Portable optical apparatus for diffuse reflectance spectroscopy

Abstract

An optical apparatus for obtaining a reflectance spectrum includes a first means for generating a light, a second means for transferring and receiving the light on a substrate, a third means for collecting a diffusely reflected light, and a fourth means for separating the diffusely reflected light from a specular reflected light to obtain information about a concentration of a chromophore in the substrate. The second means is an optic probe made of Poly(methyl methacrylate) (PMMA) material including an inner rod and an outer rod, the inner rod is nested within the outer rod for collection and for illumination, the inner rod and the outer rod are coaxial, the inner rod is longer than the outer rod, the inner rod is isolated from the outer rod with a semi mirrored isolator, the reflected light is reflected from deep within the substrate by the inner rod.

Claims

1. An optical apparatus for obtaining a reflectance spectrum; comprising: a first means for generating a light, a second means for transferring and receiving the light on a substrate, a third means for collecting a diffusely reflected light, and a fourth means for separating the diffusely reflected light from a specular reflected light to obtain information about a concentration of a chromophore in the substrate; wherein the second means is an optic probe made of Poly(methyl methacrylate) (PMMA) material, the second means comprises an inner rod and an outer rod, the inner rod is nested within the outer rod for collection and for illumination, the inner rod and the outer rod are coaxial, the inner rod is longer than the outer rod, the inner rod is isolated from the outer rod with a semi mirrored isolator, the reflected light is reflected from deep within the substrate by the inner rod.

2. The optical apparatus according to claim 1, wherein the first means is two white LEDs, a flat spectrum of each of the two white LEDs has a wavelength ranging from 350 nm to 750 nm.

3. The optical apparatus according to claim 1, wherein the second means transfers the light to the substrate through the outer rod.

4. The optical apparatus according to claim 1, wherein the second means receives the light from the substrate through the inner rod.

5. The optical apparatus according to claim 1, wherein the third means detects a diffuse reflectance spectrum by a micro spectrometer.

6. The optical apparatus according to claim 1, wherein the fourth means separates the diffusely reflected light from the specular reflected light, the diffusely reflected light carries information about the presence or the concentration of the chromophore.

7. The optical apparatus according to claim 1, wherein a micro spectrometer is placed at an uppermost position of the optical apparatus, a LED light source is placed below the micro spectrometer directed to an optic probe, the optic probe is coupled to thee LED light source and the micro spectrometer to provide a compact structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings illustrate a complete embodiment of the invention according to the best mode so far devised for the practical application of the principles thereof, and in which:

(2) FIG. 1 is a schematic and block diagram of the diffuse reflectance measurement system

(3) FIG. 2 is a schematic representation of the incident light on a skin tissue

(4) FIG. 3 shows the expanded figure of optical apparatus

(5) FIG. 4 shows the cross sectional view of optical apparatus

(6) FIG. 5 shows the top view of optical apparatus

DETAILED DESCRIPTION

(7) In FIG. 1, it is shown that the light that is produced by a white LED is directed to the skin surface. The light penetrates into the skin tissue by randomized propagation. After numerous scattering events, some of the light emerges from the skin surface. This reflected light is collected by a spectrometer to obtain the reflectance spectra. From this spectra, it is possible to determine the concentration of the target chromophore in the subcutaneous tissue by the appropriate data analyses.

(8) FIG. 2 illustrates the skin surface 1 illumination by an incident light coming from the outer PMMA rod 12. As depicted in the simplified representation, the skin includes three layers, the upper layer or epidermis 2, a middle layer or dermis 3, and subcutaneous tissue 4. Incident light 5 illuminates the skin surface and penetrates into the subcutaneous tissue. A portion of the light energy may be reflected specularly 6 which cannot not reach the light collection path. Instead, a tissue sample may absorb a portion of the light energy, resulting in absorbed light energy 7. A third phenomena includes transmitted energy 8 into the deeper tissue. Lastly, a portion of the light can be diffusely reflected 9. As shown in FIG. 1 diffusely reflected portion of light ray change the direction several times and then this portion 10 is collected by the inner PMMA rod 13. To prevent the light transmission from one rod to the other, the rods are isolated from each other by a semi mirrored isolator 14. In this way only diffusely reflected light is analyzed. Also, the semi-mirrored isolator increases the light transmission efficiency. The outer isolation is provided by the optical probe holder 11, which holds the other components of the optical apparatus.

(9) The expanded schematic view of the optical apparatus is shown in FIG. 3. Two cylindrical PMMA rods 12, 13 are placed in a nested structure and isolated from each other with an isolator material 14. Optic probe holder 11 contains a spring 16 with a spring holder 15 allowing pressure-sensitive activation mechanism. This mechanism allows the appropriate pressure on the skin surface, and thus helps providing correct measurement results. Illumination of the target skin surface is achieved by the LEDs, placed on the LED circuit card 17. After a sufficient illumination of the skin, the diffusely reflected light that is typically reflected by various depths within the tissue is collected by the inner PMMA rod and carried to the spectrometer 18. This spectrometer is placed on a circuit card 19.

(10) Referring now to FIG. 4, there is shown a cross sectional view of optical apparatus. In FIG. 4 the placement of the optical apparatus components is seen. From the top side to the bottom, spectrometer circuit card 19 is in the first place that is fixed with two screws 20. The collected light enters the spectrometer 18 through its slit 21. Collection PMMA rod 13 is directly coupled to this slit. Below the spectrometer, LED circuit card 17 is placed and fixed by two screws 24. On this card, there are two white LEDs 23 with wide flat spectrums (for example from 350 nm to 750 nm wavelengths). These LEDs are positioned adjacent the top surface of the source PMMA rod 12. Light travels through this path and reaches the skin surface.

(11) FIG. 5 shows the top view of the optical apparatus. This is a moving part inside the measurement device. When this apparatus applied on to the skin surface with a sufficient pressure, it moves inside the device and touches to a switch by a switch contact point 22. This contact activates the system and initiates the measurement.