Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Reexamination Certificate
1999-12-14
2003-05-06
Manuel, George (Department: 3737)
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
Reexamination Certificate
active
06560480
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to systems for tissue characterization based on impedance measurements, and in particular to systems for determining the locations of anomalies based on impedance measurements.
BACKGROUND OF THE INVENTION
Variations in electrical impedance of the human tissue may be indicative of tumors, lesions and other anomalies. For example, U.S. Pat. No. 4,291,708 to Frei, and U.S. Pat. No. 4,458,694, and the article, “Breast Cancer Screening by Impedance Measurements,” by G. Piperno et al., Frontiers Med. Biol. Eng., Vol. 2 pp. 111-117, the disclosures of which are incorporated herein by reference, describe systems for determining the impedance between a point on the surface of the skin and some reference point on the body of the patient. With the use of a multi-element probe, a two-dimensional impedance map of an organ such as a breast can be generated. The impedance map, describing variations in impedance along the tissue of the organ, can be used for the detection of tumors and especially malignant tumors.
An exemplary system for tissue characterization includes a multi-element probe which is pressed against the skin of a patient. The elements of the multi-element probe are kept at a ground voltage and an electrification signal is applied at some point on the patient. The elements of the multi-element probe serve as sensors which measure the current incident on the sensors and accordingly determine a measure of the impedance of the tissue beneath each element of the probe. Using the impedance values determined by the elements, a two-dimensional impedance map is generated, which map is used to detect abnormal tissue.
It is understood, however, that the system indicates the locations of abnormal tissue as a function of the locations on the skin, and gives little indication of the depth of the abnormal tissue beneath the skin. In addition, the ability to find a tumor of abnormal tissue decreases with the distance of the tumor from the surface to which the probe is pressed.
U.S. Pat. Nos. 4,617,939 and 4,539,640 describe three-dimensional mapping of the tissue impedance of the body. These patents describe measuring the impedance on a plurality of surfaces surrounding an organ and producing a three-dimensional map based on Poison's equation.
However, in many organs it is not feasible to place a sufficient number of probes on surfaces of the organ to receive a satisfactory impedance image. In addition, in some cases it is desired that the point from which the electrification signal is applied be as close as possible to the examined organ and/or that the signal be applied along a large surface. Furthermore, in some cases the image is required during a surgical procedure, especially during minimal invasive procedures, such as biopsy taking using a biopsy needle. In such cases, a surgeon performing the procedure needs to have access to the surface of the organ.
Even when there are sufficient vacant surfaces on the organ, three-dimensional mapping is cumbersome and requires complex algorithms in order to solve Poison's equation. These complex algorithms introduce errors into the measurements and/or magnify measurement errors. In addition, when the organ includes a plurality of anomalies, separation between the different anomalies becomes very difficult, since all the anomalies influence the measurements on all the surfaces.
U.S. Pat. No. 5,353,802 to Ollmar, the disclosure of which is incorporated herein by reference, describes a device for depth selective detection and characterization of surface phenomena based on impedance measurements. The device includes an electrode for applying electrical signals, an electrode for measuring signals and a control electrode for controlling the depth of the applied signals.
SUMMARY OF THE INVENTION
An object of some preferred embodiments of the present invention is to provide methods and apparatus for determining the depth of an anomaly within an organ of a patient, relative to a probe placed on a surface of the organ. The depth is determined using signals detected by the probe on the surface.
It is an object of some preferred embodiments of the present invention to provide methods for detecting anomalies which are deep within an organ, i.e., far from a probe of sensors used to detect the anomaly, which anomalies are not detectable using methods known in the art.
It is an object of some preferred embodiments of the present invention to provide a method for determining the depth of an anomaly within an organ, which method does not depend on the shape of the anomaly.
It is an object of some preferred embodiments of the present invention to provide improved methods for directing an invasive tool, such as a biopsy needle, toward an anomaly.
It is an object of some preferred embodiments of the present invention to provide improved methods for determining contact between an invasive tool and an anomaly.
An aspect of some preferred embodiments of the present invention relates to applying electrifying signals for impedance imaging of a body part at specific points relative to an array of sensors used to sense the effect of the signals. The position of an anomaly (e.g., lesion, tumor, cyst) is preferably determined according to at least one surface map generated by the array of sensors in relation to the positions of the specific points from which the electrifying signals are applied. In some preferred embodiments of the invention, the electrifying signals are applied to a small region relative to the area of the array of sensors.
In some preferred embodiments of the present invention, the electrifying signals are applied in a specific spatial pattern which increases the signal to noise ratio in the array of sensors of signals originating from anomalies which are to be detected. In a preferred embodiment in which the signals are applied from a surface opposite the sensors, the dimensionality of the applied signals is reduced so that deep anomalies receive stronger signals than anomalies close to the sensors. For example, instead of applying signals from an entire surface, signals are applied along a line, from a single point, or in the form of a dipole.
Preferably, the electrifying signals are applied in lines which are long and narrow relative to the size of an average anomaly. Alternatively or additionally, the electrifying signals are applied in other patterns and sizes, such as, large and small rings, circles, squares and rectangles. Further alternatively or additionally, electrifying signals are applied in a few geometrically unconnected regions.
In some preferred embodiments of the present invention, the electrifying signals are applied in a form which includes signals with different phases in a predetermined spatial relationship, e.g., with substantially opposite polarities. Preferably, the applied signals are in the form of a dipole. In a preferred embodiment, the electrifying signals are in the form of two parallel straight lines which have opposite and equal polarities. The distance between the lines forming the dipole is preferably adjustable.
An aspect of some preferred embodiments of the present invention relates to determining the depth of an anomaly within an organ. In a preferred embodiment of the invention, the depth is determined by inducing an electrical dipole of known orientation within the anomaly. The dipole within the anomaly induces a dipole field within the organ and this field influences the sensed values of the multi-element probe. When the dipole within the anomaly causes a field perpendicular to the probe it induces a peak within the sensors. The location and strength of the peak are indicative of the location of the anomaly. When the direction of the field of the dipole within the anomaly is parallel to the multi-element probe, the dipole induces two peaks within the sensors and the distance between the peaks is indicative of the depth of the anomaly within the organ.
The position of an anomaly, including its depth, is preferably determined based on a plurality of impedanc
Nachaliel Ehud
Ori Amos
Pearlman Andrew L.
Saad Abraham
Carella Byrne Bain Gilfillan Cecchi et al.
Manuel George
Olstein Elliot M.
Squire William
TransScan Medical Ltd.
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