Radiation diagnostic apparatus, X-ray computed tomography apparatus, and image processing method

1. A radiation diagnostic apparatus comprising:

an X-ray tube that alternately radiates radiation rays having a first level of energy and radiation rays having a second level of energy that is different from the first level of energy onto a subject;

an X-ray detector that detects radiation rays that have passed through the subject; and

a processing unit configured to:

alternately generate, at a first frame rate, an image based on the radiation rays that have been detected by the X-ray detector when the radiation rays having the first level of energy were radiated and an image based on the radiation rays that have been detected by the X-ray detector when the radiation rays having the second level of energy were radiated; and

successively generate a plurality of subtraction images in which a first site is rendered at a second frame rate higher than the first frame rate, wherein the processing unit generates one of the subtraction images by a first calculation using a first image and a second image generated next to the first image, and subsequently generates one of the subtraction images by a second calculation using the second image and a third image generated next to the second image, wherein the first and third images are the image of the first level of energy, and the second image is the image of the second level of energy.

2. The radiation diagnostic apparatus according to claim 1 , wherein

the processing unit generates the plurality of subtraction images as first subtraction images, and

the processing unit further generates a second subtraction image by using the first subtraction images that are generated before and after a contrast agent is injected to the subject.

3. The radiation diagnostic apparatus according to claim 1 , wherein

the processing unit generates, as the plurality of subtraction images, at least a subtraction image in which the first site is rendered and another subtraction image in which a second site that is different from the first site is rendered, and

the processing unit further causes a display to display the subtraction image in which the first site is rendered and the another subtraction image in which the second site is rendered.

4. The radiation diagnostic apparatus according to claim 1 , wherein the processing unit further causes a display to display the image of the first level of energy and the image of the second level of energy as well as at least one of the subtraction images.

5. The radiation diagnostic apparatus according to claim 1 , wherein the processing unit further causes a display to display the subtraction images generated consecutively as a moving picture.

6. The radiation diagnostic apparatus according to claim 1 , wherein the first calculation and the second calculation are different calculations.

7. The radiation diagnostic apparatus according to claim 6 , wherein

the first calculation is a calculation subtracting, from the first image of the first level of energy, the second image of the second level of energy generated next to the first image, and

the second calculation is a calculation subtracting, from the third image of the second level of energy, the second image of the first level of energy generated next to the first image.

8. The radiation diagnostic apparatus according to claim 1 , wherein

the processing unit alternately generates a first pair of the first image and the second image and a second pair of the third image and a fourth image, wherein the first and third images are the image of the first level of energy, and the second and fourth images are the image of the second level of energy,

the first calculation is a calculation using the first image of the first level of energy included in the first pair and the second image of the second level of energy included in the first pair, and

the second calculation is a calculation using the second image of the second level of energy included in the first pair and the third image of the first level of energy included in the second pair generated next to the first pair.

9. An X-ray computed tomography apparatus comprising:

an X-ray tube that alternately radiates X-rays having a first level of energy and X-rays having a second level of energy that is different from the first level of energy onto a subject from mutually different projection directions;

an X-ray detector that detects X-rays that have passed through the subject; and

a processing unit configured to:

alternately generate, at a first sampling rate, a piece of first projection data based on the X-rays that have been detected by the X-ray detector when the X-rays having the first level of energy were radiated and a piece of second projection data based on the X-rays that have been detected by the X-ray detector when the X-rays having the second level of energy were radiated;

successively generate a plurality of pieces of difference data at a second sampling rate higher than the first sampling rate, wherein the processing unit generates one of the pieces of difference data by a first calculation using a piece of first projection data and a piece of second projection data generated next to the piece of first projection data, and subsequently generates one of the piece of difference data by a second calculation using the piece of second projection data and a piece of third projection data generated next to the piece of second data, wherein the pieces of first and third projection data are the piece of projection data of the first level of energy, and the piece of second projection data is the piece of projection data of the second level of energy; and

reconstruct an image from the pieces of difference data.

10. The X-ray computed tomography apparatus according to claim 9 , wherein the processing unit further causes a display to display the images generated consecutively as a moving picture.

11. The X-ray computed tomography apparatus according to claim 9 , wherein the X-ray tube alternately radiates the X-rays having the first level of energy and the X-rays having the second level of energy in correspondence with every rotation of a rotating frame that rotates continuously and supports the X-ray tube and the X-ray detector such that the X-ray tube and the X-ray detector oppose each other while the subject is interposed therebetween.

12. An image processing method comprising:

alternately radiating radiation rays having a first level of energy and radiation rays having a second level of energy that is different from the first level of energy onto a subject;

detecting radiation rays that have passed through the subject;

alternately generating, at a first frame rate, an image based on the radiation rays that have been detected when the radiation rays having the first level of energy were radiated and an image based on the radiation rays that have been detected when the radiation rays having the second level of energy were radiated; and

successively generating a plurality of subtraction images in which a first site is rendered at a second frame rate higher than the first frame rate, wherein one of the subtraction images is generated by a first calculation using a first image and a second image next to the first image, and one of the subtraction images is subsequently generated by a second calculation using the second image and a third image generated next to the second image, wherein the first and third images are the image of the first level of energy, and the second image is the image of the second level of energy.

13. The imaging processing method according to claim 12 , further comprising

generating the plurality of subtraction images as first subtraction images, and

generating a second subtraction image by using the first subtraction images that are generated before and after a contrast agent is injected to the subject.

14. The imaging processing method according to claim 12 , further comprising

generating, as the plurality of subtraction images, at least a subtraction image in which the first site is rendered and another subtraction image in which a second site that is different from the first site is rendered, and

causing a display to display the subtraction image in which the first site is rendered and the another subtraction image in which the second site is rendered.

15. The imaging processing method according to claim 12 , further comprising causing a display to display the image of the first level of energy and the image of the second level of energy as well as at least one of the subtraction images.

16. The imaging processing method according to claim 12 , further comprising causing a display to display the subtraction images generated consecutively as a moving picture.

17. The imaging processing method according to claim 12 , wherein the first calculation and the second calculation are different calculations.

18. The imaging processing method according to claim 17 , wherein

the first calculation is a calculation subtracting, from the first image of the first level of energy, the second image of the second level of energy generated next to the first image, and

the second calculation is a calculation subtracting, from the third image of the second level of energy, the second image of the first level of energy generated next to the first image.

19. The imaging processing method according to claim 12 , further comprising

alternately generating a first pair of the first image and the second image and a second pair of the third image and a fourth image, wherein the first and third images are the image of the first level of energy, and the second and fourth images are the image of the second level of energy,

the first calculation is a calculation using the first image of the first level of energy included in the first pair and the second image of the second level of energy included in the first pair, and

the second calculation is a calculation using the second image of the second level of energy included in the first pair and the third image of the first level of energy included in the second pair generated next to the first pair.

20. A X-ray computed tomography apparatus comprising:

an X-ray tube that alternately radiates X-rays having a first level of energy and X-rays having a second level of energy that is different from the first level of energy onto a subject from mutually different projection directions;

an X-ray detector that detects X-rays that have passed through the subject; and

a processing unit configured to:

alternately generate, at a first frame rate, an image based on the X-rays that have been detected by the X-ray detector when the X-rays having the first level of energy were radiated and an image based on the X-rays that have been detected by the X-ray detector when the X-rays having the second level of energy were radiated; and

successively generate a plurality of subtraction images in which the first site is rendered at a second frame rate higher than the first frame rate, wherein the processing unit generates one of the subtraction images by a first calculation using a first image and a second image generated next to the first image, and subsequently generates one of the subtraction images by a second calculation using the second image and a third image generated next to the second image, wherein the first and third images are the image of the first level of energy, and the second image is the image of the second level of energy.