The influence of different signal-to-background ratios on spatial resolution and F18-FDG-PET quantification using point spread function and time-of-flight reconstruction.
BACKGROUND
F18-fluorodeoxyglucose positron-emission tomography (FDG-PET) reconstruction algorithms can have substantial influence on quantitative image data used, e.g., for therapy planning or monitoring in oncology. We analyzed radial activity concentration profiles of differently reconstructed FDG-PET images to determine the influence of varying signal-to-background ratios (SBRs) on the respective spatial resolution, activity concentration distribution, and quantification (standardized uptake value [SUV], metabolic tumor volume [MTV]).


METHODS
Measurements were performed on a Siemens Biograph mCT 64 using a cylindrical phantom containing four spheres (diameter, 30 to 70 mm) filled with F18-FDG applying three SBRs (SBR1, 16:1; SBR2, 6:1; SBR3, 2:1). Images were reconstructed employing six algorithms (filtered backprojection [FBP], FBP + time-of-flight analysis [FBP + TOF], 3D-ordered subset expectation maximization [3D-OSEM], 3D-OSEM + TOF, point spread function [PSF], PSF + TOF). Spatial resolution was determined by fitting the convolution of the object geometry with a Gaussian point spread function to radial activity concentration profiles. MTV delineation was performed using fixed thresholds and semiautomatic background-adapted thresholding (ROVER, ABX, Radeberg, Germany).


RESULTS
The pairwise Wilcoxon test revealed significantly higher spatial resolutions for PSF + TOF (up to 4.0 mm) compared to PSF, FBP, FBP + TOF, 3D-OSEM, and 3D-OSEM + TOF at all SBRs (each P < 0.05) with the highest differences for SBR1 decreasing to the lowest for SBR3. Edge elevations in radial activity profiles (Gibbs artifacts) were highest for PSF and PSF + TOF declining with decreasing SBR (PSF + TOF largest sphere; SBR1, 6.3%; SBR3, 2.7%). These artifacts induce substantial SUVmax overestimation compared to the reference SUV for PSF algorithms at SBR1 and SBR2 leading to substantial MTV underestimation in threshold-based segmentation. In contrast, both PSF algorithms provided the lowest deviation of SUVmean from reference SUV at SBR1 and SBR2.


CONCLUSIONS
At high contrast, the PSF algorithms provided the highest spatial resolution and lowest SUVmean deviation from the reference SUV. In contrast, both algorithms showed the highest deviations in SUVmax and threshold-based MTV definition. At low contrast, all investigated reconstruction algorithms performed approximately equally. The use of PSF algorithms for quantitative PET data, e.g., for target volume definition or in serial PET studies, should be performed with caution - especially if comparing SUV of lesions with high and low contrasts.
Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. julian.rogasch@st.ovgu.de.
Julian Mm
JM
Rogasch
PET Center, Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Landstraße 400, Dresden, 01328, Germany. hofheinz@hzdr.de.
Frank
F
Hofheinz
PET Center, Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Landstraße 400, Dresden, 01328, Germany. a.lougovski@hzdr.de.
Alexandr
A
Lougovski
Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. christian.furth@med.ovgu.de.
Christian
C
Furth
Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. juri.ruf@uniklinik-freiburg.de.|Klinik für Nuklearmedizin, Universitätsklinikum Freiburg, Hugstetter Straße 55, Freiburg im Breisgau, 79106, Germany. juri.ruf@uniklinik-freiburg.de.
Juri
J
Ruf
Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. oliver.grosser@med.ovgu.de.
Oliver S
OS
Großer
Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. konrad.mohnike@med.ovgu.de.
Konrad
K
Mohnike
Klinik für Strahlentherapie, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. peter.hass@med.ovgu.de.
Peter
P
Hass
Klinik für Strahlentherapie, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. mathias.walke@med.ovgu.de.
Mathias
M
Walke
Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. holger.amthauer@med.ovgu.de.
Holger
H
Amthauer
Klinik für Radiologie und Nuklearmedizin, Universitätsklinikum Magdeburg A.ö.R., Otto-von-Guericke Universität Magdeburg, Leipziger Straße 44, Magdeburg, 39120, Germany. ingo.steffen@med.ovgu.de.
Ingo G
IG
Steffen
FDG-PET/CT reconstruction; Gibbs artifact; Gibbs phenomenon; Metabolic tumor volume delineation; PSF; Radial activity concentration profile; Ringing artifact; Signal-to-background ratio; Spatial resolution; TOF