title: Compartment modeling of dynamic brain PET--the impact of scatter corrections on parameter errors.
abstract: OBJECTIVE
  The aim of this study was to investigate the effect of scatter and its correction on kinetic parameters in dynamic brain positron emission tomography (PET) tumor imaging. The 2-tissue compartment model was used, and two different reconstruction methods and two scatter correction (SC) schemes were investigated.
  
  
  METHODS
  The gate Monte Carlo (MC) software was used to perform 2 × 15 full PET scan simulations of a voxelized head phantom with inserted tumor regions. The two sets of kinetic parameters of all tissues were chosen to represent the 2-tissue compartment model for the tracer 3'-deoxy-3'-((18)F)fluorothymidine (FLT), and were denoted FLT1 and FLT2. PET data were reconstructed with both 3D filtered back-projection with reprojection (3DRP) and 3D ordered-subset expectation maximization (OSEM). Images including true coincidences with attenuation correction (AC) and true+scattered coincidences with AC and with and without one of two applied SC schemes were reconstructed. Kinetic parameters were estimated by weighted nonlinear least squares fitting of image derived time-activity curves. Calculated parameters were compared to the true input to the MC simulations.
  
  
  RESULTS
  The relative parameter biases for scatter-eliminated data were 15%, 16%, 4%, 30%, 9%, and 7% (FLT1) and 13%, 6%, 1%, 46%, 12%, and 8% (FLT2) for K1, k2, k3, k4, Va, and Ki, respectively. As expected, SC was essential for most parameters since omitting it increased biases by 10 percentage points on average. SC was not found necessary for the estimation of Ki and k3, however. There was no significant difference in parameter biases between the two investigated SC schemes or from parameter biases from scatter-eliminated PET data. Furthermore, neither 3DRP nor OSEM yielded the smallest parameter biases consistently although there was a slight favor for 3DRP which produced less biased k3 and Ki estimates while OSEM resulted in a less biased Va. The uncertainty in OSEM parameters was about 26% (FLT1) and 12% (FLT2) larger than for 3DRP although identical postfilters were applied.
  
  
  CONCLUSIONS
  SC was important for good parameter estimations. Both investigated SC schemes performed equally well on average and properly corrected for the scattered radiation, without introducing further bias. Furthermore, 3DRP was slightly favorable over OSEM in terms of kinetic parameter biases and SDs.
authors.affiliation: Department of Radiation Sciences, Umeå University, Umeå 90187, Sweden.
authors.forename: Ida
authors.initials: I
authors.lastname: Häggström
authors.affiliation: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York 10065.
authors.forename: C Ross
authors.initials: CR
authors.lastname: Schmidtlein
authors.affiliation: Department of Radiation Sciences, Umeå University, Umeå 90187, Sweden.
authors.forename: Mikael
authors.initials: M
authors.lastname: Karlsson
authors.affiliation: Department of Radiation Sciences, Umeå University, Umeå 90187, Sweden.
authors.forename: Anne
authors.initials: A
authors.lastname: Larsson
mesh_terms: D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging*; D006257:Head; D007091:Image Processing, Computer-Assisted; D007700:Kinetics; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography; D012542:Scattering, Radiation; D012984:Software