title: The clinical relevance of distortion correction in presurgical fMRI at 7T.
abstract: Presurgical planning with fMRI benefits from increased reliability and the possibility to reduce measurement time introduced by using ultra-high field. Echo-planar imaging suffers, however, from geometric distortions which scale with field strength and potentially give rise to clinically significant displacement of functional activation. We evaluate the effectiveness of a dynamic distortion correction (DDC) method based on unmodified single-echo EPI in the context of simulated presurgical planning fMRI at 7T and compare it with static distortion correction (SDC). The extent of distortion in EPI and activation shifts are investigated in a group of eleven patients with a range of neuropathologies who performed a motor task. The consequences of neglecting to correct images for susceptibility-induced distortions are assessed in a clinical context. It was possible to generate time series of EPI-based field maps which were free of artifacts in the eloquent brain areas relevant to presurgical fMRI, despite the presence of signal dropouts caused by pathologies and post-operative sites. Distortions of up to 5.1mm were observed in the primary motor cortex in raw EPI. These were accurately corrected with DDC and slightly less accurately with SDC. The dynamic nature of distortions in UHF clinical fMRI was demonstrated via investigation of temporal variation in voxel shift maps, confirming the potential inadequacy of SDC based on a single reference field map, particularly in the vicinity of pathologies or in the presence of motion. In two patients, the distortion correction was potentially clinically significant in that it might have affected the localization or interpretation of activation and could thereby have influenced the treatment plan. Distortion correction is shown to be effective and clinically relevant in presurgical planning at 7T.
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria. Electronic address: pedro.delimacardoso@meduniwien.ac.at.
authors.forename: Pedro
authors.initials: P
authors.lastname: Lima Cardoso
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria. Electronic address: barbara.dymerska@meduniwien.ac.at.
authors.forename: Barbara
authors.initials: B
authors.lastname: Dymerska
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria. Electronic address: beata.bachrata@gmail.com.
authors.forename: Beáta
authors.initials: B
authors.lastname: Bachratá
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria; Study Group Clinical fMRI, Department of Neurology, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria. Electronic address: florian.fischmeister@meduniwien.ac.at.
authors.forename: Florian Ph S
authors.initials: FPS
authors.lastname: Fischmeister
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria; Study Group Clinical fMRI, Department of Neurology, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria. Electronic address: nina.mahr@meduniwien.ac.at.
authors.forename: Nina
authors.initials: N
authors.lastname: Mahr
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria; Study Group Clinical fMRI, Department of Neurology, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria. Electronic address: eva.matt@meduniwien.ac.at.
authors.forename: Eva
authors.initials: E
authors.lastname: Matt
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria. Electronic address: siegfried.trattnig@meduniwien.ac.at.
authors.forename: Siegfried
authors.initials: S
authors.lastname: Trattnig
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria; Study Group Clinical fMRI, Department of Neurology, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria. Electronic address: roland.beisteiner@meduniwien.ac.at.
authors.forename: Roland
authors.initials: R
authors.lastname: Beisteiner
authors.affiliation: High Field Magnetic Resonance Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Lazarettgasse 14, A-1090 Vienna, Austria. Electronic address: simon.robinson@meduniwien.ac.at.
authors.forename: Simon Daniel
authors.initials: SD
authors.lastname: Robinson
mesh_terms: D000328:Adult; D016477:Artifacts; D001931:Brain Mapping / Q000379:methods* / Q000592:standards; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery; D002561:Cerebrovascular Disorders / Q000000981:diagnostic imaging* / Q000601:surgery; D017352:Echo-Planar Imaging / Q000379:methods* / Q000592:standards; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000592:standards; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000000981:diagnostic imaging* / Q000502:physiology; D019635:Neurosurgical Procedures; D011300:Preoperative Care
keywords: Dynamic distortion correction; Motor; Patients; Presurgical planning; Ultra-high field; fMRI