Apparatus, system and method of calibrating medical imaging systems

• US 20040015077A1
• Filed: 07/11/2002
• Published: 01/22/2004
• Est. Priority Date: 07/11/2002
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: Cedara Software, Corp (International Business Machines Corporation)
• Inventors: Sati, Marwan, Cyr, Martin
• Granted Patent: US 7,065,393 B2
• Time in Patent Office: Days
• US Class Current: 600/427
• CPC Class Codes: A61B 6/08 Auxiliary means for directing the radiation beam to a particular spot, e.g. using light beams
• CPC Class Codes: A61B 6/4291 the detector being combined with a grid or grating
• CPC Class Codes: A61B 6/4405 the apparatus being movable or portable, e.g. handheld or mounted on a trolley
• CPC Class Codes: A61B 6/4441 the rigid structure being a C-arm or U-arm
• 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

Abstract

A C-arm imaging device method and system are provided with position determination means for determining the position of an imaging source and an imaging apparatus, and means for determining a local gravity vector. The device and system may also be provided with a magnetic north sensor imaging source focal point displacement due to bending determination means and information storage means are also provided. The apparatus and system is used to determine position of an imaging source, position of an imaging receptor, a local gravity vector and, if applicable, magnetic field distortion, for each of a plurality of orientations of the C-arm. Imaging source focal point displacement due to bending is determined using the position of the imaging source and the position of the imaging detector in correspondence to the local gravity vector and, if applicable, magnetic field distortion, for each of the plurality of orientations. This information can be stored for use in subsequent interpolation of imaging source focal point displacement based on a specific position of an imaging receptor a specific local gravity vector. Such an apparatus and system facilitates a calibration process, and permits dispensing with one or more calibration plates

Claims

1. A method of calibrating a C-arm imaging device comprising the steps of:

determining a position of an imaging source for each of a plurality of orientations of the C-arm;

determining a position of an imaging receptor for each of the plurality of orientations;

determining a local gravity vector for each of the plurality of orientations;

determining an imaging source focal point displacement due to bending using the position of the imaging source and the position of the imaging detector in correspondence to the local gravity vector for each of the plurality of orientations; and

storing information on the position of the imaging source, the position of the imaging receptor, the gravity vector, and the imaging source focal point displacement for each of the plurality of orientations, for use in subsequent interpolation of imaging source focal point displacement based on a specific position of an imaging receptor a specific local gravity vector.

2. A method of claim 1 wherein the plurality of orientations is obtained by rotating the C-arm about a plurality of angles around a first axis and a plurality of angles around a second axis.

3. A method of claim 2 wherein the plurality of angles are spaced 10 degrees apart.

4. A method of claim 3 wherein the plurality of orientations comprise about 100 or more orientations.

5. A method of claim 1, wherein the position of the imaging source is determined by obtaining a coordinate position in three dimensional space.

6. A method of claim 1, wherein the position of the imaging receptor is determined by obtaining a coordinate position in three dimensional space.

7. A method of claim 1 wherein the local gravity vector is determined with reference to a moveable part of the C-arm.

8. A method of claim 7 wherein the local gravity vector is determined by obtaining the angular displacement of the moveable part from alignment with the local gravitational field.

9. A method of claim 7 wherein the moveable pant of the C-arm is the imaging receptor.

10. A method of claim 1 wherein the imaging source focal point displacement is determined in conjunction with reference coordinates for the imaging source.

11. A method of claim 10 wherein the imaging source focal point displacement is derived from the change in position of the imaging source from the reference coordinates for the imaging source.

12. A method of claim 1 wherein the step of storing comprises saving information in a look-up table.

13. A method of claim 1 further comprising the steps of:

determining a specific position of the imaging receptor;

determining a specific gravity vector; and

interpolating imaging source focal point displacement using the stored information.

14. A method of claim 1 further comprising the steps of:

determining a magnetic field distortion for each of the plurality of orientations; and

storing the magnetic field distortion for use in subsequent interpolation of magnetic field distortion based on a specific orientation of the C-arm.

15. A method of claim 14 wherein magnetic field distortion is determined by:

determining a reference magnetic field vector in alignment with a magnetic pole for a reference orientation of the C-arm;

determining a magnetic field vector for each of the plurality of orientations; and

determining a change in magnetic field vector from the reference magnetic field vector for each of the plurality of orientations.

16. A method of claim 15 wherein the reference magnetic field vector, the magnetic field vector for each of the plurality of orientations, and the change in magnetic field vectors are expressed in coordinate form.

17. A method of claim 1 further comprising the step of using the interpolation of imaging source focal point displacement for projecting the position of a tracked objection computer assisted surgical systems.

18. A method of claim 14 further comprising the step of using the interpolation of magnetic field distortion for projecting the position of a tracked objection in computer assisted surgical systems.

19. A C-arm imaging device comprising:

means for determining a position of an imaging source for each of a plurality of orientations of the C-arm;

means for determining a position of an imaging receptor for each of the plurality of orientations;

means for determining a local gravity vector for each of the plurality of orientations;

means for determining an imaging source focal point displacement due to bending using the position of the imaging source and the position of the imaging detector in correspondence to the local gravity vector for each of the plurality of orientations; and

means for storing information on the position of the imaging source, the position of the imaging receptor, the gravity vector, and the imaging source focal point displacement for each of the plurality of orientations, for use in subsequent interpolation of imaging source focal point displacement based on a specific position of an imaging receptor a specific local gravity vector.

20. An apparatus of claim 19 wherein the means for determining a position comprises a position sensor and a position tracker positioned proximate to the imaging source.

21. An apparatus of claim 20 wherein the imaging source is an X-ray source.

22. An apparatus of claim 19 wherein the means for determining a position comprises a position sensor and a position tracker positioned proximate to the imaging receptor.

23. An apparatus of claim 22 wherein the imaging source comprises an image intensifier

24. An apparatus of claim 19 wherein the means for determining a local gravity vector comprises a gravity sensor.

25. An apparatus of claim 24 wherein the gravity sensor is positioned on a mobile part of the C-arm.

26. An apparatus of claim 24 wherein gravity sensor is positioned proximate to the image receptor.

27. An apparatus of claim 19 fisher comprising means for determining a magnetic field distortion for each of the plurality of orientations.

28. An apparatus of claim 27 wherein the means for determining a magnetic field distortion comprises a magnetic pole sensor positioned proximate to the C-arm.

29. An apparatus of claim 28 wherein the magnetic pole sensor is positioned on a support base of the C-arm.

30. An apparatus of claim 19 wherein the C-arm is provided with a single calibration plate.

31. An apparatus of claim 28 wherein the C-arm lacks a calibration plate or dewarp grid.

32. A system for calibrating a C-arm imaging device comprising:

means for determining a position of an imaging source for each of a plurality of orientations of the C-arm;

means for determining a position of an imaging receptor for each of the plurality of orientations;

means for determining a local gravity vector for each of the plurality of orientations;

means for determining an imaging source focal point displacement due to bending using the position of the imaging source and the position of the imaging detector in correspondence to the local gravity vector for each of the plurality of orientations; and

means for storing information on the position of the imaging source, the position of the imaging receptor, the gravity vector, and the imaging source focal point displacement for each of the plurality of orientations, for use in subsequent interpolation of imaging source focal point displacement based on a specific position of an imaging receptor a specific local gravity vector.