Sprectroscopic and time-resolved optical methods and apparatus for imaging objects in turbed media

• US 6,665,557 B1
• Filed: 06/20/2000
• Issued: 12/16/2003
• Est. Priority Date: 12/01/1999
• Status: Expired due to Fees

• Current Assignee: City College of New York
• Original Assignee: The Research Foundation of State University of New York
• Inventors: Gayen, Swapan Kumar, Zevallos, Manuel E., Alfano, Robert R.
• Primary Examiner(s): SHAW, SHAWNA JEANNINE
• Application Number:
  US09/597,505
• Time in Patent Office: 1,274 Days
• Field of Search: 600/473, 600/476, 600/310, 600/322, 600/323, 600/328, 600/475, 356/40
• US Class Current: 600/473
• CPC Class Codes: A61B 5/0091 for mammography
• CPC Class Codes: A61B 5/4312 Breast evaluation or disorder diagnosis A61B5/0091 takes precedence

Abstract

Method and apparatus for imaging objects in turbid media. In one embodiment, the method comprises illuminating at least a portion of the turbid medium with substantially monochromatic light of at least two wavelengths in the 600-1500 nm spectral range. A first of the at least two wavelengths is equal to a resonance wavelength for an optical property of an object in the illuminated portion of the turbid medium but is not equal to a resonance wavelength for the turbid medium. A second of the at least two wavelengths is not equal to a resonance wavelength for either the object or the turbid medium. Light emergent from the turbid medium following each of the foregoing illuminations comprises a ballistic component, a snake component and a diffuse component. A direct shadowgram image may be obtained by preferentially passing from the emergent light, following each illumination. the ballistic and snake components thereof and detecting the preferentially passed light. Alternatively, an inverse reconstruction image may be obtained by determining, following each illumination, the intensity of the diffuse component at a plurality of points in time and then using these pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium. An image of the object with higher contrast and better quality may be obtained by using the ratio or difference of the images recorded with resonant light and non-resonant light.

Claims

1. A method of imaging an object in medium, wherein said object is a tumor and said turbid medium is a tissue, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, said first wavelength being selected from the group consisting of a wavelength in the range of 940-1010 nm, a wavelength in the range of 1120-1240 nm, and a wavelength in the range of 1400-1500 nm;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different for said optical property and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) using at least a portion of the light emergent from the turbid medium to form an image of the object in the turbid medium.

2. The method as claimed in claim 1 wherein the light emergent from the turbid medium comprises a ballistic component, a snake component and a diffuse component and wherein said using step comprises preferentially selecting from the emergent light the ballistic and snake components thereof, detecting the preferentially selected light, and forming an image of the object with the detected preferentially selected light.

3. The method as claimed in claim 2 wherein said substantially monochromatic light of said first wavelength is laser light obtained from a laser selected from the group consisting of Cr⁺⁴:

forsterite, Cr;

YAG, Cr;

Ca₂GeO₄, Ti;

sapphire, alexandrite, Cr⁺³;

LiCaAlF₆, Cr⁺³;

LiSrAlF₆, Nd;

YAG, gas, dye, solid-state, color center, and semi-conductor lasers.

4. The method as claimed in claim 2 wherein said substantially monochromatic light of said first wavelength is a pulse of light.

5. The method as claimed in claim 2 wherein said substantially monochromatic light of said first wavelength is continuous light.

6. The method as claimed in claim 2 wherein said preferential selecting step comprises gating the emergent light with a gate selected from the group consisting of a space gate, a Fourier gate, a time gate, a time/space gate, a polarization gate, a confocal gate a nonlinear optical gate, a coherence gate and a combination thereof.

7. The method as claimed in claim 6 wherein said gate is a time gate selected from the group consisting of an electronic time gate, an optical Kerr gate, a second harmonic generation cross correlation gate, a four-wave mixing gate, an upconversion gate and a combination thereof.

8. The method as claimed in claim 2 wherein said detecting step comprises detecting the preferentially selected light using a light detector selected from the group consisting of a CCD camera, a near-infrared area camera, a one-dimensional array of detectors, photodiodes, photomultiplier tubes, and a streak camera.

9. The method as claimed in claim 1 wherein said illuminating and detecting steps are performed in a backscattering geometry.

10. A method of imaging an object in a turbid medium, wherein said object is a tumor and said turbid medium is a tissue, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein said substantially monochromatic light of said first wavelength is amplitude-modulated light and wherein the light emergent from the turbid medium comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different for said optical property and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) using at least a portion of the light emergent from the turbid medium to form an image of the object in the turbid medium, wherein said using step comprises preferentially selecting from the emergent light the ballistic and snake components thereof, detecting the preferentially selected light, and forming an image of the object with the detected preferentially selected light.

11. A method of imaging an object in a turbid medium, wherein the turbid medium is a human body part, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium comprises a ballistic component, a snake component and a diffuse component, said first wavelength being selected from the group consisting of a wavelength in the range of 940-1010 nm, a wavelength in the range of 1120-1240 nm, and a wavelength in the range of 1400-1500 nm;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different for said optical property and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) using at least a portion of the light emergent from the turbid medium to form an image of the object in the turbid medium; and

(d) wherein said using step comprises preferentially selecting from the emergent light the ballistic and snake components thereof, detecting the preferentially selected light, and forming an image of the object with the detected preferentially selected light.

12. A method of imaging an object in a turbid medium, wherein the turbid medium is a human body part selected from the group consisting of the breast, the brain, the bladder, the gastrointestinal tract, the prostate, the cervix, the colon, and the eye, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium comprises a ballistic component, a snake component and a diffuse component, said first wavelength being selected from the group consisting of a wavelength in the range of 940-1010 nm a wavelength in the range of 1120-1240 nm and a wavelength in the range of 1400-1500 nm;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different for said optical property and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) using at least a portion of the light emergent from the turbid medium to form an image of the object in the turbid medium; and

(d) wherein said using step comprises preferentially selecting from the emergent light the ballistic and snake components thereof, detecting the preferentially selected light, and forming an image of the object with the detected preferentially selected light.

13. A method of imaging an object in a turbid medium, wherein the turbid medium is the breast, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium comprises a ballistic component, a snake component and a diffuse component, said first wavelength being selected from the group consisting of a wavelength in the range of 940-1010 nm, a wavelength in the range of 1120-1240 nm, and a wavelength in the range of 1400-1500 nm;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different for said optical property and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) using at least a portion of the light emergent from the turbid medium to form an image of the object in the turbid medium; and

(d) wherein said using step comprises preferentially selecting from the emergent light the ballistic and snake components thereof, detecting the preferentially selected light, and forming an image of the object with the detected preferentially selected light.

14. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different, wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object and wherein said first wavelength is selected from the group consisting of a wavelength in the range of 940-1010 nm, a wavelength in the range of 1120-1240 nm, and a wavelength in the range of 1400-1500 nm;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium.

15. The method as claimed in claim 14 wherein the light emergent from the turbid medium following illumination with each of said substantially monochromatic light of said first wavelength and said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component and wherein said method further comprises, after step (a) and before step (c), the step of preferentially selecting from the emergent light the ballistic and snake components thereof and also comprises, after step (d) and before step (f), the step of preferentially selecting from the emergent light the ballistic and snake components thereof, and wherein each of said detecting steps comprises detecting the preferentially selected light.

16. The method as claimed in claim 15 wherein said using step comprises using a difference of the resonant and non-resonant images to form an image of the object in the turbid medium.

17. The method as claimed in claim 14 wherein step (a) is performed using a light source whose wavelength output is variable and wherein step (d) is also performed using said light source.

18. The method as claimed in claim 14 wherein the light emergent from the turbid medium following illumination with each of said substantially monochromatic light of said first wavelength and said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component, wherein each of said detecting steps comprises determining the intensity of the diffuse component at a plurality of points in time and wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium.

19. The method as claimed in claim 18 wherein the image is a 2-D image.

20. The method as claimed in claim 18 wherein said illuminating and detecting steps are performed in a backscattering geometry.

21. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) preferentially selecting from the emergent light the ballistic and snake components thereof;

(d) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(e) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(f) preferentially selecting from the emergent light the ballistic and snake components thereof;

(g) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(h) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(i) using the light detected in step (d) to form a resonant image and that detected in step (h) to form a non-resonant image of the object in the turbid medium, wherein said using step comprises using a ratio of the resonant and non-resonant images to form an image of the object in the turbid medium.

22. A method of imaging an object in a turbid medium, wherein the turbid medium is a human body part, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium.

23. A method of imaging an object in a turbid medium, wherein the image is a 3-D image, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium, wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form a 3-D image of the object in the turbid medium.

24. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium, wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium;

(h) wherein said illuminating and detecting steps are performed in a transmission geometry.

25. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time and at a plurality of locations around the turbid medium;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time and at a plurality of locations around the turbid medium; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium, wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium.

26. A method of imaging an object in a turbid medium, wherein the turbid medium is a human body part, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium;

(h) wherein the light emergent from the turbid medium following illumination with each of said substantially monochromatic light of said first wavelength and said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component, wherein each of said detecting steps comprises determining the intensity of the diffuse component at a plurality of points in time and wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium.

27. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium;

(h) wherein the turbid medium is a human breast, wherein one and only one of said first wavelength and said second wavelength is a wavelength selected from the group consisting of 950-980 nm and 1150-1350 nm, wherein the light emergent from the turbid medium following illumination with each of said substantially monochromatic light of said first wavelength and said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component, wherein each of said detecting steps comprises determining the intensity of the diffuse component at a plurality of points in time and wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium.

28. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time, wherein said determining step comprises obtaining a sequence of 2-D time-sliced images using different temporal slices of the transmitted light using the ballistic, snake and diffuse photons, said different temporal slices being obtained by positioning the time gate at different points in time;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time, wherein said determining step comprises obtaining a sequence of 2-D time-sliced images using different temporal slices of the transmitted light using the ballistic, snake and diffuse photons, said different temporal slices being obtained by positioning the time gate at different points in time; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium, wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium.

29. The method as claimed in claim 28 wherein the reconstructed image is a 3-D image.

30. The method as claimed in claim 29 wherein the 3-D images are reconstructed using light of fingerprint wavelengths that are resonant with certain optical properties of the object enabling construction of a 3-D map of the said optical property, such as use of light around 1200 nm to obtain the adipose tissue distribution in the breast or an appropriate wavelength to obtain the proliferation of certain cancer in the breast.

31. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time, wherein said determining step comprises obtaining a sequence of 2-D time-sliced images using different temporal slices of the back-propagating light including the ballistic, snake and diffuse photons, said different temporal slices being obtained by positioning the gate at different points in time;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength, wherein said detecting step comprises determining the intensity of the diffuse component at a plurality of points in time wherein said determining step comprises obtaining a sequence of 2-D time-sliced images using different temporal slices of the back-propagating light including the ballistic, snake and diffuse photons, said different temporal slices being obtained by positioning the gate at different points in time; and

(p) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium.

32. The method as claimed in claim 31 wherein the reconstructed image is a 3-D image.

33. The method as claimed in claim 32 wherein the 3-D images are reconstructed using light of fingerprint wavelengths that are resonant with certain optical properties of the object enabling construction of a 3-D map of said optical property, such as use of 1200 nm light to obtain the adipose tissue distribution in the breast, or an appropriate wavelength to obtain the proliferation of certain cancer in the breast.

34. The method as claimed in claim 33 wherein 3-D maps are obtained using a resonant and a non-resonant wavelength, and a ratio of the two is used to enhance image quality and contrast.

35. The method as claimed in claim 33 wherein 3-D maps are obtained using a resonant and a non-resonant wavelength, and a difference of the two is used to enhance image quality and contast.

36. The method as claimed in claim 35 wherein the fingerprint wavelength is in the 670-790 nm range, highlighting the deoxyhemoglobin distribution.

37. The method as claimed in claim 35 wherein the fingerprint wavelength is in the 810-900 nm range, highlighting the oxyhemoglobin distribution.

38. A method of imaging an object in a turbid medium, wherein the turbid medium is the prostate, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium;

(h) wherein each of said detecting steps comprises determining the intensity of the diffuse component at a plurality of points in time by obtaining a sequence of 2-D time-sliced images using different temporal slices of the back-propagating light including the ballistic, snake and diffuse photons, said different temporal slices being obtained by positioning the gate at different points in time and wherein said using step comprises using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium, said image being a 3-D image, said 3-D image being reconstructed using a difference of wavelengths that are resonant and non-resonant with certain optical properties of the object enabling construction of a 3-D map of said optical property.

39. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein said first wavelength is in the 670-790 nm range;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength said illuminated portion of the turbid medium comprising the object, wherein said second wavelength is 800 nm;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium, and wherein the difference image highlights the deoxyhemoglobin distribution.

40. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein said first wavelength is in the 810-900 nm range;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength said illuminated portion of the turbid medium comprising the object, wherein said second wavelength is 800 nm;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium, and wherein the difference image highlights the oxyhemoglobin distribution.

41. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in step (c) to form a resonant image and that detected in step (f) to form a non-resonant image of the object in the turbid medium;

(h) wherein said first wavelength is in the 940-1010 nm range or in the 1400-1500 nm range, wherein said second wavelength is outside the two ranges, and wherein the difference image highlights the water distribution and thus enables detection of lesions that involve changes in the water content of the tissue.

42. An apparatus for imaging an object in a turbid medium, said apparatus comprising:

(a) first illuminating means for illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein said first wavelength is selected from the group consisting of a wavelength in the range of 940-1010 nm, a wavelength in the range of 1120-1240 nm and a wavelength in the range of 1400-1500 nm;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) second illuminating means for illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object;

(d) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(e) means for detecting at least a portion of the light emergent from the turbid medium following illumination by said first illuminating means and following illumination by said second illuminating means; and

(f) means for using the light detected by said detecting means to form an image of the object in the turbid medium.

43. The apparatus as claimed in claim 42 wherein the light emergent from the turbid medium following illumination with each of said substantially monochromatic light of said first wavelength and said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component and wherein said apparatus further comprises means for preferentially selecting from the emergent light for transmission to said detecting means the ballistic and snake components of the emergent light.

44. An apparatus for imaging an object in a turbid medium, said apparatus comprising:

(a) first illuminating means for illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength said illuminated portion of the turbid medium comprising the object wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) second illuminating means for illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(d) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(e) means for detecting at least a portion of the light emergent from the turbid medium following illumination by said first illuminating means and following illumination by said second illuminating means, wherein said detecting means comprises means for determining the intensity of the diffuse component at a plurality of points in time; and

(f) means for using the light detected by said detecting means to form an image of the object in the turbid medium, wherein said using means comprises means for using said pluralities of intensity determinations and a mathematical inversion algorithm to form an image of the object in the turbid medium.

45. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein said first wavelength is selected from the group consisting of a wavelength in the range of 940-1010 nm a wavelength in the range of 1120-1240 nm and a wavelength in the range of 1400-1500 nm;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength;

(d) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object;

(e) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(f) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength; and

(g) using the light detected in steps (c) and (f) to form an image of the object in the turbid medium.

46. The method as claimed in claim 45 wherein the light emergent from the turbid medium following illumination with each of said substantially monochromatic light of said first wavelength and said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component and wherein said method further comprises, after step (a) and before step (c), the step of preferentially selecting from the emergent light the ballistic and snake components thereof and also comprises, after step (d) and before step (f), the step of preferentially selecting from the emergent light the ballistic and snake components thereof, and wherein each of said detecting steps comprises detecting the preferentially selected light.

47. The method as claimed in claim 46 wherein said using step comprises using a difference of the light detected in steps (c) and (f) to form an image of the object in the turbid medium.

48. A method of imaging an object in a turbid medium, said method comprising the steps of:

(a) illuminating at least a portion of the turbid medium with substantially monochromatic light of a first wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said first wavelength comprises a ballistic component, a snake component and a diffuse component;

(b) wherein each of the turbid medium and the object has a resonance wavelength for an optical property, wherein the respective resonance wavelengths for the turbid medium and the object are different and wherein said substantially monochromatic light of said first wavelength is equal in wavelength to the resonance wavelength for said optical property of one of the turbid medium and the object;

(c) preferentially passing from the emergent light the ballistic and snake components thereof;

(d) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said first wavelength, wherein said detecting comprises detecting the preferentially passed light;

(e) illuminating at least a portion of the turbid medium with substantially monochromatic light of a second wavelength, said illuminated portion of the turbid medium comprising the object, wherein the light emergent from the turbid medium following illumination with said substantially monochromatic light of said second wavelength comprises a ballistic component, a snake component and a diffuse component;

(f) wherein said substantially monochromatic light of said second wavelength is not equal in wavelength to the resonance wavelength for said optical property of either the turbid medium or the object;

(g) preferentially passing from the emergent light the ballistic and snake components thereof;

(h) detecting at least a portion of the light emergent from the turbid medium in response to illumination with said substantially monochromatic light of said second wavelength, wherein said detecting comprises detecting the preferentially passed light; and

(i) using the light detected in steps (d) and (h) to form an image of the object in the turbid medium, wherein said using step comprises using a ratio of the light detected in steps (d) and (h) to form an image of the object in the turbid medium.