title: Prospective motion correction of 3D echo-planar imaging data for functional MRI using optical tracking.
abstract: We evaluated the performance of an optical camera based prospective motion correction (PMC) system in improving the quality of 3D echo-planar imaging functional MRI data. An optical camera and external marker were used to dynamically track the head movement of subjects during fMRI scanning. PMC was performed by using the motion information to dynamically update the sequence's RF excitation and gradient waveforms such that the field-of-view was realigned to match the subject's head movement. Task-free fMRI experiments on five healthy volunteers followed a 2 × 2 × 3 factorial design with the following factors: PMC on or off; 3.0mm or 1.5mm isotropic resolution; and no, slow, or fast head movements. Visual and motor fMRI experiments were additionally performed on one of the volunteers at 1.5mm resolution comparing PMC on vs PMC off for no and slow head movements. Metrics were developed to quantify the amount of motion as it occurred relative to k-space data acquisition. The motion quantification metric collapsed the very rich camera tracking data into one scalar value for each image volume that was strongly predictive of motion-induced artifacts. The PMC system did not introduce extraneous artifacts for the no motion conditions and improved the time series temporal signal-to-noise by 30% to 40% for all combinations of low/high resolution and slow/fast head movement relative to the standard acquisition with no prospective correction. The numbers of activated voxels (p<0.001, uncorrected) in both task-based experiments were comparable for the no motion cases and increased by 78% and 330%, respectively, for PMC on versus PMC off in the slow motion cases. The PMC system is a robust solution to decrease the motion sensitivity of multi-shot 3D EPI sequences and thereby overcome one of the main roadblocks to their widespread use in fMRI studies.
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London, UK. Electronic address: nicholas.todd@ucl.ac.uk.
authors.forename: Nick
authors.initials: N
authors.lastname: Todd
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London, UK.
authors.forename: Oliver
authors.initials: O
authors.lastname: Josephs
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London, UK.
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, UK; Laboratoire de Recherche en Neuroimagerie, Department of Clinical Neurosciences, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
authors.forename: Antoine
authors.initials: A
authors.lastname: Lutti
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
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D017352:Echo-Planar Imaging / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D019416:Head Movements; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D008297:Male; D011446:Prospective Studies; D011597:Psychomotor Performance / Q000502:physiology; D059629:Signal-To-Noise Ratio; D014796:Visual Perception / Q000502:physiology; D058067:Wavelet Analysis
keywords: 3D imaging; EPI; Functional MRI; Optical tracking; Prospective motion correction