Method and apparatus for reducing X-ray dosage in a spiral scan cone beam CT imaging system

• US 6,233,303 B1
• Filed: 07/21/1999
• Issued: 05/15/2001
• Est. Priority Date: 07/21/1999
• Status: Expired due to Term

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Siemens Corporate Research Incorporated (Siemens AG)
• Inventors: Tam, Kwok
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US09/358,071
• Time in Patent Office: 664 Days
• Field of Search: 378/4, 378/8, 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: A61B 6/06 Diaphragms
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

A scanning and data acquisition method and apparatus for three dimensional (3D) computerized tomography (CT) imaging of an ROI in an object, wherein a reconstructed image is developed by calculating reconstruction data along a plurality of line segments L formed in cone beam data acquired on a detector at a plurality of source positions about the ROI. The endpoints of the line segments L formed in the cone beam data acquired at each of the source positions is determined by a data combination mask which is applied to the cone beam data. When acquiring cone beam data near the top or bottom edges of the ROI, a radiation blocking element is operated for blocking radiation directed toward the ROI, so that only that portion of the detector is exposed to radiation.

Claims

1. Apparatus for performing three dimensional computerized tomographic imaging of a region-of-interest (ROI) in an object using a cone beam source of radiation energy, comprising:

a source of cone beam radiation energy;

a manipulator for providing a source scanning trajectory as a scan path that encircles the ROI in the object and causes an area detector and the source to traverse the scan path;

a controller coupled to the manipulator and the source for causing the source to apply radiation energy towards the object from a plurality of source positions along the scan path as the source traverses the scan path, the area detector acquiring cone beam projection data corresponding to respective portions of the object at each of said source positions;

an image reconstruction processor for applying a mask to the cone beam projection data acquired by the area detector at each of the source positions, and calculating therefrom reconstruction data along each of a plurality of line segments L formed in the masked cone beam projection data;

a radiation blocking element responsive to the controller for selectively blocking radiation directed toward the object so as to expose only a sub-portion of the area detector; and

a reconstruction processor for processing said reconstruction data for reconstructing a 3D image of the ROI in the object.

2. The apparatus of claim 1, wherein the controller causes said radiation blocking element to block radiation from reaching the sub-portion of the detector when the detector is acquiring cone beam data at source positions along first and second portions of the scan path.

3. The apparatus of claim 2, wherein said first and second portions of the scan path correspond to a π

portion of the angular range of the scan path near a top and bottom edge, respectively, of the ROI.

4. The apparatus of claim 1, wherein:

the mask applied to the cone beam projection data by the image reconstruction processor has upper and lower boundaries formed by cone beam projections onto the plane of the detector of portions of the source scan path that are above and below, respectively, the source position that acquired the data being masked, as well as a horizontal axis; and

the radiation blocking element blocks radiation directed toward the object so as to not expose a portion of the detector which resides on one side of the horizontal axis of the mask.

5. The apparatus of claim 4, wherein the controller causes said radiation blocking element to block radiation from reaching that portion of the detector which resides on an upper side of horizontal axis in the mask when the detector is acquiring cone beam data at source positions along a first portion of the scan path.

6. The apparatus of claim 5, wherein the controller causes said radiation blocking element to block radiation from reaching that portion of the detector which resides on a lower side of the horizontal axis in the mask when the detector is acquiring cone beam data during a second portion of the scan path.

7. The apparatus of claim 5, wherein said first portion of the scan path corresponds to a π

portion of the angular range of the scan path near a top edge of the ROI.

8. The apparatus of claim 6, wherein said second portion of the scan path corresponds to a π

portion of the angular range of the scan path near the bottom edge of the ROI.

9. A method for performing three dimensional computerized tomographic imaging of a region-of-interest (ROI) in an object using a cone beam source of radiation energy, comprising the steps of:

defining a source scanning trajectory as a scan path that encircles the ROI in the object and is traversed by the cone beam source;

using the cone beam source, fixed relative to an area detector with both source and detector movably positioned relative to the object, for applying radiation energy towards the object from a plurality of source positions along the scan path as said source traverses the scan path, said applying causing said area detector to acquire cone beam projection data corresponding to respective portions of the object at each of said source positions;

masking the cone beam projection data acquired at each of said source positions with a mask;

calculating reconstruction data from each of a plurality of line segments L formed in the masked cone beam projection data acquired at each of said source positions, said mask being used during said calculating step to determine the length of the line segments L formed therein;

selectively blocking radiation directed toward the object so as to expose only a sub-portion of the area detector corresponding substantially to the length of the line segments L formed in the masked cone beam projection data acquired at each of said source positions; and

reconstruction processing the reconstruction data calculated for said line segments L, for reconstructing a 3D image of the ROI in the object.

10. The method of claim 9, wherein:

the mask applied to the cone beam projection data by the image reconstruction processor has upper and lower boundaries formed by cone beam projections onto the plane of the detector of portions of the source scan path that are above and below, respectively, the source position that acquired the data being masked, as well as a horizontal axis; and

said selective radiation blocking blocks radiation directed toward the object so as to not expose a portion of the detector which resides on one side of the horizontal axis in the mask.

11. The method of claim 10, wherein said selective radiation blocking blocks radiation from reaching that portion of the detector which resides on an upper side of horizontal axis in the mask when the detector is acquiring cone beam data at source positions along a first portion of the scan path.

12. The method of claim 11, wherein said selective radiation blocking blocks radiation from reaching that portion of the detector which resides on a lower side of the horizontal axis in the mask when the detector is acquiring cone beam data during a second portion of the scan path.

13. The method of claim 11, wherein said first portion of the scan path corresponds to a π

portion of the angular range of the scan path near a top edge of the ROI.

14. The method of claim 12, wherein said second portion of the scan path corresponds to a π

portion of the angular range of the scan path near the bottom edge of the ROI.

15. The method of claim 9, wherein said selective radiation blocking blocks radiation from reaching the sub-portion of the detector when the detector acquires cone beam data at source positions along first and second portions of the scan path.

16. The method of claim 15, wherein said first and second portions of the scan path correspond to a π

portion of the angular range of the scan path near a top and bottom edge, respectively, of the ROI.