Ultra-high field functional magnetic resonance imaging (fMRI) offers the spatial resolution to measure neuronal activity at the scale of cortical layers. However, cortical depth dependent... Show moreUltra-high field functional magnetic resonance imaging (fMRI) offers the spatial resolution to measure neuronal activity at the scale of cortical layers. However, cortical depth dependent vascularization differences, such as a higher prevalence of macro-vascular compartments near the pial surface, have a confounding effect on depth-resolved blood-oxygen-level dependent (BOLD) fMRI signals. In the current study, we use hypercapnic and hyperoxic breathing conditions to quantify the influence of all venous vascular and micro-vascular compartments on laminar BOLD fMRI, as measured with gradient-echo (GE) and spin-echo (SE) scan sequences, respectively. We find that all venous vascular and micro-vascular compartments are capable of comparable theoretical maximum signal intensities, as represented by the M-value parameter. However, the capacity for vessel dilation, as reflected by the cerebrovascular reactivity (CVR), is approximately two and a half times larger for all venous vascular compartments combined compared to the micro-vasculature at superficial layers. Finally, there is roughly a 35% difference in estimates of CBV changes between all venous vascular and micro-vascular compartments, although this relative difference was approximately uniform across cortical depth. Thus, our results suggest that fMRI BOLD signal differences across cortical depth are likely caused by differences in dilation properties between macro- and micro-vascular compartments. Show less
Background: The combination of EEG and ultra-high-field (7T and above) fMRI holds the promise to relate electrophysiology and hemodynamics with greater signal to noise level and at higher spatial... Show moreBackground: The combination of EEG and ultra-high-field (7T and above) fMRI holds the promise to relate electrophysiology and hemodynamics with greater signal to noise level and at higher spatial resolutions than conventional field strengths. Technical and safety restrictions have so far resulted in compromises in terms of MRI coil selection, resulting in reduced, signal quality, spatial coverage and resolution in EEG-fMRI studies at 7 T.New method: We adapted a 64-channel MRI-compatible EEG cap so that it could be used with a closed 32-channel MRI head coil thus avoiding several of these compromises. We compare functional and anatomical as well as the EEG quality recorded with this adapted setup with those recorded with a setup that uses an open-ended 8-channel head-coil.Results: Our set-up with the adapted EEG cap inside the closed 32 channel coil resulted in the recording of good quality EEG and (f)MRI data. Both functional and anatomical MRI images show no major effects of the adapted EEG cap on MR signal quality. We demonstrate the ability to compute ERPs and changes in alpha and gamma oscillations from the recorded EEG data.Comparison with existing methods: Compared to MRI recordings with an 8-channel open-ended head-coil, the loss in signal quality of the MRI images related to the adapted EEG cap is considerably reduced.Conclusions: The adaptation of the EEG cap permits the simultaneous recording of good quality whole brain (f) MRI data using a 32 channel receiver coil, while maintaining the quality of the EEG data. Show less
Zwanenburg, J.J.M.; Versluis, M.J.; Luijten, P.R.; Petridou, N. 2011
Magnetic susceptibility based (T-2* weighted) contrast in MRI at high magnetic field strength is of great value in research on brain structure and cortical architecture, but its use is hampered by... Show moreMagnetic susceptibility based (T-2* weighted) contrast in MRI at high magnetic field strength is of great value in research on brain structure and cortical architecture, but its use is hampered by the low signal-to-noise ratio (SNR) efficiency of the conventional spoiled gradient echo sequence (GRE) leading to long scan times even for a limited number of slices. In this work, we show that high resolution (0.5 mm isotropic) T-2* weighted images of the whole brain can be obtained in 6 min by utilizing the high SNR efficiency of echo-planar imaging (EPI). A volumetric (3D) EPI protocol is presented and compared to conventional 3D GRE images acquired with the same resolution, amount of T-2* weighting, and imaging duration. Spatial coverage in 3D EPI was increased by a factor of 4.5 compared to 3D GRE, while also the SNR was increased by a factor of 2. Image contrast for both magnitude and phase between gray and white matter was similar for both sequences, with enhanced conspicuity of anatomic details in the 3D EPI images due to the increased SNR. Even at 7 T, image blurring and distortion is limited if the EPI train length remains short (not longer than the T-2* of the imaged tissue). 3D EPI provides steps (speed, whole brain coverage, and high isotropic resolution) that are necessary to utilize the benefits of high field MRI in research that employs T-2* weighted imaging. (C) 2011 Elsevier Inc. All rights reserved. Show less
