Near-infrared reflectance (NIR) spectroscopy, which has become a widely used technique in food analysis, also holds considerable promise as a nondestructive and noninvasive probe for clinical diagnosis and examinations. Since the light in the near-infrared region is able to penetrate human tissues sufficiently, the use of the NIR technique may enable one to extract useful information directly from a human body without any pain and injury. However, in spite of the potentiality of NIR spectroscopy in medicine, its applications to clinical problems are still very limited; so far, most near-infrared spectroscopic studies in the medical field are concerned with the estimation of body fat and with the quantification of cerebral oxygenation and hemodynamics. Therefore, we have started working toward novel applications of the NIR method to medical problems. In this note we demonstrate the usefulness of NIR spectroscopy with fiber optics in the noninvasive monitoring of deoxyhemoglobin in the vein; it is possible to obtain <i>in vivo</i> NIR spectra of venous blood from various parts of the human body surface, with a high signal-to-noise ratio.
Y. Ozaki, T. Matsunaga, and T. Miura, "Nondestructive and Noninvasive Monitoring of Deoxyhemoglobin in the Vein by Use of a Near-Infrared Reflectance Spectrometer with a Fiber-Optic Probe," Appl. Spectrosc. 46, 180-182 (1992)