A NIRS-EEG Synchronous Acquisition System

Functional brain imaging techniques boost the clinical diagnosis of brain diseases and neuroscience in humans. As a multimodal neuroimaging technique, simultaneously acquired Near-infrared spectroscopy(NIRS) and Electroencephalographic(EEG), with both advantages of time resolution and spatial resolution, can provide more comprehensive information about brain activity. Thus, the design of a NIRS-EEG synchronous acquisition system will provide a powerful tool for the clinical diagnosis and neuroscience. The main contents are as follows:First, we designed a technical front probe for detecting near-infrared light and EEG signal. In this paper, we set some the technical requirements of the optical probe, such as the detection limit, the dynamic range, wavelength section and the power of the light source, based on the optical properties of biological tissue; establish the equivalent current noise model of optical probe, and select the appropriate photodiode and amplifier to improve the detection performance of the optical probe according to this model. According to the characteristics of the EEG signal, a rational design of the active electrode is considered in terms of the amplifier and the electrode material.Second, in order to achieve the synchronization between the near infrared signal and EEG signal acquisition strictly, the technology of frequency division multiplexing be used. The intensity of each wavelength in each emitter is modulated to a particular frequency, the voltage signal from optical probe and EEG electrode is acquired simultaneously, using a precision analog front end. In this paper, a digital demodulator is added in system acquisition software, to separate the light intensity signal from each band.Finally, we designed a linearity testing for optical probe, the results show optical probe having a good linearity, the noise equivalent input current measured was close to the theoretical value, the detection performance can meet the system design requirements. We designed a Valsalva test, the trend of blood oxygen change calculated by our system is consistent with the prediction. Designed a dynamic optical simulator for performance comparison of system and commercial NIRS instrument ETG-4000, the results show that the quality of NIRS signal collected by this system is better than ETG-4000. To quantify the performance of EEG acquisition, we take an input noise tests, the peak to peak input voltage noise we measured is less than the rating of technical specification: JJF1388-2013. Designed a vivo experiment of EEG acquisition comparison, results show that the EEG signal collected by this system is consistent with BP amplifier in the time domain and frequency spectrum, both of them can detect α rhythm when subject close his eyes.