A novel blood volume and perfusion contrast for laminar fMRI in humans at 7T
Seminar | February 10 | 4-5 p.m. | 125 Li Ka Shing Center
Yuhui Chai, NIMH
With increased availability of ultra-high field (7T) human MRI scanners, fMRI spatial resolution has been pushed to the sub-millimeter domain, making it possible to resolve functional activity and connectivity across cortical depths/layers. Despite the great potential of laminar fMRI research in humans, its widespread application is tempered by technical constraints: (1) The gradient-echo (GE) BOLD signal is susceptible to the draining vein effect, and thus its layer-specific microvasculature signal is often washed out by the dominant signal from ascending and pial veins; (2) Anatomical reference images are typically collected by a different acquisition sequence with different geometric distortions compared to the functional images. This causes mismatches in the definition of cortical depths/layers between anatomical and functional images.
To tackle these problems, (1) We introduce an integrated VASO and PERfusion (VAPER) contrast acquired by combining the blood-suppression module of DANTE (Delay Alternating with Nutation for Tailored Excitation) pulse trains with 3D-EPI. Earlier research in cats has shown that both cerebral blood volume (CBV) and cerebral blood flow (CBF) can be used to identify layer-dependent fMRI activation with spatial specificity superior to GE-BOLD contrast. VAPER aims to integrate CBV and CBF into one contrast for laminar fMRI. (2) We collect the anatomical image with a related fMRI acquisition technique by incorporating magnetization transfer (MT) weighted imaging. This allows sufficient gray-white matter contrast to perform all laminar fMRI analysis in the native EPI space, without the need for distortion correction and registration as the resulting anatomical data is completely matched for distortion with the VAPER.
We demonstrate VAPER-fMRI using high resolution (0.8mm) to investigate details of audiovisual motion processing by examining the auditory cortex and intraparietal sulcus, in which area integration occurs and what is the laminar profile under this audiovisual convergence.