title: Extracardiac activity complicates quantitative cardiac SPECT imaging using a simultaneous transmission-emission approach.
abstract: Increased extracardiac activity confounds conventional cardiac SPECT image reconstruction using a filtered backprojection method. Others have proposed that simultaneously acquired transmission-emission (STE) images that are reconstructed with a maximum likelihood (ML) method incorporating a nonuniform attenuation correction would less likely be affected by the presence of extracardiac activity. However, this approach corrects only for decreased myocardial counts from attenuation and not for increased myocardial counts from extracardiac activity. Therefore, STE with nonuniform attenuation correction may also result in reconstruction artifacts when extracardiac activity is present.
  
  
  METHODS
  Acquisitions of phantoms with nonuniform and uniform attenuation were performed using STE and conventional approaches, in the absence and presence of extracardiac activity. All acquisitions used a triple-headed SPECT camera. STE acquisitions used fanbeam collimation and a 153Gd transmission source. STE images were reconstructed using ML, with and without nonuniform attenuation correction. Reconstructed short-axis images were quantitated, and percentage variability for each count profile was calculated.
  
  
  RESULTS
  In a nonuniform phantom configuration, STE reconstruction with nonuniform attenuation correction significantly improved image uniformity. This improvement in image uniformity was diminished with the addition of increasing extracardiac activity. In a uniform phantom, STE reconstruction with nonuniform attenuation correction significantly improved uniformity only in the presence of extracardiac activity.
  
  
  CONCLUSIONS
  The addition of attenuation correction in the presence of extracardiac activity can have complex effects on ML reconstruction with nonuniform attenuation correction, which depends on the amount of extracardiac activity and pattern of attenuation.
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8042, USA.
authors.forename: E N
authors.initials: EN
authors.lastname: Heller
authors.forename: P
authors.initials: P
authors.lastname: DeMan
authors.forename: Y H
authors.initials: YH
authors.lastname: Liu
authors.forename: D P
authors.initials: DP
authors.lastname: Dione
authors.forename: I G
authors.initials: IG
authors.lastname: Zubal
authors.forename: F J
authors.initials: FJ
authors.lastname: Wackers
authors.forename: A J
authors.initials: AJ
authors.lastname: Sinusas
mesh_terms: D016477:Artifacts; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D016013:Likelihood Functions; D008099:Liver / Q000000981:diagnostic imaging; D015609:Organotechnetium Compounds; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation / Q000379:methods*
chemical_list: D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals