Computer tomography imaging device and method

• US 9,380,984 B2
• Filed: 12/30/2009
• Issued: 07/05/2016
• Est. Priority Date: 05/26/2009
• Status: Active Grant

• Current Assignee: Nuctech Company Limited (Tsinghua Tongfang Co., Ltd.), Tsinghua University
• Original Assignee: Nuctech Company Limited (Tsinghua Tongfang Co., Ltd.), Tsinghua University
• Inventors: Li, Liang, Chen, Zhiqiang, Zhang, Li, Kang, Kejun, Li, Yuanjing, Liu, Yinong, Xing, Yuxiang, Zhao, Ziran
• Primary Examiner(s): Artman, Thomas R
• Application Number:
  US13/322,696
• Publication Number:
  US 20120140874A1
• Time in Patent Office: 2,379 Days
• Field of Search: 378/4, 382/131
• US Class Current: 1/1
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/06 Diaphragms
• CPC Class Codes: A61B 6/4452 the source unit and the detector unit being able to move relative to each other
• CPC Class Codes: A61B 6/469 for selecting a region of interest [ROI]
• 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 2211/416 Exact reconstruction
• CPC Class Codes: G06T 2211/421 Filtered back projection [FBP]
• CPC Class Codes: G06T 2211/424 Iterative

Abstract

The present invention discloses a method for performing CT imaging on a region of interest of an object under examination, comprising: acquiring the CT projection data of the region of interest; acquiring the CT projection data of region B; selecting a group of PI line segments covering the region of interest, and calculating the reconstruction image value for each PI line segment in the group; and combining the reconstruction image values in all the PI line segments to obtain the image of the region of interest. The present invention further discloses a CT imaging device using this method and a data processor therein. Since the 2D/3D slice image of the region of interest can be exactly reconstructed and obtained as long as the X-ray beam covers the region of interest and the region B, it is possible to use a small-sized detector to perform CT imaging on the region of interest at any position of a large-sized object, which reduces to a great extent the radiation dose of the X-ray during the CT scanning.

Claims

1. A method of CT imaging a region of interest of an object under examination, comprising:

acquiring first CT projection data of the region of interest, wherein the region of interest is located within an object support with respect to the object, wherein the region of interest does not abut a perimeter of the object support, wherein the first CT projection data is acquired through a first CT scan, and wherein during the first CT scan the region of interest is adjusted into a scanning field of view such that an X-ray beam of the first CT scan only covers the region of interest;

acquiring second CT projection data of region B, wherein at least a part of the region B is located outside the object support, and wherein the region B is separate from the region of interest and the region B is selected to enable the selection of a group of PI line segments covering the region of interest, and each PI line segment passing through the region of interest passes through the region B, wherein the second CT projection data is acquired through a second CT scan, and wherein during the second CT scan region B is adjusted into the scanning field of view such that an X-ray beam of the second CT scan only covers the region B; and

reconstructing the CT image of the region of interest based on the first CT projection data of the region of interest acquired in the first CT scan and the second CT projection data of the region B acquired in the second CT scan.

2. The CT imaging method according to claim 1, wherein the reconstruction of the CT image of the region of interest based on the first CT projection data of the region of interest acquired in the first CT scan and the second CT projection data of the region B acquired in the second CT scan comprises steps of:

for each PI line segment in the group of PI line segments;

calculating one dimensional Hilbert transform value of the PI line segment, and

performing a limit inverse Hilbert transform for the one dimensional Hilbert transform value to acquire the reconstruction image value of the PI line segment;

combining the reconstruction image values in all the PI lines in the group of PI line segments to obtain the image of the region of interest.

3. The CT imaging method according to claim 2, wherein the limit inverse Hilbert transform comprises step of:

performing Projection onto Convex Set (POCS) iteration between the reconstruction image domain and the Hilbert transform space domain to acquire a reconstruction image in the PI line segment that satisfies the accuracy requirement.

4. The CT imaging method according to claim 1, wherein the acquisition of the first CT projection data of the region of interest and the acquisition of the second CT projection data of the region B comprise:

performing CT scanning of the region of interest and the region B with parallel beam, sector beam or cone beam X-ray to acquire the first and second CT projection data of the region of interest and the region B respectively.

5. A non-transitory computer readable medium which stores instructions for implementing the steps of the method according to claims 1 when loaded to a computer and operated thereon.

6. A CT imaging device for CT imaging a region of interest of an object under examination, comprising:

an X-ray generator being configured to generate an X-ray beam for use in scanning;

a detector arrangement being configured to detect the X-ray passing through a scanned region so as to produce projection data;

a carrier of the object being configured to carry the object under examination in and out of the CT imaging device;

a main controller being configured to control the operation of the CT imaging device, such that a first X-ray emitted in a first CT scan from the X-ray generator only covers the region of interest so as to obtain first CT projection data of the region of interest, and such that a second X-ray emitted in a second CT scan from the X-ray generator only covers the region B so as to obtain second CT projection data of the region B, wherein the region of interest is located within an object support with respect to the object, the region of interest does not abut a perimeter of the object support, the region B is located outside the object support, wherein the region B is selected to enable the selection of a group of PI line segments covering the region of interest, and wherein each PI line segment passing through the region of interest also passes through the region B; and

a data processor being configured to reconstruct the image of the region of interest based on the first CT projection data of the region of interest acquired in the first CT scan and the second CT projection data of the region B acquired in the second CT scan.

7. The CT imaging device according to claim 6, wherein the data processor comprises:

PI line division unit being configured to provide a group of PI line segments covering the region of interest;

Hilbert transform calculation unit being configured to calculate a one dimensional Hilbert transform value along the PI line segment for each PI line segment in the group of PI line segments;

inverse Hilbert transform calculation unit being configured to perform limit inverse Hilbert transform for the one dimensional Hilbert transform value calculated by the Hilbert transform calculation unit, so as to acquire the reconstruction image value in the PI line segment; and

data reconstruction combination unit being configured to combine the reconstruction images calculated by the inverse Hilbert transform calculation unit for each PI line to obtain the image of the region of interest.

8. The CT imaging device according to claim 7, wherein the inverse Hilbert transform calculation unit performs Projection onto Convex Set (POCS) iteration between the reconstruction image domain and the Hilbert transform space domain to acquire a reconstruction image for the PI line segment that satisfies the accuracy requirement.

9. The CT imaging device according to claim 6, further comprising:

a front collimator being configured to adjust the width of the first and second X-ray beams under the control of the main controller such that the first and second X-ray beams only covers the region of interest or the region B respectively.

10. The CT imaging device according to claim 9, wherein the front collimator comprises a plurality of X-ray shielding blocks forming an X-ray emergence window of a certain shape, which X-ray shielding blocks can cooperate to change the size and the position of the X-ray emergence window.

11. The CT imaging device according to claim 10, wherein the front collimator comprises four X-ray shielding blocks, each of which is controlled by a set of servo motors and precision lead screws operating independently, such that the X-ray shielding blocks move along the precision lead screw.

12. The CT imaging device according to claim 6, further comprising:

a detector position controller being configured to control the position of the detector means such that the movement scope of the detector means can cover the positions of the region of interest and the region B.

13. The CT imaging device according to claim 12, wherein the detector position controller comprises a servo motor and a precision lead screw, wherein the detector arrangement is fixed on the precision lead screw so that it is driven by the servo motor to move along the precision lead screw.