Method and apparatus for deriving currents and potentials representative of the impedance of zones of a body

Claim 2

Medical diagnostic or investigative apparatus for deriving signals representative of the impedance of a zone of an animal body, comprising means for passing first currents between electrodes of a first group suitable for location on at least one surface of an animal body, the electrodes being, in operation, positioned to pass the first currents through a zone whose impedance is to be measured, means for deriving the potential across the zone due to the first currents and in the general direction thereof, means for passing second currents through the body between electrodes of a second group also suitable for location on at least one surface of the body to establish virtual barriers as hereinbefore defined generally coinciding with boundaries of the zone within the body, means for deriving from potentials in the body control signals representative of the positions of the said virtual barriers, and means for controlling the second currents in accordance with the control signals to control the positions of the said virtual barriers, the potential across the zone being representative of the impedance of the zone.

Claim 3

Apparatus for deriving signals representative of the impedance of a zone of a cross-section of a closed body, comprising an assembly including a supporting member, a plurality of electrode holders mounted thereon, the supporting member being arranged to encircle, in operation, a portion of the body with electrodes held by the holders in contact with the surface thereof, means for passing first currents between a plurality of the electrodes in a first group positioned to pass to the first currents through a zone whose impedance is to be measured, means for deriving the potential across the zone due to the first currents and in the general direction thereof, means for passing currents through the body between a plurality of the electrodes in a second group positioned in relation to electrodes of the first group to establish virtual barriers as hereinbefore defined generally coinciding with boundaries of the zone within the body, means for deriving from potentials in the body control signals representative of the positions of the potential barriers, and means for controlling the second currents in accordance with the control signals to control the positions of the potential barriers, the potential across the zone being representative of the impedance of the zone.

Claim 4

Apparatus for deriving signals representative of the impedance of a zone of a cross-section of a closed body, comprising an assembly including a supporting member, a plurality of electrode holders mounted thereon, the supporting member being arranged to encircle, in operation, a portion of the body with electrodes held by the holders in contact with the surface thereof, means for passing first currents between a plurality of the electrodes in a first group positioned to pass to the first currents through a zone whose impedance is to be measured, means for deriving the potential across the zone due to the first currents and in the general direction thereof, means for passing currents through the body between a plurality of the electrodes in a second group positioned in relation to electrodes of the first group to establish virtual barriers as hereinbefore defined generally coinciding with boundaries of the zone within the body, means for deriving from potentials in the body control signals representative of the positions of the potential barriers, and means for controlling the second currents in accordance with the control signals to control the positions of the potential barriers, the potential across the zone being representative of the impedance of the zone.

Claim 5

Apparatus according to Claim 1 or 2 wherein the means for deriving potential comprises a plurality of potential sensing electrodes connected to respective high input-impedance amplification means, the potential sensing electrodes are, in operation, positioned in pairs, one on each side of a virtual barrier, and the means for deriving control signals derives signals representative of the potential differences between electrodes of each pair.

Claim 6

Apparatus according to any preceding claim wherein electrode in the first and second groups is connected to a constant alternating-current generator, generators connected to electrodes in the first group generating a constant amplitude output current, and generators connected to electrodes in the second group generating output currents with amplitudes which vary according to respective control signals.

Claim 7

Apparatus according to Claim 3 or 4 insofar as dependent on Claim 1 for use in deriving the impedance of a generally rectangular zone comprising six sensing electrodes positioned on one surface of the body with one sensing electrode at each of opposite ends of the zone between two sensing electrodes outside the zone but in line with each said end, the first group of electrodes comprising two current electrodes remote from the zone, the second group of electrodes comprising two pairs of current control electrodes, each pair being positioned to pass current outside the zone parallel to sides thereof and adjacent to two sensing electrodes in line with the opposite ends of the zone.

Claim 8

Apparatus according to Claim 3 or 4 insofar as dependent on Claim 1 wherein the electrodes are positioned in two arrays each comprising electrodes in the first and second group and sensing electrodes, the arrays are positioned on different surfaces of the body and currents pass through the body from one surface to another.

Claim 9

Apparatus according to Claim 6 for use in deriving the impedance of a zone which is generally rectangular in cross-section normal to current flow wherein each array comprises a central current electrode which forms a part of the first group of electrodes, eight current control electrodes forming part of the second group of electrodes, the current electrodes forming a rectangularthree-by-three array centred on one end of the zone, and four pairs of sensing electrodes each pair being located in a row or column of the three-by-three array adjacent to the central current electrode, the means for deriving control signals deriving first difference signals from each pair of sensing electrodes to control the current supplied by the control current electrode external to that pair in the array and in the same row or column, and deriving second difference signals from each pair of first difference signals derived from adjacent pairs of sensing electrodes to control the current supplied by current control electrodes at that corner of the three-by-three array which is adjacent to those pairs of sensing electrodes.

Claim 10

Apparatus according to Claim 6 for use in deriving the impedances of a plurality of zones which are generally rectangular in cross-section normal to current flow, wherein each array is rectangular and comprises a central current electrode which forms part of the first group of electrodes, rows and columns of control current electrodes which form part of the second group of electrodes, and sensing electrodes between the current electrodes in the rows and columns, the means for deriving control signals deriving a respective control signal to control the current supplied by each control current electrode from sensing electrodes in a region adjacent to, and inward of, that control current electrode in the array, and the current supplied by each current electrode and a potential derived from at least one of the sensing electrodes adjacent to that current electrode being the current and potential representative of the impedance of a zone centred on that current electrode.

Claim 11

Apparatus according to Claim 8 wherein the means for deriving control signals derives signals according to the expression: Pnm ~ P1n+1)ni 1nm 1(n+1)m where P is potential, 1 is the distance through the body between corresponding electrodes in the two arrays, and n and m are subscripts representing positions in rows and columns, respectively with the position of the central electrode in each array as datum for both n and m.

Claim 12

Apparatus according to Claim 2 or Claim 3 or 4 insofar as dependent on Claim 2, comprising means for applying forces to the holders automatically to cause the holders to press on to the body with equal contact pressure.

Claim 13

Apparatus according to Claim 10 including means for generating respective signals representative of the displacements of each electrode from a circular datum.

Claim 14

Apparatus according to Claim 10 or 11 including means for generating respective signals representative of the inclinations of the holders from the vertical.

Claim 15

Apparatus according to Claim 2 or any of Claims 3 or 4 insofar as dependent on Claim 2, and Claims 9 to 12 including means for supplying one electrode in each holder with a current according to the expression: where lo is the current present between electrodes at the ends of a control zone passing through the centre of a cross-section of a body, n is the number of electrode holders with n = 0 for the electrode holders of the central zone, R is the radius of the ring formed when all the electrodes have zero displacement towards the centre of the body, dn is the displacement of the nth holder towards the centre of the body r(-l, is the value of rn for zone on the opposite side of the central zone from the zone with the value r1, and On is the angle between the radii passing through the electrodes corresponding ton = 0 and n.

Claim 16

Apparatus according to Claim 2, or any of Claims 3 or 4, insofar as dependent on Claim 2, and Claims 9 to 12, wherein the means for deriving control signals derives signals according to the expression: Pn Pn+1 (R~dn)cosOn (R~dn+1) C05O(n+i) where P, and Pun+1 are the potentials of sensing electrodes in the nthand (n+ 1 )th holders, respectively.

Claim 17

Apparatus according to Claim 1 or Claim 3 insofar as dependent on Claim 1 wherein the first and second groups of electrodes include and electrode common to both groups and except for the common electrode, each electrode in the first and second groups is connected to a constant alternating-current generator, generators connected to electrodes in the first group generating a constant amplitude output current, and generators connected to electrodes in the second group generating output currents with amplitudes which vary according to respective control signals.

Claim 18

Apparatus according to Claim 15 for deriving current and potential signals representative of the impedances of zones of the human body containing significant portions of the lungs, comprising two common electrodes one located over the sternum and one located over the spine, a plurality of current electrodes spaced apart along the sides of the body in the region of the chest, with sensing electrodes between the current electrodes, one current electrode on each side of the body being in the first group of electrodes, the other current electrodes being in the second group, and the current in each electrode in the second group being controlled by the potential difference between sensing electrodes adjacent thereto but on that side thereof adjacent to the nearest electrode in the first group.

Claim 21

Apparatus for deriving current and potential signals together representative of the impedance of a zone of a body substantially as hereinbefore described with reference to the accompanying drawings.

Claim 22

Apparatus for deriving current and potential signals together representative of the impedance of a zone of a body substantially as hereinbefore described with reference to the accompanying drawings.

Claim 23

Apparatus for applying electrodes to the human body substantially as herein before described with reference to Figures 7 to 11 of the accompanying drawings.

Claim 24

Apparatus for applying electrodes to the human body substantially as herein before described with reference to Figures 7 to 11 of the accompanying drawings.