US5734691A
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US
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Detector z-axis gain non-uniformity correction in a computed tomography system
Assignee: General Electric Co
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Filing: 1996-12-23
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Granted: 1998-03-31
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Expires: 2016-12-23
Abstract
Abstract The present invention, in one form, corrects any error due to varying detector cell gains in the z-direction represented in data obtained by a scan in a CT system. The CT system includes an x-ray source which emits an x-ray beam from a focal spot, through a collimator aperture, and towards a detector having a plurality of detector cells. The geometry of the x-ray beam, the width of the collimator aperture and the focal spot size are used to determine the z-profile of the x-ray beam across the detector cells. Such z-profile is used to identify effective detector cell gains. The identified effective detector cell gains, rather than actual detector cell gains, are used to correct errors due to varying detector cell gains. Particularly, the identified effective detector cell gains are employed in a known correction algorithm to correct errors. A local average in an x-direction of actual detector cell gain z-profiles is used to determine a non-rectangular norm detector gain z-profile. In one form of the present invention, and after correcting the image data for beam-hardening, the data is passed through a highpass filter to remove any data representing relatively slow, or low frequency, changes. Next, the filtered data is clipped and view averaged to remove high frequency data contents due to the objects being imaged. A slope estimate is then created. Using the slope estimate, an error estimate is generated. The error estimate is then subtracted from the beam-hardened corrected data, for example. As a result, errors due to z-axis gain variation of the detector cells are removed from the projection data array.
Inventors
- 👤 Hui Hu
- 👤 Guy M. Besson
- 👤 Hui David He
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 20:27
CPC Classifications
G; G01; G01T; G01T1/00; G01T1/29; G01T1/2914; G01T1/2985; A; A61; A61B; A61B6/00; A61B6/52; A61B6/5258; A61B6/02; A61B6/03; A61B6/032; A61B6/40; A61B6/4064; A61B6/4078; Y; Y10; Y10S; Y10S378/00; Y10S378/901
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
83 words
A method for correcting projection data for detector cell gain error in a computed tomography system, the system including an x-ray source for projecting an x-ray beam towards a detector, the detector including a plurality of detector cells, the projection data being generated from output signals from the detector cells, said method comprising: determining actual detector gain profiles; determining effective detector gain profiles; and determining error in projection data using the determined actual detector gain profiles and the determined effective detector gain profiles.
Claim 2
Independent Claim
83 words
A method for correcting projection data for detector cell gain error in a computed tomography system, the system including an x-ray source for projecting an x-ray beam towards a detector, the detector including a plurality of detector cells, the projection data being generated from output signals from the detector cells, said method comprising: determining actual detector gain profiles; determining effective detector gain profiles; and determining error in projection data using the determined actual detector gain profiles and the determined effective detector gain profiles.
Claim 3
Dependent Claim
18 words
A method in accordance with claim 1 further comprising the step of determining a norm detector gain profile.
Claim 4
Dependent Claim
26 words
A method in accordance with claim 2 wherein determining a norm detector gain profile comprises obtaining a local average of the determined actual detector gain z-profiles.
Claim 5
Dependent Claim
24 words
A method in accordance with claim 1 wherein determining effective detector gain profiles comprises the step of determining a z-profile of the x-ray beam.
Claim 6
Dependent Claim
32 words
A method in accordance with claim 4 wherein determining effective detector gain profiles comprises the step of multiplying the determined z-profile of the x-ray beam and the determined actual detector gain profiles.
Claim 7
Dependent Claim
49 words
A method in accordance with claim 4 wherein the x-ray source includes a focal spot and a collimator, and wherein determining the z-profile of the x-ray beam includes the steps of: determining a width of the collimator aperture; determining a focal spot size; and determining a fan beam geometry.
Claim 8
Dependent Claim
50 words
A method in accordance with claim 1 wherein determining error in projection data includes the steps of: high pass filtering the data; clipping the high-passed filtered data; view averaging the clipped data; creating a slope estimate based on the view-averaged data; and identifying the error data using the slope estimate.
Claim 9
Dependent Claim
17 words
A method in accordance with claim 1 wherein the computed tomography system is a single slice system.
Claim 10
Dependent Claim
16 words
A method in accordance with claim 1 wherein the computed tomography system is a multislice system.
Claim 11
Independent Claim
85 words
A system for producing a tomographic image of an object from projection data, said system comprising an x-ray source and a detector, said detector having a plurality of detector cells, said system correcting the projection data obtained from said detector cells for any error resulting from different individual gains of said cells and configured to: determine actual detector gain profiles; determine effective detector gain profiles; and determine error in projection data using the determined actual detector gain profiles and the determined effective detector gain profiles.
Claim 12
Independent Claim
85 words
A system for producing a tomographic image of an object from projection data, said system comprising an x-ray source and a detector, said detector having a plurality of detector cells, said system correcting the projection data obtained from said detector cells for any error resulting from different individual gains of said cells and configured to: determine actual detector gain profiles; determine effective detector gain profiles; and determine error in projection data using the determined actual detector gain profiles and the determined effective detector gain profiles.
Claim 13
Dependent Claim
16 words
A system in accordance with claim 10 further configured to determine a norm detector gain profile.
Claim 14
Dependent Claim
31 words
A system in accordance with claim 11 wherein to determine the norm detector gain profile, said system is configured to obtain a local average of the determined actual detector gain z-profiles.
Claim 15
Dependent Claim
26 words
A system in accordance with claim 10 wherein to determine effective detector gain profiles, said system is configured to determine a z-profile of the x-ray beam.
Claim 16
Dependent Claim
34 words
A system in accordance with claim 13 wherein to determine effective detector gain profiles, said system is configured to multiply the determined z-profile of the x-ray beam and the determined actual detector gain profiles.
Claim 17
Dependent Claim
53 words
A system in accordance with claim 13 further comprising a focal spot and a collimator having an aperture therein, and wherein to determine the z-profile of the x-ray beam, said system is further configured to: determine a width of said collimator aperture; determine a focal spot size; and determine a fan beam geometry.
Claim 18
Dependent Claim
31 words
A system in accordance with claim 15 further comprising a computer having a memory, and wherein at least the determined width of the collimator aperture is stored in said computer memory.
Claim 19
Dependent Claim
21 words
A system in accordance with claim 10 wherein said detector comprises at least one row of detector cells in a z-direction.
Claim 20
Dependent Claim
21 words
A system in accordance with claim 17 wherein said detector comprises at least two rows of detector cells in the z-direction.
References Cited (Backward Citations)
US5473656A
Cited
US5579359A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2001-03-30 | 2001-09-29 | 2002-03-31 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2005-03-30 | 2005-09-29 | 2006-03-31 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2009-03-30 | 2009-09-29 | 2010-03-31 | $7700.00 | Window Closed / Lapsed |