Virtual Endoscopy

• US 20080055308A1
• Filed: 06/02/2005
• Published: 03/06/2008
• Est. Priority Date: 06/23/2004
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Fleiter, Thorsten, Durgan, Jacob, Dekel, Doron
• Granted Patent: US 7,839,402 B2
• Time in Patent Office: Days
• US Class Current: 345/421
• CPC Class Codes: G06T 15/08 Volume rendering
• CPC Class Codes: G06T 19/00 Manipulating 3D models or images for computer graphics
• CPC Class Codes: G06T 2210/41 Medical
• CPC Class Codes: G06T 2215/06 Curved planar reformation of 3D line structures

Abstract

In a virtual endoscopy method, an unfolding axis (100, 100′) substantially along an elongated lumen (150) is divided into axis segments (110). Ray casting directions (104) are selected extending generally radially from the axis segments. At least some of the ray casting directions are tilted away from a camera position (102). Ray casting is performed along the tilted ray casting directions to define pixel values that are arranged into an unfolded view. The ray casting employs at least one of (i) volume rendering and (ii) computing a statistical characteristic of voxels (238) over a preselected distance (dinterval) along the ray casting direction into the lumen-defining structure.

Claims

1. A virtual endoscopy method for performing virtual endoscopy on a volumetric image of a lumen-defining structure having an elongated lumen, the method comprising:

determining an unfolding axis substantially within the elongated lumen and generally positioned at a camera position, the unfolding axis being divided into axis segments;

selecting ray casting directions extending generally radially from the axis segments of the unfolding axis;

tilting at least some of the ray casting directions away from the camera position based on distance between the corresponding axis segment and the camera position;

performing ray casting along the tilted ray casting directions to define pixel values; and

arranging the pixel values into an unfolded view.

2. The virtual endoscopy method as set forth in claim 1, wherein the ray casting directions corresponding to each axis segment are arranged radially symmetrically around the unfolding axis.

3. The virtual endoscopy method as set forth in claim 1, wherein the tilting generally increases with increasing distance of the axis segment from the camera position.

4. The virtual endoscopy method as set forth in claim 1, wherein the ray casting has a preselected maximum ray casting distance, and the tilting is adjusted to prevent overlap of ray castings within the preselected maximum ray casting distance.

5. The virtual endoscopy method as set forth in claim 1, wherein the amount of tilting is controlled by a user-selected unfolding perspective angle parameters.

6. The virtual endoscopy method as set forth in claim 1, wherein, for each axis segment, the tilting of the ray casting directions corresponding to the axis segment are identical, the tilted ray casting directions of the axis segment defining a cone of ray casting directions.

7. The virtual endoscopy method as set forth in claim 1, wherein the unfolding axis is straight and tangential to a lumen centerline at the camera position.

8. The virtual endoscopy method as set forth in claim 1) wherein the unfolding axis is generally curved and substantially coincides with a portion of a lumen centerline.

9. The virtual endoscopy method as set forth in claim 1, further including:

moving the camera position to an updated camera position; and

repeating the determining of an unfolding axis, the selecting of ray casting directions, the tilting of the ray casting directions, the performing of ray casting, and the arranging of the pixel values to produce an updated unfolded view for the updated camera position.

10. The virtual endoscopy method as set forth in claim 1, further including:

defining an inspection position corresponding to a structure of interest in the unfolded view;

constructing a perspective endoscopic view having (i) the camera position and (ii) looking at the inspection position;

fixing the inspection position as the center of a sphere;

in response to a user input, rotating the camera position along the surface of the sphere; and

constructing a rotated perspective endoscopic view having (i) an updated camel-a position rotated based on the user input and (ii) looking at the inspection position.

11. The virtual endoscopy method as set forth in claim 10, wherein the defining of an inspection position includes:

receiving via user interaction with the unfolded view a user selection of one of the pixels of the unfolded view, the position of the selected pixel being the inspection position.

12. The virtual endoscopy method as set forth in claim 10, further including:

displaying simultaneously with the perspective endoscopic view two orthogonal oblique views, each oblique view being parallel with a line connecting the camera position and the inspection position; and

displaying simultaneously with the rotated perspective endoscopic view two updated orthogonal oblique views, each updated oblique view being parallel with a line connecting the updated camera position and the inspection position.

13. The virtual endoscopy method as set forth in claim 10, wherein the perspective endoscopic views include less than the entire volumetric image so as to avoid obstructing the camera view of the inspection point.

14. The virtual endoscopy method as set forth in claim 1, wherein the performing of ray casting along each ray casting direction to define a pixel value corresponding to each ray casting direction includes:

performing volume rendering along the ray casting directions, the volume rendering employing the ray casting directions as illumination direction parameters.

15. The virtual endoscopy method as set forth in claim 1, wherein the performing of ray casting includes:

identifying an intersection of the ray casting direction and a lumen-defining surface of the lumen-defining structure; and

computing a statistical characteristic of voxels over a preselected distance along the ray casting direction into the lumen-defining structure.

16. The virtual endoscopy method as set forth in claim 15, wherein the statistical characteristic is one of a maximum intensity projection and an average value of voxels over the preselected distance along the ray casting direction into the lumen-defining structure.

17. The virtual endoscopy method as set forth in claim 14, wherein the performing of ray casting along each ray casting direction to define a pixel value corresponding to each ray casting direction further includes:

performing volume rendering for the ray casting directions to produce rendered voxel values representative of the intersected lumen-defining surface; and

adjusting the rendered voxel values based on the computed statistical characteristics.

18. The virtual endoscopy method as set forth in claim 17, wherein the adjusting of the rendered voxel value includes color adjustment of the rendered voxel values based on the computed statistical characteristics.

19. The virtual endoscopy method as set forth in claim 14, wherein the lumen-defining structure is an anatomical organ, the virtual endoscopy method further including:

prior to acquiring the volumetric image of the anatomical organ, administering an intravenous contrast agent providing enhanced vascular contrast in the volumetric image.

20. The virtual endoscopy method as set forth in claim 1, wherein the volumetric image of the lumen-defining structure is a volumetric computed tomography image of an organ selected from the group consisting of a colon, a bladder, a blood vessel, a trachea, and an intestine.

21. A virtual endoscopy processor that performs the virtual endoscopy method of claim 1.

32. A virtual endoscopy system comprising:

an imaging system producing a volumetric image of a lumen-defining structure; and

a processor that performs the virtual endoscopy method of claim 1.

33. The virtual endoscopy system as set forth in claim 32, wherein the imaging system includes:

a computed tomography scanner including an x-ray source revolving around an imaging region and injecting x-rays thereinto, and a detector array that detects x-rays after passing through the imaging region to produce volumetric computed tomography projection data;

a reconstruction processor that reconstructs the volumetric computed tomography projection data into the volumetric image of the lumen-defining structure.

22. A virtual endoscopy method for performing virtual endoscopy on a volumetric image of a lumen-defining structure, the method comprising:

selecting ray casting directions extending toward a lumen-defining surface of the lumen-defining structure;

computing a statistical characteristic of voxels over a preselected distance along each ray casting direction into the lumen-defining structure;

defining a pixel value for each ray casting direction based at least on the computed statistical characteristic; and

arranging the pixel values into an endoscopic view of the lumen-defining structure.

23. The virtual endoscopy method as set forth in claim 22, wherein the statistical characteristic is one of a maximum intensity projection and a minimum intensity projection over the preselected distance along the ray casting direction into the lumen-defining structure.

24. The virtual endoscopy method as set forth in claim 22, wherein the statistical characteristic is an average value of the voxels over the preselected distance along the ray casting direction into the lumen-defining structure.

25. The virtual endoscopy method as set forth in claim 22, wherein the defining of the pixel value based at least on the computed statistical characteristic includes:

performing volume rendering for each ray casting direction to produce a rendered voxel value representative of the intersected lumen-defining surface; and

adjusting the rendered voxel value based on the computed statistical characteristic.

26. The virtual endoscopy method as set forth in claim 25, wherein the adjusting of the rendered voxel value includes adjusting a color of the rendered voxel value based on the computed statistical characteristic.

27. The virtual endoscopy method as set forth in claim 22, wherein the lumen-defining structure is an anatomical organ, the virtual endoscopy method further including:

prior to acquiring the volumetric image of the anatomical organ, administering an intravenous contrast agent providing enhanced vascular contrast in the volumetric image.

28. The virtual endoscopy method as set forth in claim 22, wherein (i) the ray casting directions are selected to extend generally radially from an unfolding axis generally positioned at a camera position, and (ii) the pixel values are arranged into an unfolded endoscopic view.

29. The virtual endoscopy method as set forth in claim 28, wherein the unfolding axis is divided into a plurality of axis segments, ray casting directions are radially symmetrically arranged around each axis segment, and the virtual endoscopy method further includes:

tilting the ray casting directions away from the camera position based on distance between the corresponding axis segment and the camera position, the tilting generally increasing with increasing distance of the axis segment from the camera position.

30. The virtual endoscopy method as set forth in claim 22, wherein (i) the ray casting directions are selected to extend from a camera position, and (ii) the pixel values are arranged into a perspective endoscopic view.

31. A virtual endoscopy processor programmed to perform the virtual endoscopy method of claim 22.

34. A virtual endoscopy apparatus for performing virtual endoscopy on a volumetric image of a lumen-defining structure having a having an elongated lumen, the apparatus comprising:

a means for determining an unfolding axis substantially within the elongated lumen and generally positioned at a camera position, the unfolding axis being divided into axis segments;

a means for selecting ray casting directions extending generally radially from the axis segments of the unfolding axis;

a means for tilting at least some of the ray casting directions away from the camera position based on distance between the corresponding axis segment and the camera position;

a means for performing ray casting along the tilted ray casting directions to define pixel values; and

a means for arranging the pixel values into an unfolded view.

35. A virtual endoscopy apparatus for performing virtual endoscopy on a volumetric image of a lumen-defining structure, the method comprising:

a means for selecting ray casting directions extending toward a lumen-defining surface of the lumen-defining structure;

a means for computing a statistical characteristic of voxels over a preselected distance along each ray casting direction into the lumen-defining structure;

a means for defining a pixel value for each ray casting direction based at least on the computed statistical characteristic; and

a means for arranging the pixel values into an endoscopic view of the lumen-defining structure.