Patent US4991189A successfully refreshed from Google Patents.
US4991189A
Expired / Lapsed
US
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Collimation apparatus for x-ray beam correction
Assignee: General Electric Co
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Filing: 1990-04-16
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Granted: 1991-02-05
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Expires: 2010-04-16
Abstract
Abstract A computed tomography system corrects image errors resulting from misalignment of the fan beam as a result of placement of the x-ray tube, thermal drift of the x-ray tube anode of mechanical stresses of the gantry or x-ray tube. Misalignment is determined alternately by means of a z-axis offset detector which detects movement of the exposure area of the CT fan beam or a predictive model that calculates thermal drift of mechanical deflection of the focal spot of the x-ray tube based on previous use. The system includes a collimator with a controllable z-axis position which may be controlled to reduce z-axis offset of the fan beam exposure area or to make the fan beam more parallel with the imaging plane of the CT system.
Inventors
- 👤 Jonathan C. Boomgaarden
- 👤 Thomas L. Toth
- 👤 August O. Englert
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 16:20
CPC Classifications
A; A61; A61B; A61B6/00; A61B6/06; A61B6/02; A61B6/03; A61B6/032; A61B6/40; A61B6/4021; A61B6/52; A61B6/5258; G; G21; G21K; G21K1/00; G21K1/02
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
139 words
A computed tomography system including an x-ray source for producing a fan beam of x-rays along a fan beam plane in response to an exposure technique, the fan beam plane being at deviation angle α from an imaging plane and intersecting a detector array at position D z , comprising: a collimator means having position C z for controlling the alignment of the fan beam plane; a z-axis offset detector positioned to intercept the fan beam for producing a position signal dependant on D z ; an error calculation means for generating an error signal in response to the position signal; and a collimator controller responsive to the error signal for changing the relative position C z of the collimator with respect to the x-ray source and detector array so as to reduce the magnitude of the error signal.
Claim 2
Dependent Claim
139 words
A computed tomography system including an x-ray source for producing a fan beam of x-rays along a fan beam plane in response to an exposure technique, the fan beam plane being at deviation angle α from an imaging plane and intersecting a detector array at position D z , comprising: a collimator means having position C z for controlling the alignment of the fan beam plane; a z-axis offset detector positioned to intercept the fan beam for producing a position signal dependant on D z ; an error calculation means for generating an error signal in response to the position signal; and a collimator controller responsive to the error signal for changing the relative position C z of the collimator with respect to the x-ray source and detector array so as to reduce the magnitude of the error signal.
Claim 3
Dependent Claim
28 words
The computed tomography system of claim 1 wherein the error signal is proportional to the difference in position between D z and an alignment point D O .
Claim 4
Dependent Claim
23 words
The computed tomography system of claim 1 wherein the error signal is proportional to the difference between D z and C z .
Claim 5
Dependent Claim
141 words
A computed tomography system including an x-ray source for producing a fan beam of x-rays emanating from a focal at a position F z spot, along a fan beam plane in response to an exposure technique, the fan beam plane being at deviation angle α from an imaging plane and intersecting a detector array at position D z , comprising: a collimator means having position C z for controlling the alignment of the fan beam plane; a memory for storing previous values of exposure techniques used with the x-ray source and the time of each exposure technique; a thermodynamic/geometric model for calculating a current fan beam position D zp from the values stored in the memory; and a collimator controller responsive to the fan beam position D zp for changing the collimator position C z in response to F z .
Claim 6
Dependent Claim
141 words
A computed tomography system including an x-ray source for producing a fan beam of x-rays emanating from a focal at a position F z spot, along a fan beam plane in response to an exposure technique, the fan beam plane being at deviation angle α from an imaging plane and intersecting a detector array at position D z , comprising: a collimator means having position C z for controlling the alignment of the fan beam plane; a memory for storing previous values of exposure techniques used with the x-ray source and the time of each exposure technique; a thermodynamic/geometric model for calculating a current fan beam position D zp from the values stored in the memory; and a collimator controller responsive to the fan beam position D zp for changing the collimator position C z in response to F z .
Claim 7
Dependent Claim
28 words
The computed tomography system Of claim 4 wherein the collimator controller changes the collimator position so as to reduce the difference between D zp and C z .
Claim 8
Dependent Claim
34 words
The computed tomography system of claim 4 wherein the collimator controller changes the collimator position so as to reduce the difference between D zp and the center of the detector array D O .
Claim 9
Dependent Claim
142 words
A computed tomography system including an x-ray source, mounted on a gantry for rotation about an axis at a rotational velocity and tilt angle, and for producing a fan beam of x-rays emanating from a focal at a position F z spot, along a fan beam plane in response to an exposure technique, the fan beam plane being at deviation angle α from an imaging plane and intersecting a detector array at position D z , comprising: a collimator means having position C z for controlling the alignment of the fan beam plane; a mechanical stress model for calculating a current fan beam position D zp from the rotational velocity and the tilt angle of the gantry; and a collimator controller responsive to the fan beam position D zp for changing the collimator position C z in response to F z .
Claim 10
Dependent Claim
142 words
A computed tomography system including an x-ray source, mounted on a gantry for rotation about an axis at a rotational velocity and tilt angle, and for producing a fan beam of x-rays emanating from a focal at a position F z spot, along a fan beam plane in response to an exposure technique, the fan beam plane being at deviation angle α from an imaging plane and intersecting a detector array at position D z , comprising: a collimator means having position C z for controlling the alignment of the fan beam plane; a mechanical stress model for calculating a current fan beam position D zp from the rotational velocity and the tilt angle of the gantry; and a collimator controller responsive to the fan beam position D zp for changing the collimator position C z in response to F z .
Claim 11
Dependent Claim
28 words
The computed tomography system of claim 7 wherein the collimator controller changes the collimator position so as to reduce the difference between D zp and C z .
Claim 12
Dependent Claim
34 words
The computed tomography system of claim 7 wherein the collimator controller changes the collimator position so as to reduce the difference between D zp and the center of the detector array D O .
References Cited (Backward Citations)
US4559639A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-02-04 | 1994-08-06 | 1995-02-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-02-04 | 1998-08-06 | 1999-02-05 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-02-04 | 2002-08-06 | 2003-02-05 | $7700.00 | Window Closed / Lapsed |