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Dipole Localization
EEG with MRI
In the past, most Neurosurgical Ways were dangerous and had many
Sid effects on the patients.
Nowadays, this ways are rapidly changed by using image & signal
processing technology, Researchers often combine EEg of brain electrical
activity with MRI scans to better pinpoint the location of the activity
within the brain, so the biomedical developers use patient's MRI images
and EEG signals within a software program that determine the brain
activity accurately, this program will confirm the neurosurgeons
diagnosis.
This book provides an introduction to an accurate neuro-diagnosis; it
contains basic principles of some biomedical topics such as: Brian
anatomy, neurophysiology, EEG, Brain imaging, Brain color mapping
and EEG power Spectrum.
Through this book we tried to make the reader capable of
understanding new topics with a simpler meaning.
We aim to give the neuro-physician an insight into the optimal use of
EEG in neurological diagnosis, in some illness cases such as epilepsy or a
brain cancer; physicians should confirm their diagnosis especially if it is
necessary to a surgically treatment to brain cancer or epileptic patients.
Graduation Project
2005 - 2006
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Dipole Localization
EEG with MRI
We wish to express our sincere appreciation to our supervisors.
The special thanks are due to:
Prof. Dr. Eng. Mohammed Ibraheem Al-Adawy
Dr. Eng. Mohammed El-Dosoky
They give us more experiences to solve our problems.
We would like to acknowledge everybody help us in the preparation
of this project.
We are grateful to:
Eng. Hazem M.Abd El-Rahman
Eng. Haitham M. Mahmoud
They give us the project's idea, important related information and
some data we use.
We also are grateful to: Eng. Hussien Auf Hussien
Eng. Mahmoud Rabee
Eng. Hisham Diab
Eng. Haitham Abd Al-Latif
We learn from them much information about Visual Studio.net
And also thanks to:
Dr. Aan Ali Abd Al-kader
Eng. Shaimaa
Eng. Mohammed Ali
They give us some bio-information and data.
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2005 - 2006
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Dipole Localization
EEG with MRI
● Asmaa Abu-Baker El-sayed
[email protected]
● Asmaa Samy Hussien
[email protected]
● Eman Magdy Abd Al-Naby
[email protected]
● Haitham Salah Ahmed
[email protected]
● Mahmoud Ibraheem El-Gendy
[email protected]
● Tamer Abdel-Dayem Essayed
[email protected]
Mail Group:
[email protected]
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Dipole Localization
EEG with MRI
Part one
Important Biomedical Information
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Dipole Localization
EEG with MRI
Chapter 1
Brain Anatomy & Neurophysiology
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Contents:
1. Introduction.
2. Flowchart of nervous system.
3. Central Nervous System (CNS).
4. Neuron Structure.
5. The transmission of the nerve impulse.
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EEG with MRI
1. Introduction:
The brain (central nervous system) is essential to our survival, it integrates,
regulates, initiates, and controls functions in the whole body. The brain governs
thinking, personality, mood, the senses, and physical action.
We can speak, move, remember, and feel emotions and physical sensations
because of the complex interplay of chemical and electrical processes that take place
in our brains.
The human brain is made up of billions of nerve cells, called neurons that share
information with one another through a large array of biological and chemical
signals.
Neurons communicate with each other and with sense organs by producing and
releasing special chemicals called neurotransmitters. As a neuron receives messages
from surrounding cells, an electrical charge (nerve impulse) builds up within the
cell.
The brain performs an incredible number of tasks:
•
It controls body temperature, blood pressure, heart rate and breathing.
•
It accepts a flood of information about the world around you from your
various senses (eyes, ears, nose, etc...).
•
•
It handles physical motion when walking, talking, standing or setting.
It lets you think, dream, reason and experience emotions.
All of these tasks are coordinated, controlled and regulated by an organ
that is about the size of a small head of cauliflower.
Your brain, spinal cord and peripheral nerves make up a complex, integrated
information-processing and control system. The scientific study of the brain and
nervous system is called neuroscience or neurobiology.
The brain is responsible for all our activity thinking, learning, dreaming, and also
love. While we are sleeping we can dream which is meaning that the brain works all
time. Beside it is look like the microprocessor it also has a memory which no one
can know where it is laying in the brain.
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EEG with MRI
2. Flowchart of Nervous System:
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3. Central Nervous System:
The nervous system is a complex interconnection of nervous tissue that is
concerned with the integration and control of all bodily functions.
The nervous system is generally considered the most complex bodily system. It is
divided into several major divisions distinguished by anatomy (structure and
location) and physiology (function), including the following:
1. Central nervous system (CNS), which is enclosed within the skull and vertebral
column - brain and spinal cord.
2. Peripheral nervous system (PNS), which consists of nervous tissue outside the
skull and vertebral column-periphery (extremity) of the body.
Subdivisions of the PNS include:
Somatic system, which supplies sensory motor and sensory fibers to the skin and
skeletal muscles.
Autonomic nervous system, which supplies smooth muscle, cardiac muscle, and
glands in the body viscera. The sympathetic (stimulatory) system causes organ
changes that help the body resist stress. The parasympathetic (inhibitory) system
maintains normal function and conserves body resources.
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Dipole Localization
EEG with MRI
Structure and function of central nervous system
The brain is "a large soft mass of nerve tissue contained within the
cranium, encephalon".
Three major structures compose the brain:
1-The brain stem – automatic vital system control
2-The cerebellum – involuntary muscle control.
3-The cerebrum – voluntary movement, sensation, and intelligence.
Cerebral Cortex
Cerebral hemisphere
Corpus Callosum
Midbrain
Diencephalons
(Thalamus +
Hypothalamus)
Pons
Spinal Cord
Cerebellum
Medulla Oblongata
Brain stem
The brain stem consists of the medulla (oblongata), pons, midbrain, and
diencephalons.
Brain stem
Medulla
Pons
Mid-brain
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A) Medulla:
Automatically controls heart rate and breathing.
(Actually, most essential life systems are controlled here).
Reflex functions such as coughing, sneezing and vomiting
are associated with the medulla. Indeed, one modern
definition of clinical death is the absence of lower brain
EEG activity.
B) Pons:
Is about 2.5 cm long and forms a noticeable bulge on
the anterior surface of the brain stem. It functions as a
relay station for motor respiratory and auditory fibers from
cerebrum and cerebellum. Other impulses from eye
movement, head muscles, and taste sensors also pass
through here.
C) The mid-brain:
Is a wedge shaped portion of the stem. Midbrain tissues
function as a motor relay station for fibers passing from
the cerebrum to the cord and cerebellum. Integration of
visual and auditory reflexes, including those concerned
with avoiding objects, also occur here.
Cerebellum:
Is the second largest portion of the brain (the cerebrum is
the largest) and, essentially, integrates incoming sensory
messages to provide smooth body muscle movements,
balance, and equilibrium. This portion of the brain has an
outer cortex of gray matter and an inner medulla composed
of white matter.
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Cerebrum:
Cerebrum
Parietal lobe
Frontal lobe
Occipital lobe
Temporal lobe
The cerebrum consists of the cortex, large fiber tracts (corpus callosum) and some
deeper structures. It integrates information from all of the sense organs, initiates
motor functions, controls emotions and holds memory and thought processes.
Frontal Lobe: involved in motor skills (including speech) and cognitive functions.
•
Vision &Reading
Occipital Lobe: receives and processes visual information
directly from the eyes and relates this information to the
parietal lobe and motor cortex (frontal lobe) Vision
&Reading
Parietal Lobe: The parietal lobe receives and processes all
somatosensory input from the body (touch, pain). The rear of the parietal lobe (next
to the temporal lobe) has a section called Wernicke's area, which is
important for understanding the sensory (auditory and visual)
information associated with language. Damage to this area of
the brain produces what is called "sensory aphasia," in which
patients cannot understand language but can still produce
sounds.
•
•
•
•
•
•
Sense of touch (tactile sensation)
Appreciation of form through touch (stereo gnosis)
Response to internal stimuli (proprioception)
Sensory combination and comprehension
Some language and reading functions
Some visual functions
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EEG with MRI
Temporal Lobe: The temporal lobe processes auditory information from the ears.
•
•
•
•
•
Auditory memories
Some hearing &Visual memories
Some vision pathways &Other memory
Music &Fear
Some language &Some speech
Cerebrum consists of two hemispheres:
Right Hemisphere (the representational hemisphere)
•
•
•
•
The right hemisphere controls the left side of the body
Temporal and spatial relationships
Analyzing nonverbal information
Communicating emotion
Left Hemisphere (the categorical hemisphere)
•
•
The left hemisphere controls the right side of the body
Produce and understand language
Corpus Callosum:
Communication between the left and right side of the brain
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Gray matter:
The cerebrum contains the gray matter (neurons with no myelinated) and white
matter (myelinated neurons that enter and leave the cortex).
Generators of electric field which can be registered by scalp electrodes are groups of
neurons with uniformly oriented dendrites. The neurons permanently receive
impulses from other neurons. These signals affect dendrite synapses inducing
excitatory and inhibitory postsynaptic potentials.
Currents derived from synapses move through the dendrites and cell body to a
trigger zone in the axon base and pass through the membrane to the extracellular
space along the way. EEG is a result of summation of potentials derived from the
mixture of extracellular currents generated by populations of neurons.
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Dipole Localization
EEG with MRI
4. Neuron Structure:
Neuron is the functional unit
of the nervous system,
It contains:
1-Cell body (soma):
It contains organelles such as
(Nucleus-endoplasmic
reticulum – Golgiapparatus
(metabolic center)).
Cytoplasm of the cell body
is characteristic by present of
nissal bodies for oxygen
storage.
2-dendrites:
It like as a Branched processes extended from cytoplasm of the cell body.
Receive stimuli and conduct impulse to cell body.
3- Axon: (nerve fiber)
The nerve impulse travels in one direction only from dendrites to nerve endings.
The axon extends the entire length of the nerve cell, and some are surrounded by
a myelin sheath (segmented insulating covering).
The conduction pulse results in a wave of depolarization (action potential) similar
to that presented for heart muscle. Nerve conduction is in one direction only
(constant speed) from dendrites through axon to nerve endings.
The sensory nerves carried to the brain are known as afferent nerves, and the ones
carried away from the brain are called efferent nerves.
Nerves switch on and off in such a manner as to cause abrupt changes in cell
voltages. In effect, this nerve impulse switching is similar to electronic digital
circuit logic. Several nerve cells may be required to conduct before a triggering
threshold is reaching.
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Dipole Localization
EEG with MRI
5. The transmission of the nerve impulse:
In neurons, information passes from dendrites through the cell body and down the
axon. This is easy to remember because when you pick up an object, the sensation
travels from your fingers through your hand, and down your arm.
Transmission of information through the neurone is an electrical process.
The passage of a nerve impulse starts at a dendrite; it then travels through the cell
body, down the axon to an axon terminal. Axon terminals lie close to the dendrites
of neighbouring neurones.
When the nerve impulse reaches an axon terminal it causes the release of a
chemical (called a neurotransmitter) that travels across the gap (the synapse)
between a terminal and the dendrite of the neighbouring neurone. Neurotransmitters
stick to receptors in the neighbouring dendrite and trigger a nerve impulse that
travels down the dendrite, across the cell body, down the axon etc. Our behaviour is
the consequence of millions of cells talking to each other via these chemical and
electrical processes.
The synaptic junction between neurons:
1. Bridging the information gap between
neurons
Neurotransmitters are responsible for transmitting
information across the synaptic gap between neurons.
Neurotransmitters are stored in synaptic vesicles.
When action potentials are conducted down an axon:
• Synaptic vesicles attach themselves to the presynaptic membrane, then
• Break open and spill neurotransmitter into the synaptic cleft.
• Neurotransmitters in the synaptic cleft attach to postsynaptic receptor sites and
trigger an action potential in the postsynaptic membrane
• Some neurotransmitter attaches to presynaptic receptors (auto receptors) located
on the membrane (pre-synaptic membrane) of the cell that originally released them.
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Dipole Localization
EEG with MRI
2.' Mopping up' after information transmission
This image illustrates the main events thought to
be involved after transmitters have been released
into the synaptic cleft.
Transmitters become detached from receptors and
either:
diffuse through extracellular fluid (red
transmitter), or
• undergo reuptake (blue transmitter), or
• are broken down by enzymes (yellow
transmitter)
•
Reflex action in the human involves many reflex
arcs. A nervous reflex is an involuntary action response caused by stimulation of
an afferent nerve ending or receptor. The knee jerk in response to the tap of a
hammer is one example of a reflex arc, the components of the arc are:
1. A receptor, which detects change.
2. An afferent neuron, which conducts the nerve impulse from the sensory area to
the CNS.
3. A center or synapse, which connects neurons together.
4. A brain processing area.
5. An efferent neuron, which conducts nerve impulses from the CNS to an organ
for appropriate response.
6. An effecter or organ, which responds to maintain homeostasis.
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EEG with MRI
Chapter 2
Electroencephalogram
EEG
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Contents:
1. EEG Origin
2. EEG History
3. EEG Recording
4. EEG Waves
5. EEG Electrodes
6. Evoked-potential and Clinical studies
7. EEG Artifacts
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Dipole Localization
EEG with MRI
1. EEG Origin:
The appearance of EEG rhythmic activity in scalp recordings is only possible as
a result of the synchronized activation of massifs of neurons, the summed synaptic
events of which become sufficiently large.
The rhythmic activity may be generated by both pacemaker neurons having inner
capability of rhythmic oscillations and neurons which can not generate a rhythm
separately but can synchronize their activity through excitatory and inhibitory
connections in such a manner that constitute a network with pacemaker properties.
The oscillators have their own discharge frequency, various among different
oscillators and dependent on their internal connectivity in spite of close intrinsic
electrophysiological properties of single neurons which constitute different
oscillators. The neuronal oscillators start to act in synchrony after application of
external sensory stimulation or hidden signals from internal sources.
Figure, Neuronal oscillators inside the cortex, discharging with their
intrinsic frequencies (f1, f2, and f3), produce extracellular currents
summed on scalp surface as EEG signal. The spectral analysis decodes
these oscillators activity out of EEG record. In the rectangle window
the hypothetical scheme of neuronal oscillator is given. The axonal
collateral of basic neuron activates the circuits with excitatory and
inhibitory interneuron. The inhibitory neuron of the scheme is given
in black.
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Dipole Localization
EEG with MRI
2. EEG History:
In 1929, a German psychiatrist named Hans Berger called:
It was possible to record the feeble electric currents generated on the brain,
without opening the skull, and to depict them graphically onto a strip of paper.
Berger named this new form of recording as the electroencephalogram (EEG, for
short).
• That this activity changed according to the functional status of the brain, such as
in sleep, anesthesia, hypoxia (lack of oxygen) and in certain nervous diseases, such
as in epilepsy.
•
First EEG recorded by Hans Berger, 1circa 1928
Gray Walter, a remarkable British scientist, who, in 1936
• Proved that, by using a larger number of electrodes pasted to the scalp, each one
having a small size, it was possible to identify abnormal electrical activity in the
brain areas around a tumor, and diminished activity inside it.
• Gray Walter invented the toposcope in 1957.This was a remarkably complex
device .It had 22 cathode ray tubes (similar to a TV tube), each of them connected to
a pair of electrodes attached to the skull.
Each tube was able to depict the intensity of the several rhythms
Which compose the EEG in a particular area of the brain (the frontal, parietal and
occipital lobes… etc).
•
Gray Walter asked his subjects to perform several mental tasks, with the result that
the EEG rhythms were altered in different ways, times and parts of the brain. He was
the first to prove, for instance, that the so-called alpha rhythm (present during a
resting state) disappears from almost all the brain during a mental task which
demands awareness, being substituted by a faster rhythm, the beta waves.
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EEG with MRI
It was immediately apparent to neurologists that the toposcope could be a great
help to locate epileptic foci (the points where a convulsion originates in the brain,
due to a local lesion, tumor or functional alteration). However, it was very complex
and expensive and it did not achieve commercial success or widespread use.
The topographic study of brain electrical activity was born again only when fast
desktop computers became available in the 80s. Thus, EEG brain topography was
developed and is widely in use today. It is also called Colour Brain Mapping.
During the 1940's several researchers, including W. Gray Walter
He utilized powerful electronic strobes with new versions of EEG instrumentation to
alter brainwave activity, producing states of profound relaxation and imagery.
In 1949, brainwave signals were brought to the screen with the invention of the
Tuposcope. This breakthrough allowed the tracking of brainwave patterns (Beta,
Alpha, Theta and Delta).
In the 1950's and 1960's, research on Zen and Yoga meditators
They showed a predominance of alpha and theta waves during meditation.
Brain cells, or neurons, generate electromagnetic fields when they are active, and
if a large number of neurons are simultaneously active they can generate fields that
are detectable on the surface of the scalp.
• The special resolving power of EEG is rather worse than the other techniques
.however, one reason is that standard EEG instruments provide a fairly coarsegrained sampling of the scalp fields, usually measuring from only about 21
recording sites on the head.
• A second reason is that electric fields are smeared and distorted by the geometry
and conductive inhomogeneities of the brain, the cerebra-spinal fluid, the skull, and
the scalp.
• A third, and more fundamental reason is that, given information only about scalp
electrical fields, it impossible to disentangle the contributions of multiple generator
sites and thus to determine their locations in the brain (the inverse problem).
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EEG with MRI
3. EEG Recording:
Introduction:
It is usually taken by electrodes (small metallic discs) pasted by an electricity
conducting gel to the surface of the skull's skin (scalp).
Usage amplifier to increase the weak signal (less than a few microvolt) which is
generated in this place.
The result is a wiggly "wave". One pair of electrodes usually makes up a channel.
EEG recordings, depending on its use, can have from 8 to 40 channels recorded in
parallel. This is called multichannel EEG recording.
Brainwaves change frequencies of the EEG based on neural activity within the
brain that produced by hearing, touch, smell, vision and/or taste. These senses
respond to activity from the environment and transmit that information to the brain
via electrical signals.
These electrical potentials are measured either outside the nervous system or
directly within the central nervous system.
Neurophysiology Study
Neural activity
Recording
Location
Electroencephalography (Routine)
spontaneous
scalp surface
Electrocorticography
spontaneous
brain surface
Subdural electroencephalography
spontaneous
brain surface
Intracranial electroencephalography
spontaneous
within the brain
Evoked potentials
induced
scalp, neck, spine,
limb surface
Operative evoked potentials
induced
scalp, spinal cord
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EEG with MRI
EEG usage:
EEG brain topography is not performed in all cases requiring a recording of the
brain activity. Its main indication is to determine the presence of tumours and focal
disease of the brain (including epilepsy, arteriovenous mal-formations and stroke).
It is also appropriate when disturbances in consciousness and vigilance are
present, such as narcolepsy (the abrupt onset of sleep), Confirm or rule out brain
death in a person who is in a coma, etc.
In addition, EEG brain topography is being increasingly used to monitor the
effects of withdrawal of psychoactive drugs, and in infectious diseases of the brain,
such as meningites, as well as to follow up patients who where subjected to brain
operations.
In psychiatry, EEG brain topography has been of value in identifying disorders of
biological origin, such as schizophrenia, dementias, hyperactivity and depression,
brain atrophy and attention deficit disorders in children.
(EEG) response:
An EEG, recorded by positioning 21 or more electrodes on the intact scalp,
represents the changes of the electrical field within the brain. Generally even up to
128 and more EEG channels, each corresponding with a standard electrode position
on the scalp, can be displayed simultaneously.
The results of the EEG signals, after being registered as voltage differences
between pairs of electrodes (bipolar derivations) or between an active electrode and
a suitably constructed reference electrode (referential derivations)), are measured,
amplified and next displayed on paper or on a monitor.
The EEG itself is recorded during different behavioral conditions such as eyes closed, eyes open,
hyperventilation and photic stimulation to provoke abnormalities. However EEGs can also be
recorded during sleep or during operative procedures.
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Dipole Localization
EEG with MRI
Clinical application of the EEG:
Although the origin of EEG responses is not completely brought to light, the
signal itself proved to be a valuable tool for diagnosis in the environment of clinical
medicine, in particular in neurology, in neurosurgery and in psychiatry.
In addition to that, EEG recordings still require additional investigations in
studying epilepsy. In indicating epilepsy, it is able to detect abnormalities in
waveforms, such as spikes, sharp waves and spike wave discharges.
Not only that specific forms of epilepsy (absence epilepsy, hypsarithmia and
benign focal epilepsy of childhood) can be found, but also non-epileptic focal brain
dysfunctions possibly caused by cerebrovascular disorders, tumors, infections or
traumas and generalized brain dysfunction in case of metabolic encephalopathy,
intoxication, encephalitis or degenerative dementia are reflected by the EEG signal.
Such defects can be classified as either occurring periodically or befalling in a more
continuous fashion.
In most cases the EEG is considered to be a sensitive rather than a specific
diagnostic instrument, making it a suitable instrument to monitoring the course of a
disorder on the one hand and to determining a prognosis of the abnormality on the
other. That is, the EEG can pick up very mild degrees of brain dysfunction, but it
seldom gives much information about the exact cause of the abnormalities. In
general, one should not try to derive etiologic diagnoses from the EEG.
The EEG recording usually includes the follows steps:
1 - A subject is seated in comfortable chair in dimly illuminated room.
2 - (21) Electrodes are placed on his head according to certain scheme.
3 - The reference electrodes are chosen.
4 - Parameters of electroencephalograph and software for EEG
acquisition and storage are established.
5 - Calibration of electroencephalograph and data acquisition software is
executed.
6 - EEG is recorded.
7 - Artifacts are removed.
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Dipole Localization
EEG with MRI
4. EEG Waves:
Brain waves are the electrical wave patterns generated in every person’s brain.
These waves vary according to level of consciousness, subconsciousness and
unconsciousness and are characterized by four distinct types of brainwaves.
All of these brain waves are produced at all times. However, a predominance of
a specific desired brainwave state can be created at will, which allows a person to
potentially his or her capabilities towards achieving human excellence.
Brainwave frequencies are described in terms of hertz (Hz), or cycles per second, which are
measured by an electroencephalogram (EEG) and the volt of the signal is measured in microvolt.
EEG Bands:
EEG Bands
Delta band (δ)
Theta band (θ)
Beta band (β)
Alpha band (α)
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1) Alpha Band:
They are a frequency pattern ranging from eight to twelve hertz. They most
commonly occur when we are calm and relaxed, yet mentally alert. These
brainwaves are also present during daydreaming.
2) Beta Band:
They are the next highest frequency pattern beginnings fromm thirteen to thirty
four five hertz.
They can be separated into three sub-categories.
First is high beta, ranging from nineteen to thirty-four hertz. When high beta is the
dominant brainwave state, anxiety and stress are most likely to occur.
Second sub-category is mid beta, with frequencies ranging from fifteen to eighteen
hertz. Mid beta is characterized by action, with focus on external surroundings.
Third is SMR beta (Sensor motor Rhythm), ranging from thirteen to fifteen hertz.
While in this state, focus is also on external surroundings, but the individual is more
relaxed than in mid beta.
3) Theta Band:
Range from four to seven hertz, characterized by being deeply relaxed and
inwardly focused. This brainwave state is also associated with rapid learning and the
assimilation of new information with high retention, heightened motivation to
activate goals, bursts of creativity, insight and new behaviour patterns.
4) Delta Band:
Range from five-tenths to three hertz and are associated with being extremely
relaxed, characterized by sleep.
Researchers have proven that brainwave frequencies determine what brainwave
state is being experienced at any given time, these frequencies are generated in every
person’s brain, and are the result of outside stimulation that has been passed to the
brain via electrical signals from our different senses.
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5) Gamma Band:
They are high frequency pattern beginnings at thirty-five hertz.
While in this brainwave state, sensations are centered on being mentally,
emotionally and physically "charged" or extremely energized. These frequencies are
the highest known brainwave patterns, but are considered to be part of the beta
frequency category.
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Band type and
frequency
Delta
theta
Alpha
Beta
Frequency(HZ)
Delta<4
4≤theta<8
8≤Alpha<13
Beta>13
Amplitude(µV)
Delta<200
Theta<150 5<Alpha<100
Beta<30
Status
Deeper
sleep
Light
sleep
Wake Relax
Closed eye
Mental
activity
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EEG with MRI
5. EEG Electrodes:
Contents:
a. Basic Concepts.
b. Electrode Potential.
c. Types of Electrodes.
d. Electrode Design.
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a. Basic Concepts:
It is hardly possible to obtain satisfactory EEG without having good quality
electrodes that have been properly connected to the patient.
• Electrode: - means whereby the electrical activity of the brain communicated to
the input circuit of the amplifier in the EEG machine.
Although a remarkable variety of different types of electrodes, but there is
fundamental component that is common to all of them
This component is metal-electrolyte interface.
• Metal: -is the material of which the electrode is composed.
● Electrolyte: - may be conducting solution (gel or paste) or may be fluid of living
tissue as when electrode inserted below skin.
This means that current flow within brain becomes electron flow in the
electrodes and electrode wires.
To understand how electrical current pass through interface we must know some
basic of electrical properties of electrolyte.
Ions:
It is particles in solution that bear an electrical charge. The fact that ions are free to
move in the solution, so if applied voltage between two points in the solution, an
electric current can be made to flow in it. The current carried by ions in the solution
in the same way that current is carried by the loosely bound electrons in a metallic
conductor and this is appropriate with electrode potentials.
Ions
Electrons
electrolyte
metals
Metal – electrolyte interface:
It is the junction where flow of ions is converted into flow of electrons. It is the
place where an electrochemical phenomenon is converted into purely electrical
phenomenon.
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Recording electrode
Transducer
The electrical double layer:
Almost any kind of metal used as electrode, but electrolyte chosen usually some
kind of salt solution, principally, sodium chloride.
There is two major reasons dictate this choice:
• First:
NaCl is very soluble in water so is able to contain a high concentration of ions and
this means that solution will be good conductor.
• Second:
Na + And
−
Cl
Ions are a major constituent of the body fluids.
Despite, any metal is good conductor and could serve as recording electrode,
some metals are, at best "only poor material"
The fact that metal electrode discharges positive ions into solution when it
becomes in contact with an electrolyte.
An adjacent layer of oppositely charged ions from the solution is formed called
this result electrical double layer.
These two processes occur at different rates, depending on the species of
metal used for electrode and type of electrolyte.
The difference in the rates of these two processes results in a voltage appearing at
the electrode which termed in electrode potential "Half-cell potential".
The potential of electrode itself is always measured with respect to reference
electrode.
It isn't being possible to measure the voltage of single electrode with respect to a
solution.
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Polarization and the double layer:
Characteristics of double layer vary with different electrode materials.
The characteristics determine when an electrode will be polarizable or non
polarizable.
Example on non polarizable (reversible) silver-silver chloride electrode
(Ag-AgCl)
Ag-AgCl in solution of NaCl
Ag +
AgCl
Cl −
electrical balance between two opposing process
Polarization and polarizable electrodes:
Only a minimal transfer of charges occurs across the electrical double layer, so it
have an electrical charge on them so it like capacitor, which don't pass Dc and act as
low- frequency filter.
In recording electrodes most used polarizable type, not used non-polarizable type
due to it is expensive and technically more difficult to work with it.
And not essential in EEG work due to Dc and low-frequency voltage are not
recording in routine clinical EEGs.
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b. Electrode Potential:
When metal electrode is placed in contact with electrolyte the voltage develops
between them.
This voltage called electrode potential or ''half – cell potential'', then it connects to
the input of amplifier to be amplified then it appears as an artifact in the EEG
tracing.
But this doesn't normally happen for two reasons: •
First:
We know that two electrodes are required to record an EEG and if the
electrodes are identical the same voltage will be present on each of them. Therefore
the electrode potential will appear as common – mode signal at G1, G2 of amplifier
and be rejected by CMRR.
•
Second:
The electrode potential is a DC voltage. If this voltage were relatively stable,
the capacitor in the low frequency filter of EEG machine would block it out before it
had chance to be amplifier.
As it happen, different metals are used which have different electrode potentials.
The presence of difference in voltage between dissimilar electrodes, and it is the
principle in some interest to EEG technician.
If pair of EEG leads attached to a patient made from different metals, there could
be substantial voltage between them.
This voltage would not necessarily if it were stable (DC) because is blocked by the
capacitor in low frequency filter.
In practice, voltages are rarely stable and for this reasons they represent source of
artifact in EEG recording. (Battery effect)
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Residual potentials:
Even though both electrodes are made of the same material
In practice, some voltage frequently can be measured between them (electrode
potential of two leads may not be identical).
Number of factors can be responsible for such residual potential, which can be:
1. There may be impurities in the metal, or surface of electrodes may be
contaminated by foreign metal ion.
To avoid that:
a. The former only high – purity metals are used in recording electrodes.
b. Care in cleaning and storing is necessary to prevent surface contamination.
2. There may be foreign metal ions present in electrolyte.
To avoid that possibility:
Electrode pastes and gels should be carefully selected and protected from
contamination during use.
3. There may be difference in the concentration of the electrolyte at the two
electrodes sites through lack of homogeneity in gel used.
4. There may be different in temperature of the skin at two electrode sites, because
some metals used in electrodes have electrode potentials with temperature
coefficients in excess of 100µv/ c 0 .
The variations in voltage constitute a source of artifact in EEG tracing.
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C. Types of Electrodes.
Types of EEG
Electrodes
Needle
Surface
Flat
Cup
● Needle electrode
●Flat electrode
●Cup electrode
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Most clinical EEGs currently are done using surface electrode.
Advantage:
It is obvious, in terms of both convenience and comfort for the patient, relative
freedom from infection.
Disadvantage:
It has some factor of lower electrode impedance.
The most popular surface electrode used in clinical EEG work is:
Metal disk electrode
Disk electrodes:
1. They are circular pieces of thin metal that may be flat or cup-shaped to hold
electrolyte that forms the metal-electrolyte interface.
2. Diameter may vary from 4 mm to 10 mm (smaller disk used in infants).
3. Some cup-disk electrode have hole in the center through which the electrolyte
can be introduced after it is attached to scalp.
4. Lead, solder, silver and gold can use in the construction of disk electrodes
(Noble metals like gold being less reactive than the base metals make most stable,
drift-free electrodes).
The disks are soldered to a flexible, insulated wire, and this junction is carefully
covered by a plastic material to prevent moisture or any of electrolytes from
reaching the solder joint (must not cause penetration by water and electrolyte).
Active battery would be created at the junction of dissimilar metals.
EEG technician should never scratch the surface of electrode or bend or pull
electrode at junction between wire and disk.
Electrode should be kept dry when not in use, avoid soaking them in water for
long periods of time.
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d. Electrode Design:
Two identical pieces of felt are the cut into
circles big enough o fit onto the suction
cups. Silver wire is bent around the two
pieces of wire into a U- shape. The silver
wire is the point of contact with the
potentials derived from the brain and the
head.
Advantage of sewing the electrodes over
using the glue is that the user does not have
to worry about the degradation of the glue
due to the continuous use of the conductive electrolyte solution.
Flat electrode:
Cup electrode:
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Some step must make before setting electrodes:
The hair and surface of scalp should be clean.
Free hair oil before electrodes are applied.
Use this by hair and scalp to be washed.
Topic cleaning at measured location using alcohol.
We do this is to reduce resistance between the electrode and scalp
.
Measured resistance
Gel solution
Electrodes
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6. Evoked-potential and Clinical studies:
Contents:
a. Definitions in use
b. Evoked Potentials - Background
c. Clinical studies of five conditions Stimulus:
Keywords:
Independent component analysis (ICA)
Event-related potential (ERP)
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a. Definitions in use:
Sharp wave - Transient, clearly distinguishable from background activity, with
pointed peak at conventional paper speeds and a duration of 70-200 milliseconds.
•
•
Spike - Same as sharp wave, but with duration of 20 to less than 70 ms.
Spike-and-slow-wave complex - Pattern consisting of a spike followed by a slow
wave (classically the slow wave being of higher amplitude than the spike).
•
Multiple spike-and-slow-wave complex - Same as spike-and-slow-wave complex,
but with 2 or more spikes associated with one or more slow waves.
•
b. Evoked Potentials – Background:
Evoked potentials are nervous system electrical responses to specific sensory
stimuli. Computer averaging is necessary because their low amplitude is obscured by
spontaneous nervous system activity.
Latency is the time interval between the stimulus and the evoked potential peak.
Negative potential peaks are labeled N and positive potential peaks are labeled P.
This is the polarity of the evoked potential peak when measured using a referential
montage
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c. Clinical studies of five conditions Stimulus:
(1) Flash stimulation or flash visual-evoked response (VER):
Both subjects were connected to EEG instruments and 100 random flashes of light
were presented to subject A, while both remained reclined with semi-closed eyes.
Subject B was not told when the light was flashed for subject A, and control
correlation checks were also made at random times with no light flashes.
when one of the subjects was stimulated (25 cm in front of the face and
Grassphotic stimulator with intensity 8 or 16) in such a way that his/her brain
responded clearly (with a distinct evoked potential), the brain of the nonstimulated
subject also reacted and showed a transferred potential of a similar morphology.
VER produces activity that is largely occipital and is therefore of limited value in
mapping studies.
Its usage:
1-VER is used when detailed information is required about the occipital cortex.
2- Both VER and AER are extremely sensitive to drossiness.
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(2)Click auditory-evoked response (AER):
Generated by supra-limited stimuli via earphones (92 dB sound pressure level)
the click stimulus begins as a transient reduction in air pressure or increase in air
pressure.
(3)Eye open state:
In which the subject should seat comfortably and a visual fixation target should be
placed so as for min frontal muscle tone. No blinking.
(4) Eye closed state:
Eye movement and blink are more difficult to control during this test and allowing
the patient to relax.
Its usage:
It used to know eye movement artifact in electrodes Fp1 and Fp2.
(5)Drossy to sleep:
Allowing patient to relax so that the blinking cases is often tantamount to
allowing the subject to fall asleep or at least to become drossy notice the
progressively higher amplitude, lower frequency as sleep takes place.
Evoked Stimulus
Potential
AEP
VEP
Click auditoryevoked stimulus
visual-evoked
potential
Stimulation
Rate (Hz)
Bandwidth
(Hz)
10
100 - 1500
Sweep
Time
(msec)
20
2-3
1 - 100
200
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7. EEG Artifacts:
Contents:
a. Physiological Artifacts
b. Non-Physiological Artifacts
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a. Physiological Artifacts:
EEG artifacts appear due to external electrical or magnetic fields and subjects
movements during recording procedure. The last are caused both by muscle
electrical potentials fields and electrode displacement. Visual and automatic search
of high amplitude artifacts usually is not difficult but it's important to make every
effort to eliminate or reduce.
1- Muscle or EMG:
One of the most frequently encountered biphasic artifacts; predominantly recorded
from the frontal and temporal areas; fast in frequency and sharp in morphology (may
resemble a spike).
Commonly caused by:
Tension's being uncomfortable, moving around, clenched jaw, frowning,
swallowing, and chewing.
2-eye movement:
Occurs when blinking, eye opening and closure; generally seen greatest in frontal
or anterior temporal leads. It appears as simultaneous positive or negative waves
involving channels containing Fp1 and Fp2.
Vertical upward eye movements produce a positive potential at Fp1 and Fp2;
Vertical downward eye movements produce a negative potential at Fp1 and Fp2.
3-EKG/ECG/Electrocardiogram:
Electrical activity from the heart; sharply contoured; most prominent during
reference recording using ear, mastoid, mandible, and neck chest reference points;
greatest in patients who are overweight or have short heavy necks; most likely to
resemble an EEG abnormality when the patient has an arrhythmic heart beat.
It is difficult to eliminate; when using A1 and A2 reference points or tie ear leads
together.
4- Respiration:
This often caused by head movement during hyperventilation.
It consists of rhythmic 6 - 11 Hz activity associated with skull defects. This pattern
involves the right or left central or midtemporal regions. There is a sharp negative
and rounded positive component.
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(EMG, Eye blink and ECG artifacts)
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b. Non-Physiological Artifacts:
1) 60 Hz Interference:
Artifact created by 60 Hz activity is addressed separately because there are many
possible sources of the artifact. Some of these are electrodes, the EEG instrument,
and environmental elements. It will be removed by notch filter.
2- Electrodes and EEG Instrumentation:
An electrode artifact will appear in one channel and appear as a "pop",
simulating a spike or sharp wave, or can resemble random slow activity.
The artifacts can be related to an unstable electrode, a change in the electrolyte
(drying out or mixing with perspiration), or other instability at the scalp such as head
movement
3-External or Environment Sources:
Slow waves can come from the movement of personnel around the patient,
swaying of drapes around the bed, mopping under the bed, and the movement of
electrode wires.
(Electrodes & 60 Hz artifacts)
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Chapter 3
Dipole Source Localization
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Contents:
1. Dipole Orientation.
2. Determine dipole location.
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An electric current dipole is an elementary physical source of electric
brain potential. At any given moment, a tremendous amount of dipoles are
active inside the brain. Under certain conditions, however, it occurs to be
possible to determine the location and strength of few principle dipoles,
i.e., the dipoles that give major contribution to generation of electric field.
a.
Dipole Orientation:
The orientation of the dipole is represented by a line connecting the negative and
positive charges. A vertical or radial dipole point source is oriented from the centre
of the brain to the brain surface. A horizontal or tangential dipole is oriented parallel
to the brain surface.
A dipole source located just below the EEG electrodes produces a large EEG
response. The EEG response decreases when the dipole source becomes more
distant from the EEG electrodes.
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b. Determine dipole location:
• Tangential dipole sources are assumed to lie directly below a location midway
between the maximum positive and negative potentials.
• Radial dipole sources are assumed to lie directly below the location of maximum
potential of greatest magnitude. For example, a single maximum negative
potential is identified, the maximum positive potential is much lower in
magnitude and in an area not sampled by electrodes. The dipole source is
assumed to lie below the location of the maximum negative potential.
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Chapter 4
Brain Imaging
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Contents:
1. Introduction.
2. Positron emission tomography (PET).
3. Magnetic Resonance Imaging (MRI).
4. Computed Tomography (CT).
5. Comparison between Brain Imaging.
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1. Introduction:
Recent years have witnessed an unprecedented development in techniques for
diagnosis of neurological disorders.
Notable among them is computerized tomography (CT),
Magnetic resonance imaging (MRI), neurosonography, positron emission
tomography (PET), brain electrical activity mapping, and evoked potentials.
Most of these procedures are imaging techniques in which an image or map of
the brain is constructed that reveals structural and, in some cases, functional details.
These procedures have virtually revolutionized neurological diagnosis and
management.
Although no longer used for identification and localization of gross structural
brain lesions, electroencephalography (EEG) remains the primary diagnostic test of
brain function.
Unlike relatively new functional imaging procedures, such as functional MRI
(MRI), single-photon emission computed tomography (SPECT), and positron
emission tomography (PET), EEG provides a continuous measure of cortical
function with excellent time resolution and is relatively inexpensive. EEG is
especially valuable in investigation of patients with known or suspected seizures.
The aim is to give the physician an insight into the optimal use of EEG in
neurological diagnosis.
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2. Positron emission tomography (PET):
Using positron emission tomography
(PET) and computed tomography (CT)
proved more accurate than whole-body
magnetic resonance imaging (MRI) for
staging a variety of malignancies.
What is PET?
Its provide insight into the functional or
biochemical anatomy of the CNS. The brain images are constructed on the basis of
amount of radioactivity emitted from certain chemicals taken up by the brain.
PET (or positron emission tomography) is a medical imaging tool which assists
physicians in detecting disease. Simply stated, PET scans produce digital pictures
that can, in many cases, identify many forms of cancer, damaged heart tissue, and
brain disorders such as Alzheimer's, Parkinson's, and epilepsy.
A PET scan is very different from an ultrasound, X-ray, MRI, or CT, which
detect changes in the body structure or anatomy, such as a lesion (for example, a
sizeable tumor) or musculoskeletal injury.
A PET scan can, in many cases, identify diseases earlier and more specifically
than ultrasound, X-rays, CT, or MRI.
How Does PET Work?
The most common form of a PET scan begins with an injection of a glucosebased radiopharmaceutical (FDG), which travels through the body, eventually
collecting in the organs and tissues targeted for examination. So it provides a
measure of the cerebral glucose metabolism.
The scanner has cameras that detect the gamma rays emitted from the patient, and
turns those into electrical signals, which are processed by a computer to generate the
medical images.
This produces the digital images, which are assembled by the computer into a 3D image of the patient's body. If an area is cancerous, the signals will be stronger
there than in surrounding tissue, since more of the radiopharmaceutical (FDG) will
be absorbed in those areas.
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This activity is measured during scanning and this activity is detected by
knowing the amount of oxygen in the brain but does not give the complete
information about the rhythm that doing by the EEG as our program ACM do.
Using different compounds, PET can show blood flow, oxygen and glucose
metabolism, and drug concentrations in the tissues of the working brain. Blood flow
and oxygen and glucose metabolism reflect the amount of brain activity in different
regions and enable scientists to learn more about the physiology and neurochemistry
of the working brain. So it became useful in the study in some disorders like
epilepsy.
3. Magnetic Resonance Imaging (MRI):
What is MRI?
Magnetic Resonance Imaging (MRI) uses
non-invasive techniques (the skin or body
cavity is not cut into or entered surgically) to
create detailed images of your body. Your
doctor uses the results from these images to
aid in the diagnosis and treatment of an
injury or illness.
It is an excellent method, indeed, for
visualizing the structural details of the brain and spinal cord.
How Does MRI work?
MRI does not use ionizing radiation to create images. It takes advantage of the
water molecules in your body combined with a powerful magnetic unit and radio
frequencies to obtain images. The body part to be examined is placed into a device
known as MRI coil, which is used to transmit and receive signals from your body. A
computer interprets the signals into a series of detailed images which is then
transferred to a monitor or a sheet of film similar to x-ray film. So an image of tissue
is constructed by computer analysis of the radio-frequency energy that absorbed and
emitted by the protons in the tissue.
Risks...MRI is considered safe. There are no known health risks associated with the
magnetic field or the radio waves used by the machine nor should there be any side
effects.
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It provides better resolution than the CT scan. Because of its present
limited availability and high cost.
4. Computed Tomography (CT):
What is CT?
Computerized Axial Tomography - also known as
CAT or CT scans images your body in slices
showing the structures in that area. A computer is
used to provide clear, sharp images.
How Does CT work?
As CT x-rays pass through the designated area of your body from different
directions, they are measured by special detectors that convert them into electrical
signals (depend on difference in the quantity of x-ray absorbed by the different
tissues). A computer converts the signals into images through a mathematical
procedure called 'image reconstruction' and the images are rebuilt. These images are
viewed on monitors or printed on a sheet of film.
The shading of each point in an image is proportional to its x-ray absorption
coefficient. Intravenous injection of iodinated contrast material may be used to
enhance the density of the vascular structures.
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5. Comparison between Brain imaging types:
Procedure
Method
(CT Scan)
CT scans use a series of X-ray beams
passed through the head. The images are
then developed on sensitive film. This
method creates cross-sectional images of
the brain and shows the structure of the
brain, but not its function.
(PET)
A scanner detects radioactive material that
is injected or inhaled to produce an image
of the brain. Commonly used radioactivelylabeled material includes oxygen, fluorine,
carbon and nitrogen. When this material
gets into the bloodstream, it goes to areas of
the brain that use it. So, oxygen and glucose
accumulate in brain areas that are
metabolically active. When the radioactive
material breaks down, it gives off a neutron
and a positron. When a positron hits an
electron, both are destroyed and two
gamma rays are released. Gamma ray
detectors record the brain area where the
gamma rays are emitted. This method
provides a functional view of the brain.
Advantages:
1. Provides an image of brain activity.
Disadvantages:
1. Expensive to use.
2. Radioactive material used.
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MRI uses the detection of radio frequency
signals produced by displaced radio waves
in a magnetic field. It provides an
anatomical view of the brain.
(MRI)
Advantages:
1. No X-rays or radioactive material is
used.
2. Provides detailed view of the brain in
different dimensions.
3. Safe, painless, non-invasive.
4. No special preparation (except the
removal of all metal objects) is
required from the patient.
5. Patients can eat or drink anything
before the procedure.
Disadvantages:
1. Expensive to use.
2. Cannot be used in patients with
metallic devices, like pacemakers.
3. Cannot be used with uncooperative
patients because the patient must lie
still.
4. Cannot be used with patients who are
claustrophobic (afraid of small
places). However, new MRI systems
with a more open design are now
available.
(FMRI)
Angiography
Functional MRI detects changes in blood
flow to particular areas of the brain. It
provides both an anatomical and a
functional view of the brain.
Angiography involves a series of X-rays
after dye is injected into the blood. This
method provides an image of the blood
vessels of the brain.
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Chapter 5
Brain Cancer & Epilepsy
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Brain Cancer:
What is Brain Cancer?
The brain, like any other tissue in the body, is made up of individual cells which
are much smaller than a pinpoint, and require a microscope to see them. These cells
are the smallest units which compose the brain, and there are several different types.
A brain cancer can arise from any of the cells which make up the brain.
PET images special is how they show precise changes in cell function.
The simultaneous CT scan pinpoints the location of these abnormalities.
In fact, PET/CT scans give specialists the ability to diagnose cancer before it
reaches the stage where it can be detected by other forms of diagnostic imaging.
Primary and secondary brain tumors:
Primary brain tumors:
Primary brain tumors develop from brain cells.
Benign tumors:
Many primary brain tumors are benign, which means that they remain in the part
of the brain in which they started and do not spread into and destroy other areas of
the brain tissue. They do not spread to other parts of the body. If a benign tumor can
be removed successfully it should not cause any further problems.
Some benign tumors do re-grow slowly and if this happens, treatment with
radiotherapy or further surgery may be given.
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However, sometimes it is difficult to remove the tumor because of its position
within the brain, or because the surrounding brain tissue could be damaged by
surgery.
Secondary brain tumors:
Brain tumors can arise at any time and damage this complex organ in various
ways. Some risk factors are environmental, like radiation from previous cancer
treatment. Other risk factors are mainly due to immune system disorders, and rarely
do they run in the family. Therefore, abnormalities of genes (mutations) are the main
cause for brain cancer.
It all starts in a single cell anywhere in the brain, since any type of cell there can
become cancerous. Unlike cancer in other organs of the body, brain tumors spread
locally and cause a lot of damage to the normal tissue in the place where they
originated.
Epilepsy:
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The EEG records the electrical activity of the brain. During a seizure, the
electrical activity is abnormal. Once the seizure is over, the brain rapidly returns to
normal in most individuals.
The likelihood of recording a seizure during the EEG is small. The EEG
generally records brain waves between seizures, called interictal brain waves (called
epileptiform discharges occur on the EEG. These epileptiform discharges are sharp
appearing waves. Spikes are epileptiform discharges with a 20-70 msec).
These waves may or may not show evidence of seizure activity. The neurologist
looks for spikes or sharp waves ("epilepsy waves") to confirm the diagnosis, but the
absence of these abnormal brain waves does not eliminate seizures as a possibility.
Specific techniques, like flashing lights or 2 to 5 minutes of deep breathing
(hyperventilation), often are used to provoke abnormal brain waves so they can be
recorded. Recording the "epilepsy waves" is helpful because it confirms the
diagnosis and may identify the type of seizure disorder, but it is not necessary for
diagnosis and treatment.
Making a diagnosis of seizures does not depend only on the results of the EEG. The
neurologist also considers several other types of information.
One of the most important way is an MRI scan of your brain will be
evaluated for relevant abnormalities.
During the session you may be asked to open and close your eyes. You may also
be asked to breathe deeply for some minutes, because this could reveal or increase
abnormal brainwave patterns. You may also be asked to look at a flashing light to
show if this triggers epileptic activity. If the flashing light produces an abnormal
pattern during the EEG, the light is immediately switched off by the staff, so there is
little risk of further epileptic activity developing.
Other ways in which the EEG is used to detect epileptic activity
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Electroencephalogram (EEG)
In adults who are awake, the EEG shows mostly alpha waves and
beta waves.
The two sides of the brain show similar patterns of electrical
activity.
Normal:
There are no abnormal bursts of electrical activity and no
consistently slow brain waves detected on the EEG tracing.
If flashing lights (photo stimulation) are used during the test, one
area of the brain (the occipital region) may have a brief response
after each flash of light, but the brain waves remain normal.
The two sides of the brain show different patterns of electrical
activity. This may indicate a problem in one area or side of the
brain.
The EEG shows sudden bursts of electrical activity (spikes) or
sudden slowing of brain waves in the brain. These abnormal
discharges may be caused by a brain tumor, infection, injury,
stroke, or epilepsy. When a person has epilepsy, the location and
exact pattern of the abnormal brain waves may help determine
what type of epilepsy or seizures the person has. Keep in mind
that in many people with epilepsy, the EEG may appear
completely normal between seizures. An EEG by itself may not
diagnose or rule out epilepsy or a seizure disorder.
The EEG records abnormalities in the brain waves that may not be
Abnormal: confined to one specific area of the brain. A disorder affecting the
entire brain—such as drug intoxication, infections (encephalitis),
or metabolic disorders (such as diabetic ketoacidosis) that upset
the chemical balance in the body, including the brain—may
produce these kinds of abnormalities.
The EEG shows delta waves or an excess of theta waves in adults
who are awake. These results may indicate brain injury.
The EEG shows no electrical activity in the brain (a “flat” or
“straight-line” EEG). This indicates that brain function has
stopped, which is usually caused by lack of oxygen or blood flow
inside the brain. In some cases, severe drug-induced sedation can
produce a flat EEG. This state also can be seen in status
epilepticus after a significant amount of medication is given to
control the seizure.
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Sleep EEG:
If an EEG recorded during waking has not shown any epileptic activity, an
EEG during sleep may be recommended. This is because everyone's brainwave
patterns change dramatically During sleep. Sleep can also make the brainwave
patterns between seizures more obvious. This extra information can help with
diagnosis.
A sleep EEG is also usually recommended when someone has seizures during
sleep only. It may be carried out in hospital, or at home using an ambulatory EEG.
Sleep Deprived EEG:
Depriving someone of sleep can cause changes in the electrical activity of the
brain. Recording these changes on an EEG can provide the doctors with important
information. Sleep-deprived EEGs are often used when a routine EEG has failed to
show anything useful.
The ambulatory EEG:
When you have a seizure the EEG recorder will record the event which can be
viewed later on a special machine in the EEG laboratory. You will be asked to keep
an account of daily activities, so that they can be related to the EEG recording made
at the time. This investigation is called ambulatory EEG monitoring.
Video-telemetry:
Where there is doubt about a diagnosis of epilepsy, or where the type of seizures
someone experiences is unclear, video-telemetry can be helpful. This is a test that
uses a video camera linked to an EEG machine. The camera will visually record
your movements and at the same time the EEG machine will record your brainwave
pattern. Both the video and EEG are stored onto a computer that can be reviewed
once the test is finished. The consultant will be able to see any episodes/seizures that
you may have had, as well as any changes in your EEG at that time. The test is often
carried out over a number of days in order to increase the chances of recording one
of your seizures.
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Dipole Localization
EEG with MRI
Chapter 6
Ten - Twenty System & Montage
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EEG with MRI
Contents:
1. Introduction
2. Methodology of 10-20 system
3. Electrode Montages
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1. Introduction:
ƒ The different electrode positions are derived from measurements taken between
standard landmarks on the skull.
ƒ These measurements allow the calculation of a network of lines, which are
superimposed across the head. Electrodes are placed where the lines of this mesh
intersect.
ƒ This results in inter-electrode distances of ten and twenty percent of lines total
length.
ƒ 10-20 EEG electrode placement system established by the International
Federation of EEG societies. In this setup
Using the 10/20 International System of electrode placement, the average distance
between electrodes in an adult is 6 to 6.5 cm. Activity recorded using these
distances. However if the same activity was recorded using longer inter-electrode
distances, some activity might be seen. Therefore some double distance electrode
linkages are recommended for example FP1-C3, F3-P3, C3-O1 ...etc.
Display sensitivities of a minimum of 2 µ V/mm are required. However digital
EEG systems have the added advantage of having sensitivity values of 1.5 and 1 µ
V/mm. This 50-100 % increase in sensitivity will allow a more confident assessment
of the presence or absence of a 2 µ V signal.
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Dipole Localization
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2. Methodology of 10-20 system:
● Patient's head is mapped by four standard points:
-Nasion point
-Inion point
-Left preauricular point
-Right preauricular point
● EEG electrodes positions are derived from measurements taken among these four
standard landmarks on the skull.
● This results in inter-electrode distances of ten and twenty percent of total length.
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Letters identifying and its sub-cranial lobe:
Symbol
‘Fp’
‘F’
‘T’
‘C’
‘P’
‘O’
‘Z’
‘A’
odd
numbers
even
number
meaning
Front polar or prefrontal
lobe
Frontal lobe
Temporal lobe
Central lobe
Parietal lobe
Occipital lobe
cerebrums midline (Zero
Line)
the lobules of ear
left hemisphere
right hemisphere
There are five stages to describe the methodology by which the
nineteen electrode sites:
First Stage:
The distance between the nasion and inion is measured along
the cerebrum’s midline. The frontopolar point ‘FP’ can then be calculated and
marked at 10% of this distance, directly above the nasion. Electrode positions ‘FZ’,
‘CZ’, ‘PZ’, and point ‘O’ are then marked in succession at intervals of 20% of the
total distance (starting from ‘FP’).
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Lateral view
Second Stage:
The distance between the two preauricular points (transverse ‘CZ’), is then
measured allowing the labeling of electrode positions ‘T3’and ‘C3’ at 40% and 20%
from the midline respectively. ‘T4’ and ‘C4’ can also be found using the same
methodology as ‘T3’ and ‘C3’, this time along the opposite side of the head.
Frontal view
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Third Stage:
The circumference of the head (transverse points ‘FP’ and ‘O’ and electrode
positions ‘T3’ and ‘T4’) is then measured. Electrode position ‘FP1’ is marked at a
distance of 5% of the circumference of the head, to the left of point ‘FP’. Starting
from ‘FP1’, electrode sites ‘F7’, ‘T3’, ‘T5’, ‘O1’, ‘O2’, ‘T6’, ‘T4’, ‘F8’ and ‘FP2’
can be superimposed around the scalp (along the plane of the circumference), each
being a distance 10% of the circumference away from each other.
Superior view
Fourth Stage:
The midpoints that lie between ‘Fp1’ and ‘C3’ (on the left side of the head) and
‘Fp2’ and ‘C4’ (on the right side of the head) provide the longitudinal coordinates
for ‘F3’ and ‘F4’ respectively. Likewise, the midpoints that lie between ‘C3’ and
‘O1’ (on the left side of the head) and ‘C4’ and ‘O2’ (on the right side of the head)
provide the longitudinal coordinates for ‘P3’ and ‘P4’ respectively.
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Fifth Stage:
The midpoints that lie between ‘FZ’and ‘F7’ and ‘FZ’ and ‘F8’ define the
transverse coordinates for ‘F3’ and ‘F4’ respectively. Similarly, the midpoints that
lie between ‘PZ’ and ‘T5’ (on the rear left side of the head) and ‘PZ’ and ‘T6’ (on
the rear right side of the head) define the transverse coordinates for ‘P3’ and ‘P4’
respectively. The remaining electrodes positions, namely ‘F3’, ‘F4’, ‘P3’ and ‘P4’,
can now be found using the derived longitudinal and transverse coordinates outlined
here and in the previous stage.
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Dipole Localization
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The final 10-20 EEG electrode placement diagram:
The Modified Combinatory Nomenclature:
Modifying is by using Supplementary electrodes to improve
electroencephalographic spatial resolution and developing a more extensive
placement by subdividing the existing in
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3. Electrode Montages:
What is a montage?
Montage is the method or technique used to record EEG potentials or the pattern
of connections between the electrodes and the recording channels.
EEG montages vary according to:
1- The number of recording channels available.
2- Monitored procedure.
3- Stimulation sites.
Montage objective:
The montage should be chosen to maximize the sensitivity of the recorded
response over the affected neural pathways.
EEG montages are design to be symmetrical about the midline in order to obtain
information relating to left-right amplitude and phase differences.
Montage types:
a- unipolar derivation:
A-Common reference derivation:
ƒ Each amplifier records the difference between a scalp electrode and a reference
electrode. The same reference electrode is used for all channels. Electrodes
frequently used as the reference electrode are A1, A2, the ear electrodes, or A1 and
A2 linked together or any scalp electrode as a reference. Or the average reference is
computed as a mean of all electrodes.
ƒ The standard reference potential is assigned a value of zero.
Reference electrodes are one of the important questions in EEG recording is the site
of reference electrodes, relative to which the electric brain potentials in all other
electrodes is measured.
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The reference electrodes should be placed on a presumed “inactive” zone.
Frequently, this is the left or right earlobe or both of them. If one earlobe electrode is
used as a reference the topography of EEG rhythms is rather close to true, but there
is the systematic decrease of EEG amplitude in the electrodes which are closer to the
reference side.
If “linked” earlobes are used, this kind of asymmetry is avoided but this distorts
the EEG picture since the electric current flows inside the linking wire.
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Dipole Localization
EEG with MRI
B-Average reference derivation:
Activity from all the electrodes are measured, summed together and averaged
before being passed through a high value resistor. The resulting signal is then used
as a reference electrode and connected to input 2 of each amplifier
b- Bipolar derivation:
A bipolar chain is a series of bipolar channels in which the second electrode of
one channel becomes the first electrode of the next channel. An example would be:
Fp2-F4, F4-C4, C4-P4 and P4-O2.
Channel one:
Channel two:
I-1
Fp2
F4
I-2
F4
C4
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The necessary to have more than one type of montage:
It is necessary for the electroencephalographic man to view the EEG activity in
more than one plane. The phase reversals created by bipolar linkages make bipolar
montages particularly useful for localizing activity. Use of longitudinal, transverse,
and circumferential bipolar montages makes it possible to more precisely localize
both normal and abnormal EEG activity. Referential montages are better than
bipolar montages for accurately reflecting both the full amplitude and the true
morphology of recorded activity.
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EEG with MRI
Chapter 7
Brain Color Mapping & EEG Power Spectrum
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1. Brain Color Mapping:
Brain color mapping is a presentation of EEG parameters on a schematic head
surface by interpolating the data obtained in each single electrode into interelectrode
space. This provides the researcher with the visual image presenting multichannel
EEG in most integrative and demonstrative form.
The main feature and advantage of the map are that it presents the EEG in a form
of image that displays data sets as a whole. The visual map analysis involves
therefore both the mechanisms of imaginative and abstract thinking that makes the
process more efficient.
Now the map is usually built by linear interpolation of the potential values of three
or four neighboring electrodes, which are summarized in such a way that a
corresponding map pixel value is treated as a mathematical average, inversely
proportional to the distances from each of these electrodes. More complicated is
surface spline interpolation, which can exhibit maxima and minima between
electrodes (this is not possible in linear interpolation) and produces smoother maps.
Maximum voltage
Zero Voltage
Minimum Voltage
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2. EEG Power Spectrum:
EEG waveform is a complex wave, it maybe little resemblance to a sin wave
components.
EEG can be synthesized from a number of simpler Sin wave's components.
The reverse process of this synthesis is known as:
"Spectral Analysis"
The amplitudes of Fourier series are often expressed as a mean square
value, so, the result plot of the data is called:
"Power Spectrum"
Power Spectrum of a waveform represents a synopsis of frequency
component of a segment of EEG recording.
Fp – T4
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Fourier Transform:
● The Fourier transform (FT) is a method to uncover the rhythmic structure of EEG.
It is based on a mathematical fact that any signal defined in a given time interval can
be decomposed into a sum of sinusoidal waves of different frequencies, amplitudes
and phases.
● The squared module of FT is a real function that describes the frequency
components’ power and is hence called a power spectrum. The square root of power
spectrum, i.e. FT’s module, describes components’ amplitudes, whereas the
arctangent of the ratio of FT’s imaginary and real parts define the components’
phases.
● There is one rather practically and theoretically significant property of the FT: its
frequency resolution is the inverse to the width of the analyzed time window:
f = 1 / T . This basic fact is often called the uncertainty principle, since it means
that it is impossible to know a precise time and frequency information on a signal
simultaneously.
Indeed, large time windows provide good frequency resolution but poor time
resolution, and vice versa. To estimate a time course of EEG spectrum the so called
windowed FT is applied. In this method, FT is calculated in a window of constant
duration that moves along the EEG record.
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EEG with MRI
To increase the reliability of the spectral parameters in this technique averaging the
spectral samples got in the same time interval in a number of tasks in one subject
and across the subjects is recommended.
For practical use, the discrete fast Fourier transform (FFT) is best suited. This
method significantly economizes computational time at a cost of a restriction that the
length of time window for FT calculation, being expressed in discrete time samples,
must be a power of two.
● The FT is the most widely used method of rhythm analysis and should be
considered as a principal pilot method in EEG studies. It is included in almost all
commercially available EEG processing software.
● Power spectral analysis is a well-established method for the analysis of EEG
signals. Spectral parameters can be used to quantify pharmacological effects of
anaesthetics on the brain and the level of sedation. This method, in numerous
variations, has been applied to depth of anaesthesia monitoring and has been
incorporated into several commercially available EEG monitors.
Because of the importance of EEG power spectral analysis, we evaluated the
performance of each frequency in the power spectrum regarding detection of
awareness.
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Part Two
Dipole Localization Software
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EEG with MRI
Chapter 8
Dipole Localization Algorithm
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EEG with MRI
Contents:
1. Goal of Dipole Localization.
2. Advantages of Dipole Localization.
3. MRI Image Processing.
4. EEG Signal Processing.
5. Brain Color Mapping Algorism.
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1. Goal of Dipole Localization:
In the past, most Neurosurgical Ways were dangerous and had many Sid
effects on the patients.
Nowadays, this ways are rapidly changed by using image & signal processing
technology, Researchers often combine EEG images of brain electrical activity with
MRI scans to better pinpoint the location of the activity within the brain, so the
biomedical developers use patient's MRI images and EEG signals within a software
program that determine the brain activity accurately, this program will confirm the
neurosurgeons diagnosis.
An important application of multichannel EEG is to try to find the location of
a epileptic focus (a small spot in the brain where the abnormal activity originates and
then spreads to other parts of the brain) or of a tumor, even when they are not visible
in a x-ray or CT scan of the head.
We want to join the MRI images (High resolution) and the EEG signals
So, our software based on two basics:1- Image Processing.
2- Signal Processing.
Finally, We aim to give the neuro-physician an insight into the optimal use of
EEG in neurological diagnosis, in some illness cases such as epilepsy or a brain
cancer; physicians should confirm their diagnosis especially if it is necessary to a
surgically treatment to brain cancer or epileptic patients.
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2. Advantages of Dipole Localization:
1- Digital Video monitoring capabilities.
2- Integrated patient database with search functions.
3- Advanced montage constructor.
4- Event marker presets with quick note insert.
5- Software control over sampling frequency and filters.
6- Capable up to 128 channel recording and visualization.
7- Brain mapping.
8- Spectral analysis from multiple segments.
9- Printout of any on screen mapping or analysis.
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3. MRI Image Processing:
In this part we want to develop the 10-20 system, to make this we
want to read MRI image pixel by pixel to get the length of Hid boundary
surface.
we follow these steps:-
1- Loading of three Projection of Patient’s MRI images from the PC.
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2- Convert the MRI images to Black and White (BW) by get the average
of R.G.B of the image and comparing it with threshold value as:
Average = (red +green+blue)/3
if (average >threshold)
{
Red = 255;
Green = 255;
Blue = 255;
}
else
{
Red = 0;
Green = 0;
Blue = 0;
}
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3- Set the four markers in the frontal view (at right and left preauricular
points) and in the lateral view (at nasion and inion points)
Left preauricular
Right preauricular
Nasion
Inion
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Dipole Localization
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4- Detect the edge of the images by detect the white color between
the two markers in frontal and lateral images and the whole edge of
superior, then replace it by blue color.
5-Collect indices of the blue color edge in the array. This array contains
the index of X and Y positions and the sum. The sum is calculated by
comparing between two pixels
1
1.4
This distance (1 or 1.4) is calculated from the following equation:-
distance
=
( row diff ) 2 + ( col diff ) 2
This distance is arranged in the array match the index of this pixel, then
compute the final sum which is equal the summation of all distances.
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6- From the final sum compute the 10-20% distance getting the location
of the electrodes.
You can verify that by creating a loop that moving through the array and
compute the sum at each step and comparing it by(10%from final sum,
20% from final sum,30%from final sum …………and so on).
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7- Deduce the location of the electrode in one view with respect to the
other two views to make the projection.
The following figure shows the idea of projection.
Y
Y
Z
X
Elevation view
Side view
Z
X
Plane view
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8- Now, by using the previous idea the electrodes are distributed in
the three figures with respect to the 10-20 system.
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4. EEG Signal Processing:
The main concept of drawing:
Here in this part we would like to draw the signal that its format is discussed
previously so the main concept is drawing a straight line between every two samples
to get the signal shown.
One page
EEG Channel name
EEG Trace
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How to draw a signal:
Time between two samples
For drawing:
We must specify the number of seconds in page.
-If the number of seconds in page is 10 sec/page, then …
---the number of samples per page is:
sample _ in _ page = (no _ of _ sec/ page) * (no _ of _ sample / sec)
in pixel is:
---the step between two samples is:
Step
=
Panel _ width
Sample _ in _ page
Pixel
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--- The position of every signal in the panel will be calculated by
dividing the panel height by the number of channels that will be
drawn.
---the voltage that will be taken from the ascii file as scaled in µv will
also be calculated in pixel according to the resolution of the screen as:
Example:
1 cm --------------------Æ 25pixel
1 mm-------------------Æ2.5pixel
If the user chose for sensitivity is (.7 µv/mm)
.7 µV ------------------Æ1mm
.7 µV ------------------Æ2.5pixel
Value of file in µV------------Æ?
So by this example we can draw all montage signals by a simple
calculation.
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In our program we read the EEG files, its format is ascii (American
Standard Code for Information Interchange).
ASCII data files are sometimes called raw data files because they contain just the
data. That is, no variable definition information is included in a raw data file.
ASCII data files can be either fixed column format or freefield format.
1. Fixed-Column ASCII Format:
Fixed column format means that the values for a variable are always located in
the same column.
The values can be right next to each other, or they can be separated by one or more
spaces.
Fixed Column Format
01Martha 18 1
02
53 9
03Suzanne 10 1
04Debbie
1
07Fernandez 21 2
2. Free field ASCII Format:
In free field format the variables for each case must appear in the same order and
the values for each variable must be separated by one or more spaces or commas. A
space or comma is called a common delimit
Free field Format
01 Martha 18 1
02 " " 53
9
03,,,,,,Suzanne,,,,,10 , , 1
04,Debbie,-99,1
07, Fernandez 21 2
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Our file EEG file format is fixed ASCII format.
The file consists of two parts:
1- Header data.
2- Recording data.
Header data:
It Contains:
1- Information about the patient
2- The start second
3- The total time of recording (seconds (sec))
4- The sampling rate (HZ).
5- The unit of data recording (µv)
6- The number of channel tracing.
7- Label of channel.
The data recording:
The data of EEG is stored in the form of matrix the number of columns are the
number of channel and the number of row is the number of data sampling in the file.
We can get the number of sampling by:
No. Rows=Sampling rate*Total seconds.
By c# we read file row by row and we can get the data of header file and we can
store the EEG data recording in a matrix 2-Dand then plot it.
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Trace no.
Channel name
Data recording
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5. Brain Color Mapping Algorism:
Mapping processing and Results:
Palette box:
This box contains the gradient color between:
• The Blue and Red color:
We considered the maximum volt matches red and the
minimum volt matches blue and then makes interpolation between two
colors and two voltages to get the color matches to voltage between the
minimum and maximum voltage.
Max Voltage
(255, 0, 0)
Known Volt
Unknown color
Min voltage
(0, 0,255)
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Red − blue
max volt − minmum
The unknown Red = (
volt
=
unkwon color − red
known volt − max volt
255 − 0
max volt − minmum volt
The unknown Green = (
) ∗ (known volt − max volt) + 255
0−0
max volt − minmum volt
The unknown Blue = (
) ∗ (known volt − max volt) + 0 = 0
0 − 255
max volt − minmum volt
) ∗ (known volt − max vo
• The Red , Green and Blue:
Max voltage
(255, 0, 0)
(1)
Center voltage
(0, 255, 0)
(2)
Min voltage
(0, 0, 255)
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Dipole Localization
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We considered the maximum volt as red, the minimum volt as blue and
the Green color as the main voltage.
1) If the unknown voltage lies between maximum and main voltage;
So, makes interpolation between green and Red colors with maximum and
main voltage. So, you can get the color matches to voltage between the
maximum and main voltage.
Red − Green
unkwon color − Green
=
max volt − main volt
known volt − main volt
=
unknown Green = (
−
∗
−
0 − 255
max volt − main volt
−
+
) ∗ (known volt − main volt) + 255
2) If the unknown voltage lies between minimum and main:
We make interpolation between green and blue colors with minimum and
main voltage. So, you can get the color matches to voltage between the
minimum and main voltage.
Green − blue
main volt − minmum volt
The unknownRed = (
=
unkwon color − Green
known volt − main volt
0−0
) ∗ (knownvolt − main volt) + 0 = 0
main volt − minmumvolt
The unknown Green = (
The unknown Blue = (
255 − 0
) ∗ (known volt − main volt) + 255
main volt − minmum volt
0 − 255
) ∗ (known volt − main volt) + 0
main volt − minmum volt
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• Rainbow box:
In this box we make gradient between five colors (Orange, yellow,
green, light yellow and dark blue).
Max voltage
(255, 70, 30)
(1)
Main up Voltage
(220, 220, 0)
(2)
Center voltage
(100, 250, 50)
Main down Voltage
(4)
(100,100,255)
Min voltage
(100,100,255)
(3)
(1) If the color lies between the maximum and main up:
Orange − yellow
max volt − mainup volt
The unknown Red = (
=
unkwon color − Orange
known volt − max volt
220 − 255
mainup volt − max volt
) ∗ (known volt − max volt) + 255
The unknownGreen = (
220 − 70
) ∗ (known volt − max volt) + 70
mainup volt − max volt
The unknown Blue = (
0 − 30
) ∗ (known volt − max volt) + 30
mainup volt − max volt
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(2) If the color lies between the main up and main:
yallow − green
unkwon color − yellow
=
mainup volt − main volt
known volt − mainup volt
TheunknownRed = (
) ∗ (knownvolt − mainupvolt)+ 220
mainvolt − mainupvolt
TheunknownGreen= (
TheunknownBlue= (
100− 220
250 − 220
) ∗ (knownvolt− mainupvolt)+ 220
mainvolt− mainupvolt
50 − 0
) ∗ (knownvolt− mainupvolt)+ 50
mainvolt− mainupvolt
(3) If the color lies between the main and main down:
green - light blue
main volt − maindown volt
The unknown Red = (
=
unkwon color − lightblue
known volt − maindown volt
100 − 100
main volt − maindown volt
The unknownGreen = (
The unknown Blue = (
) ∗ (known volt − maindown volt) + 100
100 - 250
main volt − maindown volt
255 − 50
main volt − maindown volt
) ∗ (known volt − maindown volt) + 250
) ∗ (known volt − maindown volt) + 50
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(4) If the color lies between the main down and minimum:
light blue - dark blue
maindown volt − minimum volt
TheunknownRed = (
unkwon color − lightblue
known volt − maindown volt
0 − 100
) ∗ (knownvolt − maindownvolt)+ 100
min volt − maindownvolt
The unknownGreen = (
The unknown Blue = (
=
0 - 100
min volt − maindownvolt
120 − 255
min volt − maindown volt
) ∗ (known volt − maindownvolt) + 100
) ∗ (known volt − maindown volt) + 255
As shown the palate boxes show the relation between colors and voltages
represented in the EEG file for easy vision to the doctor as:
1.
This represents the maximum voltage of EEG at specific time in the
EEG file represented in Red color.
2.
This represents the minimum volt at the same time which represented in
blue color.
3.
This represents the main voltage between maximum and minimum
voltage which represented in green color.
The next step using the location of the electrode distributed in the MRI views and
represent them as a different color due to the value of voltage taken from EEG file at
specific time that the doctor want to see, as it is represent the activity of the brain at
this time.
The data of EEG signal is stored in two dimensional array number of columns
represent the number of channel and number of rows represent the number of
samples in the file taken from the patient. we take the values of voltage at every
electrodes in a specific time and compute the maximum and the minimum value of
EEG signal at this time which matches the red and blue color so we can get the color
matches the voltage between these values.
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(The activity of the brain at the location of the EEG electrodes)
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EEG with MRI
Potential mapping:
In our project we make a model of head and distribute the location of
the electrode at constant distance depending on the ten twenty system as
shown in the figure blow.
(Brain activity at specific time (as the color gradient between electrodes
Graduation Project ١١٠
2005 - 2006
Dipole Localization
EEG with MRI
• The idea of mapping:
The red circles represent the center of the image and the surrounding
points around the center have a specific color and then we make gradient
of colors between the center point and the surrounding points.
We use the idea of mapping discussed above to make area mapping
between electrodes’ voltage.
1. The following figure shows the activity of the brain at each
electrode.
2. We note that the higher voltage represented as red area, the lower
voltage represented as blue area and the other voltages are gradient
between them.
Graduation Project ١١١
2005 - 2006
Dipole Localization
EEG with MRI
3- By our program we can choose the area mapping gradient color
by the pallete dialogue.
Graduation Project ١١٢
2005 - 2006
Dipole Localization
EEG with MRI
Chapter 9
Problems Faced Us
Graduation Project ١١٣
2005 - 2006
Dipole Localization
EEG with MRI
In Our project we face many problems, we try to solve them all but some
of them we can solve and the other we hope to solve in the upgrade.
1- Difficulty in collecting data:
The basic problem is collecting real data where we want MRI images,
EEG signals and Video recording of the same patient. Most hospitals have
security in their data but we found finally some useful data .
2- Our Project with Matlab programming language:
Our project based on two important processes
1-Image processing (MRI images)
2-Signal processing (EEG signal)
These two processes are easy to carry out on a matlab but it was the first
problem as matlab does not build on executable file ,so we decided to
make our project by Visual C++.net because:
1-It can build an executable file.
2- More fast than other languages (because its compiler is nearest to
machine language)
3- Our project with VC++.net:
VC++.net is very strong language in programming ,so we do our best in
handling MRI images and how to deal with each pixel in the MRI image
(like: determine the position of it also deal with the color components of
each pixel)
4-Image processing problem:
We spent more times for finding the suitable algorithm that has minimum
error to calculate the length of edges of the MRI images
5- Drawing EEG signal and VC++.net problem:
Also we work on the EEG signal to read the data of it and draw it in a
second window but we faced with a very difficult problem, that is the
visual C++.net is not easy when we use the MFCC where every tool used
in the interfacing must be generated by the code, also VC++.net is
difficult when we generate two separate windows and link them together,
Graduation Project ١١٤
2005 - 2006
Dipole Localization
EEG with MRI
where we want to link the change happened in the first window with
second window.
6-Our project with VC#.net:
With some of searches we know that VC#.net is easy language in dealing
with the windows application and easy to link between separate two
windows, so we made our project with the VC#.net programming
language.
7- The problem in the VC#.net:
After while we found that the VC#.net is very slow than the VC++.net in
processing but VC#.net can solve our serious and basic problems, so we
continue working with it.
Graduation Project ١١٥
2005 - 2006
Dipole Localization
EEG with MRI
Chapter 10
Upgrades in
future
Graduation Project ١١٦
2005 - 2006
Dipole Localization
EEG with MRI
1. 3-D brain model:
In our project we deal with 2D MRI images to locate the EEG electrodes
with respect to the ten twenty system.
We hope to construct slices of MRI images to make 3D real model of
brain (Skull) to be more accurate when distributing EEG electrodes on the
skull.
Also we need to use the 3D real model for color mapping to locate the
accurate location for abnormal part of brain in purpose of helping
neurosurgeons.
2. Load EEG signal of EDF format (European Data Format):
Most bio-signal is stored in EDF format which minimize the size data file.
In our project we try to read the EDF file but it was difficult to read the
data stored in it, so we read the EEG signal in an ASCII format.
We hope that reading the EEG signal file in its most standard format.
3. Load MRI images from DICOM format:
MRI generates MRI images in DICOM format, but with lack of time we
did not read it in its real format, so we use the OSORIS program to
convert the MRI images from DICOM format to Bmp format.
We hope that we read images in its real format
4. Power spectrum:
We hope to add power spectrum in our project to clear a power of every
band during period of time chosen by doctor.
5. Mapping of bipolar signal:
We hopping to make a mapping of bipolar signal by subtracting two
bipolar channel that have the same type electrode to give its unipolar
value that will use in mapping.
Graduation Project ١١٧
2005 - 2006
Dipole Localization
EEG with MRI
Future Goal of our project:
EEG during fMRI is an important application depending on mainly
the same idea but in method.
EEG during fMRI is made in purpose of specify the epileptic focus of
brain by EEG and fMRI scan together in the same time but this
recurs
• Spatial filters.
• Special electrodes to bear magnetic field.
MRI image will includes the real location of electrodes in brain.
Graduation Project ١١٨
2005 - 2006
Dipole Localization
EEG with MRI
References:
www.deymed.com/truscan32nf.asp
www.valdostamuseum.org/hamsmith/quancon.html
www.emedicine.com/neuro/electroencephalography_and_evoked_potent
ials
http://medi.uni-oldenburg.de/members/ane . (PDF)
www.cerebromente.org.br/n03/tecnologia
www.aha.ru/~geivanit/EEGmanual
www.cornea.berkeley.edu
www.sccn.ucsd.edu
www.cerebromente.org.br
www.neuro.mcg.edu/amurro
http://www.aha.ru/~geivanit/EEGmanual//coherence.html
http://www.unizh.ch
http://www.waiting.com/brain function.html
http://www.waiting.com/brain anatomy.html
http://www.epilepsy.com
http://www.drugabuse.gov/index.html
http://okkxray.com/loc-advimage.html
http://kumed.com/bodyside.cfm
http//www.cheyrad.com
http://wecaremedicalmall.org/dental.html
http://epilepsy.org.uk/info.html
http://www.webmd.com
http://www.cancer-research-center.com/cancer.html
http://infoforyourhealth.com/cancer/brain/20cancer.html
http//www.hida.hih.gov/nida-notes/nnvol11lns/basics.html
http://www.canceranswevs.com
http://www.cancer.duke.edu
http://serendip.brynmawr.edu/bb/kinser/int1.html
http://salmon.psy.plym.ac.uk/year1/neurotr.html
http://www.codeproject.com
Graduation Project ١١٩
2005 - 2006