Constant image quality CT scanner with variable radiation flux density
First Claim
1. A CT scanner comprising:
- an examination region for receiving a subject that attenuates penetrating radiation more along some of a multiplicity of traversing paths than others;
a source of penetrating radiation which directs a beam of radiation through the examination region;
a motor means for rotating the radiation source through a multiplicity of angular positions around the examination region to pass the radiation through the subject along the multiplicity of traversing paths;
a means for varying the energy fluence of radiation impinging upon the subject in accordance with the angular position of the radiation source such that an average energy fluence that traverses the subject is generally constant for all angular positions of the x-ray source;
a radiation detection means for detecting the radiation with substantially the average energy fluence that has traversed the subject;
a means for reconstructing image representations from the radiation detected by the detectors.
1 Assignment
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Accused Products
Abstract
An x-ray source (20) rotates about a fixed cylinder (16) within which a subject of non-uniform cross-section is received. Radiation from the x-ray source passes through the subject and impinges on an arc of radiation detectors (28). Because the subject is of non-uniform cross-section, the average x-ray energy fluence impinging on the detectors across the arc varies with the relative angular position of the x-ray source and the subject. In one embodiment, a motor (18) which rotates the x-ray tube relative to the subject is controlled by a digital motor control (50). The digital motor control varies the rotational speed to a preselected angular velocity indicated by a look-up table (52) at each of a multiplicity of angular positions around the subject. The angular velocity is slowed when radiation is passing through thicker portions of the subject and accelerated when passing through thinner portions of the subject such that the average x-ray energy fluence received by the radiation detectors is substantially constant regardless of the angular position of the x-ray source. In another embodiment, an x-ray tube control circuit (82) alters the tube current such that the average x-ray energy fluence received by the detectors becomes angular position independent. In this manner, the signal-to-noise ratio at each angular position is the same and structural noise is eliminated in the resultant reconstructed image.
84 Citations
20 Claims
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1. A CT scanner comprising:
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an examination region for receiving a subject that attenuates penetrating radiation more along some of a multiplicity of traversing paths than others; a source of penetrating radiation which directs a beam of radiation through the examination region; a motor means for rotating the radiation source through a multiplicity of angular positions around the examination region to pass the radiation through the subject along the multiplicity of traversing paths; a means for varying the energy fluence of radiation impinging upon the subject in accordance with the angular position of the radiation source such that an average energy fluence that traverses the subject is generally constant for all angular positions of the x-ray source; a radiation detection means for detecting the radiation with substantially the average energy fluence that has traversed the subject; a means for reconstructing image representations from the radiation detected by the detectors. - View Dependent Claims (2, 3)
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4. A CT scanner comprising:
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an examination region for receiving a subject; a source of penetrating radiation which directs a beam of radiation through the examination region; a motor means for rotating the radiation source around the examination region, such that average radiation attenuation by the subject varies with an angular position of the radiation source therearound; a means for varying the x-ray energy fluence of radiation impinging upon the subject in accordance with the angular position of the radiation source such that an average x-ray energy fluence that has traversed the subject is generally constant for all angular positions of the x-ray source, the means for varying the x-ray energy fluence impinging on the subject including; a motor speed control means for selectively controlling the motor means to rotate the radiation source at selected angular velocities; and a speed designating means for designating angular velocities to the motor speed control means in accordance with the angular position of the radiation source; a radiation detection means for detecting the radiation that has traversed the subject; a means for reconstructing image representations from the radiation detected by the detectors. - View Dependent Claims (5, 6, 7)
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8. A CT scanner comprising:
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an examination region for receiving a subject; an x-ray tube in which x-rays are generated by a tube current flowing from a cathode to an anode; a motor means for rotating the radiation source around the examination region, such that average radiation attenuation by the subject varies with an angular position of the radiation source therearound; a means for varying the x-ray energy fluence of radiation impinging upon the subject in accordance with the angular position of the radiation source such that an average x-ray energy fluence that has traversed the subject is generally constant for all angular positions of the x-ray source, the means for varying the x-ray energy fluence including a means for adjusting a bias on a grid between the cathode and the anode to vary the tube current; a radiation detection means for detecting the radiation that has traversed the subject; a means for reconstructing image representations from the radiation detected by the detectors.
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9. A CT scanner comprising:
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an examination region for receiving a non-cylindrical subject; an x-ray tube in which x-rays are generated by a tube current from a cathode striking a target; a motor means for rotating the radiation source around the examination region, such that average radiation attenuation by the subject varies with an angular position of the radiation source therearound; an angular position resolving means for determining a current angular position of the x-ray tube relative to the subject; an x-ray tube current varying means connected with the angular position resolving means for varying the x-ray tube current such that the x-ray energy fluence of radiation impinging upon the subject in accordance with the angular position of the radiation source such that an average x-ray energy fluence that has traversed the subject is generally constant for all angular positions of the x-ray source; a radiation detection means for detecting the radiation that has traversed the subject; a means for reconstructing image representations from the radiation detected by the detectors. - View Dependent Claims (10, 11)
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12. A radiation examination means comprising:
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a source of penetrating radiation which rotates relative to a subject that has different radiation attenuation properties at different angular directions therethrough; a means for detecting radiation generated by the radiation source which has been transmitted through the subject; a means for determining a current angular position of the radiation source relative to the subject; a means for adjusting an energy fluence of the radiation which impinges upon the subject between each sampling of the radiation detection means in accordance with the current relative angular position of the radiation source and the radiation attenuation properties of the subject along the angular direction from the current radiation source position through the subject such that an average energy fluence of radiation that traverses the subject is held substantially constant for all angular positions of the radiation source. - View Dependent Claims (13)
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14. A CT scanner comprising:
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a source of a fan-shaped swath of radiation; a means for rotating the fan-shaped swath of radiation relative to a subject whose radiation absorbency varies with a relative angular position between the fan-shaped swath and the subject a radiation detection means for detecting the radiation which has traversed the subject; a means for selectively adjusting at least one of an amount of radiation impinging upon the subject and a rotation speed of the radiation swath in accordance with the sampled radiation and the relative angular position between the swath and the subject to adjust for the varying radiation absorbency of the subject with angular position between the fan-shaped swath and the subject such that an average energy fluence of the radiation which has traversed the subject and is detected by the detectors remains constant.
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15. A method of generating an image representation of a subject of non-uniform cross-section, the method comprising:
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generating a swath of radiation which is directed to pass through the subject; rotating the fan-shaped swath relative to the subject such that the fan-shaped swath passes through the subject from a plurality of angular orientations; repeatedly sampling the radiation which has passed through the patient at different relative angles; selectively adjusting at least one of an amount of radiation impinging upon the subject and a rotation speed of the radiation swath in accordance with the sampled radiation and the relative angular position between the swath and the subject. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification