Biomedical Engineering Reference
In-Depth Information
Chapter 14
Dynamic MRI of Small Electrical Activity
Allen W. Song, Trong-Kha Truong, Marty Woldorff
Abstract
Neuroscience methods entailing in vivo measurements of brain activity have greatly contributed to our
understanding of brain function for the past decades, from the invasive early studies in animals using
single-cell electrical recordings, to the noninvasive techniques in humans of scalp-recorded electroen-
cephalography (EEG) and magnetoencephalography (MEG), positron emission tomography (PET),
and, most recently, blood oxygenation level-dependent (BOLD) functional magnetic resonance imag-
ing (fMRI). A central objective of these techniques is to measure neuronal activities with high spatial and
temporal resolution. Each of these methods, however, has substantial limitations in this regard. Single-cell
recording is invasive and only typically records cellular activity in a single location; EEG/MEG cannot
generally provide accurate and unambiguous delineations of neuronal activation spatially; and the most
sophisticated BOLD-based fMRI methods are still fundamentally limited by their dependence on the
very slow hemodynamic responses upon which they are based. Even the latest neuroimaging methodol-
ogy (e.g., multimodal EEG/fMRI) does not yet unambiguously provide accurate localization of neuronal
activation spatially and temporally. There is hence a need to further develop noninvasive imaging meth-
ods that can directly image neuroelectric activity and thus truly achieve a high temporal resolution and
spatial specificity in humans. Here, we discuss the theory, implementation, and potential utility of an
MRI technique termed Lorentz effect imaging (LEI) that can detect spatially incoherent yet temporally
synchronized, minute electrical activities in the neural amplitude range (microamperes) when they occur
in a strong magnetic field. Moreover, we demonstrate with our preliminary results in phantoms and in
vivo, the feasibility of imaging such activities with a temporal resolution on the order of milliseconds.
Key words:
BOLD, fMRI, neuroimaging, noninvasive, Lorentz effect.
1. Introduction
Over the years, functional neuroimaging research has seen
tremendous progress and greatly improved our understanding of
brain function. The continuous pursuit to better measure neu-
ral activity has led to many exciting technical advances, including
