title: PET/MRI for Oncologic Brain Imaging: A Comparison of Standard MR-Based Attenuation Corrections with a Model-Based Approach for the Siemens mMR PET/MR System.
abstract: The aim of this study was to compare attenuation-correction (AC) approaches for PET/MRI in clinical neurooncology.Methods:Forty-nine PET/MRI brain scans were included: brain tumor studies using18F-fluoro-ethyl-tyrosine (18F-FET) (n= 31) and68Ga-DOTANOC (n= 7) and studies of healthy subjects using18F-FDG (n= 11). For each subject, MR-based AC maps (MR-AC) were acquired using the standard DIXON- and ultrashort echo time (UTE)-based approaches. A third MR-AC was calculated using a model-based, postprocessing approach to account for bone attenuation values (BD, noncommercial prototype software by Siemens Healthcare). As a reference, AC maps were derived from patient-specific CT images (CTref). PET data were reconstructed using standard settings after AC with all 4 AC methods. We report changes in diagnosis for all brain tumor patients and the following relative differences values (RDs [%]), with regards to AC-CTref: for18F-FET (A)-SUVs as well as volumes of interest (VOIs) defined by a 70% threshold of all segmented lesions and lesion-to-background ratios; for68Ga-DOTANOC (B)-SUVs as well as VOIs defined by a 50% threshold for all lesions and the pituitary gland; and for18F-FDG (C)-RD of SUVs of the whole brain and 10 anatomic regions segmented on MR images.Results:For brain tumor imaging (A and B), the standard PET-based diagnosis was not affected by any of the 3 MR-AC methods. For A, the average RDs of SUVmeanwere -10%, -4%, and -3% and of the VOIs 1%, 2%, and 7% for DIXON, UTE, and BD, respectively. Lesion-to-background ratios for all MR-AC methods were similar to that of CTref. For B, average RDs of SUVmeanwere -11%, -11%, and -3% and of the VOIs 1%, -4%, and -3%, respectively. In the case of18F-FDG PET/MRI (C), RDs for the whole brain were -11%, -8%, and -5% for DIXON, UTE, and BD, respectively.Conclusion:The diagnostic reading of PET/MR patients with brain tumors did not change with the chosen AC method. Quantitative accuracy of SUVs was clinically acceptable for UTE- and BD-AC for group A, whereas for group B BD was in accordance with CTref. Nevertheless, for the quantification of individual lesions large deviations to CTref can be observed independent of the MR-AC method used.
authors.affiliation: Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
authors.forename: Ivo
authors.initials: I
authors.lastname: Rausch
authors.affiliation: Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Lucas
authors.initials: L
authors.lastname: Rischka
authors.affiliation: Department of Clinical Physiology, Nuclear Medicine and PET, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Claes N
authors.initials: CN
authors.lastname: Ladefoged
authors.affiliation: Division of Neuroradiology, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Julia
authors.initials: J
authors.lastname: Furtner
authors.affiliation: Siemens Healthcare GmbH, Magnetic Resonance, Erlangen, Germany; and.
authors.forename: Matthias
authors.initials: M
authors.lastname: Fenchel
authors.affiliation: Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hahn
authors.affiliation: Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Rupert
authors.initials: R
authors.lastname: Lanzenberger
authors.affiliation: Division of Neuroradiology, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria.
authors.forename: Marius E
authors.initials: ME
authors.lastname: Mayerhoefer
authors.affiliation: Division of Nuclear Medicine, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria tatjana.traub-weidinger@meduniwien.ac.at.
authors.forename: Tatjana
authors.initials: T
authors.lastname: Traub-Weidinger
authors.affiliation: Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Beyer
mesh_terms: D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging*; D001932:Brain Neoplasms / Q000000981:diagnostic imaging*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000592:standards; D008279:Magnetic Resonance Imaging; D064847:Multimodal Imaging; D009942:Organometallic Compounds; D049268:Positron-Emission Tomography; D012189:Retrospective Studies; D014443:Tyrosine / Q000031:analogs & derivatives
chemical_list: C504894:68Ga-DOTANOC; D009942:Organometallic Compounds; C545932:(18F)fluoroethyltyrosine; D014443:Tyrosine
keywords: PET/MRI; attenuation correction; brain tumor imaging; quantification