were collected in 2 viewing sessions of 100 images. Two-way ANOVA and, when indicated, the Scheffe multiple comparisons test were applied to check for significant differences. Results: Little difference in the accuracy of detection or localization was seen between FBP with and without AC. OSEM with AC extended the contrast range for accurate lesion detection and localization over that of the other methods investigated. Without AC, no significant difference between OSEM and FBP reconstruction was detected. Conclusion: OSEM with AC may improve the detection and localization of thoracic gallium-labeled lesions over FBP reconstruction.

Key Words: localization receiver operating characteristic • filtered backprojection • ordered-subsets expectation maximization • attenuation correction

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