A tissue oxygenation monitor using NIR spatially resolved spectroscopy

A new clinical tissue oxygenation monitor, the NIRO-300, has been developed. In addition to monitoring changes in hemoglobin concentration and redox state of cytochrome oxidase, the instrument can measure a Tissue Oxygenation Index (TOI), which is the ratio of oxygenated to total tissue hemoglobin, by utilizing NIR spatially resolved spectroscopy (SRS). In SRS, the slope of light attenuation versus distance is measured at a distant point from the light input, from which the TOI is calculated using photon diffusion theory. Four laser diodes are used as the light source and Class 1 laser light (IEC 825) is irradiated onto the skin. A high gain and low noise amplifier is used in the detector, which enables a large emitter-detector separations of around 5cm. To evaluate the TOI measured by the NIRO-300, it was compared to the data from a blood gas analyzer (SO, value) in measurements made on phantoms containing intralipid and blood. We also made simultaneous measurements by the NIRO-300 and an NIRS machine based on time resolved spectroscopy (TRS) on human arms. In the both measurements, TOI showed an excellent correlation with the data from brood gas analyzer and the TRS machine, which suggests the efficacy of the TOI data also in clinical use.