US5438202A
Expired / Lapsed
US
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Stabilized scatter free gamma camera images
Assignee: GE Medical Systems Israel Ltd
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Filing: 1994-06-06
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Granted: 1995-08-01
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Expires: 2014-06-06
Abstract
Abstract A system for recording fewer of the events that are caused by unwanted photons with greater stability. The system locally determines the energy spectrum and fits for each pixel of the image the determined energy spectrum with a modified trial function composed of: a photopeak component of known energy shape, Compton scatter components having theoretically derived energy shapes and, when applicable, also measured or calculated energy spectra of other unwanted photons. The modified trial function also takes into consideration unknown local deviations in the outputs of electronic components. The amplitude of the photopeak distribution resulting from the fit is used to obtain the local content of wanted interactions in the image. This enables removal of Compton contamination and also the contamination caused by interaction of the gamma photons with lead components.
Inventors
- 👤 Alex Matanzon
- 👤 Gideon Berlad
- 👤 Dov Maop
- 👤 Yigal Shrem
- 👤 Adrian Sott
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 16:55
CPC Classifications
G; G01; G01T; G01T1/00; G01T1/16; G01T1/161; G01T1/164; G01T1/1641; G01T1/1647; G01T1/1642; G01T1/1648
Claims Analysis
Total Claims: 52
Claim 1
Independent Claim
252 words
A method of improving images from a gamma camera system by considering isotopes have k photopeaks where k≧1 and by reducing the contribution of unwanted photons on an image produced by a gamma ray imaging system, said method including the steps of: detecting photons impinging on a gamma ray detector in an X,Y coordinate location according to the location of the impingement on the detector, determining the energy of each detected photon, grouping each detected photon according to the determined energy in the X, Y coordinate location, accumulating counts of said grouped photons according to the determined energy level of the photons at each X, Y coordinate location, constructing an energy spectrum of each X, Y location using the accumulated counts, determining a system dependent energy distribution of different components of unwanted photons, determining the energy spread function of the gamma camera system for the known energies of the wanted photons, constructing a trial function comprising the system energy spread function multiplied by a first unknown coefficient of wanted photons plus the system dependent energy distributions of the components of unwanted photons multiplied by their unknown coefficients modifying the trial function by including in the trial function the first n derivatives of the system energy spread function of each of the k photopeaks multiplied by unknown coefficients, locally fitting the modified trail function to the constructed energy spectrum to obtain the count of the wanted photons. using the count of the wanted photons to produce an image practically free of unwanted photons.
Claim 2
Independent Claim
252 words
A method of improving images from a gamma camera system by considering isotopes have k photopeaks where k≧1 and by reducing the contribution of unwanted photons on an image produced by a gamma ray imaging system, said method including the steps of: detecting photons impinging on a gamma ray detector in an X,Y coordinate location according to the location of the impingement on the detector, determining the energy of each detected photon, grouping each detected photon according to the determined energy in the X, Y coordinate location, accumulating counts of said grouped photons according to the determined energy level of the photons at each X, Y coordinate location, constructing an energy spectrum of each X, Y location using the accumulated counts, determining a system dependent energy distribution of different components of unwanted photons, determining the energy spread function of the gamma camera system for the known energies of the wanted photons, constructing a trial function comprising the system energy spread function multiplied by a first unknown coefficient of wanted photons plus the system dependent energy distributions of the components of unwanted photons multiplied by their unknown coefficients modifying the trial function by including in the trial function the first n derivatives of the system energy spread function of each of the k photopeaks multiplied by unknown coefficients, locally fitting the modified trail function to the constructed energy spectrum to obtain the count of the wanted photons. using the count of the wanted photons to produce an image practically free of unwanted photons.
Claim 3
Dependent Claim
19 words
The method of improving images from gamma camera systems of claim 1 wherein unwanted photons include Compton scattered photons.
Claim 4
Independent Claim
96 words
The method of claim 1wherein the step of determining the system dependent energy distributions of the different components of unwanted photons comprises the steps of: determining at least part of the system independent energy distributions of the components of the unwanted photons, determining the energy spread function of the gamma camera system for the determined energies of the components of the unwanted photons, and using the determined energy distribution of unwanted photons and the energy spread function of the system to obtain a system dependent energy distribution of the unwanted photons per X, Y coordinate location.
Claim 5
Dependent Claim
20 words
The method of improving images from gamma camera systems of claim 2 wherein said unwanted photons include other unwanted photons.
Claim 6
Dependent Claim
13 words
The method of claim 2 wherein said unwanted photons include lead X-ray photons.
Claim 7
Dependent Claim
22 words
The method of claim 1 wherein the step of locally fitting the modified trial function includes obtaining the counts of unwanted photons.
Claim 8
Dependent Claim
59 words
The method of claim 1 wherein the step used to obtain the system dependent energy distributions of wanted photons includes the step of calculating the energy distributions of wanted photons for each value of discrete energy lines in a source and determining the first n derivatives of the energy spread function for each discrete energy line in the source.
Claim 9
Dependent Claim
47 words
The method of claim 3 wherein the step of using the determined energy distribution of unwanted photons and the energy spread function of the gamma ray imaging system includes convolving the energy distribution of unwanted photons with the energy spread function of the gamma ray imaging system.
Claim 10
Dependent Claim
54 words
The method of claim 1 wherein the step of using the determined energy distribution of unwanted photons and the energy spread function of the system includes the step of measuring at least one energy distribution of unwanted photons with the system whereby the measured distribution inherently includes the energy spread function of the system.
Claim 11
Dependent Claim
77 words
The method of claim 8 wherein said step of constructing a trial function comprises: summing the convolved system dependent energy distribution of the determined energy distribution of unwanted photons including the system energy distribution of Compton scattered photons and additional unwanted photons both with unknown X, Y coefficients, and locally fitting the trial function to the constructed energy spectrum to solve for the unknown X, Y coefficients and thus for determining the counts of the unscattered photons.
Claim 12
Dependent Claim
29 words
The method of claim 10 wherein said step of determining the energy distribution of unwanted photons comprises the step of: analytically determining the energy distribution of Compton scattered photons.
Claim 13
Dependent Claim
90 words
The method of claim 11 wherein the step of analytically determining the energy distribution of Compton scattered photons includes the steps of: convolving the energy distribution of the first order photon scatter probability distribution with the m order photon scatter probability distribution to determine the energy distribution of the m+1 order scattered photons where m=1,2. . .M-1, and convolving the energy distribution of the m-order scatter photons where m=1,2. . .M with the energy spread function of the system to obtain system dependent probability distributions of m order scatter photons.
Claim 14
Dependent Claim
35 words
The method of claim 12 including the step of obtaining a set of discrete functions from the energy distribution of the m-order Compton scatter photons by averaging the calculated Compton energy distributions for each grouping.
Claim 15
Dependent Claim
14 words
The method of claim 13, including the step of reducing the number of calculations.
Claim 16
Dependent Claim
24 words
The method of claim 14 wherein the step of reducing the number of calculations comprises converting discrete functions into an orthonormal set of functions.
Claim 17
Dependent Claim
38 words
The method of claim 1 wherein the fitting step includes: using quasi-local pixels to obtain local counts of the scattered photons, and doing a single parameter fit to determine the local counts at each of the discrete photopeaks.
Claim 18
Dependent Claim
61 words
The method of claim 16 wherein the step of using quasi-local pixels comprises: using large pixels comprising a (2n+1)×(2m+1) rectangle of pixels where both n and m are positive integers and the value of the large pixel is divided by the number of pixels in the large pixel and attributed to the center pixel, and evaluating all pixels in this method.
Claim 19
Dependent Claim
25 words
The method of claim 1 wherein the step of locally fitting the trial function to the constructed energy spectrum is accomplished using least square fitting.
Claim 20
Dependent Claim
26 words
The method of claim 1 wherein the step of locally fitting the trial function to the constructed energy spectrum is accomplished using a maximum likelihood fit.
Claim 21
Dependent Claim
27 words
The method of claim 1 wherein the step of locally fitting the trial function to the constructed energy spectrum is accomplished using a partial maximum likelihood fit.
Claim 22
Dependent Claim
30 words
The method of claim 1 wherein the step of locally fitting the trial function to the constructed energy spectrum is accomplished using a combined least square and maximum likelihood fit.
Claim 23
Dependent Claim
7 words
The method of claim 1 wherein n=1.
Claim 24
Dependent Claim
7 words
The method of claim 1 wherein n>1.
Claim 25
Dependent Claim
7 words
The method of claim 1 wherein k=1.
Claim 26
Dependent Claim
7 words
The method of claim 1 wherein k>1.
Claim 27
Independent Claim
262 words
A system for improving images from a gamma camera system by considering isotopes having k photopeaks where k≧1 and by reducing the contribution of unwanted photons on an image produced by a gamma ray imaging system, said system comprising: a gamma camera detector for detecting gamma photons impinging thereon at an X, Y coordinate location, means for determining the energy of each detected photon, means for grouping each detected photon according to the determined energy in the X, Y coordinate location, means for accumulating counts of said grouped photons according to the determined energy level of the photons at each X, Y coordinate location, means for constructing an energy spectrum of each X, Y location using the accumulated counts, means for determining a system dependent energy distribution of different components of unwanted photons, means for determining the energy spread function of the gamma camera system for the known energies of the wanted photons, means for constructing a trial function comprising the system energy spread function multiplied by a first unknown coefficient of wanted photons plus the system dependent energy distributions of the components of unwanted photons multiplied by their unknown coefficients, means for modifying the trial function by including in the trial function the first n derivatives of the system energy spread function of each of the k photopeaks multiplied by unknown coefficients, means for locally fitting the modified trial function to the constructed energy spectrum to obtain the count of the wanted photons, means for using the count of the wanted photons to produce an image practically free of unwanted photons.
Claim 28
Independent Claim
262 words
A system for improving images from a gamma camera system by considering isotopes having k photopeaks where k≧1 and by reducing the contribution of unwanted photons on an image produced by a gamma ray imaging system, said system comprising: a gamma camera detector for detecting gamma photons impinging thereon at an X, Y coordinate location, means for determining the energy of each detected photon, means for grouping each detected photon according to the determined energy in the X, Y coordinate location, means for accumulating counts of said grouped photons according to the determined energy level of the photons at each X, Y coordinate location, means for constructing an energy spectrum of each X, Y location using the accumulated counts, means for determining a system dependent energy distribution of different components of unwanted photons, means for determining the energy spread function of the gamma camera system for the known energies of the wanted photons, means for constructing a trial function comprising the system energy spread function multiplied by a first unknown coefficient of wanted photons plus the system dependent energy distributions of the components of unwanted photons multiplied by their unknown coefficients, means for modifying the trial function by including in the trial function the first n derivatives of the system energy spread function of each of the k photopeaks multiplied by unknown coefficients, means for locally fitting the modified trial function to the constructed energy spectrum to obtain the count of the wanted photons, means for using the count of the wanted photons to produce an image practically free of unwanted photons.
Claim 29
Dependent Claim
19 words
The system of improving images from gamma camera systems of claim 26 wherein unwanted photons include Compton scattered photons.
Claim 30
Dependent Claim
100 words
The system of claim 26 wherein the means of determining the system dependent energy distributions of the different components of unwanted photons comprises: means for determining at least part of the system independent energy distributions of the components of the unwanted photons, means for determining the energy spread function of the gamma camera system for the determined energies of the components of the unwanted photons, and means for using the determined energy distribution of unwanted photons and the energy spread function of the system to obtain a system dependent energy distribution of the unwanted photons per X, Y coordinate location.
Claim 31
Dependent Claim
20 words
The system of improving images from gamma camera systems of claim 27 wherein said unwanted photons include other unwanted photons.
Claim 32
Dependent Claim
13 words
The system of claim 27 wherein said unwanted photons include lead X-ray photons.
Claim 33
Dependent Claim
22 words
The system of claim 26 wherein the means for locally fitting the modified trial function includes obtaining the counts of unwanted photons.
Claim 34
Dependent Claim
59 words
The system of claim 26 wherein the means for obtaining the system dependent energy distributions of wanted photons includes means for calculating the energy distributions of wanted photons for each value of discrete energy lines in a source and means for determining the first n derivatives of the energy spread function for each discrete energy line in the source.
Claim 35
Dependent Claim
49 words
The system of claim 28 wherein the means for using the determined energy distribution of unwanted photons and the energy spread function of the gamma ray imaging system includes means for convolving the energy distribution of unwanted photons with the energy spread function of the gamma ray imaging system.
Claim 36
Dependent Claim
53 words
The system of claim 26 wherein the means for using the determined energy distribution of unwanted photons and the energy spread function of the system includes means for measuring at least one energy distribution of unwanted photons with the system whereby the measured distribution inherently includes the energy spread function of the system.
Claim 37
Dependent Claim
81 words
The system of claim 33 wherein said means for constructing a trial function comprises: means for summing the convolved system dependent energy distribution of the determined energy distribution of unwanted photons including the system energy distribution of Compton scattered photons and additional unwanted photons both with unknown X, Y coefficients, and means for locally fitting the trial function to the constructed energy spectrum to solve for the unknown X, Y coefficients and thus for determining the counts of the unscattered photons.
Claim 38
Dependent Claim
28 words
The system of claim 35 wherein said means for determining the energy distribution of unwanted photons comprises: means for analytically determining the energy distribution of Compton scattered photons.
Claim 39
Dependent Claim
91 words
The system of claim 36 wherein the means for analytically determining the energy distribution of Compton scattered photons includes: means for convolving the energy distribution of the first order photon scatter probability distribution with the m order photon scatter probability distribution to determine the energy distribution of the m+1 order scattered photons where m=1,2. . .M-1, and means for convolving the energy distribution of the m-order scatter photons where m=1,2. . .M with the energy spread function of the system to obtain system dependent probability distributions of m order scatter photons.
Claim 40
Dependent Claim
34 words
The system of claim 37 including means for obtaining a set of discrete functions from the energy distribution of the m-order Compton scatter photons by averaging the calculated Compton energy distributions for each grouping.
Claim 41
Dependent Claim
13 words
The system of claim 38, including means for reducing the number of calculations.
Claim 42
Dependent Claim
26 words
The system of claim 39 wherein the means for reducing the number of calculations comprises means for converting discrete functions into an orthonormal set of functions.
Claim 43
Dependent Claim
43 words
The system of claim 26 wherein the means for fitting includes: means for using quasi-local pixels to obtain local counts of the scattered photons, and means for doing a single parameter fit to determine the local counts at each of the discrete photopeaks.
Claim 44
Dependent Claim
65 words
The system of claim 41 wherein the means for using quasi-local pixels comprises: means for using large pixels comprising a (2n+1)×(2m+1) rectangle of pixels where both n and m are positive integers and the value of the large pixel is divided by the number of pixels in the large pixel and attributed to the center pixel, and means for evaluating all pixels in this method.
Claim 45
Dependent Claim
24 words
The system of claim 26 wherein the means for locally fitting the trial function to the constructed energy spectrum comprises least square fitting means.
Claim 46
Dependent Claim
27 words
The system of claim 26 wherein the means for locally fitting the trial function to the constructed energy spectrum comprises means for performing a maximum likelihood fit.
Claim 47
Dependent Claim
28 words
The system of claim 26 wherein the means for locally fitting the trial function to the constructed energy spectrum comprises means for performing a partial maximum likelihood fit.
Claim 48
Dependent Claim
31 words
The system of claim 26 wherein the means for locally fitting the trial function to the constructed energy spectrum comprises means for performing a combined least square and maximum likelihood fit.
Claim 49
Independent Claim
6 words
The system of claim 26wherein n=1.
Claim 50
Dependent Claim
7 words
The system of claim 26 wherein n>1.
Claim 51
Dependent Claim
7 words
The system of claim 26 wherein k=1.
Claim 52
Dependent Claim
7 words
The system of claim 26 wherein k>1.
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) | 1998-07-31 | 1999-01-30 | 1999-08-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-07-31 | 2003-01-30 | 2003-08-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-07-31 | 2007-01-30 | 2007-08-01 | $7700.00 | Window Closed / Lapsed |