Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Reexamination Certificate
2001-05-18
2004-07-06
Marmor, Charles (Department: 3736)
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
C600S554000
Reexamination Certificate
active
06760616
ABSTRACT:
TECHNICAL FIELD
The present invention is related to tissue surveillance systems.
BACKGROUND OF THE INVENTION
Systems and methods exist for determining when a probe, needle, catheter or other devices make contact with a particular tissue, e.g., U.S. Pat. No. 5,836,990 to Li entitled “Method and Apparatus for Determining Electrode/Tissue Contact”. The Li patent teaches a method for determining when a catheter makes contact with tissue covered with an ionic liquid. The system measures the electrical impedance at a distal end of the catheter and determines tissue contact has been made when the impedance increases. The system does not identify the type of tissue contacted and presumes the tissue is covered in an ionic liquid. Accordingly, a need exists for a system and method that identify tissue and use this information in medical procedures.
Systems and method also exist for controlling the level of ablation of tissue. These systems monitor the impedance of tissue being ablated to determine if the ablation energy is optimal. The systems generally measure impedance to within approximately 20 ohms. These systems do not determine when sufficient therapy has been applied to the tissue and employ impedance measurement with low tolerance levels. Accordingly, a need exists for a system that may control any form of therapy by monitoring characteristics of an electrical signal applied to the tissue.
SUMMARY OF THE INVENTION
The present invention provides a system in which an electrical signal is applied to a tissue via electrodes disposed on a tissue probe. The electrical signal applied to the tissue preferably comprises a frequency variable current or voltage that is preferably applied to the tissue using a sliding frequency scale.
In accordance with the present invention, the response to the applied signal is measured as the signal passes through tissue disposed at, around, or adjacent to, the probe. The inventors have found that different tissue types display different electrical transmission properties, including different capacitance and impedance properties. Accordingly, by measuring the electrical characteristics of the response signal, it is possible to determine the type of tissue through which the signal is passing. Preferably, this is accomplished by comparison to known exemplary signal characteristics for various tissue types. Further, when the probe is known to be a first tissue, the system and method may determine when the probe is advanced into a different tissue based on the changed electrical characteristics of the signal applied the probe.
In accordance with the present invention, the electrical signal characteristics that are monitored may include the phase shift between the voltage and current passing through a selected tissue, and the impedance of the selected tissue. The present inventors have experimentally determined that these properties vary from one tissue type to another. In a preferred aspect of the present invention, the electrical signal applied to the tissue may be a sliding frequency signal so a frequency spectrum of phase shift and impedance of a tissue is determined, however, any electrical, magnetic, or optical signal whose phase relationship and impedance to passage through the tissue may be measured can be used.
In a preferred method, a probe is advanced to a position in, at, or adjacent to, a selected tissue and an electrical signal is applied to the tissue by an electrode on the probe. The response to this signal is then measured and compared against electrical, magnetic, or optical transmission characteristics for the various tissue types. For example, the present invention provides a method and system for determining whether the conductive tip of a pedicle probe or pedicle screw is located in one of cortical bone, cancellous bone, and cortical bone near a boundary with soft tissue, whether the conductive tip of a cannula is located adjacent to one of nerve tissue and annulus tissue, and whether the conductive tip of a cathode is located adjacent to one of nerve tissue and prostate gland tissue.
Further, the inventors have discovered that the signal transmission characteristics of various tissues vary as a function of the tissue's health. Accordingly, the present system can also be used to determine tissue health (for various tissue types) by comparing the signal responses of tissue (in response to stimulation by the probe) to responses for healthy tissue.
The present inventors have determined that different cell/tissue types exhibit different capacitive effects. In addition, these capacitive effects vary considerably between living and dead cells. Accordingly in another aspect of the invention, the present system discriminates between living and dead tissues. This feature of the invention is particularly useful when the present system is used in conjunction with a tissue ablation system. For instance, the tissue ablation system may be prevented from providing unnecessary energy to ablate tissue and thereby protect surrounding tissue.
Moreover, the present system can be adapted to sense the presence of a particular type(s) of tissue as the probe is advanced through the patient's body. Such a feature of the present invention is particularly advantageous when sensing for the presence of nerve tissue. Specifically, the probe can be advanced through the patient's body, with the response to the electrical stimulation emitted by the probe being continuously monitored such that as nerve tissue is approached; the response signal will begin to exhibit characteristics indicative of nerve tissue.
Such nerve sensing features of the present invention can be used, for example, to sense for the presence of spinal nerves when advancing surgical equipment (which may include cutting, drilling, screw insertion, implant, and tissue ablation systems) towards the patient's intervertebral space.
In an optional aspect of the present invention, a probe having an electrode positioned thereon is replaced with a probe, which is itself electrified. For example, an electrified needle or an electrified trocar or cannula can be used as the probe. An advantage of having the entire probe emit the signal (rather than just an electrode disposed thereon) is that the probe itself can be made to smaller dimensions, particularly in the case of an electrified needle.
In optional aspects of the present invention, the probe is mono-polar. Specifically, only a first electrode is disposed on the probe. A second electrode is then positioned some distance away from the first electrode at another location on the body. Alternately, the probe may be bi-polar with both the first and second electrodes positioned on the probe itself. Additionally, the probe may include a plurality of bi-polar electrodes placed along the probe (such as around the tip and the length of the probe) to determine tissue types around the probe.
In a preferred aspect of the present invention, the measurement of the phase angle relationship between the voltage and current of the signal and impedance of the signal may be used to determine: (1) the type of tissue in which the probe is located, (2) the health of the tissue, (3) the relative location of the tip of the probe (ie: in cases where the electrode is disposed in the tip of the probe); and (4) any combination of (1), (2) and (3). As such, by gathering data mapped by analyzing the response signal, measured characteristics can be used to correlate: (1) tissue identity, (2) tissue health, and (3) tissue location.
In addition, the present invention can be adapted to: (5) locate specific tissue within a body; (6) control application of therapy to tissue; (7) detect the state of health of tissue; (8) navigate to tissue; and (9) any combination of the above.
In one embodiment, the invention is a tissue system including a computer system having an analog to digital (A/D) converter and digital to analog (D/A) converter interface (PCI board), that may be used to generate the control signal which is applied to the electrode or conductive tip of the probe. The c
Foley Kevin
Hoey Michael F.
Stone Corbett W.
Marmor Charles
Nu Vasive, Inc.
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