Claims
- 1. An X-ray computerized tomography apparatus for imaging a subject comprising:
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- X-ray detector means facing the X-ray tube unit for detecting X rays passing through the subject, the detector means including an array of X-ray detector elements; and
- position determining means for determining a position of the X-ray focal point in accordance with a history of X-ray emission, the history beginning when the X-ray tube is at an ambient temperature and including information on X-ray tube voltage, X-ray tube current, and periods of X-ray emission and pausing.
- 2. The X-ray computerized tomography apparatus according to claim 1, in which the position determining means stores data representing curves along which the X-ray focal point is expected to move to a reference position after X-ray emission is terminated, and also data representing distances for which the X-ray focal point is expected to move away from the reference position and which have been measured by varying the tube voltage, the tube current, and the X-ray emission period, and said position determining means determines the position of the X-ray focal point from the curves and the distances in accordance with the history.
- 3. An X-ray computerized tomography apparatus for imaging a subject comprising:
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- X-ray detector means facing the X-ray tube unit for detecting X rays passing through the subject, the detector means including an array of X-ray detector elements;
- position determining means for determining a position of the X-ray focal point;
- storage means for storing compensation data used to achieve uniform sensitivity of the X-ray detector elements, the compensation data having been obtained at a plurality of positions of the X-ray focal point;
- compensation means for compensating output signals from said X-ray detector elements in accordance with the compensation data in accordance with the position of the X-ray focal point determined by said position determining means; and
- reconstruction means for reconstructing a tomography image in accordance with data output from said compensation means.
- 4. The apparatus according to claim 3, in which said position determining means includes
- a pair of X-ray detecting elements arranged adjacent to the X-ray detector elements and in the direction of the X-ray focal point movement such that a portion of the X-rays emitted from said X-ray tube unit irradiate the pair of X-ray detecting elements directly, the X-ray detecting elements being equally irradiated at an ambient temperature, and an irradiated area of one of the pair of X-ray detecting elements increases and that of another one of the X-ray detecting elements decreases in accordance with the movement of the X-ray focal point; and
- position calculating means for calculating the position of the X-ray focal point on the basis of a comparison of output signals from said pair of X-ray detecting elements.
- 5. The apparatus according to claim 4, in which said pair of detector elements are each comprise a scintillator for converting X-rays to light and a photodiode for converting the light to electricity.
- 6. The apparatus according to claim 3, in which said position determining means determines the position of the X-ray focal point in accordance with a history of X-ray emission beginning with an ambient temperature of the X-ray tube, said history including time of an emission period and a pause period.
- 7. The apparatus according to claim 6, in which said position determining means stores data representing curves along which the X-ray focal point is expected to move to a reference position after the X-ray emission is terminated, and also data representing distances for which the X-ray focal point is expected to move away from the reference position and which have been measured by varying the tube voltage, the tube current and the X-ray emission period, and said position determining means determines the position of the X-ray focal point from the curves and the distances in accordance with the history.
- 8. The apparatus according to claim 3, in which said position determining means comprises a plurality of temperature sensors attached to various components located within said X-ray tube unit, and means for calculating the position of the X-ray focal point based on temperatures detected by said temperature sensors.
- 9. The apparatus according to claim 8, in which said position determining means multiplies each of the temperatures detected by said temperature sensors by a thermal expansion coefficient of each of said components, adds the multiplying products, calculates a moving distance of the X-ray focal point from the reference position at on ambient temperature on the basis of the added product, and determines a position of the X-ray focal point on the basis of the moving distance.
- 10. An X-ray computerized tomography apparatus for imaging a subject comprising:
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- X-ray detector means facing the X-ray tube unit for detecting X rays passing through the subject, the detector means including an array of X-ray detector elements;
- position determining means for determining a position of the X-ray focal point;
- storage means for storing compensation data used to achieve a uniform sensitivity of the X-ray detector elements at a reference position, the compensation data having been obtained at the reference position;
- focal point returning means for returning the X-ray focal point to the reference position in accordance with the position of the X-ray focal point determined by said position determining means;
- compensation means for compensating output signals from said X-ray detector elements on the basis of the compensation data; and
- reconstruction means for reconstructing a tomography image on the basis of data output from said compensation means.
- 11. The apparatus according to claim 10, in which said position determining means includes
- a pair of X-ray detecting elements arranged adjacent the X-ray detector elements and such that a portion of the X rays emitted from said X-ray tube unit irradiate said pair of X-ray detecting elements directly, the portion of the X rays equally irradiating said pair of X-ray detecting elements at an ambient temperature, an irradiated area of one of the X-ray detecting elements increases and that of another one of the X-ray detecting elements decreases in accordance with the movement of the X-ray focal point; and
- position calculating means for calculating the position of the X-ray focal point on the basis of a comparison of output signals from said pair of X-ray detecting elements.
- 12. The apparatus according to claim 11, in which said position determining means comprises a plurality of X-ray detecting elements arranged in a direction in which the X-ray focal point moves, for receiving some of the X rays emitted from said X-ray tube unit, and position calculating means for calculating the position of the X-ray focal point from differences among outputs generated by said X-ray detecting elements.
- 13. The apparatus according to claim 11, in which said detector elements are each comprise a scintillator for converting X-rays to light and a photodiode for converting the light to electricity.
- 14. The apparatus according to claim 13, in which the number of said detector elements is two, and said two detector elements are equally irradiated with said some of the X rays when said X-ray focal point is located at a reference position.
- 15. The apparatus according to claim 10, in which said position determining means determines the position of the X-ray focal point in accordance with a history of X-ray emission, the history beginning when the X-ray tube unit is at an ambient temperature and including information on periods of X-ray emission and pausing.
- 16. The apparatus according to claim 15, in which said position determining means obtains said history from a tube voltage and a tube current to be applied and supplied to said X-ray tube unit, a time at which said X-ray tube unit is to start emitting X rays, and a period during which said X-ray tube unit is to keep emitting X rays to the subject.
- 17. The apparatus according to claim 15, in which said position determining means stores data representing curves along which the X-ray focal point is expected to move to a reference position after the X-ray emission is terminated, and also data representing distances for which the X-ray focal point is expected to move away from the reference position and which have been measured by varying the tube voltage, the tube current and the X-ray emission period, and said position determining means determines the position of the X-ray focal point from the curves and the distances in accordance with the history.
- 18. The apparatus according to claim 10, in which said position determining means comprises a plurality of temperature sensors attached to various components located within said X-ray tube unit, and means for calculating the position of the X-ray focal point based on temperatures detected by said temperature sensors.
- 19. The apparatus according to claim 18, in which said position determining means multiplies each of the temperatures detected by said temperature sensors by a thermal expansion coefficient of said each of components, adds for the multiplying products calculates a moving distance of the X-ray focal point from the reference position at low temperature on the basis of the adding product, and determines a position of the X-ray focal point on the basis of the moving distance.
- 20. The apparatus according to claim 10, in which the focal point returning means moves the X-ray tube unit such that the X-ray focal point returns to the reference position.
- 21. The apparatus according to claim 10, in which said X-ray tube unit includes a cathode for emitting an electron beam and an anode having a surface inclined to a path in which the electron beam travels from said cathode, for emitting X rays from a point on said surface when bombarded with the electron beam, said anode is shifted along said path in accordance with a thermal state of said X-ray tube unit, to thereby shift the X-ray focal point from the reference position, and the X-ray focal point shifting means deflects the electron beam, to thereby apply the electron beam onto that position on the surface of said anode which is identical to the reference position with respect to the path of the electron beam.
- 22. An X-ray computerized tomography apparatus for imaging a subject comprising:
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- X-ray detector means facing the X-ray tube unit for detecting X rays passing through the subject, the detector means including an array of X-ray detector elements; and
- position determining means for determining a position of the X-ray focal point, including
- a pair of X-ray detecting elements arranged such that a portion of the X-rays emitted from said X-ray tube unit directly irradiate said pair of X-ray detecting elements, the portion of the X rays equally irradiating said pair of X-ray detecting elements at an ambient temperature, an irradiated area of one of the pair of X-ray detecting elements increases and that of the other one of the pair of X-ray detecting elements decreases in accordance with the movement of the X-ray focal point, and said pair of X-ray detecting elements being arranged adjacent to said X-ray detector elements, and
- calculating means for calculating the position of the X-ray focal point on the basis of a comparison of output signals from said pair of X-ray detecting elements.
- 23. An X-ray computerized tomography apparatus for imaging a subject comprising:
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- X-ray detector means facing the X-ray tube unit for detecting X rays passing through the subject, the detector means including an array of X-ray detector elements; and
- position determining means for determining a position of the X-ray focal point comprising at least one temperature sensor attached to various components located within said X-ray tube unit, and means for calculating the position of the X-ray focal point on the basis of a temperature detected by said temperature sensor.
- 24. An X-ray computerized tomography apparatus for imaging a subject comprising;
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- X-ray detector means facing said X-ray tube unit for detecting X rays passing through the subject, the detector means including an array of X-ray detector elements for detecting X-rays transmitted through the subject; and
- position determining means for determining a position of the X-ray focal point comprising a pair of X-ray detecting elements and calculating means for calculating the position of the X-ray focal point on the basis of a comparison of output signals from said pair of X-ray detecting elements, said pair of X-ray detecting elements arranged such that the comparison of the output signals changes in accordance with the movement of the X-ray focal point and such that the part of the X-rays emitted from said X-ray tube unit directly irradiate said pair of X-ray detecting elements, said pair of X-ray detecting elements arranged adjacent to said X-ray detector elements.
- 25. An X-ray computerized tomography apparatus for imaging a subject comprising:
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- an array of X-ray detector elements facing the X-ray tube unit for detecting X rays passing through the subject;
- a memory device for storing data representative of focal point movement as a function of voltage, current, and X-ray emission time of the X-ray tube;
- a measuring unit for measuring the voltage, current and X-ray emission time of the X-ray tube; and
- a CPU for calculating from the stored data the position of the X-ray focal point as a function of the measured voltage, current and X-ray emission time of the X-ray tube.
- 26. An X-ray computerized tomography apparatus for imaging a subject comprising:
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- an array of X-ray detector elements facing the X-ray tube unit for detecting X rays passing through the subject;
- at least one temperature sensor attached to various components located within said X-ray tube unit; and
- a CPU for calculating the position of the X-ray focal point on the basis of a temperature detected by the at least one temperature sensor.
- 27. An X-ray computerized tomography apparatus for imaging a subject comprising;
- an X-ray tube unit for emitting X rays from an X-ray focal point, the X-ray focal point being movable due to heat generated by the emission of the X rays;
- an array of X-ray detector elements for detecting X-rays transmitted through the subject;
- a pair of X-ray detecting elements; and
- a CPU for calculating the position of the X-ray focal point on the basis of a comparison of output signals from said pair of X-ray detecting elements, said pair of X-ray detecting elements arranged such that the comparison of the output signals changes in accordance with the movement of the X-ray focal point and such that the part of the X-rays emitted from said X-ray tube unit directly irradiate said pair of X-ray detecting elements, said pair of X-ray detecting elements arranged adjacent to said X-ray detector elements.
Priority Claims (2)
Number |
Date |
Country |
Kind |
4-325159 |
Dec 1992 |
JPX |
|
5-057645 |
Mar 1993 |
JPX |
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Parent Case Info
This application is a continuation, of application Ser. No. 08/160,727, filed Dec. 2, 1993, now abandoned.
US Referenced Citations (7)
Foreign Referenced Citations (1)
Number |
Date |
Country |
0467532A2 |
Jan 1992 |
EPX |
Continuations (1)
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Number |
Date |
Country |
Parent |
160727 |
Dec 1993 |
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