Image enhancement in optical coherence tomography using deconvolution

• US 5,994,690 A
• Filed: 03/17/1998
• Issued: 11/30/1999
• Est. Priority Date: 03/17/1997
• Status: Expired due to Term

• Current Assignee: Joseph A. Izatt, Manish D. Kulkarni, Michael V. Sivak
• Original Assignee: Joseph A. Izatt, Manish D. Kulkarni, Michael V. Sivak
• Inventors: Izatt, Joseph A., Sivak, Michael V., Kulkarni, Manish D.
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/040,128
• Time in Patent Office: 623 Days
• Field of Search: 250/216, 250/559.4, 250/559.39, 250/208.1, 250/363.02, 250/363.04, 356/345, 356/346, 356/347, 378/4, 378/36, 378/37
• US Class Current: 250/216
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G01B 2290/35 Mechanical variable delay line
• CPC Class Codes: G01B 9/02002 using two or more frequencies
• CPC Class Codes: G01B 9/02007 Two or more frequencies or sources used for interferometric measurement using only beat G01B9/02003
• CPC Class Codes: G01B 9/02069 Synchronization of light source or manipulator and detector
• 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
• CPC Class Codes: G01N 21/4795 spatially resolved investigating of object in scattering medium in vivo A61B

Abstract

The present invention provides an improved optical coherence tomography system and involves estimating the impulse response (which is indicative of the actual reflecting and scattering sites within a tissue sample) from the output interferometric signal of an interferometer according to the following steps: (a) acquiring auto-correlation data from the interferometer system; (b) acquiring cross-correlation data from the interferometer system having the biological tissue sample in the sample arm; and (c) processing the auto-correlation data and the cross correlation data to produce an optical impulse response of the tissue. The impulse response may be obtained from the cross-correlation and auto-correlation data by: (d) obtaining an auto-power spectrum from the auto-correlation data by performing a Fourier transform on the auto-correlation data; (e) obtaining a cross-power spectrum from the cross-correlation data by performing a Fourier transform on the cross-correlation data; (f) obtaining a transfer function of the LSI system by taking a ratio of the cross-power spectrum to the auto-power spectrum; and (g) obtaining the optical impulse response of the LSI system by performing an inverse-Fourier transform on the transfer function. Preferably, coherent demodulation is used in combination with the above deconvolution technique to resolve closely-spaced reflecting sites in the sample. By utilizing both the magnitude and phase data of the demodulated interferometric signals, the OCT system of the present invention is able to distinguish between closely spaced reflecting sites within the sample.

Claims

1. A method for generating interferogram data of a sample in an optical coherence tomography system, the optical coherence tomography system including a main interferometer having an optical radiation source and a sample arm, the method comprising the steps of:

acquiring auto-correlation data for the main interferometer;

acquiring cross-correlation data from the main interferometer with the sample in the sample arm; and

processing the auto-correlation data and the cross-correlation data to produce an optical impulse response of the tissue.

2. The method of claim 1, wherein the processing step includes the step of performing complex deconvolution on the auto-correlation data and the cross-correlation data.

3. The method of claim 2, wherein the processing step includes the step of performing coherent demodulation on the auto-correlation data and the cross-correlation data.

4. The method of claim 3, wherein the processing step includes the steps of:

obtaining an auto-power spectrum from the auto-correlation data by performing a Fourier transform on a magnitude portion of the demodulated auto-correlation data;

obtaining a cross-power spectrum from the cross-correlation data by performing a Fourier transform on a magnitude portion of the demodulated cross-correlation data;

obtaining a transfer function from the cross-power spectrum and auto-power spectrum by obtaining a complex conjugate of a ratio of the cross-power spectrum to the auto-power spectrum; and

obtaining the optical impulse response by performing an inverse Fourier transform on the transfer function.

5. The method of claim 3, wherein the processing step includes the steps of:

obtaining an auto-power spectrum from the auto-correlation data by performing a Fourier transform on magnitude and phase portions of the demodulated auto-correlation data;

obtaining a cross-power spectrum from the cross-correlation data by performing a Fourier transform on magnitude and phase portions of the demodulated cross-correlation data;

obtaining a transfer function from the cross-power spectrum and auto-power spectrum by obtaining a complex conjugate of a ratio of the cross-power spectrum to the auto-power spectrum; and

obtaining the optical impulse response by performing an inverse Fourier transform on the transfer function.

6. The method of claim 1, wherein the processing step includes the steps of:

obtaining an auto-power spectrum from the auto-correlation data by performing a Fourier transform on the auto-correlation data;

obtaining a cross-power spectrum from the cross-correlation data by performing a Fourier transform on the cross-correlation data;

obtaining a transfer function from a ratio of the cross-power spectrum to the auto-power spectrum; and

obtaining the optical impulse response by performing an inverse Fourier transform on the transfer function.

7. The method of claim 6, wherein the processing step further includes the step of performing coherent demodulation on the auto-correlation data and the cross-correlation data.

8. The method of claim 6, further comprising the step of obtaining a windowed transfer function.

9. The method of claim 8, wherein the windowing function is customized according to the optical radiation source.

10. The method of claim 6, further comprising the steps of:

generating a calibration interferogram with a calibration interferometer having a high-coherence radiation source, a sample arm, an optical reflector in the sample arm, a reference arm, and a scanning optical reflector in the reference arm, the scanning optical reflector being coupled to a scanning device of the main interferometer;

detecting regular features in the calibration interferogram;

generating a digital clock signal from the regular features detected from the calibration interferogram; and

synchronizing the cross-correlation data and auto-correlation data acquisition steps using the digital clock signal.

11. The method of claim 6, further comprising the step of obtaining a filtered transfer function.

12. The method of claim 1, wherein the processing step includes the steps of:

obtaining an auto-power spectrum from the auto-correlation data by performing a Fourier transform on the auto-correlation data;

obtaining a cross-power spectrum from the cross-correlation data by performing a Fourier transform on the cross-correlation data;

obtaining a transfer function from the cross-power spectrum and auto-power spectrum by taking a ratio of the cross-power spectrum to the auto-power spectrum; and

obtaining the optical impulse response by performing an inverse Fourier transform on the transfer function.

13. The method of claim 1, further comprising the step of monitoring reference arm path length of the main interferometer, wherein the processing step includes the step of compensating for velocity fluctuations detected during the monitoring step.

14. The method of claim 1, further comprising the steps of:

generating a calibration interferogram with a calibration interferometer having a high-coherence radiation source, a sample arm, an optical reflector in the sample arm, a reference arm, and a scanning optical reflector in the reference arm, the scanning optical reflector being coupled to a scanning device of the main interferometer;

detecting regular features in the calibration interferogram;

generating a digital clock signal from the regular features detected from the calibration interferogram; and

synchronizing the cross-correlation data and auto-correlation data acquisition steps using the digital clock signal.

15. The method of claim 1, further comprising the steps of:

generating a calibration interferogram with a calibration interferometer having a high-coherence radiation source, a sample arm, an optical reflector in the sample arm, a reference arm, and a scanning optical reflector in the reference arm, the scanning optical reflector being coupled to a scanning device of the main interferometer;

detecting regular intervals in the calibration interferogram;

digitizing the auto-correlation interferogram data and the cross-correlation interferogram data; and

resampling the digitized auto-correlation interferogram data and the digitized cross-correlation interferogram data at the regular intervals.

16. The method of claim 1, wherein the step of acquiring auto-correlation data includes the step of placing an optical reflector in the sample arm of the main interferometer.

17. The method of claim 1, further comprising the step of detecting an envelope of the impulse response.

18. The method of claim 17 wherein the detecting step includes the step of demodulating the impulse response.

19. The method of claim 1, further comprising the step of detecting a magnitude portion of the impulse response.

20. The method of claim 1, wherein the processing step includes the step of performing iterative deconvolution on the auto-correlation and cross-correlation data.

21. The method of claim 1, further comprising the step of incorporating a sample probe portion of the main interferometer into an endoscopic or surgical instrument.

22. The method of claim 21, further comprising the step of scanning the endoscopic or surgical instrument along a portion of a patient'"'"'s gastrointestinal tract tissue to monitor fine structures.

23. An optical coherence tomography system comprising:

a low coherence optical radiation source;

a first translating reference optical reflector;

a first beam splitter, splitting the radiation source into two paths, one path directed to a sample and the other path directed to the first reference reflector;

a first beam combiner for combining beams reflected from the sample with beams reflected from the first reference reflector;

a first optical detector for acquiring a data package from the first beam combiner;

a Fourier transform device, operatively coupled to an output of the first optical detector for generating a power spectrum from the data package;

a processor device, operatively coupled to an output of the Fourier transform device and having access to a memory device, for generating a transfer function with the power spectrum; and

an inverse-Fourier transform device, operatively coupled to an output of the processor device, for generating an impulse response from the transfer function.

24. The optical coherence tomography system of claim 23, further comprising:

a demodulator device, operatively coupled between the first optical detector and the Fourier transform device.

25. The optical coherence tomography system of claim 24, further comprising:

an analog-to-digital converter device, operatively coupled between the demodulator device and the Fourier transform device.

26. The optical coherence tomography system of claim 25, further comprising:

a calibration interferometer, including a high-coherence source, a sample arm, a reference arm, a calibrating optical reflector in the sample arm, and a second translating reference reflector in the reference arm, a second beam splitter, splitting the high-coherence source into two paths, one path directed to the calibrating optical reflector in the sample arm and the other path directed to the second reference reflector in the reference arm coupled to the first translating reference optical reflector, a second beam combiner combining beams reflected from the calibration optical reflector in the sample arm with beams reflected from the second reference reflector in the reference arm, and a second optical detector acquiring a calibration interferogram from the second beam combiner; and

an interval detection device coupled to an output of the second optical detector, detecting regular features in the calibration interferogram; and

a clock generator, operatively coupled to an output of the interval detection device and generating a digital clock signal from the regular features detected in the calibration interferogram by the interval detection device;

wherein, the analog-to-digital converter device includes a clock input operatively coupled to an output of the clock generator, whereby the analog-to-digital converter is synchronized by the calibration interferometer.

27. The optical coherence tomography system of claim 23, further comprising:

an analog-to-digital converter device, operatively coupled between the first optical detector and the Fourier transform device.

28. The optical coherence tomography system of claim 23, further comprising:

a calibration interferometer, including a high-coherence source, a sample arm, a reference arm, a calibration optical reflector in the sample arm, and a second translating reference reflector in the reference arm, a second beam splitter, splitting the high-coherence source into two paths, one path directed to the calibration optical reflector in the sample arm and the other path directed to the second reference reflector in the reference arm coupled to the first translating reference optical reflector, a second beam combiner combining beams reflected from the calibration optical reflector in the sample arm with beams reflected from the second reference reflector in the reference arm, and a second optical detector acquiring a calibration interferogram from the second beam combiner; and

a thresholding device operatively coupled to an output of the second optical detector, detecting regular features in the calibration interferogram; and

an interpolation device, operatively coupled to an output of the interval detection device and operatively coupled between the first optical detector and the Fourier transform device, the interpolation device resampling the interferogram data from the first optical detector at regular intervals developed by the thresholding device.

29. An optical coherence tomography system comprising:

a main interferometer including an optical radiation source and a sample arm, the main interferometer generating a cross-correlation data output of a sample in the sample arm;

a means for generating or calculating an auto-correlation data output; and

a data processing system, operatively coupled to an output of the main interferometer, processing the auto-correlation data and the cross-correlation data to produce an optical impulse response of the sample.

30. The optical coherence tomography system of claim 29, wherein the data processing system includes:

a Fourier transform device, operatively coupled to the output of the main interferometer, generating an auto-power spectrum from the auto-correlation data and generating a cross-power spectrum from the cross-correlation data;

a processor device, operatively coupled to an output of the Fourier transform device, generating a transfer function using the auto-power spectrum and the cross-power spectrum; and

an inverse-Fourier transform device, operatively coupled to an output of the processor device, generating an impulse response from the transfer function.

31. The optical coherence tomography system of claim 30, further comprising a means for generating a multi-dimensional image from multiple outputs of the inverse-Fourier transform device.

32. The optical coherence tomography system of claim 29, further comprising:

a scanner for scanning a reference optical reflector or a sample probe of the main interferometer;

a calibration interferometer, including a high-coherence source, a sample arm, a calibration optical reflector in the sample arm, and a reference optical reflector coupled to the scanner of the main interferometer, the calibration interferometer generating a calibration interferogram;

an interval detection device coupled to an output of the calibration interferometer, detecting regular features in the calibration interferogram; and

a clock generator, operatively coupled to an output of the interval detection device, generating a digital clock signal from the regular features detected in the calibration interferogram by the interval detection device;

wherein, the data processing system includes a clock input operatively coupled to an output of the clock generator, whereby the data processing system is synchronized by the calibration interferometer.

33. The optical coherence tomography system of claim 29, further comprising:

a scanner for scanning a reference optical reflector or a sample probe of the main interferometer;

a calibration interferometer, including a high-coherence source, a sample arm, a calibration optical reflector in the sample arm, and a reference optical reflector coupled to the scanner of the main interferometer, the calibration interferometer generating a calibration interferogram;

a thresholding device operatively coupled to an output of the calibration interferometer, detecting regular features in the calibration interferogram; and

an interpolation device, operatively coupled to an output of the interval detection device and operatively coupled between the main interferometer and the data processing system, the interpolation device resampling the auto-correlation and cross-correlation interferogram data from the main interferometer at regular intervals developed by the thresholding device.

34. The optical coherence tomography system of claim 29, further comprising a demodulator device operatively coupled between the main interferometer and the data processing system.

35. The optical coherence tomography system of claim 29, wherein the main interferometer includes a sample probe incorporated into an endoscopic or surgical examination device.

36. An optical coherence tomography system, comprising:

an electromagnetic radiation source generating source radiation;

a reference optical reflector;

means for directing the source radiation to a sample;

means for directing the source radiation to a reference reflector;

means for combining reflected radiation from the sample and from the reference reflector, to produce combined reflected radiation; and

means for obtaining an estimate of an optical impulse response from the combined reflected radiation.

37. The optical coherence tomography system of claim 36, further comprising:

means for adjusting the optical path length between the radiation source and the reference reflector; and

means to produce a one-dimensional data set from the estimated impulse response.

38. The optical coherence tomography system of claim 37, further comprising means for correcting irregularities in a scan rate of the optical path length adjustment means.

39. A method for generating interferogram data of a sample in an optical coherence tomography system, the optical coherence tomography system including a main interferometer having an optical radiation source and a sample arm, the method comprising the steps of:

acquiring auto power spectra for the main interferometer;

acquiring cross power spectra from the main interferometer with the sample in the sample arm; and

processing the auto power spectra and the cross power spectra to produce an optical impulse response of the tissue.