Intrinsic and swept-source raman spectroscopy
The present invention pertains to a method and an apparatus for Raman spectroscopy of human tissue. Human tissue is illuminated with a laser emitting a first wavelength of light. A Raman signal is measured and optical properties are determined at this wavelength such that the measured Raman signal can be corrected based on determined optical properties. Determined optical properties may be the scattering coefficient and absorption coefficient of the tissue. A system for Raman spectroscopy of human tissue includes a frequency sweeping laser light source for illumination, and a filtered detector for collecting the Raman signal.
1. A method for Raman spectroscopy of human tissue comprising:
illuminating said human tissue with an amplitude-modulated laser emitting light at a first wavelength;
collecting elastically scattered excitation light scattered by said human tissue and originating from said laser emitting light for purposes of correction for turbidity-induced variations;
deriving time domain optical data from signals corresponding to time of detection of said collected light;
determining a scattering coefficient and an absorption coefficient of said human tissue from said time domain optical data;
measuring a Raman signal from said human tissue at a first Raman wavelength from said scattered light originating from said laser emitting light; and
correcting said Raman signal for turbidity-induced variations based on said scattering coefficient and said absorption coefficient of said human tissue from said time domain optical data.
2. The method of claim 1 further comprising:
determining a diffuse reflectance of said human tissue at said first wavelength.
3. The method of claim 1 further comprising:
deriving a temporal point spread function of said Raman signal of said human tissue at said first Raman wavelength.
4. The method of claim 3 further comprising:
determining said scattering coefficient of said human tissue at said first Raman wavelength based on said temporal point spread function; and
determining said absorption coefficient of said human tissue at said first Raman wavelength based on said temporal point spread function.
5. The method of claim 1 further comprising:
sweeping said laser over a range of wavelengths.
6. The method of claim 1 wherein said first Raman wavelength is a Stokes Raman wavelength.
7. The method of claim 1 wherein said first Raman wavelength is an Anti-Stokes Raman wavelength.
8. A method for Raman spectroscopy of human tissue comprising:
illuminating said human tissue with an amplitude-modulated laser emitting light at a first wavelength;
collecting elastically scattered excitation light scattered by said human tissue and originating from said laser emitting light for purposes of correction for turbidity-induced variations;
deriving time domain optical data from signals corresponding to time of detection of said collected light;
determining a scattering coefficient of said human tissue based on said time domain optical data;
determining an absorption coefficient of said human tissue based on said time domain optical data;
measuring a Raman signal from said human tissue at a first Raman wavelength from said scattered light; and
correcting said Raman signal for turbidity-induced variations based on said scattering coefficient and said absorption coefficient based on said time domain optical data.
9. The method of claim 8 wherein said first Raman wavelength is a Stokes Raman wavelength.
10. The method of claim 8 wherein said first Raman wavelength is an Anti-Stokes Raman wavelength.
11. The method of claim 8 further comprising:
sweeping said laser over a range of wavelengths.
12. The method of claim 8 wherein said scattering coefficient of said human tissue is determined at said first wavelength and said absorption coefficient of said human tissue is determined at said first wavelength.
13. A system for Raman spectroscopy comprising:
a frequency sweeping laser light source for illuminating a sample;
a filter positioned after said sample in an optical path from said laser light source to said sample for allowing Raman wavelengths of scattered light from said sample to pass through said filter;
a detector positioned after said filter in said optical path from said laser light to said sample and said filter for detecting an optical signal of said Raman wavelengths of scattered light from said sample corresponding to time of detection of said scattered light; and
a processor configured to correct said optical signal for turbidity-induced variations based on a scattering coefficient and an absorption coefficient of said sample determined with time domain optical data of said scattered light originating from said laser light source.
14. The system of claim 13 wherein said filter is tilted at an angle off-axis with respect to an axis of said light from said sample.
15. The system of claim 13 further comprising:
a signal generator coupled to said laser light source configured to generate a digital modulation signal associated with a pseudo-random code sequence; and
a processor coupled to said detector configured to derive a temporal point spread function of said sample from said light from said sample.