Biomedical Engineering Reference
In-Depth Information
Chapter 1
Dynamic Imaging of Brain Function
Fahmeed Hyder
Abstract
In recent years, there have been unprecedented methodological advances in the dynamic imaging of
brain activities. Electrophysiological, optical, and magnetic resonance methods now allow mapping of
functional activation (or deactivation) by measurement of neural activity (e.g., membrane potential, ion
flux, neurotransmitter flux), energy metabolism (e.g., glucose consumption, oxygen consumption, crea-
tine kinase flux), and functional hyperemia (e.g., blood oxygenation, blood flow, blood volume). Prop-
erties of the glutamatergic synapse are used to model activities at the nerve terminal and their associated
changes in energy demand and blood flow. This approach reveals that each method measures different
tissue- and/or cell-specific components with characteristic spatiotemporal resolution. While advantages
and disadvantages of different methods are apparent and often used to supersede one another in terms
of specificity and/or sensitivity, no particular technique is
the
optimal dynamic brain imaging method
because each method is unique in some respect. Since the demand for energy substrates
is
a fundamental
requirement for function, energy-based methods may allow quantitative dynamic imaging in vivo. How-
ever, there are exclusive neurobiological insights gained by combining some of these different dynamic
imaging techniques.
Key words:
fMRI, glia, GABA, glutamate, glutamine, lactate, multi-modal, neuroimaging.
1. Introduction
The brain is a highly complex organ, both anatomically
(1)
and
physiologically
(2)
, requiring an impressive arsenal of techno-
logical tools to study it. In recent years, neuroscientists and
neurophysiologists have benefited from the emergence of sev-
eral dynamic imaging techniques. Currently, a variety of electro-
physiological, optical, and magnetic resonance methods allow in
vivo probing of brain activities in terms of transients in neuronal
activity as well as their fundamentally associated energetic and
hyperemic events
(3)
. Since these functional imaging methods
either measure directly or exploit relationships between electrical,
