Mo Shahdloo1, Daniel Papp2, Urs Schüffelgen1, Karla L. Miller2, Matthew Rushworth1, and Mark Chiew2
1Wellcome Centre for Integrative Neuroimaging, Department of Experimental Psychology, University of Oxford, Oxford, United Kingdom, 2Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
1Wellcome Centre for Integrative Neuroimaging, Department of Experimental Psychology, University of Oxford, Oxford, United Kingdom, 2Wellcome Centre for Integrative Neuroimaging, FMRIB, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
B0 field fluctuations cause significant unaliasing artefacts when imaging awake behaving non-human primates. We proposed a method to estimate these fluctuations, effectively reducing the artefacts, without the need for extra scans or sequence modification.
Figure 4. (a) Distortion due to a simulated linear field perturbation was applied on the fully-sampled reference frame from in vivo data. (b) In-plane accelerated data were synthesised by retrospectively undersampling at R=2, 4. Multiband data were synthesised by adding the data across two slices (R=3x2). Field perturbation leads to calibration inconsistency, manifested as strong unaliasing artefacts. The perturbation was estimated and the data were corrected, yielding a reconstructions that have significant reduced unaliasing artefacts and corrected geometric distortion.
Figure 1. Linear magnetic field perturbation is cast as a linear shift of the k-space data for each navigator line at the reference frame (green dots), yielding shifted navigator lines (red dots). Separate GRAPPA operators (Gx, Gy) trained on calibration data to map each k-space point to their adjacent point across the orthogonal Cartesian grid can shift points on the grid (blue arrows). Partial shifts (red arrows) can be cast as fractional powers of the operators. Field perturbations were estimated by finding the shifts between navigators at each frame and those at the reference frame.
