Surgery – Truss – Pad
Patent
1993-12-23
1996-11-19
Rimell, Sam
Surgery
Truss
Pad
128734, A61B 505
Patent
active
055752926
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to applied potential tomography (APT) to achieve electrical impedance imaging.
APT techniques have been described in GB 2119520, GB 2160323, WO 89/09564, or GB 9013177.2 which permit the electrical impedance changes which occur within a conducting body to be imaged. The electrical impedance changes are measured by applying electrical currents to, and measuring the differences of electrical potential between, a number of electrodes placed around the boundary of a plane through the conducting body, e.g. the thorax, which is circumscribed by a plurality of spaced apart electrodes. An algorithm has been described which permits the measurements thus obtained to be converted into an image of the electrical impedance changes which have occurred since some reference time. The impedance changes represented in these images may have occurred at any point in the conducting body. The image value depends upon the products of the true size of the impedance change and a sensitivity factor which may vary with position inside the body. This sensitivity factor has maximum value in the plane of the electrodes and diminishes with increasing distance from that plane. It is clear that if no significant impedance changes occur in the plane of the electrodes, then the technique can be used to image impedance changes which occur off-plane at other locations in the body.
In some circumstances however, it is difficult or undesirable to place the electrodes around a plane that will pass through the origin of the impedance change.
In situations where all impedance changes occur deep within the conducting body, and no significant changes occur at or near the surface, the electrode plane can be placed on the surface of the body and used to image the impedance changes beneath the electrode plane. In the human body, for example, large impedance changes occur in the heart during the cardiac cycle but comparatively little impedance change occurs in the skin over the same time period.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided an APT method for investigating a region within a body in which a plurality of surface-contact electrodes are located in a closed loop or rosette array on one planar, or nominally planar, skin surface of the body distant from the region under investigation, the electrodes being electrically connected to data acquisition and processing equipment.
According to a second aspect of the present invention, there is provided apparatus for use in carrying out the above defined method, comprising a plurality of surface-contact electrodes arranged on a common flexible carrier applicable to a planar or nominally planar skin area of a body to be investigated, to locate said electrodes in a closed loop, or rosette array on said area.
Thus, with the method and apparatus of the invention, if for instance the planar, or nominally planar surface is the anterior surface of the human chest, in the vicinity of the heart, images can be produced of the impedance changes within the heart using an overlying surface electrode plane, for by confining all measurement electrodes to one surface of the conducting body, the impedance imaging technique may be used where it is difficult or undesirable to place the electrodes around a plane that will pass through the origin of the impedance change. However, this electrode arrangement will usually be limited to those situations e.g. heart investigations, where the impedance changes in the surface electrode plane are not significant.
In one embodiment, the electrodes may be attached around the perimeter of a preferably circular, and preferably transparent carrier--a synthetic plastics material being particularly suitable. A thin, flexible sheet of synthetic plastics material is particularly suitable, which sheet may be of circular or annular form. For a rosette array of 16 electrodes, a circular carrier may be marked-out with radii at 22.5.degree. on each of which an electrode is approximately located, w
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Barber David C.
Brown Brian H.
McArdle Francis J.
British Technology Group Limited
Rimell Sam
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