Method and apparatus for recording three-dimensional distribution of light backscattering potential in transparent and semi-transparent structures

• US 6,307,634 B2
• Filed: 01/06/2001
• Issued: 10/23/2001
• Est. Priority Date: 05/15/1998
• Status: Expired due to Term

• Current Assignee: Carl Zeiss Meditec Incorporated (Carl-Zeiss-Stiftung)
• Original Assignee: Laser Diagnostic Technologies, Inc. (Carl-Zeiss-Stiftung)
• Inventors: Baumgartner, Angela, Hitzenberger, Christoph
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): NATIVIDAD, PHILIP SANA
• Application Number:
  US09/755,917
• Publication Number:
  US 20010000978A1
• Time in Patent Office: 290 Days
• Field of Search: 356/484-485, 356/487
• US Class Current: 356/484
• CPC Class Codes: A61B 3/102 for optical coherence tomography [OCT]
• CPC Class Codes: A61B 3/12 for looking at the eye fundus, e.g. ophthalmoscopes A61B3/13 takes precedence
• CPC Class Codes: G01B 11/2441 using interferometry
• CPC Class Codes: G01B 11/255 for measuring radius of curvature measuring diameter G01B11/08

Abstract

An apparatus is disclosed for generating data representative of a three-dimensional distribution of the light backscattering potential of a transparent or semi-transparent object such as a human eye. The apparatus includes an interferometer, both the reference beam and measurement beam of which are directed toward the object and reflected by respective reference and measurement sites thereof, such that axial motion of the object during measurement affects both beams equally. The measurement beam is raster scanned transversely across each measurement site for which data is obtained. Also, the frequency of one of the beams is shifted by a non-moving frequency shifter, such that the reflected beams combine and are modulated by a heterodyne heat frequency, which is detected when the object path difference is matched with the interferometer path difference. Because the non-moving frequency shifter can effectively generate a beat frequency of about 40 MHz, relatively rapid transverse and longitudinal scanning are facilitated.

Claims

1. An apparatus for measuring the distribution profile of a light scattering potential of an object defining a plurality of measurement sites, comprising:

(b) at least one light source generating a plurality of light beams including at least one reference light beam and at least one measurement light beam, the light beams having short coherence length;

(c) at least one frequency shifter positioned in at least one beam path of the light beams;

(d) a receiver receiving reflected light from at least one measurement site and from at least one reference site, the receiver generating a signal representative thereof;

(f) at least one optical scanner positioned to direct at least the measurement light beam to at least one selectable measurement site;

(g) at least one polarizer and one quarter wave plate, wherein the polarizer and the quarter wave plate are positioned in a return beam path such that light in the return beam path returning from the object is directed to avoid passing the frequency shifter, wherein the signal generated by the receiver is usable for determining a multi-dimensional distribution of a light scattering potential of the object.

2. The apparatus claim of 1, wherein the reference site and measurement sites are at selectable locations defined by the object, such that axial motion of the object relative to the light beams equally affects the reference light beam and the measurement light beam.

3. The apparatus of claim 1, further comprising a Michelson interferometer, the interferometer comprising a single beam splitter at which the measurement light beam and the reference light beam overlap.

4. The apparatus of claim 1, further comprising a dispersion compensation element positioned in at least one of the measurement light beam and the reference light beam.

5. The apparatus of claim 1, further comprising at least one movable path delay unit, wherein a focusing lens and the optical scanner direct the measurement light beam in three dimensional space and wherein a profile of the scattering potential of the object is mapped by establishing the focal point of the measurement light beam at plural measurement sites and controlling a path delay between the measurement light beam and the reference light beam using the path delay unit.

6. The apparatus of claim 1, further comprising at least one spatial filter in the measurement light beam or the reference light beam such that the spatial filter is positioned at a focal point conjugate to a focal point of either the reference site, or a measurement site.

7. The apparatus of claim 1, wherein the signal generated at the receiver has a beat frequency when a traveling distance of the reference light beam and a traveling distance of the measurement light beam are substantially matched.

8. An apparatus for measuring the distribution profile of a light scattering potential of an object defining at least one reference site and a plurality of measurement sites, the apparatus comprising:

(b) a plurality of light beams comprising at least one reference light beam and at least one measurement light beam, the light beams having short coherence length;

(c) at least one frequency shifter positioned in at least one beam path of the light beams;

(d) an optics system including at least one focusing lens, the optics system directing the measurement light beam to a measurement site and directing the reference light beam to the reference site, the optics system directing reflected light from a selected measurement site and from the reference site to a receiver generating an output signal;

(e) an optical scanner positioned in at least the measurement light beam and directing the measurement light beam to at least one selectable measurement site; and

(f) at least two beam splitters, the measurement light beam and the reference light beam substantially overlapping at the beam splitters.

9. The apparatus claim of 8, wherein the optics system comprises at least one measurement beam focusing lens in a measurement beam path and at least one reference beam focusing lens in a reference beam path, such that the reference site and the measurement site are selectable at different focal planes.

10. The apparatus of claim 8, further comprising a dispersion compensation element positioned in at least one of the measurement light beam and the reference light beam.

11. The apparatus of claim 8, further comprising at least one movable path delay unit, wherein a focusing lens and the optical scanner direct the measurement light beam in three dimensional space and wherein a profile of the scattering potential of the object is mapped by establishing the focal point of the measurement light beam at plural measurement sites and controlling a path delay between the measurement light beam and the reference light beam using the path delay unit.

12. The apparatus of claim 8, further comprising at least one spatial filter in the measurement light beam or the reference light beam such that the spatial filter is positioned at a focal point conjugate to a focal point of either the reference site, or a measurement site.

13. The apparatus of claim 8, wherein the signal generated at the receiver has a beat frequency when a traveling distance of the reference light beam and a traveling distance of the measurement light beam are substantially matched.

14. An apparatus for measuring the distribution profile of a light scattering potential of a fundus layers of the eye, comprising:

(a) a light source generating a plurality of light beams including at least one reference light beam and at least one measurement light beam;

(b) at least one frequency shifter positioned in at least one beam path of the light beams;

(c) a plurality of optics directing the measurement light beam to a measurement site and the reference light beam to the reference site, the optics further directing reflected light from a selected measurement site and from the reference site to a receiver generating an ouput signal;

(d) at least one optical scanner positioned in at least the measurement light beam to direct the measurement light beam to at least one selectable measurement site; and

(e) at least one beam path compensator element in the measurement light beam, such that a coherence layer from which the signal is derived has a curvature which is substantially matched with a curvature of the fundus layers when the measurement light beam is scanned by the optical scanner.

15. The apparatus of claim 14, wherein the beam path compensator element is selected from the group including:

a glass plate with plane parallel surfaces, and a pair of movable wedges forming plane parallel surfaces with adjustable optical thickness.

16. The apparatus of claim 14, further comprising at least one movable path delay unit, wherein a focusing lens and the optical scanner direct the measurement light beam in three dimensional space and wherein a profile of the scattering potential of the eye is mapped by establishing the focal point of the measurement light beam at plural measurement sites and controlling a path delay between the measurement light beam and the reference light beam using the path delay unit.

17. The apparatus of claim 14, further comprising at least one spatial filter in the measurement light beam or the reference light beam such that the spatial filter is positioned at a focal point conjugate to a focal point of either the reference site, or a measurement site.

18. The apparatus of claim 14, wherein the signal generated at the receiver has a beat frequency when a traveling distance of the reference light beam and a traveling distance of the measurement light beam are substantially matched.

19. The apparatus of claim 14, further comprising a dispersion compensation element positioned in at least one of the measurement light beam and the reference light beam.

20. A method for measuring the distribution profile of light scattering potential of an object, comprising:

(a) generating light beams with short coherence length;

(b) scanning at least one of the light beams in at least one dimension with at least one optical scanner;

(c) shifting the optical frequency of at least one of the light beams with a non-moving frequency shifter;

(d) directing the light beams toward the object with an optics system including a first focusing lens in the measurement light beam such that the measurement light beam forms a focal point at a measuring site, and a second focusing lens in the reference light beam such that the reference light beam forms a focal point at a reference site, the measurement site and the reference site being selectable at different focal planes defined by the object;

(e) directing reflected light beams from the object to a receiver;

(f) controlling at least one path delay unit such that a travel distance of the measurement light beam and a travel distance of the reference light beam are substantially matched; and

(g) generating a signal using the receiver, the signal having a beat frequency defined at least in part by the controlling act, whereby axial motion of the object relative to an incident direction of the light beams with respect to the object equally affects the reference light beam and the measurement light beam.

21. The method of claim 20, wherein the path delay unit comprises at least one translationally movable mirror or retroreflector to selectively establish the length of one arm of travel for at least one of:

the measurement light beam, or the reference light beam.

22. The method of claim 20, further comprising moving the focusing lens in the measurement light beam such that a profile of the scattering potential can be mapped by positioning the focal point of the measurement light beam and controlling the path delay unit to selected locations defined by the object.

23. The method of claim 20, further comprising inserting at least one dispersion compensator element in at least one of the measurement light beam or the reference light beam.

24. The method of claim 20, further comprising inserting at least one spatial filter in the measurement light beam or in the reference light beam such that the spatial filter is positioned at a focal point conjugate to the focal point of either the reference site or a measurement site.

25. The method of claim 20, wherein the path delay unit comprises at least one translationally movable mirror or retroreflector to selectively establish the length of one arm of travel for at least one of:

the measurement light beam, or the reference light beam.

26. A method of measuring the distribution profile of light scattering potential of an object, comprising:

(a) generating light beams with short coherence length;

(b) scanning at least one of the light beams in at least one dimension with at least one optical scanner;

(c) shifting the optical frequency of at least one of the light beams with a non-moving frequency shifter;

(d) directing the light beams toward the object with a plurality of optics;

(e) controlling at least one path delay unit such that the travel distance of the measurement light beam and the travel distance of the reference light beam are matched;

(f) generating a signal defining a beat frequency established at least in part by the controlling act; and

(f) inserting a polarizer and a quarter wave plate in a light beam path including the frequency shifter, such that at least the measurement light beam is directed to avoid passing the frequency shifter in its return from the object.

27. The method of claim 26, wherein the path delay unit comprises at least one translationally movable mirror or retroreflector to selectively establish the length of one arm of travel for at least one of:

the measurement light beam, or the reference light beam.

28. The method of claim 26, further comprising moving the focusing lens in the measurement light beam such that a profile of the scattering potential can be mapped by positioning the focal point of the measurement light beam and controlling the path delay unit to selected locations defined by the object.

29. The method of claim 26, further comprising inserting at least one dispersion compensator element in at least one of the measurement light beam or the reference light beam.

30. The method of claim 26, further comprising inserting at least one spatial filter in the measurement light beam or in the reference light beam such that the spatial filter is positioned at a focal point conjugate to the focal point of either a reference site or a measurement site.

31. A method of measuring the distribution profile of light scattering potential of an object, comprising:

(a) generating light beams with short coherence length;

(b) scanning at least one of the light beams in at least one dimension with at least one optical scanner;

(c) shifting the optical frequency of at least one of the light beams with a non-moving frequency shifter;

(d) directing the light beams towards the object with a plurality of optics comprising a first focusing lens in the measurement light beam such that the measurement light beam forms a focal point at a measurement site, and a second focusing lens in the reference light beam such that the reference light beam forms a focal point at a reference site, the measurement site and the reference site being selected at different focal planes defined by the object;

(e) controlling at least one path delay unit such that a travel distance of the measurement light beam and a travel distance of the reference light beam are matched;

(f) generating a signal defining a beat frequency established at least in part by the controlling act; and

(g) directing the measurement light beam and the reference light beam to substantially overlap each other at at least two beam splitters in incident and reflected propagation directions relative to the object.

32. The method of claim 31, wherein the path delay unit comprises at least one translationally movable mirror or retroreflector to selectively establish the length of one arm of travel for at least one of:

the measurement light beam, or the reference light beam.

33. The method of claim 31, further comprising moving the focusing lens in the measurement light beam such that a profile of the scattering potential can be mapped by positioning the focal point of the measurement light beam and controlling the path delay unit to selected locations defined by the object.

34. The method of claim 31, further comprising inserting at least one dispersion compensator element in at least one of the measurement light beam or the reference light beam.

35. The method of claim 31, further comprising inserting at least one spatial filter in the measurement light beam or in the reference light beam such that the spatial filter is positioned at a focal point conjugate to the focal point of either the reference site or a measurement site.

36. A method of measuring the distribution profile of light scattering potential of a fundus layers of the eye, comprising:

(a) generating light beams with short coherence length;

(b) scanning at least one of the light beams in at least one dimension with at least one optical scanner;

(c) shifting the optical frequency of at least one of the light beams with a non-moving frequency shifter;

(d) directing the light beams towards the eye using a plurality of optics;

(e) controlling at least one path delay unit such that a travel distance of the measurement light beam and a travel distance of the reference light beam are matched;

(f) generating a signal defining a beat frequency established at least in part by the controlling act; and

(g) inserting at least one path compensator element in the measurement light beam path such that a coherence layer from which the signal is derived has a curvature that substantially matches the curvature of the fundus layers of the eye when the measurement light beam is scanned by the optical scanner.

37. The method of claim 36, wherein the path compensator element is selected from the group including:

a glass plate with plane parallel surfaces, and a pair of movable wedges forming plane parallel surfaces with adjustable optical thickness.

38. The method of claim 36, further comprising moving a focusing lens in the measurement light beam such that a profile of the scattering potential can be mapped by positioning the focal point of the measurement light beam and controlling the path delay unit to selected locations defined by the object.

39. The method of claim 36, further comprising inserting at least one dispersion compensator element in at least one of the measurement light beam or the reference light beam.

40. The method of claim 36, further comprising inserting at least one spatial filter in the measurement light beam or in the reference light beam such that the spatial filter is positioned at a focal point conjugate to the focal point of either the reference site or a measurement site.