Voxel-driven spiral reconstruction for cone-beam computer tomography

• US 20060140338A1
• Filed: 01/28/2004
• Published: 06/29/2006
• Est. Priority Date: 02/05/2003
• Status: Active Grant

• Current Assignee: Siemens Healthcare GMBH (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Stierstorfer, Karl, Bruder, Herbert, Lauritsch, Gunter
• Granted Patent: US 7,529,335 B2
• Time in Patent Office: Days
• US Class Current: 378/15
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: G06T 11/006 Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods

Abstract

A method is disclosed for generating computer tomography images using a 3D image reconstruction method. According to the method, to scan an object to be examined using a cone-shaped bundle of rays originating from a focal point and a planar, preferably multi-line detector for detecting the bundle of rays, the focal point is displaced along a spiral trajectory around the object to be examined. The detector delivers output data corresponding to the detected radiation and image voxels from the scanned examined object are reconstructed from the optionally pre-processed output data, the image voxels reflecting the attenuation coefficients of the respective voxel. Each image voxel is reconstructed separately from projection data, which covers a projection angular range of at least 108° and an approximate weighting is carried out for each voxel considered in order to standardise the projection data using the voxel.

Claims

1. A method for generating images in computed tomography using 3D image reconstruction, the method comprising:

scanning an examination object by moving a focus on a spiral focal track about the examination object using a conical beam emanating from the focus and using a planar detector for detecting the beam, the detector supplying output data corresponding to the detected radiation; and

reconstructing image voxels from the scanned examination object from the output data and reproducing attenuation coefficients of the respective voxel,

each image voxel being reconstructed separately from projection data that include a projection angular range of at least 180°

, and

an approximate weighting taking place for each voxel considered in order to normalize the projection data used relating to the voxel.

2. The method as claimed in claim 1, wherein, in order to reconstruct an image voxel, using all the detector data along a straight line that runs through the cone beam projection of the image voxel and is aligned in the direction of the projection of the spiral tangent.

3. The method as claimed in claim 1, wherein the image data of the detector image are subjected to a cosine weighting for compensating oblique radiation.

4. The method as claimed in claim 1, wherein data not directly available are obtained from the available data by interpolation from neighboring detector data.

5. The method as claimed in claim 1, wherein during the weighting for compensating the data redundancy, two measuring beams (Sa, Sb) are regarded as redundant precisely when it holds that:

(θ

_a=(2k·

π

+θ

_b and p_a=p_b) or (θ

_a=(2k+1)·

π

+θ

_b and p_a=−

p_b), where

k represents an arbitrary natural number,

θ

represents the projection angle, and

p represents the distance from the z-axis.

6. The method as claimed in claim 5, wherein the redundant data are multiplied by generalized Parker weights.

7. The method as claimed in claim 1, wherein a ramp filter that is manipulated with the aid of a smoothing window is applied to the normalized data.

8. The method as claimed in claim 1, wherein a distance weighting is performed for the purpose of 3D back projection into the voxel considered.

9. The method as claimed in claim 1, wherein the method is used for cardiac computer tomography by at least one of selecting, weighting and sorting the measured data in accordance with the movement phases of an examined heart.

10. A CT unit for scanning an examination object, comprising:

a beam emanating from at least one focus and a detector array that is of planar design and has a multiplicity of distributed detector elements for detecting the rays of the beam, the at least one focus being movable relative to the examination object on at least one focal track that runs around the examination object and a detector array situated opposite;

means for collecting detector data, filtering and 3D back projection; and

means for processing the measured data being fashioned in such a way to carry out the method as claimed in claim 1.

11. Computer program product including program elements that during operation in a CT unit, execute the method as claimed in claim 1.

12. The method as claimed in claim 2, wherein the image data of the detector image are subjected to a cosine weighting for compensating oblique radiation.

13. The method as claimed in claim 1, wherein data not directly available are obtained from the available data by interpolation from neighboring detector data.

14. The method as claimed in claim 2, wherein during the weighting for compensating the data redundancy, two measuring beams (Sa, Sb) are regarded as redundant precisely when it holds that:

(θ

_a=(2k·

π

+θ

_b and p_a=p_b) or (θ

_a=(2k+1)·

π

+θ

_b and p_a=−

p_b), where

k represents an arbitrary natural number,

θ

represents the projection angle, and

p represents the distance from the z-axis.

15. The method as claimed in claim 14, wherein the redundant data are multiplied by generalized Parker weights.

16. A CT unit for scanning an examination object, comprising:

a beam emanating from at least one focus and a detector array that is of planar design and has a multiplicity of distributed detector elements for detecting the rays of the beam, the at least one focus being movable relative to the examination object on at least one focal track that runs around the examination object and a detector array situated opposite; and

means for reconstructing image voxels from the scanned examination object from the output data and reproducing attenuation coefficients of the respective voxel, each image voxel being reconstructed separately from projection data that include a projection angular range of at least 180°

, and an approximate weighting taking place for each voxel considered in order to normalize the projection data used relating to the voxel.