Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Reexamination Certificate
2000-12-28
2004-07-27
Marmor, Charles (Department: 3736)
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
C600S300000
Reexamination Certificate
active
06768921
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved method and apparatus for detecting and diagnosing disease states in a living organism by using a plurality of electrical impedance measurements.
BACKGROUND OF THE INVENTION
Methods for screening and diagnosing diseased states within the body are based on sensing a physical characteristic or physiological attribute of body tissue, and then distinguishing normal from abnormal states from changes in the characteristic or attribute. For example, X-ray techniques measure tissue physical density, ultrasound measures acoustic density, and thermal sensing techniques measures differences in tissue heat. Another measurable property of tissue is its electrical impedance; i.e., the resistance tissue offers to the flow of electrical current through it. Values of electrical impedance of various body tissues are well known through studies on intact humans or from excised tissue made available following therapeutic surgical procedures. In addition, it is well documented that a decrease in electrical impedance occurs in tissue as it undergoes cancerous changes. This finding is consistent over many animal species and tissue types, including, for example human breast cancers.
There have been a number of reports of attempts to detect breast tumors using electrical impedance imaging, such as, for example, U.S. Pat. No. 4,486,835. However, there are basic problems when trying to construct an image from impedance data. Electrical current does not proceed in straight lines or in a single plane; it follows the path of least resistance, which is inevitably irregular and three-dimensional. As a result, the mathematics for constructing the impedance image is very complex and requires simplifying assumptions that greatly decrease image fidelity and resolution.
A cancer, however, need not be “seen” to be detected; its presence can be detected by a marker associated with it, in this case a change in its electrical impedance, and a technique sensitive to the marker.
One technique for screening and diagnosing diseased states within the body using electrical impedance is disclosed in U.S. Pat. No. 6,122,544. In this patent data are obtained in organized patterns from two anatomically homologous body regions, one of which may be affected by disease. One subset of the data so obtained is processed and analyzed by structuring the data values as elements of an n×n impedance matrix. The matrices can be further characterized by their eigenvalues and eigenvectors. These matrices and/or their eigenvalues and eigenvectors can be subjected to a pattern recognition process to match for known normal or disease matrix or eigenvalue and eigenvectors patterns. The matrices and/or their eigenvalues and eigenvectors derived from each homologous body region can also be compared, respectively, to each other using various analytical methods and then subject to criteria established for differentiating normal from diseased states.
SUMMARY OF THE PRESENT INVENTION
The present invention is directed to an improved method and apparatus for detecting and diagnosing disease states in a living organism by using a plurality of electrical impedance measurements. Although the present invention can be applied to any two homologous body regions, the application discussed scans for the presence or absence of breast abnormalities, and particularly benign and malignant tumors. While not intending to be bound by any particular theory, the method of the invention may arise from the following assumptions and hypotheses:
1. The tumor or tumors will occur either in only one breast, or if in both, at different homologous locations;
2. Both breasts are structurally similar, and therefore can be expected to be approximate mirror images (homologous) with respect to their impedance characteristics;
3. If impedance measurements are taken in a multiplicity of directions or paths across the breast (called an impedance scan in the present application), the presence of tumors, which are known to have a significantly lower impedance than the normal tissue they replace, will distort or change the impedance in at least some of the paths of current flow;
4. The magnitude of decreased impedance is greater for malignant tumors than for benign ones, providing a method for differentiating between these tumor types; and
5. There will always be some differences in impedance between breasts in a normal individual; but these differences will be less than the differences when a cancer is present.
The methodology of the present invention is implemented by a data acquisition and analysis apparatus that was developed for the special requirements of the invention. An improved breast electrode array is also provided of a design and construction that allows excellent conformability of the array to a breast surface and precise positioning of electrodes. This ensures that the multiplicity of positions that impedance measurements are obtained from in a first body part correspond as precisely as possible to the multiplicity of positions that measurements are obtained from in another, homologous, second body part. The apparatus has a number of innovations that provide rapid, accurate impedance measurements from a large number of electrode combinations, and virtually immediate data analysis and display. Impedance data are obtained in organized patterns from two anatomically homologous body regions, one of which may be affected by disease.
In one embodiment of the invention, electrodes are selected so that the impedance data obtained can be considered to represent elements of an n×n impedance matrix. Then two matrix differences are calculated to obtain a diagnostic metric from each. In one, the absolute difference between homologous right and left matrices, on an element-by-element basis, is calculated; in the second, the same procedure is followed except relative matrix element difference is calculated.
In another embodiment of the invention, the differences between corresponding impedance readings in the two body parts are compared in variety of ways that allow the calculation of metrics that can serve either as an indicator of the presence of disease or localize the disease to a specific breast quadrant or sector. Impedance differences are also displayed in a circular pixel plot in a representation of the frontal plane of the breast in this disclosure, although other shape plots in the same or other planes could effectively be produced with suitable choice of electrode geometry and positioning. The use of impedance differences subtracts out a voluminous and complex amount of impedance data produced by irregular, three-dimensional current paths, since under generally normal circumstances, the paths can be expected to be substantially identical in both body parts. Remaining differences are assumed to be due to disease states, and are much more manageable analytically.
Whereas the illustrated example of the present invention is a novel and improved method and apparatus for detecting and locating breast cancers, the invention can also be applied to other diseases or conditions in which there is a distinguishable difference in electrical impedance in the tissue as a result of the disease or condition. The present invention can also be used for detecting and locating diseases or conditions in any region of the body in which the electrical impedance of the region containing the disease or condition can be compared to an essentially identical, normal body region; for example, right and left forearms, right and left thighs, or right and left calves. Moreover, the present invention can be used to detect and locate diseases or conditions in any region of the body in which the electrical impedance of the region containing the disease or condition can be compared to another normal body region that, while not entirely identical, is consistently and constantly different; for example, right and left sides of the abdomen. In other words, the differences between the two regions being compared is a known constant in a heal
Darmos George P.
Gavrilov Ilya
Graovac Milan
Organ Leslie W.
Safaee-Rad Reza
Marmor Charles
Z-Tech (Canada) Inc.
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