Inspection purpose
1. epilepsy: EEG is the most valuable in the diagnosis of epilepsy, which is helpful to determine the diagnosis and classification, judge the prognosis and analyze the curative effect;
2. Brain trauma: a slight injury that is difficult to determine by ordinary examination, and EEG may find abnormalities;
3. It is helpful to diagnose brain tumor or injury;
4. It is very valuable to judge whether there is an organic disease in the brain, especially to judge whether it is a mental symptom caused by psychosis or encephalitis, and to distinguish hysteria, fraud or real brain disease;
5. Used for biofeedback therapy.
Preparation before inspection
1. Don't grease your hair, so as not to affect the inspection;
2. Have a full meal to prevent hypoglycemia from affecting your performance;
3. Stop using various drugs 3 days before the examination. If the drug cannot be stopped, the name, dosage and usage of the drug should be explained for the doctor's reference.
Matters needing attention
1. Don't be nervous when checking. Put the receiving electrode on the scalp instead of electrifying;
2. Relax the muscles of the whole body to avoid EMG interference;
3. Open your eyes, close your eyes or breathe excessively as required by the doctor.
British doctor Richard Caton first observed brain waves in animals in 1875. Encouraged by the success of William Einstein's electrocardiogram, Hans Berger decided to use a series galvanometer to measure the electrical activity of the brain.
Figure: Radio waves displayed by color scanning. Red and yellow indicate brain activity, and blue indicates inactivity.
First, Berger exposed the surface of the dog's brain and measured the current outside the brain. Then, he put the electrode under the scalp, which was removed during brain surgery. Finally, he was able to record brain waves through his skull and collect electroencephalograms (EEGs) of his family, friends and other volunteers.
Berger first identified two different types of brain waves, which he called A wave and B wave respectively, and later named other waveforms with other Greek letters. When people are thinking, resting and sleeping, EEG will show different wave patterns. Left: EEG track during seizure.
EEG is very useful for the diagnosis of epilepsy. Epilepsy is a disease involving sensory, motor and consciousness disorders. Anyone can induce epilepsy by accident, electric shock or high fever. Those who are particularly prone to seizures should take drugs to reduce the possibility of seizures.
Human tissue cells always spontaneously and continuously produce very weak bioelectric activity. Electroencephalogram (EEG) is obtained by extracting the electrical activity of brain cells with electrodes placed on the scalp, amplifying it by EEG machine and recording it on special paper. When pathological or functional changes occur in brain tissue, this curve also changes, thus providing basis for clinical diagnosis and treatment.
References:
What is the significance of EEG in the diagnosis of cerebrovascular diseases?
Electroencephalogram (EEG) is a technique to amplify and record the bioelectric activity of human brain tissue, which is mainly used for the examination of nervous system diseases. Because it reflects the functional state of "living" brain tissue, it has been playing an important role in the diagnosis of nervous system diseases since it appeared in the 1930s.
EEG is mainly used for the diagnosis of epilepsy, brain trauma, brain tumor and other diseases. Although the EEG of cerebrovascular disease has no specific changes, it is still of great significance for diagnosis and prognosis, as well as for differentiation from brain tumors. In the acute stage of cerebrovascular disease, 90% EEG is abnormal, mainly slow wave increase, especially in the diseased side.
Cerebral hemorrhage is often accompanied by disturbance of consciousness, brain edema and ventricular hemorrhage, and only some mild patients have mild localized abnormalities.
The EEG of subarachnoid hemorrhage, because arteriovenous malformation usually occurs on the surface of cerebral hemisphere, may appear localized or hemispheric abnormality due to cerebral blood circulation disorder. Sometimes the other side can be perverted. With the improvement of the disease, the amplitude of slow wave decreases and the frequency increases.
After cerebral infarction, focal slow waves can appear within a few hours, and this change often improves or disappears after several weeks. The damage of acute ischemic cerebrovascular disease is most common in the middle cerebral artery, so the focus changes mainly in the temporal lobe. If it is a transient ischemic attack, there is no abnormality in EEG between attacks. At the time of attack, some EEG may be abnormal, and such patients are more prone to cerebral infarction.
Whether it is cerebral infarction or mild cerebral hemorrhage, the main manifestation is the increase of localized slow waves. If the lesion causes extensive compression of the brain stem, it can cause diffuse slow waves on both sides. If the lesion is small or deep, the EEG may be normal.
Electroencephalogram is also helpful to distinguish cerebrovascular disease from brain tumor. The abnormal EEG of patients with brain tumor is getting more and more serious, while that of patients with cerebrovascular disease is just the opposite.
Dynamic observation of EEG changes is also of great value in judging prognosis. Clinical symptoms gradually improved, abnormal EEG changes gradually decreased or disappeared, and the prognosis was good; The clinical symptoms did not improve significantly, and the EEG was gradually aggravated, with poor prognosis.
What is the placement position and connection mode of scalp electrodes?
Routine EEG refers to scalp EEG recorded in normal physiological conditions, quiet and comfortable state according to the prescribed unified method and time. At present, the standard electrode placement method recommended by the International Electroencephalography Society is the most widely used in clinic, in which FP is the frontal pole, Z is the midline electrode, FZ is the frontal pole, CZ is the midpoint, PZ is the vertex, O is the occipital point, T is the temporal point, and A is the earlobe electrode. The serial number of the recording electrode is usually odd on the left and even on the right. The number of electrodes placed on the whole scalp and ears is 2 1. The characteristic of this placement method is that the position of the head electrode is consistent with the anatomical division of the cerebral cortex, and the arrangement of the electrodes is proportional to the size and shape of the skull. The electrodes are placed in the main area of the head corresponding to the convex surface of the cerebral cortex.
Electrodes in a certain order or purposeful combination are called leads, and unipolar leads and bipolar leads are commonly used in EEG recording. There should be at least 3 ~ 4 leads at a time, and there should be a combination of unipolar leads and bipolar leads to observe abnormal discharge and locate diagnosis. Generally speaking, unipolar leads can better locate epileptic foci, while bipolar leads have less waveform and amplitude distortion.
What's the difference between portable dynamic EEG and routine EEG?
The so-called portable dynamic electroencephalograph (AEEG) is a miniature cassette recorder, which records and stores EEG signals through electrodes placed on the scalp of patients, and can continuously record the EEG performance of patients during waking, various activities and sleep for 24 hours. 24-hour ambulatory EEG monitoring makes up for the deficiency of routine EEG. Patients can not only carry around and move freely, but also record for a long time. The positive rate of diagnosis is also higher than that of routine EEG, which is of great value for EEG research of epilepsy.
Compared with 24-hour dynamic EEG, conventional EEG is economical and convenient, but its disadvantage is that it can't record the EEG state for a long time, so there are fewer opportunities to capture epileptic waves, and the in-depth and detailed study of EEG has certain limitations.
What should I pay attention to when doing EEG?
① Wash your hair and don't apply oily substances.
② EEG room should be quiet and comfortable.
Have a good sleep the night before (except those who are deprived of sleep) and eat something before doing it.
(4) The operator should be affable, explain the requirements to the patient, make the patient fully understand and cooperate, and strictly follow the instructions of the operator.
⑤ The electrode plate should be placed gently and accurately to make it close to the skin, which is the key to doing EEG well.
⑥ For those who are too young or unable to cooperate, chloral hydrate or enema should be taken orally when necessary.
⑦ For patients with febrile convulsion, it is best to have an EEG examination 10 day after the symptoms stop.
What is a normal EEG like?
In addition to individual differences, healthy people have their own characteristics at different ages of life, but as far as normal adult EEG is concerned, its waveform, amplitude, frequency and phase have certain characteristics. Clinically, waveforms are divided into the following four types according to frequency:
β wave: The frequency is above 13C/S, and the amplitude is about half that of δ wave, especially in the forehead and central area.
Alpha wave: the frequency is 8 ~ 13C/s, and the amplitude is 25 ~ 75μ V, which is most obvious in the occipital region. Both sides are almost synchronous, and delta waves appear repeatedly, which is called theta rhythm.
Φ wave: The frequency is 4 ~ 7c/s, the amplitude is 20 ~ 40μ V, which is normal brain electrical activity of children, bilateral symmetry, and it is more common in temporal area.
δ wave: The frequency is below 4C/S, and the δ rhythm is mainly in the frontal area, which is the main wave rate of normal children. Single, non-localized δ waves less than 20μV are normal and local δ waves are abnormal. Δ wave and β wave are collectively called slow waves.
Because children's brain tissue is constantly developing and maturing, their normal EEG often has no clear or strict boundaries because of their age, and the specific content is very complicated, which is difficult for non-professionals to master.
What are the factors that affect EEG?
The main factors affecting EEG are age, individual differences, state of consciousness, external stimuli, mental activity, drug influence and brain diseases. Among them, age and individual differences are related to brain biological characteristics and genetic psychological factors. The brain wave changes caused by external stimuli and mental activities belong to some physiological changes of brain functional activities. The brain wave changes caused by drugs and brain diseases are often pathological, but they may also be transient and reversible.
(1) Age and individual differences
As an important aspect of objectively reflecting the functional state of the brain, EEG is closely related to age. For example, in children, EEG can observe the changes of brain waves with age. Brain waves can show obvious differences at different ages. On the other hand, due to the age difference in the development level of brain excitation inhibition mechanism in childhood, the response to various internal and external factors is more significant than that of adults, and obvious brain wave abnormalities are prone to occur, with a wider range of abnormalities, but the corresponding disappearance is faster than that of adults. The appearance of abnormal brain waves in childhood is also related to age. Different ages have different abnormal wave patterns, especially epilepsy. After adulthood, brain waves gradually stabilized, and after middle age, with the gradual decline of brain function, brain waves also changed. In old age, due to cerebral ischemia injury or brain atrophy, most of them will have meaningful brain wave abnormalities. Most of the individual differences of brain waves appear after 1 year. With the increase of age, the differences of adult brain waves have become quite significant. Many research results show that EEG has a certain relationship with genetic and psychological characteristics, but various environmental factors after birth also have a certain influence on the formation of brain and psychological personality.
(2) state of consciousness
Electroencephalogram can reflect the change of consciousness awakening level. If adults are sleepy when they are awake, the amplitude of EEG will begin to decline from the dominant pattern of α wave and will soon turn into a ripple state. After falling asleep, the changes of brain waves will be further obvious, roughly parallel to the depth of sleep. In pathological state, the abnormality of brain wave shape is related to the cause and degree. In addition to extensive or diffuse waves, other abnormal waves can be seen. Clinically, these abnormal wave patterns are often used to infer the cause and degree of consciousness disorder and to determine the location of the disease.
(3) external stimulation and psychological activities
The rhythm of brain waves is generally susceptible to mental activities. For example, when subjects concentrate on something or do mental arithmetic, the alpha rhythm is suppressed and becomes a low-amplitude beta wave. The stronger the mental activity, the more obvious the inhibitory effect of α wave, and the external stimulus can also cause the same change. This is why the surrounding environment should be quiet when doing EEG, and the subjects should relax and not think about problems.
(4) Changes of physiological conditions in vivo
Clinically, such as ischemia and hypoxia, hyperglycemia, hypoglycemia, body temperature changes, menstrual cycle changes, pregnancy, basal metabolism, etc. all directly affect the biochemical metabolism of brain tissue, so brain waves also change accordingly. For example, when brain tissue acidosis occurs, cerebral blood vessels dilate and cerebral blood flow increases, which will cause the amplitude of brain waves to decrease and fast waves appear.
(5) Drug effect
Clinically, most drugs have direct or indirect effects on brain function, especially those drugs that directly act on the central nervous system, which can cause obvious brain wave changes. The specific changes are closely related to individual differences, drug types, medication methods and doses. If taken orally, brain wave changes will occur at the beginning and when the dose is increased. Some brain wave changes will continue to exist in a short time after stopping the drug, and even rebound, and the brain waves will be enhanced. This is the reason why the clinical treatment of epilepsy cannot be suddenly changed or stopped.
What is EEG artifact? What are the common factors that cause artifacts?
The artifact of EEG, also known as artifact or interference, refers to the reflection of potential activities from outside the brain in EEG signals. The appearance of artifacts often brings difficulties to the reading, analysis and judgment of EEG, especially some artifacts are very similar to epileptic waves, which can easily lead to misdiagnosis in clinic, so it is very important to correctly identify and eliminate artifacts.
There are many factors that cause false errors, and there are various manifestations, but they can be summarized from two aspects: instrument and human body. Among them, the false errors from the instrument include: tracer failure, poor electrode contact or failure, AC interference and so on. Errors from the human body include eyelid and eyeball movements, muscle contraction, electrocardiogram, breathing, crying, skin sweating, blood vessel pulsation and so on.