CT cone beam scanner with fast and complete data acquistion and accurate and efficient regional reconstruction

• US 6,014,419 A
• Filed: 11/07/1997
• Issued: 01/11/2000
• Est. Priority Date: 11/07/1997
• Status: Expired due to Fees

• Current Assignee: Imagingtech, Inc.
• Original Assignee: Imagingtech, Inc.
• Inventors: Hu, Hui
• Primary Examiner(s): Bruce, David Vernon
• Application Number:
  US08/966,155
• Time in Patent Office: 795 Days
• Field of Search: 378/4, 378/15, 378/901
• US Class Current: 378/4
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

A method is provided for reconstructing an image of an object, for use in an imaging system wherein a detector is mounted for measuring radiation emanating in a cone beam of rays which converge at a focal point. The method includes the step of establishing relative movement between the cone beam focal point and the object along a composite scan path, comprising primary and supplementary scan path components, the supplementary path usefully comprising a linear or helical path. The method further includes acquiring a set of cone beam data of the object with the detector during movement along the supplementary scan path component, computing a set of values of an intermediate function from the cone beam data, each of said computed values having an associated location defined by a prespecified point grid lying on the detector plane, and employing each of the computed values in a back-projection operation to determine the value of a reconstruction function, for use in forming an image of the object. The method also includes a strategy of imaging longitudinally-unbounded object section by section

Claims

1. In an imaging system wherein a detector is mounted for measuring radiation emanating in a cone beam of rays which converge at a focal point, a method for reconstructing an image of an object comprising the steps of:

establishing relative movement between said cone beam focal point and said object along a composite scan path, comprising primary and supplementary scan path components;

acquiring a set of cone beam data of said object with said detector during movement along said supplementary scan path component, said cone beam data associated with said supplementary scan path to be used only for deriving information which cannot be derived from other cone beam data that is associated with the primary scan path;

computing a set of values of an intermediate function from said cone beam data, each of said computed values having an associated location defined by a prespecified point grid lying on the detector plane; and

employing each of said computed values to compute the supplementary component of a reconstruction function of said object.

2. The method of claim 1 wherein said object comprises a longitudinally-unbounded object, and said method comprises the further steps of:

defining a scan field of view relative to said imaging system;

determining error propagation distance in the direction along the normal of a plane containing the primary scan path;

modifying the definition of the scan field of view, according to said error propagation distance; and

generating the reconstruction within the modified field of view from the composite scan path.

3. The method of claim 2 wherein:

repeated supplementary scans are made at different selected locations along a Z-axis positioned with respect to said object until an entire longitudinal extent of the longitudinally-unbounded object is imaged.

4. The method of claim 2 wherein:

repeated primary scans are made at different selected locations along a Z-axis positioned with respect to said object until an entire region of interest of the object is imaged.

5. The method of claim 4 wherein:

the maximum longitudinal displacement between adjacent primary scans, along said Z-axis, is chosen so that within said object no gap exists between the modified fields of view of said adjacent primary scans.

6. The method of claim 1 wherein:

said supplementary scan path component comprises at least a linear component.

7. The method of claim 1 wherein:

said primary scan path component comprises at least a circular component.

8. The method of claim 1 wherein:

said value of said reconstruction function is computed by means of interpolation of values of said intermediate function.

9. The method of claim 1 wherein:

said step of computing the values of said intermediate function comprises summing weighted cone beam data only along the lines representing those planes not intersecting the primary scan path.

10. The method of claim 1 wherein:

said supplementary scan path component comprises at least a helical component.

11. In an imaging system wherein a detector is mounted for measuring radiation emanating in a cone beam of rays which converge at a focal point, a method for reconstructing an image of an object comprising the steps of:

establishing relative movement between said cone beam focal point and said object along a composite scan path, comprising primary and supplementary scan path components;

acquiring a set of cone beam data of said object with said detector during movement along said supplementary scan path component;

computing a set of values of an intermediate function from said cone beam data, each of said computed values having an associated location defined by a prespecified point grid lying on the detector plane, said values of said intermediate function being computed on the detector plane on a grid whose sampling spacing is substantially greater than that of the detector elements projected on the detector plane; and

employing each of said computed values to compute the supplementary component of a reconstruction function of said object.

12. In an imaging system wherein a detector is mounted for measuring radiation emanating in a cone beam of rays which converse at a focal point, a method for reconstructing an image of an object comprising the steps of:

computing at least one part of the said reconstruction on a sparser three-dimensional image grid, which, compared with a full-size image grid, has a larger spacing between points in the x, y, and/or z directions;

combining thumbnail reconstructions of all said computed parts;

generating a combined full size reconstruction of said computed parts from the combined thumbnail reconstructions by interpolation; and

combining the interpolated full size reconstruction with the full-size reconstructions of other parts to produce the complete full-size reconstruction.

13. In an imaging system wherein a detector is mounted for measuring radiation emanating in a cone beam of rays which converge at a focal point, a method for reconstructing an image of the object comprising the steps of:

establishing relative movement between said cone beam focal point and said object along a composite scan path comprising primary and curved supplementary components;

acquiring a set of cone beam data of said object with said detector during movement along said curved supplementary scan path; and

deriving an intermediate function from said cone beam data for use in forming the supplementary component of the reconstruction function of said object.

14. The method of claim 13 wherein:

said method includes acquiring a second set of cone beam data of said object during movement along said primary scan path, generating a primary component reconstruction function from said second set of cone beam data, and combining said primary component reconstruction function with said supplementary component reconstruction function to provide an image of said object.

15. The method of claim 14 wherein said method includes the steps of:

computing at least one part of the said reconstruction on a sparser three-dimensional image grid, which, compared with a full-size image grid, has a larger spacing between points in the x, y, and/or z directions;

combining thumbnail reconstructions of all said computed parts;

generating a combined full size reconstruction of said computed parts from the combined thumbnail reconstructions by interpolation; and

combining the interpolated full size reconstruction with the full-size reconstructions of other parts to produce the complete full-size reconstruction.

16. The method of claim 14 wherein:

said reconstruction method includes a filtering step applied to at least some parts of the said reconstruction in selected relation to the backprojection step.

17. The method of claim 14 wherein said object comprises a longitudinally-unbounded object, and said method comprises the further steps of:

defining a scan field of view relative to said imaging system;

determining error propagation distance in the direction along the normal of a plane containing the primary scan path

modifying the definition of the scan field of view, according to said error propagation distance; and

generating the reconstruction within the modified field of view from the composite scan path.

18. The method of claim 19 wherein:

the maximum longitudinal displacement between adjacent primary scans, along said Z-axis is chosen so that within said object no gap exists between the modified fields of view of said adjacent primary scans.

19. The method of claim 17 wherein:

repeated primary scans are made at different selected locations, along a Z-axis positioned with respect to said object until an entire region of interest of the object is imaged.

20. The method of claim 17 wherein:

repeated supplementary scans are made at different selected locations along a Z-axis positioned with respect to said object until an entire longitudinal extent of the longitudinally-unbounded object is imaged.

21. The method of claim 13 wherein:

said supplementary scan path component comprises at least a helical component.

22. The method of claim 13 wherein:

said primary scan path component comprises at least a circular component.

23. The method of claim 13 wherein:

said value of said reconstruction function is computed by means of interpolation of values of said intermediate function.

24. The method of claim 13 wherein:

the values of said intermediate function are computed on a detector plane on a grid whose sampling spacing is substantially greater than that of the detector elements projected on the detector plane.

25. The method of claim 13 wherein said deriving step comprises:

computing a set of values of an intermediate function from said cone beam data, each of said computed values having an associated location defined by a prespecified point grid lying on the detector plane; and

employing each of said computed values to compute the supplementary component of reconstruction of said object.

26. The method of claim 13 wherein:

said cone beam data associated with movement along the supplementary scan path is used only for deriving information which cannot be derived from other cone beam data that is associated with the primary scan path.

27. The method of claim 13 wherein:

said step of computing the values of said intermediate function comprises summing weighted cone beam data only along the lines representing those planes not intersecting the primary scan path.