System and method for reconstruction of the human ear canal from optical coherence tomography scans

• US 20060276709A1
• Filed: 04/17/2006
• Published: 12/07/2006
• Est. Priority Date: 03/11/2003
• Status: Active Grant

• Current Assignee: Ali Khamene, Frank Sauer, Martin W. Masters, Therese Velde
• Original Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Inventors: Masters, Martin W., Sauer, Frank, Khamene, Ali, Velde, Therese
• Granted Patent: US 7,949,385 B2
• Time in Patent Office: Days
• US Class Current: 600/416
• CPC Class Codes: A61B 5/0066 Optical coherence imaging
• CPC Class Codes: A61B 5/1077 Measuring of profiles
• CPC Class Codes: H04R 2225/77 Design aspects, e.g. CAD, of hearing aid tips, moulds or housings
• CPC Class Codes: H04R 25/658 Manufacture of housing parts

Abstract

A method for reconstructing an ear canal from optical coherence tomography (OCT) scan data of an ear comprises extracting frame numbers and line numbers of interference intensities corresponding to one or more markers on an OCT scan guide, receiving reference frame numbers and lines numbers for one or more markers, determining a starting position and direction for the OCT ear scan from the ear scan marker frame and line numbers and the reference marker frame and line numbers, for each scan line, finding a pixel number of a maximum interference intensity value, and determining an offset distance of said pixel from said scan guide, and reconstructing a surface of the ear canal from the distance offset data.

Claims

1. A method for reconstructing an ear canal, comprising the steps of:

providing a set of optical coherence tomography (OCT) scan data of an ear comprising frames and scan lines of pixels that form a 3D data set whose values are interference intensities;

extracting frame numbers and line numbers of interference intensities corresponding to one or more markers on an OCT scan guide;

receiving reference frame numbers and lines numbers for said one or more markers;

determining a starting position and direction for said OCT ear scan from the ear scan marker frame and line numbers and said reference marker frame and line numbers;

for each scan line, finding a pixel number of a maximum interference intensity value, and determining an offset distance of said pixel from said scan guide; and

reconstructing said surface of said ear canal from said distance offset data.

2. The method of claim 1, wherein an offset distance d of a pixel j from the guide is computed from

3. The method of claim 1, wherein said ear canal surface can be reconstructed from

{right arrow over (p)}(i, j)={right arrow over (p)}₀+{right arrow over (c)}(t)+d(j)(sin(α

){right arrow over (u)}+cos(α

){right arrow over (v)}),

wherein {right arrow over (p)}(i, j) represents a scan line i perpendicular to guide, j a pixel along the scan line, {right arrow over (p)}₀ is a starting position in space of the scan, {right arrow over (c)}(t) a curved path of the guide, t is a position on the guide corresponding to the scan line i, and a is a scan line angle, and {right arrow over (u)} and {right arrow over (v)} two unit vectors perpendicular to each other defining a 2D coordinate frame in a plane perpendicular to the curve {right arrow over (c)}(t).

4. The method of claim 3, wherein

5. The method of claim 3, wherein said unit vectors {right arrow over (u)} and {right arrow over (v)} are defined by

6. The method of claim 1, wherein said OCT scan data is obtained by providing an OCT scanning apparatus including a guide containing a rotatable probe, sliding and rotating said probe in said guide, emitting near infrared light from said probe at predetermined intervals, measuring interference of reflected light with a reference signal, and saving said interference data in a computer readable storage medium.

7. The method of claim 1, comprising, for each scan line, selecting those pixels with an interference intensity value above a pre-determined threshold and determining an offset distance of said selected pixels from said scan guide.

8. The method of claim 1, comprising, prior to finding a pixel number of a maximum interference intensity value for a scan line, discarding the intensity values at the beginning of a scan line, wherein said beginning values correspond to reflections from the scan guide itself.

9. The method of claim 1, wherein said reference marker frame numbers and lines numbers were extracted from OCT scan data of a calibration object.

10. The method of claim 9, wherein extracting said reference marker frame numbers and lines numbers from OCT scan data of a calibration object comprises:

providing a set of optical coherence tomography (OCT) scan data of a calibration object marked to indicate an angular direction of 0, said scan data comprising frames and scan lines of pixels that form a 3D data set whose values are interference intensities acquired using a calibration guide comprising one or more markers on said guide;

extracting frame numbers and line numbers of interference intensities corresponding to said markers on said calibration guide; and

determining spatial positions of said markers on said calibration guide from said frame number and said line numbers.

11. The method of claim 10, wherein said marker positions on the guide are calculated from:

12. The method of claim 1, wherein the starting position t_start and direction α

_start are computed from a marker position t_marker and direction α

_marker from

13. A method for reconstructing an ear canal, comprising the steps of:

providing a scanning guide for an optical coherence tomography (OCT) system, said guide comprising one or more markers on its outer surface;

providing OCT scan data of a hollow calibration object acquired using said scanning guide, said scan data comprising frames and scan lines of pixels that form a 3D data set whose values are interference intensities;

extracting from said calibration object scan data reference frame numbers and line numbers of interference intensities corresponding to said one or more markers on said OCT scan guide;

providing a set of optical coherence tomography (OCT) scan data of an ear acquired using said scanning guide, said scan data comprising a 3D data set of interference intensity values;

extracting from said ear scan data frame numbers and line numbers of interference intensities corresponding to said one or more markers on said OCT scan guide; and

determining a starting position and direction for said OCT ear scan from said ear scan frame numbers and line numbers of said one or more markers and said reference frame numbers and line numbers of said one or more markers.

14. The method of claim 13, further comprising, for each scan line, finding a pixel number of a maximum interference intensity value, and determining an offset distance of said pixel from said scan guide;

and reconstructing said a surface of said ear canal from said distance offset data.

15. The method of claim 13, wherein said scanning guide has at least two strait portions and a curved portion, said scanning guide adapted to containing a rotatable scanning probe,

16. The method of claim 15, wherein said calibration object comprises a first fixture at a first end, a second fixture at a second end, said fixtures adapted to securely hold said calibration guide on said strait portions, and a groove along a portion of an outer surface to indicate an angular direction of 0, wherein said groove does not extend over the outer surface of said fixtures.

17. The method of claim 16, wherein extracting from said calibration object further comprises:

finding a last frame in which an interference intensity from said first fixture appears, and a first frame in which an interference intensity from said groove appears;

selecting a center line of said groove from said first frame in which said groove appears as defining a starting angular direction of 0;

determining the frame number of said first frame in which said groove appears from a length of one of said strait portions of said scanning guide and a speed of said probe, said frame number defining a starting position;

for each scan line, finding a pixel number of a maximum interference intensity value, and determining an offset distance of said pixel from said scan guide; and

reconstructing said a surface of said calibration object from said distance offset data.

18. A program storage device readable by a computer, tangibly embodying a program of instructions executable by the computer to perform the method steps for reconstructing an ear canal, comprising the steps of:

providing a set of optical coherence tomography (OCT) scan data of an ear comprising frames and scan lines of pixels that form a 3D data set whose values are interference intensities;

extracting frame numbers and line numbers of interference intensities corresponding to one or more markers on an OCT scan guide;

receiving reference frame numbers and lines numbers for said one or more markers;

determining a starting position and direction for said OCT ear scan from the ear scan marker frame and line numbers and said reference marker frame and line numbers;

for each scan line, finding a pixel number of a maximum interference intensity value, and determining an offset distance of said pixel from said scan guide; and

reconstructing said surface of said ear canal from said distance offset data.

19. The computer readable program storage device of claim 18, wherein an offset distance d of a pixel j from the guide is computed from

20. The computer readable program storage device of claim 18, wherein said ear canal surface can be reconstructed from

{right arrow over (p)}(i, j)={right arrow over (p)}₀+{right arrow over (c)}(t)+d(j)(sin(α

){right arrow over (u)}+cos(α

){right arrow over (v)}),

wherein {right arrow over (p)}(i, j) represents a scan line i perpendicular to guide, j a pixel along the scan line, {right arrow over (p)}₀ is a starting position in space of the scan, {right arrow over (c)}(t) a curved path of the guide, t is a position on the guide corresponding to the scan line i, and a is a scan line angle, and {right arrow over (u)} and {right arrow over (v)} are two unit vectors perpendicular to each other defining a 2D coordinate frame in a plane perpendicular to the curve {right arrow over (c)}(t).

21. The computer readable program storage device of claim 20, wherein

22. The computer readable program storage device of claim 20, wherein said unit vectors {right arrow over (u)} and {right arrow over (v)} are defined by

23. The computer readable program storage device of claim 18, wherein said OCT scan data is obtained by providing an OCT scanning apparatus including a guide containing a rotatable probe, sliding and rotating said probe in said guide, emitting near infrared light from said probe at predetermined intervals, measuring interference of reflected light with a reference signal, and saving said interference data in a computer readable storage medium.

24. The computer readable program storage device of claim 18, said method comprising, for each scan line, selecting those pixels with an interference intensity value above a pre-determined threshold and determining an offset distance of said selected pixels from said scan guide.

25. The computer readable program storage device of claim 18, said method comprising, prior to finding a pixel number of a maximum interference intensity value for a scan line, discarding the intensity values at the beginning of a scan line, wherein said beginning values correspond to reflections from the scan guide itself.

26. The computer readable program storage device of claim 18, wherein said reference marker frame numbers and lines numbers were extracted from OCT scan data of a calibration object.

27. The computer readable program storage device of claim 26, wherein extracting said reference marker frame numbers and lines numbers from OCT scan data of a calibration object comprises:

providing a set of optical coherence tomography (OCT) scan data of a calibration object marked to indicate an angular direction of 0, said scan data comprising frames and scan lines of pixels that form a 3D data set whose values are interference intensities acquired using a calibration guide comprising one or more markers on said guide;

extracting frame numbers and line numbers of interference intensities corresponding to said markers on said calibration guide; and

determining spatial positions of said markers on said calibration guide from said frame number and said line numbers.

28. The computer readable program storage device of claim 27, wherein said marker positions on the guide are calculated from:

29. The computer readable program storage device of claim 18, wherein the starting position t_start and direction α

_start are computed from a marker position t_marker and direction α

_marker from