Spatially-resolved Near Infrared Spectroscopy And Its Applications In Non-invasive Monitoring Of Cerebral Oxygenation

Human cerebral oxygenation can be non-invasively, continuously and quantitatively monitored in real time using near infrared spectroscopy (NIRS), which is greatly valuable in clinical cerebral protection. This work is focused on non-invasively and quantitatively detecting human tissue oxygenation parameters especially regional tissue oxygen saturation (rSO₂) using NIRS based on spatially-resolved spectroscopy (SRS), and applying the SRS NIRS in monitoring cerebral oxygenation during cardiopulmonary bypass (CPB).This dissertation can be divided into three parts. The first part (chapter 2, 3 and 4) is focused on the basic principles, key problems and validation of the SRS NIRS. Based on the theoretical framework of tissue optics, we firstly elucidated the basic principles and technical implementations of detecting tissue rSO₂ using SRS NIRS. By organically integrating the basic principles with the technical implementations, we then analyzed and solved the following key problems of the SRS NIRS: (1) selecting the optimal distance between the two detectors based on the SRS NIRS; (2) selecting the optimal distances between the light source and the two detectors according to the geometrical structures and the optical characteristics of human head, in order to achieve the optimal coupling between the probe and human cerebral tissue so that the influences of the overlying tissues can be eliminated; (3) correcting the error of rSO2 induced by the dispersion of the emitting wavelengths of the light source.We validated the SRS NIRS by calibrating the rSO₂ using blood gas analysis. We made up the liquid tissue model whose optical characteristics are close to human tissue in the near infrared band. We changed the oxygen saturation of the model by inflating oxygen or adding a certain amount of reducer into it. Based on our long-term experiments, we discovered that the oxygen saturation of the model could be decreased like a"stair"using a certain amount of sodium hydrosulfite (Na₂S₂O₄) as the inorganic reducer. Thus multi steady oxygenation levels can be obtained, which is in favor of improving the calibration accuracy. The calibration results indicate that the rSO₂ measured by the SRS NIRS is little influenced by the background absorptions, which is consistent with our related theoretical discussions. The results also indicate that the rSO₂ is also little influenced by the overlying tissues if the optimal coupling between the probe and the tissue being detected can be achieved.The second part (chapter 5) is focused on the applications of the SRS NIRS in clinical cerebral protection during CPB. Using the SRS NIRS, we monitored the cerebral oxygenation of 15 patients non-invasively during CPB. The results indicate that cerebral rSO₂ is negatively correlated with body temperature and positively correlated with perfusion rate during CPB, so it can reflect the dynamic balance between cerebral oxygen supply and consumption. Thus surgeons can maintain the normal cerebral oxygenation status to avoid cerebral hypoxia by rationally regulating the related physiological parameters such as body temperature and perfusion rate, which is in favor of cerebral protection. The results also indicate that comparing with the pulse oxygen saturation (SpO₂) and the mixed venous oxygen saturation (SvO₂), cerebral rSO₂ non-invasively monitored by the SRS NIRS is significantly advantageous because cerebral oxygenation status can be much better reflected by it.The third part (chapter 6) is the brief introduction of upgrading the SRS NIRS into the product (TSAH-100) which integrates the independent intellectual properties of our group, and expanding the clinical applications of the product. The main efforts made by the author are also indicated.