Image reconstruction method for a computed tomography apparatus

• US 5,995,580 A
• Filed: 05/28/1998
• Issued: 11/30/1999
• Est. Priority Date: 06/02/1997
• Status: Expired due to Term

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Schaller, Stefan
• Primary Examiner(s): Bruce, David Vernon
• Application Number:
  US09/086,151
• Time in Patent Office: 551 Days
• Field of Search: 378/4, 378/15, 378/901
• 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
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

An exact image reconstruction method for computed tomography allows the reconstruction of a sub-volume of interest in a long subject from cone beam or pyramid beam CT data using a spiral focus path. A two-stage reconstruction process is utilized that, by line integration over the detector, first calculates 3D radon values of a sub-volume of interest defined only for the respective φ-plane for each φ-plane of a 3D spherical coordinate system. For each φ-plane, the sub-volume of interest is limited toward the exterior by the radius of the measurement field and is upwardly and downwardly limited by curved surfaces that arise by the locus of a straight line perpendicular to the φ-plane under consideration proceeding to each focus point of a spiral segment.

Claims

1. A method for reconstructing an image of an examination subject in a 3D-spherical coordinate system comprising a plurality of φ

-planes in an x-ray computed tomography system, comprising the steps of;

conducting a spiral scan of an examination subject by rotating an x-ray beam, having an x-ray beam geometry, around a measurement field in which the examination subject is disposed, said x-ray beam proceeding through a plurality of projections from a plurality of successive focus point locations, said measurement field having a measurement field radius;

detecting x-rays from said x-ray beam attenuated by said examination subject during said spiral scan, said radiation detector producing detector values dependent on the x-rays incident thereon;

conducting line integrations along a plurality of lines over data derived from said detector values to obtain intermediate data;

for each of said φ

-planes, calculating 3D radon values representing plane integrals of integration planes containing said straight lines from said intermediate data for a sub-volume of interest defined only for a respective φ

-plane and limiting said sub-volume of interest by said measurement field radius and by respective curved surfaces defined by a locus of a straight line proceeding perpendicularly to said respective φ

-plane and proceeding from said focus point locations positioned on a spiral segment of said spiral scan.

2. A method as claimed in claim 1 wherein the step of conducting a spiral scan comprises conducting a spiral scan using an x-ray beam having cone beam geometry.

3. A method as claimed in claim 1 wherein the step of conducting a spiral scan comprises conducting a spiral scan using an x-ray beam having pyramidal beam geometry.

4. A method as claimed in claim 1 comprising the additional step of limiting calculation of plane integrals to respective sub-areas of interest, each sub-area of interest being defined as that part of a respective integration plane located inside said sub-volume of interest defined for said respective φ

-plane, by dividing projections having a focus point location on one of said curved surfaces into two sub-fans by one of said straight lines lying in the respective integration plane as well as in one of said curved surfaces; and

comprising the further step of assembling said sub-area of interest by linear combination of sub-fans.

5. A method as claimed in claim 4 comprising the additional step of selecting a least noise-infested combination as said linear combination of sub-fans.