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Design a Electronenceohaplogram (EEG) transmission and receving system using
infrared waves for states of sleep
Project
Su...
2
APPROVAL SHEET
Project Entitled: Design a Electronenceohaplogram (EEG) transmission and receving system
using infrared w...
3
Table	of	Contents	
CHAPTER	1	..............................................................................................
4
5.1.3	 Low	pass	Filter	....................................................................................................
5
Chapter 1
Introduction
EEG is an acronym for Electroencephalograph. This is a recording ("graph") of electrical signals
...
6
frequency band of the beta waves is 13-30 Hz; these are detectable over the parietal and frontal
lobes. The delta waves ...
7
1.1 Motivation
We came across the use of EEG waveforms in medicine during our In Plant Training. We were quite
impressed...
8
receiver so that no obstacle is created for the surgeon while he is operating as well as he gets a proper
report of the ...
9
1.4 Work Done
1.4.1 Demonstration of the Equipment - We have seen the working of this equipment during our In
Plant Trai...
10
Chapter 2
ANATOMY OF THE BRAIN
The figure below shows the anatomy of the brain. We will define each and every part labe...
11
2.1. Brainstem - The lower extension of the brain where it connects to the spinal cord. Neurological
functions located ...
12
Fig: - Frontal lobe of the brain
2.2.1 Frontal Lobe - Front part of the brain; involved in planning, organizing, proble...
13
2.2.3 Occipital Lobe - Region in the back of the brain, which processes visual information.
Not only is the occipital l...
14
Left Hemisphere Sequential Analysis: systematic,
logical interpretation of information.
Interpretation and production o...
15
Frontal Lobe
Ventral View (From Bottom)
Side View
Cognition and memory.
Prefrontal area: The ability to
concentrate and...
16
environment space.
î Inability to write.
Occipital Lobe
Primary visual reception area.
Primary visual association area:...
17
Hypothalamus.
Basal Ganglia
Sub cortical gray matter nuclei.
Processing link between thalamus and
motor cortex. Initiat...
18
Chapter 3
THE EEG SIGNAL
From the EEG signal it is possible to differentiate alpha, beta, delta, and theta waves as wel...
19
• 3.4 Delta waves - 3 Hz or less
3.1 Alpha waves:
1. Alpha waves generally are seen in all age groups but are most comm...
20
Chapter 4
THE BASIC PRINCIPLES OF EEG DIAGNOSIS
The EEG signal is closely related to the level of consciousness of the ...
21
4.1 MORPHOLOGY:
This section identifies some normal waveforms, including K complex, V waves, lambda
waves, positive occ...
22
4.1.3 Lambda waves
Fig 4.3 – Lambda – POSTS
1. Lambda waves occur in the occipital regions bilaterally as positive (upg...
23
4.1.6 Mu waves - Wicket rhythm or rhythm en arceau
Fig 4.4 – MU Wave pattern
1. Mu waves are runs of rhythmic activity ...
24
4.1.8 Benign epileptic transients of sleep
Fig 4.5 – Benign epileptic wave form
1. These sharp, usually small waves occ...
25
Chapter 5
Instrumentation
5.1 Block Diagram of EEG Preamplifier and Transmitter:
Fig 5.1 EEG Transmitter Block diagram
...
26
Fig 5.2 Buffer Amplifiers and Electrodes
5.1.2 Instrumentation Amplifier - As we know that the amplitude of EEG signal
...
27
Fig.5.3 Instrumentation Amplifier
5.1.3 Low pass Filter - Here, 2nd
order low pass Butterworth filter is used. This fil...
28
Fig.5.4 Low Pass circuit
5.1.4 High Pass Filter: - Here, 1st
order high pass filter is used. This filter is designed
to...
29
Here the input is given at the pin no.7 and the output in the form of square wave is
taken at pin no.11. The frequency ...
30
Figure 5.7 Infrared Driver
5.2 Description of RECEIVER Circuit:
5.2.1 Infrared Receiver:
Infrared light generated by th...
31
The amplifier is used as a “multiple feedback” band pass filter. The filter components are the
0.068-microfarad capacit...
32
Fig. 5.8 – Pin Configuration of 4046
Fig 5.9 - Internal circuit of 4046
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Design a EEG transmission and receving system using infrared waves for states of sleep

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Design a EEG transmission and receving system using infrared waves for states of sleep

  1. 1. Design a Electronenceohaplogram (EEG) transmission and receving system using infrared waves for states of sleep Project Submitted in partial fulfillment of the requirements For the degree of BACHELOR OF ENGINEERING By VIRAJ N.SHAH RAHUL T.N.U NAIR VIJIT MISHRA SHASHANK S. TOTRE Under the guidance of Prof. Bhavesh Parmar DEPARTMENT OF BIOMEDICAL ENGINEERING MGM COLLEGE OF ENGINEERING AND TECHNOLOGY UNIVERSITY OF MUMBAI 2004-2005
  2. 2. 2 APPROVAL SHEET Project Entitled: Design a Electronenceohaplogram (EEG) transmission and receving system using infrared waves for neurological disorders Submitted by: VIRAJ N.SHAH RAHUL T.N.U NAIR VIJIT MISHRA SHASHANK S.TOTRE in partial fulfillment of the degree of B.E. in Biomedical Engineering is approved. Guides Examiners _____________________ ______________________ _____________________ ______________________ ________________________ _____________________ Head of the Department Principal Date:
  3. 3. 3 Table of Contents CHAPTER 1 ................................................................................................................................ 5 INTRODUCTION ......................................................................................................................... 5 1.1 MOTIVATION .............................................................................................................................. 7 1.2 BASIC BACKGROUND .................................................................................................................... 7 1.3 ORGANISATION OF THE REPORT .................................................................................................... 8 1.4 WORK DONE .............................................................................................................................. 9 1.4.1 Demonstration of the Equipment .................................................................................... 9 1.4.2 Block Diagram Description ............................................................................................... 9 CHAPTER 2 .............................................................................................................................. 10 ANATOMY OF THE BRAIN ........................................................................................................ 10 2.1. BRAINSTEM ............................................................................................................................. 11 2.1.1 Medulla Oblongata .................................................................................................... 11 2.1.2 Midbrain .................................................................................................................... 11 2.1.3 Pons ........................................................................................................................... 11 2.1.4 Cerebellum ................................................................................................................. 11 2.2 THE LOBES OF THE BRAIN ............................................................................................................ 11 2.2.1 Frontal Lobe ................................................................................................................... 12 2.2.2 Parietal Lobe .................................................................................................................. 12 2.2.3 Occipital Lobe ................................................................................................................ 13 2.2.4 Temporal Lobe ............................................................................................................... 13 2.3. BRAIN FUNCTIONS & DISORDERS ................................................................................................. 13 CHAPTER 3 .............................................................................................................................. 18 THE EEG SIGNAL ...................................................................................................................... 18 3.1 ALPHA WAVES: .......................................................................................................................... 19 3.2 BETA WAVES: ............................................................................................................................ 19 3.3 THETA WAVES: .......................................................................................................................... 19 3.4 DELTA WAVES: .......................................................................................................................... 19 CHAPTER 4 .............................................................................................................................. 20 THE BASIC PRINCIPLES OF EEG DIAGNOSIS ............................................................................... 20 4.1 MORPHOLOGY: ..................................................................................................................... 21 4.1.1 K complex: ...................................................................................................................... 21 4.1.2 V waves .......................................................................................................................... 21 4.1.3 Lambda waves ............................................................................................................... 22 4.1.4 Positive occipital sharp transients of sleep [POSTS] ....................................................... 22 4.1.5 Sleep spindles ................................................................................................................. 22 4.1.6 Mu waves - Wicket rhythm or rhythm en arceau .......................................................... 23 4.1.7 Spikes and sharp waves ................................................................................................. 23 4.1.8 Benign epileptic transients of sleep ............................................................................... 24 CHAPTER 5 .............................................................................................................................. 25 INSTRUMENTATION ................................................................................................................ 25 5.1 BLOCK DIAGRAM OF EEG PREAMPLIFIER AND TRANSMITTER: ............................................................ 25 5.1.1 Buffer Amplifier ......................................................................................................... 25 5.1.2 Instrumentation Amplifier ......................................................................................... 26
  4. 4. 4 5.1.3 Low pass Filter ........................................................................................................... 27 5.1.4 High Pass Filter .......................................................................................................... 28 5.1.5 V to F converter ......................................................................................................... 28 5.1.6 Infrared Driver ........................................................................................................... 29 5.2 DESCRIPTION OF RECEIVER CIRCUIT: ........................................................................................... 30
  5. 5. 5 Chapter 1 Introduction EEG is an acronym for Electroencephalograph. This is a recording ("graph") of electrical signals ("electro") from the brain ("encephalo"). They are recorded on chart paper that moves underneath pens that are connected to galvanometers that read the electrical signals from electrodes on the scalp. These electrodes do not send any electricity to the person. They only receive electrical signals naturally generated by the brain. Electroencephalography (EEG) waveforms generally are classified according to their frequency, amplitude, and shape, as well as the sites on the scalp at which they are recorded. The most familiar classification uses EEG waveform frequency (e.g. alpha, beta, and theta). Information about waveform frequency and shape is combined with the age of the patient, state of alertness or sleep, and head site to determine significance. Normal EEG waveforms are defined and described by the following criteria: Ø Frequency (Hertz, Hz) is the initial characteristic used to define normal or abnormal EEG rhythms. Ø Most waves of 7.5 Hz and higher frequencies are normal findings in the EEG of an awaked adult. Waves with a frequency of 7 Hz or less often are classified as abnormal in awaked adults, although they normally can be seen in children or in adults who are asleep. In certain situations, EEG waveforms of an appropriate frequency for age and state of alertness are considered abnormal because they occur at an inappropriate scalp location or demonstrate irregularities in rhythmicity or amplitude. Ø Some waves are recognized by their shape, head distribution, and symmetry. Certain patterns are normal at specific ages or states of alertness and sleep. Ø The morphology of a wave may resemble specific shapes, such as vertex (V) waves seen over the vertex of the scalp in stage 2 sleep or triphasic waves that occur in the setting of various encephalopathies. From the EEG signal it is possible to differentiate alpha (α), beta (β), delta (δ), and theta (Ө) waves as well as spikes associated with epilepsy. The alpha waves have the frequency spectrum of 8-13 Hz and can be measured from the occipital region in an awaked person when the eyes are closed. The
  6. 6. 6 frequency band of the beta waves is 13-30 Hz; these are detectable over the parietal and frontal lobes. The delta waves have the frequency range of 0.5-4 Hz and are detectable in infants and sleeping adults. The theta waves have the frequency range of 4-8 Hz and are obtained from children and sleeping adults. The EEG signal is closely related to the level of consciousness of the person. As the activity increases, the EEG shifts to higher dominating frequency and lower amplitude. When the eyes are closed, the alpha waves begin to dominate the EEG. When the person falls asleep, the dominant EEG frequency decreases. In a certain phase of sleep, rapid eye movement called (REM) sleep; the person dreams and has active movements of the eyes, which can be seen as a characteristic EEG signal. In deep sleep, the EEG has large and slow deflections called delta waves. No cerebral activity can be detected from a patient with complete cerebral death. 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 spikewave 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. EEG may be prescribed by doctors to study the patient with a problem of Epilepsy, brain disorders, etc. Hence, now-a-days EEG is getting a wider scope for its applications.
  7. 7. 7 1.1 Motivation We came across the use of EEG waveforms in medicine during our In Plant Training. We were quite impressed by the developments taking place in this field and also the growing significance it is gaining with its wider applications. It is considered as a boon to the patients with any kind of brain disorders, as also in case of other fields. These are readings that can provide extensive study of the brain and it’s functioning. Also, an important factor in India, it is not expensive and very user friendly, causing no irritation to the patient or the person kept under study. Hence, the patient can get quick results in his case study and can get proper treatment by the diagnosis of the result achieved from the EEG recordings, thus ensuring fast recovery. In hospital, EEG is not only monitored in OPD patients but also during surgeries, especially in Cardiac Bypass surgeries, where the surgeon tries to monitor the proper functioning of the brain. The operating theatre is always full with equipments and adding on a EEG machine with all its wires would further jam up the OT. We, decided to make the EEG recording process wireless or rather somewhat wire free. This would help in easing the problem of the surgeon as the EEG wires would not add more congestion to the existing system. So, we decide to make this machine, which would transmit EEG from the main machine connected to the patient to the computer or a receiver and display the waveform. 1.2 Basic Background The purpose of this equipment is to study the wave patterns obtained from the patient’s brain and do proper analysis of those waveforms. As we have introduced the use of Infrared in our circuitry, this can also be used for the purpose of telemetry also, other than our main purpose of recording the EEG signal during a surgery. This is possible with the use of a good range Infra-Red transmitter and
  8. 8. 8 receiver so that no obstacle is created for the surgeon while he is operating as well as he gets a proper report of the brain functioning. As the patient will be induced during the surgery or rather he is anesthetized , the surgeon expect a certain wave pattern. Any distortion in this wave can be taken as malfunctioning in the brain activity, thereby giving the surgeon an alarm of what is happening. It can also help in preventing a patient from going in comma as the state of the brain can be studied and thereby necessary steps can be taken. It was thereby concluded that for intensive care patients, OT patients and OPD patients EEG recording via transmission can prove to be a boon and can be used without any harm or side effect. 1.3 Organisation Of The Report Our report consists of the basic introduction about the equipment. It also includes the basic principle, brain physiology & physiological effects of the equipment. This report consists of the explanation of the various block of the circuit diagram. It also includes the varied results and the discussions we had during the making of the equipment. It has the General Purpose PCB designing concepts and it also essays the problems we faced during the making of the project. The report also includes EEG waveforms collected using 10 subjects in various situations under different degrees of brain activity. We have tried our level best to analyze these different waveforms and have summed them up in our report.
  9. 9. 9 1.4 Work Done 1.4.1 Demonstration of the Equipment - We have seen the working of this equipment during our In Plant Training. The demonstration helped us in understanding the details of the basic blocks of the EEG machine. 1.4.2 Block Diagram Description - Under the guidance of our project incharge, we modified the block diagram of the machine and included IC LM324 instead of IC INA111 and IC 741.
  10. 10. 10 Chapter 2 ANATOMY OF THE BRAIN The figure below shows the anatomy of the brain. We will define each and every part labeled in the figure and explain the role played by them. Fig: - The image on the left is the outside of the brain, viewed from the side, showing the major lobes (frontal, parietal, temporal and occipital) and the brain stem structures (pons, medulla oblongata, and cerebellum). The image on the right is a side-view showing the location of the limbic system inside the brain. The limbic system consists of a number of structures, including the fornix, hippocampus, cingulate gyrus, amygdala, the parahippocampal gyrus and parts of the thalamus.
  11. 11. 11 2.1. Brainstem - The lower extension of the brain where it connects to the spinal cord. Neurological functions located in the brainstem include those necessary for survival (breathing, digestion, heart rate, blood pressure) and for arousal (being awake and alert). Most of the cranial nerves come from the brainstem. The brainstem is the pathway for all fiber tracts passing up and down from peripheral nerves and spinal cord to the highest parts of the brain. 2.1.1 Medulla Oblongata - The medulla oblongata functions primarily as a relay station for the crossing of motor tracts between the spinal cord and the brain. It also contains the respiratory, vasomotor and cardiac centers, as well as many mechanisms for controlling reflex activities such as coughing, gagging, swallowing and vomiting 2.1.2 Midbrain - The midbrain serves as the nerve pathway of the cerebral hemispheres and contains auditory and visual reflex centers. Fig: - The Brain Stem 2.1.3 Pons - The pons is a bridge-like structure, which links different parts of the brain and serves as a relay station from the medulla to the higher cortical structures of the brain. It contains the respiratory center. 2.1.4 Cerebellum - The portion of the brain (located at the back) which helps coordinate movement (balance and muscle coordination). Damage may result in ataxia, which is a problem of muscle coordination. This can interfere with a person's ability to walk, talk, eat, and to perform other self-care tasks. 2.2 The Lobes of the Brain – The major lobes of the brain are Frontal, Parietal, Temporal and Occipital. They can be described individually as follows:-
  12. 12. 12 Fig: - Frontal lobe of the brain 2.2.1 Frontal Lobe - Front part of the brain; involved in planning, organizing, problem solving, selective attention, personality and a variety of "higher cognitive functions" including behavior and emotions. 2.2.1.1 The anterior (front) portion of the frontal lobe is called the prefrontal cortex. It is very important for the "higher cognitive functions" and the determination of the personality. 2.2.1.2 The posterior (back) of the frontal lobe consists of the premotor and motor areas. Nerve cells that produce movement are located in the motor areas. The premotor areas serve to modify movements. 2.2.1.3 The frontal lobe is divided from the parietal lobe by the central culcus. 2.2.2 Parietal Lobe - One of the two parietal lobes of the brain located behind the frontal lobe at the top of the brain. 2.2.2.1 Parietal Lobe, Right - Damage to this area can cause visuo-spatial deficits (e.g., the patient may have difficulty finding their way around new, or even familiar, places). 2.2.2.2 Parietal Lobe, Left - Damage to this area may disrupt a patient's ability to understand spoken and/or written language. 2.2.2.3 The parietal lobes contain the primary sensory cortex which controls sensation (touch, pressure). Behind the primary sensory cortex is a large association area that controls fine sensation (judgment of texture, weight, size, shape).
  13. 13. 13 2.2.3 Occipital Lobe - Region in the back of the brain, which processes visual information. Not only is the occipital lobe mainly responsible for visual reception, it also contains association areas that help in the visual recognition of shapes and colors. Damage to this lobe can cause visual deficits. 2.2.4 Temporal Lobe - There are two temporal lobes, one on each side of the brain located at about the level of the ears. These lobes allow a person to tell one smell from another and one sound from another. They also help in sorting new information and are believed to be responsible for short-term memory. 2.2.4.1 Right Lobe - Mainly involved in visual memory (i.e., memory for pictures and faces). 2.2.4.2 Left Lobe - Mainly involved in verbal memory (i.e., memory for words and names). 2.3. Brain functions & Disorders - The function of the various parts of the brain described above and the various disorders associated with them have been summarized in the table shown below. Brain Structure Function Associated Signs and Symptoms Cerebral Cortex Ventral View (From bottom) The outermost layer of the cerebral hemisphere, which is composed of gray matter. Cortices are asymmetrical. Both hemispheres are able to analyze sensory data, perform memory functions, learn new information, form thoughts and make decisions.
  14. 14. 14 Left Hemisphere Sequential Analysis: systematic, logical interpretation of information. Interpretation and production of symbolic information: language, mathematics, abstraction and reasoning. Memory stored in a language format. Right Hemisphere Holistic Functioning: processing multi-sensory input simultaneously to provide "holistic" picture of one's environment. Visual spatial skills. The right hemisphere coordinates holistic functions such as dancing and gymnastics. Memory is stored in auditory, visual and spatial modalities. Corpus Callosum Connects right and left hemisphere to allow for communication between the hemispheres. Forms roof of the lateral and third ventricles. î Damage to the Corpus Callosum may result in "Split Brain" syndrome.
  15. 15. 15 Frontal Lobe Ventral View (From Bottom) Side View Cognition and memory. Prefrontal area: The ability to concentrate and attend, elaboration of thought. The "Gatekeeper"; (judgment, inhibition). Personality and emotional traits. Movement: Motor Cortex (Brodman's): voluntary motor activity. Premotor Cortex: storage of motor patterns and voluntary activities. Language: motor speech î Impairment of recent memory, inattentiveness, inability to concentrate, behavior disorders, difficulty in learning new information. Lack of inhibition (inappropriate social and/or sexual behavior). Emotional liability. "Flat" affect. î Contra lateral plegia, paresis. î Expressive/motor aphasia. Parietal Lobe Processing of sensory input, sensory discrimination. Body orientation. Primary/ secondary somatic area. Inability to discriminate between sensory stimuli. î Inability to locate and recognize parts of the body (Neglect). î Severe Injury: Inability to recognize self. î Disorientation of
  16. 16. 16 environment space. î Inability to write. Occipital Lobe Primary visual reception area. Primary visual association area: Allows for visual interpretation. î Primary Visual Cortex: loss of vision opposite field. î Visual Association Cortex: loss of ability to recognize object seen in opposite field of vision, "flash of light", "stars". Temporal Lobe Auditory receptive area and association areas. Expressed behavior. Language: Receptive speech. Memory: Information retrieval. Hearing deficits. î Agitation, irritability, childish behavior. î Receptive/ sensory aphasia. Limbic System Olfactory pathways: Amygdala and their different pathways. Hippocampi and their different pathways. Limbic lobes: Sex, rage, fear; emotions. Integration of recent memory, biological rhythms. î Loss of sense of smell. î Agitation, loss of control of emotion. Loss of recent memory.
  17. 17. 17 Hypothalamus. Basal Ganglia Sub cortical gray matter nuclei. Processing link between thalamus and motor cortex. Initiation and direction of voluntary movement. Balance (inhibitory), Postural reflexes. Part of extra pyramidal system: regulation of automatic movement. î Movement disorders: chorea, tremors at rest and with initiation of movement, abnormal increase in muscle tone, difficulty- initiating movement. î Parkinson's.
  18. 18. 18 Chapter 3 THE EEG SIGNAL From the EEG signal it is possible to differentiate alpha, beta, delta, and theta waves as well as spikes associated with epilepsy. An example of each waveform is given in Figure The alpha waves have the frequency spectrum of 8-13 Hz and can be measured from the occipital region in an awake person when the eyes are closed. The frequency band of the beta waves is 13-30 Hz; these are detectable over the parietal and frontal lobes. The delta waves have the frequency range of 0.5-4 Hz and are detectable in infants and sleeping adults. The theta waves have the frequency range of 4-8 Hz and are obtained from children and sleeping adults. Fig3.1: - Some examples of EEG waves. • 3.1 Alpha waves - 8-13 Hz • 3.2 Beta waves - Greater than 13 Hz • 3.3 Theta waves - 3.5-7.5 Hz
  19. 19. 19 • 3.4 Delta waves - 3 Hz or less 3.1 Alpha waves: 1. Alpha waves generally are seen in all age groups but are most common in adults. 2. They occur rhythmically on both sides of the head but are often slightly higher in amplitude on the nondominant side, especially in right-handed individuals. 3. They tend to be present posteriorly more than anteriorly and are especially prominent with closed eyes and with relaxation. 4. Alpha activity disappears normally with attention (eg, mental arithmetic, stress, opening eyes). In most instances, it is regarded as a normal waveform. 5. An abnormal exception is alpha coma, most often caused by hypoxic-ischemic encephalopathy of destructive processes in the pons (eg, intracerebral hemorrhage). In alpha coma, alpha waves are distributed uniformly both anteriorly and posteriorly in patients who are unresponsive to stimuli. 3.2 Beta waves: 1. Beta waves are observed in all age groups. 2. They tend to be small in amplitude and usually are symmetric and more evident anteriorly. 3. Many drugs, such as barbiturates and benzodiazepines, augment beta waves. 3.3 Theta waves: 1. Theta waves normally are seen in sleep at any age. In awake adults, these waves are abnormal if they occur in excess. 2. Theta and delta waves are known collectively as slow waves. 3.4 Delta waves: 1. These slow waves have a frequency of 3 Hz or less. 2. They normally are seen in deep sleep in adults as well as in infants and children. 3. Delta waves are abnormal in the awake adult. 4. Often, they have the largest amplitude of all waves. 5. Delta waves can be focal (local pathology) or diffuse (generalized dysfunction).
  20. 20. 20 Chapter 4 THE BASIC PRINCIPLES OF EEG DIAGNOSIS The EEG signal is closely related to the level of consciousness of the person. As the activity increases, the EEG shifts to higher dominating frequency and lower amplitude. When the eyes are closed, the alpha waves begin to dominate the EEG. When the person falls asleep, the dominant EEG frequency decreases. In a certain phase of sleep, rapid eye movement called (REM) sleep; the person dreams and has active movements of the eyes, which can be seen as a characteristic EEG signal. In deep sleep, the EEG has large and slow deflections called delta waves. No cerebral activity can be detected from a patient with complete cerebral death. Examples of the above-mentioned waveforms are figure shown below: Fig 4.1: - Various EEG responses obtained for different body conditions
  21. 21. 21 4.1 MORPHOLOGY: This section identifies some normal waveforms, including K complex, V waves, lambda waves, positive occipital sharp transients of sleep (POSTS), spindles, mu rhythm, spikes, sharp waves, and certain delta waves (polyphasic and monophasic shapes). These waves are recognized by their shape and form and secondarily by their frequency. They include waves that may be normal in some settings and abnormal in others (eg, spikes, sharp waves). 4.1.1 K complex: Fig 4.2 – K complex 1. K complex waves are large-amplitude delta frequency waves, sometimes with a sharp apex. 2. They can occur throughout the brain and usually are higher in amplitude and more prominent in the bifrontal regions. 3. Usually symmetric, they occur each time the patient is aroused partially from sleep. 4. Semiarousal often follows brief noises; with longer sounds, repeated K complexes can occur. 5. K complexes sometimes are followed by runs of generalized rhythmic theta waves; the whole complex is termed an arousal burst. 4.1.2 V waves 1. V waves are sharp waves that occur during sleep. They are largest and most evident at the vertex bilaterally and usually symmetrically. 2. They show phase reversal at the vertex. 3. V waves tend to occur especially during stage 2 sleep and may be multiple. 4. Often, they occur after sleep disturbances (eg, brief sounds) and, like K complexes, may occur during brief semiarousals. 5. V waves are easy to recognize.
  22. 22. 22 4.1.3 Lambda waves Fig 4.3 – Lambda – POSTS 1. Lambda waves occur in the occipital regions bilaterally as positive (upgoing) waves. 2. They are triangular in shape and generally symmetric. 3. They occur in the awake patient and are said to be most evident when the subject stares at a blank, uniform surface. 4. Lambda waves occur when reading and occasionally when watching TV. 5. Morphologically, they are similar to POSTS both in form and in occipital distribution. 4.1.4 Positive occipital sharp transients of sleep [POSTS] 1. POSTS are triangular waves that occur in the bilateral occipital regions as positive (upgoing) waves. 2. They can be multiple and usually are symmetric. 3. POSTS occur in sleeping patients and are said to be most evident in stage 2 of sleep, although they are not uncommon in stage 1. 4. POSTS are similar if not identical to lambda waves both morphologically and in the occipital distribution. 4.1.5 Sleep spindles 1. Spindles are groups of waves that occur during many sleep stages but especially in stage 2. 2. They have frequencies in the upper levels of alpha or lower levels of beta. 3. Lasting for a second or less, they increase in amplitude initially and then decrease slowly. The waveform resembles a spindle. 4. They usually are symmetric and are most obvious in the parasagittal regions.
  23. 23. 23 4.1.6 Mu waves - Wicket rhythm or rhythm en arceau Fig 4.4 – MU Wave pattern 1. Mu waves are runs of rhythmic activity that have a specific shape. They are rounded in one direction with a sharp side in the other direction. 2. Frequency is one half of the fast (beta) activity. 3. Mu waves disappear with motor acts of the contralateral hand or arm. 4. Unlike alpha activity, they are not blocked by eye opening. 5. They often are asymmetric. 6. Mu waves are seen best when the cortex is exposed or if bone defects (e.g., post surgical) are present in the skull. 7. They tend to be more evident over the motor cortex and in the parasagittal regions. 4.1.7 Spikes and sharp waves 1. These are recognized by their height, their sharp top, and their narrow base. 2. Spikes and sharp waves usually are abnormal. 3. They can be normal in the following settings: a. V waves of sleep in the parasagittal regions in stage 2 sleep can be normal. b. Small, sharp spikes of sleep or benign epileptiform transients of sleep (BETS) are nonpathologic. They occur in the temporal regions, often switching from side to side. They do not have slow-following waves as do most of the pathologic spikes of epilepsy. c. Numerous artifacts resemble spikes, but they are distinguished by other waves that may be present, by observation of the patient while they are occurring, and by experience. d. POSTS can have a sharp contour yet be quite normal. They occur in the occipital regions bilaterally during sleep.
  24. 24. 24 4.1.8 Benign epileptic transients of sleep Fig 4.5 – Benign epileptic wave form 1. These sharp, usually small waves occur on one or both sides (usually asynchronously), especially in the temporal and frontal regions. 2. BETS are rare in children but are more frequent in adults and elderly persons. 3. Although they can occur in epileptic patients, BETS often are seen in individuals without epilepsy and can be regarded as a probable normal variant.
  25. 25. 25 Chapter 5 Instrumentation 5.1 Block Diagram of EEG Preamplifier and Transmitter: Fig 5.1 EEG Transmitter Block diagram The figure1 shows the block diagram of EEG preamplifier and transmitter circuit. The input is taken with the help of three surface electrodes placed on three positions: - a) Left b) Right c) Common The different stages of above block diagram are explained as follows: - 5.1.1 Buffer Amplifier - First stage is the buffer amplifiers, which provides the impedance matching at the inputs of instrumentation amplifier. The differential mode signal is given to both the buffer amplifiers. One from right electrode and other from left electrode. While common electrode is connected to the common point of non- inverting terminals of two buffer amplifiers as shown in circuit diagram in fig.
  26. 26. 26 Fig 5.2 Buffer Amplifiers and Electrodes 5.1.2 Instrumentation Amplifier - As we know that the amplitude of EEG signal varies from 2 to 200 µVolt. So we have to use instrumentation amplifier. Here, the gain of the amplifier is taken as 1100. With 1st stage gain of 11 and 2nd stage gain is100. At the output of two capacitors are connected which provides A.C. coupling to nullify the D.C. offset. 5.1.2.1 Design- The gain of instrumentation amplifier is given by A = Av1 x Av2 = (1 + 2R1) ( R4 ) R2 R3 1st stage: Av1 = 11 = (1 + 2R1 ) R2 Select R2 = 20KΩ (pot) We get, R1 = 100KΩ 2nd stage: Av2 = R4 R3 Select R3 = 10 KΩ We get R4 = 1 MΩ
  27. 27. 27 Fig.5.3 Instrumentation Amplifier 5.1.3 Low pass Filter - Here, 2nd order low pass Butterworth filter is used. This filter is designed to pass all frequency below 5Hz. Along with filtering this circuit also provides a gain of 2 to the EEG signal. To achieve adequate filtering the two low pass filter stages are used. 5.1.3.1 Design of Low Pass Filter (L.P.F.): The higher cut-off frequency is given by Fh = 1 . 2Π √ (R1 R2 C1 C2 ) Select R1 = R2 = R and C1 = C2 = C. 20 Hz = 1 . 2 Π R C Select C = 0.1µf. We get, R = 10 KΩ
  28. 28. 28 Fig.5.4 Low Pass circuit 5.1.4 High Pass Filter: - Here, 1st order high pass filter is used. This filter is designed to pass all frequency above 20 Hz. This stage also provides a gain of 10 to the EEG signal. So, after all stages the overall gain of this circuit becomes 44000. 5.1.4.1 Design of High Pass Filter (H.P.F.): fl = 1 . 2 Π R C Select C = 4.7 µf. We get R = 10 KΩ Fig.5.5 High Pass Filter 5.1.5 V to F converter - Voltage to frequency converter is basically a transmitter circuit. For the transmission of captured EEG signal, IC XR2206 is used. IC 2206 is an important waveform generator IC This IC is capable of generating the sine wave, ramp, triangular and square wave output. But in our case we are interested in square wave only which will be used later to drive an infrared LED. The basic circuit diagram of IC2206 as a transmitter is shown below in fig.: -
  29. 29. 29 Here the input is given at the pin no.7 and the output in the form of square wave is taken at pin no.11. The frequency of output at pin no.11 will be directly proportional to the amplitude of input signal given to the pin no. 7. i.e. if amplitude of EEG signal is high than the frequency of square wave will be high and vice versa. This square wave signal is used to drive the next stage. Fig.5.6 EEG transmission Circuit 5.1.6 Infrared Driver - Now two infrared LEDs are used which are driven by a BJT, which will be either in high state or low state as its input is square wave. According to the amplitude of EEG signal the infrared LED will transmit the signal. If the frequency is high then the transmission of the EEG signal will be quicker and vice-versa.
  30. 30. 30 Figure 5.7 Infrared Driver 5.2 Description of RECEIVER Circuit: 5.2.1 Infrared Receiver: Infrared light generated by the LED’s is picked up at the receiver by a special infrared phototransistor. Referring to the circuit diagram of the receiver, the phototransistor is connected with its cathode to the +9 v rail via an RC de-coupling network; while the anode is connected via 470k resistor to the ground. In operation the phototransistor acts as a current source i.e. it generates the current proportional to the incident light. This current signal is converted to a voltage signal by the 470k transistor. The signal from the phototransistor is fed to the input T2 of a FET. The FET offers a high input impedance, low output impedance. Output of FET is fed to a Band pass filter consisting of transistor T3 and T4. The center frequency of the filter is about 10 KHz signal from the transmitter, even allowing for some mistuning yet it affectively eliminates interference from the other sources. (e.g. fluorescent light) Disregarding the two 0.0068-microfarad capacitors (C5, C6) for the moment, T3 and T4 form a second stage-inverting amplifier. Both transistors operate as CE amplifiers with the second stage providing two separate outputs, one from the junction of the two 330-ohm transistor and the second from T4’s collector. The first output has a low impedance and is used to drive the filter and to provide DC feedback via the 47k resistor to bias T3.
  31. 31. 31 The amplifier is used as a “multiple feedback” band pass filter. The filter components are the 0.068-microfarad capacitors (C5, C6) and the 47k bias resistors, which together with the low output impedance of the previous FET stage determine the center frequency Q of the filter. The collector output of T4 provides an amplified version of the filter output. This output is DC coupled to the next stage, which consists of transistor T5, is another common amplifier circuit. A 0.1-microfarad emitter bypass capacitor is included to provide further attenuation of unwanted low frequency signals. The CD4046BC micro power phase-locked loop (PLL) consists of a low power, linear, voltage-controlled oscillator (VCO), a source follower, a zener diode, and two-phase comparators. The two-phase comparators have a common signal input and a common comparator input. The signal input can be directly coupled for a large voltage signal, or capacitively coupled to the self-biasing amplifier at the signal input for a small voltage signal. Phase comparator I, an exclusive OR gate, provides a digital error signal (phase comp. I Out) and maintains 90° phase shifts at the VCO center frequency. Between signal input and comparator input (both at 50% duty cycle), it may lock onto the signal input frequencies that are close to harmonics of the VCO center frequency. Phase comparator II is an edge-controlled digital memory network. It provides a digital error signal (phase comp. II Out) and lock-in signal (phase pulses) to indicate a locked condition and maintains a 0° phase shift between signal input and comparator input. The linear voltage-controlled oscillator (VCO) produces an output signal (VCO Out) whose frequency is determined by the voltage at the VCOIN input, and the capacitor and resistors connected to pin C1A, C1B, R1 and R2. The source follower output of the VCOIN (demodulator Out) is used with an external resistor of 10 kW or more. The INHIBIT input, when high, disables the VCO and source follower to minimize standby power consumption. The zener diode is provided for power supply regulation, if necessary.
  32. 32. 32 Fig. 5.8 – Pin Configuration of 4046 Fig 5.9 - Internal circuit of 4046

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