US5265013A
Expired / Lapsed
US
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Compensation of computed tomography data for X-ray detector afterglow artifacts
Assignee: General Electric Co
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Filing: 1990-11-19
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Granted: 1993-11-23
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Expires: 2010-11-19
Abstract
Abstract An x-ray CT system has a detector which revolves about the object being imaged to acquire attenuation data from many different angles through a range of at least 180°. The response of the detector has a time lag which as the detector revolves tends to blur the attenuation data. The acquired data is compensated for the resolution degradation by convolving the data with a function that is the inverse of a response function of the detector. An image can be reconstructed from this compensated data. However, this compensation process tends to reintroduce noise that was reduced by the blurring. As a result, a modified version of the detector response function is applied to the compensated data to reduce the noise without degrading the image resolution to an unacceptable level.
Inventors
- 👤 Kevin F. King
- 👤 Carl R. Crawford
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 00:14
CPC Classifications
G; G06; G06T; G06T12/00; G06T12/10; Y; Y10; Y10S; Y10S128/00; Y10S128/92; Y10S128/922
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
88 words
A method for producing an image with a CT system the steps comprising: acquiring a set of attenuation values from a radiation detector; convolving the set of attenuation values with a function that is substantially the inverse of only a portion of an impulse response function of the radiation detector which portion corresponds to a function having a decay constant corresponding to a primary speed of the radiation detector, said convolving producing a second set of values; and reconstructing an image from values produced by said convolving step.
Claim 2
Independent Claim
88 words
A method for producing an image with a CT system the steps comprising: acquiring a set of attenuation values from a radiation detector; convolving the set of attenuation values with a function that is substantially the inverse of only a portion of an impulse response function of the radiation detector which portion corresponds to a function having a decay constant corresponding to a primary speed of the radiation detector, said convolving producing a second set of values; and reconstructing an image from values produced by said convolving step.
Claim 3
Dependent Claim
26 words
The method for producing an image as recited in claim 1 wherein said reconstructing step forms an image by back projecting the second set of values.
Claim 4
Independent Claim
90 words
A method for producing an image with a CT system, the steps comprising: acquiring a set of attenuation values from a radiation detector; convolving the set of attenuation values with a function that is substantially the inverse of an impulse response function of the radiation detector, said convolving producing a second set of values; convolving the second set of values with a function derived from the impulse response function of the radiation detector to produce a third set of values; and reconstructing an image from the third set of values.
Claim 5
Independent Claim
90 words
A method for producing an image with a CT system, the steps comprising: acquiring a set of attenuation values from a radiation detector; convolving the set of attenuation values with a function that is substantially the inverse of an impulse response function of the radiation detector, said convolving producing a second set of values; convolving the second set of values with a function derived from the impulse response function of the radiation detector to produce a third set of values; and reconstructing an image from the third set of values.
Claim 6
Dependent Claim
26 words
The method for producing an image as recited in claim 3 wherein said reconstructing step forms an image by back projecting the third set of values.
Claim 7
Independent Claim
102 words
A method for producing an image with a CT system the steps comprising: acquiring a first set of x-ray attenuation values by periodically sampling at an interval Δt a signal produced by an x-ray detector, where y n designates a specific x-ray attenuation value; producing a second set of data values from the first set of x-ray attenuation data values, in which each data value x n is given by the function: ##EQU4## where τ is a response decay time constant of the x-ray detector; and reconstructing an image by a back projection technique based on the second set of data values.
Claim 8
Independent Claim
102 words
A method for producing an image with a CT system the steps comprising: acquiring a first set of x-ray attenuation values by periodically sampling at an interval Δt a signal produced by an x-ray detector, where y n designates a specific x-ray attenuation value; producing a second set of data values from the first set of x-ray attenuation data values, in which each data value x n is given by the function: ##EQU4## where τ is a response decay time constant of the x-ray detector; and reconstructing an image by a back projection technique based on the second set of data values.
Claim 9
Dependent Claim
28 words
The method for producing an image as recited in claim 5 wherein τ is a response decay time constant of the x-ray detector which is of shortest duration.
Claim 10
Dependent Claim
70 words
The method for producing an image as recited in claim 5 further comprising: producing a third set of data values in which each data value z n is given by the function: z.sub.n =z.sub.n-1 e.sup.-Δt/τ' +x.sub.n (1-e.sup.-Δt/τ') where τ' is a fraction of the response decay time constant τ of the x-ray detector; and wherein said step of reconstructing an image comprises back projecting the third set of data values.
Claim 11
Dependent Claim
22 words
The method for producing an image as recited in claim 7 wherein τ' is substantially one-half the response decay time constant τ.
Claim 12
Independent Claim
123 words
A method for producing an image with a CT system having a detector that exhibits an afterglow phenomenon, the steps comprising: acquiring a signal from a detector that is indicative of an amount of radiation passing through an object; digitally sampling the signal from a detector to produce a plurality of n attenuation values, where n is a positive integer; filtering the attenuation values with a digital finite impulse response filter to compensate for the effects due to the afterglow phenomenon; digitally sampling results of said filtering step to produce a plurality of attenuation samples, in which the number of attenuation samples is given by the mathematical expression n/m, where m is an positive integer; and reconstructing an image from the attenuation samples.
Claim 13
Independent Claim
123 words
A method for producing an image with a CT system having a detector that exhibits an afterglow phenomenon, the steps comprising: acquiring a signal from a detector that is indicative of an amount of radiation passing through an object; digitally sampling the signal from a detector to produce a plurality of n attenuation values, where n is a positive integer; filtering the attenuation values with a digital finite impulse response filter to compensate for the effects due to the afterglow phenomenon; digitally sampling results of said filtering step to produce a plurality of attenuation samples, in which the number of attenuation samples is given by the mathematical expression n/m, where m is an positive integer; and reconstructing an image from the attenuation samples.
Claim 14
Dependent Claim
26 words
The method for producing an image as recited in claim 9 wherein said filtering step further includes filtering the attenuation values with a digital low-pass filter.
Claim 15
Dependent Claim
24 words
The method for producing an image as recited in claim 9 wherein said reconstructing step forms an image by back projecting the attenuation samples.
Claim 16
Dependent Claim
19 words
The method for producing an image as recited in claim 9 wherein m has a value greater than one.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1996-11-22 | 1997-05-24 | 1997-11-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2000-11-22 | 2001-05-24 | 2001-11-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2004-11-22 | 2005-05-24 | 2005-11-23 | $7700.00 | Window Closed / Lapsed |