title: Impact of Point-Spread Function Modeling on PET Image Quality in Integrated PET/MR Hybrid Imaging.
abstract: The aim of this study was to systematically assess the quantitative and qualitative impact of including point-spread function (PSF) modeling into the process of iterative PET image reconstruction in integrated PET/MR imaging.
  
  
  METHODS
  All measurements were performed on an integrated whole-body PET/MR system. Three substudies were performed: an (18)F-filled Jaszczak phantom was measured, and the impact of including PSF modeling in ordinary Poisson ordered-subset expectation maximization reconstruction on quantitative accuracy and image noise was evaluated for a range of radial phantom positions, iteration numbers, and postreconstruction smoothing settings; 5 representative datasets from a patient population (total n = 20, all oncologic (18)F-FDG PET/MR) were selected, and the impact of PSF on lesion activity concentration and image noise for various iteration numbers and postsmoothing settings was evaluated; and for all 20 patients, the influence of PSF modeling was investigated on visual image quality and number of detected lesions, both assessed by clinical experts. Additionally, the influence on objective metrics such as changes in SUVmean, SUVpeak, SUVmax, and lesion volume was assessed using the manufacturer-recommended reconstruction settings.
  
  
  RESULTS
  In the phantom study, PSF modeling significantly improved activity recovery and reduced the image noise at all radial positions. This effect was measurable only at a high number of iterations (>10 iterations, 21 subsets). In the patient study, again, PSF increased the detected activity in the patient's lesions at concurrently reduced image noise. Contrary to the phantom results, the effect was notable already at a lower number of iterations (>1 iteration, 21 subsets). Lastly, for all 20 patients, when PSF and no-PSF reconstructions were compared, an identical number of congruent lesions was found. The overall image quality of the PSF reconstructions was rated better when compared with no-PSF data. The SUVs of the detected lesions with PSF were substantially increased in the range of 6%-75%, 5%-131%, and 5%-148% for SUVmean, SUVpeak, and SUVmax, respectively. A regression analysis showed that the relative increase in SUVmean/peak/max decreases with increasing lesion size, whereas it increases with the distance from the center of the PET field of view.
  
  
  CONCLUSIONS
  In whole-body PET/MR hybrid imaging, PSF-based PET reconstructions can improve activity recovery and image noise, especially at lateral positions of the PET field of view. This has been demonstrated quantitatively in phantom experiments as well as in patient imaging, for which additionally an improvement of image quality could be observed.
authors.affiliation: Institute of Medical Physics, Friedrich-Alexander-University of Erlangen-Nürnberg, Erlangen, Germany bassim.aklan@imp.uni-erlangen.de.
authors.forename: Bassim
authors.initials: B
authors.lastname: Aklan
authors.affiliation: High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Oehmigen
authors.affiliation: Institute for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany.
authors.forename: Karsten
authors.initials: K
authors.lastname: Beiderwellen
authors.affiliation: Department of Nuclear Medicine, University Hospital Essen, Essen, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Ruhlmann
authors.affiliation: Institute of Medical Physics, Friedrich-Alexander-University of Erlangen-Nürnberg, Erlangen, Germany.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Paulus
authors.affiliation: Siemens Healthcare Sector, Erlangen, Germany University of Surrey, Guildford, Surrey, United Kingdom.
authors.forename: Bjoern W
authors.initials: BW
authors.lastname: Jakoby
authors.affiliation: Clinic for Nuclear Medicine, University Hospital Erlangen, Erlangen, Germany; and.
authors.forename: Philipp
authors.initials: P
authors.lastname: Ritt
authors.affiliation: Institute of Medical Physics, Friedrich-Alexander-University of Erlangen-Nürnberg, Erlangen, Germany High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany Erwin L. Hahn Institute for MRI, University of Duisburg-Essen, Essen, Germany.
authors.forename: Harald H
authors.initials: HH
authors.lastname: Quick
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D064847:Multimodal Imaging; D009369:Neoplasms / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: Jaszczak phantom; PET/MR hybrid imaging; point-spread function (PSF); standardized uptake value (SUV)