title: Phantom evaluation of a cardiac SPECT/VCT system that uses a common set of solid-state detectors for both emission and transmission scans.
abstract: BACKGROUND
  We developed a cardiac SPECT system (X-ACT) with low dose volume CT transmission-based attenuation correction (AC). Three solid-state detectors are configured to form a triple-head system for emission scans and reconfigured to form a 69-cm field-of-view detector arc for transmission scans. A near mono-energetic transmission line source is produced from the collimated fluorescence x-ray emitted from a lead target when the target is illuminated by a narrow polychromatic x-ray beam from an x-ray tube. Transmission scans can be completed in 1 min with insignificant patient dose (deep dose equivalent <5 muSv).
  
  
  METHODS
  We used phantom studies to evaluate (1) the accuracy of the reconstructed attenuation maps, (2) the effect of AC on image uniformity, and (3) the effect of AC on defect contrast (DC). The phantoms we used included an ACR phantom, an anthropomorphic phantom with a uniform cardiac insert, and an anthropomorphic phantom with two defects in the cardiac insert.
  
  
  RESULTS
  The reconstructed attenuation coefficient of water at 140 keV was .150 +/- .003/cm in the uniform region of the ACR phantom, .151 +/- .003/cm and .151 +/- .002/cm in the liver and cardiac regions of the anthropomorphic phantom. The ACR phantom images with AC showed correction of the bowing effect due to attenuation in the images without AC (NC). The 17-segment scores of the images of the uniform cardiac insert were 78.3 +/- 6.5 before and 87.9 +/- 3.3 after AC (average +/- standard deviation). The inferior-to-anterior wall ratio and the septal-to-lateral wall ratio were .99 and 1.16 before and 1.02 and 1.00 after AC. The DC of the two defects was .528 and .156 before and .628 and .173 after AC.
  
  
  CONCLUSIONS
  The X-ACT system generated accurate attenuation maps with 1-minute transmission scans. AC improved image quality and uniformity over NC.
authors.affiliation: Digirad Corporation, 13950 Stowe Drive, Poway, CA 92064, USA. chbai@digirad.com
authors.forename: Chuanyong
authors.initials: C
authors.lastname: Bai
authors.forename: Richard
authors.initials: R
authors.lastname: Conwell
authors.forename: Joel
authors.initials: J
authors.lastname: Kindem
authors.forename: Hetal
authors.initials: H
authors.lastname: Babla
authors.forename: Mike
authors.initials: M
authors.lastname: Gurley
authors.forename: Romer
authors.initials: R
authors.lastname: De Los Santos
authors.forename: Rex
authors.initials: R
authors.lastname: Old
authors.forename: Randy
authors.initials: R
authors.lastname: Weatherhead
authors.forename: Samia
authors.initials: S
authors.lastname: Arram
authors.forename: Jamshid
authors.initials: J
authors.lastname: Maddahi
mesh_terms: D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D055414:Myocardial Perfusion Imaging; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation* / Q000379:methods