Surface Roughness Measurement Methods and Apparatus

• US 20080123106A1
• Filed: 12/23/2005
• Published: 05/29/2008
• Est. Priority Date: 12/27/2004
• Status: Abandoned Application

• Current Assignee: BC Cancer Agency, David Mclean, Haishan Zeng, Harvey Liu, Lioudmila Tchvialeva, Tim Lee
• Original Assignee: BC Cancer Agency
• Inventors: Zeng, Haishan, Lui, Harvey, Lee, Tim K., McLean, David I., Tchvialeva, Lioudmila
• Application Number:
  US11/722,878
• Publication Number:
  US 20080123106A1
• Time in Patent Office: Days
• US Class Current: 356/600
• CPC Class Codes: A61B 5/0066 Optical coherence imaging
• CPC Class Codes: A61B 5/444 Evaluating skin marks, e.g. mole, nevi, tumour, scar
• CPC Class Codes: A61B 5/445 Evaluating skin irritation or skin trauma, e.g. rash, eczema, wound, bed sore
• CPC Class Codes: G01B 11/303 using photoelectric detection means
• CPC Class Codes: G01J 9/02 by interferometric methods using interferometers for measuring optically the linear dimensions of objects G01B9/02
• CPC Class Codes: G01N 2021/479 Speckle
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence

Abstract

Surface roughness measurements are made by illuminating a surface with coherent light to generate a speckle pattern and studying characteristics of the speckle pattern. The disclosed techniques may be applied to measuring the surface roughness of skin or other biological surfaces. Skin roughness information may be used in the diagnosis of conditions such as malignant melanoma. Methods and apparatus for measuring the coherence length of optical sources involve extracting information about speckle patterns resulting when light from the optical sources interacts with a surface having a known roughness.

Claims

1. A method for measuring roughness of an area of a biological surface in vivo, the method comprising:

illuminating an area of a biological surface of a subject with coherent optical radiation and allowing the optical radiation to scatter from the area of the biological surface to yield a speckle pattern;

making measurements of intensity of the optical radiation in the speckle pattern; and

,

based upon results of the measurements, computing a measure of roughness of the area of the biological surface.

2. A method according to claim 1 wherein making measurements of intensity of the optical radiation in the speckle pattern comprises imaging light scattered from the area of the biological surface onto a two-dimensional imaging detector.

3. A method according to claim 2 wherein the imaging detector comprises an array of pixels and a mean size of speckles at the imaging detector of speckles in the speckle pattern is at least 5 times greater than a center-to-center spacing of adjacent pixels in the array.

4. A method according to claim 2 comprising imaging at least 500 speckles onto the imaging detector.

6. A method according to claim 2 wherein computing the measure of roughness of the area of the biological surface comprises determining a contrast of the speckle pattern and computing the measure of roughness of the area of the biological surface based on the contrast of the speckle pattern.

7. A method according to claim 6 wherein the measure of roughness is proportional to:

8. A method according to claim 7 wherein the measure of roughness is given by:

9. A method according to claim 8 comprising computing a value for the calibration constant by:

placing a roughness standard having a known roughness in place of the area of the biological surface;

illuminating the roughness standard with the optical radiation to yield a standard speckle pattern;

computing a contrast of the standard speckle pattern; and

,

calculating a value for the calibration constant from the known roughness and the contrast of the standard speckle pattern.

11. A method according to claim 8 wherein determining the contrast of the speckle pattern comprises identifying a center of the speckle pattern and computing the contrast based on values lying within an annular ring around the center of the speckle pattern.

12. A method according to claim 6 wherein a wavelength of the optical radiation is shorter than 600 nm.

13. A method according to claim 6 wherein the optical radiation comprises green or blue light.

14. A method according to claim 2 wherein the optical radiation is polarized and making measurements of intensity of the optical radiation in the speckle pattern comprises making measurements of intensity of a component of the optical radiation in the speckle pattern, the component having a predetermined polarization.

15. A method according to claim 2 wherein the optical radiation is polarized and making measurements of intensity of the optical radiation in the speckle pattern comprises making measurements of intensity of at least two components of the optical radiation, the two components having different polarizations.

16. A method according to claim 15 wherein the two polarizations are substantially perpendicular.

17. A method according to claim 16 wherein computing a measure of roughness of the area of the biological surface comprises computing the value A given by:

18. A method according to claim 2 wherein the optical radiation has a coherence length of 500 μ

m or less.

21. A method according to claim 1 wherein making measurements of intensity of the optical radiation in the speckle pattern is performed during an exposure time of 2 ms or less.

26. A method according to claim 1 wherein illuminating an area of the biological surface of a subject with coherent optical radiation comprises illuminating the area of the biological surface with optical radiation having first and second distinct wavelengths and, separately for each of the wavelengths, obtaining multiple measurements of an intensity at a point in the speckle pattern.

27. A method according to claim 26 comprising ensemble averaging the multiple measurements for each of the first and second wavelengths.

28. A method according to claim 27 wherein the following inequality between the first and second wavelengths and the roughness of the area of the biological surface holds:

29. A method according to claim 26 comprising moving the area of the biological surface relative to a source of the optical illumination between taking the multiple measurements.

30. A method according to claim 26 comprising computing the value:

31. A method according to claim 1 wherein illuminating the area of the biological surface comprises illuminating the area of the biological surface with the optical radiation incident from first and second angles.

32. A method according to claim 31 comprising, obtaining an image comprising Young'"'"'s fringes resulting from the combination of first and second speckle patterns, the first speckle pattern resulting from illumination at the first angle and the second speckle pattern resulting from illumination at the second angle.

33. A method according to claim 32 comprising computing a visibility of a Young'"'"'s fringe and wherein computing the measure of roughness of the area of the biological surface is based at least in part on the visibility.

34. A method according to claim 33 wherein computing the visibility comprises computing a value V given by:

35. A method according to claim 33 wherein computing the measure of roughness is based on visibilities of a plurality of Young'"'"'s fringes.

36. A method according to claim 35 wherein obtaining an image comprising Young'"'"'s fringes comprises imaging the first and second speckle patterns at an imaging detector, wherein, at the imaging detector, the Young'"'"'s fringes have a spacing that is less than ⅛

of a width of an area of the imaging detector that is responsive to the optical radiation.

37. A method according to claim 1 comprising aligning the optical radiation to be incident on a lesion on the area of the biological surface.

38. A method according to claim 37 wherein aligning the optical radiation comprises displaying an image of the area of the biological surface together with indicia indicating a point at which the optical radiation will illuminate the biological surface.

39. A method according to claim 37 comprising performing the method with the optical radiation aligned to be incident on the lesion to obtain a first measure of roughness and repeating the method with the optical radiation aligned to be incident on a part of the biological surface off of the lesion to obtain a second measure of roughness.

40. A method according to claim 2 comprising providing the roughness measure as an input to an automatic diagnostic system wherein the biological surface comprises skin.

5. (canceled)

10. (canceled)

19-20. -20. (canceled)

22-25. -25. (canceled)

41. (canceled)

42. A method according to claim 41 comprising, in the automatic diagnostic system, increasing a probability of the skin being affected by malignant melanoma in response to the roughness measure indicating a roughness being below a threshold roughness.

44. A method according to claim 41 comprising, in the automatic diagnostic system, increasing a probability of the skin being affected by seborrheic keratosis in response to the roughness measure indicating a roughness being above a threshold roughness.

46. A method according to claim 41 wherein the automatic diagnostic system comprises a function for distinguishing between seborrheic keratosis, dysplastic nevus, and melanoma and the method comprises providing the roughness measure, or a value derived from the roughness measure, as an input to the function.

47. A method according to claim 41 wherein the automatic diagnostic system has a function for distinguishing between squamous cell carcinoma and one or more conditions selected from the group consisting of:

warts, actinic keratosis, and Bowen disease and the method comprises providing the roughness measure, or a value derived from the roughness measure, as an input to the function.

48. A method according to claim 47 comprising, in the automatic diagnostic system, increasing a probability of the skin being affected by squamous cell carcinoma in response to the roughness measure indicating a roughness being below a threshold roughness.

43. (canceled)

45. (canceled)

49-55. -55. (canceled)

56. Apparatus for measuring the roughness of a biological surface, the apparatus comprising a light source emitting optical radiation having a coherence length of 300 μ

m or less;

an imaging detector located to detect the optical radiation after the optical radiation has been scattered from a biological surface; and

,

a processor connected to receive image data from the imaging detector and configured to;

compute a contrast of a speckle pattern in the scattered optical radiation; and

,

compute a roughness of the biological surface from the contrast.

57. Apparatus according to claim 56 comprising an opaque light shield extending around the light source and imaging detector, the light shield having an edge that can be brought to bear against the biological surface.

58. Apparatus according to claim 56 comprising a support surface located in a known relationship to the light source and imaging detector wherein, with the support surface bearing against a biological surface, optical radiation from the light source can illuminate an area of the biological surface to yield a speckle pattern detectable by the imaging detector.

62. Apparatus according to claim 58 comprising a first light guide providing an optical path for carrying the scattered optical radiation to the imaging detector and a second light guide disposed to carry the optical radiation from the light source and to emit the optical radiation to illuminate a biological surface to be studied.

64. Apparatus according to claim 62 wherein the second light guide is coaxial with the first light guide.

72. Apparatus according to claim 56 wherein the light source has a variable coherence length.

73. Apparatus according to claim 72 wherein the light source comprises a plurality of narrow-band filters each having a different bandwidth and being disposed to be selectively interposed in a path of the optical radiation.

59-61. -61. (canceled)

63. (canceled)

65. Apparatus according to claim 63 wherein ends of the first and second light guides are substantially equidistant from a biological surface to be studied.

66-71. -71. (canceled)

74. (canceled)