Interference of EEG machine

    EEG machine is a device that can diagnose brain disease. This paper mainly analyzes the causes of interference and the specific method to eliminate the interference.
The EEG is a kind of curve [1], which is a kind of clinical diagnostic value for brain diseases. It is a kind of clinical diagnostic value for brain diseases. It is very easy to be identified and excluded from the [2].
Brain electrical signals generated by brain cell activity is a very weak biological electrical signal, generally only 100 ~ 5 V, it must be amplified to 120dB or so, can be described in mind. Therefore, even though extremely small interference electromagnetic wave, after 1 ~ 500000 times the amplitude amplification, in the electroencephalogram or EEG monitor output terminal, also will produce extremely strong interference wave, so that the recorded waveform is not smooth, jitter, influence brain wave record, the final impact on the clinical diagnosis of [3]. The interference of EEG is a frequent problem, which we introduce from three aspects: the cause of interference and the corresponding exclusion method.
1 operation
The scalp resistance increases will cause great disturbance, generally at 20 K PI below normal, more than 20 K PI, should check the circuit lead. Therefore, the test must be the grease on the scalp clean, not clean the grease, can be used to clean the alcohol cotton repeatedly. The operator should find the electrode position, because each access electrode is more, the use of personnel is easy to neglect, so that individual or part of the electrode position is not correct, resulting in brain electrical signal is weakened, the large machine to put a large number of results but lead to greater interference signal. But also pay attention to check the electrode and the electrode arm earlobe is good contact.
In order to reduce the polarization interference, the electrode should be immersed in the normal saline, but this may cause the electrode and electrode clip oxidation, corrosion, rust, produce conductive contact. Available more than 600 sandpaper dipped in clean water. The electrode clip is connected to the wire, and is often used to move, which is easy to break. Usually can back up a few cable connection, so that time to replace the bad line. The other end of the connecting line is also easy to be oxidized, and it should be regularly cleaned.
If the test electrode head tension, the bandage too tight, it is easy to produce EMG interference. You can ask the participants to relax, smooth breathing, eyes closed. Insulation material, such as rubber pad or dry wood, can greatly reduce the interference in the test seat and foot pad.
EEG is best not to use fluorescent lamps, fluorescent lamps can be used to produce a lot of interference. The test position should be far from the fluorescent lamp and the electronic energy saving lamp. Electroencephalogram room to far away from the X machine, the operation room electrosurgical interference. Away from the streets and roads, the electric spark plug, the electric spark is also a great source of interference. It is impossible to carry out brain waves in the road near the car.
2 common mode rejection ratio
The interference in EEG is mainly the reduction of common mode rejection ratio. Interference signals from the machine balance input circuit into, if the input circuit resistance, distributed capacitance and inductance absolute balance, in theory, the signal can be completely eliminated, not to interfere. In fact, circuit design can not be completely balanced in the process. When the machine is out of the factory, the manufacturers have to balance the input circuit with high degree of balance. After use for a long time, due to balanced input circuits and components aging, aging, resulting in balance to reduce the degree of common mode rejection ratio decreased with the increasing interference. So it is important to check and adjust the common mode rejection ratio. The quality of the input circuit of some old EEG machine is poor, and the amplifier is more easily to be reduced by double three pole electronic tube.
The adjustment of common mode rejection ratio can be operated according to the requirements of the specification. Considered to some EEG machine without the explanation, the available body of electromagnetic induction is used in military near the lead wire in the terminal machine produced a not too big nor too small to the interference wave, and then adjust the pre amplifier common mode rejection than the potentiometer, the interference and the minimum amplitude can be.
3 ground wire
In use, the majority of the hospital is the first ECG machine, after the acquisition of EEG machine. Some map, afraid of trouble, the EEG and ECG machines sharing a ground wire. In addition to individual hospital original ECG machine wire embedding quality high and electroencephalograph can barely use outside, most hospitals is electrocardiogram machine without interference, and electroencephalograph appear great interference, unable to work. This is because the intensity of the signal intensity of the EEG signal is 100 times less than that of the signal intensity.