Magnetic Resonance Imaging of Human Brain Anatomy and Function

National Institute Of Neurological Disorders And Stroke

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Abstract

The overarching goal of this project is to develop an improved understanding of brain anatomy and function through application of state-of-the-art MRI techniques and conjoint analysis of functional MRI (fMRI) and electrophysiological signals (EEG, ECoG). EEG and fMRI activity patterns contain a wealth of information that allows detailed study of the major communication pathways in the brain as well as the major clusters of brain regions that work together to subserve specific functions. Over recent years, studies in AMRI and other labs have made increasingly clear that EEG and fMRI activity patterns are highly dependent on brain arousal state and may undergo major changes over time scales as short as several seconds. In addition, arousal state changes are accompanied by changes in autonomic physiology that, by themselves, may lead to fMRI signal changes. To study this in detail, AMRI has been performing overnight sleep studies in which EEG, fMRI and autonomic signals are acquired concurrently. As of yet, over 50 such studies have been completed and data analysis is underway. In part, this is being done in a collaborative manner, including the groups of Gulio Bernardi (University of Lucca), Zhiwei Ma (Shanghai Tech), and Xiao Liu (Penn State University). Another 5 subjects are planned to be studied this year, after which final data analysis will start. AMRI has collaborated with Xiao Liu to study the effect of momentary changes in arousal on fMRI, EEG and autonomic signals. A prototypical sequence of events was identified in which EEG spectral changes precede fMRI changes, and are accompanied by changes in respiration and heart rate. In addition, the blood volume changes associated with the fMRI signal led to changes in CSF flow with each arousal change. This suggest that CSF movement is facilitated by momentary changes in arousal state and may imply that CSF-mediated glymphatic waste clearance depends on fluctuations in arousal state. This study was published in Neuroimage. Further analysis along these lines is under way, and includes data from the Human Connectome Project, and the Allen Brain Institute. Over the years, AMRI has investigated ways to distinguish between the effects of changes in iron and myelin on MRI contrast, with the goal of characterizing pathology in neurodegenerative disorders such as MS, ALS, and Parkinsons Disease. At high magnetic field, magnetic susceptibility contrast is exquisitely sensitive to these changes, however this contrast type is difficult to interpret. This makes distinguishing between iron and myelin difficult. In 2023, we performed a series of studies (in-vivo and on fixed brain tissue) to investigate whether T2 contrast (at high field) may facilitate distinguishing between iron and myelin. The rationale was that, at high field, T2 would be predominantly affected by iron and to a much lesser extent by myelin. This proved largely true, but remaining sensitivity to myelin, precluded robust quantification of iron based on T2 contrast alone. In fact, the analysis revealed that the contribution of myelin to T2 varied over the brain with an apparent dependence on axon diameter. Initial results of this analysis were presented at the 2023 ISMRM meeting and a journal article is under preparation.