title: Respiratory average CT for attenuation correction in myocardial perfusion SPECT/CT.
abstract: OBJECTIVE
  Cine average CT (CACT) and interpolated average CT (IACT) have been proposed to improve attenuation correction (AC) for PET/CT in oncologic and cardiac studies. This study aims to evaluate their effectiveness on myocardial perfusion SPECT/CT using computer simulation and physical phantom experiments.
  
  
  METHODS
  We first simulated normal male with99mTc-sestamibi distribution using digital XCAT phantom with respiratory motion amplitudes of 2, 3, and 4 cm. Average activity and attenuation maps represented static SPECT and CACT, while the attenuation maps of end-inspiration and end-expiration represented two helical CTs (HCTs), respectively. Sixty noise-free and noisy projections were simulated over 180° using an analytical parallel-hole projector. We then filled 673 MBq99mTc into an anthropomorphic torso phantom with normal heart or heart with a defect which placed on a programmable respiratory platform to model various respiratory amplitudes. Sixty projections were acquired over 180° using a clinical SPECT/CT scanner. The CACT, standard HCT, and 2 HCTs at extreme phases were acquired. Interpolated CT phases were generated between them using affine plus b-spline registration, and IACT was obtained by averaging the interpolated phases and the 2 original extreme phases for both simulation and phantom experiments. Projections were reconstructed with AC using CACT, IACT, and HCTs, respectively. Polar and 17-segment plots were analyzed by relative difference (RD) of the uptake. Two regions-of-interest (ROI) were drawn on the defect and background area to obtain the intensity ratio (IR).
  
  
  RESULTS
  No substantial difference was observed on the polar plots generated from different AC methods, while the quantitative RD measurements showed that SPECTCACTwere most similar to the original phantom, followed by SPECTIACT, with RDmax<8 and <10% in the simulation study. The RD of SPECTHCTsdeviated from the original phantom and SPECTCACTin various segments, with RDmaxof 19.76 and 16.68% in the simulation and phantom experiment, respectively. The IR of SPECTHCTsfluctuated more from the truth for higher motion amplitude.
  
  
  CONCLUSIONS
  Both CACT-AC and IACT-AC reduced respiratory artifacts and improved quantitation in myocardial perfusion SPECT as compared to HCT-AC. The use of IACT further reduced the radiation dose.
authors.affiliation: Biomedical Imaging Laboratory, Department of Electrical and Computer Engineering, Faculty of Science and Technology, University of Macau, Avenida da Universidade, Taipa, Macau SAR, China.
authors.forename: Duo
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taipei, Taiwan.|Department of Nuclear Medicine, National PET/Cyclotron Center, Taipei Veterans General Hospital, Taipei, Taiwan.
authors.forename: Bang-Hung
authors.initials: BH
authors.lastname: Yang
authors.affiliation: Department of Biomedical Imaging and Radiological Sciences, National Yang Ming University, Taipei, Taiwan.|Department of Nuclear Medicine, National PET/Cyclotron Center, Taipei Veterans General Hospital, Taipei, Taiwan.
authors.forename: Nien Yun
authors.initials: NY
authors.lastname: Wu
authors.affiliation: Biomedical Imaging Laboratory, Department of Electrical and Computer Engineering, Faculty of Science and Technology, University of Macau, Avenida da Universidade, Taipa, Macau SAR, China. gretamok@umac.mo.
authors.forename: Greta Seng Peng
authors.initials: GS
authors.lastname: Mok
mesh_terms: D016477:Artifacts; D003198:Computer Simulation; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008953:Models, Anatomic; D009038:Motion; D055414:Myocardial Perfusion Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals; D012119:Respiration; D000072098:Single Photon Emission Computed Tomography Computed Tomography / Q000379:methods*; D017256:Technetium Tc 99m Sestamibi; D060726:Torso / Q000000981:diagnostic imaging
chemical_list: D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi
keywords: Attenuation correction; Myocardial perfusion; Respiratory artifacts; SPECT/CT