Patent EP0527482A1 successfully refreshed from Google Patents.
EP0527482A1
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Method and apparatus for determining biocurrent distribution within subject
Assignee: Hitachi Ltd
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Filing: 1992-08-12
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Granted: —
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Expires: 2012-08-12
Abstract
Abstract A living body is replaced by a 3-D network (step 1). Admittance connected to lines forming the 3-D network is calculated (step 2). Position rt and magnitude qt=(jtx,jty,jtz) of a current dipole are assumed, and current sources jtx, jty and jtz are connected in parallel with lines coupled to a node (it,jt,kt) (step 3). Node equations are formulated, and an admittance matrix Y is derived (step 4). An inverse matrix Y' of Y is calculated, and body surface potential generated by the current sources is calculated by using the inverse matrix Y' (steps 5-8). Then, rt and qt minimizing cost function which is sum total of squares of differences between measured values of body surface potential and the above described calculated values for all measuring points are derived (steps 9 and 10). Thereby potential distribution on the body surface can be calculated with due regard to the shape of the living body and conductivity distribution in the living body on the basis of the assumed current dipole. On the basis of measured data of potential distribution on the body surface, therefore, the position and magnitude of the current dipole can be estimated with high precision.
Inventors
- 👤 Yukiko Hitachi Ogura
- 👤 Kensuke Sekihara
- 👤 Hisaaki Ochi
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 07:16
CPC Classifications
A; A61; A61B; A61B5/00; A61B5/24; A61B5/242; G; G06; G06F; G06F2218/00; G06F2218/22
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
199 words
A method for determining biocurrent distribution within a subject (1), comprising the steps of: measuring potentials at a plurality of points on a surface of said subject; assuming a 3-D arrangement of predetermined cells in said subject (step 1); deriving physical properties of said subject in positions of said cells; determining admittances (Yx,Yy,Yz) of lines defining external shapes of said cells on the basis of said physical properties (step 2); assuming biocurrent distribution within said subject and assuming at least one current source (Jx,Jy,Jz) connected in parallel with said lines on the basis of each assumed biocurrent distribution (step 3); calculating potentials of nodes of positions corresponding to at least said measuring points in a 3-D network formed by said lines, on the basis of the admittances of said lines and the assumed current sources connected in parallel with said lines (steps 4-8); changing positions and current magnitudes of said assumed current sources while comparing said calculated potentials with said measured potentials, and determining the positions and current magnitudes of the current sources on the basis of a result of comparison (steps 9 and 10); and determining said biocurrent distribution in reality on the basis of determined current sources.
Claim 2
Dependent Claim
12 words
A method according to Claim 1, wherein said physical property is conductivity.
Claim 3
Dependent Claim
49 words
A method according to Claim 1, wherein said current source determining step comprises the step of determining said current sources so as to minimize sum total (C), over all of said measuring points, of integer-th power of absolute value of difference between said calculated potential and said measured potential.
Claim 4
Dependent Claim
42 words
A method according to Claim 1, wherein said potential calculating step comprises the step of formulating simultaneous equations (equation 4) formed by the Kirchhoff's first law with respect to all nodes of the above described 3-D network and solve the simultaneous equations.
Claim 5
Dependent Claim
159 words
A method according to Claim 4, wherein said cells comprise cubes and said 3-D network formed by the lines comprises a 3-D cubic cell network, and said step of calculating potentials of nodes in a 3-D network comprises the steps of: making an element of an mth row of an nth column in a coefficient matrix equivalent to sum of admittances of lines connected to an mth node when m is equivalent to n; making an element of an mth row of an nth column in said coefficient matrix equivalent to product of admittance of a line located between the mth node and an adjacent nth node and -l when m is different from n; and making a column vector having potential at the mth node as an element equivalent to product of a column vector having sum of currents flowing from current sources connected to said node as an element and an inverse matrix of said coefficient matrix.
Claim 6
Dependent Claim
83 words
A method according to Claim 5, wherein said step of calculating potentials of nodes in a 3-D network comprises the steps of: making potential at an mth node equivalent to product of a column vector having sum of currents flowing from current sources connected to said node as an element and a row vector having an mth row of an inverse matrix of said coefficient matrix as an element; and calculating potentials of at least one node simultaneously in a parallel processing computer.
Claim 7
Dependent Claim
43 words
A method according to Claim 2, wherein said step of deriving conductivities of cells comprises the steps of: dividing a 3-D magnetic resonance image or X-ray image of said subject into pixels respectively corresponding to said cells; and deriving conductivities of said pixels.
Claim 8
Dependent Claim
42 words
A method according to Claim 7, wherein said pixel conductivity is discriminated on the basis of proportion, in said cell, of a living body tissue which can be discriminated by said magnetic resonance or X-ray and which has a conductivity already known.
Claim 9
Dependent Claim
40 words
A method according to Claim 7, wherein said pixel conductivity comprises a value obtained by multiplying conductivity of a living body tissue in each pixel by proportion of said living body tissue in said pixel and summing the resultant products.
Claim 10
Dependent Claim
28 words
A method according to Claim 1, wherein predetermined nodes of said 3-D network coincide with points located on the surface of said subject whereat voltage has been measured.
Claim 11
Dependent Claim
15 words
A method according to Claim 1, wherein said cells take the shape of triangular pyramid.
Claim 12
Dependent Claim
37 words
A method according to Claim 1, wherein cells in said subject each contacting an interface of a portion having a different conductivity take the shape of triangular pyramid whereas other cells take the shape of rectangular parallelepiped.
Claim 13
Dependent Claim
82 words
A method according to claim 1, further comprising the steps of: measuring magnetic fields at a plurality of second points on the surface of said subject; calculating magnetic fields at said second points on the basis of said determined biocurrent distribution (Fig. 15, step 20); and changing the positions and/or magnitudes of said determined current sources while comparing said calculated magnetic fields with said measured magnetic fields, and correcting said biocurrent distribution on the basis of a result of comparison (step 30).
Claim 14
Dependent Claim
57 words
A method according to Claim 13, wherein said biocurrent distribution correcting step comprises the step of correcting the positions and magnitudes of said current sources so that the sum total of integer-th powers of absolute values of differences between said calculated magnetic fields and said measured magnetic fields for all of said second points may be minimized.
Claim 15
Dependent Claim
19 words
A method according to Claim 13, wherein said second points coincide with said points whereat potential has been measured.
Claim 16
Independent Claim
255 words
A method for determining biocurrent distribution within a subject (Fig. 10), comprising the steps of: measuring potentials at a plurality of points on a surface of said subject (1); measuring magnetic fields at said points; assuming a 3-D arrangement of predetermined cells in said subject (step 1); deriving physical properties of said subject in positions of said cells; determining admittances (Yx,Yy,Yz) of lines defining external shapes of said cells on the basis of said physical property (step 2); assuming biocurrent distribution within said subject and assuming at least one current source (Jx,Jy,Jz) connected in parallel with said lines on the basis of each assumed biocurrent distribution (step 3); calculating potentials of nodes of positions corresponding to at least said measuring points in a 3-D network formed by said lines, on the basis of the admittances of said lines and the assumed current sources connected in parallel with said lines (steps 4-8); calculating magnetic fields at said measuring points on the basis of said assumed biocurrent distribution (step 20); and determining current vectors and positions thereof so as to minimize sum of product obtained by multiplying sum total of integer-th power values of absolute values of differences between said calculated potentials and said measured potentials for all of said measuring points by a first predetermined coefficient and product obtained by multiplying sum total of integer-th power values of absolute values of differences between said calculated magnetic fields and said measured magnetic fields for all of said measuring points by a second predetermined coefficient (step 10, 21).
Claim 17
Independent Claim
190 words
A method for determining biocurrent distribution within a subject, comprising the steps of: measuring potentials at a plurality of points on a surface of said subject (1); assuming a 3-D arrangement of predetermined cells in said subject; deriving physical properties of said subject in positions of said cells; determining impedances (Zx,Zy,Zz) of lines defining external shapes of said cells on the basis of said physical properties; assuming biocurrent distribution within said subject and assuming at least one voltage source (ex,ey,ez) connected in series with said lines on the basis of said assumed biocurrent distribution; calculating potentials of nodes of positions corresponding to at least said measuring points in a 3-D network formed by said lines, on the basis of the impedances of said lines and the assumed voltage sources connected in series with said lines; changing positions and voltage magnitudes of said assumed voltage sources while comparing said calculated potentials with said measured potentials, and determining the positions and voltage magnitudes of the voltage sources on the basis of a result of comparison; and determining said biocurrent distribution in reality on the basis of determined voltage sources and said impedances.
Claim 18
Dependent Claim
78 words
A method according to Claim 17, wherein said potential calculating step comprises the steps of: formulating simultaneous equations (equation 13) for all lines of said 3-D network according to Kirchhoff's second law; calculating currents flowing through all lines by solving said simultaneous equations; deriving potential difference across each line on the basis of a current flowing through each line and impedance of that line; and calculating potentials at said measuring points on the basis of said potential difference.
Claim 19
Independent Claim
199 words
An apparatus for determining biocurrent distribution within a subject (1), comprising: means (2,3,4) for measuring potentials at a plurality of points on a surface of said subject; means (10,12) for deriving physical properties of said subject in positions of predetermined cells assumed in said subject, said cells forming a 3-D arrangement; means (14,21) for determining admittances of lines defining an external shape of each of said cells on the basis of said physical properties; means (16,18,22) for setting at least one current source connected in parallel with said lines on the basis of biocurrent distribution assumed in said subject; means (24) for calculating potentials of nodes of positions corresponding to at least said measuring points in a 3-D network formed by said lines, on the basis of the admittances of said lines and said current sources connected in parallel with said lines; means (23,25,30) for changing positions and current magnitudes of said current sources while comparing said calculated potentials with said measured potentials, and determining the positions and current magnitudes of the current sources on the basis of a result of comparison; and means (22) for determining said biocurrent distribution in reality on the basis of determined current sources.
Claim 20
Dependent Claim
87 words
An apparatus according to claim 19, further comprising: means (42,3,4) for measuring magnetic fields at a plurality of second points on the surface of said subject; means (40) for calculating magnetic fields at said second points on the basis of said determined biocurrent distribution; and means (26) for changing the positions and/or magnitudes of said determined current sources while comparing said calculated magnetic fields with said measured magnetic fields, and correcting the positions and magnitudes of said current sources on the basis of a result of comparison.
Claim 21
Independent Claim
258 words
An apparatus for determining biocurrent distribution within a subject, comprising: means (21,3,4) for measuring potentials at a plurality of points on a surface of said subject (1); means (42,3,4) for measuring magnetic fields at said points; means (10,12) for deriving physical properties of said subject in positions of predetermined cells assumed in said subject, said cells forming a 3-D arrangement; means (14,21) for determining admittances of lines defining an external shape of each of said cells on the basis of said physical properties; means (16,18,22) for setting at least one current source connected in parallel with said lines on the basis of biocurrent distribution assumed in said subject; means (24) for calculating potentials of nodes of positions corresponding to at least said measuring points in a 3-D network formed by said lines, on the basis of the admittances of said lines and said current sources connected in parallel with said lines; means (40) for calculating magnetic fields at said measuring points on the basis of said assumed biocurrent distribution; and means (26) for determining positions and magnitudes of said current sources so as to minimize sum of product obtained by multiplying sum total of integer-th power values of absolute values of differences between said calculated potentials and said measured potentials for all of said measuring points by a first predetermined coefficient and product obtained by multiplying sum total of integer-th power values of absolute values of differences between said calculated magnetic fields and said measured magnetic fields for all of said measuring points by a second predetermined coefficient.
Claim 22
Independent Claim
197 words
An apparatus for determining biocurrent distribution within a subject, comprising: means for measuring potentials at a plurality of points on a surface of said subject (1); means for deriving physical properties of said subject in positions of predetermined cells assumed in said subject, said cells forming a 3-D arrangement; means for determining impedances (Zx,Zy,Zz) of lines defining an external shape of each of said cells on the basis of said physical properties; means for setting at least one voltage source (ex,ey,ez) connected in series to said lines on the basis of biocurrent distribution assumed in said subject; means for calculating potentials of nodes of positions corresponding to at least said measuring points in a 3-D network formed by said lines, on the basis of the impedances of said lines and said voltage sources connected in series to said lines; means for changing positions and voltage magnitudes of said voltage sources while comparing said calculated potentials with said measured potentials, and determining the positions and voltage magnitudes of the voltage sources on the basis of a result of comparison; and means for determining said biocurrent distribution in reality on the basis of determined voltage sources and said impedances.
References Cited (Backward Citations)
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