Other Biopotentials-08-s [Compatibility Mode]

8/7/2019 Other Biopotentials-08-s [Compatibility Mode]

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Medical Instrumentation I

Other Biopotentials

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asan - as asDepartment of Electrical EngineeringCollege of Engineering

American University of Sharjah


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Major Divisions of the CNS

Forebrain Cerebrum, Diencephalon

Brainstem

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Cerebellum Spinal Cord


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Brain Function brainstem: stalk of brain, along which nerve fibers

send information between spinal chord and higherbrain structures.

thalamus: relay station, integrates sensoryinformation before it is sent to cortex (with theexception of smell).

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cerebellm: fine muscle movement control. white matter: contains fibers which interconnect

thalamus and cortex (mostly myelinated axons, 1cm3 volume may contain 107 fibers).

grey matter (cortex): 2-3 mm thick, total surface areaof 1600 cm2, contains about 1010 neurons. Eachneuron has about 103 to 105 synapses. Cortex is

responsible for our conscious experience.


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Electroencephalography (EEG)Electroencephalography (EEG)

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EEG is the recording of the electrical activity of theEEG is the recording of the electrical activity of the

brain as measured on the scalp with electrodes.brain as measured on the scalp with electrodes.


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Characteristics of the EEGCharacteristics of the EEG The frequency contents of the EEG varies with alertness andThe frequency contents of the EEG varies with alertness and

mental activity.mental activity.

Bandwidth:Bandwidth: 00..55 3030 HZ and Amplitude:HZ and Amplitude: 55 300300VV Delta (Delta () waves:) waves: 00..55 44HzHz -- during deep sleep, youngduring deep sleep, young

children and brain diseases.children and brain diseases.

-- --

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..

Alpha (Alpha () waves:) waves: 88--1313 HzHz -- Normal, a wake, quiet person.Normal, a wake, quiet person.

Beta (Beta () waves:) waves: 1313--2222 HzHz -- Associated with intense mentalAssociated with intense mentalactivity.activity.

Gamma (Gamma () waves:) waves: 2222--3030 HzHz Associated with attentionAssociated with attentionand sensory stimulus.and sensory stimulus.


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Clinical UsesClinical Uses

Study sleep patternsStudy sleep patterns

Epilepsy diagnosis.Epilepsy diagnosis.

Used with EMG to study neuromuscularUsed with EMG to study neuromuscular

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a o og es.a o og es. Determine level of anesthesiaDetermine level of anesthesia

Help in locating tumors.Help in locating tumors.

Brain response to stimulus.Brain response to stimulus.

Detect and monitor brain injuryDetect and monitor brain injury


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EEG Block diagram

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Electrodes System Electrodes transfer ionic currents from cerebral tissues intoelectrical signal used by electronic amplifiers.

The most common electrode placement system is the 10-20

system. The head is mapped by 4 points: (1) Nasion, (2) Inions, (3) Left ear and (4) Right ear.

The spacing between (1) and (2), (3) and (4) are divided are

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.

The head is mapped using 7 standard letters. These letters are:

O for Occipital P for Parietal

C for Central F for Frontal

FP for frontal pole T for Temporal A for Auricular

19 electrodes are used.


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Electrodes System

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Electrodes System

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Electrodes System Unipolar arrangement: a number of scalp leads (-ve) are

connected to a common point (ear lobe)

Bipolar arrangement: inter connection between variouscombination of electrodes.

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Montage is a combination of electrodes, which is assignedto each channel. An example is shown below:

Chann

el

1 2 3 4 5 6 7 8

Lead 1 FP1 F7 T3 T5 FP3 F8 T4 T6

Lead 2 F7 T3 T5 O1 F8 T4 T6 O2


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Generalised epilepsy EEG

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Signal Averaging Apply Mstimuli, and recordresulting Mresponses.

Align Mresponses to form

an ensemble with eachresponse EP aligned intime.

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responses in the ensembleto get the EP estimate

avgnotavg

M

iavg

SNRMSNR

xMx

=

=

1

1


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Evoked Potentials

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Brainstem Auditory Evoked Potential

(BAEP)

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Somatosensory Evoked Potential

(SEP)

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Electromyography (EMG) It is an important instrument, which measures the

electrical activity of muscles. Signals are obtained

using needle or surface electrodes. Clinical Uses include Diagnosis of neuromuscular

disorders, Measure of relaxation, An indication of

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musc e ac v y, an e ec on o muscu ar ys rop y.

Amplitude: 1 - 10mV

Bandwidth: 10 1KHz for surface and 10 5KHz forneedle measurements. The EMG signal looks like

random signals. Signals can be taken to a speaker , where a

neurologist will listen to the EMG .


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EMG Gait Signal

0. 2

0. 3

0. 4

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0 500 1000 1500 2000 2500 3000

-0.3

-0.2

-0.1

0

0. 1


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Electroretinogram (ERG) Amplitude: 0 1mV

Bandwidth: DC 50Hz.

An active electrode on thecornea, with saline solutionbridging the gap between

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e e ec ro e an ecornea, and placing areference electrode to theearlobe. The retina is

stimulated with light. Adifferential voltage isamplified and recorded andsignal averaging is used.


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Other Potentials Electrooculogram (EOG): Amplitude: 503500v. Bandwidth: dc

- 50 Hz. EOG is recorded to reflect the eye position. Surfaceelectrodes are used at the left and right sides of the eye (nose,

temple). The EOG is used to record eye movements duringsleep and dream.

The Electrogastrogram (EGG): Amplitude up to 500 mv.

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. - . .

electrical activity of the gut. Fetal Electrocardiography (FECG): v signal corrupted by

maternal ECG and random muscular noise. Various techniqueshave been used (Simple substructure, Adaptive noise canceling,

Autocorrelation). Still under research. His-Bundle Electrocardiogram (HBE): the electrical activity of

the bundle of His of the specialized conduct-system of the heat.Intensive techniques are used to detect and locate these signals

on body surface.

Other Biopotentials-08-s [Compatibility Mode]

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