title: Objective Bayesian fMRI analysis-a pilot study in different clinical environments.
abstract: Functional MRI (fMRI) used for neurosurgical planning delineates functionally eloquent brain areas by time-series analysis of task-induced BOLD signal changes. Commonly used frequentist statistics protect against false positive results based on a p-value threshold. In surgical planning, false negative results are equally if not more harmful, potentially masking true brain activity leading to erroneous resection of eloquent regions. Bayesian statistics provides an alternative framework, categorizing areas as activated, deactivated, non-activated or with low statistical confidence. This approach has not yet found wide clinical application partly due to the lack of a method to objectively define an effect size threshold. We implemented a Bayesian analysis framework for neurosurgical planning fMRI. It entails an automated effect-size threshold selection method for posterior probability maps accounting for inter-individual BOLD response differences, which was calibrated based on the frequentist results maps thresholded by two clinical experts. We compared Bayesian and frequentist analysis of passive-motor fMRI data from 10 healthy volunteers measured on a pre-operative 3T and an intra-operative 1.5T MRI scanner. As a clinical case study, we tested passive motor task activation in a brain tumor patient at 3T under clinical conditions. With our novel effect size threshold method, the Bayesian analysis revealed regions of all four categories in the 3T data. Activated region foci and extent were consistent with the frequentist analysis results. In the lower signal-to-noise ratio 1.5T intra-operative scanner data, Bayesian analysis provided improved brain-activation detection sensitivity compared with the frequentist analysis, albeit the spatial extents of the activations were smaller than at 3T. Bayesian analysis of fMRI data using operator-independent effect size threshold selection may improve the sensitivity and certainty of information available to guide neurosurgery.
authors.affiliation: Department for Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London London, UK ; Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London London, UK.
authors.forename: Joerg
authors.initials: J
authors.lastname: Magerkurth
authors.affiliation: Department for Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London London, UK.
authors.forename: Laura
authors.initials: L
authors.lastname: Mancini
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London London, UK.
authors.forename: William
authors.initials: W
authors.lastname: Penny
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London London, UK.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Flandin
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London London, UK.
authors.forename: John
authors.initials: J
authors.lastname: Ashburner
authors.affiliation: Department for Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London London, UK.
authors.forename: Caroline
authors.initials: C
authors.lastname: Micallef
authors.affiliation: Department for Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London London, UK.
authors.forename: Enrico
authors.initials: E
authors.lastname: De Vita
authors.affiliation: Centre for Medical Image Computing, University College London London, UK.
authors.forename: Pankaj
authors.initials: P
authors.lastname: Daga
authors.affiliation: Department for Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London London, UK.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: White
authors.affiliation: Siemens Healthcare Camberley, UK.
authors.forename: Craig
authors.initials: C
authors.lastname: Buckley
authors.affiliation: Department for Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London London, UK.
authors.forename: Adam K
authors.initials: AK
authors.lastname: Yamamoto
authors.affiliation: Centre for Medical Image Computing, University College London London, UK.
authors.forename: Sebastien
authors.initials: S
authors.lastname: Ourselin
authors.affiliation: Neuroradiological Academic Unit, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London London, UK.
authors.forename: Tarek
authors.initials: T
authors.lastname: Yousry
authors.affiliation: Department for Brain Repair and Rehabilitation, UCL Institute of Neurology, University College London London, UK.
authors.forename: John S
authors.initials: JS
authors.lastname: Thornton
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London London, UK.
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Weiskopf
keywords: bayesian statistics; effect size; false negative; false positive; interventional MRI; motor cortex; neurosurgical planning; passive fMRI