Method for extraction of optical properties from diffuse reflectance spectra

• US 20060247532A1
• Filed: 05/02/2005
• Published: 11/02/2006
• Est. Priority Date: 05/02/2005
• Status: Active Grant

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Palmer, Gregory M., Ramanujam, Nirmala
• Granted Patent: US 7,570,988 B2
• Time in Patent Office: Days
• US Class Current: 600/476
• CPC Class Codes: A61B 5/0091 for mammography
• CPC Class Codes: A61B 5/415 the glands, e.g. tonsils, adenoids or thymus
• CPC Class Codes: A61B 5/418 lymph vessels, ducts or nodes
• CPC Class Codes: A61B 5/4312 Breast evaluation or disorder diagnosis A61B5/0091 takes precedence
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G01N 21/474 Details of optical heads therefor, e.g. using optical fibres
• CPC Class Codes: G01N 21/4795 spatially resolved investigating of object in scattering medium in vivo A61B

Abstract

An iterative process calculates the absorption and scattering coefficients of tissue from a set of diffuse reflectance measurements made with an optical spectrometer operating in the UV-VIS spectral range. The relationship between measured diffuse reflectance and the absorption and scattering coefficients is modeled using a Monte Carlo simulation.

Claims

1. A method for calculating the scattering and absorption characteristics of tissue, the steps comprising:

a) acquiring a set of diffuse reflectance measurements from the tissue;

b) establishing a set of tissue optical parameters;

c) calculating model reflectance values using the set of tissue optical parameters and a model which relates diffuse reflectance to tissue optical parameters;

d) calculating the sum of squares error between the measured diffuse reflectance and the model reflectance values;

e) repeatedly updating optical parameters and repeating steps c) and d) until the sum of squares error is substantially minimized; and

f) calculating the scattering and absorption characteristics of the tissue from the updated optical parameters that yield a minimum sum of squares error.

2. The method as recited in claim 1 in which said model is a Monte Carlo model.

3. The method as recited in claim 2 in which the optical parameters include absorber concentration, scatterer size, and scatterer density, and the scattering and absorption characteristics of the tissue includes the scattering coefficient μ

_s of the tissue and the absorption coefficient μ

_a of the tissue.

4. The method as recited in claim 3 which includes calculating the absorption coefficient pta from the absorber concentration using Beer'"'"'s law.

5. The method as recited in claim 3 which includes calculating the scattering coefficient μ

_s from the scatterer size and scatterer density using Mie'"'"'s theory.

6. The method as recited in claim 1 which includes:

g) acquiring a set of diffuse reflectance measurements from a phantom having known optical properties; and

h) normalizing the set of diffuse measurements of tissue acquired in step a) using the measurements acquired in step

7. The method as recited in claim 6 which includes:

i) normalizing the model reflectance values acquired in step c) using the measurements acquired in step g) prior to performing step d).

8. The method as recited in claim 1 in which one tissue optical parameter is absorber concentration and the method further includes outputting the absorber concentration optical parameter updated in step e).

9. A method for calculating the scattering and absorption characteristics of an object, the steps comprising:

a) acquiring a set of diffuse reflectance measurements from the object;

b) establishing a set of object optical parameters;

c) calculating model reflectance values using the set of object optical parameters and a model which relates diffuse reflectance to object optical parameters;

d) calculating the sum of squares error between the measured diffuse reflectance and the model reflectance values;

e) repeatedly updating optical parameters and repeating steps c) and d) until the sum of squares error is substantially minimized; and

f) calculating the scattering and absorption characteristics of the object from the updated optical parameters that yield a minimum sum of squares error.

10. The method as recited in claim 9 in which said model is a Monte Carlo model.

11. The method as recited in claim 10 in which the optical parameters include absorber concentration, scatterer size, and scatterer density, and the scattering and absorption characteristics of the object includes the scattering coefficient μ

_s of the object and the absorption coefficient μ

_a of the object.

12. The method as recited in claim 11 which includes calculating the absorption coefficient μ

_a from the absorber concentration using Beer'"'"'s law.

13. The method as recited in claim 11 which includes calculating the scattering coefficient h from the scatterer size and scatterer density using Mie'"'"'s theory.

14. The method as recited in claim 9 which includes:

g) acquiring a set of diffuse reflectance measurements from a phantom having known optical properties; and

h) normalizing the set of diffuse measurements of the object acquired in step a) using the measurements acquired in step

15. The method as recited in claim 14 which includes:

i) normalizing the model reflectance values acquired in step c) using the measurements acquired in step g) prior to performing step d).

16. The method as recited in claim 9 in which one object optical parameter is absorber concentration and the method further includes outputting the absorber concentration optical parameter updated in step e).