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The development of magnetic susceptibility weighted magnetoencephalography

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Call No.	Ph.D. 2011
Author	Burke, Broc A.
Title	The development of magnetic susceptibility weighted magnetoencephalography
Date	2011
Abstract	The measurement of human brain function is the goal of many noninvasive medical imaging modalities. Two sources of physiological contrast are commonly targeted to achieve this goal. The most direct approach to measuring neuronal activity is with electroencephalography (EEG) or magnetoencephalography (MEG). Indirect methods of imaging neural activity measure tissue metabolism with positron emission tomography (PET) and single photon emission computed tomography (SPECT), or via the hemodynamic response measured with functional magnetic resonance imaging (fMRI) and functional near infrared spectroscopy (fNIRS). Each modality provides a different perspective on human brain function. Fundamental new understanding now requires simultaneous measurement of the neural electric and the metabolic activity. From a clinical standpoint, multiple neurological and hematological conditions affect the local vascular response to neural activity. The need for studies of this link termed neurovascular coupling has led to the development of multimodal brain imaging techniques. In the present work, a novel neuroimaging technique is introduced that is capable of simultaneously measuring concentration changes in deoxygenated hemoglobin (HbR) and the magnetic fields generated by neuroelectrical activity. The hemodynamic measurements were performed by exploiting the difference in HbR's magnetic susceptibility relative to the surrounding tissue. A DC magnetic field (weaker than the Earth's magnetic field) was applied to induce magnetic dipoles in the human head. The resultant magnetic field was measured (p<0.05) by an array of superconducting quantum interference devices (SQUIDs). These SQUIDs also provided measurements of the magnetic fields generated by spatiotemporally synchronous neural activity (p<0.05). A method is presented for modifying a MEG system and tomographically reconstructing the resulting magnetic field measurements to produce images of magnetic susceptibility with an estimated positional error of ?1 cm at cortical depth. Additional material on the support equipment developed to enable this technology is also presented, including the design and analysis of a magnetically shielded room. The combination of the support equipment, tomographic method, and simultaneous acquisition of HbR and neuroelectric activity with a single sensor set will scientifically enable advancements in the topic of neurovascular coupling and clinically provide novel diagnostic capability with low patient risk and cost for institutions with MEGs.
Description	xi, 113 leaves : ill. (some col.) 28 cm.
Format	application/pdf
Advisor	Diamond, Solomon G. Grant, Ellen Hansen, Eric W. Paulsen, Keith D.
Subject	Magnetoencephalography -- Technique.; Magnetic susceptibility.
College	Thayer School of Engineering,
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Copyright	All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means without permission in writing from the author.
DOI	http://dx.doi.org/10.1349/ddlp.333

Title	Page 1
Format	application/pdf
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Full Text	THE DEVELOPMENT OF MAGNETIC SUSCEPTIBILITY WEIGHTED MAGNETOENCEPHALOGRAPHY A Thesis Submitted to the Faculty in partial fulfillment of the requirements for the degree of Doctor of Philosophy by BROC A. BURKE Thayer School of Engineering Dartmouth College Hanover, New Hampshire June 2011 Examining Committee: Chairman_______________________ Solomon G. Diamond Member________________________ P. Ellen Grant Member________________________ Eric W. Hansen Member________________________ Keith D. Paulsen ___________________ Brian W. Pogue Dean of Graduate Studies

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