Diffuse reflectance spectroscopy

#This application claims the benefit of U.S. patent application Ser. No 09/819,776, entitled “Improved Diffuse Reflectance Monitoring Apparatus,” filed Mar. 28, 2001, which is a continuation of U.S. patent application Ser. No. 09/324,286, filed Jun. 2, 1999, now U.S. Pat. No. 6,230,034, which is a continuation of U.S. patent application Ser. No. 08/871,366, filed Jun. 9, 1997, now U.S. Pat. No. 5,935,062, which is a continuation-in-part of U.S. patent application Ser. No. 08/513,094, filed on Aug. 9, 1995, now U.S. Pat. No. 5,636,633, all of which are incorporated herein by reference.

#The present invention relates generally to diffuse reflectance spectroscopy; and more particularly, to an improved method and apparatus for the spectroscopic measurement or analysis of biological attributes of tissue; and still more particularly, to an improved method and apparatus including a specular reflectance control device for use in such a measurement system.

#The need and demand for an accurate, non-invasive method for determining biological attributes of tissue is well documented. Accurate, non-invasive determination of blood glucose, as an example, could reduce many of the complications associated with diabetes. Similarly, accurate, noninvasive determination of various disease states could allow faster, more convenient screening and diagnosis, allowing more effective treatment.

#The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.

#FIG. 1 is a simplified schematic showing the alternative responses to light incident on an analyte-containing tissue, including specular reflection, diffuse reflection, absorption and transmission;

#FIG. 2 is a schematic representation of the effect on specular reflectance utilizing input and output rays symmetric about a center focus;

#FIG. 1 is a schematic representation of light energy incident on an analyte-containing tissue sample. A tissue sample 12 includes an upper layer or epidermis 16, a middle layer or dermis 18 and subcutaneous tissue 19. Incident light 10 illuminates the tissue sample 12, wherein portions of the light energy may be transmitted through the tissue sample, resulting in transmitted light 26 exiting the opposing side of the tissue sample. Alternatively, a tissue sample may absorb a portion of the light energy, resulting in absorbed light energy 24 as heat. A third phenomena includes specular reflection 14 of a portion of the incident light 10. Finally, a portion of the light energy can be diffusely reflected 30.

#The diffusely reflected light 30 undergoes several refractions due to contact with the various components within the tissue sample. Eventually a portion of the diffusely reflected light energy 30 returns to the surface of the tissue sample 12 and exits back through the skin surface to the measuring device. Thus, both specular reflected light 14 and diffuse reflected light 30 combine and are directed back toward the instrument. Of the light directed toward the instrument, the diffusely reflected light 30 can contain desirable information concerning the biological attribute of interest. The specularly reflected light can contains information on the avascular epidermis, which can contain less or no information concerning the biological attribute of interest.

#Problems associated with diffuse reflectance sampling of tissue can be reduced by the distribution of the input and output optics based on center symmetry. In a center symmetry configuration, the light rays 10 are focused onto the tissue sample 12 by an optical system, incorporating lenses. Light rays that are specularly reflected from the surface of the tissue 12 generally exit the optical system on the opposite side of the beam focus.