Method and apparatus for calibrating an intra-operative X-ray system

• US 5,923,727 A
• Filed: 09/30/1997
• Issued: 07/13/1999
• Est. Priority Date: 09/30/1997
• Status: Expired due to Term

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Siemens Corporate Research Incorporated (Siemens AG)
• Inventors: Navab, Nassir
• Primary Examiner(s): Porta, David P.
• Application Number:
  US08/940,923
• Time in Patent Office: 651 Days
• Field of Search: 378/20, 378/62, 378/63, 378/204, 378/205, 378/206, 378/207
• US Class Current: 378/207
• CPC Class Codes: A61B 6/547 involving tracking of position of the device or parts of the device
• CPC Class Codes: A61B 6/583 using calibration phantoms
• CPC Class Codes: A61B 6/584 determining position of components of the apparatus or device using images of the phantom

Abstract

Apparatus for calibrating an intra-operative X-ray system having an X-ray source and a detector includes an optical camera associated with the X-ray source; an optical camera associated with the detector; an X-ray phantom placed within a field of view of the X-ray system during an off-line process; an optical phantom placed within a field of view of the optical cameras during the off-line process as well as the on-line process (called the patient run); and apparatus for computing a respective projection matrix from an image provided by any of the X-ray source and detector, and the optical cameras. A method to obtain the projection matrices characterizing the X-ray imaging geometry during the patient run, using the projection matrices associated to X-ray geometry as well as the optical cameras computed during an off-line process, and the projection matrices associated to the optical cameras during the patient run. The relative motion of the apparatus between the off-line and on-line process is computed using the projection matrices characterizing the imaging geometry of the optical cameras. This information leads us to the modification of the off-line estimation of X-ray imaging geometry and to the characterization of its on line imaging geometry.

Claims

1. A method for calibrating an intra-operative X-ray system having an X-ray source and a detector, said method comprising the steps of:

(1) performing an off-line process comprising;

(a) initializing said X-ray system into an arbitrary position,

(b) placing into a position an X-ray phantom,

(c) placing into a first position an optical phantom,

(d) taking an off-line X-ray image,

(e) taking an optical image by a camera associated with said X-ray source,

(f) taking an off-line optical image by a camera associated with said detector; and

(2) performing an on-line process comprising;

(A) initializing said X-ray system into a position,

(B) placing into a second position said optical phantom,

(C) taking an on-line X-ray image,

(D) taking an on-line optical image by a camera associated with said X-ray source, and

(E) taking an optical image by a camera associated with said detector; and

(3) combining information from said off-line optical images and said off-line X-ray image and the on-line optical images so as to derive a projection matrix for use in an image reconstruction process using said on-line X-ray image.

2. A method for calibrating an intra-operative X-ray system as recited in claim 1, wherein said second position of said optical phantom in step 2-(B) is the same as said first position of said optical phantom in step 1-(c).

3. A method for calibrating an intra-operative X-ray system as recited in claim 1, wherein said second position of said optical phantom in step 2-(B) is displaced from said first position of said optical phantom in step 1-(c).

4. A method for calibrating an intra-operative X-ray system as recited in claim 3, including a step of determining spatial relationship parameters of said first position of said optical phantom relative to said second position of said optical phantom.

5. A method for calibrating an intra-operative X-ray system as recited in claim 4, wherein step (3) includes combining of said spatial relationship parameters of said first position of said optical phantom so as to derive said projection matrix for use in an image reconstruction process.

6. A method for calibrating an intra-operative X-ray system as recited in claim 1, including a step of utilizing said projection matrix so as to form a reconstructed image.

7. A method for calibrating an intra-operative X-ray having an X-ray source and a detector system, said method comprising the steps of:

(A) performing an off-line process comprising;

(a) initializing said X-ray system into an initial position, as closely as possible to its position when a patient is present,

(b) placing into position an X-ray phantom,

(c) placing into position an optical phantom,

(d) taking off-line, a radiographic image,

(e) computing and storing a projection matrix P_x

(f) taking off-line, an optical image by a camera associated with said X-ray source,

(g) computing from said optical image and storing a projection matrix P_sc

(h) taking off-line, an optical image by a camera associated with said detector, and

(i) computing from said optical image and storing a projection matrix P_dc ; and

(B) performing an on-line process comprising;

(1) placing into position an optical phantom,

(2) taking on-line, a radiographic image,

(3) taking on-line, an optical image by a camera associated with said X-ray source,

(4) computing from said optical image and storing a projection matrix p_sc

(5) taking on-line, an optical image by a camera associated with said detector,

(7) computing from said optical image and storing a projection matrix p_dc, and

(8) calculating an X-ray projection matrix P_x from said foregoing matrices P_x, P_sc, P_dc, p_sc, p_dc.

8. A method for calibrating an intra-operative X-ray having an X-ray source and a detector system during a rotational run around the patient, said method comprising the steps of:

(A) performing an off-line process comprising;

(a) initializing said X-ray system into a starting position (i),

(b) placing into position an X-ray phantom,

(c) placing into position an optical phantom,

(d) taking off-line, a radiographic image,

(e) computing and storing a projection matrix P_xⁱ

(f) taking off-line, an optical image by a camera associated with said X-ray source,

(g) computing from said optical image and storing a projection matrix P_scⁱ

(h) taking off-line, an optical image by a camera associated with said detector,

(i) computing from said optical image and storing a projection matrix P_dcⁱ

(j) rotating said X-ray system to the next position (i+1)

(k) repeating steps (d) through (j) unless the end position is reached; and

(B) performing an on-line process comprising;

(1) initializing said X-ray system into said starting position (i),

(2) placing into position an optical phantom,

(3) taking on-line, a radiographic image,

(4) taking on-line, an optical image by a camera associated with said X-ray source,

(5) computing from said optical image and storing a projection matrix p_scⁱ

(6) taking on-line, an optical image by a camera associated with said detector,

(7) computing from said optical image and storing a projection matrix p_dcⁱ

(8) calculating an X-ray projection matrix P_xⁱ from said foregoing matrices P_xⁱ, P_scⁱ, P_dcⁱ, p_scⁱ, p_dcⁱ ;

(9) rotating said X-ray system tp the next position (i+1),

(10) repeating (3) through (9) unless the end position is reached, and

(11) applying said projection matrices P_xⁱ to an image reconstruction process.

10. Apparatus for calibrating an intra-operative X-ray system as recited in claim 8, wherein said optical camera associated with said X-ray source is mounted in fixed spatial relationship with and proximate said X-ray source.

12. Apparatus for calibrating an intra-operative X-ray system as recited in claim 10, wherein said X-ray phantom comprises X-ray opaque reference bodies supported in an X-ray transparent body.

14. Apparatus for calibrating an intra-operative X-ray system as recited in claim 12, including means for utilizing said respective projection matrices so as to form a reconstructed image.

9. Apparatus for calibrating an intra-operative X-ray system having an X-ray source and a detector, said apparatus comprising:

an optical camera associated with said X-ray source;

an optical camera associated with said detector;

an X-ray phantom placed within a field of view of said X-ray system;

an optical phantom placed within a field of view of said optical cameras; and

means for computing a respective projection matrix from an image provided by any of said X-ray source and detector, and said optical cameras.

11. Apparatus for calibrating an intra-operative X-ray system as recited in claim 9, wherein said optical camera associated with said detector is mounted in fixed spatial relationship with and proximate said detector.

13. Apparatus for calibrating an intra-operative X-ray system as recited in claim 11, wherein said optical phantom comprises visible reference marks formed on an X-ray transparent body.

15. A method for calibrating an intra-operative X-ray having an X-ray source and a detector system during a rotational run around a patient, said method comprising the steps of:

beginning at a starting position and taking a radiographic image of an X-ray phantom from a first spatial position and taking respective optical images of an optical phantom from respective second and third spatial positions, said first and second spatial positions being in fixed relationship relative to said first spatial position, wherein said optical and X-ray phantoms are in fixed spatial relationship to one another; and

deriving and storing respective projection matrices from said images.

16. A method for calibrating an intra-operative X-ray in accordance with claim 15 wherein said steps are repeated up to an end position of said run.

17. A method for calibrating an intra-operative X-ray in accordance with claim 16 wherein the steps recited in claim 8 are performed without a patient being present.

18. A method for calibrating an intra-operative X-ray in accordance with claim 17, comprising the following steps with a patient being present:

beginning at said starting position and taking respective optical images of said optical phantom from said first and second spatial positions in fixed relationship relative to said first spatial position;

deriving respective projection matrices from said images; and

calculating an X-ray projection matrix from said projection matrices.

19. A method for calibrating an intra-operative X-ray in accordance with claim 18 wherein said steps are performed without said X-ray phantom being present.

20. A method for calibrating an intra-operative X-ray in accordance with claim 19 wherein said steps are repeated up to an end position of said run.

21. A method for calibrating an intra-operative X-ray in accordance with claim 20 wherein an X-ray image is taken at each step.

22. A method for calibrating an intra-operative X-ray in accordance with claim 21 wherein said respective X-ray projection matrices for said steps are utilized for calibration of said X-ray image.

23. A method for calibrating an intra-operative X-ray having an X-ray source and a detector system during a rotational run around a patient, said method comprising the steps of:

beginning at a starting position and taking a radiographic image of an X-ray phantom from a first spatial position and taking respective optical images of an optical phantom from respective second and third spatial positions, said first and second spatial positions being in known relationship relative to said first spatial position, wherein said optical and X-ray phantoms are in known spatial relationship to one another; and

deriving and storing respective projection matrices from said images.

24. A method for calibrating an intra-operative X-ray in accordance with claim 23 wherein said steps are repeated up to an end position of said run.

25. A method for calibrating an intra-operative X-ray in accordance with claim 24 wherein the steps recited in claim 8 are performed without a patient being present.

26. A method for calibrating an intra-operative X-ray in accordance with claim 25, comprising the following steps with a patient being present:

beginning at said starting position and taking respective optical images of said optical phantom from said first and second spatial positions in known relationship relative to said first spatial position;

deriving respective projection matrices from said images; and

calculating an X-ray projection matrix from said projection matrices and from said known relationships recited in claim 23.

27. A method for calibrating an intra-operative X-ray in accordance with claim 26 wherein said steps are performed without said X-ray phantom being present.

28. A method for calibrating an intra-operative X-ray in accordance with claim 27 wherein said steps are repeated up to an end position of said run.

29. A method for calibrating an intra-operative X-ray in accordance with claim 28 wherein an X-ray image is taken at each step.

30. A method for calibrating an intra-operative X-ray in accordance with claim 29 wherein said respective X-ray projection matrices for said steps are utilized for calibration of said X-ray image.