title: A Monte Carlo study for optimizing the detector of SPECT imaging using a XCAT human phantom.
abstract: BACKGROUND
  Acquiring a high quality image has assigned an important concern for obtaining accurate diagnosis in nuclear medicine. Detector is a critical component of Single Photon Emission Computed Tomography (SPECT) imaging system for giving accurate information from exact pattern of radionuclide distribution in the target organ. The images are strongly affected by the attenuation, scattering, and response of the detector. The conventional detector is mainly made from sodium iodide activated by thallium [NaI(Tl)] in nuclear medicine imaging.
  
  
  OBJECTIVE
  This study has planned to introduce a suitable for an optimized SPECT imaging. SIMIND Monte Carlo program was utilized for simulating a SPECT imaging system with a NaI(Tl) detector, and a low-energy high-resolution (LEHR) collimator.
  
  
  METHODS
  The Planar and SPECT scans of a 99mTc point source and also an extended Cardiac-Torso (XCAT) computerized phantom with the experiment and simulated systems were prepared. After verification and validation of the simulated system, the similar scans of the phantoms were compared from the point of view of image quality for 7 scintillator crystals including: NaI(Tl), BGO, YAG:Ce, YAP:Ce, LuAG:Ce, LaBr3 and CZT. The parameters of energy and spatial resolution, and sensitivity of the systems were compared. Images were analyzed quantitatively by SSIM algorithm with Zhou Wang and Rouse/Hemami methods, and also qualitatively by two nuclear medicine specialists.
  
  
  RESULTS
  Energy resolutions of the mentioned crystals obtained were: 9.864, 9.8545, 10.229, 10.221, 10.230, 10.131and10.223 percentage for 99mTc photopeak 140 Kev, respectively. Finally, SSIM indexes for the related phantom images were calculated to 0.794, 0.738, 0.735, 0.607, 0.760 and 0.811 compared to the NaI(Tl) acquired images, respectively. Medical diagnosis of the SPECT images of the phantom showed that the system with BGO crystal potentially provides a better detectability for hot and cold lesions in the liver of XCAT phantom.
  
  
  CONCLUSIONS
  The results showed that BGO crystal has a high sensitivity and resolution, and also provides a better lesion detectability from the point of view of image quality on XCAT phantom.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Khoshakhlagh
authors.affiliation: Department of Medical Physics, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran. pirayeshj@gmail.com.
authors.forename: Jalil
authors.initials: J
authors.lastname: Pirayesh Islamian
authors.forename: Seyyed Mohammad
authors.initials: SM
authors.lastname: Abedi
authors.forename: Babak
authors.initials: B
authors.lastname: Mahmoudian
authors.forename: Masoud
authors.initials: M
authors.lastname: Shayesteh Azar
mesh_terms: D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D015233:Models, Statistical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation*; D014159:Transducers
keywords: SIMIND simulation; SSIM algorithm; XCAT phantom; gamma detector