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US5579359A
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Methods and apparatus for calibrating detector cell output signals
Assignee: General Electric Co
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Filing: 1995-12-21
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Granted: 1996-11-26
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Expires: 2015-12-21
Abstract
Abstract The present invention, in one form, is a method for determining and applying a ZCAL correction vector to the channel outputs from the detector array in a multi-slice CT system. More specifically, and in accordance with one embodiment of the present invention, the signal gain for each detector cell, or channel, at multiple z-axis locations is measured. For each channel, a correction polynomial Q n is fitted to the signal variation curve as a function of z-axis position so that the correction polynomial value multiplied by its channel signal produces a constant value over the operational range of z-axis positions. Beam positions (Z r ) are measured as a function of each position reference signal (D r ) and the Z position of the beam at the sensor channel and the location of the focal spot are determined. The z-axis location for each channel and the ZCAL correction vector are then determined. The ZCAL correction vector is then multiplied by the channel signal to calibrate the channel signal.
Inventors
- 👤 Thomas L. Toth
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 09:34
CPC Classifications
A; A61; A61B; A61B6/00; A61B6/02; A61B6/03; A61B6/032; A61B6/40; A61B6/4064; A61B6/4085; A61B6/58; A61B6/582; A61B6/585; G; G01; G01N; G01N23/00; G01N23/02; G01N23/04; G01N23/046; A61B6/4021; G01N2223/00; G01N2223/40; G01N2223/419; G01N2223/60; G01N2223/612; Y; Y10; Y10S; Y10S378/00; Y10S378/901
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
146 words
A method for calibrating projection data in a multi-slice computed tomography system, the computed tomography system including an x-ray source and a detector array having at least two rows of detector cells, said method comprising the steps of: determining the signal gain for each detector cell at multiple z-axis locations; fitting a correction polynomial Q n to a signal variation curve as a function of z-axis position so that the correction polynomial value multiplied by its channel signal produces a constant value over the operational range of z-axis positions; determining beam positions (Z r ) as a function of each position reference signal (D r ) and the Z position of the beam at a sensor channel; determining a z-axis location for each detector cell and a correction vector for each cell; and multiplying each channel signal by the correction vector to calibrate each channel signal.
Claim 2
Independent Claim
146 words
A method for calibrating projection data in a multi-slice computed tomography system, the computed tomography system including an x-ray source and a detector array having at least two rows of detector cells, said method comprising the steps of: determining the signal gain for each detector cell at multiple z-axis locations; fitting a correction polynomial Q n to a signal variation curve as a function of z-axis position so that the correction polynomial value multiplied by its channel signal produces a constant value over the operational range of z-axis positions; determining beam positions (Z r ) as a function of each position reference signal (D r ) and the Z position of the beam at a sensor channel; determining a z-axis location for each detector cell and a correction vector for each cell; and multiplying each channel signal by the correction vector to calibrate each channel signal.
Claim 3
Dependent Claim
35 words
A method in accordance with claim 1 wherein in determining the signal gain for each detector cell at multiple z-axis locations is measured, the z-axis beam location is measured by a z-axis beam position sensor.
Claim 4
Dependent Claim
44 words
A method in accordance with claim 2 wherein the computed tomography system further includes a collimator and wherein in determining the signal gain of each channel at multiple z locations, the collimator is indexed through a set of z-axis positions during a calibration scan.
Claim 5
Dependent Claim
63 words
A method in accordance with claim 1 wherein the z location (Z n ) for each channel is related to the position of the x-ray source focal spot by: Z.sub.n =(C-f)d.sub.n /S.sub.n +f where: Z=position of beam on detector f=position of focal spot in Z-axis C=position of collimation point in Z-axis d=detector to focal spot distance s=source to collimation distance; and n=channel index.
Claim 6
Dependent Claim
31 words
A method in accordance with claim 4 wherein the correction polynomial Q n is: Q.sub.n =a.sub.n +b.sub.n Z.sub.n +c.sub.n Z.sub.n.sup.2 where Q n =reciprocal channel gain as a function of Z.
Claim 7
Dependent Claim
55 words
A method in accordance with claim 5 wherein beam positions (Z r ) are measured as a function of each position reference signal (D r ) according to the equation: Z.sub.r =a.sub.r +b.sub.r D.sub.r +c.sub.r D.sub.r.sbsb.n.sup.2 where Z r =Z position at Z sensing channel as a function of the differential signal D r .
Claim 8
Dependent Claim
18 words
A method in accordance with claim 6 wherein the location of the focal spot is determined by: ##EQU2##
Claim 9
Dependent Claim
141 words
A computer for a computed tomography system including an x-ray source and a detector array having at least two rows of detector cells, said computer configured to calibrate projection data and programmed to: determine the signal gain for each detector cell at multiple z-axis locations; fit a correction polynomial Q n to a signal variation curve as a function of z-axis position so that the correction polynomial value multiplied by its channel signal produces a constant value over the operational range of z-axis positions; determine beam positions (Z r ) as a function of each position reference signal (D r ) and the Z position of the beam at a sensor channel; determine a z-axis location for each detector cell and a correction vector for each cell; and multiply each channel signal by the correction vector to calibrate each channel signal.
Claim 10
Dependent Claim
141 words
A computer for a computed tomography system including an x-ray source and a detector array having at least two rows of detector cells, said computer configured to calibrate projection data and programmed to: determine the signal gain for each detector cell at multiple z-axis locations; fit a correction polynomial Q n to a signal variation curve as a function of z-axis position so that the correction polynomial value multiplied by its channel signal produces a constant value over the operational range of z-axis positions; determine beam positions (Z r ) as a function of each position reference signal (D r ) and the Z position of the beam at a sensor channel; determine a z-axis location for each detector cell and a correction vector for each cell; and multiply each channel signal by the correction vector to calibrate each channel signal.
Claim 11
Dependent Claim
35 words
A computer in accordance with claim 8 wherein in determining the signal gain for each detector cell at multiple z-axis locations is measured, the z-axis beam location is measured by a z-axis beam position sensor.
Claim 12
Dependent Claim
44 words
A computer in accordance with claim 9 wherein the computed tomography system further includes a collimator and wherein in determining the signal gain of each channel at multiple z locations, the collimator is indexed through a set of z-axis positions during a calibration scan.
Claim 13
Dependent Claim
63 words
A computer in accordance with claim 1 wherein the z location (Z n ) for each channel is related to the position of the x-ray source focal spot by: Z.sub.n =(C-f)d.sub.n /S.sub.n +f where: Z=position of beam on detector f=position of focal spot in Z-axis C=position of collimation point in Z-axis d=detector to focal spot distance s=source to collimation distance; and n=channel index.
Claim 14
Dependent Claim
31 words
A computer in accordance with claim 11 wherein the correction polynomial Q n is: Q.sub.n =a.sub.n +b.sub.n Z.sub.n +c.sub.n Z.sub.n.sup.2 where Q n =reciprocal channel gain as a function of Z.
Claim 15
Dependent Claim
55 words
A computer in accordance with claim 12 wherein beam positions (Z r ) are measured as a function of each position reference signal (D r ) according to the equation: Z.sub.r =a.sub.r +b.sub.r D.sub.r +c.sub.r D.sub.r.sbsb.n.sup.2 where Z r =Z position at Z sensing channel as a function of the differential signal D r .
Claim 16
Dependent Claim
18 words
A computer in accordance with claim 13 wherein the location of the focal spot is determined by: ##EQU3##
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1999-11-26 | 2000-05-27 | 2000-11-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2003-11-26 | 2004-05-27 | 2004-11-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2007-11-26 | 2008-05-27 | 2008-11-26 | $7700.00 | Window Closed / Lapsed |