Diabetics would benefit greatly from a device capable of providing continuous noninvasive monitoring of their blood glucose levels. The optical scattering coefficient of tissue depends on the concentration of glucose in the extracellular fluid. A feasibility study was performed to evaluate the sensitivity of the tissue reduced scattering coefficient in response to step changes in the blood glucose levels of diabetic volunteers. Estimates of the scattering coefficient were based on measurements of the diffuse reflectance on the skin at distances of 1-10 mm from a point source. A correlation was observed between step changes in blood glucose concentration and tissue reduced scattering coefficient in 30 out of 41 subjects measured.

A near infrared spectrometer has been constructed which is capable of performing spatially resolved diffuse reflectance measurements in the wavelength range of 0.9 -1.6 m. In this technique, broadband light is delivered by an optical fiber to a point on the tissue surface and diffusely reflected light is collected by 300 im fibers located at 15 distances ranging between 1.0 to 10.0 mm from the source. The light from the detector fibers is imaged with a monochromator onto an InGaAs photodiode array. Wavelengths can be selected by automated scanning ofthe monochromator grating. A diffusion theory model fit to the reflectance versus distance data has been used to estimate the absorption and scattering coefficients (jtand p ') of phantoms and tissue under analysis. Reflectance measurements have been performed on tissue simulating water-based phantoms as well as in vivo on different skin locations. The absorption coefficient of skin was found to have a spectral structure similar to that of water. Unexpected spectral features in the scattering coefficient ofskin were observed which may be a result ofnot considering the layered structure ofskin in the current model. The temporal stability of the system has been demonstrated on tissue-simulating phantoms and human volunteers, indicating that the reflectance measurement may be suitable for in vivo monitoring of physiologically induced changes in the absorption and scattering coefficients.

No abstract