Transcript Electrodes for Reception and Stimulation in the Body

ELECTRODES FOR
RECEPTION AND
STIMULATION IN THE BODY
Electrodes for Reception and Stimulation
in the Body
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Electrodes can be used two basic ways in medical
applications.
They can be used for reception, to receive signals from
the body, such as for diagnosing carpal tunnel and
other nerve disorders or for impedance imaging and
monitoring.
Electrodes can also be used for stimulation, for example,
delivering shocks for cardiac defibrillation or pacing,
delivering pulsed electromagnetic fields for pain
therapy and healing of muscle, bones, and nerves, or
for stimulating the brain for control of Parkinson’s
disease or mental disorders.
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They can also be used for invasive heat treatments such as
cardiac ablation, and for measuring the dielectric properties
of body tissues and other materials.
Electrodes for either stimulation or reception can be used
over very large regions of the body, smaller regions, or very
localized areas.
They can be invasive, external, in vitro, or completely
separated from the body.
For all applications, maintaining good electrical contact
between the electrode and the body is very important.
Conductive gels are often used (such as in ECG
measurements). and specialized materials are used to
prevent buildup of nonconductive fibrous tissue (scar tissue)
around implantable electrodes.
Electrodes for Reception
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Electrophysiological Assessment
Clinical electrophysiological assessment, also called
electroneuromyography (ENMG; or when only
associated with a muscle, electromyography [EMG]), is
used to determine the function and integrity of specific
parts of the neuromuscular system.
The neuromuscular junction, skeletal muscles, peripheral
sensory nerve fibers, reflexes, and some central nervous
system pathways can be tested using ENMG, even
individual motor neurons.
Surface electrodes are the least localized and least
invasive.
Cont...
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Needle electrodes are more localized and more
invasive.
Miniaturized needle electrodes made out of silicon are
the most localized and are generally meant to be
implanted in the body (and hence are the most
invasive).
Sometimes both stimulation and recording electrodes
are used simultaneously to determine the effect of
stimulating a region and determine if the signals pass
through the neural system as expected.
2. Intracellular Recording: Receiving
Signals from Brain and Nerves
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These studies have been used extensively for the
development and assessment of neurotransmitter drugs and
an overall study of the nervous system.
Until, there has been no way to perform these tests in a
living organism, because the nerve cells are too small.
Recently, a number of groups have been developing very
tiny electrodes and arrays of electrodes made by etching
silicon, and have been able to receive signals from
individual neurons.
Although still used mainly for research, this technology
is rapidly progressing toward commercial applications
that focus on individual nerve stimulation more than
neural recording.
3.Impedance Imaging
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It would be extremely useful if impedance measurements
could be used to map the impedance of the interior of
the body.
Such a map would provide not only morphometric
information like that provided by x-ray computed
tomography (CT) scans, but also additional physiological
information.
One method for mapping impedance would be to use an
array of electrodes around the periphery of the body,
as illustrated in Figure
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These reconstruction techniques work well with x-rays
because the x-rays travel in straight lines through the
body.
These same reconstruction techniques do not work well
with impedance imaging, however, because the currents
do not travel in straight lines between the electrodes
through the body.
Special techniques have been used to try to account for
differing current paths, but with limited success.
If impedance imaging could be made useful, it would
have the advantage of being simpler and less expensive
than some other imaging techniques