Cortical lamina-dependent blood volume changes in human brain at 7 T

Abstract

Highlights: 21• A CBV-sensitive fMRI method is developed for high resolution fMRI in humans. 22• Lamina-dependent CBV fMRI responses are shown in humans. 23• VASO cortical profiles are validated with Fe-contrast agent fMRI in animals. 24• Sensitivity to large veins can be minimized using VASO-CBV instead of BOLD fMRI. 25• Ipsilateral fMRI responses to finger-tapping are positive in M1 and negative in S1. 26 27 Abstract 28Cortical layer-dependent high (sub-millimeter) resolution functional magnetic resonance imaging 29 (fMRI) in human or animal brain can be used to address questions regarding the functioning of 30 cortical circuits, such as the effect of different afferent and efferent connectivity on activity in 31 specific cortical layers. The sensitivity of gradient echo (GE) blood oxygenation level dependent 32 (BOLD) responses to large draining veins reduces its local specificity and can render the 33 interpretation of the underlying laminar neural activity impossible. Application of the more spatially 34 specific cerebral blood volume (CBV) based fMRI in humans has been hindered by the low sensitivity 35 of the non-invasive modalities available. Here, a Vascular Space Occupancy (VASO) variant, adapted 36 for use at high field, is further optimized to capture layer-dependent activity changes in human 37 motor cortex at sub-millimeter resolution. Acquired activation maps and cortical profiles show that 38 the VASO signal peaks in grey matter at 0.8 -1.6 mm depth, and deeper compared to the superficial 39 and vein-dominated GE-BOLD responses. Validation of the VASO signal change versus well-40 established iron-oxide contrast agent based fMRI methods in animals showed the same cortical 41 profiles of CBV change, after normalization for lamina-dependent baseline CBV. In order to evaluate 42 its potential of revealing small lamina-dependent signal differences due to modulations of the input-43 output characteristics, layer-dependent VASO responses were investigated in the ipsilateral 44 hemisphere during unilateral finger tapping. Positive activation in ipsilateral primary motor cortex 45 *7. Manuscript Click here to view linked References 2 and negative activation in ipsilateral primary sensory cortex were observed. This feature is only 1 visible in high-resolution fMRI where opposing sides of a sulcus can be investigated independently 2 because of a lack of partial volume effects. Based on the results presented here we conclude that 3 VASO offers good reproducibility, high sensitivity, and lower sensitivity than GE-BOLD to changes in 4 larger vessels, making it a valuable tool for layer-dependent fMRI studies in humans. 5Abbreviations: BOLD = blood oxygenation level dependent; CBV = cerebral blood volume; CNR = 6 contrast-to-noise ratio; CSF = cerebrospinal fluid; ΔCBV = change in CBV; EPI = echo planar imaging; 7 Fe = iron; fMRI = functional magnetic resonance imaging; GE = gradient echo; GM = grey matter; ROI 8 = region of interest; SNR = signal-to-noise ratio; SS-SI-VASO = slice-selective slab-inversion VASO...

The relationship between oscillatory EEG activity and the laminar-specific BOLD signal

“…Although a recent study explored the feasibility of measuring laminar-specific activity with magnetoencephalography (MEG) (13), most recent advances in measuring laminar activity in humans have been made using high-resolution functional MRI (fMRI) (14)(15)(16)(17)(18). In this study, we make use of these recent developments to investigate the relationship between electrophysiology and the laminar-specific blood oxygen level-dependent (BOLD) signal.…”

Laminar fMRI: Applications for cognitive neuroscience

“…In another example, Huber et al (2015) were able to improve the relatively low signal-to-noise of CBV-based laminar fMRI by using a higher in-plane resolution than the slice thickness, something which was only feasible because the folding pattern of the brain region of interest, the 'hand-knob' region of primary motor cortex, has a relatively simple and predictable folding pattern.…”

Design of Crisscrossed Double-Layer Birdcage Coil for Improving B1+Field Homogeneity for Small-Animal Magnetic Resonance Imaging at 300 MHz

“…HF MRI scanner have found use in a wide range of medical applications from neuroimaging to oncological investigations for the image quality they provide [3][4][5]. In this backdrop, researchers have designed and developed various geometries of the RF coil that provides the excitation pulse for generating the transmitting (B 1 + ) field and highly sensitive receiving fields (B 1 − ) for the MR signals emitted from the imaged subject [6,7].…”