IMAGE RECONSTRUCTING METHOD AND X-RAY CT APPARATUS

• US 20070121779A1
• Filed: 10/06/2006
• Published: 05/31/2007
• Est. Priority Date: 10/07/2005
• Status: Active Grant

• Current Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Original Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Inventors: Hagiwara, Akira, Nishide, Akihiko, Morikawa, Kotoko
• Granted Patent: US 7,639,772 B2
• Time in Patent Office: Days
• 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: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating

Abstract

The slice thickness of tomograms of an X-ray CT apparatus is to be kept as constant as practicable within an xy plane. In projected data before three-dimensional back-projection, after convolving row-directional filter of an X-ray detector whose filter coefficient is adjusted channel by channel, three-dimensional back-projection is performed to achieve image reconstruction thereby to control the slice thickness of tomograms according to the distance from the center of the xy plane. The slice thickness is controlled to keep it as constant as practicable independent of the distance from that center to regulate the picture quality of tomograms. Further, the relative density of distances on the reconstruction plane of X-ray detector data or projection data projected on the reconstruction plane is controlled by creating virtual projection data thereby to improve the picture quality of tomograms.

Claims

1. An image reconstructing method for reconstructing a tomogram based on projection data collected by a multi-row X-ray detector for detecting X-rays radiated from the X-ray generating device, the image reconstructing method comprising:

a first step of convolving row-directional filter on said projection data;

a second step of convolving a reconstructing function on said data obtained by said first step; and

a third step of reconstructing by performing three-dimensional back-projection process based on data obtained by said second step.

2. An image reconstructing method for reconstructing a tomogram based on projection data collected by a multi-row X-ray detector for detecting X-rays radiated from the X-ray generating device, the image reconstructing method comprising:

a first step of convolving a reconstructing function on said projection data;

a second step of convolving row-directional filter on the data obtained by said first step; and

a third step of reconstructing by performing three-dimensional back-projection process based on the data obtained by said second step.

3. An X-ray CT apparatus comprising:

X-ray generating device;

a multi-row X-ray detector which detects X-rays radiated from said X-ray generating device;

data collecting device which collects projection data by rotating said X-ray generating device and said multi-row X-ray detector around a center of rotation between the X-ray generating device and the multi-row X-ray detector;

row-directional filtering device for convolving row-directional filter on the projection data collected by said data collecting device;

reconstruction convolving device for convolving a reconstructing function on the projection data obtained said row-directional filtering device; and

back-projecting device for reconstructing a tomogramic view by three-dimensional back projecting the projection data obtained processing by said reconstruction convoluting device.

5. The X-ray CT apparatus according to claim 3, wherein:

said data collecting device collects data by conventional scanning, helical scanning or cine scanning.

7. The X-ray CT apparatus according to claim 3, wherein:

a filter coefficient of said row-directional filter differs from one channel to another of said multi-row X-ray detector.

9. The X-ray CT apparatus according to claim 3, wherein:

a filter coefficient of said row-directional filter differs from one row to another of said multi-row X-ray detector.

11. The X-ray CT apparatus according to claim 3, wherein:

a filter coefficient of said row-directional filter is deconvolution filter.

13. The X-ray CT apparatus according to claim 3, wherein:

said back-projecting device processes weighted addition in said row direction by any one of linear weighted addition, multi-point weighted addition, and weighted addition with a nonlinear weighting coefficient.

15. The X-ray CT apparatus according to claim 3, wherein:

said three-dimensional back-projection device including back-projecting projection data of an X-ray detector row virtualized to the projection data by said X-ray detector created by weighted addition or row-directional filtering.

17. The X-ray CT apparatus according to claim 3, wherein:

the projection data of said X-ray detector and the virtual projection data created by weighted addition or row-directional filtering of the virtualized X-ray detector are combined and matched on a reconstruction plane in said three-dimensional back-projection process, and the process is proceeded so as to substantially equalize the interval on the reconstruction plane with the data in a given direction and the interval on the reconstruction plane with the in a direction opposed by 180 degrees.

19. The X-ray CT apparatus according to claim 17, wherein:

total number of projected data rows combining the number of projection data of said X-ray detector rows and the number of projection data of the virtualized X-ray detector rows is optimized in each projection direction and 180 degrees to the projecting direction or the direction opposed by substantially 180 degrees.

21. The X-ray CT apparatus according claim 17, wherein:

total number of projection data rows combining the number of projection data of said X-ray detector rows and the number of projection data of the virtualized X-ray detector rows is unified to a maximum number of each projecting direction in all of the projecting directions.

4. An X-ray CT apparatus comprising:

X-ray generating device;

a multi-row X-ray detector which detects X-rays radiated from said X-ray generating device;

data collecting device which collects projection data by rotating said X-ray generating device and said multi-row X-ray detector around a center of rotation between the X-ray generating device and the multi-row X-ray detector;

reconstruction convolving device for convolving a reconstructing function on the projection data collected by said data collecting device;

row-directional filtering device for convolving row-directional filter in the row direction based on the projected data obtained by said reconstruction convoluting device; and

back-projecting device for reconstructing a tomogramic view by three-dimensional back projecting the projection data obtained processing by said row-directional filtering device.

6. The X-ray CT apparatus according to claim 4, wherein:

said data collecting device collects data by conventional scanning, helical scanning or cine scanning.

8. The X-ray CT apparatus according to claim 4, wherein:

a filter coefficient of said row-directional filter differs from one channel to another of said multi-row X-ray detector.

10. The X-ray CT apparatus according to claim 4, wherein:

a filter coefficient of said row-directional filter differs from one row to another of said multi-row X-ray detector.

12. The X-ray CT apparatus according to claim 4, wherein:

a filter coefficient of said row-directional filter is deconvolution filter.

14. The X-ray CT apparatus according to claim 4, wherein:

said back-projecting device processes weighted addition in said row direction by any one of linear weighted addition, multi-point weighted addition, and weighted addition with a nonlinear weighting coefficient.

16. The X-ray CT apparatus according to claim 4, wherein:

said three-dimensional back-projection device including back-projecting projection data of an X-ray detector row virtualized to the projection data by said X-ray detector created by weighted addition or row-directional filtering.

18. The X-ray CT apparatus according to claim 4, wherein:

the projection data of said X-ray detector and the virtual projection data created by weighted addition or row-directional filtering of the virtualized X-ray detector are combined and matched on a reconstruction plane in said three-dimensional back-projection process, and the process is proceeded so as to substantially equalize the interval on the reconstruction plane with the data in a given direction and the interval on the reconstruction plane with the in a direction opposed by 180 degrees.

20. The X-ray CT apparatus according to claim 18, wherein:

total number of projected data rows combining the number of projection data of said X-ray detector rows and the number of projection data of the virtualized X-ray detector rows is optimized in each projection direction and 180 degrees to the projecting direction or the direction opposed by substantially 180 degrees.

22. The X-ray CT apparatus according claim 18, wherein:

total number of projection data rows combining the number of projection data of said X-ray detector rows and the number of projection data of the virtualized X-ray detector rows is unified to a maximum number of each projecting direction in all of the projecting directions.