X-ray computer tomograph

• US 20030053597A1
• Filed: 10/10/2002
• Published: 03/20/2003
• Est. Priority Date: 09/29/2000
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Flohr, Thomas, Ohnesorge, Bernd
• Granted Patent: US 6,735,273 B2
• Time in Patent Office: Days
• US Class Current: 378/156
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/06 Diaphragms
• CPC Class Codes: A61B 6/4021 involving movement of the focal spot
• CPC Class Codes: A61B 6/4035 the source being combined with a filter or grating
• CPC Class Codes: A61B 6/405 Source units specially adapted to modify characteristics of the beam during the data acquisition process A61B6/4021, A61B6/4035 take precedence
• CPC Class Codes: A61B 6/482 involving multiple energy imaging
• 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: G06T 2211/408 Dual energy
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction

Abstract

An X-ray computer tomography apparatus is disclosed wherein a beam filter arrangement (26) that comprises regions (28, 30) of different filter material or/and different thickness profile of the filter material is arranged in the beam path preceding an examination subject. For multi-spectra beam hardening correction with estimation of the base material lengths, the computer tomography apparatus is fashioned for implementing projections of the examination subject given different effective material thickness or/and different effective material of the beam filter arrangement (26).

Claims

1. X-ray computer tomograph apparatus comprising

a radiator-detector arrangement (10, 18) that supplies projection measured values for each slice projection of an examination subject (16) in allocation to a plurality of detection channels of the detector (18) distributed over the entire projection region of this slice projection, each of said projection measured values being representative of the attenuation of the x-radiation in the respective detection channel produced by the examination subject (16), whereby the radiator-detector (10, 18) arrangement is fashioned for respectively supplying a plurality of at least two projection measured values given respectively different average energy of the x-radiation entering into the examination subject for multi-spectra beam hardening correction in allocation to each detection channel lying within the projection region of a slice projection;

an electronic evaluation and reconstruction unit (22) connected to the radiator-detector arrangement (10, 18) that is fashioned for determining a beam hardening-corrected projection value for each of the projection measured values and of reconstructing a tomographic image of the examination subject (16) upon employment of the corrected projection values; and

energy influencing means (26) for influencing the average energy of the x-radiation entering into the examination subject (16),

characterized in that the energy influencing means (26) comprise a beam filter arrangement (26) arranged in the beam path preceding the examination subject that comprises regions (28, 30) of different filter material or/and different thickness profile of the filter material for influencing the average energy of the x-radiation, and in that the radio-detector (10, 18) arrangement is fashioned for respectively supplying a plurality of at least two projection measured values given respectively different filter material or/and different thickness profile of the filter material of the beam filter arrangement (26) in allocation to each detection channel lying within the projection region of a slice projection.

2. Computer tomography arrangement according to claim 1, characterized in that the beam filter arrangement (26) is interchangeably mounted at the radiator-detector arrangement (10, 18).

3. Computer tomography arrangement according to claim 1 or 2, characterized in that beam filter arrangement (26a) is held at a diaphragm carrier (36a) arranged radiator-proximate that carries a diaphragm arrangement (38a) for beam shaping of the x-radiation emitted by the radiator (10).

4. Computer tomography arrangement according to one of the claims 1 through 3, characterized in that the radiator (10) of the radiator-detector arrangement (10, 18) is implemented with at least two spring foci (12, 14) between which it can be switched in alternation;

in that the beam filter arrangement (26)—

in allocation to each of the spring foci (12, 14)—

respectively comprises a region (28, 30) of different filter material or/and different thickness profile of the filter material, and in that the radiator-detector arrangement (10, 18) is fashioned for supplying a respective projection measured value for each of the spring foci (12, 14) in allocation to each detection channel lying within the projection region of a slice projection.

5. Computer tomography arrangement according to claim 4, characterized in that the evaluation and reconstruction unit (22) is fashioned for determining an effective projection value by weighted summation from corrected projection values determined in allocation to respectively one of the detection channels and respectively allocated to one of the spring foci (12, 14) and for reconstructing the tomographic image upon employment of the effective projection values.

6. Computer tomography arrangement according to claim 4 or 5, characterized in that the evaluation and reconstruction unit (22) is fashioned for reconstructing the tomographic image for a plurality of projection channels per slice projection that is equal to a multiple of the plurality of detection channels lying within the projection region of the respective slice projection corresponding to the plurality of spring foci (12, 14), whereby the evaluation and reconstruction (22) is fashioned for employing the corrected projection values determined in allocation to respectively one of the detection channels for all spring foci (12, 14) in the reconstruction of the tomographic image as corrected projection values of neighboring projection channels.

7. Computer tomography arrangement according to one of the claims 1 through 6, characterized in that the detector (18a) of the radiator-detector arrangement (10a, 18a) is implemented with a plurality of detector elements (20a) arranged in at least two lines (Z1 through Z4) lying above one another, an identical detection channel being allocated to their detector elements (20a) lying above one another in a respective column;

in that the beam filter arrangement (26a)—

in allocation to at least a sub-plurality of at least two detector elements (20a) of each column of detector elements (20a) lying within the projection region of a slice projection—

respectively comprises a region of different filter material or/and different thickness profile of the filter material; and

in that the radiator-detector arrangement (10a, 18a) is fashioned for supplying a respective projection measured value for each detector element (20a) from this sub-plurality of detector elements (20a) in allocation to each column of detector elements (20a) lying within the projection region of this slice projection.

8. Computer tomography arrangement according to claim 7, characterized in that the evaluation and reconstruction unit (22a) is for determining an effective projection value by weighted summation from the corrected projection values determined in allocation to respectively one of the columns and respectively allocated to one of the detector elements (20a) from the sub-plurality of detector elements (20a) and of reconstructing the tomographic image upon employment of the effective projection values.