Raman spectroscopy of airway gases

• US 5,450,193 A
• Filed: 04/11/1994
• Issued: 09/12/1995
• Est. Priority Date: 02/24/1992
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Perry, Jeffrey, Gray, Damien F., Pittaro, Richard J., Hopkins, George W. II, Carlsen, William F., Simons, Tad D.
• Primary Examiner(s): McGraw, Vincent P.
• Assistant Examiner(s): HANTIS, KAREN
• Application Number:
  US08/226,245
• Time in Patent Office: 519 Days
• Field of Search: 356/301, 356/246
• US Class Current: 356/301
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption
• CPC Class Codes: G01J 3/44 Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry

Abstract

Method and apparatus for determining the composition and concentration of gases present in a patient'"'"'s airway by measurement of the spectrum of Raman scattered light from these gases. The efficiency is improved by collecting Raman scattered light generated outside the collection region. The gases present are assumed to be drawn from a predetermined set of gases with known Raman scattering spectra, and the concentrations are determined by solution of a matrix equation Ac=b, where the c vector components are the unknown concentrations and the b vector components are determined from measurements of the Raman scattering intensifies in a plurality of wavelength or wavenumber intervals. The linear system of equations represented by the matrix equation may be overdetermined and may require solution by non-conventional methods, such as singular value decomposition.

Claims

1. An apparatus for determining a spectral signature of an unknown gas in a single measurement comprising:

a reflective tube, having an aperture and a highly reflective surface, receiving and holding the unknown gas;

a light beam at a selected wavelength illuminating the unknown gas to produce Raman scattered light that is indicative of the spectral signature, wherein a first and a second portion of the Raman scattered light exits through the aperture and a third portion remains in the reflective tube;

wherein the first portion includes Raman scattered light originating from a collection region which is proximate to the aperture and the second portion includes Raman scattered light originating from outside the collection region;

the surface reflecting the second portion of the Raman scattered light such that the second portion is redirected and exits through the aperture;

a spectrometer, receiving the Raman scattered light that exits the aperture, dispersing the received Raman scattered light according to spectral wavelengths; and

an array of photodetectors, each photodetector corresponding to one of the spectral wavelengths, each photodetector detecting the dispersed Raman scattered light and producing an output signal at a strength proportional to [the concentration of]the detected dispersed Raman scattered light;

wherein the spectral signature corresponding to the strength of the output signals identifies and quantifies the unknown gas.

2. The apparatus, as defined in claim 1, the selected wavelength being between 500 nm and 850 nm, inclusively.

3. The apparatus, as defined in claim 1, the reflective tube further including two opposing ends, wherein the aperture of the reflective tube is a region in one of the two opposing ends, the aperture being transparent to the Raman scattered light.

4. The apparatus, as defined in claim 1, wherein the aperture is a region of the reflective tube that is transparent to Raman scattered light so that the first and second portions of Raman scattered light exits through the aperture.

5. The apparatus, as defined in claim 1, wherein the aperture is a partial circumferential band on the reflective tube that is transparent to Raman scattered light so that the first and second portions of Raman scattered light exits through the aperture.

6. The apparatus, as defined in claim 1, wherein the aperture is a narrow, longitudinally oriented band on the reflective tube that is transparent to Raman scattered light so that the first and second portions of Raman scattered light exits through the aperture.