Apparatus and method for reducing spectral complexity in optical sampling

• US 20030191393A1
• Filed: 04/04/2002
• Published: 10/09/2003
• Est. Priority Date: 04/04/2002
• Status: Active Grant

• Current Assignee: Inlight Solutions, Inc.
• Original Assignee: Inlight Solutions, Inc.
• Inventors: Maynard, John D., Ridder, Trent, Johnson, Robert D., Abbink, Russell E.
• Granted Patent: US 6,684,099 B2
• Time in Patent Office: Days
• US Class Current: 600/473
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/6824 Arm or wrist

Abstract

An optical sampling subsystem and method that reduces the effect of errors in an optical sampling subsystem when heterogeneously distributed samples are measured in the path of a spectrometer. The optical sampling subsystem is used to collect the non-uniformly distributed radiation exiting the heterogeneous sample and produce a uniform irradiance at its output. The output is then directed into the wavenumber (inverse of wavelength in centimeters) dispersive or modulating device of the spectrometer. The resulting spectra exhibit less spectral complexity arising from components of the sampling subsystem design and the heterogeneous sample, in particular, the effect of wavenumber shift is minimized. Improved quantitative predictions, qualitative analysis and calibration transfer are direct consequences of the reduced spectral complexity.

Claims

1. A sampling subsystem for use in optical analysis of a sample comprising:

a sample head for receiving the sample for optical analysis including an illumination source optically coupled to the sample head for irradiating the sample and a plurality of optical fibers having input ends and output ends wherein the input ends are mounted in the sample head in spaced relation for receiving at least a portion of the radiation which is diffusely reflected by the sample and transmitting the radiation to the output end of the optical fibers; and

means for homogenizing at least a portion of the radiation exiting the output end of the optical fibers, the means for homogenizing at least a portion of the radiation disposed between the output end of the optical fiber and an input to a spectrometer wavelength dispersive or modulating device.

2. The sampling subsystem of claim 1, wherein said means for homogenizing said radiation is a light pipe.

3. The sampling subsystem of claim 2, wherein said light pipe has a polygonal cross section.

4. The sampling subsystem of claim 2, wherein said light pipe includes one or more bends to achieve angular homogenization.

5. The sampling subsystem of claim 1, wherein angular homogenization is achieved, at least in part by passing the radiation through a glass diffuser.

6. The sampling subsystem of claim 2, wherein said light pipe includes a diffusely reflective coating on the interior surface thereof.

7. A sampling subsystem for use in optical analysis of a sample comprising:

a sample head for receiving the sample thereon, the sample head having a plurality of illumination optical fibers, each with an input end and an output end, the input ends receiving radiation and the output ends mounted within the sample head to transmit radiation into the sample, the sample head further including a plurality of receiver optical fibers, each with an input end and an output end, the input ends mounted in spaced relation in the sample head for receiving at least a portion of the radiation that is diffusely reflected from the sample and transmit the radiation to the output ends; and

a radiation homogenizer optically coupled to the output ends of the receiver optical fibers disposed between the output ends of the receiver optical fibers and an input to a spectrometer wavelength dispersive or modulating device for homogenizing the radiation prior to measurement.

8. The sampling subsystem of claim 7, wherein said radiation homogenizer is a light pipe.

9. The sampling subsystem of claim 8, wherein said light pipe has a polygonal cross section.

10. The sampling subsystem of claim 8, wherein said light pipe includes one or more bends to achieve angular homogenization.

11. The sampling subsystem of claim 7, wherein angular homogenization is achieved, at least in part, by passing the radiation through a glass diffuser.

12. The sampling subsystem of claim 8, wherein said light pipe includes a diffusely reflective coating on the interior surface thereof.

13. A spectroscopic system for determining property of a heterogeneous sample, the apparatus comprising:

a light source that generates light;

a sampling means for coupling at least a portion of the generated light to tissue and collecting the light modified by the tissue, the sampling means including a sample head for receiving a sample and a plurality of receiver optical fibers including input ends and output ends, the input ends disposed in the sample head for collecting at least a portion of the light modified by the tissue, the output ends optically coupled to an input end of a radiation homogenizer;

a spectrometer optically coupled to an output end of the radiation homogenizer for measuring the optical information of the modified light collected from the tissue; and

means for processing the optical information to determine a property of the sample.

14. The spectroscopic system of claim 13, wherein said radiation homogenizer is a light pipe.

15. The spectroscopic system of claim 14, wherein said light pipe has a polygonal cross section.

16. The spectroscopic system of claim 14, wherein said light pipe includes one or more bends to achieve angular homogenization.

17. The spectroscopic system of claim 13, wherein angular homogenization is achieved, at least in part, by passing the radiation through a glass diffuser.

18. The spectroscopic system of claim 14, wherein said light pipe includes a diffusely reflective coating on the interior surface thereof.

19. An apparatus for non-invasively detecting a property of human tissue by near-infrared spectroscopy comprising:

an illumination subsystem which generates near-infrared light including at least one wavelength indicative of the property in human tissue;

a tissue sampling subsystem optically coupled to the illumination subsystem which receives at least a portion of the infrared light, the tissue sampling subsystem including means for irradiating human tissue with at least a portion of the received infrared light and a plurality of optical fibers for collecting at least a portion of the light diffusely reflected from the human tissue, the plurality of optical fibers each including an output end optically coupled to means for spatially and angularly homogenizing the collected light;

an FTIR spectrometer subsystem optically coupled to the means for homogenizing the collected light to receive at least a portion of the homogenized light, the FTIR spectrometer subsystem including a spectrometer that creates an interferogram, the FTIR spectrometer subsystem further including a detector which receives the interferogram and converts the interferogram to an electrical representation;

a data acquisition subsystem which receives the electrical representation of the interferogram, the data acquisition subsystem including means for amplifying and filtering the electrical representation and converting a resulting electrical signal to its digital representation; and

a computing subsystem for receiving the digital representation and further including a multivariate algorithm for detecting the property in human tissue.

20. The apparatus of claim 19, wherein said means for homogenizing said radiation is a light pipe.

21. The apparatus of claim 20, wherein said light pipe has a polygonal cross section.

22. The apparatus of claim 20, wherein said light pipe includes one or more bends to achieve angular homogenization.

23. The apparatus of claim 19, wherein angular homogenization is achieved, at least in part by passing the radiation through a glass diffuser.

24. The apparatus of claim 20, wherein said light pipe includes a diffusely reflective coating on the interior surface thereof.

25. A spectroscopic system for measuring analyte concentration in a sample, the system comprising:

a radiation source emitter, the emitter emitting radiation;

a sampler subsystem for transmitting radiation from the source to a sample, the sampler subsystem including a plurality of receiver optical fibers for collecting a portion of the radiation subsequent to interaction with the sample;

a radiation homogenizer disposed to receive the radiation collected by the receiver optical fiber, wherein the homogenizer homogenizes at least a portion of the radiation; and

a detector for receiving at least a portion of the homogenized radiation subsequent to interacting with the sample and the radiation homogenizer.

26. The spectroscopic system of claim 25, wherein the sampler subsystem includes a means for channeling the emitted radiation to the sample source.

27. The spectroscopic system of claim 26, wherein the channeling means is at least one fiber optic wire.

28. The spectroscopic system of claim 26, wherein the channeling means is at least one mirror.

29. The spectroscopic system of claim 26, wherein the channeling means is at least one optic lens.

30. The spectroscopic system of claim 25, wherein the radiation homogenizer is a light pipe, wherein the light pipe has a proximal end, a distal end, and a length of material therebetween, the light pipe further having a cross-sectional area.

31. The spectroscopic system of claim 30, wherein the light pipe includes a plurality of bends.

32. The spectroscopic system of claim 31, wherein the plurality of bends form an S-shaped bend.

33. The spectroscopic system of claim 30, wherein the cross-sectional area of the light pipe is polygonal in shape.

34. The spectroscopic system of claim 33, wherein the polygonal shape includes all polygonal forms having three to an infinite number of sides.

35. The spectroscopic system of claim 25, wherein the sample is biological tissue.

36. The spectroscopic system of claim 25, wherein the sample is a human appendage, or a portion thereof.

37. The spectroscopic system of claim 25, wherein the analyte measured is glucose.

38. The spectroscopic system of claim 25, wherein the analyte measured is alcohol.

39. The spectroscopic system of claim 25, wherein the spectroscopic system includes at least one bandpass filter.

40. A method for homogenizing radiation for spectroscopic analysis, the method comprising the steps of:

providing a spectroscopic system, wherein the system comprises a radiation source emitter, a sample having an analyte concentration, a sampler including a plurality of optical fibers for collecting a portion of the radiation after interaction with the sample,

a radiation homogenizer, and a radiation detector;

emitting radiation by means of the radiation source emitter;

illuminating the sample with the radiation;

collecting at least a portion of the radiation after interaction with the sample with the plurality of optical fibers;

homogenizing the radiation exiting the plurality of optical fibers; and

detecting the analyte concentration within the sample source.

41. The method for homogenizing radiation for spectroscopic analysis of claim 40, wherein the radiation homogenizer is a light pipe.