Rensselaer Polytechnic Institute

David Isaacson

Margaret Cheney

Jonathan C Newell

David G Gisser

John C Goble

Gary Jude Saulnier

Erkki Somersalo

Raymond D Cook

Eli L Isaacson

In electrical impedance tomography systems, the precision of voltage measurement is a critical factor in the results. Usually, the voltage values to be measured are limited by the necessity of limiting currents through the body to safe values. An effective method for increasing the apparent precision of the voltmeters is to use non-sinusoidal current patterns that produce the largest voltage variations in regions of most importance. This invention discloses several improvements in the methods by which the images resulting from any system of hardware that permits simultaneous injection of currents to all electrodes and voltage measurements at all electrodes, may be improved. One such improvement is a technique to find the shapes of the best current patterns to distinguish two different distributions of admittivity, conductivity, and permittivity in the region surrounded by electrodes. Another is a more complex procedure for finding the best shapes of the current patterns to best characterize an unknown pattern of admittivity, conductivity, or permittivity. Yet another is a procedure for calculating the values of voltages that would have been measured had sinusoidal sets of current been used, when actually using non-sinusoidal current patterns. This permits any standard reconstruction algorithm based on sinusoidal currents to be used with non-sinusoidal currents.

Process for producing optimal current patterns for electrical impedance

An apparatus for electrical impedance imaging of a body includes an array of multiple electrodes. Each is connected to an adjustable amplitude precision current source of fixed frequency and an oversampling type digital voltmeter. The current amplitudes are set to produce a series of spatial current patterns, all orthogonal to each other, and each applied for only a short time interval while voltages are measured. The voltage and current values are used to create real and reactive impedance images of the interior of the body.

High-speed electric tomography

A method for the impedance imaging of a three-dimensional body utilizes electrtodes on the outer surface of the body which receive a set of current patterns. The resulting voltage patterns are measured at the outer boundary of the body. Synthesized resulting patterns are then calculated for inner boundaries of the body, each at a selected incremental distance inwardly of the outer boundary. The synthesis step is repeated for successive inner boundaries until the center of the body is reached. The measured and synthesized patterns are utilized to calculate or otherwise find various medium properties in the body, such as the electric conductivity and electric permittivity for the body. These impedance characteristics based on the measured and synthesized patterns are used to produce an image of the body.

Layer stripping process for impedance imaging

A method in electrical impedance tomography uses an adaptive repeated series of calculations and measurements to determine the best current pattern for a body having an initially unknown internal conductivity, for producing the best electrical impedance image for the body. Initially, an arbitrary current pattern and conductivity is utilized to generate a voltage pattern which is measured and compared with the theoretical voltage pattern based on the arbitrary conductivity and current patterns. When both the current pattern and the conductivity yielded by the process closely match values derived by measurements, the voltage pattern is used to produce the image.

Current patterns for electrical impedance tomography

A method for obtaining sets of current patterns for three-dimensionally imaging the interior of a body having an internal resistivity using electrical impedance tomography comprises providing an array of electrodes arranged in a plurality of groups for an impedance imaging system. A linearly independent set of current patterns is also established for forming a basis for each group. A constant pattern is then adjoined to each basis for forming an augmented basis for each group. A tensor product is then taken of the augmented basis for forming a tensor product basis. Finally, the constant pattern from the tensor product basis is removed in order to establish a basis of current patterns for being applied to the array of electrodes.

Three-dimensional impedance imaging process

A method of practicing electrical impedance tomography produces three-dimensional images of a body. First, one applies certain special current patterns to the body through an array of electrodes attached to the surface. For each current pattern, one measures the voltage at each electrode, thus obtaining a corresponding pattern of voltages. These data are then used in a certain special reconstruction process, which enables a full three-dimensional reconstruction to be done in a short time. The result is a display of an approximation to the electric conductivity and/or electric permittivity in the interior of the body.

Three-dimensional impedance imaging processes

In an electrical impedance imaging system that is capable of forming images based on internal resistivity of a body, an array of electrodes is applied to the surface of the body and energized by a plurality of current generators. Each current generator is controlled to produce current patterns containing single fixed magnitudes. The current generators are also controlled to apply current to the respective electrode only when the current generator is at peak current value to minimize transient conditions and maximize the rate at which images can be produced.

Current patterns for impedance tomography

A method and apparatus for an electric current computed tomography system having an array of electrodes determines the best pattern of currents to apply to the electrodes based on the precision of the system for distinguishing between a known conductivity in a body and an unknown conductivity. An arbitrary current pattern is first applied to the array, which is at the surface of the body. Measurements are then taken for the resulting voltage pattern of the unknown conductivity. Calculations are then made to determine the calculated voltage pattern for the selected conductivity. The absolute value of the difference between the calculated and measured voltage patterns are then taken and, from this, a new current pattern is calculated. If the difference between the new current pattern and the arbitrary current pattern is less than the precision of the system, the arbitrary current pattern is applied to the electrodes. More likely, however, the difference will be greater than the precision. In this case, the new current pattern is applied to the electrodes and the measurements and calculations are repeated to generate a still further new current pattern. The difference between the previous and the new current pattern is then taken and again compared to the precision of the system. By repeating this process, the best current pattern is eventually reached.

Growing community of inventors

Latham, NY, United States of America

David Isaacson