title: Accuracy of 3-dimensional reconstruction algorithms for the high-resolution research tomograph.
abstract: The high-resolution research tomograph (HRRT) is a dedicated human brain PET scanner. At present, iterative reconstruction methods are preferred for reconstructing HRRT studies. However, these iterative reconstruction algorithms show bias in short-duration frames. New algorithms such as the shifted Poisson ordered-subsets expectation maximization (SP-OSEM) and ordered-subsets weighted least squares (OSWLS) showed promising results in bias reduction, compared with the recommended ordinary Poisson OSEM (OP-OSEM). The goal of this study was to evaluate quantitative accuracy of these iterative reconstruction algorithms, compared with 3-dimensional filtered backprojection (3D-FBP).
  
  
  METHODS
  The 3 above-mentioned 3D iterative reconstruction methods were implemented for the HRRT. To evaluate the various 3D iterative reconstruction techniques quantitatively, several phantom studies and a human brain study (n=5) were performed.
  
  
  RESULTS
  OSWLS showed a low and almost linearly increasing coefficient of variation (SD over average activity concentration), with decreasing noise-equivalent count rates. In decay studies, OSWLS showed good agreement with the 3D-FBP gray matter (GM)-to-white matter (WM) contrast ratio (<4%), and OP-OSEM and SP-OSEM showed agreement within 6% and 7%, respectively. For various frame durations, both SP-OSEM and OP-OSEM showed the fewest errors in GM-to-WM contrast ratios, varying 75% between different noise-equivalent count rates; this variability was much higher for other iterative methods (>92%). 3D-FBP showed the least variability (34%). Visually, OSWLS hardly showed any artifacts in parametric images and showed good agreement with 3D-FBP data for parametric images, especially in the case of reference-tissue kinetic methods (slope, 1.02; Pearson correlation coefficient, 0.99).
  
  
  CONCLUSIONS
  OP-OSEM, SP-OSEM, and OSWLS showed good performance for phantom studies. In addition, OSWLS showed better results for parametric analysis of clinical studies and is therefore recommended for quantitative HRRT brain PET studies.
authors.affiliation: Department of Nuclear Medicine & PET Research, VU University medical center, Amsterdam, The Netherlands. f.vvelden@vumc.nl
authors.forename: Floris H P
authors.initials: FH
authors.lastname: van Velden
authors.forename: Reina W
authors.initials: RW
authors.lastname: Kloet
authors.forename: Bart N M
authors.initials: BN
authors.lastname: van Berckel
authors.forename: Adriaan A
authors.initials: AA
authors.lastname: Lammertsma
authors.forename: Ronald
authors.initials: R
authors.lastname: Boellaard
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging; D002250:Carbon Radioisotopes / Q000737:chemistry; D003080:Cold Temperature; D005442:Flumazenil / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography; D012680:Sensitivity and Specificity
chemical_list: D002250:Carbon Radioisotopes; D005442:Flumazenil