Doppler flow imaging using optical coherence tomography

• US 6,735,463 B2
• Filed: 12/21/1999
• Issued: 05/11/2004
• Est. Priority Date: 06/02/1997
• Status: Expired due to Term

• Current Assignee: Andrew Rollins, Joseph A. Izatt, Manish D. Kulkarni, Michael V. Sivak, Siavash Yazdanfar
• Original Assignee: Andrew Rollins, Joseph A. Izatt, Manish D. Kulkarni, Michael V. Sivak, Siavash Yazdanfar
• Inventors: Izatt, Joseph A., Yazdanfar, Siavash, Sivak, Michael V., Kulkarni, Manish D., Rollins, Andrew
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US09/468,674
• Publication Number:
  US 20030023153A1
• Time in Patent Office: 1,603 Days
• Field of Search: 600/473, 600/476, 600/479, 600/480, 600/477, 600/475, 600/309, 600/310, 600/407, 356/39, 356/345, 356/346, 250/356.1, 250/363.01, 250/370.08
• US Class Current: 600/476
• CPC Class Codes: A61B 5/0066 Optical coherence imaging
• CPC Class Codes: A61B 5/0073 by tomography, i.e. reconstruction of 3D images from 2D projections A61B5/0066 takes precedence
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G01B 2290/35 Mechanical variable delay line
• CPC Class Codes: G01B 2290/60 Reference interferometer, i.e. additional interferometer not interacting with object
• CPC Class Codes: G01B 9/02045 using the Doppler effect
• CPC Class Codes: G01B 9/02069 Synchronization of light source or manipulator and detector
• CPC Class Codes: G01B 9/02071 by measuring path difference independently from interferometer
• CPC Class Codes: G01B 9/02072 by calibration or testing of interferometer
• CPC Class Codes: G01B 9/02083 characterised by particular signal processing and presentation
• CPC Class Codes: G01B 9/02091 Tomographic interferometers, e.g. based on optical coherence

Abstract

A method for generating a velocity-indicating, tomographic image of a sample in an optical coherence tomography system includes the steps of (a) acquiring cross-correlation data from the interferometer; (b) generating a grayscale image from the cross-correlation data indicative of a depth-dependent positions of scatterers in the sample; (c) processing the cross-correlation data to produce a velocity value and location of a moving scatterer in the sample; (d) assigning a color to the velocity value; and (f) merging the color into the grayscale image, at a point in the grayscale image indicative of the moving scatterer'"'"'s location, to produce a velocity-indicating, tomographic image. Preferably a first color is assigned for a positive velocity value and a second color is assigned for a negative velocity value.

Claims

1. A method for generating a velocity-indicating, tomographic image of a sample in an optical coherence tomography system, the optical coherence tomography system including an interferometer, the method comprising the steps of:

acquiring cross-correlation data from the interferometer;

processing the cross-correlation data to produce a velocity value and a depth-dependent position of a scatterer in the sample; and

generating an image displaying a representation of the velocity and depth-dependent position of the scatterer in the sample.

2. A method of carrying optical coherence tomography, comprising

making multiple A-scans for each lateral position of a sample arm, calculate velocity estimates for each A-scan, and

average the velocity estimates together to produce a velocity estimate for a given lateral position of the sample arm.

3. A method for generating a tomographic image of a sample comprising the steps of:

(a) acquiring cross-correlation data from an interferometer; and

(b) generating a first image from the cross-correlation data, said first image being indicative of a velocity and a location of at least one moving scatterer in the sample.

4. The method of claim 3, wherein the first image is indicative of a velocity and a location of a plurality of scatterers within the sample.

5. The method of claim 3, wherein the cross-correlation data is acquired using an interferometer having a reference arm and a sample arm.

6. The method of claim 5, further comprising:

(c) generating a second image from the cross-correlation data, said second image being indicative of depth-dependent positions of at least one scatterer in the sample.

7. The method of claim 3, wherein the second image is indicative of depth-dependent positions of a plurality of scatterers in the sample.

8. The method of claim 6, wherein the first image is a grayscale image.

9. The method of claim 6, further comprising:

(d) merging the first image into the second image, at a point indicative of the location of the at least one moving scatterer, to produce a velocity-indicating, tomograpbic image.

10. The method of claim 9, further comprising:

.

(e) displaying at least one of the first image, the second image, and the velocity-indicating tomographic image.

11. The method of claim 9, wherein step (d) includes:

overlaying the second image onto the first image.

12. The method of claim 5, wherein step (b) includes:

repeating step (a) a plurality of times for a lateral position of the sample arm;

coherently demodulating the cross-correlation data at a Doppler shift frequency of the reference arm;

performing a time-frequency analysis step on the cross-correlation data to produce a power spectrum estimate comprised of a plurality of depth-dependent power spectrum values;

averaging the power spectrum estimates calculated from each repeat of step (a); and

calculating depth-dependent velocity values for each of the averaged power spectrum values.

13. The method of claim 6, wherein step (b) includes:

processing the cross-correlation data to produce a velocity value and a location of the at least one moving scatterer in the sample; and

assigning a color to the velocity value.

14. The method of claim 13, wherein:

the processing step includes coherently demodulating the cross-correlation data at a Doppler shift frequency of the reference arm; and

the assigning step includes assigning a first color for a positive velocity value and assigning a second color for a negative velocity value.

15. The method of claim 14, wherein the assigning step further includes:

setting at least one of the brightness, shade, density, hue, intensity, and saturation of the color according to a magnitude of the velocity value.

16. The method of claim 15, wherein the assigning step further includes:

selecting at least one of (i) a minimum positive threshold velocity value, (ii) a minimum negative threshold value (iii) a maximum positive saturation velocity value, and (iv) a maximum negative saturation velocity value;

wherein velocities larger than one of the maximum positive and negative saturation velocity values are assigned a color corresponding to the color of one of the positive and negative saturation velocity values; and

wherein the velocities smaller than one of the minimum positive and negative threshold velocity values are assigned to be transparent in color.

17. The method of claim 16, wherein the assigning step includes:

assigning at least one of a color and a shade to each velocity value; and

setting the brightness of each assigned color according to a magnitude of the velocity value.

18. The method of claim 13, wherein the processing step includes:

performing a time-frequency analysis on the cross-correlation data to extract spectral information from the cross-correlation data as a function of depth.

19. The method of claim 18, wherein the time frequency analysis step includes performing a short-time Fourier transform on the cross-correlation data.

20. The method of claim 18, wherein:

the time-frequency analysis step includes the step of introducing the cross-correlation data through a plurality of band-pass filters, one portion of the plurality of band-pass filters passing frequencies below a Doppler shift frequency of the reference arm and another portion of the plurality of band-pass filters passing frequencies above the Doppler shift frequency of the reference arm, the output of the plurality of band-pass filters representing a depth-dependent power spectrum; and

the processing step includes the step of calculating a centroid from the power spectrum, indicative of an estimate of mean scatter velocity, the estimate being the velocity value.

21. The method of claim 15, wherein:

the method further comprises the step of coherently demodulating the cross-correlation data at the Doppler shift frequency of the reference arm;

the time-frequency analysis step includes the step of introducing the demodulated cross-correlation data through a plurality of complex band-pass filters, one portion of the plurality of complex band-pass filters passing frequencies below a Doppler shift frequency of the reference arm and another portion of the plurality of complex band-pass filters passing frequencies above the Doppler shift frequency of the reference arm, the output of the plurality of complex band-pass filters representing a depth-dependent power spectrum;

the processing step includes the step of calculating a centroid from the power spectrum, indicative of an estimate of mean scatter velocity, the estimate being the velocity value; and

the assigning step includes the steps of assigning one color for a positive velocity value and assigning another color for a negative velocity value.

22. The method of claim 15, wherein:

the method further comprises the step of coherently demodulating the cross-correlation data at the Doppler shift frequency of the reference arm to generate in-phase cross-correlation data and quadrature cross-correlation data;

the time-frequency analysis step includes the steps of;

introducing the in-phase cross-correlation data through a first plurality of band-pass filters, one portion of the first plurality of band-pass filters passing frequencies below a Doppler shift frequency of the reference arm and another portion of the first plurality of band-pass filters passing frequencies above the Doppler shift frequency of the reference arm;

introducing the quadrature cross-correlation data through a second plurality of band-pass filters, one portion of the second plurality of band-pass filters passing frequencies below a Doppler shift frequency of the reference arm and another portion of the second plurality of band-pass filters passing frequencies above the Doppler shift frequency of the reference arm;

squaring the output of each of the first and second pluralities of band-pass filters;

summing the squares; and

taking a square root of the sum to produce a depth-dependent power spectrum;

the processing step includes the step of calculating a centroid from the power spectrum, indicative of an estimate of mean scatter velocity, the estimate being the velocity value; and

the assigning step includes the steps of assigning one color for a positive velocity value and assigning another color for a negative velocity value.

23. The method of claim 15, wherein:

the method further comprises the step of coherently demodulating the cross-correlation data at a frequency ƒ

_I;

the time-frequency analysis step includes the step of introducing the demodulated cross-correlation data through a plurality of complex band-pass filters, one portion of the plurality of complex band-pass filters passing frequencies below a Doppler shift frequency of the reference arm minus ƒ

_I and another portion of the plurality of complex band-pass filters passing frequencies above the Doppler shift frequency of the reference arm minus ƒ

_I, the output of the plurality of complex band-pass filters representing a depth-dependent power spectrum;

the processing step includes the step of calculating a centroid from the power spectrum, indicative of an estimate of mean scatter velocity, the estimate being the velocity value; and

the assigning step includes the steps of assigning one color for a positive velocity value and assigning another color for a negative velocity value.

24. The method of claim 18, wherein:

the method further comprises the step of coherently demodulating the cross-correlation data at a frequency ƒ

_I to generate in-phase cross-correlation data and quadrature cross-correlation data;

the time-frequency analysis step includes the steps of;

introducing the in-phase cross-correlation data through a first plurality of band-pass filters, one portion of the first plurality of band-pass filters passing frequencies below a Doppler shift frequency of the reference arm minus ƒ

_I and another portion of the first plurality of band-pass filters passing frequencies above the Doppler shift frequency of the reference arm minus ƒ

_I,

introducing the quadrature cross-correlation data through a second plurality of band-pass filters, one portion of the second plurality of band-pass filters passing frequencies below a Doppler shift frequency of the reference arm minus F_I and another portion of the second plurality of band-pass filters passing frequencies above the Doppler shift frequency of the reference arm minus ƒ

_I,

squaring the output of each of the first and second pluralities of band-pass filters,

summing the squares, and

talking a square root of the sum to produce a depth-dependent power spectrum;

the processing step includes the step of calculating a centroid from the power spectrum, indicative of an estimate of mean scatter velocity, the estimate being the velocity value; and

the assigning step includes the steps of assigning one color for a positive velocity value and assigning another color for a negative velocity value.

25. The method of claim 19, wherein:

the time-frequency analysis step is performed upon a plurality of time-windows of the cross correlation data to produce a corresponding plurality of depth-dependent power spectrum values;

the processing step further includes the step of calculating depth-dependent velocity values for each of the power spectrum values; and

the assigning step is performed for each of the plurality of depth-dependent velocity values.

26. The method of claim 19, wherein:

the time-frequency analysis step is performed upon a plurality of time-windows of the cross-correlation data to produce a corresponding plurality of depth-dependent power spectrum values; and

the processing step further includes calculating depth-dependent velocity values for each of the power spectrum values, the velocity value having the greatest magnitude being indicative of an estimate of mean scatter velocity.

27. The method of claim 25, wherein the calculating step includes the step of calculating a centroid, indicative of an estimate of mean scatter velocity, for each of the power spectrum values.

28. The method of claim 27, wherein the plurality of time-windows overlap one another.

29. The method of claim 25, wherein the calculating step includes:

determining the location of a Doppler spectral peak within the power spectrum values; and

calculating a centroid, indicative of mean scatter velocity, for each of the power spectrum values associated with frequencies distributed symmetrically about the Doppler spectral peak.

30. The method of claim 13, wherein:

step (a) and the processing step are repeated a plurality of times for a lateral position of the sample arm;

the method includes the step of averaging the velocity values produced in the processing steps to generate an average velocity value; and

the assigning step includes the step of assigning a color to the average velocity value.

31. The method of claim 13, wherein:

step (a) includes the step of repeatedly acquiring cross-correlation data at a predetermined range of depths, producing a plurality of cross-correlation data readings at the predetermined range of depths; and

the processing step includes the step of performing a time-frequency analysis on the plurality of cross-correlation readings to obtain at least one velocity estimate at the predetermined range of depths.

32. The method of claim 13, wherein:

step (a) includes the step of repeatedly acquiring cross-correlation data for a lateral position of the sample arm; and

the processing step includes the step of performing a time-frequency analysis on the plurality of cross-correlation readings to obtain at least one velocity estimate at the lateral position of the sample arm.

33. The method of claim 13, wherein:

step (a) includes repeatedly acquiring cross-correlation data at a predetermined range of depths for a lateral position of to sample arm;

the processing step includes the step of performing a time-frequency analysis on the plurality of cross-correlation readings to obtain at least one velocity estimate at the predetermined range of depths and lateral position.

34. The method of claim 13, wherein the processing step includes:

digitizing the cross-correlation data; and

performing a time-frequency analysis on the digitized cross-correlation data.

35. A method of generating a real-time velocity-indicating image of a sample in an optical coherence tomography system, the optical coherence tomography system including an interferometer having a reference arm and a sample arm, the method comprising the steps of:

(a) acquiring cross-correlation data from the interferometer;

(b) coherently demodulating the cross-correlation data at a Doppler shift frequency of the reference arm, said demodulating generating an in-phase demodulated output and a quadrature demodulated output;

(c) from the in-phase and quadrature demodulated outputs, calculating a central velocity estimate and a flow turbulence estimate for at least one moving scatterer in the sample;

(d) calculating a magnitude-only OCT image from the in-phase and quadrature demodulated outputs; and

(e) merging the central velocity estimate and the flow turbulence estimate with the magnitude-only OCT image.

36. The method of claim 35, wherein step (e) includes:

calculating real and imaginary components of a complex auto-correlation of the in-phase and quadrature demodulated outputs;

calculating the central velocity estimate from the real component of the complex auto-correlation; and

calculating the turbulence estimate from the imaginary component of the complex auto-correlation.

37. A method of generating a real-time velocity-indicating image of a sample in an optical coherence tomography system, the optical coherence tomography system including an interferometer having a reference arm and a sample arm, the method comprising the steps of:

(a) acquiring cross-correlation data from the interferometer;

(b) calculating a central velocity estimate and a flow turbulence estimate for at least one moving scatterer in the sample;

(c) calculating a magnitude-only OCT image from the in-phase and quadrature demodulated outputs; and

(d) merging the central velocity estimate and the flow turbulence estimate with the magnitude-only OCT image.

38. The method of claim 37, wherein calculating the central velocity estimate includes:

eliminating amplitude variation from the cross-correlation data to provide a fundamental sinusoidal frequency signal component;

splitting the fundamental sinusoidal frequency signal component into two paths, one of said paths being phase shifted by 90°

; and

passing the two paths through a phase detector.

39. An optical coherence tomography system comprising:

an interferometer including a light source, a sample arm and a reference arm, the interferometer generating a cross-correlation data output of a sample in the sample arm; and

a data processing system, operatively coupled to the interferometer, for processing the cross-correlation data to generate a first image from the cross-correlation data indicative of depth dependent positions of scatterers in the sample, and for processing the cross-correlation data to generate a second image from the cross-correlation data indicative of a velocity value and a location of at least one moving scatterer in the sample.

40. The optical coherence tomography system of claim 39, wherein the first image is a grayscale image.

41. The optical coherence tomography system of claim 39, wherein the data processing system includes:

means for assigning a color to the velocity value.

42. The optical coherence tomography system of claim 41, wherein the data processing system includes:

means for merging the second image into the first image at a point in the first image indicative of the location of the at least one moving scatterer.

43. The optical coherence tomography system of claim 39, wherein the data processing system includes:

a demodulation device, operatively coupled to the output of the interferometer;

a Fourier transform device, operatively coupled to the output of the demodulation device; and

a velocity estimation device operatively coupled to the output of the Fourier transform device.

44. The optical coherence tomography system of claim 43, further comprising:

a calibration interferometer operatively coupled to the output of the demodulation device for synchronizing processing of the cross-correlation data from the interferometer according to fluctuations in the reference arm.

45. The optical coherence tomography system of claim 39, wherein the data processing system includes:

a plurality of band-pass filters, operatively coupled to the output of the interferometer, one portion of the plurality of band-pass filters passing frequencies below a Doppler shift frequency of the reference arm and another portion of the plurality of band-pass filters passing frequencies above the Doppler shift frequency of the reference arm; and

a velocity estimation device operatively coupled to the output of the plurality of band-pass filters.

46. The optical coherence tomography system of claim 39, wherein the data processing system includes:

a demodulation device, operatively coupled to the output of the interferometer;

a plurality fo complex band-pass filters, operatively coupled to the output of the demodulation device, one portion of the plurality of complex band-pass filters passing frequencies below a Doppler shift frequency of the reference arm and another portion of the plurality of complex band-pass filters passing frequencies above the Doppler shift frequency of the reference arm; and

a velocity estimation device operatively coupled to the output of the plurality of band-pass filters.

47. The optical coherence tomography system of claim 39, wherein the data processing system includes:

a demodulation device, operatively coupled to the output of the interferometer, having an in-phase data output and a quadrature data output;

a first plurality of band-pass filters, operatively coupled to the in-phase data output of the demodulation device, one portion of the first plurality of band-pass filters passing frequencies below a Doppler shift frequency of the reference arm and another portion of the first plurality of band-pass filters passing frequencies above the Doppler shift frequency of the reference arm;

a second plurality of band-pass filters, operatively coupled to the quadrature data output of the demodulation device, one portion of the second plurality of band-pass filters passing frequencies below a Doppler shift frequency of the reference arm and another portion of the second plurality of band-pass filters passing frequencies above the Doppler shift frequency of the reference arm; and

a velocity estimation device operatively coupled to the output of the first and second pluralities of band-pass filters.

48. The optical coherence tomography system of claim 39, wherein the data processing system includes:

a demodulator, operatively coupled to the output of the interferometer, for simultaneously demodulating cross-correlation data at a plurality of frequencies.

49. The optical coherence tomography system of claim 48, wherein the demodulator includes:

a waveform synthesizer which generates a reference waveform as a sum of a desired number of sinusoids at a plurality of frequencies;

a mixer having two inputs operatively coupled to the waveform synthesizer and the output of the interferometer; and

a low-pass filter, operatively coupled to an output of the mixer, said low-pass filter having a cutoff frequency.