Method and apparatus for X-ray CT imaging

1. An apparatus for X-ray CT imaging, comprising:

an X-ray irradiation unit configured to irradiate an X-ray toward a subject;

an X-ray detector having a plurality of X-ray detection elements along a channel direction and a row direction;

a couch on which the subject can be arranged;

a rotation unit on which the X-ray irradiation unit is disposed and rotates around the couch;

a controller configured to execute a helical scan while fluctuating an X-ray focal spot along a body axis direction of the subject by controlling the X-ray irradiation unit; and

an image processing unit configured to generate a reconstructed image based on data acquired by the helical scan, wherein

the controller is further configured to set a magnitude of fluctuation of the X-ray focal spot based on a distance between the X-ray focal spot and a rotation center axis, a distance between the X-ray focal spot and a center of the X-ray detector, and a pitch of the plurality of X-ray detection elements.

2. The apparatus for X-ray CT imaging of claim 1 , wherein the controller is further configured to set the magnitude of fluctuation D to be

D

<

d

·

SOD

2

·

(

SDD

-

SOD

)

,

wherein SOD is defined as the distance between the X-ray focal spot and the rotation center axis of the X-ray irradiation unit and the X-ray detector, SDD is defined as the distance between the X-ray focal spot and the center of the X-ray detector, and d is defined as the pitch of the plurality of X-ray detection elements.

3. The apparatus for X-ray CT imaging of claim 2 , wherein the controller is further configured to control the helical scan so that a helical pitch is substantially equal to (n +0.5) dc, wherein n is an integer and dc is a projected pitch, which is a projected length of the pitch of the plurality of X-ray detection elements at a rotation center axis of the X-ray irradiation unit and the X-ray detector.

4. The apparatus for X-ray CT imaging of claim 3 , wherein the controller is further configured to control the helical scan so that the helical pitch is substantially equal to 2.5 dc.

5. The apparatus for X-ray CT imaging of claim 3 , wherein

the image processing unit is further configured to generate the reconstructed image based on direct data acquired by the helical scan; and

the controller is further configured to set the magnitude of fluctuation D to be

D

=

d

·

SOD

4

·

(

SDD

-

SOD

)

.

6. The apparatus for X-ray CT imaging of claim 3 , wherein

the image processing unit is further configured to generate the reconstructed image based on direct data and complementary data acquired by the helical scan; and

the controller is further configured to set the magnitude of fluctuation D to be

D

=

d

·

SOD

8

·

(

SDD

-

SOD

)

.

7. The apparatus for X-ray CT imaging of claim 2 , wherein the controller is further configured to control the helical scan so that a helical pitch is substantially equal to (2n +1) dc, wherein n is an integer and dc is a projected pitch, which is a projected length of the pitch of the plurality of X-ray detection elements at a rotation center axis of the X-ray irradiation unit and the X-ray detector.

8. The apparatus for X-ray CT imaging of claim 7 , wherein

the image processing unit is further configured to generate the reconstructed image based on direct data and complementary data acquired by the helical scan; and

the controller is further configured to set the magnitude of fluctuation D to be

D

=

d

·

SOD

4

·

(

SDD

-

SOD

)

.

9. The apparatus for X-ray CT imaging of claim 7 , wherein the controller is further configured to control the helical scan so that the helical pitch is substantially 3 dc.

10. The apparatus for X-ray CT imaging of claim 1 , wherein the controller is further configured to set the magnitude of fluctuation D to be

D

<

d

·

SOD

4

·

(

SDD

-

SOD

)

,

wherein SOD is defined as the distance between the X-ray focal spot and the rotation center axis of the X-ray irradiation unit and the X-ray detector, SDD is defined as the distance between the X-ray focal spot and the center of the X-ray detector, and d is defined as the pitch of the plurality of X-ray detection elements.

11. A method for X-ray CT imaging, comprising:

irradiating an X-ray toward a subject arranged on a couch, using an X-ray irradiation unit;

detecting the X-ray using an X-ray detector having a plurality of X-ray detection elements along a channel direction and a row direction;

rotating a rotation unit, on which the X-ray irradiation unit is disposed, around the couch;

executing a helical scan while fluctuating an X-ray focal spot along a body axis direction of the subject by controlling the X-ray irradiation unit;

generating a reconstructed image based on data acquired by the helical scan; and

setting a magnitude of fluctuation of the X-ray focal spot based on a distance between the X-ray focal spot and a rotation center axis, a distance between the X-ray focal spot and a center of the X-ray detector, and a pitch of the plurality of X-ray detection elements.

12. The method for X-ray CT imaging of claim 11 , wherein the setting step comprises setting the magnitude of fluctuation D to be

D

<

d

·

SOD

2

·

(

SDD

-

SOD

)

,

wherein SOD is defined as the distance between the X-ray focal spot and the rotation center axis of the X-ray irradiation unit and the X-ray detector, SDD is defined as the distance between the X-ray focal spot and the center of the X-ray detector, and d is defined as the pitch of the plurality of X-ray detection elements.

13. The method for X-ray CT imaging of claim 12 , wherein the executing step further comprises controlling the helical scan so that a helical pitch is substantially equal to (n +0.5) dc, wherein n is an integer and dc is a projected pitch, which is a projected length of the pitch of the plurality of X-ray detection elements at a rotation center axis of the X-ray irradiation unit and the X-ray detector.

14. The method for X-ray CT imaging of claim 13 , wherein the helical pitch is substantially equal to 2.5 dc.

15. The method for X-ray CT imaging of claim 13 , wherein

the generating step comprises generating the reconstructed image based on direct data acquired by the helical scan; and

the setting step comprises setting the magnitude of fluctuation D to be

D

=

d

·

SOD

4

·

(

SDD

-

SOD

)

.

16. The method for X-ray CT imaging of claim 13 , wherein

the generating step comprises generating the reconstructed image based on direct data and complementary data acquired by the helical scan; and

the setting step comprises setting the magnitude of fluctuation D to be

D

=

d

·

SOD

8

·

(

SDD

-

SOD

)

.

17. The method for X-ray CT imaging of claim 12 , wherein the executing step further comprises controlling the helical scan so that a helical pitch is substantially equal to (2n +1) dc, wherein n is an integer and de is a projected pitch, which is a projected length of the pitch of the plurality of X-ray detection elements at a rotation center axis of the X-ray irradiation unit and the X-ray detector.

18. The method for X-ray CT imaging of claim 17 , wherein

the generating step comprises generating the reconstructed image based on direct data and complementary data acquired by the helical scan; and

the setting step comprises setting the magnitude of fluctuation D to be

D

=

d

·

SOD

4

·

(

SDD

-

SOD

)

.

19. The method for X-ray CT imaging of claim 17 , wherein the helical pitch is substantially equal to 3 dc.

20. The method for X-ray CT imaging of claim 11 , wherein the setting step comprises setting the magnitude of fluctuation D to be

D

<

d

·

SOD

4

·

(

SDD

-

SOD

)

,

wherein SOD is defined as the distance between the X-ray focal spot and the rotation center axis of the X-ray irradiation unit and the X-ray detector, SDD is defined as the distance between the X-ray focal spot and the center of X-ray detector, and d is defined as the pitch of the plurality of X-ray detection elements.