Calibration device for location of CT x-ray generator and detector, calibration method using the calibration device, and calibration method for CT system
View Patent ↗A calibration device for location of a CT X-ray generator and detector includes a splitting window, a splitting window bracket configured to support the splitting window, an integral bracket, and a spring including a first end connected to the splitting window bracket and a second end connected to the integral bracket.
1. A calibration device for location of a CT X-ray generator and detector, said calibration device comprising:
a splitting window;
a splitting window bracket configured to support the splitting window;
an integral bracket; and
a spring comprising a first end connected to the splitting window bracket and a second end connected to the integral bracket.
2. The calibration device according to claim 1 , wherein the splitting window includes four parts divided by two center lines, two windows opened at two parts at opposite angles in the four parts.
3. The calibration device according to claim 1 , further comprising a bolt configured to adjust the splitting window.
4. The calibration device according to claim 2 , further comprising a bolt configured to adjust the splitting window.
5. A calibration method of using a calibration device to calibrate location for a CT X-ray generator and detector, the calibration device including a splitting window, a splitting window bracket configured to support the splitting window, an integral bracket, and a spring having a first end connected to the splitting window bracket and a second end connected to the integral bracket, said method comprising:
placing the calibration device in a first position on a scan plane;
exposing the calibration device at 0 degree and at 180 degree using the CT X-ray generator;
obtaining an offset of a tube based on a relationship among an x-ray profile projected on the detector, the tube, and an ISO center; and
adjusting the tube according to the offset to position a focal spot of the tube and a center of a collimator onto the scan plane.
6. The calibration method according to claim 5 , further comprising:
placing one calibration device of a plurality of devices on each of a left side, a center, and a right side of channels of the detector;
exposing the plurality of calibration devices;
acquiring data after exposure obtained by the detector;
calculating an amount of misalignment at the left side, the center, and the right side based on the acquired data; and
adjusting the detector such that the amount of misalignment is substantially zero.
7. The calibration method according to claim 5 , wherein obtaining an offset of a tube further comprises:
calculating a displacement a of a center of the calibration device on the detector when the calibration device is moved from the first position to a second position; and
obtaining an offset ?? of the tube using:
??
=
a
×
C
×
E
A
×
D
wherein C represents a distance from the focal spot of the tube to the second position; E represents a distance from the focal spot of the tube to an aperture of the collimator; A represents a distance from the focal spot of the tube to the detector; and D represents a distance from the first position to the second position.
8. The calibration method according to claim 6 , wherein obtaining an offset of a tube further comprises:
calculating a displacement a of a center of the calibration device on the detector when the calibration device is moved from the first position to a second position; and
obtaining an offset ?? of the tube using:
??
=
a
×
C
×
E
A
×
D
wherein C represents a distance from the focal spot of the tube to the second position; E represents a distance from the focal spot of the tube to an aperture of the collimator; A represents a distance from the focal spot of the tube to the detector; and D represents a distance from the first position to the second position.
9. The calibration method according to claim 7 , wherein obtaining a displacement a of a center of the calibration on the detector further comprises obtaining the displacement a when the calibration device is moved from the first position to the second position using:
a
=
(
T
×
A
)
(
1
+
γ
)
2
(
1
-
γ
)
X
wherein,
X
=
P
A
-
P
B
P
A
+
P
B
where γ represents a ratio of the calibration device to an air projection; T is an x-ray thickness at a center of rotation; P A represents an average projection data in an A Window; and P B represents an average projection data in a B Window.
10. The calibration method according to claim 8 , displacement a of a center of the calibration on the detector further comprises obtaining the displacement a when the calibration device is moved from the first position to the second position using:
a
=
(
T
×
A
)
(
1
+
γ
)
2
(
1
-
γ
)
X
wherein,
X
=
P
A
-
P
B
P
A
+
P
B
where γ represents a ratio of the calibration device to an air projection; T is an x-ray thickness at a center of rotation; P A represents an average projection data in an A Window; and P B represents an average projection data in a B Window.
11. A calibration method for a CT system comprising:
calibrating a plane of rotation;
calibrating a beam on a window;
aligning a detector with a focal spot of a tube when the tube is cool;
aligning a collimator with the detector in an x-direction;
calibrating the collimator in a z-direction; and
re-performing the steps in sequence based on an offset in the z-direction of the focal spot obtained in calibrating the collimator in the z-direction until the offset approximates to zero.
12. The calibration method according to claim 11 , wherein calibrating the plane of rotation further comprises:
placing a calibration device in a first position on a scan plane;
exposing the calibration device at 0 degree and at 180 degree using a CT x-ray generator;
obtaining an offset of the tube based on a relationship among an x-ray profile projected on the detector, the tube, and an ISO center; and
adjusting the tube based on the offset to position the focal spot and a center of the collimator onto the scan plane.
13. The calibration method according to claim 12 , wherein calibrating a beam on a window comprises:
placing one calibration device of a plurality of calibration devices on a left side, a center, and a right side of channels of the detector;
exposing the plurality of calibration devices;
acquiring data after exposure obtained by the detector;
calculating an amount of misalignment at the left side, the center, and the right side based on the obtained data; and
adjusting the detector such that the amount of misalignment is substantially zero.
14. The calibration method according to claim 13 , wherein obtaining an offset of the tube further comprises:
calculating a displacement a of a center of the calibration device on the detector when the calibration device is moved from the first position to a second position; and
obtaining and offset ?? of the tube using:
??
=
a
×
C
×
E
A
×
D
wherein C represents a distance from the focal spot of the tube to the second position; E represents a distance from the focal spot of the tube to an aperture of the collimator; A represents a distance from the focal spot of the tube to the detector; and D represents a distance from the first position to the second position.
15. The calibration method according to claim 14 , displacement a of a center of the calibration on the detector further comprises obtaining the displacement a when the calibration device is moved from the first position to the second position using:
a
=
(
T
×
A
)
(
1
+
γ
)
2
(
1
-
γ
)
X
wherein,
X
=
P
A
-
P
B
P
A
+
P
B
where γ represents a ratio of the calibration device to an air projection; T is an x-ray thickness at a center of rotation; P A represents an average projection data in an A Window; and P B represents an average projection data in a B Window.
16. The calibration method according to claim 11 , wherein a calibration device includes a splitting window, calibrating a beam on a window further comprises calibrating the beam using the splitting window of the calibration device.
17. The calibration method according to claim 11 , wherein a calibration device includes a splitting window, said method further comprising distinguishing a position of the beam on the detector using the splitting window of the calibration device.
18. The calibration method according to claim 12 , wherein exposing the calibration device at 0 degree and at 180 degree further comprises:
exposing the calibration device at 0 degree when the calibration device is located at the first position; and
exposing the calibration device at 180 degree when the calibration device is located at a second position.
19. The calibration device according to claim 1 , wherein the splitting window is configured to distinguish a position of a beam on the detector.
20. The calibration device according to claim 1 , wherein the spring is configured to adjust a position of the splitting window with respect to the detector.