X-ray computer tomography apparatus

1. An X-ray computer tomography apparatus comprising:

an X-ray tube which generates cone beam X rays;

a two-dimensional array type X-ray detector which detects X-rays transmitted through an object and generates projection data;

a rotating mechanism which supports the X-ray tube, together with the X-ray detector, so as to be rotatable around the object;

a reconstruction processing unit which reconstructs a full scan image based on projection data, of the projection data, which corresponds to a view count corresponding to one rotation and also reconstructs a short scan image based on projection data corresponding to a view count smaller than the view count corresponding to one rotation;

a CT value shift distribution generating unit which generates a spatial distribution of CT value shifts originating from the smaller view count based on the full scan image and the short scan image; and

a correcting unit which corrects the short scan image based on the spatial distribution of the CT value shifts.

2. The apparatus according to claim 1 , wherein the reconstruction processing unit changes a view count of projection data used for reconstruction of the short scan image in two end portions of a reconstruction area in accordance with a reconstruction position on a rotation axis.

3. The apparatus according to claim 1 , wherein the CT value shift distribution generating unit includes

a difference image generating unit which generates a difference image by subtracting the short scan image from the full scan image; and

a threshold processing unit which generates the CT value shift distribution by applying threshold processing to the difference image.

4. The apparatus according to claim 3 , wherein the CT value shift distribution generating unit further includes a low-pass filter unit which applies low-pass filtering to the CT value shift distribution.

5. The apparatus according to claim 1 , further comprising a combining processing unit which partially combines the full scan image and the short scan image.

6. The apparatus according to claim 1 , further comprising a combining processing unit which combines a central portion of the full scan image and an annular portion of the short scan image.

7. An image processing apparatus comprising:

a storage unit which stores projection data acquired by using cone beam X-rays;

a reconstruction processing unit which reconstructs a full scan image based on projection data corresponding to a view count corresponding to one rotation and also reconstructs a short scan image based on projection data corresponding to a view count smaller than the view count corresponding to one rotation;

a CT value shift distribution generating unit which generates a spatial distribution of CT value shifts originating from the smaller view count based on the full scan image and the short scan image; and

a correcting unit which corrects the short scan image based on the spatial distribution of the CT value shifts.

8. The apparatus according to claim 7 , wherein the reconstruction processing unit changes a view count of projection data used for reconstruction of the short scan image in two end portions of a reconstruction area in accordance with a reconstruction position on a rotation axis.

9. The apparatus according to claim 7 , wherein the CT value shift distribution generating unit includes

a difference image generating unit which generates a difference image by subtracting the full scan image and the short scan image from each other; and

a threshold processing unit which generates the CT value shift distribution by applying threshold processing to the difference image.

10. The apparatus according to claim 9 , wherein the CT value shift distribution generating unit further includes a low-pass filter unit which applies low-pass filtering to the CT value shift distribution.

11. The apparatus according to claim 7 , further comprising a combining processing unit which partially combines the full scan image and the short scan image.

12. The apparatus according to claim 7 , further comprising a combining processing unit which combines a central portion of the full scan image and an annular portion of the short scan image.

13. An image generating method comprising:

reconstructing a full scan image based on projection data, of projection data acquired by using cone beam X-rays, which corresponds to a view count corresponding to one rotation;

reconstructing a short scan image based on projection data, of the projection data, which corresponds to a view count smaller than the view count corresponding to one rotation;

generating a spatial distribution of CT value shifts originating from the smaller view count based on the full scan image and the short scan image; and

correcting the short scan image based on the spatial distribution of the CT value shifts.

14. The method according to claim 13 , wherein a view count of projection data used for reconstruction of the short scan image in two end portions of a reconstruction area is changed in accordance with a reconstruction position on a rotation axis.

15. The method according to claim 13 , wherein in generating a spatial distribution of CT value shifts,

a difference image is generated by subtracting the full scan image and the short scan image from each other, and

the CT value shift distribution is generated by applying threshold processing to the difference image.

16. The method according to claim 13 , wherein in generating a spatial distribution of CT value shifts, low-pass filtering is applied to the CT value shift distribution.

17. The method according to claim 16 , further comprising partially combining the full scan image and the short scan image.

18. The method according to claim 13 , further comprising combining a central portion of the full scan image and an annular portion of the short scan image.