X-RAY CT APPARATUS, A METHOD FOR CHANGING THE HELICAL PITCH, AN IMAGE RECONSTRUCTION PROCESSING APPARATUS, AN IMAGE RECONSTRUCTION PROCESSING METHOD, AND AN IMAGE RECONSTRUCTION PROCESSING PROGRAM

Abstract

The X-ray CT apparatus that performs a scan after a pre-scan, comprising a reconstruction part reconstructing the pre-scan image of said subject to be examined from transmission data detected by said detector during said pre-scan, and also reconstructing the scan image of said subject to be examined from the transmission data detected by said detector during said scan; and a scan controlling part initiating a scan by directly changing the helical pitch of said bed from the stopped position for said pre-scan to the position toward an ending edge of the reconstruction area of the image. The scan controlling part initiates the scan at a first helical pitch by which X-rays for a predetermined number of views can be emitted at a starting edge of the reconstruction area of the image, and, after X-rays for the predetermined number of views is emitted, the scan at a second helical pitch continues.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a real preparatory scan by a conventional X-ray CT apparatus.

FIG. 2 shows technology for imaging the conventional area including an area with physical movement and an area without physical movement.

FIG. 3 shows the structure that controls the variable helical scan by X-ray CT apparatus according to the present embodiment.

FIG. 4 is a pattern diagram that shows a screen for setting imaging conditions.

FIG. 5 shows the method of calculating the first helical pitch HP_new.

FIG. 6 shows an operation of creating data for the HP-distance sequence.

FIG. 7 is a block diagram that shows the overall structure of an X-ray CT apparatus according to the present embodiment.

FIG. 8 is a flowchart that shows how projection data is obtained in accordance with the HP-distance sequence of the X-ray CT apparatus.

FIG. 9 is a graph that shows the helical pitch for the overall reconstruction area of the image.

FIG. 10 shows the method of calculating the number of views for a variable helical scan with a helical pitch value of 0.

FIG. 11 shows how the scan area is created for a helical scan with a pitch value of 0.

FIG. 12 is a flowchart that shows the initial operations of obtaining projection data, including a first helical pitch of 0 in accordance with the HP-distance sequence.

FIG. 13 is a graph that shows the helical pitch for initial operations. The vertical axis thereof shows the helical pitch, and the horizontal axis shows the time.

FIG. 14 is a block diagram that shows the structure of the image reconstruction processing apparatus, which is an embodiment of the image reconstruction processing technology according to the present embodiment.

FIG. 15 is a block diagram that shows the functions of this image reconstruction processing apparatus.

FIG. 16 is a diagram that shows projection data stored in the projection data storage unit as well as the biological signal data.

FIG. 17 shows pattern diagrams of the biological signal synchronization reconstruction method.

FIG. 18 shows pattern diagrams of reconstruction in asynchronization with the biological signal.

FIG. 19 is a diagram that shows the feathering process.

FIG. 20 is a flowchart that shows the operation of the image reconstruction process.

Claims

1. An X-ray CT apparatus having an X-ray tube emitting an X-ray, a detector detecting X-rays transmitted through a subject to be examined, and a bed on which said subject to be examined is placed, wherein, after a pre-scan causing said X-ray tube to emit X-rays with said X-ray tube, said detector and said bed at stopped positions, said X-ray tube and said detector are moved relative to said bed to perform a scan over an reconstruction area of an image, comprising: a reconstruction part configured to reconstruct the pre-scan image of said subject to be examined from transmission data detected by said detector during said pre-scan, and also to reconstruct the scan image of said subject to be examined from the transmission data detected by said detector during said scan;a switching control part configured to switch from said pre-scan to said scan; anda scan controlling part, when it is switched to said scan by said switching control part, configured to scan by changing the helical pitch from the stopped position for said pre-scan directly to the position toward an ending edge of the reconstruction area of the image, wherein:said scan controlling part scans at a first helical pitch by which X-rays for a predetermined number of views can be emitted at a starting edge of the reconstruction area of the image, and then, after X-rays for the predetermined number of views is emitted, the scan at a predetermined second helical pitch is controlled to continue.

2. The X-ray CT apparatus according to claim 1, wherein said predetermined number of views is the number of views required to reconstruct the image at the starting edge of the reconstruction area of the image.

3. The X-ray CT apparatus according to claim 1, wherein said predetermined number of views is the number of views insufficient to reconstruct the image at the starting edge of the reconstruction area of the image if the scan is initiated at said second helical pitch, and said first helical pitch is the maximum pitch at which X-rays can be emitted for said number of views that is insufficient.

4. The X-ray CT apparatus according to claim 1, wherein if the scan is initiated at said second helical pitch, said predetermined number of views is the number of views insufficient to reconstruct the image at the starting edge of the reconstruction area of the image, and wherein said first helical pitch has a value of 0.

5. The X-ray CT apparatus according to claim 1, further comprising a calculating part configured to calculate the first helical pitch at which X-rays for the predetermined number of views can be emitted at the starting edge of the reconstruction area of the image.

6. The X-ray CT apparatus according to claim 1, further comprising a calculating part, based on the relative position between one of the edges of the area where X-rays is emitted and the starting edge of said reconstruction area of the image during the pre-scan, configured to calculate the first helical pitch at which X-rays for said predetermined number of views can be emitted to said starting edge until said one of the edges has passed said starting edge.

7. The X-ray CT apparatus according to claim 1, wherein said reconstruction part also reconstructs an image in a area where said helical pitch is being changed.

8. A method for changing the helical pitch of an X-ray CT apparatus having an X-ray tube emitting an X-ray, a detector detecting X-rays transmitted through a subject to be examined, and a bed on which said subject to be examined is placed, wherein, after a pre-scan causing said X-ray tube to emit X-rays with said X-ray tube, said detector and said bed at stopped positions, said X-ray tube and said detector are moved relative to said bed to perform a scan over an reconstruction area of the image, comprising: reconstructing the pre-scan image of said subject to be examined from transmission data based on X-rays detected by said detector during said pre-scan;switching between said pre-scan and said scan; andinitiating the scan, in response to the switching, by changing the helical pitch from a stopped position for said pre-scan directly to the position toward an ending edge of the reconstruction area of the image; andreconstructing the scan image of said subject to be examined from the transmission data based on X-rays detected by said detector during said scan, wherein:for initiating the scan, the scan is initiated at a first helical pitch by which X-rays for a predetermined number of views can be emitted at a starting edge of the reconstruction area of the image, and wherein, after X-rays for said predetermined number of views is emitted, the scan at a predetermined second helical pitch is controlled to continue.

9. The method for changing the helical pitch according to claim 8, wherein said predetermined number of views is the number of views required to reconstruct the image at the starting edge of the reconstruction area of the image.

10. The method for changing the helical pitch according to claim 8, wherein said predetermined number of views is the number of views insufficient to reconstruct the image at the starting edge of the reconstruction area of the image if the scan is initiated at said second helical pitch, and said first helical pitch is the maximum pitch at which X-rays can be emitted for said number of views that is insufficient.

11. The method for changing the helical pitch according to claim 8, wherein if the scan is initiated at said second helical pitch, said predetermined number of views is the number of views insufficient to reconstruct the image at the starting edge of the reconstruction area of the image, and said first helical pitch has a value of 0.

12. The method for changing the helical pitch according to claim 8, further comprising calculating the first helical pitch at which X-rays for the predetermined number of views can be emitted at the starting edge of the reconstruction area of the image.

13. The method for changing the helical pitch according to claim 8, further comprising calculating, based on the relative position between one of the edges of the area where X-rays is emitted and the starting edge of said reconstruction area of the image during the pre-scan, the first helical pitch at which X-rays for said predetermined number of views can be emitted to said starting edge until said one of the edges has passed said starting edge.

14. The method for changing the helical pitch according to claim 8, wherein when reconstructing, an image in a area where said helical pitch is being changed, is also reconstructed.

15. An X-ray CT apparatus having an X-ray tube emitting an X-ray, a detector detecting X-rays transmitted through a subject to be examined, and a bed on which said subject to be examined is placed, said X-ray CT apparatus reconstructing the image of the subject to be examined from a transmission data obtained by emitting X-rays to the subject to be examined, comprising: an input part configured to specify the area which is reconstructed in synchronization with a biological signal and the area which is reconstructed in asynchronization with the biological signal;a scan controlling part configured to perform a helical scan by moving said X-ray tube and said detector relative to said bed, and also to change the moving speed of said bed during a continuous single helical scan;a detecting part configured to detect the biological signal of the subject to be examined;a memory part configured to store the transmission data obtained during said helical scan and the said biological signal data in a correlated way;a segmentation part configured to segment said transmission data into a first transmission data that corresponds to the area reconstructed in synchronization with said biological signal and a second transmission data that corresponds to the area reconstructed in asynchronization with said biological signal, while partly overlapping in the vicinity of both boundaries;a biological-signal synchronization reconstructing part configured to reconstruct a synchronized image of said subject to be examined based on said biological signal data and said first transmission data;a biological-signal asynchronization reconstructing part configured to reconstruct an asynchronized image of said subject to be examined from said second transmission data without using said biological signal data; anda combining part configured to create a combined image that the synchronized image reconstructed by said biological-signal synchronization reconstructing part and the asynchronized image reconstructed by said biological-signal asynchronization reconstructing part are combined with weighting addition at said partly overlapped area.

16. The X-ray CT apparatus according to claim 15, wherein said scan controlling part slows down the moving speed of said bed to the speed that the biological signal for multiple cycles can be detected, during the helical scan of the area to be reconstructed in synchronization with said biological signal.

17. The X-ray CT apparatus according to claim 15, wherein said combining part gradually changes said weighing in the vicinity of the end of said synchronized image and said asynchronized image.

18. The X-ray CT apparatus according to claim 15, wherein said detecting part is an electrocardiographic equipment that detects heart rate of the subject to be examined and creates electrocardiographic data, and said memory part stores such data as said biological signal data.

19. The X-ray CT apparatus according to claim 15, wherein said detecting part is a respiration sensor that detects respiration of the subject to be examined and creates respiration data, and said memory part stores such data as said biological signal data.

20. An image reconstruction processing apparatus, comprising: an input part configured to specify the area which is reconstructed in synchronization with a biological signal and the area which is reconstructed in asynchronization with the biological signal;a memory part configured to store the transmission data obtained by a continuous single helical scan and a biological signal data of the subject to be examined obtained during said helical scan in a correlated way;a segmentation part configured to segment said transmission data into a first transmission data that corresponds to the area reconstructed in synchronization with said biological signal and a second transmission data that corresponds to the area reconstructed in asynchronization with said biological signal, while partly overlapping in the vicinity of both boundaries;a biological-signal synchronization reconstructing part configured to reconstruct a synchronized image of said subject to be examined based on said biological signal data and said first transmission data;a biological-signal asynchronization reconstructing part configured to reconstruct an asynchronized image of said subject to be examined from said second transmission data without using said biological signal data; anda combining part configured to create a combined image that the synchronized image reconstructed by said biological-signal synchronization reconstructing part and the asynchronized image reconstructed by said biological-signal asynchronization reconstructing part are combined with weighting addition at said partly overlapped area.

21. The X-ray CT apparatus according to claim 20, wherein said combining part gradually changes said weighing in the vicinity of the end of said synchronized image and said asynchronized image.

22. The image reconstruction processing apparatus according to claim 20, wherein said memory part stores the electrocardiographic data as said biological signal data.

23. The image reconstruction processing apparatus according to claim 20, wherein said memory part stores the respiration data as said biological signal data.

24. An image reconstruction processing method comprising: storing a transmission data of a subject to be examined obtained by a continuous single helical scan and a biological signal data of the subject to be examined obtained during said helical scan;segmenting said transmission data into a first transmission data that corresponds to the area reconstructed in synchronization with said biological signal and a second transmission data that corresponds to the area reconstructed in asynchronization with said biological signal, while partly overlapping in the vicinity of both boundaries;reconstructing a synchronized image of said subject to be examined based on said biological signal data and said first transmission data;reconstructing an asynchronized image of said subject to be examined from said second transmission data without using said biological signal data; andcreating a combined image that the synchronized image reconstructed in said reconstruction with synchronization and the asynchronized image reconstructed in said reconstruction with asynchronization are combined with weighting addition at said partly overlapped area.

25. The image reconstruction processing method according to claim 24, wherein said weighting gradually changes in the vicinity of the end of said synchronized image and said asynchronized image in said creation of the combined image.

26. The image reconstruction processing method according to claim 25, wherein the electrocardiographic data is stored as said biological signal data.

27. The image reconstruction processing method according to claim 26, wherein the respiration data is stored as said biological signal data.

28. A program product including programming code for image reconstruction processing, the program product being stored on a computer readable medium, the programming code comprising: specifying the area which is reconstructed in synchronization with a biological signal and the area which is reconstructed in asynchronization with the biological signal on a computer;storing the transmission data obtained during a continuous single helical scan and the said biological signal data of the subject to be examined obtained during said helical scan in a correlated way;segmenting said transmission data into a first transmission data that corresponds to the area reconstructed in synchronization with said biological signal and a second transmission data that corresponds to the area reconstructed in asynchronization with said biological signal, while partly overlapping in the vicinity of both boundaries;reconstructing a synchronized image of said subject to be examined based on said biological signal data and said first transmission data;reconstructing an asynchronized image of said subject to be examined from said second transmission data without using said biological signal data; andcreating a combined image that the synchronized image reconstructed in said reconstruction with synchronization and the asynchronized image reconstructed in said reconstruction with asynchronization are combined with weighting addition at said partly overlapped area.

29. The program product according to claim 28, wherein said weighting gradually changes in the vicinity of the end of said synchronized image and said asynchronized image.

30. The program product according to claim 28, wherein the electrocardiographic data is stored as said biological signal data.

31. The program product according to claim 28, wherein the respiration data is stored as said biological signal data.