title: Optimization of time-of-flight reconstruction on Philips GEMINI TF.
abstract: OBJECTIVE
  The aim of this study is to optimize different parameters in the time-of-flight (TOF) reconstruction for the Philips GEMINI TF. The use of TOF in iterative reconstruction introduces additional variables to be optimized compared to conventional PET reconstruction. The different parameters studied are the TOF kernel width, the kernel truncation (used to reduce reconstruction time) and the scatter correction method.
  
  
  METHODS
  These parameters are optimized using measured phantom studies. All phantom studies were acquired with a very high number of counts to limit the effects of noise. A high number of iterations (33 subsets and 3 iterations) was used to reach convergence. The figures of merit are the uniformity in the background, the cold spot recovery and the hot spot contrast. As reference results we used the non-TOF reconstruction of the same data sets.
  
  
  RESULTS
  It is shown that contrast recovery loss can only be avoided if the kernel is extended to more than 3 standard deviations. To obtain uniform reconstructions the recommended scatter correction is TOF single scatter simulation (SSS). This also leads to improved cold spot recovery and hot spot contrast. While the daily measurements of the system show a timing resolution in the range of 590–600 ps, the optimal reconstructions are obtained with a TOF kernel full-width at half-maximum (FWHM) of 650–700 ps. The optimal kernel width seems to be less critical for the recovered contrast but has an important effect on the background uniformity. Using smaller or wider kernels results in a less uniform background and reduced hot and cold contrast recovery.
  
  
  CONCLUSIONS
  The different parameters studied have a large effect on the quantitative accuracy of the reconstructed images. The optimal settings from this study can be used as a guideline to make an objective comparison of the gains obtained with TOF PET versus PET reconstruction.
authors.affiliation: MEDISIP Research Group ELIS-IBBT-IBITECH, Ghent University, University Hospital Ghent, De Pintelaan 185, Blok B, 9000 Ghent, Belgium. Stefaan.Vandenberghe@Ugent.be
authors.forename: Stefaan
authors.initials: S
authors.lastname: Vandenberghe
authors.forename: Larry
authors.initials: L
authors.lastname: van Elmbt
authors.forename: Michel
authors.initials: M
authors.lastname: Guerchaft
authors.forename: Enrico
authors.initials: E
authors.lastname: Clementel
authors.forename: Jeroen
authors.initials: J
authors.lastname: Verhaeghe
authors.forename: Anne
authors.initials: A
authors.lastname: Bol
authors.forename: Ignace
authors.initials: I
authors.lastname: Lemahieu
authors.forename: Max
authors.initials: M
authors.lastname: Lonneux
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D012542:Scattering, Radiation; D013997:Time Factors