Method and apparatus for performing quantitative analysis and imaging surfaces and subsurfaces of turbid media using spatially structured illumination

• US 6,958,815 B2
• Filed: 03/18/2003
• Issued: 10/25/2005
• Est. Priority Date: 03/19/2002
• 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: Cuccia, David, Durkin, Anthony J., Tromberg, Bruce J., Bevilacqua, Frederic
• Primary Examiner(s): EVANS, FANNIE L
• Application Number:
  US10/391,166
• Publication Number:
  US 20030184757A1
• Time in Patent Office: 952 Days
• Field of Search: 356/445, 356/446, 356/603, 356/604
• US Class Current: 356/445
• CPC Class Codes: G01N 21/49 within a body or fluid

Abstract

Illumination with a pattern of light allows for subsurface imaging of a turbid medium or tissue, and for the determination of the optical properties over a large area. Both the average and the spatial variation of the optical properties can be noninvasively determined. Contact with the sample or scanning is not required but may be desired. Subsurface imaging is performed by filtering the spectrum of the illumination in the Fourier domain but other filtering approaches, such as wavelet transform, principle component filter, etc may be viable as well. The depth sensitivity is optimized by changing the spatial frequency of illumination. A quantitative analysis of the average optical properties and the spatial variation of the optical properties is obtained. The optical properties, i.e. reduced scattering and absorption coefficients are determined from the modulated transfer function, MTF.

Claims

1. A method of determining surface or subsurface optical properties of a sample of turbid media over an area of the sample with a single measurement comprising:

exposing the sample to a periodic pattern of illumination;

receiving the data image from the sample;

selecting a region of interest of the sample;

transforming the data image of the selected region of interest of the sample;

spatially filtering the transformed data image of the selected region of interest of the sample; and

reconstructing the filtered transformed data image of the selected region of interest of the sample.

2. The method of claim 1 where exposing the sample to a periodic pattern of illumination comprises exposing the sample to a periodic pattern of illumination dots.

3. The method of claim 2 where the periodic pattern of dots is characterized by a periodic distance between the dots and where exposing the sample to a periodic pattern comprises probing the sample to a depth of approximately one half the dot spacing at the sample surface.

4. The method of claim 1 where the periodic pattern is characterized by a periodic distance and where exposing the sample to a periodic pattern comprises probing the sample to a depth which is a function of the periodic distance.

5. The method of claim 4 further comprising exposing the sample to a plurality of periodic patterns, each of which is characterized by a periodic distance so that exposing the sample to a plurality of periodic patterns comprises probing the sample to a plurality of depths.

6. The method of claim 1 further comprising determining a modulation transfer function of the periodic pattern of illumination.

7. The method of claim 6 where determining a modulation transfer function of the turbid sample for the periodic pattern of illumination comprises:

exposing a homogenous standard with a predetermined periodic pattern having a known measurable and reproducible spatial Fourier spectrum;

receiving a reflectance data image from the standard;

selecting a region of interest of the sample;

transforming the reflectance data image of the standard;

ratioing the transformed data image of the selected region of the sample with the reflectance data image of the standard to obtain a map of the modulation transfer function;

generating a map of scattering and absorption properties from the map of the modulation transfer function; and

generating averages of scattering and absorption properties of the sample from the modulation transfer function.

8. The method of claim 1 where exposing the sample to a periodic pattern of illumination, receiving the data image, Fourier transforming the data image, spatially filtering the transformed data image, and reconstructing the filtered transformed data image is repeated for various regions of interest to provide a map of the optical properties.

9. The method of claim 1 where exposing the sample to a periodic pattern of illumination, receiving the data image, Fourier transforming the data image, spatially filtering the transformed data image, and reconstructing the filtered transformed data image is repeated for areas of different sizes to provide multiscale analysis of the sample.

10. The method of claim 9 where providing multiscale analysis is provided post-processing without retaking the data image.

32. The method of claim 1 further comprising repeating exposing the sample to a periodic pattern of illumination, receiving the data image from the sample, selecting a region of interest of the sample, transforming the data image of the selected region of interest of the sample, spatially filtering the transformed data image of the selected region of interest of the sample;

and reconstructing the filtered transformed data image of the selected region of interest of the sample over a temporal span without changing the periodic pattern of illumination in order to track dynamic changes in the sample over time.

11. A method of determining surface or subsurface optical properties of a sample of turbid media over an area of the sample with a single measurement comprising:

exposing the sample to a periodic pattern of illumination;

receiving the data image of the sample;

exposing a homogenous standard with a predetermined periodic pattern having a known spatial Fourier spectrum;

receiving a reflectance data image from the standard;

selecting a region of interest of the sample;

Fourier transforming the data image of the selected region of interest of the sample;

selecting a region of interest of the standard;

Fourier transforming the reflectance data image of the selected region of interest of the standard; and

ratioing the transformed data image of the sample with the reflectance data image of the standard to obtain a map of the modulation transfer function.

12. The method of claim 11 where exposing the sample to a periodic pattern of illumination is repeated with a sequence of different wavelengths and/or filters.

13. The method of claim 11 further comprising generating a map of scattering and absorption properties from the map of the modulation transfer function.

14. The method of claim 11 further comprising generating averages of scattering and absorption properties of the sample from the modulation transfer function.

15. The method of claim 11 where exposing the sample and standard to a periodic pattern of illumination, receiving the data image of the sample and reflectance data image of the standard;

Fourier transforming the data image of the sample and the reflectance data image of the standard, and ratioing the transformed data image of the sample with the reflectance data image of the standard to obtain a map of the modulation transfer function is repeated for areas of different sizes to provide multiscale analysis of the sample.

16. An apparatus of determining subsurface optical properties of a sample of turbid media over an area of the sample with a single measurement comprising:

a source to expose the sample to a periodic pattern of illumination;

a camera to receive the data image from the sample; and

a signal processor to Fourier transform the data image of the sample, to spatially filter the transformed data image of the sample, and to reconstruct the filtered transformed data image of the sample.

17. The apparatus of claim 16 where the signal processor is a computer.

18. The apparatus of claim 16 where the signal processor is an optical spatial filter.

19. The apparatus of claim 16 where source generates a periodic pattern of illumination dots.

20. The apparatus of claim 19 where the periodic pattern of dots is characterized by a periodic distance between the dots and where the source probes the sample to a depth of approximately one half the dot spacing.

21. The apparatus of claim 16 where the periodic pattern is characterized by a periodic distance and where the source probes the sample to a depth which is a function of the periodic distance.

22. The apparatus of claim 21 where the source exposes the sample to a plurality of periodic patterns, each of which is characterized by a periodic distance so that exposing the sample to a plurality of periodic patterns comprises a source which probes the sample to a plurality of depths.

23. The apparatus of claim 16 where the signal processor deduces a modulation transfer function of the periodic pattern of illumination.

24. The apparatus of claim 23 where the source exposes a homogenous standard with a predetermined periodic pattern having a known spatial Fourier spectrum, the camera receives a reflectance data image from the standard, the signal processor Fourier transforms the reflectance data image of the standard, and ratios the transformed data image of the sample with the transformed reflectance data image of the standard to obtain a map of the modulation transfer function.

25. The apparatus of claim 24 where the signal processor generates a map of scattering and absorption properties from the map of the modulation transfer function.

26. The apparatus of claim 16 where the signal processor generates averages of scattering and absorption properties of the sample from the modulation transfer function.

27. The apparatus of claim 16 where repeated exposures of the sample by the source, repeated collection of data images by the camera, repeated Fourier transforming the data image, spatially filtering the transformed data image, and reconstructing the filtered transformed data image by the signal processor is performed for areas of different sizes to provide multiscale analysis of the sample.

28. An apparatus of determining subsurface optical properties of a sample of turbid media over an area of the sample with a single measurement comprising:

a homogenous standard with a periodic pattern having a known spatial Fourier spectrum;

a source to expose the sample and the standard to a periodic pattern of illumination;

a camera to receive the data image of the sample and a reflectance data image from the standard;

a signal processor to Fourier transform the data image of the sample, Fourier transform the reflectance data image of the standard, and ratio the transformed data image of the sample with the reflectance data image of the standard to obtain a map of the modulation transfer function.

29. The apparatus of claim 28 where the signal processor generates a map of scattering and absorption properties from the map of the modulation transfer function.

30. The apparatus of claim 28 where the signal processor generates averages of scattering and absorption properties of the sample from the modulation transfer function.

31. The apparatus of claim 28 where the source repeatedly exposes the sample and standard to a periodic pattern of illumination, the camera repeatedly receives the data image of the sample and reflectance data image of the standard;

and the signal processor repeatedly Fourier transforms the data image of the sample and the reflectance data image of the standard, and repeatedly ratios the transformed data image of the sample with the reflectance data image of the standard to repeatedly obtain a map of the modulation transfer function for areas of different sizes to provide multiscale analysis of the sample.