Suhyung Park¹, Salvatore Torrisi², Jennifer Townsend², Alexander Beckett², and David Feinberg^1,2
1University of California, Berkeley, Berkeley, CA, United States, ²Advanced MRI Technologies, Sebastopol, CA, United States

3D GRASE is used for cortical layer and columnar fMRI in the absence of signal confounds from draining veins. Its use has been limited by limited slice coverage with blurring. We developed highly accelerated 3D GRASE with controlled T2 blurring by combining compressed sensing with variable flip angles. Compared with current GRASE acquisitions, the proposed method demonstrates that 1) through-plane random encoding with VFA increases the slice coverage with a sharper point spread function, 2) reduced TE from in--plane random encoding provides a high SNR efficiency, and 3) the resulting image sharpness and SNR efficiency lead to increased BOLD activation. 

Atena Akbari¹, Saskia Bollmann¹, Tonima S Ali ¹, and Markus Barth^1,2,3
1Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia, ²ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, Brisbane, Australia, ³School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Australia

In this study, we used the “cortical vascular model” for human V1 at 7T to simulate the laminar VAscular-Space-Occupancy (VASO) signal change. For comparison, we conducted  VASO experiments on a group of healthy subjects to measure laminar signal change in V1. Results show a very good agreement between the model prediction and the experimental results once the volume changes of the different vascular compartments (arterioles, capillaries, venules) are taken into account. 

Lars Kasper¹, Maria Engel¹, Jakob Heinzle², Matthias Mueller-Schrader², Jonas Reber¹, Thomas Schmid¹, Christoph Barmet¹, Bertram Jakob Wilm¹, Klaas Enno Stephan^2,3,4, and Klaas Paul Pruessmann^1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland, ²Translational Neuromodeling Unit, Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland, ³Wellcome Trust Centre for Neuroimaging, University College London, London, United Kingdom, ⁴Max Planck Institute for Metabolism Research, Cologne, Germany

We investigate the spatial specificity of sub-millimeter (0.8mm) single-shot spiral fMRI, and its feasibility for functional phase contrast. Scrutinizing activation patterns of a visual paradigm in 6 subjects, we find that significant contrast changes occur between adjacent voxels, contributing to the evidence of spatial specificity of spiral acquisition as well as gradient echo BOLD contrast, and its possible applications in laminar or columnar fMRI. Furthermore, the vessel-localized nature of the phase activation suggests its suitability for masking macrovascular confound effects.

Andrew T. Morgan¹, Nils Nothnagel¹, Jozien Goense¹, and Lars Muckli^1
1Institute of Neuroscience & Psychology, University of Glasgow, Glasgow, United Kingdom

Motivated by recent functional line-scanning recordings in rodents, we developed a procedure to record human cortical layers at high spatial (200 μm) and temporal resolution (100 ms). Our technique addresses challenges associated with human line-scanning, such as planning around cortical folding and restrictive SAR limitations. Our results show that line-scanning of human cortical layers corroborates electrophysiological measurements of tuning properties in primary visual cortex. These results demonstrate that line-scanning is a promising technique for investigating local functional circuits in human cortex.

Fuyixue Wang^1,2, Zijing Dong^1,3, Qiyuan Tian¹, Jingyuan Chen¹, Anna Izabella Blazejewska¹, Timothy G. Reese¹, Jonathan R. Polimeni^1,2, and Kawin Setsompop^1,2
1A. A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ²Harvard-MIT Health Sciences and Technology, MIT, Cambridge, MA, United States, ³3Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA, United States

BOLD fMRI based on T₂ contrast has the promise to provide exclusively microvascular specificity, which would optimize the ability of fMRI signals to accurately reflect and localize neuronal activity. However, it is challenging in practice to achieve pure T₂ weighting. Here we employ a new highly-efficient acquisition and reconstruction framework based on EPI, Echo-Planar Time-resolved Imaging (EPTI), and extend it to generate blurring- and distortion-free data with purely T₂ weighting. We evaluate the technique through a cortical-depth analysis of activation in human visual cortex and demonstrate that it achieves the desired microvascular specificity.

Daniel Haenelt^1,2, Nikolaus Weiskopf¹, Lenka Vaculciakova^1,2, Roland Mueller¹, Shahin Nasr^3,4, Jonathan Polimeni^3,4, Roger Tootell^3,4, Laurentius Huber⁵, Martin Sereno⁶, and Robert Trampel^1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²International Max Planck Research School on Neuroscience of Communication: Function, Structure, and Plasticity, Leipzig, Germany, ³Athinoula A. Martinos Center for Biomedical Imaging, Boston, MA, United States, ⁴Department of Radiology, Harvard Medical School, Boston, MA, United States, ⁵Department of Cognitive Neuroscience, Maastricht Brain Imaging Center, Maastricht, Netherlands, ⁶Department of Psychology, San Diego State University, San Diego, CA, United States

Functional MRI studies classically rely on the use of GE-EPI sequences. However, the GE-based signal is inherently sensitive to large veins, which impairs its use in high-resolution fMRI application. Other BOLD- and CBV-based approaches like SE-EPI and SS-SI-VASO, respectively, promise a higher specificity at the expense of sensitivity. In the present work, we tested if ocular dominance columns (ODCs) can be detected using GE-EPI, SE-EPI and SS-SI-VASO at 7 T. ODCs could be reliably mapped using all three acquisition methods. Furthermore, we could show for the first time ODCs in humans by exploiting the functional CBV response using SS-SI-VASO.

Laurentius Huber¹, Emily Finn², Sean Marrett², Sriranga Kashyap¹, Arman Khojandi², Rainer Goebel¹, Peter Bandettini², and Benedikt Poser^1
1MBIC, Uni Maastricht, Faculty of Psychology and Neuroscience, Maastricht, Netherlands, ²SFIM, NIMH, Bethesda, MD, United States

With recent advances in ultra-high-field MRI hardware and sequence mechanisms, it has become possible to measure CBV-weighted fMRI signal across cortical layers. While initial proof-of-principle layer-fMRI studies in primary brain areas with conventional fMRI task designs are promising, layer-fMRI has not yet realized its full potential to map layer-dependent functional connectivity across large-scale brain networks. In this study, we investigate the applicability of CBV-weighted layer-fMRI to assess functional connectivity during resting-state and naturalistic tasks. We can map common resting-state networks and characterize their internal layer-dependent signatures with respect to directionality and cortical hierarchy.

Xingfeng Shao¹, Kay Jann^1,2, Kai Wang¹, Fanhua Guo³, Peng Zhang³, and Danny JJ Wang^1,2
1Mark & Mary Stevens Neuroimaging and Informatics Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States, ²Department of Neurology, University of Southern California, Los Angeles, CA, United States, ³State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China

In-vivo laminar CBF fMRI was performed by high resolution (0.5×0.5×1.5 mm³) inner-volume GRASE with optimized pCASL labeling at 7T. Activation of finger-tapping task (5 blocks, TA=10 min) was reliably detected in all 4 subjects. Both rest/FT CBF peaks in the middle layers, which corresponds to highest capillary density in cortex layer IV. FT evoked CBF increase shows one peak in middle layer, and a second shoulder in deep layer. The capability to provide quantitative CBF measurements at both baseline and task activation with high specificity to neuronal activities is a unique strength of ASL fMRI compared to other fMRI techniques.

Jacco A de Zwart¹, Peter van Gelderen¹, and Jeff H Duyn^1
1Advanced MRI section, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States

Blood oxygen-level dependent (BOLD) functional MRI (fMRI) based on gradient-echo EPI is the most commonly used fMRI method due to its high sensitivity and robustness. However, large vein contribution negatively affects spatial localization of BOLD activation, of crucial importance for laminar and other high-resolution fMRI applications. Perfusion and blood volume-based methods have been shown to increase spatial accuracy of activation maps. Here we demonstrate feasibility of single-shot perfusion labeling (SSPL) fMRI at up to 1 mm³ resolution, a reference-less perfusion fMRI method twice as efficient as FAIR in which background signal is suppressed, improving temporal stability.

Yuhui Chai¹, Linqing Li², Yicun Wang³, Larentius Huber⁴, Benedikt Poser⁴, Jeff Duyn³, and Peter Bandettini^1,2
1Section on Functional Imaging Methods, Laboratory of Brain and Cognition, NIMH, NIH, Bethesda, MD, United States, ²Functional MRI Core, NIMH, NIH, Bethesda, MD, United States, ³Advanced MRI Section, Laboratory of Functional and Molecular Imaging, NINDS, NIH, Bethesda, MD, United States, ⁴Maastricht Brain Imaging Center, Faculty of Psychology and Neuroscience, University of Maastricht, Maastricht, Netherlands

In most previous laminar fMRI studies, cortical layers are defined based on an anatomical image that is collected by a different acquisition technique and exhibits different geometric distortion compared to the functional images. We introduce to generate a magnetization transfer (MT) weighted anatomical reference, using identical acquisition design as fMRI measurement. Cortical surface and depth can be reconstructed directly from this MT-weighted anatomical EPI image and all laminar analysis can be performed in the native fMRI image space without the need for distortion correction and registration.