title: Vascular autorescaling of fMRI (VasA fMRI) improves sensitivity of population studies: A pilot study.
abstract: The blood oxygenation level-dependent (BOLD) signal is widely used for functional magnetic resonance imaging (fMRI) of brain function in health and disease. The statistical power of fMRI group studies is significantly hampered by high inter-subject variance due to differences in baseline vascular physiology. Several methods have been proposed to account for physiological vascularization differences between subjects and hence improve the sensitivity in group studies. However, these methods require the acquisition of additional reference scans (such as a full resting-state fMRI session or ASL-based calibrated BOLD). We present a vascular autorescaling (VasA) method, which does not require any additional reference scans. VasA is based on the observation that slow oscillations (<0.1Hz) in arterial blood CO2 levels occur naturally due to changes in respiration patterns. These oscillations yield fMRI signal changes whose amplitudes reflect the blood oxygenation levels and underlying local vascularization and vascular responsivity. VasA estimates proxies of the amplitude of these CO2-driven oscillations directly from the residuals of task-related fMRI data without the need for reference scans. The estimates are used to scale the amplitude of task-related fMRI responses, to account for vascular differences. The VasA maps compared well to cerebrovascular reactivity (CVR) maps and cerebral blood volume maps based on vascular space occupancy (VASO) measurements in four volunteers, speaking to the physiological vascular basis of VasA. VasA was validated in a wide variety of tasks in 138 volunteers. VasA increased t-scores by up to 30% in specific brain areas such as the visual cortex. The number of activated voxels was increased by up to 200% in brain areas such as the orbital frontal cortex while still controlling the nominal false-positive rate. VasA fMRI outperformed previously proposed rescaling approaches based on resting-state fMRI data and can be readily applied to any task-related fMRI data set, even retrospectively.
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London WC1N 3BG, United Kingdom. Electronic address: samira.kazan@ucl.ac.uk.
authors.forename: Samira M
authors.initials: SM
authors.lastname: Kazan
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London WC1N 3BG, United Kingdom.
authors.forename: Siawoosh
authors.initials: S
authors.lastname: Mohammadi
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London WC1N 3BG, United Kingdom.
authors.forename: Martina F
authors.initials: MF
authors.lastname: Callaghan
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London WC1N 3BG, United Kingdom.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Flandin
authors.affiliation: NMR-Unit, Max Planck Institute for Human Cognition and Brain Sciences, Leipzig, Germany.
authors.forename: Laurentius
authors.initials: L
authors.lastname: Huber
authors.affiliation: Cognitive, Clinical and Computational Neuroimaging Lab, Imperial College, Hammersmith Hospital, University of London, London W12 0NN, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: Leech
authors.affiliation: Department of Psychology, University of Sheffield, Western Bank, Sheffield S10 2TN, United Kingdom.
authors.forename: Aneurin
authors.initials: A
authors.lastname: Kennerley
authors.affiliation: MR Centre of Excellence, Centre for Medical Physics and Biomedical Engineering, Medical University of Vienna, Waehringer Guertel 18-20, Vienna A-1090, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Windischberger
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London WC1N 3BG, United Kingdom; Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Weiskopf
mesh_terms: D000465:Algorithms; D001931:Brain Mapping; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005189:False Positive Reactions; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D006935:Hypercapnia / Q000473:pathology; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000097:blood; D010865:Pilot Projects; D017397:Prefrontal Cortex / Q000098:blood supply; D015656:Respiratory Mechanics / Q000502:physiology; D014793:Visual Cortex / Q000098:blood supply; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: ALFF; Autorescaling; BOLD fMRI; Group analysis; Vascularization differences