title: Voxel-based comparison of state-of-the-art reconstruction algorithms for 18F-FDG PET brain imaging using simulated and clinical data.
abstract: The resolution of a PET scanner (2.5-4.5mm for brain imaging) is similar to the thickness of the cortex in the (human) brain (2.5mm on average), hampering accurate activity distribution reconstruction. Many techniques to compensate for the limited resolution during or post-reconstruction have been proposed in the past and have been shown to improve the quantitative accuracy. In this study, state-of-the-art reconstruction techniques are compared on a voxel-basis for quantification accuracy and group analysis using both simulated and measured data of healthy volunteers and patients with epilepsy.
  
  
  METHODS
  Maximum a posteriori (MAP) reconstructions using either a segmentation-based or a segmentation-less anatomical prior were compared to maximum likelihood expectation maximization (MLEM) reconstruction with resolution recovery. As anatomical information, a spatially aligned 3D T1-weighted magnetic resonance image was used. Firstly, the algorithms were compared using normal brain images to detect systematic bias with respect to the true activity distribution, as well as systematic differences between two methods. Secondly, it was verified whether the algorithms yielded similar results in a group comparison study.
  
  
  RESULTS
  Significant differences were observed between the reconstructed and the true activity, with the largest errors when using (post-smoothed) MLEM. Only 5-10% underestimation in cortical gray matter voxel activity was found for both MAP reconstructions. Higher errors were observed at GM edges. MAP with the segmentation-based prior also resulted in a significant bias in the subcortical regions due to segmentation inaccuracies, while MAP with the anatomical prior which does not need segmentation did not. Significant differences in reconstructed activity were also found between the algorithms at similar locations (mainly in gray matter edge voxels and in cerebrospinal fluid voxels) in the simulated as well as in the clinical data sets. Nevertheless, when comparing two groups, very similar regions of significant hypometabolism were detected by all algorithms.
  
  
  CONCLUSIONS
  Including anatomical a priori information during reconstruction in combination with resolution modeling yielded accurate gray matter activity estimates, and a significant improvement in quantification accuracy was found when compared to post-smoothed MLEM reconstruction with resolution modeling. AsymBowsher provided the most accurate subcortical GM activity estimates. It is also reassuring that the differences found between the algorithms did not hamper the detection of hypometabolic regions in the gray matter when performing a voxel-based group comparison. Nevertheless, the size of the detected clusters differed. More elaborated and application-specific studies are required to decide which algorithm is best for a group analysis.
authors.affiliation: KU Leuven - University of Leuven, Department of Imaging & Pathology, Nuclear Medicine & Molecular Imaging, Herestraat 49, B-3000 Leuven, Belgium; KU Leuven - University of Leuven, University Hospitals Leuven, Medical Imaging Research Center (MIRC), Herestraat 49, B-3000 Leuven, Belgium. Electronic address: Kathleen.Vunckx@uz.kuleuven.be.
authors.forename: K
authors.initials: K
authors.lastname: Vunckx
authors.affiliation: KU Leuven - University of Leuven, University Hospitals Leuven, Medical Imaging Research Center (MIRC), Herestraat 49, B-3000 Leuven, Belgium; KU Leuven - University of Leuven, Department of Neurosciences, Lab. for Cognitive Neurology, Herestraat 49, B-3000 Leuven, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Dupont
authors.affiliation: KU Leuven - University of Leuven, Department of Imaging & Pathology, Nuclear Medicine & Molecular Imaging, Herestraat 49, B-3000 Leuven, Belgium; KU Leuven - University of Leuven, University Hospitals Leuven, Medical Imaging Research Center (MIRC), Herestraat 49, B-3000 Leuven, Belgium; University Hospitals Leuven, Department of Nuclear Medicine, Herestraat 49, B-3000 Leuven, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Goffin
authors.affiliation: KU Leuven - University of Leuven, University Hospitals Leuven, Medical Imaging Research Center (MIRC), Herestraat 49, B-3000 Leuven, Belgium; KU Leuven - University of Leuven, Department of Neurosciences, Lab. for Epilepsy Research, Herestraat 49, B-3000 Leuven, Belgium; University Hospitals Leuven, Department of Neurology, Herestraat 49, B-3000 Leuven, Belgium.
authors.forename: W
authors.initials: W
authors.lastname: Van Paesschen
authors.affiliation: KU Leuven - University of Leuven, Department of Imaging & Pathology, Nuclear Medicine & Molecular Imaging, Herestraat 49, B-3000 Leuven, Belgium; KU Leuven - University of Leuven, University Hospitals Leuven, Medical Imaging Research Center (MIRC), Herestraat 49, B-3000 Leuven, Belgium; University Hospitals Leuven, Department of Nuclear Medicine, Herestraat 49, B-3000 Leuven, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Van Laere
authors.affiliation: KU Leuven - University of Leuven, Department of Imaging & Pathology, Nuclear Medicine & Molecular Imaging, Herestraat 49, B-3000 Leuven, Belgium; KU Leuven - University of Leuven, University Hospitals Leuven, Medical Imaging Research Center (MIRC), Herestraat 49, B-3000 Leuven, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Nuyts
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging*; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: (18)F-FDG PET; Anatomical prior; Brain imaging; Iterative reconstruction; Voxel-based comparison