Working principle and interference elimination of EEG

Human tissues and cells, total in spontaneously continue to produce a very weak bioelectric activity using the scalp electrode installation will be the electrical activity of cells leads to and after amplification electroencephalograph recorded waveform, amplitude, frequency and phase of graphics, curve, that is, the EEG machine. When the brain pathology or function change, this curve will change corresponding, so as to clinical diagnosis and treatment of brain and nervous system diseases, such as malformation of central nervous system infection, intracranial tumors and chronic disease, cerebrovascular disease, brain injury and epilepsy, etc. provide according to. When the neuron is affected by heredity and pathology,

Electrochemical or drug stimulation, has destroyed the balance of cell membrane, produce highly depolarization, then can generate action potentials, the local action potential will destroy the balance of a cell membrane, this a series of repeated recovery and biochemical physics process of cell membrane damage, constitute the action potential in neurons and nerve cell membrane of one-way transmission, the EEG signal and the amplitude range is 10-100 Mu V, electroencephalograph is picking up the extremely weak EEG signals are amplified and tracing recording instrument, apparatus for the diagnosis of nervous system diseases, its basic principle diagram as follows:

Input box is a metal shielding box, scalp electrode wire is connected through the input box and EEG machine input terminal, EEG machines on the market today general in the input box buffer amplifier to reduce noise. Selection of different lead and signal channels by lead selector. Because the EEG signal is weak, and the amplitude is very low, it is required that the EEG machine has a high amplification gain, so the EEG machine uses the multi pole amplification technology to realize its high gain. Also required to have a high ratio of its mode suppression. The stability of the power supply also has strict requirements, generally in the power supply voltage fluctuations + 10%, the output voltage change is less than 0.01%, especially the supply of pre amplifier stage power supply voltage fluctuations should be less than 0.5 V.

The size of the contact resistance of the electrode and the skin, and EEG recording quality is directly related and general contact resistance should be less than 20K, if more than this value must clean the skin, treatment of electrodes or the better electrode paste, in order to ensure the measurement accuracy, so EEG machine is provided with an electric electrode skin contact impedance measuring device. As the change of the amplitude of EEG signal is larger, it is required that the gain control can be adjusted by multiple gears. 2 the elimination of interference of EEG

Due to the EEG signal is a kind of extremely weak biological signals, in the signal acquisition, amplification, the process is prone to interference. When the disturbance of cerebral motor, in order to describe the waveform is not smooth, jitter, affect clinical diagnosis. EEG machine interference can be divided into external interference and internal interference. The main performance is the interference calibration waveform in normal EEG time with interference. The reason is that the grounding is bad, the input short circuit, the skin, the electrode contact resistance is too large and the influence of the surrounding environment. Machine fault caused by interference performance is either fixed or the underlying EEG timing disturbance has existed, the detection can be the gain switch placed in the "0", the preamplifier input shorted to ground, to see whether the existence of interference, the main reason is component aging, differential amplifier tube symmetry and power supply filter circuit fault and so on, to exclude the interference, we have to use from the outside to the inside, from the simple to the complex method to think. Should first check whether there around other appliances at work, as far as possible away from these can produce electromagnetic wave equipment, and view the electrode box and lead wires and the patient is met metallic bedstead or an instrument shell, to testing machine ground is good, but also pay attention to the internal modules of the grounding in the detection of EEG recording interference occurs, should pay attention to check signal acquisition amplification processing pathway, check with scalp electrodes are connected properly, electrode box all sockets and lead wire plug contact is good. Also check the circuit board components, because there are many identical amplification pathway, so it can be for component replacement method to find, pay attention to check the machine power supply filter, a voltage stabilizing circuit, in particular, to pay attention to filter capacitor, voltage regulator tubes, three terminal voltage stabilizing block.

Interference and elimination of EEG in the course of using and testing

The heart and brain electrocardiogram machine is the general use of hospital diagnosis and inspection equipment. But in the process of using the diagnosis and the examination, the communication interference of the heart and brain is the most common and the most difficult problem. The interference phenomenon has a direct impact on the accuracy of the ECG waveform map, so that the waveform generated by the recorder has a mutation, which directly affects the doctor's diagnosis.

1 leakage current interference.

Heart electroencephalogram in diagnosis of indoor AC power possible leakage current, the alternating current through the test instrument, floor, body and some other poor insulator and instrument grounding wire to form a loop, resulting in cardiovascular and ECG recorder described the waveform forming modulation interference.

2 space interference. When there is a large power transformer, motor and the use of high-power alternating current equipment, the electromagnetic field will be on the line, the formation of radiation, absorption and modulation and so on. That is, the leakage flux exists, it will have a larger disturbance around, the magnetic field effect in the lead line of the heart and brain electric meter, it will produce the induced current, affecting the accuracy of the recording chart of the ECG machine.

3 interference of power supply system. A strong destructive interference, such as the performance of the interference of under voltage, overvoltage, surge, and so on, most likely to cause damage to the instrument and equipment.

The idea of eliminating interference: