This slide has been prepared in detaied manner and will help you.
The topics covered are:-
1- introduction
2.circuit diagram and its explaination
3.working
4. features
5.advantages / disadvantages
6. the top vendors
4. Electroencephalogram
An EEG machine is a device that records the electrical activity
of the brain. It contain electrodes that can detect brain activity
when placed on a subject’s scalp. The electrodes record the
brain wave patterns and the EEG machine sends the data to a
computer or cloud server.
7. ELECTRODES
Electrodes are used to record EEG
signals.
They are made of a conducting material
commonly metals with some underlying
conductive paste or gel to improve
contact with the skin.
An ideal electrode should transduce the
voltage underneath it without altering it in
any way.
However, real electrodes have limits on
their performance, including the
frequency range over which they are
accurate and the buildup of charge on
the electrode.
Gold or gold-plated electrodes have
commonly been used for scalp EEG
Recording.
8. (A) International 10-20 system for electrode
placement.
(B) 10-10 or 10% system for electrode placement. Ele
ctrodes in black have different names from the
corresponding electrodes of the International 10-20
system
(T7 = T3; T8 = T4; P7 = T5; P8 = T6).
9.
10. JACKBOX
Jackbox is the
electrode board
where each individual
pin of the electrodes is
plugged to pre-amplify
and convert the
analogue signal to one
that is digital.
11. ELECTRODE MONOTAGE SELECTOR
Montage means the placement of the electrodes. The EEG can be
monitored with either a bipolar montage or a referential one.
Bipolar means that you have two electrodes per one channel, so
you have a reference electrode for each channel.
12. EEG AMPLIFIERS
5.
The amplification factor is referred to
as gain and may be expressed as
Vout/ Vin
1.
Electrical signals produced by the brain
are in the order of microvolts.
4.
An amplifier multiplies an input voltage
By a constant usually lying in the range
of up to 1,000,000.
2.
They have to be magnified so that the
voltage changes can be given sufficient
power to be graphically displayed either
on paper or on a computer screen
3.
When measured directly at the cortical
surface, these voltages are on the order
of 10 mV.
13. FILTERS
The fact that the potential differences fluctuate as a function of time implies that the
recorded signals have a certain bandwidth. For the majority of EEG investigations the
recorded signal lies between 1 Hz and 70 Hz.
Information will be lost if the frequency response of the recording channel is narrower
than the frequency range of the EEG signal.
If the frequency range of the recording channel is wider than the bandwidth of the EEG
signal, noise in the recorded data will contain additional irrelevant information.
EEG recording channels are equipped with adjustable high pass and low pass filters by
which the frequency response can be restricted to the frequency band of interest.
For standard recordings, the low frequency filter should not be higher than 1 Hz with
the corresponding time constant of 0.16 s
14. USES OF FILTERS
Low-pass filter to filter out
frequencies above 40 or 50 Hz.
For standard recordings, the low
frequency filter should not be
higher than 1 Hz with the
corresponding time constant of
0.16 s
EEG signal processing is to
apply a high-pass filter to
filter out slow frequencies
less than 0.1 Hz or often
even 1 Hz.Distortion of higher
frequency components is also
possible when the high
frequency filter is set lower
than 70 Hz.
a notch filter is used to reject
the 60 Hz or 50 Hz power line
noise. The notch is a very
selective filter with a very high
rejection just for a tiny frequency b
and around the selected
frequency.
HIGHPASSFILTER NOTCHFILTERLOWPASSFILTER
15.
16. WRITE OUT
The final link between the patient and a
legible EEG tracing is the writer. In
conventional EEG machines, a
pen-ink-paper system is employed
The speed of the paper mechanism
should include 30 mm/s with at least the
additional speeds of 15 mm and 60 mm/s
selectable during operation.
The writing points of the different
channels should be aligned on a line
perpendicular to the direction of paper
travel without the use of special tools
and without the need for bending the
writer arms.
17. A sample EEG recording showing a focal spiketypical of a seizure
18. OUTPUT
The number of channels that an EEG machine
has is related to the number of electrodes used.
The more channels, the more detailed the brain
wave picture.This means that the output from
the machine is actually the difference in
electrical activity picked up by the two electrodes
19. Abnormal results from an electroencephalogram can indicate:
Migraines
Bleeding (haemorrhage)
Head injury
Tissue damage
Seizures
Swelling (edema)
Substance abuse
Sleep disorders
Tumours
21. Applications of EEG:
1. EEG is mainly used in studying the properties of cerebral and neural networks in
neurosciences.
2. It is used to monitor the neurodevelopment and sleep patterns of infants in ICU and e
nable the physician to use this information to enhance daily medical care.
3. In epilepsy, EEG is used to map brain areas and to receive localization information pri
or to a surgery.
4. The EEG neuro-feedback or EEG bio-feedback or EEG bio-feedback has many applic
ations such as treating for physiological disorders and neurological disorders such as epi
lepsy.
5. Many disorders as chronic anxiety, depression etc can be found out using as EEG pat
tern.
23. Advantages of EEG:
1.Theyare functionallyfast, relativelycheap and safe wayof checkingthe functioningof
different areasof brain.
2. High precision time measurements
3.Today'sEEGtechnologycan accuratelydetect brainactivityat a resolution of a single
millisecond.
4.EEGelectrodes are simplystuckonto the scalp. It is therefore a non-invasive procedure.
5. EEG is simple to operate.
25. Disadvantages of EEG:
1.The main disadvantage of EEG recording is poor spatial resolution.
2.The EEG signal is not useful for pin-pointing the exact source of activity. In other
words they are not very exact.
3.EEG waveform does not researchers to distinguish between activities originating in different
but closely adjacent locations.
27. Features of EEG:
• Hardware costs are lower when comparedwithother imagingtechniquessuchas
MRIscanning.
• EEGsensors can be deployed intoa wide varietyof environments.
• EEGallows higher temporalresolution on theorder of milliseconds.
• EEGis relativelytolerable to subject movementsas comparedto MRI.
• The silent nature of EEGallowsfor better study of the responses.
• In EEGsome voltage componentscan be detected even when the subject is not
respondingto stimuli.
