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Preliminary results of functional line-scanning in humans: submillimeter, subsecond resolution evoked responses

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Yu,  X
Research Group Translational Neuroimaging and Neural Control, Max Planck Institute for Biological Cybernetics, Max Planck Society;
Max Planck Institute for Biological Cybernetics, Max Planck Society;

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Citation

Raimondo, L., Knapen, T., Oliveira, I., Yu, X., van der Zwaag, W., & Siero, J. (2019). Preliminary results of functional line-scanning in humans: submillimeter, subsecond resolution evoked responses. Magnetic Resonance Materials in Physics, Biology and Medicine, 32(Supplement 1): S22.06, S334.


Cite as: http://hdl.handle.net/21.11116/0000-0004-B9A3-3
Abstract
Purpose/Introduction: In order to advance fundamental and clinical neuroscience it is necessary to understand the relative contributions of large vessel and microvessel signals in human cortex BOLD fMRI responses. Line-scanning fMRI 1, 2, 3 achieves extremely high reso- lution across both cortical depth (250 l m) and time (100 ms), by sacrificing volume coverage and resolution along the cortical surface. This unprecedented spatiotemporal resolution can allow us to identify microvessel responses and to characterize the distribution of blood flow across cortical depth. Here we present preliminary results of a human line-scanning fMRI experiment investigating hemodynamic signals in human visual cortex. Subjects and Methods: Two volunteers were scanned at 7T (Philips) with a 32 channel receive head coil (Nova Medical). Line scans were acquired with: line resolution = 250 l m, TR/TE = 103/12 ms, 2400 timepoints, flip angle = 16 ° , array size = 720, line thick- ness = 2.5 mm, in-plane line width = 5 mm, fat suppression using SPIR. Two saturation pulses (5 ms pulse duration) were used to suppress the signal outside the line of interest. The phase-encoding in the direction perpendicular to the line was turned off 2 . The line was positioned in right/left direction, crossing the visual cortex (Fig. 1). Data was acquired during intermittent bilateral visual stimulation in 4 runs. Visual stimuli were 8 Hz flickering gratings, presented for 750 ms with an exponential ISI distribution (mean of 2 s, plus a minimum of 2 s). Reconstruction was performed offline with MatLab and Gyrotools. Multiple coil data were combined weighting the signal with the temporal signal to noise ratio (tSNR) per coil; tSNR was computed for the coil-combined data. HRF shape was estimated by deconvolution from the timeseries using ‘nideconv’. Results: Figure 2 shows line-scanning profiles along the human visual cortex. tSNR was comparable to sub-millimeter 3D-imaging and sufficient for BOLD signal detection 4 . From the results of the functional experiment (Figures 2b and 3), active points along the line due to visual stimulation are detectable in both primary visual cortex (V1) and lateral occipital cortex (LOC). The BOLD response peaks are measured at around 5 s post stimulus-onset. Positive responses are followed by an undershoot in all active regions. Discussion/Conclusion: Our line scanning results indicate that hemodynamic response function mapping with very high spatiotem- poral resolutions can be achieved in humans. Overall, the line- scanning fMRI technique seems very promising due to its potential in detailed mapping of hemodynamics in humans for clinical research on small vessel diseases but also for fundamental neuroscience at the mesoscopic scale (cortical lamina).