Late Breaking Abstract Submission
Alessio Fracasso1, Serge Dumoulin2, Natalia Petridou3
1University of Glasgow, Glasgow, United Kingdom, 2Spinoza Brain Imaging Center, Amsterdam, The Netherlands, 3University Medical Center, Utrecht, The Netherlands
Spinoza Brain Imaging Center
Amsterdam, The Netherlands
Columns and layers are fundamental organizational units of the brain. Well known examples of cortical columns are the ocular dominance columns (ODCs) in primary visual cortex and the column-like stripe-based arrangement in the second visual area V2 (Hubel & Wiesel, 1977; Mountcastle, 1997).
The spatial scale of columns and layers is beyond the reach of conventional neuroimaging, but the advent of high field magnetic resonance imaging (MRI) scanners (UHF, 7 Tesla and above) has opened the possibility to acquire data at this spatial scale, in-vivo and non-invasively in humans (Chaimow et al., 2018).
The most prominent non-invasive technique to study brain function is blood oxygen level dependent (BOLD) fMRI, which measures brain activity indirectly via the changes in hemodynamics. One of the key determinants in assessing the ability of high-resolution BOLD fMRI to resolve cortical columns and layers is the point-spread function (PSF) of the BOLD response which related to the spatial extent of neuronal activity.
In this study we take advantage of the stripe-based arrangement present in visual area V2 (Dumoulin et al., 2017), coupled with sub-millimetre anatomical and gradient-echo BOLD (GE BOLD) acquisition at 7T to obtain PSF estimates along cortical depth in human participants.
Stimuli were generated using Matlab. The contrast polarity reversed at a temporal frequency of either 1.5 or 7.5 Hz, alternated in a block design of 13s/block (Figure 1).
Functional data were acquired using a 3-dimensional segmented gradient-echo (GE) echo-planar-imaging (EPI) sequence with 29 coronal slices and acquisition time of 2.6 s per volume, and the following parameters: TR/TE 35/25 ms, flip angle 20 degrees, SENSE factor 3.5 in the right-left direction, echo planar factor: 17, bandwidth (in the phase-encode direction): 59 Hz/pixel with estimated blurring in the phase-encode direction of ~2% (Haacke et al., 1999) voxel size = 0.9 × 0.9 × 1.0 mm, FOV = 120 (right-left) × 120 (feet-head) × 29 (anterior-posterior) mm3, 80 time-frames, scan duration about 4 min. Each subject participated in at least two fMRI sessions, and each session comprised between 4 and 7 scans. fMRI data were acquired with a 7T Philips Achieva scanner using a volume transmit (Nova Medical, MA, USA) and a 16-channel receive surface-coil (Petridou et al., 2013).
High-resolution T1-weighted (T1-w) anatomical MR images were acquired with the 7T scanner and a 32-channel head coil (Nova Medical, MA, USA) in a separate session. The images were obtained with a 3-dimensional MPRAGE sequence adjusted to obtain a strong myelin contrast (white matter, WM) in grey matter (GM) (Fracasso et al., 2016). Sequence parameters were: inversion delay TI = 1200ms, time delay between inversion pulses TD = 6000ms, TR/TE 8/3 ms, flip angle: 8 degrees, voxel size = 0.5 mm isotropic, FOV: 140 × 140 × 30 mm, 60 coronal slices, bandwidth 202 Hz/pixel, turbo factor: 275, adiabatic inversion, and no acceleration. The imaging volume was placed at about the same location in the visual cortex as for the functional images.
We observed a positive linear relation between the full-width-half-max (FWHM, PSF) estimated from the GE-BOLD data and normalized cortical depth at the single participant level as well as across all participants (Figure 2).
Portions of cortex closer to the white matter boundary were characterized by a PSF of approximately ~0.8mm, compared to estimates from locations closer to the cerebro-spinal fluid surface, yielding PSF estimates of approximately ~1.8mm (Figure 2).
We postulate that GE BOLD measurements can resolve the underlying neuronal spatial organization with an accuracy below 1mm deeper in the cortex with this spatial specificity degrading closer to the pial surface. Our results provide an estimate of functional PSFs along cortical depth in human participants, useful for studies aimed at probing fine-scale cortical organizations in human neocortex.
Modeling and Analysis Methods:
Activation (eg. BOLD task-fMRI)
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Anatomy and Functional Systems
Cortical Anatomy and Brain Mapping
Novel Imaging Acquisition Methods:
BOLD fMRI 2
Physiology, Metabolism and Neurotransmission :
Cerebral Metabolism and Hemodynamics 1
HIGH FIELD MR
1|2Indicates the priority used for review
My abstract is being submitted as a Software Demonstration.
Please indicate below if your study was a "resting state" or "task-activation” study.
Healthy subjects only or patients (note that patient studies may also involve healthy subjects):
Was any human subjects research approved by the relevant Institutional Review Board or ethics panel?
NOTE: Any human subjects studies without IRB approval will be automatically rejected.
Was any animal research approved by the relevant IACUC or other animal research panel?
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Chaimow, D., Yacoub, E., Ugurbil, K., Shmuel, A., 2018. Spatial specificity of the functional MRI blood oxygenation response relative to neuronal activity. NeuroImage 164:32-47.
Dumoulin, S.O., Harvey, B.M., Fracasso, A., Zuiderbaan, W., Luijten, P.R., Wandell, B.A., Petridou, N., 2017. In vivo evidence of functional and anatomical stripe-based subdivisions in human V2 and V3. Scientific reports 7:733.
Fracasso, A., van Veluw, S.J., Visser, F., Luijten, P.R., Spliet, W., Zwanenburg, J.J.M., Dumoulin, S.O., Petridou, N., 2016. Lines of Baillarger in vivo and ex vivo: Myelin contrast across lamina at 7T MRI and histology. NeuroImage 133:163-75.
Haacke, E., Brown, R., Thompson, M., Venkatesan, R., 1999. Magnetic Resonance Imaging: Physical Principles and Sequence Design. John Wiley and Sons, New York.
Hubel, D.H., Wiesel, T.N., 1977. Ferrier lecture. Functional architecture of macaque monkey visual cortex. Proceedings of the Royal Society of London. Series B, Biological sciences 198:1-59.
Mountcastle, V.B., 1997. The columnar organization of the neocortex. Brain : a journal of neurology 120 ( Pt 4):701-22.
Petridou, N., Italiaander, M., van de Bank, B.L., Siero, J.C., Luijten, P.R., Klomp, D.W., 2013. Pushing the limits of high-resolution functional MRI using a simple high-density multi-element coil design. NMR in biomedicine 26:65-73.