Adaptive detector masking for speed-up of cone beam reconstruction

• US 5,878,103 A
• Filed: 06/30/1997
• Issued: 03/02/1999
• Est. Priority Date: 06/30/1997
• Status: Expired due to Term

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Siemens Corporate Research Incorporated (Siemens AG)
• Inventors: Samarasekera, Supun, Sauer, Frank
• Primary Examiner(s): Porta, David P.
• Assistant Examiner(s): Bruce, David Vernon
• Application Number:
  US08/884,248
• Time in Patent Office: 610 Days
• Field of Search: 378/4, 378/15, 378/94
• 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: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

A scanning and data acquisition technique for three dimensional (3D) computerized tomographic (CT) imaging of an object, wherein scanning at a plurality of positions along a source scanning trajectory causes an area detector to acquire cone beam projection data corresponding to a shadow of said object at each of scanning positions and Radon derivative data is calculated by processing line integral values from cone beam projection data. In order to improve the calculation efficiency of the Radon derivative calculation, calculation of the Radon derivative data uses a determination of the left and right boundaries of the shadow for each of the scanning positions, and calculates the Radon derivative data only using projection data from within the determined boundaries.

Claims

1. A scanning and data acquisition method for three dimensional (3D) computerized tomography (CT) imaging of an object in a field of view radially centered on a predetermined axis, the method comprising the steps of:

applying cone beam energy from a cone beam source to at least a portion of the object;

defining a source scanning trajectory as a path traversed by the source;

using the cone beam source, fixed relative to an area detector with both source and detector movably positioned relative to the object, to scan about the object;

specifying the source scanning trajectory as a spiral path defining a plurality of spaced stages on a predetermined geometric surface surrounding the field of view such that each plane passing through the field of view intersects the scanning trajectory in at least one point and intersects the area detector, the area detector comprising a plurality of detector elements arranged in an array of rows and columns and having a height that extends sufficiently along a direction generally parallel to the predetermined axis so as to span at least two consecutive stages of the spiral path having the largest spacing therebetween;

scanning at a plurality of positions along the source scanning trajectory to cause the detector elements of said area detector to acquire cone beam projection data corresponding to a shadow of said object on the detector at each of said scanning positions;

calculating Radon derivative data by processing line integral values from the cone beam projection data acquired at each of said scanning positions; and

reconstructing an image of the object using said Radon derivative data;

wherein said step of calculating Radon derivative data includes a preliminary determination step for determining left and right boundaries of said shadow on the detector at each of said scanning positions, and then excluding cone beam projection data determined to be outside said left and right boundaries when calculating said Radon derivative data.

2. The method of claim 1, wherein said determination step is carried out by a pre-processing step before any processing of line integral values by said calculating step.

3. The method of claim 1, wherein said determination step is carried out during said calculating step by calculating a plurality of vertical line integrals for each object projection, and analyzing said vertical line integrals to determine the left and right boundaries.

4. The method of claim 1, wherein said determination step determines left and right boundaries as straight vertical lines.

5. The method of claim 1, wherein said determination step determines left and right boundaries as curved vertical lines.

6. A scanning and data acquisition apparatus for three dimensional (3D) computerized tomography (CT) imaging of an object in a field of view radially centered on a predetermined axis, comprising:

means for applying cone beam energy from a cone beam source to at least a portion of the object;

means for defining a source scanning trajectory as a path traversed by the source;

means for using the cone beam source, fixed relative to an area detector with both source and detector movably positioned relative to the object, to scan about the object;

means for specifying the source scanning trajectory as a spiral path defining a plurality of spaced stages on a predetermined geometric surface surrounding the field of view such that each plane passing through the field of view intersects the scanning trajectory in at least one point and intersects the area detector, the area detector comprising a plurality of detector elements arranged in an array of rows and columns and having a height that extends sufficiently along a direction generally parallel to the predetermined axis so as to span at least two consecutive stages of the spiral path having the largest spacing therebetween;

means for scanning at a plurality of positions along the source scanning trajectory to cause the detector elements of said area detector to acquire cone beam projection data corresponding to a shadow of said object on the detector at each of said scanning positions;

preliminary processing means for determining left and right boundaries of said shadow on the detector at each of said scanning positions; and

reconstruction processing means for processing acquired cone beam projection data for reconstructing an image of the object, said reconstruction processing means being responsive to the left and right boundaries of said shadow as determined by said preliminary processing means, for excluding cone beam projection data that is outside the determined left and right boundaries, when processing cone beam projection data for reconstructing the image.

7. The apparatus of claim 6, wherein said reconstruction processing means calculates Radon derivative data by processing line integral values from the cone beam projection data acquired at each of said scanning positions, said line integrals having a length in the cone beam projection data that is determined by the left and right boundaries of each shadow.

8. The apparatus of claim 6, wherein said preliminary processing means calculates a plurality of vertical line integrals in the cone beam projection data acquired at each of said scanning positions, and analyzes said vertical line integrals to determine the left and right boundaries of each shadow.

9. The apparatus of claim 6, wherein said preliminary processing means determines the left and right boundaries as straight vertical lines.

10. The apparatus of claim 6, wherein said preliminary processing means determines the left and right boundaries as curved vertical lines.