Enhanced low and high frequency resting EEG activity in patients with chronic severe obsessive-compulsive and psychotic disorders (original) (raw)
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Recent applications of UHF-MRI in the study of human brain function and structure: a review
NMR in biomedicine, 2015
The increased availability of ultra-high-field (UHF) MRI has led to its application in a wide range of neuroimaging studies, which are showing promise in transforming fundamental approaches to human neuroscience. This review presents recent work on structural and functional brain imaging, at 7 T and higher field strengths. After a short outline of the effects of high field strength on MR images, the rapidly expanding literature on UHF applications of blood-oxygenation-level-dependent-based functional MRI is reviewed. Structural imaging is then discussed, divided into sections on imaging weighted by relaxation time, including quantitative relaxation time mapping, phase imaging and quantitative susceptibility mapping, angiography, diffusion-weighted imaging, and finally magnetization-transfer imaging. The final section discusses studies using the high spatial resolution available at UHF to identify explicit links between structure and function. Copyright © 2015 John Wiley & Sons, Ltd.
Parcellation of human amygdala in vivo using ultra high field structural MRI
NeuroImage, 2011
Histological studies show that human amygdala is subdivided into several nuclei with specific connections to other brain areas. One such study has been recently used as the basis of a probabilistic amygdala map, to enable in vivo identification of specifically located functions within the amygdala and connections to it. The involvement of the amygdala in cognition, emotion and action, which may underlie several psychiatric disorders, points to a need for discrimination of these nuclei in living human brains using different techniques. Structural MRI scans of the human amygdala at standard field strengths (≤ 3 T) have shown a region of generally featureless gray matter. Apparently homogeneous regions may reveal internal structure, however, when improved imaging strategies and better SNR are available. The goal of this study is the in vivo anatomical segmentation of the amygdala using high resolution structural MR data. The use of different MRI tissue contrast mechanisms at high field strengths has been little explored so far. Combining two different contrasts, and using cutting-edge image analysis, the following study provides a robust clustering of three amygdala components in vivo using 7 T structural imaging.
NeuroImage, 2012
Ultra-high field MRI (≥7 T) has recently shown great sensitivity to depict patterns of tissue microarchitecture. Moreover, recent studies have demonstrated a dependency between T 2 * and orientation of white matter fibers with respect to the main magnetic field B 0 . In this study we probed the potential of T 2 * mapping at 7 T to provide new markers of cortical architecture. We acquired multi-echo measurements at 7 T and mapped T 2 * over the entire cortex of eight healthy individuals using surface-based analysis. B 0 dependence was tested by computing the angle θ z between the normal of the surface and the direction of B 0 , then fitting T 2 *(θ z ) using model from the literature. Average T 2 * in the cortex was 32.20+/−1.35 ms. Patterns of lower T 2 * were detected in the sensorimotor, visual and auditory cortices, likely reflecting higher myelin content. Significantly lower T 2 * was detected in the left hemisphere of the auditory region (p<0.005), suggesting higher myelin content, in accordance with previous investigations. B 0 orientation dependence was detected in some areas of the cortex, the strongest being in the primary motor cortex (ΔR 2 *=4.10 Hz). This study demonstrates that quantitative T 2 * measures at 7 T MRI can reveal patterns of cytoarchitectural organization of the human cortex in vivo and that B 0 orientation dependence can probe the coherency and orientation of gray matter fibers in the cortex, shedding light into the potential use of this type of contrast to characterize cyto-/myeloarchitecture and to understand the pathophysiology of diseases associated with changes in iron and/or myelin concentration.
Ultrahigh field systems and applications at 7 T and beyond: Progress, pitfalls, and potential
Magnetic Resonance in Medicine, 2012
About 150 researchers around the world convened at the Chateau Lake Louise on February 20-23, 2011 to present and discuss the latest research in human and animal imaging and spectroscopy at field strengths of 7 T or above (termed ultrahigh field) at the third ISMRM-sponsored high field workshop. The clear overall message from the workshop presentations and discussion is that ultrahigh field imaging is gaining momentum with regard to new clinically relevant findings, anatomic and functional MRI results, susceptibility contrast advancements, solutions to high field-related image quality challenges, and to generally push the limits of resolution and speed of high field imaging. This meeting report is organized in a manner reflecting the meeting organization itself, covering the seven sessions that were approximately titled: (1) high field overview from head to body to spectroscopy; (2) susceptibility imaging; (3) proffered session on susceptibility, ultrafast imaging, unique contrast at 7 T, and angiography; (4) neuroscience applications; (5) proffered session on coils, shimming, parallel imaging, diffusion tensor imaging, and MRI-PET fusion; (6) high field animal imaging and spectroscopy, as well as a vendor overview, and Cutting edge technology at 7 T. Magn Reson Med 67:317-321,
separation: Magnetic susceptibility source separation toward iron and myelin mapping in the brain
Neuroimage, 2021
Obtaining a histological fingerprint from the in-vivo brain has been a long-standing target of magnetic resonance imaging (MRI). In particular, non-invasive imaging of iron and myelin, which are involved in normal brain functions and are histopathological hallmarks in neurodegenerative diseases, has practical utilities in neuroscience and medicine. Here, we propose a biophysical model that describes the individual contribution of paramagnetic (e.g., iron) and diamagnetic (e.g., myelin) susceptibility sources to the frequency shift and transverse relaxation of MRI signals. Using this model, we develop a method,-separation, that generates the voxel-wise distributions of the two sources. The method is validated using computer simulation and phantom experiments, and applied to ex-vivo and in-vivo brains. The results delineate the well-known histological features of iron and myelin in the specimen, healthy volunteers, and multiple sclerosis patients. This new technology may serve as a practical tool for exploring the microstructural information of the brain.
Bridging the Gap between System and Cell: The Role of Ultra-High Field MRI in Human Neuroscience
Vital Models: The Making and Use of Models in the Brain Sciences. Progress in Brain Research, Volume 233.
The volume of published research at the levels of systems and cellular neuroscience continues to increase at an accelerating rate. At the same time, progress in psychiatric medicine has stagnated and scientific confidence in cognitive psychology research is under threat due to careless analysis methods and underpowered experiments. With the advent of ultra-high-field MRI, with submillimetre image voxels, imaging neuroscience holds the potential to bridge the cellular and systems levels. Use of these accurate and precisely localized quantitative measures of brain activity may go far in providing more secure foundations for psychology, and hence for more appropriate treatment and management of psychiatric illness. However, fundamental issues regarding the construction of testable mechanistic models using imaging data require careful consideration. This chapter summarizes the characteristics of acceptable models of brain function, and provides concise descriptions of the relevant types of neuroimaging data that have recently become available. Approaches to data-driven experiments and analyses are described that may lead to more realistic conceptions of the competences of neural assemblages, as they vary across the brain’s complex neuroanatomy. Robert Turner (primary author) & Daniel De Haan (secondary author). Forthcoming in VITAL MODELS: THE MAKING AND USE OF MODELS IN THE BRAIN SCIENCES, Volume 233, eds., Nikolas Rose Tara Mahfoud Sam McLean
Superficial white matter imaging: Contrast mechanisms and whole-brain in vivo mapping
Science Advances
Superficial white matter (SWM) contains the most cortico-cortical white matter connections in the human brain encompassing the short U-shaped association fibers. Despite its importance for brain connectivity, very little is known about SWM in humans, mainly due to the lack of noninvasive imaging methods. Here, we lay the groundwork for systematic in vivo SWM mapping using ultrahigh resolution 7 T magnetic resonance imaging. Using biophysical modeling informed by quantitative ion beam microscopy on postmortem brain tissue, we demonstrate that MR contrast in SWM is driven by iron and can be linked to the microscopic iron distribution. Higher SWM iron concentrations were observed in U-fiber–rich frontal, temporal, and parietal areas, potentially reflecting high fiber density or late myelination in these areas. Our SWM mapping approach provides the foundation for systematic studies of interindividual differences, plasticity, and pathologies of this crucial structure for cortico-cortical...
Comparing Like with Like: the Power of Knowing Where You Are
Brain connectivity, 2014
Magnetic resonance imaging can now provide human brain images of structure, function, and connectivity with isotropic voxels smaller than one millimeter, and thus much smaller than the cortical thickness. This resolution, achievable in a scan time of less than 1 h, enables visualization of myeloarchitectural layer structure, intracortical variations in functional activity-recorded in changes in blood oxygenation level dependent signal or cerebral blood volume CBV-and intracortical axonal orientational structure via diffusion-weighted magnetic resonance imaging. While recent improvements in radiofrequency receiver coils now enable excellent image data to be obtained at 3T, scanning at the ultra-high field of 7T offers further gains in signal-to-noise ratio and speed of image acquisition, with a structural image resolution of about 300 lm. These improvements throw into sharp question the strategies that have become conventional for the analysis of functional imaging data, especially the practice of spatial smoothing of raw functional data before further analysis. Creation of a native cortical map for each human subject that provides a reliable individual parcellation into cortical areas related to Brodmann Areas enables a strikingly different approach to functional image analysis. This proposed approach involves surface registration of the cortices of groups of subjects using maps of the longitudinal relaxation time T1 as an index of myelination, and methods for inferring statistical significance that do not entail spatial smoothing. The outcome should be a far more precise comparison of like-with-like cortical areas across subjects, with the potential to greatly increase experimental power, to discriminate activity in neighboring cortical areas, and to enable correlation of function and connectivity with specific cytoarchitecture. Such analyses should enable a far more convincing modeling of brain mechanisms than current graph-based methods that require gross oversimplification of brain activity patterns in order to be computationally tractable.
Cerebral cortex (New York, N.Y. : 1991), 2014
The precise delineation of auditory areas in vivo remains problematic. Histological analysis of postmortem tissue indicates that the relation of areal borders to macroanatomical landmarks is variable across subjects. Furthermore, functional parcellation schemes based on measures of, for example, frequency preference (tonotopy) remain controversial. Here, we propose a 7 Tesla magnetic resonance imaging method that enables the anatomical delineation of auditory cortical areas in vivo and in individual brains, through the high-resolution visualization (0.6 × 0.6 × 0.6 mm(3)) of intracortical anatomical contrast related to myelin. The approach combines the acquisition and analysis of images with multiple MR contrasts (T1, T2*, and proton density). Compared with previous methods, the proposed solution is feasible at high fields and time efficient, which allows collecting myelin-related and functional images within the same measurement session. Our results show that a data-driven analysis...