Quantitative broadband absorption and scattering spectroscopy in turbid media by combined frequency-domain and steady state methodologies

• US 7,428,434 B2
• Filed: 07/09/2002
• Issued: 09/23/2008
• 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.
• Primary Examiner(s): Casler; Brian L.
• Assistant Examiner(s): RAMIREZ, JOHN FERNANDO
• Application Number:
  US10/191,693
• Publication Number:
  US 20030023172A1
• Time in Patent Office: 2,268 Days
• Field of Search: 600/473, 600/476, 600/407, 600/310, 600/322, 356/300, 356/303, 356/318, 356/317, 356/326, 356/337
• 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 at a plurality of specified wavelengths for determining absolute photon absorption coefficient values and absolute photon scattering coefficient values of the turbid medium at such discrete wavelengths;

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

calibrating the relative 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 spectrum values and scattering coefficient spectrum values to obtain an absorption coefficient spectrum for the turbid medium sample.

2. A method in accordance with claim 1 wherein the relative spectrum is calibrated by calculating from the frequency-domain photon migration measurements absolute values at the specified wavelengths and scaling the relative spectrum values to fit these absolute reflectance values.

3. A method in accordance with claim 1 wherein the scattering coefficient spectrum is determined by fitting the absolute scattering coefficient values determined at the specified wavelengths to a matching power law curve for the desired wavelength range.

4. A method in accordance with claim 1 wherein the absorption coefficient spectrum is determined by numerical calculation at each wavelength of the absolute absorption coefficient value based on the calibrated reflectance value and the scattering coefficient spectrum obtained from the calibrated reflectance and/or transmittance spectrum and absolute scattering coefficient spectrum curves.

5. A method of analyzing turbid tissue comprising:

simultaneously emitting light from a plurality of different modulated light sources into tissue;

emitting light from a steady state broadband or multi-spectral light source into the tissue;

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

combining predetermined characteristics of the collected light from the different modulated light sources used in a frequency-domain photon migration measurement with the light from the steady state broadband or multi-spectral source used in steady-state measurements to provide a light spectrum as an indication of the composition of the traversed human body tissue based on an optical model.

6. A method in accordance with claim 5 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.

7. A method in accordance with claim 5 wherein the light photons from the different light sources are applied in a sequential manner.

8. A method of analyzing turbid media comprising:

performing frequency-domain photon migration measurements on a turbid medium sample within a first spectral range;

performing steady-state measurements within a second spectral range on the same turbid medium sample; and

combining the results of the frequency-domain photon migration measurements with the results of the steady-state measurements for obtaining a unique spectrum for the turbid medium sample across the second spectral range, which is greater than the first spectral range.

9. An apparatus for analyzing turbid media comprising:

means for performing frequency-domain photon migration measurements on a turbid medium sample using a limited number of optical wavelengths;

means for performing broadband steady-state measurements on the same turbid media sample; and

means for combining results of the frequency-domain photon migration measurements with results of the steady-state measurements for producing an absorption coefficient spectrum for the turbid medium sample over a spectral range as defined by the means for performing broadband steady-state measurements.

10. Apparatus for analyzing turbid media comprising:

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

means for modulating the light emitted by the laser diodes;

a broadband, steady state light source having a defined spectral range;

where modulated light from the laser diodes and light from the broadband light source is delivered in free space to a delivery point on a surface of a turbid medium sample;

a collection point on the surface of the turbid medium sample for collecting light after propagation through the turbid medium sample, such collection point being fixed at a predetermined distance from the delivery point;

an analyzer for measuring at least one characteristic of the modulated light received in free space at the collection point from the laser diodes after propagation through the turbid medium sample;

a spectrograph for producing a spectrum of the light received in free space at the collection point from the broadband light source after propagation through the turbid medium sample; and

a data processing circuit which combines the results of the analyzer with results of the spectrograph to produce an absorption coefficient spectrum of the turbid medium sample as defined by the spectral range of the broadband light source.