A Multi-channel Blood Oxygenation Monitoring System Using Near-infrared Spectroscopy

Near-infrared spectrum(NIRS) technology, which can fulfill the real time and non-invasive in-vivo measurements of blood oxygen metabolizing, was widely used in biomedical field and many equipment and measure means about the technology were developed .Most of those are fixed light source-detector , so it can only monitor the change of blood oxygen metabolizing in a certain depth. And the design with a single detector can't satisfy the requirement of multi-channel signal acquirement. In this thesis, we designed a set of NIRS measure system base on the correlation detection theory with the use of single chip processor. It uses LED as light source with wavelength of 735nm, 805nm and 850nm modulated by square wave pulse. Detector is high sensitive PIN chip OPT101 with high responsibility and low quiescent current. The acquired signal is sent to phase sensitive detecting module CD505R2 to be demodulated. The software includes a single chip processor program and a PC program. The single chip processor program can set the amplifier gain, control AD conversion and communicate with PC. The upper site workstation also has three functional modules such as serial communication, measuring parameter setting and display acquired result. After calculating the dark noise, fiber-out power and estimating the gain between different channel, we prove the accuracy and precision of the system through a series of standard sample experiments, then we monitor the change of blood volume and oxygen concentration in different light source-detector distance in forearm and forehead. The result show that the fat and epidermis have effects on the measure result of forearm greatly, and the blood volume information in forehead are also affected by the thickness of frontal bone. The accurate measuring result lie on the appropriate selection of light source-detector distance. The application of NIRS measure system with flexible light source-detector distance can help us to select the appropriate detection depth in tissue and to know the blood oxygen information as accurate as possible. It makes great sense with noninvasive detection of blood oxygen metabolizing in tissue.