title: The association of tumor-to-background ratios and SUVmax deviations related to point spread function and time-of-flight F18-FDG-PET/CT reconstruction in colorectal liver metastases.
abstract: BACKGROUND
  The maximum standardized uptake value (SUVmax) is a common clinical parameter for quantification in F18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT), but it is influenced by image reconstruction. The aim of this study was to analyze the association of SUVmax deviations related to point spread function (PSF) and time-of-flight (TOF) reconstruction with tumor-to-background ratios (TBR) in colorectal liver metastases (CRLM).
  
  
  METHODS
  Fifteen patients (f, 6; m, 9; median age, 59 years; range, 32 to 72 years) with 28 liver metastases were included retrospectively. FDG-PET/CT imaging (median activity, 237 MBq; range, 231 to 252 MBq; median uptake, 61 min; range, 55 to 67 min) was performed on a Siemens Biograph mCT 64 followed by image reconstruction using 3D-ordered subset expectation maximization (3D-OSEM) or 3D-OSEM with PSF modeling - both with and without TOF information. Differences in SUVmax were analyzed using the Friedman test and Wilcoxon test for paired non-parametric data. The correlation of inter-method differences with the lesions' TBR was studied using Spearman's rank correlation coefficient (rho). Differences between lesions with low (<4.8) and high (>4.8) TBR were analyzed using the Mann-Whitney U test (TBR measured with 3D-OSEM; binarized by its median).
  
  
  RESULTS
  There was a significant correlation of the lesions' TBR with relative SUVmax differences related to PSF (PSF + TOF vs. 3D-OSEM + TOF, rho = 0.61; PSF vs. 3D-OSEM, rho = 0.52) or TOF (PSF + TOF vs. PSF, rho = -0.58; 3D-OSEM + TOF vs. 3D-OSEM, rho = -0.61). Accordingly, PSF algorithms only showed higher SUVmax than non-PSF algorithms in lesions with a high TBR (median differences at low/high TBR, +2.6%/+9.1% [PSF + TOF vs. 3D-OSEM + TOF]; +0.7%/+6.4% [PSF vs. 3D-OSEM]). TOF integration also led to higher SUVmax but mainly at low TBR (low/high TBR, +10.4%/+1.8% [PSF + TOF vs. PSF]; +8.6%/-0.1% [3D-OSEM + TOF vs. 3D-OSEM]).
  
  
  CONCLUSIONS
  Both PSF and TOF reconstruction resulted in a substantial alteration of SUVmax in CRLM. TOF provided the highest SUVmax increase in low-contrast lesions while - vice versa - PSF showed the most relevant increase in high-contrast lesions. Thus, one should be aware that quantitative analyses of lesions with varying TBR, e.g., in radiotherapy or follow-up studies, may be mainly affected by either PSF or TOF reconstruction, respectively.
authors.affiliation: Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Julian Mm
authors.initials: JM
authors.lastname: Rogasch
authors.affiliation: Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Ingo G
authors.initials: IG
authors.lastname: Steffen
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, PET Center, Institute of Radiopharmaceutical Cancer Research, Bautzner Landstraße 400, Dresden, 01328 Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Hofheinz
authors.affiliation: Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Oliver S
authors.initials: OS
authors.lastname: Großer
authors.affiliation: Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Furth
authors.affiliation: Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Konrad
authors.initials: K
authors.lastname: Mohnike
authors.affiliation: Klinik für Strahlentherapie, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Hass
authors.affiliation: Klinik für Strahlentherapie, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Walke
authors.affiliation: Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Ivayla
authors.initials: I
authors.lastname: Apostolova
authors.affiliation: Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120 Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Amthauer
keywords: Colorectal liver metastases; F18-FDG-PET/CT; PSF; Reconstruction algorithm; SUVmax; TOF; Target volume definition; Tumor-to-background ratio