Broadband absorption spectroscopy in turbid media by combined frequency-domain and steady state methodologies

• US 20030023172A1
• Filed: 07/09/2002
• Published: 01/30/2003
• Est. Priority Date: 07/27/2001
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Tromberg, Bruce J., Bevilacqua, Frederic, Cerussi, Albert E., Jakubowski, Dorota, Berger, Andrew J.
• Granted Patent: US 7,428,434 B2
• Time in Patent Office: Days
• US Class Current: 600/476
• CPC Class Codes: A61B 5/0091 for mammography
• CPC Class Codes: A61B 5/4312 Breast evaluation or disorder diagnosis A61B5/0091 takes precedence

Abstract

A technique for measuring broadband near-infrared absorption spectra of turbid media that uses a combination of frequency-domain and steady-state reflectance methods. Most of the wavelength coverage is provided by a white-light steady-state measurement, whereas the frequency-domain data are acquired at a few selected wavelengths. Coefficients of absorption and reduced scattering derived from the frequency-domain data are used to calibrate the intensity of the steady-state measurements and to determine the reduced scattering coefficient at all wavelengths in the spectral window of interest. The absorption coefficient spectrum is determined by comparing the steady-state reflectance values with the predictions of diffusion theory, wavelength by wavelength. Absorption spectra of a turbid phantom and of human breast tissue in vivo, derived with the combined frequency-domain and steady-state technique, agree well with expected reference values.

Claims

1. A method of analyzing turbid media comprising:

performing frequency-domain photon migration measurements on a turbid medium sample;

performing steady-state reflectance measurements on the same turbid medium sample;

and combining the results of the frequency-domain photon migration measurements with the results of the steady-state reflectance measurements for obtaining a unique spectrum for the turbid medium sample.

2. A method in accordance with claim 1 wherein the unique spectrum is a calibrated reflectance spectrum for the turbid medium sample.

3. A method in accordance with claim 2 wherein the steady-state reflectance measurements provide a relative reflectance spectrum and the calibrated reflectance spectrum is obtained by scaling the relative reflectance spectrum to fit absolute reflectance values determined at a plurality of discrete wavelengths by the frequency-domain photon migration measurements.

4. A method in accordance with claim 1 wherein the unique spectrum is a photon absorption coefficient spectrum for the turbid medium sample.

5. A method in accordance with claim 4 wherein a photon scattering coefficient spectrum is determined from the frequency-domain photon migration measurements, the reflectance measurements provide a reflectance spectrum and the absorption coefficient spectrum is calculated from the scattering coefficient spectrum and the reflectance spectrum.

6. A method in accordance with claim 1 wherein the frequency-domain photon migration measurements are made at a plurality of discrete wavelengths.

7. A method in accordance with claim 1 wherein the frequency-domain photon migration measurements are made by sequentially exposing the sample to light emitted by a plurality of laser diodes which emit light at different wavelengths.

8. A method in accordance with claim 1 wherein the steady-state reflectance measurements are made by exposing the sample to white light emitted by a white light source.

9. A method of analyzing turbid media comprising:

performing frequency-domain photon migration measurements on a turbid medium sample at a plurality of discrete wavelengths for determining photon absorption coefficient values and photon scattering coefficient values of the turbid medium at such discrete wavelengths;

performing steady-state reflectance measurements on the same turbid medium sample for determining a relative reflectance spectrum for the sample;

calibrating the relative reflectance spectrum obtained from the steady-state measurements in accordance with the discrete absorption and scattering coefficient values obtained from the frequency-domain measurements;

determining a scattering coefficient spectrum from the discrete scattering coefficient values obtained from the frequency-domain measurements;

and combining calibrated reflectance spectrum values and scattering coefficient spectrum values to obtain an absorption coefficient spectrum for the turbid medium sample.

10. A method in accordance with claim 9 wherein the relative reflectance spectrum is calibrated by calculating from the frequency-domain photon migration measurements absolute reflectance values at the discrete wavelengths and scaling the relative reflectance spectrum to fit these absolute reflectance values.

11. A method in accordance with claim 9 wherein the scattering coefficient spectrum is determined by fitting the scattering coefficient values determined at the discrete wavelengths to a matching power law curve for the desired wavelength range.

12. A method in accordance with claim 9 wherein the absorption coefficient spectrum is determined by numerical calculation at each wavelength of the absorption coefficient value based on the calibrated reflectance value and the scattering coefficient value obtained from the calibrated reflectance spectrum and scattering coefficient spectrum curves.

13. Apparatus for analyzing turbid media comprising:

apparatus for performing frequency-domain photon migration measurements on a turbid medium sample;

apparatus for performing steady-state reflectance measurements on the same turbid media sample;

and apparatus for combining results of the frequency-domain photon migration measurements with results of the steady-state reflectance measurements for producing an absorption coefficient spectrum for the turbid medium sample.

14. Apparatus in accordance with claim 13 wherein the apparatus for performing frequency-domain photon migration measurements includes:

a plurality of laser diodes for emitting light energy at a plurality of different wavelengths;

a delivery optical fiber for delivering light energy from the laser diodes to the turbid medium sample;

and a mechanism for receiving light energy arriving at a collection point on the turbid medium sample and measuring a characteristic of the collected light energy.

15. Apparatus in accordance with claim 13 wherein the apparatus for performing steady-state measurements includes:

a white light source for emitting white light;

a delivery optical fiber for delivering light energy from the white light source to the turbid medium sample;

and a spectrograph mechanism for receiving white light energy arriving at a spaced collection point on the turbid medium sample and producing therefrom a reflectance spectrum for the turbid medium sample.

16. Apparatus for analyzing turbid media comprising:

a plurality of laser diodes for emitting light energy at a plurality of different wavelengths;

a mechanism for modulating the light energy emitted by the laser diodes;

a white light source for emitting white light;

at least one delivery optical fiber for delivering modulated light energy from the laser diodes and white light from the white light source to a delivery point on a surface of a turbid medium sample;

a collection optical fiber for collecting emitted light energy arriving at a collection point on the surface of the turbid medium sample after traveling through the turbid medium sample, such collection point being fixed at a predetermined distance from the delivery point;

an analyzer mechanism coupled to the collection optical fiber for measuring at least one characteristic of the modulated light energy received from the laser diodes after passage through the turbid medium sample;

a spectrograph mechanism coupled to the collection optical fiber for producing a reflectance spectrum for the white light received from the white light source after passage through the turbid medium sample;

and a data processing mechanism for combining results of the analyzer mechanism measurements with results of the spectrograph mechanism measurements for producing a photon absorption coefficient spectrum for the turbid medium sample.

17. A method of analyzing human body tissue in vivo comprising:

emitting light photons from a plurality of different laser diode light sources into human body tissue from a predetermined delivery point on the surface of a human body;

emitting light photons from a white light source into the same human body tissue from the same predetermined delivery point on the surface of the human body;

collecting the light photons received at a spaced collection point on the surface of the human body after such light photons have traveled through the human body tissue intermediate the delivery and collection points;

and combining predetermined characteristics of the collected light photons from the different light sources to provide an indication of the composition of the traversed human body tissue.

18. A method in accordance with claim 17 wherein the indication of the composition of the traversed human body tissue takes the form of a photon absorption coefficient spectrum for the traversed human body tissue.

19. A method in accordance with claim 17 wherein the light photons from the different light sources are applied in a sequential manner.

20. A method in accordance with claim 17 wherein the human body tissue is female human breast tissue, the delivery and collection points are located on the surface of a female human breast and the resulting indication of tissue composition can be used to detect an abnormal tissue condition.