Fiber optic illumination and detection patterns, shapes, and locations for use in spectroscopic analysis

• US 6,411,373 B1
• Filed: 10/08/1999
• Issued: 06/25/2002
• Est. Priority Date: 10/08/1999
• Status: Expired due to Fees

• Current Assignee: GLT Acquisition Corporation
• Original Assignee: Instrumentation Metrics Inc.
• Inventors: Monfre, Stephen, Elliott, Barry C., Grochocki, Frank S., Garside, Jeffrey J., Ruchti, Timothy L., Kees, Glenn Aaron
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Lauchman, Layla
• Application Number:
  US09/415,389
• Time in Patent Office: 991 Days
• Field of Search: 385/115, 385/116, 385/123, 385/120, 385/121, 356/39, 356/301, 600/310, 600/182
• US Class Current: 356/39
• CPC Class Codes: G01N 21/474 Details of optical heads therefor, e.g. using optical fibres

Abstract

The invention provides a design process that is used in the determination of the pattern of detector and illumination optical fibers at the sampling area of a subject. Information about the system, specifically a monochromator (e.g. to determine the optimal number of fibers at an output slit) and the bundle termination at a detector optics stack (e.g. to determine the optimal number of fibers at the bundle termination), is of critical importance to this design. It is those numbers that determine the ratio and number of illumination to detection fibers, significantly limiting and constraining the solution space. Additional information about the estimated signal and noise in the skin is necessary to maximize the signal-to-noise ratio in the wavelength range of interest. Constraining the fibers to a hexagonal perimeter and prescribing a hex-packed pattern, such that alternating columns contain illumination and detection fibers, yields optimal results. In the preferred embodiment of the invention, two detectors share the totality of the detection fibers at the sampling interface. A third group of detection fibers is used for classification purposes.

Claims

1. A method for optimizing fiber optic illumination and detection patterns, shapes, and locations for use in the estimation of analytes, comprising the steps of:

systematically exploring patterns, shapes, and fiber locations to optimize an optical system design by maximizing desirable quantities in a model of said optical system; and

estimating from said optical system model a received signal.

2. The method of claim 1, wherein said model includes signal-to-noise ratio.

3. The method of claim 2, wherein said received signal is proportional to the ratio of pathlength of an average photon in a sample to its total pathlength;

and wherein said noise is approximately proportional to the intensity of said sample as a function of wavelength and detector to illumination fiber separation distance.

4. The method of claim 1, further comprising the step of:

determining a number of fibers at a light source output and at a fiber bundle termination at a detector optics stack input;

wherein said optimization is constrained by said light source output and said fiber bundle termination to allow a particular pattern of illumination and detection fibers to be investigated and optimized; and

determining the shape of a perimeter of a fiber layout from said optimization.

5. The method of claim 1, further comprising the steps of:

providing a computer program for interactive design and analysis of an arbitrary fiber layout;

saving designs created thereby; and

using said designs as inputs into a genetic algorithm that selects the best designs and attempts to improve upon them.

6. The method of claim 5, wherein an optimized pattern is modified as necessary to yield a regular pattern throughout and to fit said pattern into a selected external geometry.

7. The method of claim 6, wherein said external geometry is either of a hexagon or a rectangle.

8. The method of claim 1, further comprising the step of:

providing a separate fiber optic detection field to improve subject classification.

9. The method of claim 8, wherein placement of said separate fiber optic detection field is any of:

omitted; and

determined through a weighted combination of any of;

classification, performance, noise, inter-sample precision, and intra-sample precision.

10. The method of claim 1, wherein light from detector fibers is focused onto a detector.

11. The method of claim 10, wherein said detector fiber bundle is substantially the same shape as said detector to maximize the amount of light leaving the detector fibers that strikes the detector.

12. The method of claim 1, wherein light is provided by a monochromator;

and wherein optical slit height for said monochromator is determined according to;

$\mathrm{Optical}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Slit}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Height}=\left(\#<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Rows}-1\right)*\frac{\sqrt{3}}{2}*\mathrm{Fiber}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Diameter}+\mathrm{Core}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Diameter}.$

13. The method of claim 2, wherein noise is modeled as sample intensity, which is a function of distance and wavelength, expressed as:

14. The method of claim 1, further comprising the step of:

providing an evaluation function, which is a function of wavelength, and which takes into consideration a separation in fiber distances, signal-to-noise ratio, and light source and detector optics stack characteristics.

15. The method of claim 13, wherein said evaluation function is determined for a i^th detector as follows:

${\mathrm{EF}}_i<br><br>\left(\mathrm{\lambda <br><br>}\right)=\underset{\mathrm{Illum}}{\sum <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{{\mathrm{Detec}}_i}{\sum <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>S<br><br>\left(\mathrm{\lambda <br><br>},d\right)*\frac{1}{N<br><br>\left(\mathrm{\lambda <br><br>},d\right)}*\mathrm{DP}<br><br>\left(\#<br><br>{\mathrm{Detec}}_i\right)*\mathrm{MP}<br><br>\left(\#<br><br>\mathrm{Illum}\right)*\mathrm{MSP}<br><br>\left(\#<br><br>\mathrm{Illum}\right)*\mathrm{SF}<br><br>\left(\mathrm{Type},\mathrm{Size}\right),$

where EF_i is the evaluation function for the i^th detector;

the signal, S, and noise, N, are functions of wavelength, λ

, and illumination to detection fiber separation distance d;

DP is a detector penalty as a function of the number of detection fibers;

MP is a light source penalty as a function of the number of illumination fibers;

MSP is a light source size penalty as a function of the number of illumination fibers; and

SF is a scaling factor that is a function of fiber sizes and types.

16. A method for optimizing fiber optic illumination and detection patterns, shapes, and locations for use in the noninvasive estimation of analytes, comprising the steps of:

systematically exploring patterns, shapes, and fiber locations to optimize an optical system design by maximizing desirable quantities in a model of said optical system; and

providing an evaluation function.

17. The method of claim 16, further comprising the step of:

determining said evaluation function for a i^th detector as follows;

${\mathrm{EF}}_i<br><br>\left(\mathrm{\lambda <br><br>}\right)=\underset{\mathrm{Illum}}{\sum <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\underset{{\mathrm{Detec}}_i}{\sum <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>S<br><br>\left(\mathrm{\lambda <br><br>},d\right)*\frac{1}{N<br><br>\left(\mathrm{\lambda <br><br>},d\right)}*\mathrm{DP}<br><br>\left(\#<br><br>{\mathrm{Detec}}_i\right)*\mathrm{MP}<br><br>\left(\#<br><br>\mathrm{Illum}\right)*\mathrm{MSP}<br><br>\left(\#<br><br>\mathrm{Illum}\right)*\mathrm{SF}<br><br>\left(\mathrm{Type},\mathrm{Size}\right),$

where EF_i is the evaluation function for the i^th detector;

the signal, S, and noise, N, are functions of wavelength, λ

, and illumination to detection fiber separation distance d;

DP is a detector penalty as a function of the number of detection fibers;

MP is a light source penalty as a function of the number of illumination fibers;

MSP is a light source size penalty as a function of the number of illumination fibers; and

SF is a scaling factor that is a function of fiber sizes and types.

18. The method of claim 17, further comprising the steps of:

determining a signal-to-noise ratio for each unique fiber distance;

multiplying said signal-to-noise ratio by a number that is equal to the number of detector/illumination fiber pairs at that distance;

determining signal and noise once for each unique fiber distance;

saving a value determined thereby for later use;

pre-determining distances between all fibers; and

using a look-up table to determine a separation distance between any two specific fibers.

19. The method of claim 17, wherein said evaluation function optimizes a design for maximum signal-to-noise ratio at a selected wavelength.

20. The method of claim 19, wherein said evaluation function is given by:

${\mathrm{BestDesign}}_i=\max <br><br>\left(\underset{\mathrm{\lambda <br><br>}=2100<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{nm}}{\overset{2250<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{nm}}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{EF}}_i<br><br>\left(\mathrm{\lambda <br><br>}\right)\right).$

21. A process for determining a pattern of detection and illumination optical fiber bundles for use in sampling of a subject, comprising the steps of:

limiting and constraining a solution space by characterizing information about an illumination and sampling system to determine a ratio and number of illumination to detection fibers; and

estimating signal and noise at a location where said subject is sampled to maximize the signal-to-noise ratio in a wavelength range of interest.

22. The method of claim 21, wherein illumination is provided by a monochromator;

and wherein a monochromator output slit is characterized to determine an optimal number of illumination fibers.

23. The method of claim 21, wherein detection is provided by a bundle termination at a detector optics stack;

and wherein said detector optics stack is characterized to determine an optimal number of detection fibers.

24. A detection and illumination optical fiber bundle for sampling of a subject, comprising:

a plurality of optical fibers constrained to either of a hexagonal or a rectangular perimeter and prescribing a hex-packed pattern, wherein alternating columns contain illumination and detection fibers, and wherein two detectors share the totality of detection fibers at a sampling interface.

25. The fiber optic bundle of claim 24, further comprising:

a separate group of detection fibers used for classification purposes.

26. The fiber optic bundle of claim 24, wherein fibers are positioned such that each end of a bundle center fiber is centered at an opposing end of the bundle;

and

wherein each end of each and every other fiber in the bundle has a position at one end of said bundle that corresponds to position of said fiber'"'"'s opposing end at the opposing end of said bundle.

27. The fiber optic bundle of claim 24, wherein said detection and illumination fibers have the same characteristics.

28. The fiber optic bundle of claim 27, wherein said fiber characteristics comprise any of type, size, numeric aperture, and core-to-clad ratio.

29. The fiber optic bundle of claim 25, wherein placement of said separate fiber optic detection field is any of:

omitted; and

determined through a weighted combination of any of;

classifications performance, noise, inter-sample precision, and intra-sample precision.

30. A computer readable medium upon which a computer program is stored, said computer program capable of instructing a computer to implement a method for optimizing fiber optic illumination and detection patterns, shapes, and locations for use in estimation of analytes, said method comprising the steps of:

systematically exploring patterns, shapes, and fiber locations to optimize an optical system design by maximizing desirable quantities in a model of said optical system; and

estimating from said optical system model a received signal.