Methods for Functional Brain Imaging
Methods for Functional Brain Imaging

Author: Thomas Witzel (Ph. D.)

Publisher:

Published: 2011

Total Pages: 99

ISBN-13:

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Magnetic resonance imaging (MRI) has demonstrated the potential for non-invasive mapping of structure and function (fMRI) in the human brain. In this thesis, we propose a series of methodological developments towards improved fMRI of auditory processes. First, the inefficiency of standard fMRI that acquires brain volumes one slice at a time is addressed. The proposed single-shot method is capable, for the first time, of imaging the entire brain in a single-acquisition while still maintaining adequate spatial resolution for fMRI. This method dramatically increases the temporal resolution of fMRI (20 fold) and improves sampling efficiency as well as the ability to discriminate against detrimental physiological noise. To accomplish this it exploits highly accelerated parallel imaging techniques and MRI signal detection with a large number of coil elements. We then address a major problem in the application of fMVIRI to auditory studies. In standard fMRI, loud acoustic noise is generated by the rapid switching of the gradient magnetic fields required for image encoding, which interferes with auditory stimuli and enforces inefficient and slow sampling strategies. We demonstrate a fMRI method that uses parallel imaging and redesigned gradient waveforms to both minimize and slow down the gradient switching to substantially reduce acoustic noise while still enabling rapid acquisitions for fMRI. Conventional fMRI is based on a hemodynamic response that is secondary to the underlying neuronal activation. In the final contribution of this thesis, a novel image contrast is introduced that is aimed at the direct observation of neuronal magnetic fields associated with functional activation. Early feasibility studies indicate that the imaging is sensitive to oscillating magnetic fields at amplitudes similar to those observed by magnetoencephalography.

Ultra-High Field Neuro MRI
Ultra-High Field Neuro MRI

Author: Karin Markenroth Bloch

Publisher: Elsevier

Published: 2023-08-21

Total Pages: 628

ISBN-13: 0323999530

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Ultra-High Field Neuro MRI is a comprehensive reference and educational resource on the current state of neuroimaging at ultra-high field (UHF), with an emphasis on 7T. Sections cover the MR physics aspects of UHF, including the technical challenges and practical solutions that have enabled the rapid growth of 7T MRI. Individual chapters are dedicated to the different techniques that most strongly benefit from UHF, as well as chapters with a focus on different application areas in anatomical, functional and metabolic imaging. Finally, several chapters highlight the neurological and psychiatric applications for which 7T has shown benefits. The book is aimed at scientists who develop MR technologies and support clinical and neuroscience research, as well as users who want to benefit from UHF neuro MR techniques in their work. It also provides a comprehensive introduction to the field. Presents the opportunities and technical challenges presented by MRI at ultra-high field Describes advanced ultra-high field neuro MR techniques for clinical and neuroscience applications Enables the reader to critically assess the specific UHF advantages over currently available techniques at clinical field strengths

Ultra High Field Magnetic Resonance Imaging
Ultra High Field Magnetic Resonance Imaging

Author: Pierre-Marie Robitaille

Publisher: Springer Science & Business Media

Published: 2007-12-31

Total Pages: 487

ISBN-13: 0387496483

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The foundation for understanding the function and dynamics of biological systems is not only knowledge of their structure, but the new methodologies and applications used to determine that structure. This volume in Biological Magnetic Resonance emphasizes the methods that involve Ultra High Field Magnetic Resonance Imaging. It will interest researchers working in the field of imaging.

Multimodal Imaging in Neurology
Multimodal Imaging in Neurology

Author: Hans-Peter Müller

Publisher: Morgan & Claypool Publishers

Published: 2008

Total Pages: 85

ISBN-13: 1598295500

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The field of brain imaging is developing at a rapid pace and has greatly advanced the areas of cognitive and clinical neuroscience. The availability of neuroimaging techniques, especially magnetic resonance imaging (MRI), functional MRI (fMRI), diffusion tensor imaging (DTI) and magnetoencephalography (MEG) and magnetic source imaging (MSI) has brought about breakthroughs in neuroscience. To obtain comprehensive information about the activity of the human brain, different analytical approaches should be complemented. Thus, in "intermodal multimodality" imaging, great efforts have been made to combine the highest spatial resolution (MRI, fMRI) with the best temporal resolution (MEG or EEG). "Intramodal multimodality" imaging combines various functional MRI techniques (e.g., fMRI, DTI, and/or morphometric/volumetric analysis). The multimodal approach is conceptually based on the combination of different noninvasive functional neuroimaging tools, their registration and cointegration. In particular, the combination of imaging applications that map different functional systems is useful, such as fMRI as a technique for the localization of cortical function and DTI as a technique for mapping of white matter fiber bundles or tracts. This booklet gives an insight into the wide field of multimodal imaging with respect to concepts, data acquisition, and postprocessing. Examples for intermodal and intramodal multimodality imaging are also demonstrated.

Ultrahigh Field Functional Magnetic Resonance Electrical Impedance Tomography (fMREIT) in Neural Activity Imaging
Ultrahigh Field Functional Magnetic Resonance Electrical Impedance Tomography (fMREIT) in Neural Activity Imaging

Author: Fanrui Fu

Publisher:

Published: 2019

Total Pages: 185

ISBN-13:

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A direct Magnetic Resonance (MR)-based neural activity mapping technique with high spatial and temporal resolution may accelerate studies of brain functional organization.The most widely used technique for brain functional imaging is functional Magnetic Resonance Image (fMRI). The spatial resolution of fMRI is high. However, fMRI signals are highly influenced by the vasculature in each voxel and can be affected by capillary orientation and vessel size. Functional MRI analysis may, therefore, produce misleading results when voxels are nearby large vessels. Another problem in fMRI is that hemodynamic responses are slower than the neuronal activity. Therefore, temporal resolution is limited in fMRI. Furthermore, the correlation between neural activity and the hemodynamic response is not fully understood. fMRI can only be considered an indirect method of functional brain imaging.Another MR-based method of functional brain mapping is neuronal current magnetic resonance imaging (ncMRI), which has been studied over several years. However, the amplitude of these neuronal current signals is an order of magnitude smaller than the physiological noise. Works on ncMRI include simulation, phantom experiments, and studies in tissue including isolated ganglia, optic nerves, and human brains. However, ncMRI development has been hampered due to the extremely small signal amplitude, as well as the presence of confounding signals from hemodynamic changes and other physiological noise. Magnetic Resonance Electrical Impedance Tomography (MREIT) methods could have the potential for the detection of neuronal activity. In this technique, small external currents are applied to a body during MR scans. This current flow produces a magnetic field as well as an electric field. The altered magnetic flux density along the main magnetic field direction caused by this current flow can be obtained from phase images. When there is neural activity, the conductivity of the neural cell membrane changes and the current paths around the neurons change consequently. Neural spiking activity during external current injection, therefore, causes differential phase accumulation in MR data. Statistical analysis methods can be used to identify neuronal-current-induced magnetic field changes.

Advancing Ultra-high Field MRI Functional and Structural Applications
Advancing Ultra-high Field MRI Functional and Structural Applications

Author:

Publisher:

Published: 2022

Total Pages: 0

ISBN-13:

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Magnetic resonance imaging (MRI) has shown to be a valuable tool for studying the human brain, allowing in-vivo visualization of structures and anatomy in great detail, especially at Ultra-High field strengths (≥ 7T). MRI is not limited by anatomical and structural information. It can study the brain’s anatomy, functionality, connectivity (functional and structural), and chemical metabolism. Functional MRI (fMRI), for instance, enables the investigation of brain function mechanisms in-vivo with a non-invasive advantage compared to other tools. The present thesis focuses on advanced MRI techniques for ultra-high field strength (≥ 7T), specifically for neuroscience applications. Combined with the higher field strength, these techniques provide better imaging quality and precise brain activity measurement. For example, high-quality anatomical T1 weighted images are essential for several MRI applications, notably, to serve as an anatomical reference in fMRI and gray matter segmentation. Unfortunately, increased field strength also induces non-uniformities in the transmit field (B1+) that can compromise image contrast non-uniformly. One of the goals of the present thesis was to investigate new strategies to overcome this issue. Regarding the functional brain investigation, the gradient-echo (GRE) is the typical method of choice for fMRI applications. Despite its high sensitivity to deoxyhemoglobin variations and widespread availability, the gradient-echo (GRE) BOLD signal is predominantly driven by the large draining vessels resulting in a limited spatial specificity, especially for 7T or higher field strength applications in which the BOLD sensitivity (susceptibility effect) is higher compared to lower static field scanners. In this context, we investigated an alternative fMRI method called vascular space occupancy (VASO) that promises higher spatial specificity than the typical GRE BOLD. To achieve the aim of this thesis, we used four approaches (chapters 2-5).

High-Field MR Imaging
High-Field MR Imaging

Author: Jürgen Hennig

Publisher: Springer Science & Business Media

Published: 2011-08-31

Total Pages: 261

ISBN-13: 3540850902

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This book describes the current status of the very rapidly developing field of high-field MR and examines the possibilities, challenges, and limitations of this fascinating technology. In the initial chapters, the basic technological background is explained in a non-technical way so as to promote understanding of the issues and concepts and avoid overwhelming the reader with excessive detail. Safety issues, methods, and contrast are then carefully considered. The final part of the book examines the diverse applications of high-field MR imaging in radiology, neuroscience, oncology, and other fields, with the aid of numerous high-quality illustrations. All chapters are written by leading experts who have taken great care to illustrate the potential and progress of the field in an informative and accessible manner. The book will appeal to all with a potential interest in the application of high-field MR imaging, including radiologists, neuroscientists, and oncologists.

Magnetic Resonance Brain Imaging
Magnetic Resonance Brain Imaging

Author: Jörg Polzehl

Publisher: Springer Nature

Published: 2023-11-12

Total Pages: 268

ISBN-13: 3031389492

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This book discusses modelling and analysis of Magnetic Resonance Imaging (MRI) data of the human brain. For the data processing pipelines we rely on R, the software environment for statistical computing and graphics. The book is intended for readers from two communities: Statisticians, who are interested in neuroimaging and look for an introduction to the acquired data and typical scientific problems in the field and neuroimaging students, who want to learn about the statistical modeling and analysis of MRI data. Being a practical introduction, the book focuses on those problems in data analysis for which implementations within R are available. By providing full worked-out examples the book thus serves as a tutorial for MRI analysis with R, from which the reader can derive its own data processing scripts. The book starts with a short introduction into MRI. The next chapter considers the process of reading and writing common neuroimaging data formats to and from the R session. The main chapters then cover four common MR imaging modalities and their data modeling and analysis problems: functional MRI, diffusion MRI, Multi-Parameter Mapping and Inversion Recovery MRI. The book concludes with extended Appendices on details of the utilize non-parametric statistics and on resources for R and MRI data. The book also addresses the issues of reproducibility and topics like data organization and description, open data and open science. It completely relies on a dynamic report generation with knitr: The books R-code and intermediate results are available for reproducibility of the examples.