Tissue Oxygen Concentration Measurement Based On NIRS

Near infra-red spectroscopy (NIRS) is of great interest for chemical and structural analysis in cells, tissues and organs. During the period of evolution of in vivo NIRS efforts have been focused very much on human clinical monitoring, for example for fetal, neonatal and adult cerebral oxygen monitoring. Other applications in muscle, breast and tumours have, nevertheless, also been important. Since NIRS has a high ability of penetrating tissues, the emergence light, after absorption and scattering by tissues, has large valuable information, to base a measurement and analysis strategy for physiology and pathology.After studying a great deal of documents, building on other people's suggestions, progressive improvements have made in simplicity of multilayered tissue. Also the mathematical formula is developed, which converts the measured changes in light attenuation at wavelengths into corresponding concentration changes for the substances of interest (HbO2, Hb). Measurement system is based on the multi-wavelength LED as light source and OPT 101 as a detector with high responsibility and low quiescent current. NI USB-9215A data acquisition device provides 16-bit simultaneous sampling analog inputs with integrated signal conditioning. Then the data is transmitted to the PC for further processing.In this paper, a serial of standard experiments are done to validate the performance of the system, such as the dark noise, stability and precision. Next, we monitor the change of blood volume and oxygen concentration in the occlusion arterial and venous blood flow in forearm. The results are shown consonant with the theoretical analysis. During those experiments we also do study on the affections of flexible light source-detector distance, which can help us to select the appropriate detection depth in tissue and to know the blood oxygen information as accurate as possible.