In vivo structural and flow imaging

1. A method of imaging, comprising:

scanning a sample with an incident beam from a light source;

detecting one or more spectral interference signals from the sample and a reference mirror;

modulating the one or more spectral interference signals at a constant frequency while scanning the sample in a cross-sectional direction (B scan); and

obtaining at least one image of the sample from the modulated one or more spectral interference signals, the at least one image including a full range structural image of the sample or a separated structure/flow image of the sample.

2. The method of claim 1 , wherein said modulating comprises modulating the one or more spectral interference signals at a constant frequency.

3. The method of claim 1 , wherein said obtaining at least one image comprises:

separating structure information of the sample and flow information of the sample; and

obtaining a first image and a second image, the first image including the structure information and the second image including the flow information.

4. The method of claim 1 , wherein said scanning comprises scanning the sample with the incident beam in x and λ directions to obtain a first two-dimensional (2-D) spectral interferogram data set, said x direction including one or more columns and said λ direction including one or more rows.

5. The method of claim 4 , wherein said obtaining the at least one image comprises:

calculating discrete analytic functions, along the x-direction and row by row in the λ direction of the first 2-D data set, to obtain a complex valued function of the first 2-D data set; and

converting the complex valued function of the first 2-D data set from a spectral domain to a time domain, column by column in the x direction, to obtain the at least one image of the sample.

6. The method of claim 5 , wherein said calculating discrete analytic functions comprises Hilbert-transforming the first 2-D data set.

7. The method of claim 5 , wherein said converting the complex valued function of the first 2-D data set comprises Fourier-transforming the complex valued function of the first 2-D data set.

8. The method of claim 4 , further comprising scanning the sample with the incident beam in the x and λ directions along y direction to obtain a second 2-D spectral interferogram data set, said first and second 2-D data sets forming a three-dimensional spectral interferogram data set.

9. The method of claim 1 , wherein said obtaining at least one image comprises obtaining the separated structure/flow image of the sample, and wherein the flow image of the sample is indicative of a direction of flow of the sample.

10. The method of claim 9 , wherein a collection of all the B scans of the sample when the reference mirror moves toward the incident beam gives the flow away from the incident beam direction.

11. The method of claim 9 , wherein a collection of all the B scans of the sample when the mirror moves away from the incident beam gives the flow toward the incident beam direction.

12. The method of claim 1 , wherein the modulating comprises modulating the one or more spectral interference signals by a linear translation of the reference mirror.

13. The method of claim 1 , wherein the modulating comprises modulating the one or more spectral interference signals by offsetting the incident beam.

14. The method of claim 1 , wherein the modulating comprises modulating the one or more spectral interference signals by stretching an optical fiber providing the incident beam.

15. The method of claim 1 , wherein the modulating at a constant frequency comprises modulating at a frequency having a constant value and a constant polarity.

16. A method for imaging, comprising:

scanning a flowing sample with an incident beam from a light source;

detecting one or more spectral interference signals from the flowing sample and a reference mirror;

modulating digitally the one or more spectral interference signals from the flowing sample at a constant frequency;

obtaining an image from the modulated one or more spectral interference signals, the image indicative of a direction of flow of the flowing sample.

17. The method of claim 16 , wherein the digital modulation comprises:

obtaining a cross-sectional data point from a flowing sample at a dimension of (x,λ), h(λ,x), at any one time;

performing an interpolation for h(λ,x) from λ space to k space along the λ dimension column by column to obtain h(k,x);

calculating a Fourier transform column by column along the λ dimension, resulting in H(z,x) that possesses positive and negative spaces in z;

forming two functions from H(z,x) forcing negative space of H(z,x) equal to zero to form H 1 (z,x), and forcing positive space of H(z,x) equal to zero to form H 2 (z,x); modulating H 1 (z,x) and H 2 (z,x) digitally with a frequency of f 0 along the x dimension to obtain modulated signals H 1 ′(z,x) and H 2 ′(z,x);

performing an inverse Fourier transformation to H 1 ′(z,x) and H 2 ′(z,x) along the z dimension and take only real parts or imaginary parts of results that form h 1 (k,x) and h 2 (k,x);

calculating an analytic function along the x dimension row by row in the λ dimension to obtain a complex valued function of data from the inverse Fourier transformation operation resulting in ĥ 1 (k,x) and ĥ 2 (k,x);

performing a Fourier transformation of ĥ 1 (k,x) and ĥ 2 (k,x) along the k dimension to obtain complex optical images, H 1 (z,x) and H 2 (z,x) and obtain magnitudes of results; and

separating |H 1 (z,x)| and |H 2 (z,x)| at zero delay line (z=0) to form four images of the flowing sample.

18. The method of claim 17 , wherein two of said four images represent structural images of the flowing sample.

19. The method of claim 17 , wherein one of said four images represents a flow image indicative of flow moving toward an incident probe beam.

20. The method of claim 17 , wherein one of said four images represents a flow image indicative of flow moving away from an incident probe beam.

21. The method of claim 16 , wherein the digital modulation comprises:

obtaining a cross-sectional data point from a flowing sample at a direction of (x,λ), h(λ,x), at any one time;

performing an interpolation for h(λ,x) from λ space to k space along an λ direction column by column to obtain h(k,x);

calculating a Fourier transform row by row along an x direction, resulting in H(k,f) having positive and negative spaces in f;

forming three functions from H(k,f) by:

multiplying a first rectangle function t 1 (k,f) to form H 1 (k,f);

multiplying a second rectangle function t 2 (k,f) to form H 2 (k,f); and

multiplying a third rectangle function t 3 (k,f) to form H 3 (k,f);

calculating analytic functions along an f direction row by row in k direction to obtain a complex valued function of the three functions resulting in ĥ 1 (k,x), ĥ 2 (k,x), and ĥ 3 (k,x);

performing a Fourier transformation of ĥ 1 (k,x), ĥ 2 (k,x), and ĥ 3 (k,x) along the k direction to obtain the complex optical images, H 1 (z,x), H 2 (z,x), and H 3 (z,x) and obtain magnitudes of the images; and

separating |H 1 (z,x)|, |H 2 (z,x)| and |H 3 (z,x)|at zero delay line (z=0) to form six images of the flowing sample.

22. The method of claim 21 , wherein two of said six images represent structural images of the flowing sample.

23. The method of claim 21 , wherein two of said six images represent flow images of the sample without indication of flow directions.

24. The method of claim 21 , wherein one of said six images represents a flow image indicative of flow moving toward an incident probe beam.

25. The method of claim 21 , wherein one of said six images represents a flow image indicative of flow moving away from an incident probe beam.

26. A system for in vivo imaging, comprising:

an optical coherence tomography apparatus; and

one or more processors coupled to the apparatus and adapted to cause the apparatus to:

scan a sample with an incident beam from a light source;

detect one or more spectral interference signals from the sample and a reference mirror;

modulate the one or more spectral interference signals by a linear translation of a reference mirror while scanning the sample in a cross-sectional direction; and

obtain at least one image of the sample from the modulated one or more spectral interference signals, the at least one image including a full range structural image of the sample or a separated structure/flow image of the sample.

27. The system of claim 26 , wherein the optical coherence tomography apparatus includes a reference arm including a mirror mounted on a modulating device for modulating the one or more spectral interference signals.

28. The system of claim 26 , wherein the one or more processors are adapted to cause the apparatus to scan the sample with the incident beam in x and λ directions to obtain a first two-dimensional (2-D) spectral interferogram data set, said x direction including one or more columns and said λ direction including one or more rows.

29. The system of claim 28 , wherein the one or more processors are adapted to cause the apparatus to obtain the at least one image by:

calculating discrete analytic functions, along the x-direction and row by row in the λ direction of the first 2-D data set, to obtain a complex valued function of the first 2-D data set; and

converting the complex valued function of the first 2-D data set from a spectral domain to a time domain, column by column in the x direction, to obtain the at least one image of the sample.