Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI at Ultra-high Field Saskia Bollmann1, Steffen Bollmann1, Alexander Pucket2, Andrew Janke1, Markus Barth1 1Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia 2Queensland Brain Institute, The University of Queensland, Brisbane, Australia

Realignment in fMRI Realignment = correct for motion Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Realignment in fMRI Realignment = correct for motion Affine coregistration: 3 translation + 3 rotation parameters Realignment

Nonlinear Deformations in fMRI Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Nonlinear Deformations in fMRI Through Interaction with the main magnetic field1 Cardiac pulsation  tissue displacement of up to 2 mm2 Reduces Temporal signal-to-noise-ratio (tSNR) Spatial specificity Can not be corrected using affine transformations 1Dymerska et al., 2016, NeuroImage; 2Soellinger, 2008, Zurich

Minimum Deformation Atlassing (MDA)1 Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Minimum Deformation Atlassing (MDA)1 Non-linear realignment (NR) technique Can average sub-voxel boundaries Reduces partial-volume effects Applied to single-subject fMRI time series MDA 1Janke and Ullmann, 2015, Methods

Impact of Physiological Noise on Serial Correlations in Fast Simultaneous Multislice (SMS) EPI at 7T - Saskia Bollmann - # 5308 Data Acquisition MAGNETOM 7T (Siemens) with a 32-channel head coil (Nova Medical) CMRR SMS1,2 implementation (release 11a) + slice-GRAPPA2 + leak-block3 low-resolution sequence TR = 589 ms, voxel size = 2.5 mm isotropic, GRAPPA x SMS: 2 x 4, 581 volumes high-resolution sequence TR = 1999 ms, voxel size = 1.3 mm isotropic, GRAPPA x SMS: 3 x 3, 188 volumes 1 participant performing a 6-minute rhythmic finger-tapping task using a block-design (18s block length) 1Feinberg et al., 2010, PLOS ONE; 2Setsompop et al., 2012, MRM; 3Cauley et al., 2014, MRM

1Ashburner et al., 2005, NeuroImage, 2Penny et al., 2003, NeuroImage Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Data Analysis MDA: Linear realignment + non-linear robust averaging of low resolution images Data sets Low resolution (LR) High resolution (HR) Low resolution low resolution + non-linear realignment (LRNR) Outcome measure tSNR maps Segmentation1 results Posterior probability maps2 MDA 1Ashburner et al., 2005, NeuroImage, 2Penny et al., 2003, NeuroImage

Spatial Specificity – Mean Images Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Spatial Specificity – Mean Images LR LRNR HR Low resolution (LR): pronounced partial volume effects between CSF, grey and white matter Low resolution + non-linear realignment (LRNR): reduced partial volume effects, anatomical features match the high resolution reference image High resolution (HR): clear delineation of CSF, grey and white matter

Sensitivity – Temporal SNR Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Sensitivity – Temporal SNR LR LRNR HR LR: highest tSNR LRNR: slightly reduced tSNR, contains anatomical features HR: substantially (~50 %) reduced tSNR

Spatial Specificity – Segmentation Results Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Spatial Specificity – Segmentation Results LR LRNR HR LR: course structures, only large gyri visible LRNR: fine-grained structures discernible, matching high resolution images HR: most detailed segmentation

Sensitivity – Posterior Probability Maps Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Sensitivity – Posterior Probability Maps LR LRNR HR threshold: effect size of 1% with log odds ratio of 10 LR: response in M1 and SMA LRNR: similar spatial extent of activation, but better visibility of borders between gyri (circle) HR: similar activation sides, but lower spatial extent

1Dymerska et al., 2016, NeuroImage Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Discussion Main disadvantage: long computation time of ~ 2 days Correction of B0 effects might be possible with different techniques1 Reduction in tSNR unclear Reduction of non-linear deformation through physiological effects remains to be assessed 1Dymerska et al., 2016, NeuroImage

Conclusion MDA for single-subject fMRI: Reduced partial volume effects Non-linear Realignment Using Minimum Deformation Averaging for Single-subject fMRI - Saskia Bollmann - # 5338 Conclusion MDA for single-subject fMRI: Reduced partial volume effects Improve segmentation results Better delineation of activation patterns Could enable advanced surface-based analysis schemes for low resolution data1 1Khan et al., 2011, Graph. Models.