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Intracerebral current source estimation apparatus and program

外国特許コード F110004286
整理番号 A092-08WO
掲載日 2011年7月13日
出願国 カナダ
出願番号 2471746
公報番号 2471746
公報番号 2471746
出願日 平成14年12月27日(2002.12.27)
公報発行日 平成15年7月17日(2003.7.17)
公報発行日 平成29年2月14日(2017.2.14)
国際出願番号 JP2002013739
国際公開番号 WO2003057035
国際公開日 平成15年7月17日(2003.7.17)
優先権データ
  • 特願2001-400519 (2001.12.28) JP
  • 2002WO-JP13739 (2002.12.27) WO
発明の名称 (英語) Intracerebral current source estimation apparatus and program
発明の概要(英語) (CA2471746)
By applying an appropriate current to a virtual curved surface between a current source and an observation surface, it is possible to restore an electromagnetic field generated by the current source.
As the curved surface approaches the current source, the current spread over the curved surface becomes smaller.
According to this fact, Beyes estimation is performed for t he current source to restore the observation data.
In this estimation, the mode l posteriori probability becomes maximum when the curved surface includes the current source.
That is, by checking the model posteriori probability, it is possible to estimate the position of the current source including the depth direction.
Moreover, when it is possible to simultaneously use observation data obtained by other observation means, the information is involved in the hierarchical pre-distribution when performing the Bayes estimation so as to perform estimation with a higher accuracy.
特許請求の範囲(英語) [claim1]
1. A computer-implemented brain current source estimating method for estimating, based on an electromagnetic field observed outside a scalp, a position of a current source as a source of said electromagnetic field existing in a brain, comprising the steps of receiving measurements of an observed electromagnetic field observed outside a scalp;
setting, in a computer simulation of the brain, a plurality of computer simulated curved surfaces having depths from brain surface different from each other and shapes not intersecting with each other, and setting lattice points on each of said computer simulated curved surfaces;
automatically estimating, on each of said computer simulated curved surfaces, a current distribution for recovering said observed electromagnetic field, wherein said step of automatically estimating a current distribution includes a step of setting, when said current distribution is estimated in accordance with variational Bayesian estimation, a hierarchical prior distribution representing a localized condition of said current source in said variational Bayesian estimation, based on an expansion of the current distribution estimated on each one of said computer simulated curved surfaces and a difference between an electromagnetic field recovered based on said current distribution and said observed electromagnetic field, identifying one computer simulated curved surface among said plurality of computer simulated curved surfaces as a true curved surface on which said current source exists, so that said expansion and said difference attain relative minimums at said identified computer simulated curved surface;
and outputting a position corresponding to said identified computer simulated curved surface as the position of said current source, wherein the above steps are performed by one or more computers programmed to perform the above steps
[claim2]
2. The brain current source estimating method according to claim 1, wherein said step of automatically estimating said current distribution includes the step of determining posterior probability by Bayesian estimation method from prior distribution and observation data of said electromagnetic field;
and said step of identifying as a true curved surface on which said current source exists includes the step of identifying a computer simulated curved surface of which corresponding said posterior probability attains the maximum, among said computer simulated curved surfaces.
[claim3]
3. The brain current source estimating method according to claim 2, wherein said step of automatically estimating a current distribution includes the step of identifying a first computer simulated curved surface closest to said brain surface and having posterior probability attaining a relative maximum, among said plurality of computer simulated surfaces, while successively moving from a computer simulated curved surface on the side of the brain surface to a deeper side, and said step of identifying a curved surface as a true curved surface on which said current source exists includes the steps of identifying a localized current distribution corresponding to a point of relative maximum of said current distribution, on said first computer simulated curved surface, separating a plurality of local surfaces each including said localized current distribution, and fixing, among said plurality of local surfaces, local surfaces other than a local surface as an object of identification, moving said local surface as an object of identification in the depth direction, and identifying positions where said posterior probability attains the relative maximum, successively from the side closer to said brain surface
[claim4]
4. The brain current source estimating method according to claim 3, wherein in said step of automatically estimating a current distribution, said current distribution is estimated with a first spatial resolution;
said method further comprising the step of re-estimating said current distribution with a second spatial resolution higher than said first resolution and resolution of said plurality of computer simulated curved surfaces in the depth direction being improved.
[claim5]
5. The brain current source estimating method according to claim 1, wherein said stop of setting a hierarchical prior distribution includes the step of setting the hierarchical prior distribution using observation data obtained by other observation method independent of said observation of electromagnetic field for said estimation of the current source.
[claim6]
6. A brain current source estimating apparatus for estimating, based on an electromagnetic field observed outside a scalp, a position of a current source as a source of said electromagnetic field existing in a brain, comprising:
measurement receiving means for receiving measurements of an observed electromagnetic field observed outside a scalp, computer simulated curved surface setting means for setting, in a computer simulation of the brain, a plurality of computer simulated curved surfaces having depths from brain surface different from each other and shapes not intersecting with each other, and setting lattice points on each of said computer simulated curved surfaces;
current distribution estimating means for automatically estimating, on each of said computer simulated curved surfaces, a current distribution for recovering said observed electromagnetic field, wherein said current distribution estimating means includes condition setting means for setting, when said current distribution is estimated in accordance with variational Bayesian estimation, a hierarchical prior distribution representing a localized condition of said current source in said variational Bayesian estimation;
and current source identifying means for selectively identifying, based on an expansion of the current distribution estimated on each one of said computer simulated curved surfaces and a difference between an electromagnetic field recovered based on said current distribution and said observed electromagnetic field, one computer simulated curved surface among said plurality of computer simulated curved surfaces as a true curved surface on which said current source exists, so that said expansion and said difference attain relative minimums at said identified computer simulated curved surface.
[claim7]
7. The brain current source estimating apparatus according to claim 6, wherein said automatic current distribution estimating means includes posterior probability determining means for determining posterior probability by
Bayesian estimation method from prior distribution and observation data of said electromagnetic field;
and said current source identifying means includes computer simulated curved surface identifying means for identifying a computer simulated curved surface of which corresponding said posterior probability attains the maximum, among said computer simulated curved surfaces.
[claim8]
8. The brain current source estimating apparatus according to claim 7, wherein said automatic current distribution estimating means includes shallowest computer simulated curved surface identifying means for identifying a first computer simulated curved surface closest to said brain surface and having posterior probability attaining a relative maximum, among said plurality of computer simulated surfaces, while successively moving from a computer simulated curved surface on the side of the brain surface to a deeper side;
and said current source identifying means includes localized current distribution identifying means for identifying a localized current distribution corresponding to a point of relative maximum of said current distribution, on said first computer simulated curved surface, local surface extracting means for separating a plurality of local surfaces each including said localized current distribution, and local surface position identifying means for fixing, among said plurality of local surfaces, local surfaces other than a local surface serving as an object of identification, moving said local surface as an object of identification in the depth direction, and identifying positions where said posterior probability attains the relative maximum, successively from the side closer to said brain surface.
[claim9]
9. The brain current source estimating apparatus according to claim 8, wherein said automatic current distribution estimating means estimates said current distribution with a first spatial resolution and thereafter re-estimates said current distribution with a second spatial resolution higher than said first resolution and resolution of said plurality of computer simulated curved surfaces in the depth direction being improved.
[claim10]
10. The brain current source estimating apparatus according to claim 6, wherein said condition setting means sets the hierarchical prior distribution using observation data obtained by other observation method independent of said observation of electromagnetic field for said estimation of the current source.
[claim11]
11. A computer readable storage medium storing program code for causing a computer to estimate, based on an electromagnetic field observed outside a scalp, a position of a current source as a source of said electromagnetic field existing in a brain, the program code causing the computer to perform a method comprising the steps of:
receiving measurements of an observed electromagnetic field observed outside a scalp;
setting, in a computer simulation of the brain, a plurality of computer simulated curved surfaces having depths from brain surface different from each other and shapes not intersecting with each other, and setting lattice points on each of said computer simulated curved surfaces;
automatically estimating, on each of said computer simulated curved surfaces, a current distribution for recovering said observed electromagnetic field, wherein said step of automatically estimating a current distribution includes a step of setting, when said current distribution is estimated in accordance with variational Bayesian estimation, a hierarchical prior distribution representing a localized condition of said current source in said variational Bayesian estimation, based on an expansion of the current distribution estimated on each one of said computer simulated curved surfaces and a difference between an electromagnetic field recovered based on said current distribution and said observed electromagnetic field, selectively identifying one computer simulated curved surface among said plurality of computer simulated curved surfaces as a true curved surface on which said current source exists, so that said expansion and said difference attain relative minimums at said identified computer simulated curved surface;
and outputting a position corresponding to said identified computer simulated curved surface as the position of said current source.
[claim12]
12. The computer readable storage medium according to claim 11, wherein said step of automatically estimating said current distribution includes the step of determining posterior probability by Bayesian estimation method from prior distribution and observation data of said electromagnetic field;
and said step of identifying as a true curved surface on which said current source exists includes the step of identifying a computer simulated curved surface of which corresponding said posterior probability attains the maximum, among said computer simulated curved surfaces.
[claim13]
13. The computer readable storage medium according to claim 12, wherein said step of automatically estimating a current distribution includes the step of identifying a first computer simulated curved surface closest to said brain surface and having posterior probability attaining a relative maximum, among said plurality of computer simulated surfaces, while successively moving from a computer simulated curved surface on the side of the brain surface to a deeper side;
and said step of identifying a curved surface as a true curved surface on which said current source exists includes the steps of identifying a localized current distribution corresponding to a point of relative maximum of said current distribution, on said first computer simulated curved surface, separating a plurality of local surfaces each including said localized current distribution, and fixing, among said plurality of local surfaces, local surfaces other than a local surface serving as an object of identification, moving said local surface as an object of identification in the depth direction, and identifying positions where said posterior probability attains the relative maximum, successively from the side closer to said brain surface.
[claim14]
14. The computer readable storage medium according to claim 13, wherein in said step of automatically estimating a current distribution, said current distribution is estimated with a first spatial resolution, said method further comprising the step of re-estimating said current distribution with a second spatial resolution higher than said first resolution and resolution of said plurality of computer simulated curved surfaces in the depth direction being improved.
[claim15]
15. The computer readable storage medium according to claim 11, wherein setting the hierarchical prior distribution uses observation data obtained by other observation method independent of said observation of electromagnetic field for said estimation of the current source.
  • 出願人(英語)
  • ATR - ADVANCED TELECOMMUNICATIONS RESEARCH INSTITUTE
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • 発明者(英語)
  • SATO MASA-AKI
国際特許分類(IPC)
参考情報 (研究プロジェクト等) CREST Creating the Brain AREA
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