Abstract:
Cells that are in the process division are vulnerable to damage by AC electric fields that have specific frequency and field strength characteristics. The selective destruction of rapidly dividing cells can therefore be accomplished by imposing an AC electric field in a target region for extended periods of time at particular frequencies with particular filed strengths. Some of the cells that divide while the field is applied will be damaged, but the cells that do not divide will not be harmed. This selectively damages rapidly dividing cells like bacteria, but does not harm normal cells that are not dividing. Since the vulnerability of the dividing cells is strongly related to the alignment between the long axis of the dividing cells and the lines of force of the electric field, improved results can be obtained when the field is sequentially imposed in different directions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 14/731,903, filed Jun. 5, 2015, which is a continuation of U.S. application Ser. No. 13/782,579, filed Mar. 1, 2013, which is a divisional of U.S. application Ser. No. 12/958,623, filed Dec. 2, 2010. Application Ser. No. 12/958,623 claims the benefit of U.S. provisional application 61/266,392, filed Dec. 3, 2009; and application Ser. No. 12/958,623 is also a continuation-in-part of U.S. patent application Ser. No. 12/146,918, filed Jun. 26, 2008, which (1) claims the benefit of U.S. provisional application 60/947,212, filed Jun. 29, 2007, and (2) is also a continuation-in-part of U.S. patent application Ser. No. 11/111,439, filed Apr. 21, 2005, which (a) claims the benefit of U.S. provisional application 60/565,065, filed Apr. 23, 2004, and U.S. provisional application 60/639,873, filed Dec. 27, 2004; (b) is a continuation-in-part of U.S. patent application Ser. No. 11/074,318, filed Mar. 7, 2005, which is a continuation-in-part of U.S. patent application Ser. No. 10/315,576, filed Dec. 10, 2002, which is a continuation-in-part of U.S. patent application Ser. No. 10/285,313, filed Oct. 31, 2002, which is a continuation-in-part application of U.S. patent application Ser. No. 10/263,329, filed Oct. 2, 2002; (c) is a continuation-in-part of U.S. patent application Ser. No. 10/402,327, filed Mar. 28, 2003, which is a continuation-in-part of U.S. patent application Ser. No. 10/204,334, filed Oct. 16, 2002, which is the U.S. national phase of PCT/IB01/00202, filed Feb. 16, 2001, which claims the benefit of U.S. provisional application 60/183,295, filed Feb. 17, 2000; and (d) is a continuation-in-part of U.S. patent application Ser. No. 10/288,562, filed Nov. 5, 2002, which claims the benefit of U.S. provisional application 60/338,632, filed Nov. 6, 2001. Each of the above-referenced applications is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention concerns selective destruction of rapidly dividing cells in a localized area, and more particularly, selectively destroying target cells without destroying nearby non-target cells by applying an electric field with specific characteristics in vitro or to a region in a living patient. 
     BACKGROUND 
     All living organisms proliferate by cell division, including cell cultures, microorganisms (such as bacteria, mycoplasma, yeast, protozoa, and other single-celled organisms), fungi, algae, plant cells, etc. Dividing cells of organisms can be destroyed, or their proliferation controlled, by methods that are based on the sensitivity of the dividing cells of these organisms to certain agents. For example, certain antibiotics stop the multiplication process of bacteria. 
     The process of eukaryotic cell division is called “mitosis”, which involves nice distinct phases (see Darnell et al., Molecular Cell Biology, New York: Scientific American Books, 1986, p. 149). During interphase, the cell replicates chromosomal DNA, which begins condensing in early prophase. At this point, centrioles (each cell contains 2) begin moving towards opposite poles of the cell. In middle prophase, each chromosome is composed of duplicate chromatids. Microtubular spindles radiate from regions adjacent to the centrioles, which are closer to their poles. By late prophase, the centrioles have reached the poles, and some spindle fibers extend to the center of the cell, while others extend from the poles to the chromatids. The cells then move into metaphase, when the chromosomes move toward the equator of the cell and align in the equatorial plane. Next is early anaphase, during which time daughter chromatids separate from each other at the equator by moving along the spindle fibers toward a centromere at opposite poles. The cell begins to elongate along the axis of the pole; the pole-to-pole spindles also elongate. Late anaphase occurs when the daughter chromosomes (as they are now called) each reach their respective opposite poles. At this point, cytokinesis begins as the cleavage furrow begins to form at the equator of the cell. In other words, late anaphase is the point at which pinching the cell membrane begins. During telophase, cytokinesis is nearly complete and spindles disappear. Only a relatively narrow membrane connection joins the two cytoplasms. Finally, the membranes separate fully, cytokinesis is complete and the cell returns to interphase. 
     In meiosis, the cell undergoes a second division, involving separation of sister chromosomes to opposite poles of the cell along spindle fibers, followed by formation of a cleavage furrow and cell division. However, this division is not preceded by chromosome replication, yielding a haploid germ cell. Bacteria also divide by chromosome replication, followed by cell separation. However, since the daughter chromosomes separate by attachment to membrane components; there is no visible apparatus that contributes to cell division as in eukaryotic cells. 
     It is well known that tumors, particularly malignant or cancerous tumors, grow uncontrollably compared to normal tissue. Such expedited growth enables tumors to occupy an ever-increasing space and to damage or destroy tissue adjacent thereto. Furthermore, certain cancers are characterized by an ability to transmit cancerous “seeds”, including single cells or small cell clusters (metastases), to new locations where the metastatic cancer cells grow into additional tumors. 
     The rapid growth of tumors, in general, and malignant tumors in particular, as described above, is the result of relatively frequent cell division or multiplication of these cells compared to normal tissue cells. The distinguishably frequent cell division of cancer cells is the basis for the effectiveness of existing cancer treatments, e.g., irradiation therapy and the use of various chemo-therapeutic agents. Such treatments are based on the fact that cells undergoing division are more sensitive to radiation and chemo-therapeutic agents than non-dividing cells. Because tumors cells divide much more frequently than normal cells, it is possible, to a certain extent, to selectively damage or destroy tumor cells by radiation therapy and/or chemotherapy. The actual sensitivity of cells to radiation, therapeutic agents, etc., is also dependent on specific characteristics of different types of normal or malignant cell types. Thus, unfortunately, the sensitivity of tumor cells is not sufficiently higher than that many types of normal tissues. This diminishes the ability to distinguish between tumor cells and normal cells, and therefore, existing cancer treatments typically cause significant damage to normal tissues, thus limiting the therapeutic effectiveness of such treatments. Furthermore, the inevitable damage to other tissue renders treatments very traumatic to the patients and, often, patients are unable to recover from a seemingly successful treatment. Also, certain types of tumors are not sensitive at all to existing methods of treatment. 
     There are also other methods for destroying cells that do not rely on radiation therapy or chemotherapy alone. For example, ultrasonic and electrical methods for destroying tumor cells can be used in addition to or instead of conventional treatments. Electric fields and currents have been used for medical purposes for many years. The most common is the generation of electric currents in a human or animal body by application of an electric field by means of a pair of conductive electrodes between which a potential difference is maintained. These electric currents are used either to exert their specific effects, i.e., to stimulate excitable tissue, or to generate heat by flowing in the body since it acts as a resistor. Examples of the first type of application include the following: cardiac defibrillators, peripheral nerve and muscle stimulators, brain stimulators, etc. Currents are used for heating, for example, in devices for tumor ablation, ablation of malfunctioning cardiac or brain tissue, cauterization, relaxation of muscle rheumatic pain and other pain, etc. 
     Another use of electric fields for medical purposes involves the utilization of high frequency oscillating fields transmitted from a source that emits an electric wave, such as an RF wave or a microwave source that is directed at the part of the body that is of interest (i.e., target). In these instances, there is no electric energy conduction between the source and the body; but rather, the energy is transmitted to the body by radiation or induction. More specifically, the electric energy generated by the source reaches the vicinity of the body via a conductor and is transmitted from it through air or some other electric insulating material to the human body. 
     In a conventional electrical method, electrical current is delivered to a region of the target tissue using electrodes that are placed in contact with the body of the patient. The applied electrical current destroys substantially all cells in the vicinity of the target tissue. Thus, this type of electrical method does not discriminate between different types of cells within the target tissue and results in the destruction of both tumor cells and normal cells. 
     Electric fields that can be used in medical applications can thus be separated generally into two different modes. In the first mode, the electric fields are applied to the body or tissues by means of conducting electrodes. These electric fields can be separated into two types, namely (1) steady fields or fields that change at relatively slow rates, and alternating fields of low frequencies that induce corresponding electric currents in the body or tissues, and (2) high frequency alternating fields (above 1 MHz) applied to the body by means of the conducting electrodes. In the second mode, the electric fields are high frequency alternating fields applied to the body by means of insulated electrodes. 
     The first type of electric field is used, for example, to stimulate nerves and muscles, pace the heart, etc. In fact, such fields are used in nature to propagate signals in nerve and muscle fibers, central nervous system (CNS), heart, etc. The recording of such natural fields is the basis for the ECG, EEG, EMG, ERG, etc. The field strength in these applications, assuming a medium of homogenous electric properties, is simply the voltage applied to the stimulating/recording electrodes divided by the distance between them. These currents can be calculated by Ohm&#39;s law and can have dangerous stimulatory effects on the heart and CNS and can result in potentially harmful ion concentration changes. Also, if the currents are strong enough, they can cause excessive heating in the tissues. This heating can be calculated by the power dissipated in the tissue (the product of the voltage and the current). 
     When such electric fields and currents are alternating, their stimulatory power, on nerve, muscle, etc., is an inverse function of the frequency. At frequencies above 1-10 KHz, the stimulation power of the fields approaches zero. This limitation is due to the fact that excitation induced by electric stimulation is normally mediated by membrane potential changes, the rate of which is limited by the RC properties (time constants on the order of 1 ms) of the membrane. 
     Regardless of the frequency, when such current inducing fields are applied, they are associated with harmful side effects caused by currents. For example, one negative effect is the changes in ionic concentration in the various “compartments” within the system, and the harmful products of the electrolysis taking place at the electrodes, or the medium in which the tissues are imbedded. The changes in ion concentrations occur whenever the system includes two or more compartments between which the organism maintains ion concentration differences. For example, for most tissues, [Ca ++ ] in the extracellular fluid is about 2×10 −3  M, while in the cytoplasm of typical cells its concentration can be as low as 10 −7  M. A current induced in such a system by a pair of electrodes, flows in part from the extracellular fluid into the cells and out again into the extracellular medium. About 2% of the current flowing into the cells is carried by the Ca ++  ions. In contrast, because the concentration of intracellular Ca ++  is much smaller, only a negligible fraction of the currents that exits the cells is carried by these ions. Thus, Ca ++  ions accumulate in the cells such that their concentrations in the cells increases, while the concentration in the extracellular compartment may decrease. These effects are observed for both DC and alternating currents (AC). The rate of accumulation of the ions depends on the current intensity ion mobilities, membrane ion conductance, etc. An increase in [Ca ++ ] is harmful to most cells and if sufficiently high will lead to the destruction of the cells. Similar considerations apply to other ions. In view of the above observations, long term current application to living organisms or tissues can result in significant damage. Another major problem that is associated with such electric fields, is due to the electrolysis process that takes place at the electrode surfaces. Here charges are transferred between the metal (electrons) and the electrolytic solution (ions) such that charged active radicals are formed. These can cause significant damage to organic molecules, especially macromolecules and thus damage the living cells and tissues. 
     In contrast, when high frequency electric fields, above 1 MHz and usually in practice in the range of GHz, are induced in tissues by means of insulated electrodes, the situation is quite different. These type of fields generate only capacitive or displacement currents, rather than the conventional charge conducting currents. Under the effect of this type of field, living tissues behave mostly according to their dielectric properties rather than their electric conductive properties. Therefore, the dominant field effect is that due to dielectric losses and heating. Thus, it is widely accepted that in practice, the meaningful effects of such fields on living organisms, are only those due to their heating effects, i.e., due to dielectric losses. 
     In U.S. Pat. No. 6,043,066 (&#39;066) to Mangano, a method and device are presented which enable discrete objects having a conducting inner core, surrounded by a dielectric membrane to be selectively inactivated by electric fields via irreversible breakdown of their dielectric membrane. One potential application for this is in the selection and purging of certain biological cells in a suspension. According to the &#39;066 patent, an electric field is applied for targeting selected cells to cause breakdown of the dielectric membranes of these tumor cells, while purportedly not adversely affecting other desired subpopulations of cells. The cells are selected on the basis of intrinsic or induced differences in a characteristic electroporation threshold. The differences in this threshold can depend upon a number of parameters, including the difference in cell size. 
     The method of the &#39;066 patent is therefore based on the assumption that the electroporation threshold of tumor cells is sufficiently distinguishable from that of normal cells because of differences in cell size and differences in the dielectric properties of the cell membranes. Based upon this assumption, the larger size of many types of tumor cells makes these cells more susceptible to electroporation and thus, it may be possible to selectively damage only the larger tumor cell membranes by applying an appropriate electric field. One disadvantage of this method is that the ability to discriminate is highly dependent upon cell type, for example, the size difference between normal cells and tumor cells is significant only in certain types of cells. Another drawback of this method is that the voltages which are applied can damage some of the normal cells and may not damage all of the tumor cells because the differences in size and membrane dielectric properties are largely statistical and the actual cell geometries and dielectric properties can vary significantly. 
     What is needed in the art and has heretofore not been available is an apparatus for destroying dividing cells, wherein the apparatus better discriminates between dividing cells, including single-celled organisms, and non-dividing cells and is capable of selectively destroying the dividing cells or organisms with substantially no effect on the non-dividing cells or organisms. 
     SUMMARY 
     While they are dividing, cells are vulnerable to damage by AC electric fields that have specific frequency and field strength characteristics. The selective destruction of rapidly dividing cells can therefore be accomplished by imposing an AC electric field in a target region for extended periods of time. Some of the cells that divide while the field is applied will be damaged, but the cells that do not divide will not be harmed. This selectively damages rapidly dividing cells like tumor cells, but does not harm normal cells that are not dividing. Since the vulnerability of the dividing cells is strongly related to the alignment between the long axis of the dividing cells and the lines of force of the electric field, improved results are obtained by sequentially imposing the field in different directions. 
     A major use of the present apparatus is in the treatment of tumors by selective destruction of tumor cells with substantially no effect on normal tissue cells, and thus, the exemplary apparatus is described below in the context of selective destruction of tumor cells. It should be appreciated however, that for purpose of the following description, the term “cell” may also refer to a single-celled organism (eubacteria, bacteria, yeast, protozoa), multi-celled organisms (fungi, algae, mold), and plants as or parts thereof that are not normally classified as “cells”. The exemplary apparatus enables selective destruction of cells undergoing division in a way that is more effective and more accurate (e.g., more adaptable to be aimed at specific targets) than existing methods. Further, the present apparatus causes minimal damage, if any, to normal tissue and, thus, reduces or eliminates many side-effects associated with existing selective destruction methods, such as radiation therapy and chemotherapy. The selective destruction of dividing cells using the present apparatus does not depend on the sensitivity of the cells to chemical agents or radiation. Instead, the selective destruction of dividing cells is based on distinguishable geometrical characteristics of cells undergoing division, in comparison to non-dividing cells, regardless of the cell geometry of the type of cells being treated. 
     According to one exemplary embodiment, cell geometry-dependent selective destruction of living tissue is performed by inducing a non-homogenous electric field in the cells using an electronic apparatus. 
     It has been observed by the present inventor that, while different cells in their non-dividing state may have different shapes, e.g., spherical, ellipsoidal, cylindrical, “pancake-like”, etc., the division process of practically all cells is characterized by development of a “cleavage furrow” in late anaphase and telophase. This cleavage furrow is a slow constriction of the cell membrane (between the two sets of daughter chromosomes) which appears microscopically as a growing cleft (e.g., a groove or notch) that gradually separates the cell into two new cells. During the division process, there is a transient period (telophase) during which the cell structure is basically that of two sub-cells interconnected by a narrow “bridge” formed of the cell material. The division process is completed when the “bridge” between the two sub-cells is broken. The selective destruction of tumor cells using the present electronic apparatus utilizes this unique geometrical feature of dividing cells. 
     When a cell or a group of cells are under natural conditions or environment, i.e., part of a living tissue, they are disposed surrounded by a conductive environment consisting mostly of an electrolytic inter-cellular fluid and other cells that are composed mostly of an electrolytic intra-cellular liquid. When an electric field is induced in the living tissue, by applying an electric potential across the tissue, an electric field is formed in the tissue and the specific distribution and configuration of the electric field lines defines the direction of charge displacement, or paths of electric currents in the tissue, if currents are in fact induced in the tissue. The distribution and configuration of the electric field is dependent on various parameters of the tissue, including the geometry and the electric properties of the different tissue components, and the relative conductivities, capacities and dielectric constants (that may be frequency dependent) of the tissue components. 
     The electric current flow pattern for cells undergoing division is very different and unique as compared to non-dividing cells. Such cells including first and second sub-cells, namely an “original” cell and a newly formed cell, that are connected by a cytoplasm “bridge” or “neck”. The currents penetrate the first sub-cell through part of the membrane (“the current source pole”); however, they do not exit the first sub-cell through a portion of its membrane closer to the opposite pole (“the current sink pole”). Instead, the lines of current flow converge at the neck or cytoplasm bridge, whereby the density of the current flow lines is greatly increased. A corresponding, “mirror image”, process that takes place in the second sub-cell, whereby the current flow lines diverge to a lower density configuration as they depart from the bridge, and finally exit the second sub-cell from a part of its membrane closes to the current sink. 
     When a polarizable object is placed in a non-uniform converging or diverging field, electric forces act on it and pull it towards the higher density electric field lines. In the case of dividing cell, electric forces are exerted in the direction of the cytoplasm bridge between the two cells. Since all intercellular organelles and macromolecules are polarizable, they are all force towards the bridge between the two cells. The field polarity is irrelevant to the direction of the force and, therefore, an alternating electric having specific properties can be used to produce substantially the same effect. It will also be appreciated that the concentrated and inhomogeneous electric field present in or near the bridge or neck portion in itself exerts strong forces on charges and natural dipoles and can lead to the disruption of structures associated with these members. 
     The movement of the cellular organelles towards the bridge disrupts the cell structure and results in increased pressure in the vicinity of the connecting bridge membrane. This pressure of the organelles on the bridge membrane is expected to break the bridge membrane and, thus, it is expected that the dividing cell will “explode” in response to this pressure. The ability to break the membrane and disrupt other cell structures can be enhanced by applying a pulsating alternating electric field that has a frequency from about 50 KHz to about 500 KHz. When this type of electric field is applied to the tissue, the forces exerted on the intercellular organelles have a “hammering” effect, whereby force pulses (or beats) are applied to the organelles numerous times per second, enhancing the movement of organelles of different sizes and masses towards the bridge (or neck) portion from both of the sub-cells, thereby increasing the probability of breaking the cell membrane at the bridge portion. The forces exerted on the intracellular organelles also affect the organelles themselves and may collapse or break the organelles. 
     Advantageously, when non-dividing cells are subjected to these electric fields, there is no effect on the cells; however, the situation is much different when dividing cells are subjected to the present electric fields. Thus, the present electronic apparatus and the generated electric fields target dividing cells, such as tumors or the like, and do not target non-dividing cells that is found around in healthy tissue surrounding the target area. Furthermore, since the present apparatus utilizes insulated electrodes, the above mentioned negative effects, obtained when conductive electrodes are used, i.e., ion concentration changes in the cells and the formation of harmful agents by electrolysis, do not occur with the present apparatus. This is because, in general, no actual transfer of charges takes place between the electrodes and the medium, and there is no charge flow in the medium where the currents are capacitive. 
     It should be appreciated that the present electronic apparatus can also be used in applications other than treatment of tumors in the living body. In fact, the selective destruction utilizing the present apparatus can be used in conjunction with any organism that proliferates by division, for example, tissue cultures, microorganisms, such as bacteria, mycoplasma, protozoa, fungi, algae, plant cells, etc. Such organisms divide by the formation of a groove or cleft as described above. As the groove or cleft deepens, a narrow bridge is formed between the two parts of the organism, similar to the bridge formed between the sub-cells of dividing animal cells. Since such organisms are covered by a membrane having a relatively low electric conductivity, similar to an animal cell membrane described above, the electric field lines in a dividing organism converge at the bridge connecting the two parts of the dividing organism. The converging field lines result in electric forces that displace polarizable elements and charges within the dividing organism. 
     One aspect of the invention relates to a method of selectively destroying or inhibiting the growth of bacteria located within a target region of a patient. This method includes the steps of administering an antibiotic against the bacteria, so that a therapeutically effective dose arrives in the target region and capacitively coupling an AC electric field into the target region of the patient while the therapeutically effective dose is present at the target region, wherein the electric field has frequency characteristics that correspond to a vulnerability of the bacteria, and wherein the electric field is strong enough to damage, during cell division, a significant portion of the bacteria whose long axis is generally aligned with the lines of force of the electric field. The strength of the electric field in at least a portion of the target region is between 2 V/cm and 100 V/cm, and the electric field leaves non-dividing cells located within the target region substantially unharmed. The coupling step is repeated until a therapeutically significant portion of the bacteria die. 
     Another aspect of the invention relates to a method of selectively destroying or inhibiting the growth of bacteria located within a target region. This method includes the steps of capacitively coupling an AC electric field into the target region. The frequency of the electric field is between 5 MHz and 20 MHz, and the strength of the electric field in at least a portion of the target region is between 2 V/cm and 100 V/cm. The electric field has frequency characteristics that correspond to a vulnerability of the bacteria and the electric field is strong enough to damage, during cell division, a significant portion of the bacteria whose long axis is generally aligned with the lines of force of the electric field, and leave non-dividing cells located within the target region substantially unharmed. The coupling step is repeated until a therapeutically significant portion of the bacteria die. 
     Another aspect of the invention relates to an apparatus for selectively destroying or inhibiting the growth of bacteria located within a target region of a patient. This apparatus includes a first pair of insulated electrodes, and each of the electrodes has a surface configured to facilitate capacitive coupling of an electric field into the patient&#39;s body. The apparatus also includes an AC voltage source operatively connected to the electrodes. The AC voltage source and the electrodes are configured so that, when the electrodes are placed against the patient&#39;s body and the AC voltage source is activated, an AC electric field is capacitively coupled into the target region of the patient via the electrodes. The frequency of the electric field is between 5 MHz and 20 MHz, and the strength of the electric field in at least a portion of the target region is between 2 V/cm and 100 V/cm. The imposed electric field has frequency characteristics that correspond to a vulnerability of the bacteria, and is strong enough to damage, during cell division, a significant portion of the bacteria whose long axis is generally aligned with the lines of force of the electric field. The electric field also leaves non-dividing cells located within the target region substantially unharmed. 
     The above, and other objects, features and advantages of the present apparatus will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1E  are simplified, schematic, cross-sectional, illustrations of various stages of a cell division process; 
         FIGS. 2A and 2B  are schematic illustrations of a non-dividing cell being subjected to an electric field; 
         FIGS. 3A, 3B and 3C  are schematic illustrations of a dividing cell being subjected to an electric field according to one exemplary embodiment, resulting in destruction of the cell ( FIG. 3C ) in accordance with one exemplary embodiment; 
         FIG. 4  is a schematic illustration of a dividing cell at one stage being subject to an electric field; 
         FIG. 5  is a schematic block diagram of an apparatus for applying an electric according to one exemplary embodiment for selectively destroying cells; 
         FIG. 6  is a simplified schematic diagram of an equivalent electric circuit of insulated electrodes of the apparatus of  FIG. 5 ; 
         FIG. 7  is a cross-sectional illustration of a skin patch incorporating the apparatus of  FIG. 5  and for placement on a skin surface for treating a tumor or the like; 
         FIG. 8  is a cross-sectional illustration of the insulated electrodes implanted within the body for treating a tumor or the like; 
         FIG. 9  is a cross-sectional illustration of the insulated electrodes implanted within the body for treating a tumor or the like; 
         FIGS. 10A-10D  are cross-sectional illustrations of various constructions of the insulated electrodes of the apparatus of  FIG. 5 ; 
         FIG. 11  is a front elevational view in partial cross-section of two insulated electrodes being arranged about a human torso for treatment of a tumor container within the body, e.g., a tumor associated with lung cancer; 
         FIGS. 12A-12C  are cross-sectional illustrations of various insulated electrodes with and without protective members formed as a part of the construction thereof; 
         FIG. 13  is a schematic diagram of insulated electrodes that are arranged for focusing the electric field at a desired target while leaving other areas in low field density (i.e., protected areas); 
         FIG. 14  is a cross-sectional view of insulated electrodes incorporated into a hat according to a first embodiment for placement on a head for treating an intra-cranial tumor or the like; 
         FIG. 15  is a partial section of a hat according to an exemplary embodiment having a recessed section for receiving one or more insulated electrodes; 
         FIG. 16  is a cross-sectional view of the hat of  FIG. 15  placed on a head and illustrating a biasing mechanism for applying a force to the insulated electrode to ensure the insulated electrode remains in contact against the head; 
         FIG. 17  is a cross-sectional top view of an article of clothing having the insulated electrodes incorporated therein for treating a tumor or the like; 
         FIG. 18  is a cross-sectional view of a section of the article of clothing of  FIG. 17  illustrating a biasing mechanism for biasing the insulated electrode in direction to ensure the insulated electrode is placed proximate to a skin surface where treatment is desired; 
         FIG. 19  is a cross-sectional view of a probe according to one embodiment for being disposed internally within the body for treating a tumor or the like; 
         FIG. 20  is an elevational view of an unwrapped collar according to one exemplary embodiment for placement around a neck for treating a tumor or the like in this area when the collar is wrapped around the neck; 
         FIG. 21  is a cross-sectional view of two insulated electrodes with conductive gel members being arranged about a body, with the electric field lines being shown; 
         FIG. 22  is a cross-sectional view of the arrangement of  FIG. 21  illustrating a point of insulation breakdown in one insulated electrode; 
         FIG. 23  is a cross-sectional view of an arrangement of at least two insulated electrodes with conductive gel members being arranged about a body for treatment of a tumor or the like, wherein each conductive gel member has a feature for minimizing the effects of an insulation breakdown in the insulated electrode; 
         FIG. 24  is a cross-sectional view of another arrangement of at least two insulated electrodes with conductive gel members being arranged about a body for treatment of a tumor or the like, wherein a conductive member is disposed within the body near the tumor to create a region of increased field density; 
         FIG. 25  is a cross-sectional view of an arrangement of two insulated electrodes of varying sizes disposed relative to a body; and 
         FIG. 26  is a cross-sectional view of an arrangement of at least two insulated electrodes with conductive gel members being arranged about a body for treatment of a tumor or the like, wherein each conductive gel member has a feature for minimizing the effects of an insulation breakdown in the insulated electrode. 
         FIGS. 27A-C  show a configuration of electrodes that facilitates the application of an electric field in different directions. 
         FIG. 28  shows a three-dimensional arrangement of electrodes about a body part that facilitates the application of an electric field in different directions. 
         FIGS. 29A and 29B  are graphs of the efficiency of the cell destruction process as a function of field strength for melanoma and glioma cells, respectively. 
         FIGS. 30A and 30B  are graphs that show how the cell destruction efficiency is a function of the frequency of the applied field for melanoma and glioma cells, respectively. 
         FIG. 31A  is a graphical representation of the sequential application of a plurality of frequencies in a plurality of directions. 
         FIG. 31B  is a graphical representation of the sequential application of a sweeping frequency in a plurality of directions. 
         FIG. 32A  depicts the construction of the electrodes used in an experiment on bacteria. 
         FIG. 32B  depicts a test chamber used in an experiment on bacteria. 
         FIG. 32C  depicts a setup that was used to induce fields in the test chamber. 
         FIGS. 33A and 33B  show the effect of treating bacteria with electric fields at different frequencies. 
         FIG. 34  shows the effect of treating bacteria with electric fields at different field strengths. 
         FIGS. 35A and 35B  show the effect of treating bacteria with electric fields at different switching rates. 
         FIG. 36  shows the results of this repeated exposure test of  P. aeruginosa  to electric fields. 
         FIG. 37  shows the electric field distribution in and around a bacteria. 
         FIGS. 38A and 38B  show the magnitude of the forces acting on dipoles inside dividing bacteria. 
         FIG. 39  shows the results of an in vivo experiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is made to  FIGS. 1A-1E  which schematically illustrate various stages of a cell division process.  FIG. 1A  illustrates a cell  10  at its normal geometry, which can be generally spherical (as illustrated in the drawings), ellipsoidal, cylindrical, “pancake-like” or any other cell geometry, as is known in the art.  FIGS. 1B-1D  illustrate cell  10  during different stages of its division process, which results in the formation of two new cells  18  and  20 , shown in  FIG. 1E . 
     As shown in  FIGS. 1B-1D , the division process of cell  10  is characterized by a slowly growing cleft  12  which gradually separates cell  10  into two units, namely sub-cells  14  and  16 , which eventually evolve into new cells  18  and  20  ( FIG. 1E ). A shown specifically in  FIG. 1D , the division process is characterized by a transient period during which the structure of cell  10  is basically that of the two sub-cells  14  and  16  interconnected by a narrow “bridge”  22  containing cell material (cytoplasm surrounded by cell membrane). 
     Reference is now made to  FIGS. 2A and 2B , which schematically illustrate non-dividing cell  10  being subjected to an electric field produced by applying an alternating electric potential, at a relatively low frequency and at a relatively high frequency, respectively. Cell  10  includes intracellular organelles, e.g., a nucleus  30 . Alternating electric potential is applied across electrodes  28  and  32  that can be attached externally to a patient at a predetermined region, e.g., in the vicinity of the tumor being treated. When cell  10  is under natural conditions, i.e., part of a living tissue, it is disposed in a conductive environment (hereinafter referred to as a “volume conductor”) consisting mostly of electrolytic inter-cellular liquid. When an electric potential is applied across electrodes  28  and  32 , some of the field lines of the resultant electric field (or the current induced in the tissue in response to the electric field) penetrate the cell  10 , while the rest of the field lines (or induced current) flow in the surrounding medium. The specific distribution of the electric field lines, which is substantially consistent with the direction of current flow in this instance, depends on the geometry and the electric properties of the system components, e.g., the relative conductivities and dielectric constants of the system components, that can be frequency dependent. For low frequencies, e.g., frequencies lower than 10 KHz, the conductance properties of the components completely dominate the current flow and the field distribution, and the field distribution is generally as depicted in  FIG. 2A . At higher frequencies, e.g., at frequencies of between 10 KHz and 1 MHz, the dielectric properties of the components becomes more significant and eventually dominate the field distribution, resulting in field distribution lines as depicted generally in  FIG. 2B . 
     For constant (i.e., DC) electric fields or relatively low frequency alternating electric fields, for example, frequencies under 10 KHz, the dielectric properties of the various components are not significant in determining and computing the field distribution. Therefore, as a first approximation, with regard to the electric field distribution, the system can be reasonably represented by the relative impedances of its various components. Using this approximation, the intercellular (i.e., extracellular) fluid and the intracellular fluid each has a relatively low impedance, while the cell membrane  11  has a relatively high impedance. Thus, under low frequency conditions, only a fraction of the electric field lines (or currents induced by the electric field) penetrate membrane  11  of the cell  10 . At relatively high frequencies (e.g., 10 KHz-1 MHz), in contrast, the impedance of membrane  11  relative to the intercellular and intracellular fluids decreases, and thus, the fraction of currents penetrating the cells increases significantly. It should be noted that at very high frequencies, i.e., above 1 MHz, the membrane capacitance can short the membrane resistance and, therefore, the total membrane resistance can become negligible. 
     In any of the embodiments described above, the electric field lines (or induced currents) penetrate cell  10  from a portion of the membrane  11  closest to one of the electrodes generating the current, e.g., closest to positive electrode  28  (also referred to herein as “source”). The current flow pattern across cell  10  is generally uniform because, under the above approximation, the field induced inside the cell is substantially homogeneous. The currents exit cell  10  through a portion of membrane  11  closest to the opposite electrode, e.g., negative electrode  32  (also referred to herein as “sink”). 
     The distinction between field lines and current flow can depend on a number of factors, for example, on the frequency of the applied electric potential and on whether electrodes  28  and  32  are electrically insulated. For insulated electrodes applying a DC or low frequency alternating voltage, there is practically no current flow along the lines of the electric field. At higher frequencies, the displacement currents are induced in the tissue due to charging and discharging of the electrode insulation and the cell membranes (which act as capacitors to a certain extent), and such currents follow the lines of the electric field. Fields generated by non-insulated electrodes, in contrast, always generate some form of current flow, specifically, DC or low frequency alternating fields generate conductive current flow along the field lines, and high frequency alternating fields generate both conduction and displacement currents along the field lines. It should be appreciated, however, that movement of polarizable intracellular organelles according to the present invention (as described below) is not dependent on actual flow of current and, therefore, both insulated and non-insulated electrodes can be used efficiently. Advantages of insulated electrodes include lower power consumption, less heating of the treated regions, and improved patient safety. 
     According to one exemplary embodiment of the present invention, the electric fields that are used are alternating fields having frequencies that are in the range from about 50 KHz to about 500 KHz, and preferably from about 100 KHz to about 300 KHz. For ease of discussion, these type of electric fields are also referred to below as “TC fields”, which is an abbreviation of “Tumor Curing electric fields”, since these electric fields fall into an intermediate category (between high and low frequency ranges) that have bio-effective field properties while having no meaningful stimulatory and thermal effects. These frequencies are sufficiently low so that the system behavior is determined by the system&#39;s Ohmic (conductive) properties but sufficiently high enough not to have any stimulation effect on excitable tissues. Such a system consists of two types of elements, namely, the intercellular, or extracellular fluid, or medium and the individual cells. The intercellular fluid is mostly an electrolyte with a specific resistance of about 40-100 Ohm*cm. As mentioned above, the cells are characterized by three elements, namely (1) a thin, highly electric resistive membrane that coats the cell; (2) internal cytoplasm that is mostly an electrolyte that contains numerous macromolecules and micro-organelles, including the nucleus; and (3) membranes, similar in their electric properties to the cell membrane, cover the micro-organelles. 
     When this type of system is subjected to the present TC fields (e.g., alternating electric fields in the frequency range of 100 KHz-300 KHz) most of the lines of the electric field and currents tend away from the cells because of the high resistive cell membrane and therefore the lines remain in the extracellular conductive medium. In the above recited frequency range, the actual fraction of electric field or currents that penetrates the cells is a strong function of the frequency. 
       FIG. 2  schematically depicts the resulting field distribution in the system. As illustrated, the lines of force, which also depict the lines of potential current flow across the cell volume mostly in parallel with the undistorted lines of force (the main direction of the electric field). In other words, the field inside the cells is mostly homogeneous. In practice, the fraction of the field or current that penetrates the cells is determined by the cell membrane impedance value relative to that of the extracellular fluid. Since the equivalent electric circuit of the cell membrane is that of a resistor and capacitor in parallel, the impedance is a function of the frequency. The higher the frequency, the lower the impedance, the larger the fraction of penetrating current and the smaller the field distortion (Rotshenker S. &amp; Y. Palti,  Changes in fraction of current penetrating an axon as a function of duration of stimulating pulse , J. Theor. Biol. 41; 401-407 (1973). 
     As previously mentioned, when cells are subjected to relatively weak electric fields and currents that alternate at high frequencies, such as the present TC fields having a frequency in the range of 50 KHz-500 KHz, they have no effect on the non-dividing cells. While the present TC fields have no detectable effect on such systems, the situation becomes different in the presence of dividing cells. 
     Reference is now made to  FIGS. 3A-3C  which schematically illustrate the electric current flow pattern in cell  10  during its division process, under the influence of alternating fields (TC fields) in the frequency range from about 100 KHz to about 300 KHz in accordance with one exemplary embodiment. The field lines or induced currents penetrate cell  10  through a part of the membrane of sub-cell  16  closer to electrode  28 . However, they do not exit through the cytoplasm bridge  22  that connects sub-cell  16  with the newly formed yet still attached sub-cell  14 , or through a part of the membrane in the vicinity of the bridge  22 . Instead, the electric field or current flow lines—that are relatively widely separated in sub-cell  16 —converge as they approach bridge  22  (also referred to as “neck”  22 ) and, thus, the current/field line density within neck  22  is increased dramatically. A “mirror image” process takes place in sub-cell  14 , whereby the converging field lines in bridge  22  diverge as they approach the exit region of sub-cell  14 . 
     It should be appreciated by persons skilled in the art that homogeneous electric fields do not exert a force on electrically neutral objects, i.e., objects having substantially zero net charge, although such objects can become polarized. However, under a non-uniform, converging electric field, as shown in  FIGS. 3A-3C , electric forces are exerted on polarized objects, moving them in the direction of the higher density electric field lines. It will be appreciated that the concentrated electric field that is present in the neck or bridge area in itself exerts strong forces on charges and natural dipoles and can disrupt structures that are associated therewith. One will understand that similar net forces act on charges in an alternating field, again in the direction of the field of higher intensity. 
     In the configuration of  FIGS. 3A and 3B , the direction of movement of polarized and charged objects is towards the higher density electric field lines, i.e., towards the cytoplasm bridge  22  between sub-cells  14  and  16 . It is known in the art that all intracellular organelles, for example, nuclei  24  and  26  of sub-cells  14  and  16 , respectively, are polarizable and, thus, such intracellular organelles are electrically forced in the direction of the bridge  22 . Since the movement is always from lower density currents to the higher density currents, regardless of the field polarity, the forces applied by the alternating electric field to organelles, such as nuclei  24  and  26 , are always in the direction of bridge  22 . A comprehensive description of such forces and the resulting movement of macromolecules of intracellular organelles, a phenomenon referred to as “dielectrophoresis” is described extensively in literature, e.g., in C. L. Asbury &amp; G. van den Engh, Biophys. J. 74, 1024-1030, 1998, the disclosure of which is hereby incorporated by reference in its entirety. 
     The movement of the organelles  24  and  26  towards the bridge  22  disrupts the structure of the dividing cell, change the concentration of the various cell constituents and, eventually, the pressure of the converging organelles on bridge membrane  22  results in the breakage of cell membrane  11  at the vicinity of the bridge  22 , as shown schematically in  FIG. 3C . The ability to break membrane  11  at bridge  22  and to otherwise disrupt the cell structure and organization can be enhanced by applying a pulsating AC electric field, rather than a steady AC field. When a pulsating field is applied, the forces acting on organelles  24  and  26  have a “hammering” effect, whereby pulsed forces beat on the intracellular organelles towards the neck  22  from both sub-cells  14  and  16 , thereby increasing the probability of breaking cell membrane  11  in the vicinity of neck  22 . 
     A very important element, which is very susceptible to the special fields that develop within the dividing cells is the microtubule spindle that plays a major role in the division process. In  FIG. 4 , a dividing cell  10  is illustrated, at an earlier stage as compared to  FIGS. 3A and 3B , under the influence of external TC fields (e.g., alternating fields in the frequency range of about 100 KHz to about 300 KHz), generally indicated as lines  100 , with a corresponding spindle mechanism generally indicated at  120 . The lines  120  are microtubules that are known to have a very strong dipole moment. This strong polarization makes the tubules, as well as other polar macromolecules and especially those that have a specific orientation within the cells or its surrounding, susceptible to electric fields. Their positive charges are located at the two centrioles while two sets of negative poles are at the center of the dividing cell and the other pair is at the points of attachment of the microtubules to the cell membrane, generally indicated at  130 . This structure forms sets of double dipoles and therefore they are susceptible to fields of different directions. It will be understood that the effect of the TC fields on the dipoles does not depend on the formation of the bridge (neck) and thus, the dipoles are influenced by the TC fields prior to the formation of the bridge (neck). 
     Since the present apparatus (as will be described in greater detail below) utilizes insulated electrodes, the above-mentioned negative effects obtained when conductive electrodes are used, i.e., ion concentration changes in the cells and the formation of harmful agents by electrolysis, do not occur when the present apparatus is used. This is because, in general, no actual transfer of charges takes place between the electrodes and the medium and there is no charge flow in the medium where the currents are capacitive, i.e., are expressed only as rotation of charges, etc. 
     Turning now to  FIG. 5 , the TC fields described above that have been found to advantageously destroy tumor cells are generated by an electronic apparatus  200 .  FIG. 5  is a simple schematic diagram of the electronic apparatus  200  illustrating the major components thereof. The electronic apparatus  200  generates the desired electric signals (TC signals) in the shape of waveforms or trains of pulses. The apparatus  200  includes a generator  210  and a pair of conductive leads  220  that are attached at one end thereof to the generator  210 . The opposite ends of the leads  220  are connected to insulated conductors  230  that are activated by the electric signals (e.g., waveforms). The insulated conductors  230  are also referred to hereinafter as isolects  230 . Optionally and according to another exemplary embodiment, the apparatus  200  includes a temperature sensor  240  and a control box  250  which are both added to control the amplitude of the electric field generated so as not to generate excessive heating in the area that is treated. 
     The generator  210  generates an alternating voltage waveform at frequencies in the range from about 50 KHz to about 500 KHz (preferably from about 100 KHz to about 300 KHz) (i.e., the TC fields). The required voltages are such that the electric field intensity in the tissue to be treated is in the range of about 0.1 V/cm to about 10 V/cm. To achieve this field, the actual potential difference between the two conductors in the isolects  230  is determined by the relative impedances of the system components, as described below. 
     When the control box  250  is included, it controls the output of the generator  210  so that it will remain constant at the value preset by the user or the control box  250  sets the output at the maximal value that does not cause excessive heating, or the control box  250  issues a warning or the like when the temperature (sensed by temperature sensor  240 ) exceeds a preset limit. 
     The leads  220  are standard isolated conductors with a flexible metal shield, preferably grounded so that it prevents the spread of the electric field generated by the leads  220 . The isolects  230  have specific shapes and positioning so as to generate an electric field of the desired configuration, direction, and intensity at the target volume and only there so as to focus the treatment. 
     The specifications of the apparatus  200  as a whole and its individual components are largely influenced by the fact that at the frequency of the present TC fields (50 KHz-500 KHz), living systems behave according to their “Ohmic”, rather than their dielectric properties. The only elements in the apparatus  200  that behave differently are the insulators of the isolects  230  (see  FIGS. 7-9 ). The isolects  200  consist of a conductor in contact with a dielectric that is in contact with the conductive tissue thus forming a capacitor. 
     The details of the construction of the isolects  230  is based on their electric behavior that can be understood from their simplified electric circuit when in contact with tissue as generally illustrated in  FIG. 6 . In the illustrated arrangement, the potential drop or the electric field distribution between the different components is determined by their relative electric impedance, i.e., the fraction of the field on each component is given by the value of its impedance divided by the total circuit impedance. For example, the potential drop on element ΔV A =A/(A+B+C+D+E). Thus, for DC or low frequency AC, practically all the potential drop is on the capacitor (that acts as an insulator). For relatively very high frequencies, the capacitor practically is a short and therefore, practically all the field is distributed in the tissues. At the frequencies of the present TC fields (e.g., 50 KHz to 500 KHz), which are intermediate frequencies, the impedance of the capacitance of the capacitors is dominant and determines the field distribution. Therefore, in order to increase the effective voltage drop across the tissues (field intensity), the impedance of the capacitors is to be decreased (i.e., increase their capacitance). This can be achieved by increasing the effective area of the “plates” of the capacitor, decrease the thickness of the dielectric or use a dielectric with high dielectric constant. 
     In order to optimize the field distribution, the isolects  230  are configured differently depending upon the application in which the isolects  230  are to be used. There are two principle modes for applying the present electric fields (TC fields). First, the TC fields can be applied by external isolects and second, the TC fields can be applied by internal isolects. 
     Electric fields (TC fields) that are applied by external isolects can be of a local type or widely distributed type. The first type includes, for example, the treatment of skin tumors and treatment of lesions close to the skin surface.  FIG. 7  illustrates an exemplary embodiment where the isolects  230  are incorporated in a skin patch  300 . The skin patch  300  can be a self-adhesive flexible patch with one or more pairs of isolects  230 . The patch  300  includes internal insulation  310  (formed of a dielectric material) and the external insulation  260  and is applied to skin surface  301  that contains a tumor  303  either on the skin surface  301  or slightly below the skin surface  301 . Tissue is generally indicated at  305 . To prevent the potential drop across the internal insulation  310  to dominate the system, the internal insulation  310  must have a relatively high capacity. This can be achieved by a large surface area; however, this may not be desired as it will result in the spread of the field over a large area (e.g., an area larger than required to treat the tumor). Alternatively, the internal insulation  310  can be made very thin and/or the internal insulation  310  can be of a high dielectric constant. As the skin resistance between the electrodes (labeled as A and E in  FIG. 6 ) is normally significantly higher than that of the tissue (labeled as C in  FIG. 6 ) underneath it (1-10 KΩ vs. 0.1-1 KΩ), most of the potential drop beyond the isolects occurs there. To accommodate for these impedances (Z), the characteristics of the internal insulation  310  (labeled as B and D in  FIG. 6 ) should be such that they have impedance preferably under 100 KΩ at the frequencies of the present TC fields (e.g., 50 KHz to 500 KHz). For example, if it is desired for the impedance to be about 10 K Ohms or less, such that over 1% of the applied voltage falls on the tissues, for isolects with a surface area of 10 mm 2 , at frequencies of 200 KHz, the capacity should be on the order of 10 −10  F., which means that using standard insulations with a dielectric constant of 2-3, the thickness of the insulating layer  310  should be about 50-100 microns. An internal field 10 times stronger would be obtained with insulators with a dielectric constant of about 20-50. 
     Using an insulating material with a high dielectric constant increases the capacitance of the electrodes, which results in a reduction of the electrodes&#39; impedance to the AC signal that is applied by the generator  1  (shown in  FIG. 5 ). Because the electrodes A, E are wired in series with the target tissue C, as shown in  FIG. 6 , this reduction in impedance reduces the voltage drop in the electrodes, so that a larger portion of the applied AC voltage appears across the tissue C. Since a larger portion of the voltage appears across the tissue, the voltage that is being applied by the generator  1  can be advantageously lowered for a given field strength in the tissue. 
     The desired field strength in the tissue being treated is preferably between about 0.1 V/cm and about 10 V/cm, and more preferably between about 2 V/cm and 3 V/cm or between about 1 V/cm and about 5 V/cm. If the dielectric constant used in the electrode is sufficiently high, the impedance of the electrodes A, E drops down to the same order of magnitude as the series combination of the skin and tissue B, C, D. One example of a suitable material with an extremely high dielectric constant is CaCu 3 Ti 4 O 12 , which has a dielectric constant of about 11,000 (measured at 100 kHz). When the dielectric constant is this high, useful fields can be obtained using a generator voltage that is on the order of a few tens of Volts. 
     Since the thin insulating layer can be very vulnerable, etc., the insulation can be replaced by very high dielectric constant insulating materials, such as titanium dioxide (e.g., rutile), the dielectric constant can reach values of about 200. There a number of different materials that are suitable for use in the intended application and have high dielectric constants. For example, some materials include: lithium niobate (LiNbO 3 ), which is a ferroelectric crystal and has a number of applications in optical, pyroelectric and piezoelectric devices; yttrium iron garnet (YIG) is a ferromagnetic crystal and magneto-optical devices, e.g., optical isolator can be realized from this material; barium titanate (BaTiO 3 ) is a ferromagnetic crystal with a large electro-optic effect; potassium tantalate (KTaO 3 ) which is a dielectric crystal (ferroelectric at low temperature) and has very low microwave loss and tunability of dielectric constant at low temperature; and lithium tantalate (LiTaO 3 ) which is a ferroelectric crystal with similar properties as lithium niobate and has utility in electro-optical, pyroelectric and piezoelectric devices. Insulator ceramics with high dielectric constants may also be used, such as a ceramic made of a combination of Lead Magnesium Niobate and Lead Titanate. It will be understood that the aforementioned exemplary materials can be used in combination with the present device where it is desired to use a material having a high dielectric constant. 
     One must also consider another factor that affects the effective capacity of the isolects  230 , namely the presence of air between the isolects  230  and the skin. Such presence, which is not easy to prevent, introduces a layer of an insulator with a dielectric constant of 1.0, a factor that significantly lowers the effective capacity of the isolects  230  and neutralizes the advantages of the titanium dioxide (rutile), etc. To overcome this problem, the isolects  230  can be shaped so as to conform with the body structure and/or (2) an intervening filler  270  (as illustrated in  FIG. 10C ), such as a gel, that has high conductance and a high effective dielectric constant, can be added to the structure. The shaping can be pre-structured (see  FIG. 10A ) or the system can be made sufficiently flexible so that shaping of the isolects  230  is readily achievable. The gel can be contained in place by having an elevated rim as depicted in  FIGS. 10C and 10C ′. The gel can be made of hydrogels, gelatins, agar, etc., and can have salts dissolved in it to increase its conductivity.  FIGS. 10A-10C ′ illustrate various exemplary configurations for the isolects  230 . The exact thickness of the gel is not important so long as it is of sufficient thickness that the gel layer does not dry out during the treatment. In one exemplary embodiment, the thickness of the gel is about 0.5 mm to about 2 mm. Preferably, the gel has high conductivity, is tacky, and is biocompatible for extended periods of time. One suitable gel is AG603 Hydrogel, which is available from AmGel Technologies, 1667 S. Mission Road, Fallbrook, Calif. 92028-4115, USA. 
     In order to achieve the desirable features of the isolects  230 , the dielectric coating of each should be very thin, for example from between 1-50 microns. Since the coating is so thin, the isolects  230  can easily be damaged mechanically or undergo dielectric breakdown. This problem can be overcome by adding a protective feature to the isolect&#39;s structure so as to provide desired protection from such damage. For example, the isolect  230  can be coated, for example, with a relatively loose net  340  that prevents access to the surface but has only a minor effect on the effective surface area of the isolect  230  (i.e., the capacity of the isolects  230  (cross section presented in  FIG. 12B ). The loose net  340  does not affect the capacity and ensures good contact with the skin, etc. The loose net  340  can be formed of a number of different materials; however, in one exemplary embodiment, the net  340  is formed of nylon, polyester, cotton, etc. Alternatively, a very thin conductive coating  350  can be applied to the dielectric portion (insulating layer) of the isolect  230 . One exemplary conductive coating is formed of a metal and more particularly of gold. The thickness of the coating  350  depends upon the particular application and also on the type of material used to form the coating  350 ; however, when gold is used, the coating has a thickness from about 0.1 micron to about 0.1 mm. Furthermore, the rim illustrated in  FIG. 10  can also provide some mechanical protection. 
     However, the capacity is not the only factor to be considered. The following two factors also influence how the isolects  230  are constructed. The dielectric strength of the internal insulating layer  310  and the dielectric losses that occur when it is subjected to the TC field, i.e., the amount of heat generated. The dielectric strength of the internal insulation  310  determines at what field intensity the insulation will be “shorted” and cease to act as an intact insulation. Typically, insulators, such as plastics, have dielectric strength values of about 100V per micron or more. As a high dielectric constant reduces the field within the internal insulator  310 , a combination of a high dielectric constant and a high dielectric strength gives a significant advantage. This can be achieved by using a single material that has the desired properties or it can be achieved by a double layer with the correct parameters and thickness. In addition, to further decreasing the possibility that the insulating layer  310  will fail, all sharp edges of the insulating layer  310  should be eliminated as by rounding the corners, etc., as illustrated in  FIG. 10D  using conventional techniques. 
       FIGS. 8 and 9  illustrate a second type of treatment using the isolects  230 , namely electric field generation by internal isolects  230 . A body to which the isolects  230  are implanted is generally indicated at  311  and includes a skin surface  313  and a tumor  315 . In this embodiment, the isolects  230  can have the shape of plates, wires or other shapes that can be inserted subcutaneously or a deeper location within the body  311  so as to generate an appropriate field at the target area (tumor  315 ). 
     It will also be appreciated that the mode of isolects application is not restricted to the above descriptions. In the case of tumors in internal organs, for example, liver, lung, etc., the distance between each member of the pair of isolects  230  can be large. The pairs can even by positioned opposite sides of a torso  410 , as illustrated in  FIG. 11 . The arrangement of the isolects  230  in  FIG. 11  is particularly useful for treating a tumor  415  associated with lung cancer or gastro-intestinal tumors. In this embodiment, the electric fields (TC fields) spread in a wide fraction of the body. 
     In order to avoid overheating of the treated tissues, a selection of materials and field parameters is needed. The isolects insulating material should have minimal dielectric losses at the frequency ranges to be used during the treatment process. This factor can be taken into consideration when choosing the particular frequencies for the treatment. The direct heating of the tissues will most likely be dominated by the heating due to current flow (given by the I*R product). In addition, the isolect (insulated electrode)  230  and its surroundings should be made of materials that facilitate heat losses and its general structure should also facilitate head losses, i.e., minimal structures that block heat dissipation to the surroundings (air) as well as high heat conductivity. Using larger electrodes also minimizes the local sensation of heating, since it spreads the energy that is being transferred into the patient over a larger surface area. Preferably, the heating is minimized to the point where the patient&#39;s skin temperature never exceeds about 39° C. 
     Another way to reduce heating is to apply the field to the tissue being treated intermittently, by applying a field with a duty cycle between about 20% and about 50% instead of using a continuous field. For example, to achieve a duty cycle of 33%, the field would be repetitively switched on for one second, then switched off for two seconds. Preliminary experiments have shown that the efficacy of treatment using a field with a 33% duty cycle is roughly the same as for a field with a duty cycle of 100%. In alternative embodiments, the field could be switched on for one hour then switched off for one hour to achieve a duty cycle of 50%. Of course, switching at a rate of once per hour would not help minimize short-term heating. On the other hand, it could provide the patient with a welcome break from treatment. 
     The effectiveness of the treatment can be enhanced by an arrangement of isolects  230  that focuses the field at the desired target while leaving other sensitive areas in low field density (i.e., protected areas). The proper placement of the isolects  230  over the body can be maintained using any number of different techniques, including using a suitable piece of clothing that keeps the isolects at the appropriate positions.  FIG. 13  illustrates such an arrangement in which an area labeled as “P” represents a protected area. The lines of field force do not penetrate this protected area and the field there is much smaller than near the isolects  230  where target areas can be located and treated well. In contrast, the field intensity near the four poles is very high. 
     The following Example serves to illustrate an exemplary application of the present apparatus and application of TC fields; however, this Example is not limiting and does not limit the scope of the present invention in any way. 
     Example 1 
     To demonstrate the effectiveness of electric fields having the above described properties (e.g., frequencies between 50 KHz and 500 KHz) in destroying tumor cells, the electric fields were applied to treat mice with malignant melanoma tumors. Two pairs of isolects  230  were positioned over a corresponding pair of malignant melanomas. Only one pair was connected to the generator  210  and 200 KHz alternating electric fields (TC fields) were applied to the tumor for a period of 6 days. One melanoma tumor was not treated so as to permit a comparison between the treated tumor and the non-treated tumor. After treatment for 6 days, the pigmented melanoma tumor remained clearly visible in the non-treated side of the mouse, while, in contrast, no tumor is seen on the treated side of the mouse. The only areas that were visible discernable on the skin were the marks that represented the points of insertion of the isolects  230 . The fact that the tumor was eliminated at the treated side was further demonstrated by cutting and inversing the skin so that its inside face was exposed. Such a procedure indicated that the tumor has been substantially, if not completely, eliminated on the treated side of the mouse. The success of the treatment was also further verified by histopathological examination. 
     The present inventor has thus uncovered that electric fields having particular properties can be used to destroy dividing cells or tumors when the electric fields are applied to using an electronic device. More specifically, these electric fields fall into a special intermediate category, namely bio-effective fields that have no meaningful stimulatory and no thermal effects, and therefore overcome the disadvantages that were associated with the application of conventional electric fields to a body. It will also be appreciated that the present apparatus can further include a device for rotating the TC field relative to the living tissue. For example and according to one embodiment, the alternating electric potential applies to the tissue being treated is rotated relative to the tissue using conventional devices, such as a mechanical device that upon activation, rotates various components of the present system. 
     Moreover and according to yet another embodiment, the TC fields are applied to different pairs of the insulated electrodes  230  in a consecutive manner. In other words, the generator  210  and the control system thereof can be arranged so that signals are sent at periodic intervals to select pairs of insulated electrodes  230 , thereby causing the generation of the TC fields of different directions by these insulated electrodes  230 . Because the signals are sent at select times from the generator to the insulated electrodes  230 , the TC fields of changing directions are generated consecutively by different insulated electrodes  230 . This arrangement has a number of advantages and is provided in view of the fact that the TC fields have maximal effect when they are parallel to the axis of cell division. Since the orientation of cell division is in most cases random, only a fraction of the dividing cells are affected by any given field. Thus, using fields of two or more orientations increases the effectiveness since it increases the chances that more dividing cells are affected by a given TC field. 
     In vitro experiments have shown that the electric field has the maximum killing effect when the lines of force of the field are oriented generally parallel to the long axis of the hourglass-shaped cell during mitosis (as shown in  FIGS. 3A-3C ). In one experiment, a much higher proportion of the damaged cells had their axis of division oriented along the field: 56% of the cells oriented at or near 0° with respect to the field were damaged, versus an average of 15% of cells damaged for cells with their long axis oriented at more than 22° with respect to the field. 
     The inventor has recognized that applying the field in different directions sequentially will increase the overall killing power, because the field orientation that is most effectively in killing dividing cells will be applied to a larger population of the dividing cells. A number of examples for applying the field in different directions are discussed below. 
       FIGS. 27A, 27B, and 27C  show a set of 6 electrodes E 1 -E 6 , and how the direction of the field through the target tissue  1510  can be changed by applying the AC signal from the generator  1  (shown in  FIG. 1 ) across different pairs of electrodes. For example, if the AC signal is applied across electrodes E 1  and E 4 , the field lines F would be vertical (as shown in  FIG. 27A ), and if the signal is applied across electrodes E 2  and E 5 , or across electrodes E 3  and E 6 , the field lines F would be diagonal (as shown in  FIGS. 27B and 27C , respectively). Additional field directions can be obtained by applying the AC signal across other pairs of electrodes. For example, a roughly horizontal field could be obtained by applying the signal across electrodes E 2  and E 6 . 
     In one embodiment, the AC signal is applied between the various pairs of electrodes sequentially. An example of this arrangement is to apply the AC signal across electrodes E 1  and E 4  for one second, then apply the AC signal across electrodes E 2  and E 5  for one second, and then apply the AC signal across electrodes E 3  and E 6  for one second. This three-part sequence is then repeated for the desired period of treatment. Because the efficacy in cell-destruction is strongly dependant on the cell&#39;s orientation, cycling the field between the different directions increases the chance that the field will be oriented in a direction that favors cell destruction at least part of the time. 
     Of course, the 6 electrode configuration shown in  FIGS. 27A-C  is just one of many possible arrangements of multiple electrodes, and many other configurations of three or more electrodes could be used based on the same principles. 
     Application of the field in different directions sequentially is not limited to two dimensional embodiments, and  FIG. 28  shows how the sequential application of signals across different sets of electrodes can be extended to three dimensions. A first array of electrodes A 1 -A 9  is arranged around body part  1500 , and a last array of electrodes N 1 -N 9  is arranged around the body part  1500  a distance W away from the first array. Additional arrays of electrodes may optionally be added between the first array and the last array, but these additional arrays are not illustrated for clarity (so as not to obscure the electrodes A 5 -A 9  and B 5 -B 8  on the back of the body part  1500 ). 
     As in the  FIG. 27  embodiment, the direction of the field through the target tissue can be changed by applying the AC signal from the generator  1  (shown in  FIG. 1 ) across different pairs of electrodes. For example, applying the AC signal between electrodes A 2  and A 7  would result in a field in a front-to-back direction between those two electrodes, and applying the AC signal between electrodes A 5  and A 9  would result in a roughly vertical field between those two electrodes. Similarly, applying the AC signal across electrodes A 2  and N 7  would generate diagonal field lines in one direction through the body part  1500 , and applying the AC signal across electrodes A 2  and B 7  would generate diagonal field lines in another direction through the body part. 
     Using a three-dimensional array of electrodes also makes it possible to energize multiple pairs of electrodes simultaneously to induce fields in the desired directions. For example, if suitable switching is provided so that electrodes A 2  through N 2  are all connected to one terminal of the generator, and so that electrodes A 7  through N 7  are all connected to the other terminal of the generator, the resulting field would be a sheet that extends in a front-to-back direction for the entire width W. After the front-to-back field is maintained for a suitable duration (e.g., one second), the switching system (not shown) is reconfigured to connect electrodes A 3  through N 3  to one terminal of the generator, and electrodes A 8  through N 8  to the other terminal of the generator. This results in a sheet-shaped field that is rotated about the Z axis by about 40° with respect to the initial field direction. After the field is maintained in this direction for a suitable duration (e.g., one second), the next set of electrodes is activated to rotate the field an additional 40° to its next position. This continues until the field returns to its initial position, at which point the whole process is repeated. 
     Optionally, the rotating sheet-shaped field may be added (sequentially in time) to the diagonal fields described above, to better target cells that are oriented along those diagonal axes. 
     Because the electric field is a vector, the signals may optionally be applied to combinations of electrodes simultaneously in order to form a desired resultant vector. For example, a field that is rotated about the X axis by 20° with respect to the initial position can be obtained by switching electrodes A 2  through N 2  and A 3  through N 3  all to one terminal of the generator, and switching electrodes A 7  through N 7  and A 8  through N 8  all to the other terminal of the generator. Applying the signals to other combinations of electrodes will result in fields in other directions, as will be appreciated by persons skilled in the relevant arts. If appropriate computer control of the voltages is implemented, the field&#39;s direction can even be swept through space in a continuous (i.e., smooth) manner, as opposed to the stepwise manner described above. 
       FIGS. 29A and 29B  depict the results of in vitro experiments that show how the killing power of the applied field against dividing cells is a function of the field strength. In the  FIG. 29A  experiment, B16F1 melanoma cells were subjected to a 100 kHz AC field at different field strengths, for a period of 24 hours at each strength. In the  FIG. 29B  experiment, F-98 glioma cells were subjected to a 200 kHz AC field at different field strengths, for a period of 24 hours at each strength. In both of these figures, the strength of the field (EF) is measured in Volts per cm. The magnitude of the killing effect is expressed in terms of TER, which is which is the ratio of the decrease in the growth rate of treated cells (GR T ) compared with the growth rate of control cells (GR C ). 
             TER   =         G   ⁢           ⁢     R   C       -     G   ⁢           ⁢     R   T           G   ⁢           ⁢     R   C               
The experimental results show that the inhibitory effect of the applied field on proliferation increases with intensity in both the melanoma and the glioma cells. Complete proliferation arrest (TER=1) is seen at 1.35 and 2.25 V/cm in melanoma and glioma cells, respectively.
 
       FIGS. 30A and 30B  depict the results of in vitro experiments that show how the killing power of the applied field is a function of the frequency of the field. In the experiments, B16F1 melanoma cells ( FIG. 30A ) and F-98 glioma cells ( FIG. 30B ) were subjected to fields with different frequencies, for a period of 24 hours at each frequency.  FIGS. 30A and 30B  show the change in the growth rate, normalized to the field intensity (TER/EF). Data are shown as mean+SE. In  FIG. 30A , a window effect is seen with maximal inhibition at 120 kHz in melanoma cells. In  FIG. 30B , two peaks are seen at 170 and 250 kHz. Thus, if only one frequency is available during an entire course of treatment, a field with a frequency of about 120 kHz would be appropriate for destroying melanoma cells, and a field with a frequency on the order of 200 kHz would be appropriate for destroying glioma cells. 
     Not all the cells of any given type will have the exact same size. Instead, the cells will have a distribution of sizes, with some cells being smaller and some cells being larger. It is believed that the best frequency for damaging a particular cell is related to the physical characteristics (e.g., the size) of that particular cell. Thus, to best damage a population of cells with a distribution of sizes, it can be advantageous to apply a distribution of different frequencies to the population, where the selection of frequencies is optimized based on the expected size distribution of the target cells. For example, the data on  FIG. 30B  indicates that using two frequencies of 170 kHz and 250 kHz to destroy a population of glioma cells would be more effective than using a single frequency of 200 kHz. 
     Note that the optimal field strengths and frequencies discussed herein were obtained based on in vitro experiments, and that the corresponding parameters for in vivo applications may be obtained by performing similar experiments in vivo. It is possible that relevant characteristics of the cell itself (such as size and/or shape) or interactions with the cell&#39;s surroundings may result in a different set of optimal frequencies and/or field strengths for in vivo applications. 
     When more than one frequency is used, the various frequencies may be applied sequentially in time. For example, in the case of glioma, field frequencies of 100, 150, 170, 200, 250, and 300 kHz may be applied during the first, second, third, fourth, fifth, and sixth minutes of treatment, respectively. That cycle of frequencies would then repeat during each successive six minutes of treatment. Alternatively, the frequency of the field may be swept in a stepless manner from 100 to 300 kHz. 
     Optionally, this frequency cycling may be combined with the directional cycling described above.  FIG. 31A  is an example of such a combination using three directions (D 1 , D 2 , and D 3 ) and three frequencies (F 1 , F 2 , and F 3 ). Of course, the same scheme can be extended to any other number of directions and/or frequencies.  FIG. 31B  is an example of such a combination using three directions (D 1 , D 2 , and D 3 ), sweeping the frequency from 100 kHz to 300 kHz. Note that the break in the time axis between t 1  and t 2  provides the needed time for the sweeping frequency to rise to just under 300 kHz. The frequency sweeping (or stepping) may be synchronized with directional changes, as shown in  FIG. 31A . Alternatively, the frequency sweeping (or stepping) may be asynchronous with respect to the directional changes, as shown in  FIG. 31B . 
     In an alternative embodiment, a signal that contains two or more frequencies components simultaneously (e.g., 170 kHz and 250 kHz) is applied to the electrodes to treat a populations of cells that have a distribution of sizes. The various signals will add by superposition to create a field that includes all of the applied frequency components. 
     Turning now to  FIG. 14  in which an article of clothing  500  according to one exemplary embodiment is illustrated. More specifically, the article of clothing  500  is in the form of a hat or cap or other type of clothing designed for placement on a head of a person. For purposes of illustration, a head  502  is shown with the hat  500  being placed thereon and against a skin surface  504  of the head  502 . An intra-cranial tumor or the like  510  is shown as being formed within the head  502  underneath the skin surface  504  thereof. The hat  500  is therefore intended for placement on the head  502  of a person who has a tumor  510  or the like. 
     Unlike the various embodiments illustrated in  FIGS. 1-13  where the insulated electrodes  230  are arranged in a more or less planar arrangement since they are placed either on a skin surface or embedded within the body underneath it, the insulated electrodes  230  in this embodiment are specifically contoured and arranged for a specific application. The treatment of intra-cranial tumors or other lesions or the like typically requires a treatment that is of a relatively long duration, e.g., days to weeks, and therefore, it is desirable to provide as much comfort as possible to the patient. The hat  500  is specifically designed to provide comfort during the lengthy treatment process while not jeopardizing the effectiveness of the treatment. 
     According to one exemplary embodiment, the hat  500  includes a predetermined number of insulated electrodes  230  that are preferably positioned so as to produce the optimal TC fields at the location of the tumor  510 . The lines of force of the TC field are generally indicated at  520 . As can be seen in  FIG. 14 , the tumor  510  is positioned within these lines of force  520 . As will be described in greater detail hereinafter, the insulated electrodes  230  are positioned within the hat  500  such that a portion or surface thereof is free to contact the skin surface  504  of the head  502 . In other words, when the patient wears the hat  500 , the insulated electrodes  230  are placed in contact with the skin surface  504  of the head  502  in positions that are selected so that the TC fields generated thereby are focused at the tumor  510  while leaving surrounding areas in low density. Typically, hair on the head  502  is shaved in selected areas to permit better contact between the insulated electrodes  230  and the skin surface  504 ; however, this is not critical. 
     The hat  500  preferably includes a mechanism  530  that applies a force to the insulated electrodes  230  so that they are pressed against the skin surface  502 . For example, the mechanism  530  can be of a biasing type that applies a biasing force to the insulated electrodes  230  to cause the insulated electrodes  230  to be directed outwardly away from the hat  500 . Thus, when the patient places the hat  500  on his/her head  502 , the insulated electrodes  230  are pressed against the skin surface  504  by the mechanism  530 . The mechanism  530  can slightly recoil to provide a comfortable fit between the insulated electrodes  230  and the head  502 . In one exemplary embodiment, the mechanism  530  is a spring based device that is disposed within the hat  500  and has one section that is coupled to and applies a force against the insulated electrodes  230 . 
     As with the prior embodiments, the insulated electrodes  230  are coupled to the generator  210  by means of conductors  220 . The generator  210  can be either disposed within the hat  500  itself so as to provide a compact, self-sufficient, independent system or the generator  210  can be disposed external to the hat  500  with the conductors  220  exiting the hat  500  through openings or the like and then running to the generator  210 . When the generator  210  is disposed external to the hat  500 , it will be appreciated that the generator  210  can be located in any number of different locations, some of which are in close proximity to the hat  500  itself, while others can be further away from the hat  500 . For example, the generator  210  can be disposed within a carrying bag or the like (e.g., a bag that extends around the patient&#39;s waist) which is worn by the patient or it can be strapped to an extremity or around the torso of the patient. The generator  210  can also be disposed in a protective case that is secured to or carried by another article of clothing that is worn by the patient. For example, the protective case can be inserted into a pocket of a sweater, etc.  FIG. 14  illustrates an embodiment where the generator  210  is incorporated directly into the hat  500 . 
     Turning now to  FIGS. 15 and 16 , in one exemplary embodiment, a number of insulated electrodes  230  along with the mechanism  530  are preferably formed as an independent unit, generally indicated at  540 , that can be inserted into the hat  500  and electrically connected to the generator (not shown) via the conductors (not shown). By providing these members in the form of an independent unit, the patient can easily insert and/or remove the units  540  from the hat  500  when they may need cleaning, servicing and/or replacement. 
     In this embodiment, the hat  500  is constructed to include select areas  550  that are formed in the hat  500  to receive and hold the units  540 . For example and as illustrated in  FIG. 15 , each area  550  is in the form of an opening (pore) that is formed within the hat  500 . The unit  540  has a body  542  and includes the mechanism  530  and one or more insulated electrodes  230 . The mechanism  530  is arranged within the unit  540  so that a portion thereof (e.g., one end thereof) is in contact with a face of each insulated electrode  230  such that the mechanism  530  applies a biasing force against the face of the insulated electrode  230 . Once the unit  540  is received within the opening  550 , it can be securely retained therein using any number of conventional techniques, including the use of an adhesive material or by using mechanical means. For example, the hat  500  can include pivotable clip members that pivot between an open position in which the opening  550  is free and a closed position in which the pivotable clip members engage portions (e.g., peripheral edges) of the insulated electrodes to retain and hold the insulated electrodes  230  in place. To remove the insulated electrodes  230 , the pivotable clip members are moved to the open position. In the embodiment illustrated in  FIG. 16 , the insulated electrodes  230  are retained within the openings  550  by an adhesive element  560  which in one embodiment is a two sided self-adhesive rim member that extends around the periphery of the insulated electrode  230 . In other words, a protective cover of one side of the adhesive rim  560  is removed and it is applied around the periphery of the exposed face of the insulated electrode  230 , thereby securely attaching the adhesive rim  560  to the hat  500  and then the other side of the adhesive rim  560  is removed for application to the skin surface  504  in desired locations for positioning and securing the insulated electrode  230  to the head  502  with the tumor being positioned relative thereto for optimization of the TC fields. Since one side of the adhesive rim  560  is in contact with and secured to the skin surface  540 , this is why it is desirable for the head  502  to be shaved so that the adhesive rim  560  can be placed flushly against the skin surface  540 . 
     The adhesive rim  560  is designed to securely attach the unit  540  within the opening  550  in a manner that permits the unit  540  to be easily removed from the hat  500  when necessary and then replaced with another unit  540  or with the same unit  540 . As previously mentioned, the unit  540  includes the biasing mechanism  530  for pressing the insulated electrode  230  against the skin surface  504  when the hat  500  is worn. The unit  540  can be constructed so that side opposite the insulated electrode  230  is a support surface formed of a rigid material, such as plastic, so that the biasing mechanism  530  (e.g., a spring) can be compressed therewith under the application of force and when the spring  530  is in a relaxed state, the spring  530  remains in contact with the support surface and the applies a biasing force at its other end against the insulated electrode  230 . The biasing mechanism  530  (e.g., spring) preferably has a contour corresponding to the skin surface  504  so that the insulated electrode  230  has a force applied thereto to permit the insulated electrode  230  to have a contour complementary to the skin surface  504 , thereby permitting the two to seat flushly against one another. While the mechanism  530  can be a spring, there are a number of other embodiments that can be used instead of a spring. For example, the mechanism  530  can be in the form of an elastic material, such as a foam rubber, a foam plastic, or a layer containing air bubbles, etc. 
     The unit  540  has an electric connector  570  that can be hooked up to a corresponding electric connector, such as a conductor  220 , that is disposed within the hat  500 . The conductor  220  connects at one end to the unit  540  and at the other end is connected to the generator  210 . The generator  210  can be incorporated directly into the hat  500  or the generator  210  can be positioned separately (remotely) on the patient or on a bedside support, etc. 
     As previously discussed, a coupling agent, such as a conductive gel, is preferably used to ensure that an effective conductive environment is provided between the insulated electrode  230  and the skin surface  504 . Suitable gel materials have been disclosed hereinbefore in the discussion of earlier embodiments. The coupling agent is disposed on the insulated electrode  230  and preferably, a uniform layer of the agent is provided along the surface of the electrode  230 . One of the reasons that the units  540  need replacement at periodic times is that the coupling agent needs to be replaced and/or replenished. In other words, after a predetermined time period or after a number of uses, the patient removes the units  540  so that the coupling agent can be applied again to the electrode  230 . 
       FIGS. 17 and 18  illustrate another article of clothing which has the insulated electrodes  230  incorporated as part thereof. More specifically, a bra or the like  700  is illustrated and includes a body that is formed of a traditional bra material, generally indicated at  705 , to provide shape, support, and comfort to the wearer. The bra  700  also includes a fabric support layer  710  on one side thereof. The support layer  710  is preferably formed of a suitable fabric material that is constructed to provide necessary and desired support to the bra  700 . 
     Similar to the other embodiments, the bra  700  includes one or more insulated electrodes  230  disposed within the bra material  705 . The one or more insulated electrodes are disposed along an inner surface of the bra  700  opposite the support  710  and are intended to be placed proximate to a tumor or the like that is located within one breast or in the immediately surrounding area. As with the previous embodiment, the insulated electrodes  230  in this embodiment are specifically constructed and configured for application to a breast or the immediate area. Thus, the insulated electrodes  230  used in this application do not have a planar surface construction but rather have an arcuate shape that is complementary to the general curvature found in a typical breast. 
     A lining  720  is disposed across the insulated electrodes  230  so as to assist in retaining the insulated electrodes in their desired locations along the inner surface for placement against the breast itself. The lining  720  can be formed of any number of thin materials that are comfortable to wear against one&#39;s skin and in one exemplary embodiment, the lining  720  is formed of a fabric material. 
     The bra  700  also preferably includes a biasing mechanism  800  as in some of the earlier embodiments. The biasing mechanism  800  is disposed within the bra material  705  and extends from the support  710  to the insulated electrode  230  and applies a biasing force to the insulated electrode  230  so that the electrode  230  is pressed against the breast. This ensures that the insulated electrode  230  remains in contact with the skin surface as opposed to lifting away from the skin surface, thereby creating a gap that results in a less effective treatment since the gap diminishes the efficiency of the TC fields. The biasing mechanism  800  can be in the form of a spring arrangement or it can be an elastic material that applies the desired biasing force to the insulated electrodes  230  so as to press the insulated electrodes  230  into the breast. In the relaxed position, the biasing mechanism  800  applies a force against the insulated electrodes  230  and when the patient places the bra  700  on their body, the insulated electrodes  230  are placed against the breast which itself applies a force that counters the biasing force, thereby resulting in the insulated electrodes  230  being pressed against the patient&#39;s breast. In the exemplary embodiment that is illustrated, the biasing mechanism  800  is in the form of springs that are disposed within the bra material  705 . 
     A conductive gel  810  can be provided on the insulated electrode  230  between the electrode and the lining  720 . The conductive gel layer  810  is formed of materials that have been previously described herein for performing the functions described above. 
     An electric connector  820  is provided as part of the insulated electrode  230  and electrically connects to the conductor  220  at one end thereof, with the other end of the conductor  220  being electrically connected to the generator  210 . In this embodiment, the conductor  220  runs within the bra material  705  to a location where an opening is formed in the bra  700 . The conductor  220  extends through this opening and is routed to the generator  210 , which in this embodiment is disposed in a location remote from the bra  700 . It will also be appreciated that the generator  210  can be disposed within the bra  700  itself in another embodiment. For example, the bra  700  can have a compartment formed therein which is configured to receive and hold the generator  210  in place as the patient wears the bra  700 . In this arrangement, the compartment can be covered with a releasable strap that can open and close to permit the generator  210  to be inserted therein or removed therefrom. The strap can be formed of the same material that is used to construct the bra  700  or it can be formed of some other type of material. The strap can be releasably attached to the surrounding bra body by fastening means, such as a hook and loop material, thereby permitting the patient to easily open the compartment by separating the hook and loop elements to gain access to the compartment for either inserting or removing the generator  210 . 
     The generator  210  also has a connector  211  for electrical connection to the conductor  220  and this permits the generator  210  to be electrically connected to the insulated electrodes  230 . 
     As with the other embodiments, the insulated electrodes  230  are arranged in the bra  700  to focus the electric field (TC fields) on the desired target (e.g., a tumor). It will be appreciated that the location of the insulated electrodes  230  within the bra  700  will vary depending upon the location of the tumor. In other words, after the tumor has been located, the physician will then devise an arrangement of insulated electrodes  230  and the bra  700  is constructed in view of this arrangement so as to optimize the effects of the TC fields on the target area (tumor). The number and position of the insulated electrodes  230  will therefore depend upon the precise location of the tumor or other target area that is being treated. Because the location of the insulated electrodes  230  on the bra  700  can vary depending upon the precise application, the exact size and shape of the insulated electrodes  230  can likewise vary. For example, if the insulated electrodes  230  are placed on the bottom section of the bra  700  as opposed to a more central location, the insulated electrodes  230  will have different shapes since the shape of the breast (as well as the bra) differs in these areas. 
       FIG. 19  illustrates yet another embodiment in which the insulated electrodes  230  are in the form of internal electrodes that are incorporated into in the form of a probe or catheter  600  that is configured to enter the body through a natural pathway, such as the urethra, vagina, etc. In this embodiment, the insulated electrodes  230  are disposed on an outer surface of the probe  600  and along a length thereof. The conductors  220  are electrically connected to the electrodes  230  and run within the body of the probe  600  to the generator  210  which can be disposed within the probe body or the generator  210  can be disposed independent of the probe  600  in a remote location, such as on the patient or at some other location close to the patient. 
     Alternatively, the probe  600  can be configured to penetrate the skin surface or other tissues to reach an internal target that lies within the body. For example, the probe  600  can penetrate the skin surface and then be positioned adjacent to or proximate to a tumor that is located within the body. 
     In these embodiments, the probe  600  is inserted through the natural pathway and then is positioned in a desired location so that the insulated electrodes  230  are disposed near the target area (i.e., the tumor). The generator  210  is then activated to cause the insulated electrodes  230  to generate the TC fields which are applied to the tumor for a predetermined length of time. It will be appreciated that the illustrated probe  600  is merely exemplary in nature and that the probe  600  can have other shapes and configurations so long as they can perform the intended function. Preferably, the conductors (e.g., wires) leading from the insulated electrodes  230  to the generator  210  are twisted or shielded so as not to generate a field along the shaft. 
     It will further be appreciated that the probes can contain only one insulated electrode while the other can be positioned on the body surface. This external electrode should be larger or consist of numerous electrodes so as to result in low lines of force-current density so as not to affect the untreated areas. In fact, the placing of electrodes should be designed to minimize the field at potentially sensitive areas. Optionally, the external electrodes may be held against the skin surface by a vacuum force (e.g., suction). 
       FIG. 20  illustrates yet another embodiment in which a high standing collar member  900  (or necklace type structure) can be used to treat thyroid, parathyroid, laryngeal lesions, etc.  FIG. 20  illustrates the collar member  900  in an unwrapped, substantially flat condition. In this embodiment, the insulated electrodes  230  are incorporated into a body  910  of the collar member  900  and are configured for placement against a neck area of the wearer. The insulated electrodes  230  are coupled to the generator  210  according to any of the manner described hereinbefore and it will be appreciated that the generator  210  can be disposed within the body  910  or it can be disposed in a location external to the body  910 . The collar body  910  can be formed of any number of materials that are traditionally used to form collars  900  that are disposed around a person&#39;s neck. As such, the collar  900  preferably includes a means  920  for adjusting the collar  900  relative to the neck. For example, complementary fasteners (hook and loop fasteners, buttons, etc.) can be disposed on ends of the collar  900  to permit adjustment of the collar diameter. 
     Thus, the construction of the present devices are particularly well suited for applications where the devices are incorporated into articles of clothing to permit the patient to easily wear a traditional article of clothing while at the same time the patient undergoes treatment. In other words, an extra level of comfort can be provided to the patient and the effectiveness of the treatment can be increased by incorporating some or all of the device components into the article of clothing. The precise article of clothing that the components are incorporated into will obviously vary depending upon the target area of the living tissue where tumor, lesion or the like exists. For example, if the target area is in the testicle area of a male patient, then an article of clothing in the form of a sock-like structure or wrap can be provided and is configured to be worn around the testicle area of the patient in such a manner that the insulated electrodes thereof are positioned relative to the tumor such that the TC fields are directed at the target tissue. The precise nature or form of the article of clothing can vary greatly since the device components can be incorporated into most types of articles of clothing and therefore, can be used to treat any number of different areas of the patient&#39;s body where a condition may be present. 
     Now turning to  FIGS. 21-22  in which another aspect of the present device is shown. In  FIG. 21 , a body  1000 , such as any number of parts of a human or animal body, is illustrated. As in the previous embodiments, two or more insulated electrodes  230  are disposed in proximity to the body  1000  for treatment of a tumor or the like (not shown) using TC fields, as has been previously described in great detail in the above discussion of other embodiments. The insulated electrode  230  has a conductive component and has external insulation  260  that surrounds the conductive component thereof. Each insulated electrode  230  is preferably connected to a generator (not shown) by the lead  220 . Between each insulated electrode  220  and the body  1000 , a conductive filler material (e.g., conductive gel member  270 ) is disposed. The insulated electrodes  230  are spaced apart from one another and when the generator is actuated, the insulated electrodes  230  generate the TC fields that have been previously described in great detail. The lines of the electric field (TC field) are generally illustrated at  1010 . As shown, the electric field lines  1010  extend between the insulated electrodes  230  and through the conductive gel member  270 . 
     Over time or as a result of some type of event, the external insulation  260  of the insulated electrode  230  can begin to breakdown at any given location thereof. For purpose of illustration only,  FIG. 22  illustrates that the external insulation  260  of one of the insulated electrodes  230  has experienced a breakdown  1020  at a face thereof which is adjacent the conductive gel member  270 . It will be appreciated that the breakdown  1020  of the external insulation  260  results in the formation of a strong current flow-current density at this point (i.e., at the breakdown  1020 ). The increased current density is depicted by the increased number of electric field lines  1010  and the relative positioning and distance between adjacent electric field lines  1010 . One of the side effects of the occurrence of breakdown  1020  is that current exists at this point which will generate heat and may burn the tissues/skin which have a resistance. In  FIG. 22 , an overheated area  1030  is illustrated and is a region or area of the tissues/skin where an increased current density exits due to the breakdown  1020  in the external insulation  260 . A patient can experience discomfort and pain in this area  1030  due to the strong current that exists in the area and the increased heat and possible burning sensation that exist in area  1030 . 
       FIG. 23  illustrates yet another embodiment in which a further application of the insulated electrodes  230  is shown. In this embodiment, the conductive gel member  270  that is disposed between the insulated electrode  230  and the body  1000  includes a conductor  1100  that is floating in that the gel material forming the member  270  completely surrounds the conductor  1100 . In one exemplary embodiment, the conductor  1100  is a thin metal sheet plate that is disposed within the conductor  1100 . As will be appreciated, if a conductor, such as the plate  1100 , is placed in a homogeneous electric field, normal to the lines of the electric field, the conductor  1100  practically has no effect on the field (except that the two opposing faces of the conductor  1100  are equipotential and the corresponding equipotentials are slightly shifted). Conversely, if the conductor  1100  is disposed parallel to the electric field, there is a significant distortion of the electric field. The area in the immediate proximity of the conductor  1100  is not equipotential, in contrast to the situation where there is no conductor  1100  present. When the conductor  1100  is disposed within the gel member  270 , the conductor  1100  will typically not effect the electric field (TC field) for the reasons discussed above, namely that the conductor  1100  is normal to the lines of the electric field. 
     If there is a breakdown of the external insulation  260  of the insulated electrode  230 , there is a strong current flow-current density at the point of breakdown as previously discussed; however, the presence of the conductor  1100  causes the current to spread throughout the conductor  1100  and then exit from the whole surface of the conductor  1100  so that the current reaches the body  1000  with a current density that is neither high nor low. Thus, the current that reaches the skin will not cause discomfort to the patient even when there has been a breakdown in the insulation  260  of the insulated electrode  230 . It is important that the conductor  1100  is not grounded as this would cause it to abolish the electric field beyond it. Thus, the conductor  1100  is “floating” within the gel member  270 . 
     If the conductor  1100  is introduced into the body tissues  1000  and is not disposed parallel to the electric field, the conductor  1100  will cause distortion of the electric field. The distortion can cause spreading of the lines of force (low field density-intensity) or concentration of the lines of field (higher density) of the electric field, according to the particular geometries of the insert and its surroundings, and thus, the conductor  1100  can exhibit, for example, a screening effect. Thus, for example, if the conductor  1100  completely encircles an organ  1101 , the electric field in the organ itself will be zero since this type of arrangement is a Faraday cage. However, because it is impractical for a conductor to be disposed completely around an organ, a conductive net or similar structure can be used to cover, completely or partially, the organ, thereby resulting in the electric field in the organ itself being zero or about zero. For example, a net can be made of a number of conductive wires that are arranged relative to one another to form the net or a set of wires can be arranged to substantially encircle or otherwise cover the organ  1101 . Conversely, an organ  1103  to be treated (the target organ) is not covered with a member having a Faraday cage effect but rather is disposed in the electric field  1010  (TC fields). 
       FIG. 24  illustrates an embodiment where the conductor  1100  is disposed within the body (i.e., under the skin) and it is located near a target (e.g., a target organ). By placing the conductor  1100  near the target, high field density (of the TC fields) is realized at the target. At the same time, another nearby organ can be protected by disposing the above described protective conductive net or the like around this nearby organ so as to protect this organ from the fields. By positioning the conductor  1100  in close proximity to the target, a high field density condition can be provided near or at the target. In other words, the conductor  1100  permits the TC fields to be focused at a particular area (i.e., a target). 
     It will also be appreciated that in the embodiment of  FIG. 24 , the gel members  260  can each include a conductor as described with reference to  FIG. 23 . In such an arrangement, the conductor in the gel member  260  protects the skin surface (tissues) from any side effects that may be realized if a breakdown in the insulation of the insulated electrode  230  occurs. At the same time, the conductor  1100  creates a high field density near the target. 
     There are a number of different ways to tailor the field density of the electric field by constructing the electrodes differently and/or by strategically placing the electrodes relative to one another. For example, in  FIG. 25 , a first insulated electrode  1200  and a second insulated electrode  1210  are provided and are disposed about a body  1300 . Each insulated electrode includes a conductor that is preferably surrounded by an insulating material, thus the term “insulated electrode”. Between each of the first and second electrodes  1200 ,  1210  and the body  1300 , the conductive gel member  270  is provided. Electric field lines are generally indicated at  1220  for this type of arrangement. In this embodiment, the first insulated electrode  1200  has dimensions that are significantly greater than the dimensions of the second insulated electrode  1210  (the conductive gel member for the second insulated electrode  1210  will likewise be smaller). 
     By varying the dimensions of the insulated electrodes, the pattern of the electric field lines  1220  is varied. More specifically, the electric field tapers inwardly toward the second insulated electrode  1210  due to the smaller dimensions of the second insulated electrode  1210 . An area of high field density, generally indicated at  1230 , forms near the interface between the gel member  270  associated with the second insulated electrode  1210  and the skin surface. The various components of the system are manipulated so that the tumor within the skin or on the skin is within this high field density so that the area to be treated (the target) is exposed to electric field lines of a higher field density. 
       FIG. 26  also illustrates a tapering TC field when a conductor  1400  (e.g., a conductive plate) is disposed in each of the conductive gel members  270 . In this embodiment, the size of the gel members  270  and the size of the conductors  1400  are the same or about the same despite the differences in the sizes of the insulated electrodes  1200 ,  1210 . The conductors  1400  again can be characterized as “floating plates” since each conductor  1400  is surrounded by the material that forms the gel member  270 . As shown in  FIG. 26 , the placement of one conductor  1400  near the insulated electrode  1210  that is smaller than the other insulated electrode  1200  and is also smaller than the conductor  1400  itself and the other insulated electrode  1200  is disposed at a distance therefrom, the one conductor  1400  causes a decrease in the field density in the tissues disposed between the one conductor  1400  and the other insulated electrode  1200 . The decrease in the field density is generally indicated at  1410 . At the same time, a very inhomogeneous tapering field, generally indicated at  1420 , changing from very low density to very high density is formed between the one conductor  1400  and the insulated electrode  1210 . One benefit of this exemplary configuration is that it permits the size of the insulated electrode to be reduced without causing an increase in the nearby field density. This can be important since electrodes that having very high dielectric constant insulation can be very expensive. Some insulated electrodes, for example, can cost $500.00 or more; and further, the price is sensitive to the particular area of treatment. Thus, a reduction in the size of the insulated electrodes directly leads to a reduction in cost. 
     As used herein, the term “tumor” refers to a malignant tissue comprising transformed cells that grow uncontrollably. Tumors include leukemias, lymphomas, myelomas, plasmacytomas, and the like; and solid tumors. Examples of solid tumors that can be treated according to the invention include sarcomas and carcinomas such as, but not limited to: fibrosarcoma, myxosarcoma, liposarcoma, chondrosarcoma, osteogenic sarcoma, chordoma, angiosarcoma, endotheliosarcoma, lymphangiosarcoma, lymphangioendotheliosarcoma, synovioma, mesothelioma, Ewing&#39;s tumor, leiomyosarcoma, rhabdomyosarcoma, colon carcinoma, pancreatic cancer, breast cancer, ovarian cancer, prostate cancer, squamous cell carcinoma, basal cell carcinoma, adenocarcinoma, sweat gland carcinoma, sebaceous gland carcinoma, papillary carcinoma, papillary adenocarcinomas, cystadenocarcinoma, medullary carcinoma, bronchogenic carcinoma, renal cell carcinoma, hepatoma, bile duct carcinoma, choriocarcinoma, seminoma, embryonal carcinoma, Wilms&#39; tumor, cervical cancer, testicular tumor, lung carcinoma, small cell lung carcinoma, bladder carcinoma, epithelial carcinoma, glioma, astrocytoma, medulloblastoma, craniopharyngioma, ependymoma, pinealoma, hemangioblastoma, acoustic neuroma, oligodendroglioma, meningioma, melanoma, neuroblastoma, and retinoblastoma. Because each of these tumors undergoes rapid growth, any one can be treated in accordance with the invention. The invention is particularly advantageous for treating brain tumors, which are difficult to treat with surgery and radiation, and often inaccessible to chemotherapy or gene therapies. In addition, the present invention is suitable for use in treating skin and breast tumors because of the ease of localized treatment provided by the present invention. 
     In addition, the present invention can control uncontrolled growth associated with non-malignant or pre-malignant conditions, and other disorders involving inappropriate cell or tissue growth by application of an electric field in accordance with the invention to the tissue undergoing inappropriate growth. For example, it is contemplated that the invention is useful for the treatment of arteriovenous (AV) malformations, particularly in intracranial sites. The invention may also be used to treat psoriasis, a dermatologic condition that is characterized by inflammation and vascular proliferation; and benign prostatic hypertrophy, a condition associated with inflammation and possibly vascular proliferation. Treatment of other hyperproliferative disorders is also contemplated. 
     Furthermore, undesirable fibroblast and endothelial cell proliferation associated with wound healing, leading to scar and keloid formation after surgery or injury, and restenosis after angioplasty or placement of coronary stents can be inhibited by application of an electric field in accordance with the present invention. The non-invasive nature of this invention makes it particularly desirable for these types of conditions, particularly to prevent development of internal scars and adhesions, or to inhibit restenosis of coronary, carotid, and other important arteries. 
     In addition to treating tumors that have already been detected, the above-described embodiments may also be used prophylactically to prevent tumors from ever reaching a detectable size in the first place. For example, the bra embodiment described above in connection with  FIGS. 17 and 18  may be worn by a woman for an 8 hour session every day for a week, with the week-long course of treatment being repeated every few months to kill any cells that have become cancerous and started to proliferate. This mode of usage is particularly appropriate for people who are at high risk for a particular type of cancer (e.g., women with a strong history of breast cancer in their families, or people who have survived a bout of cancer and are at risk of a relapse). The course of prophylactic treatment may be tailored based on the type of cancer being targeted and/or to suit the convenience of the patient. For example, undergoing a four 16 hour sessions during the week of treatment may be more convenient for some patients than seven 8 hour session, and may be equally effective. 
     Example 2 
     Experiments were also performed on two different types of bacteria— Pseudomonas aeruginosa  strain PAO1 and  Staphylococcus aureus  strain SH1000. All strains were grown in LB media (1.0% Bacto tryptone, 0.5% Yeast extract, 1% NaCl). Broth cultures of freshly plated bacteria strains were grown in 3 ml of liquid medium at 37° C. for 15 hours in an orbital shaker (220 RPM) and diluted in fresh LB broth to a predetermined absorbance at 595 nm which yielded the desired CFU per ml. 
       FIG. 32A  depicts the construction of the electrodes  1610  used in the experiment. Each electrode is 15 mm long and 5 mm high. It include an electrical conductor  1611  with its outer face coated with a thin layer of lead magnesium niobate-lead titanate (PMN-PT) ceramic insulation  1612 , which has a high dielectric constant (∈&gt;5000) such that their capacitance was about 10 nF each. The rear of the conductor  1611  was insulated using a 5 mm layer  1614  of 353ND medical grade epoxy (Epoxy Technology, Billerica, Mass., USA) and a wire  1613  is connected to the conductor  1611 . Of course, it may be appropriate to vary the dimensions of the electrodes depending on the intended application. 
       FIG. 32B  depicts a test chamber that includes four electrodes  1610 , arranged in pairs and positioned in a 50 mm Petri dish  1626 . The electrodes were held in place by a polycarbonate holder  1624 . Electric fields were generated in the test chamber by applying an AC voltage across one pair of opposing electrodes, then applying an AC voltage across the other pair of opposing electrodes, in an alternating sequence to produce electric fields in the medium that are oriented at 90° with respect to each other. The electrodes were placed 23 mm apart. The electrodes were completely insulated from the medium in the Petri dish by the ceramic insulation  1614  on the face of the electrode  1610 , so the field is capacitively coupled through the layer  1614  into the target region. 
       FIG. 32C  depicts a setup that was used to induce fields in the test chamber  1620 . The output of a sinewave generator  1632  (Model 662, OR-X, Israel) is routed to an RF amplifier  1634  (75A250, AR worldwide, Souderton, Pa., USA), and the output of the RF amplifier  1634  is routed to a field direction switching relay  1636  that either imposes the amplified sine wave between the upper and lower electrodes or between the right and left electrodes. The switching relay is configured to switch back and forth between those two states periodically, thereby switching the direction of the field at the desired interval. The entire field generating system was placed inside a Faraday cage  1644  in order to meet the guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields of the International Non-Ionizing Radiation Committee (INIRC). 
     Temperature was measured continuously using insulated T type thermocouple (Omega, Stamford, Conn.) with its tip positioned at the center of the chamber  1620 . The thermocouples were connected to a TC-08 Thermocouple Data Logger (Pico Technologies, UK) the output of which was connected to computer  1630 . When high field frequencies (30-50 MHz) were used, the fields interfered with the temperatures measurements. So to measure the temperature, the field was temporarily turned off for two seconds during each temperature measurement. 
     As electric fields are associated with heat production, the chamber temperature was held at the desired value by computer feedback control of the amplitude of the waveform at the input of the power amplifier. The electric field intensities in the culture medium were measured using a shielded coaxial probe having two exposed tips fixed at a distance of 1 cm. The probe was connected, through a coaxial cable, to a 190B floating scope meter (Fluke, The Netherlands). Field intensities were measured at the end of each treatment by dipping the probe in the culture media, such that the two measuring points were in parallel with the lines of the electric field. Field intensities are expressed as peak-to-peak voltage per centimeter distance (V/cm). 
     Overnight bacterial cultures were diluted in fresh LB broth to an OD that corresponds to bacterial counts of 1×10 7  Colony Forming Units (CFU)/ml. Petri plates containing the electric fields chamber  1620  were filled with 7 ml of the diluted cultures, and placed inside a pre-cooled incubator (FOC 225I, Velp Scientifica). Fields were applied for 2 hours for  S. aureus  and 2.5 hours for  P. aeruginosa  with the field direction alternating every 300 ms (i.e., 300 ms in one direction followed by 300 ms in the other direction). Preliminary experiments indicated that these durations were sufficient to allow for approximately one order of magnitude growth of the control (unexposed to electric fields) group. 
     Temperature within the chamber  1620  was controlled by modifying the field strength within a predetermined range since the field causes heating. The electric fields chamber temperature reached 37±0.2° C. within the first 5 minutes of the experiment in both the treated group and in the control group. (The control bacteria groups were not exposed to the electric fields, but were temperature-controlled to match the temperature in the test groups.) 
     At the end of treatment, the cultures were stirred several times by up and down pipetting. Four aliquots of 250 μl were dispensed into a 96 MicroWells plate (Nunclon™ Δ, Nunc, Denmark) and the OD was determined spectrophotometrically with a microplate reader (Infinite 200, Tecan, Austria) at 750 nm. The optical densities (ODs) of the blanks, which consisted of uninoculated LB, were subtracted from the ODs of the inoculated plates. The percentage of growth for each well was calculated by dividing the OD of the wells by that of the control: (OD 750mm  of treated wells/ OD750nm  of the control well)×100. 
     The effect of the electric fields&#39; frequency was tested by applying fields between 100 kHz and 50 MHz. The results, depicted in  FIGS. 33A and 33B , show that 2-4V/cm electric fields inhibit the growth of the  S. aureus  (after 2 hours treatment) and  P. aeruginosa  (after 2.5 hours treatment), respectively. The calculated effect, expressed in % (using the scale on the left side of the graphs), is based on OD measurements. Averages of at least two independent experiments±standard errors are presented. The corresponding average field intensities±standard errors are indicated by the solid line (using the scale on the right side of the graphs). 
     The results show that the growth inhibition is frequency dependent, having a maximum growth inhibition at 10 MHz fields for both  S. aureus  and  P. aeruginosa . Note that as the electric fields generating system was designed to maintain a constant temperature in the chamber by adjustment of the field intensity, and therefore the fields&#39; intensities vary between the different frequency tests. The field intensity variations in the tests was limited to a range of ±1 V/cm. The results presented are means±standard errors (SE) of at least 2 independent experiments, each consisting of 6-8 plates. Higher field frequencies were not tested due to equipment limitations. 
     The effect of the electric fields&#39; intensity was tested by applying 10 MHz fields to  S. aureus  at different intensities for 6 hours. The relative growth, based on CFU counts, is expressed as a percentage of the heat control±standard errors. The initial  S. aureus  concentration in this set of experiments was 0.5-1×10 5  CFU/ml. As seen in  FIG. 34 , the growth inhibition is field intensity dependent reaches a plateau of just above an 80% inhibition, at field intensities of about 2-2.5 V/cm. Note that although this intensity worked best for treating  S. aureus  at 10 MHz, field strengths between 0.5 and 10 V/cm may be used. 
     The effect of the switching rate of the electric fields between the two perpendicular directions was tested by applying 10 MHz, 3.5 V/cm fields and varying the switching rate (i.e., the time the field was applied in each direction). The dependency of the fields&#39; inhibitory effect is illustrated in  FIGS. 35A and 35B  for  S. aureus  and  P. aeruginosa , respectively (after treatment for 2 hours for  S. aureus  or 2.5 hours for  P. aeruginosa ). The results indicate that for  S. aureus , durations of 100 mSec, 1 Sec, and 30 Sec resulted in a significantly higher inhibition than the other durations tested. In the case of  P. aeruginosa  the maximal inhibition was observed when the duration of each field direction was 30 Sec. 
     The combined effect of the electric fields and antibiotics was also tested. Chloramphenicol was obtained as powder and dissolved in EtOH (99%, Frutarom). All the stock solutions were filter sterilized and held at −20° C. until use. Serial twofold dilutions of each antibiotic agent were prepared following NCCLS guidelines. The MIC of an antibiotic was defined as the lowest concentration that completely inhibited growth of the organism, as determined by the unaided eye. These results were in agreement with over 95% inhibition compared with that of drug-free wells, as determined using the microplate reader at 750 nm. The MIC of electric fields was defined as the lowest intensity that inhibits growth by 80% or more compared with control, as determined using the microplate reader. 
     Drug interactions with the electric fields were assessed according to the checkerboard method, with the following modifications:  S. aureus  inocula were diluted in LB medium containing the antibiotic to final concentration of 0.5 to 1.0×10 5  CFU/ml. The final concentrations of the chloramphenicol ranged from 0.125 to 16 μg/ml. Petri dishes containing the electric fields chamber were filled with 7 ml of the diluted cultures, and placed inside a pre cooled incubator. Fields were applied for 6 hours with the field direction alternating every 300 ms and the field intensities were varied by changing the incubator ambient temperature. Thus, lower ambient temperatures allowed for higher field intensities while maintaining the proper culture temperature of 37° C. Control plates containing the same electric fields chambers were placed in a pre-warmed incubator set at 37° C. At the end of the treatment, the cultures were stirred by pipetting the plate content up and down. Quadruplicates of 250 μl each were transferred to a 96 MicroWells plate (Nunc) and the OD was determined using Tecan microplate reader. Cultures were subjected to serial 10-fold dilution (up to 1/10,000) by adding 20 μl of sample to 180 μl of saline solution (0.85% NaCl), from which 80 μl aliquots were plated on LB agar plates (1.5% agar, 1.0% Bacto tryptone, 1% NaCl, 0.5% Yeast extract). CFU counts were performed after overnight incubation at 37° C. The results were grouped and the effect was calculated by dividing the OD or CFU of the experiments plates with those of the control plates. 
     To evaluate the effect of the combinations, the fractional inhibitory concentration (FIC) was calculated for the electric fields and for each antibiotic. The following formulas were used to calculate the FIC index:
 
FIC of electric fields=MIC of electric fields in combination/MIC of electric fields alone,
 
FIC of drug  B =MIC of drug  B  in combination/MIC of drug  B  alone,
 
and
 
FIC index=FIC of electric fields+FIC of drug  B.  
 
Synergy was defined as an FIC index of ≦0.5. Indifference was defined as an FIC index of &gt;0.5 but of ≦4. Antagonism was defined as an FIC index of &gt;4.
 
     The MIC of chloramphenicol against  S. aureus  was found to be 4 μg/ml, similar to the concentrations reported in the literature. The combined effect of electric fields and chloramphenicol on the growth of  S. aureus  is given in Table 1. The results demonstrate that there is an additive effect between electric fields and chloramphenicol. As seen, in the presence of 4 V/cm 10 MHz electric fields applied for 6 hours, with the field direction alternating every 300 ms, much lower concentrations of chloramphenicol (1 μg/ml) are sufficient to produce complete inhibition of the growth of  S. aureus . The FIC index was found to be 0.625, indicating that there is an additive effect for the combined exposure to electric fields and chloramphenicol. Note that these calculations are based on OD measurements. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 0 V/cm 
                 0.5-2.0 V/cm 
                 2.0-2.5 V/cm 
                 3.5-4.5 V/cm 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 0 μg/ml 
                 100% 
                 62% 
                 32% 
                 19% 
               
               
                 0.25 μg/ml   
                 66% 
                 39% 
                 51% 
                 13% 
               
               
                 0.5 μg/ml   
                 45% 
                 16% 
                 20% 
                 21% 
               
               
                 1 μg/ml 
                 30% 
                 26% 
                 6% 
                 2% 
               
               
                 4 μg/ml 
                 7% 
                 13% 
                 2% 
                 0% 
               
               
                   
               
             
          
         
       
     
     Note that while the examples above used an antibiotic, other therapeutic agents may be substituted for antibiotics in appropriate situations. 
     Tests were also performed to determine whether repeated exposure of  P. aeruginosa  to electric fields could select for bacteria that are resistant to the fields. For this test, overnight bacterial cultures were diluted in fresh LB broth to an OD that corresponds to bacterial counts of 1×10 6  CFU/ml. Bacteria were exposed to 10 MHz electric fields of approximately 5 V/cm for 6 hours as described above, with the field direction alternating every 300 ms. Control bacteria groups, placed in inactivated electric fields chambers, were positioned in a pre-warmed incubator. The electric fields&#39; effect was determined based on the OD measurements. After the initial electric fields inhibition experiment, the fields&#39; effect was determined anew daily, for four passages as follows: samples from the plates treated with electric fields were pooled and used again for electric fields effect determination in the subsequent generation. In parallel, the fields&#39; effect evolution during these subcultures was compared concomitantly with each new generation, using bacteria harvested from control wells (wells cultured in the pre-warmed incubator). The relative effect was calculated for each experiment from the ratio of inhibition obtained for a given subculture to that obtained for first-time exposure. 
     The results of this repeated exposure test of  P. aeruginosa  to electric fields are presented in  FIG. 36 . As demonstrated, four passages of exposure to electric fields did not result in development of resistance, and the inhibition percentage remained around 70% in each iteration. 
     Numerical calculations, based on finite element mesh, were used in order to calculate the electric field distribution inside dividing  P. aeruginosa  and  S. aureus , and the following geometries and parameters were used for the calculations:  P. aeruginosa  was assumed to be an ellipse with a large radius of 2.0 μm and a small radius of 0.6 μm having two membranes (external and internal) of 8 nm thickness. The two membranes were assumed to be separated by a periplasmic space of 50 nm. The dividing bacterium furrow diameter was assumed to be 0.2 μm and the applied external field was 20 V/cm. Since no published data on the electric properties of  P. aeruginosa  was found, the following data for  E. coli  was substituted in the calculations: inner membrane conductivity−1 μS/m, outer membrane conductivity−3 mS/m, medium conductivity−0.5 S/m, cytoplasm conductivity−0.5 S/m and the conductivity of the periplasmic space−50 mS/m. 
       S. aureus  was assumed to be a sphere with a radius of 0.6 μm and a membrane thickness of 8 nm. The bacterial cell wall thickness was assumed to be 20 nm, and the dividing bacterium furrow diameter was assumed to be 0.2 μm. The applied external field was 20 V/cm. In the simulation the membrane conductivity was assumed to be 1 μS/m, and the cell wall conductivity 10 mS/m. The conductivity of the medium was 0.5 S/m and the conductivity of the cytoplasm was assumed to be 0.8 S/m. 
     The electric field distribution in and around  P. aeruginosa  and  S. aureus  was calculated using finite element mesh method, and the results are depicted in  FIGS. 37 and 38 . In the simulation ( FIG. 37 ) it is seen that the inside dividing rod-like bacteria, close to the furrow, the electric field is strongest and is non uniform. This non uniformity generates dielectrophoresis forces. When the field intensity is 20 V/cm, the magnitude of the Force acting on a dipole of 3000 debyes inside dividing bacteria as a function of field frequency is depicted in  FIG. 38A  for  P. aeruginosa , which peaks at about 2 MHz, and depicted in  FIG. 38B  for  S. aureus , which peaks at about 7 MHz. 
     In vivo tests were also performed to test the ability of electric fields to inhibit the growth of bacterial pathogen in vivo. 2×10 8    S. aureus  bacteria were injected S.C. into the dorsum of 8 weeks old female ICR mice. Mice in which abscess was developed in the site of injection within 24 hours were anesthetized and 4 electrodes were placed on their back. The electrodes were similar to those described above but also contained a thermistor positioned inside the electrodes near the electrode surface. The electrodes were arranged in two electrode pairs positioned perpendicular to each other so as to generate electric fields in two different directions, spaced 90° apart, and the distance between each electrode within any given pair was 2 cm. Note, however, that alternative electrode configurations may be used, e.g., as discussed above in connection with  FIGS. 27 and 28 . 
     Mice in the control group were identical to those in the electric fields group, but carrying heating electrodes. Mice were held in an IVC system (Techniplast, Italy) whose cages were modified in order to allow for electric fields application inside the cage. 10 MHz electric fields were applied for 48 hours at a nominal field strength of about 5 V/cm, with the field direction alternating every 300 ms, and the temperature at the electrode surface was monitored continuously. The electrodes temperature was held at the desired value by computer feedback control of the amplitude of the waveform at the input of the power amplifier. Sham control electrodes were heated to the same temperature as the electric fields electrodes. No adverse side effects were observed. After 48 hours the mice were anesthetized, sacrificed, and the electrodes were removed. A 2×2 cm square of the skin surrounding the abscess was harvested, weighed and homogenized. The homogenate was serially diluted and plated in triplicates for CFU determination. The initial  S. aureus  concentration in these experiments was 2×10 7  CFU/ml. The results of this experiment are depicted in  FIG. 39 , which indicate that the electric fields can inhibit bacterial growth in mature abscesses. 
     Depending on the location of the target region within the body, the electrodes may be either placed on the patient&#39;s body or implanted in the patient&#39;s body. For example, in a patient with an infected cyst, the electrodes could be implanted near the cyst. Note that the Megahertz-range frequencies that were found to be effective against bacteria have virtually no impact on eukaryotic cells, so specificity is excellent, and adverse side effects are not a major concern. Optionally, different frequencies may be applied to the target region, either simultaneously or sequentially, to target one or more types of bacteria that may be present, as discussed above in connection with the other embodiments. The method may also be used in vitro, e.g., to combat bacteria in food, on media, cell cultures, etc. 
     Example 3 
     In vivo experiments were also performed on  Pseudomonas aeruginosa  strain PAO1 in lungs of infected mice. For this example, bacteria were grown in LB media (1.0% Bacto tryptone, 0.5% Yeast extract, 1.0% NaCl (Frutarom, Haifa, Israel). Broth cultures of freshly plated bacteria were grown in 250 ml of liquid medium at 37° C. in an orbital shaker at 220 RPM (New Brunswick Scientific, N.J., USA) up to logarithmic phase, centrifuged and resuspended in saline containing 15% glycerol. Stocks were divided into aliquots of 50 μl each containing 2.17×10 7  Colony Forming Units (CFU)/ml and kept at −70° C. until use. 
     Experiments were conducted on 7- to 8-week-old (body weight 26-35 g) ICR female mice obtained from Harlan laboratories (Israel). Mice were housed under standard conditions of light and temperature, and were fed standard laboratory chow and water ad libitum. Electric fields were generated by 2 pairs of parallel metal electrodes, 15 mm-long; 3 mm-high. The front of the electrodes was completely insulated from the medium by a ceramic [(lead magnesium niobate-lead titanate (PMN-PT) (EDO, New York, N.Y.)] having a very high dielectric constant (∈&gt;5000) such that their capacitance was about 10 nF each. The back of the electrodes was insulated by a 2.5 mm thick layer of 353ND medical grade epoxy (Epoxy Technology, Billerica, Mass., USA). Each electrode contained a thermistor placed within the epoxy directly on top of the ceramic in order to allow for constant monitoring of the electrodes&#39; temperature. 
     The four insulated electrodes were attached to the skin using hydrogel after mouse depilation. The electrodes were wrapped with leucoplast and electrodes wires were connected to the Electric fields generating system or to the sham control system. The four electrodes were functionally divided into two pairs, identified by the red or blue wires. The electrode pairs were placed so as to create two perpendicular field directions at the center of the animal body. 
     In order to allow for electric fields generation in mice, while maintaining the strict isolation required when working with animal infected with pathogens, the mice were held in an Individually Ventilated Cage system (IVC) (TouchSLIM™, Techniplast, Italy) that was modified as follows: Each cage (GR900, Techniplast, Italy) was split by a polycarbonate partition into two units, each housing one mouse. Each mouse was treated with a separate field generator consisting of an RF amplifier (75A250, AR worldwide, Souderton, Pa., USA) activated by a sine-wave generator (Model 662, OR-X, Israel). Six hermetically sealed, shielded electric connection sockets (SM3416 BNC, S.M. electronics, TX, USA) were positioned at the front panel of the cage. Each socket allowed for the connection (by means of coax cables) of a connection box placed inside the cage to an exterior device; an RF amplifier or a temperature measuring system. The connection box served for transferring the electric currents to the mice electrodes, and the mice temperature readout to the computer. 
     The entire IVC system, together with the electric fields generating system, were placed inside a Faraday cage in order to meet the guidelines for limiting personnel exposure to time-varying electric, magnetic, and electromagnetic (International Non-Ionizing Radiation Committee—INIRC). To avoid field interference with temperature measurements, temperatures were measured periodically while the field was briefly turned off. 
     As electric fields are associated with heat production, the electrodes surface temperature was kept constant at the desired level by computer feedback control of the field amplitude. The current source output was switched, every 300 ms, between the two electrodes pairs. This interval was found previously to be effective against  P. aeruginosa  while preventing the formation of temperature gradients that could affect bacterial growth rate (Giladi et al., 2008). The lung temperature was measured periodically by inserting a thermocouple connected to a temperature data logger (TC08 USB) (Pico technology, Cambridgeshire, UK) into the mouse trachea. 
     Two control groups were set in each experiment: sham heat control, and non treated control (referred to as “Control”). Control electrodes of identical size and shape to the electric fields electrodes, were placed on mice of the two control groups. The Sham heat electrodes produced equal temperature changes to those produced by the field electrodes by means of a heating resistor incorporated within them, and the sham heat electrodes were placed in the same positions as the real electrodes. Except for the differences in the electrodes, the control mice and the sham heat treated mice were held in conditions identical to those of the electric fields treated mice. 
     The electric field intensity was measured using a shielded coaxial cable and probe having two exposed tips positioned at a distance of 1 cm from each other. The probe was connected to a floating input oscilloscope (190B Fluke, The Netherlands). Field intensities within lungs were measured by performing a 5 mm long incision in the thoracic skin of an anesthetized mouse and inserting the measurement probe at an intercostal space to a depth of 5 mm into the thorax. The probe was oriented such that the line connecting the two measuring points was parallel to the lines of the electric field. Field intensities are expressed as peak-to-peak volts per centimeter distance (V/cm). 
     Mice were rendered neutropenic (neutrophil counts, &lt;100/mm 3 ), as described in Andes and Craig (1998), by two intraperitoneal injections of cyclophosphamide; four days before infection (150 mg/kg of body weight) and an additional injection one day before infection (100 mg/kg of body weight). The pulmonary infection model of Takeda et al., (2006) was used with minor modifications: Anesthetized ICR mice were challenged intra-nasally with 20 μL of saline containing various concentrations (10 4 -10 7  CFU/ml) of  P. aeruginosa  strain PAO1. On the day of infection, immediately before use, frozen bacterial cultures were thawed and diluted in saline to the desired concentration. Anesthetized mice were challenged intra-nasally with the bacterial suspension. Mice were sacrificed at 0, 3, 6, 9, 24, and 48 hours after infection in order to determine CFU counts in their lungs. After skin disinfection with 70% alcohol, lungs from sacrificed mice were removed aseptically, photographed, weighted and their CFU content was determined. 
     Application of electric fields to the mouse torso was carried out as follows: 4 days before infection, the torso of anesthetized mice was shaved with electrical clippers and depilated using cold wax. Electric fields treatment was applied through four insulated electrodes placed around the mouse torso so as to generate fields of two perpendicular directions. Mice were placed inside the IVC cages and the electrodes were connected to the connection box. Application of electric fields began 3 hours after infection and was maintained for 48 h with two brief stops daily for monitoring the physical condition of the mice. After 48 h of treatment, the mice were sacrificed and bacterial numbers in lung were determined. 
     The combined effect of electric fields and antibiotics was tested using Ceftazidime, an agent recommended by the infectious disease society of America for the treatment of hospital acquired pneumonia. 
     Experiments were conducted as described above for electric fields treatment of  P. aeruginosa  pulmonary infection with the following modifications: mice were challenged intra-nasally with a predetermined bacterial titer. Ceftazidime (5 mg/kg body weight) was administered intra-peritoneally twice daily for 48 hours starting 3 h after infection. Antibiotic administration was stopped at least 12 h before experiment termination. 
     Cold sterile saline was added to each lung sample tube, saline:tissue weight ratio being 10:1. Tubes were placed in an ice bath and the suspensions were homogenized using Omni tissue homogenizer (Omni, Ga., USA) with Omni disaggregation tips. Appropriate suspension dilutions were plated on LB agar plates and kept at 37° C. for 24 h. Bacterial counts were expressed as number of  P. aeruginosa  CFU per lung. 
     Bacterial growth in the lungs of each mouse was expressed using the following formula: log(CFU T48 /CFU T0 ), where CFU T48  is the CFU counts in the mouse lungs at the end of treatment and CFU T0  is the initial number of bacteria used for inoculation in the specific experiment. The results of all mice that received the same treatment were pooled and the average bacterial growth was calculated for each group. T test with two tailed distribution and equal variance was used to compare the mean values. 
     Lungs were first inflated with formaldehyde to their normal volume and then underwent fixation. The specimens were processed and embedded in paraffin wax. Histological sections of 5 μm were cut, stained with haematoxylin-eosin (HE) and examined using light microscopy by an independent expert who was blinded to the source of the sections. A semi-quantitative grading scheme was used to evaluate the extent of the lesions in the sections as follows: minimal (grade 1) lesions involving less than 10% of the lung section; mild (grade 2), 11%-40%; moderate (grade 3), 41%-80%; marked (grade 4), 81%-100%. 
     The results of the experiments are described below. Field intensities and temperature measurements were done during electric fields treatment and sham heat application. The average electric fields intensities in the lungs were 12±4 V/cm. Under these conditions lung temperature was identical to, or up to 1° C. lower than the electrode surface temperatures which were set to 37° C. for both the electric fields and the sham heat control. 
     Pulmonary infection was induced by intranasal administration of different amounts of  P. aeruginosa  strain PAO1 to neutropenic ICR mice. Bacteria concentrations that were found to induce a severe pulmonary infection which persisted for at least 48 h were around 5×10 4  CFU/mouse. Higher concentrations (5×10 5  CFU/mouse) resulted in a high mortality rate (100% within the first 24 h) while lower concentrations (5×10 3  CFU/mouse) resulted in a complete recovery. 
     Table 2 shows the electric fields&#39; effect on mice with  P. aeruginosa  lung infection, used alone and combined with ceftazidime. The log CFU at both the start of treatment (T0) and 48 hours later (T48) is listed in table 2. Table 3 shows the electric fields&#39; effect on mice with  P. aeruginosa  lung infection, used alone and combined with ceftazidime. The growth listed in table 3 is relative to the inoculums after 48 hours of treatment. Table 4 shows the electric fields&#39; effect on mice with  P. aeruginosa  lung infection, used alone and combined with ceftazidime. The lung weights listed in table 4 are the weights at the end of the 48 hour treatment. 
     
       
         
               
               
             
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Number of bacteria (CFU) in the lungs of infected mice 
               
             
          
           
               
                   
                 without ceftazidime 
                 with ceftazidime 
               
             
          
           
               
                   
                 Log CFU 
                 Log CFU 
                 P values 
                   
                 Log CFU 
                 Log CFU 
                 P values 
                   
               
               
                   
                 (T0) ± 
                 (T48) ± 
                 compared 
                 # of 
                 (T0) ± 
                 (T48) ± 
                 compared 
                 # of 
               
               
                   
                 STDEV 
                 STDEV 
                 to control 
                 mice 
                 STDEV 
                 STDEV 
                 to control 
                 mice 
               
               
                   
                   
               
             
          
           
               
                 fields 
                 3.6 ± 0.2 
                 4.1 ± 1.5 
                 &lt;0.001 
                 17 
                 4.6 ± 0.2 
                 5.0 ± 1.7 
                 0.005 
                 36 
               
               
                 sham 
                 3.6 ± 0.2 
                 5.0 ± 2.5 
                 0.009 
                 20 
                 4.6 ± 0.2 
                 6.0 ± 2.3 
                 0.398 
                 27 
               
               
                 heat 
               
               
                 control 
                 3.6 ± 0.2 
                 7.5 ± 2.7 
                   
                 24 
                 4.6 ± 0.2 
                 6.5 ± 2.5 
                   
                 40 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                   P. aeruginosa  growth in mice lungs 
               
             
          
           
               
                   
                 without ceftazidime 
                 with ceftazidime 
               
             
          
           
               
                   
                 log CFU/lung 
                 P values 
                 log CFU/lung 
                 P values 
               
               
                   
                 (T48/T0) 
                 compared 
                 (T48/T0) 
                 compared 
               
               
                   
                 (±STDEV) 
                 to Control 
                 (±STDEV) 
                 to Control 
               
               
                   
                   
               
             
          
           
               
                 fields 
                 0.5 ± 1.6 
                 &lt;0.001 
                 0.4 ± 1.7 
                 0.004 
               
               
                 sham heat 
                 1.6 ± 2.5 
                 &lt;0.01 
                 1.3 ± 2.2 
                 0.4 
               
               
                 control 
                 3.8 ± 2.8 
                   
                 1.9 ± 2.5 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 Average lungs weight in mice 
               
               
                   
                 with pulmonary infection after treatment 
               
             
          
           
               
                   
                 without ceftazidime 
                 with ceftazidime 
               
             
          
           
               
                   
                   
                 P values 
                   
                 P values 
               
               
                   
                 weight in mg 
                 compared 
                 weight in mg 
                 compared 
               
               
                   
                 (±STDEV) 
                 to Control 
                 (±STDEV) 
                 to Control 
               
               
                   
                   
               
             
          
           
               
                 fields 
                 257 ± 32 
                 &lt;0.001 
                 244 ± 31 
                 &lt;0.001 
               
               
                 sham heat 
                 290 ± 49 
                 &lt;0.001 
                 275 ± 60 
                 0.047 
               
               
                 control 
                 377 ± 97 
                   
                 310 ± 77 
               
               
                   
               
             
          
         
       
     
     48 hours electric fields treatment of mice suffering from pulmonary infection resulted in 3.4 log reduction in the CFU content of the treated mice as compared to the untreated control mice (see Table 2). The sham heated control treatment resulted in 2.5 log reduction as compared to the control mice (see Table 2). The average bacterial growth [log(CFU T48 /CFU T0 )] of both electric fields treated mice and the sham heat treated mice was significantly lower than in the control mice (see Table 3). A significant reduction was also observed in the weight of lungs of electric fields treated mice as compared to both the sham heated control mice (P=0.02) and to the untreated control mice (P&lt;0.001) (see Table 4). Finally, histopathology examination of the lung samples of the mice that were treated with electric fields were rated as normal to grade 1 with focal acute inflammation. In contrast, lungs of control mice or the sham heat group were rated as grade 2 to 3 associated with acute necrotizing pneumonia and the presence of numerous bacterial colonies. 
     Experiments were also performed to test the effects of combined treatment of pulmonary infection caused by  P. aeruginosa  by electric fields combined with ceftazidime. The inoculums that were found to induce a persistent pulmonary infection in the presence of ceftazidime (10 mg/kg BW/day) alone were around 5×10 5  CFU per mouse. The results presented in Table 2 demonstrate that 48 h combined treatments of electric fields and ceftazidime resulted in a 1.5 log reduction in the lung CFU content compared to the antibiotic-only treated control. The combined treatment of sham heat and ceftazidime did not result in a significant count reduction compared to the control (see Table 2). Bacterial growth [log(CFU T48 /CFU T0 )] in the lungs of mice treated with electric fields and ceftazidime was significantly lower than in the control mice (P=0.004) (see Table 3). The average lung weight was significantly lower in both the ceftazidime/electric fields combination treatment group (P&lt;0.001) and in the ceftazidime/sham heat combination treatment group (P=0.047) as compared to the control group (see Table 4). 
     The results obtained demonstrate that electric fields, previously shown to be an effective in-vitro tool for combating bacterial pathogens (Giladi et al., 2008), are also effective in the in-vivo arena. Specifically, it was demonstrated that electric fields, applied by means of external insulated electrodes, have a significant inhibitory effect on the growth of a bacterial pathogen in-vivo. The inhibitory effect was observed when electric fields were applied either as a sole treatment or as an adjuvant to antibiotic therapy. 
     One striking outcome of the electric fields application was the fact that the number of bacteria in the lungs of electric fields treated mice was increased only by a fraction of an order of magnitude compared to the number in the inoculums used for infection, while at the same time the number of bacteria in the control group grew by 3.8 orders of magnitude. This observation could be the consequence of either an electric fields inhibitory effect or a bactericidal effect. Histopathology analysis demonstrated that in the electric fields treated mice, the lung morphology was normal with no evidence of a former massive infection. Thus it is reasonable to assume that the electric fields treatment led to cell proliferation arrest, rather than to the elimination of the bacteria after thriving in the lungs. Supportive evidence for this conclusion can be found in the results of the experiment in which combined electric fields/ceftazidime treatment was tested. Ceftazidime is a third-generation cephalosporin antibiotic with a broad bactericidal activity against Gram positive and Gram negative bacteria. Like other beta-lactam antibiotics, ceftazidime is most effective against dividing bacteria. Indeed, ceftazidime treatment of 10 mg/kg BW/day, alone, resulted in a growth reduction of close to 2 logs, compared to the non treated lungs (1.9 vs. 3.8 respectively, see Table 3). Yet, the combined treatment of electric fields and ceftazidime did not lead to a reduction in the bacterial growth compared to the electric fields treatment alone (0.4 vs. 0.5, respectively, see Table 3), nor did it reduce CFU counts in the lungs compared to the inoculums suggesting that bacterial growth was arrested. 
     Previously we demonstrated that application of electric fields in vitro led only to a 20% reduction in the number of treated bacteria compared to the control, which is considerably less than the inhibition that occurred in the in vivo study discussed herein. One possible explanation for the enhanced efficacy in the in vivo experiments could be derived from the fact that the electric Fields inhibitory effect is positively correlated with field intensity (Giladi et al., 2008). While the electric fields intensity in the in vitro experiments was limited to 4 V/cm, in order to avoid over heating of the culture, the electric fields intensity in the in vivo experiments was significantly higher (i.e., about 12 V/cm). The application of such electric fields with higher intensities was made possible in view of the active heat removal that occurs in the mouse&#39;s body. 
     Experimental data obtained for both microorganisms and proliferating living cells, such as cancer cells, indicates that higher field intensities result in higher efficacy. However, there is a practical limit on field intensity due to the heat generated under the electrodes and within the treated animal, and the relevant anatomy&#39;s ability to carry that heat away. 
     For example, in the case of a human brain, the blood can carry away the heat that is generated in the tissue, and the total blood flow is about 2000 cc/min. Assuming that we want to keep the temperature of the brain below 39° C., which is 2° above the normal body temperature, this blood flow should be able to carry away 4000 calories/min, which corresponds to about 280 W. We should therefore be able to apply 278 W safely to the brain. Since the side to side electric resistance of the human brain is about 100 Ohms, and power equals voltage squared divided by resistance, we should be able to use a voltage of 167 V safely. This voltage drops over a distance of about 10 cm, in which case the field strength will be about 17 V/cm. Thus, for the brain, it would be reasonable to operate at field strengths between 5 and 20 V/cm, and more preferably at field strengths between 10 and 17 V/cm. 
     In the case of resting skin, the blood flow is sufficient to handle fields of 5 V/cm, and in the case of hyperemic heated skin the blood flow is sufficient to handle fields of 50 V/cm or even 80 V/cm. It is therefore expected that practical useful fields will range from 2 V/cm to 100V/cm, depending on the treated organ and its state. Note that the above calculations are for RMS Voltage, and not peak to peak voltage. 
     Another possible factor for the enhanced efficacy of the electric fields treatment in the in vivo arena could be related to the fact that the sham heat treatment also led to an inhibitory effect on bacterial growth. Though the sham heat control effect was smaller than the electric fields effect, it was nevertheless significant. Bacterial growth inhibition due to elevated temperatures may result from either a direct effect of the heat on bacterial growth or from local and systemic “host” reactions and responses to the heating. The former hypothesis was tested in vitro by comparing the growth rate of  P. aeruginosa  at various temperatures within the range of normal to febrile temperatures. Similar to the reports in the literature (Magnusson et al., 1995), we found that the growth rate of  P. aeruginosa  is positively correlated with increase in the temperature in the range of 34-38° C. Thus we can rule out the possibility of a direct effect of heat on bacterial growth. The alternative notion, i.e. that local and systemic host reactions to elevated temperatures negatively affect bacterial growth is not new. In fact, heat and fever were used as a tool against microbial pathogens for over a century (reviewed by Atkins, 1982 and Hasday et al., 2000). There are numerous reports regarding the effect of elevated host temperatures on the growth of bacterial pathogens demonstrating for example that: fever induced after Malaria inoculation can serve as a treatment against  Treponema pallidum  (Wagner-Jauregg, 1919), febrile core temperature is essential for optimal host defense against  Klebsialla pneumonia  peritonitis in mice (Jiang et al., 2000), fever in elderly patients with community-acquired pneumonia is positively correlated with high survival rates (Ahkee et. al, 1997) and maintaining a normal core body temperature (36.6±0.5° C.) after anesthesia decreases the incidence of infectious complications in patients undergoing colorectal resection (Kurz et al., 1996). Amongst the mechanisms suggested to play a role in the antibacterial effect of heat, augmentation of the innate immune function is probably the most intensively studied one (Hanson, 1993; Hasday et al., 2001; Mackowiak et al., 1983; Lederman et al., 1987; Rosenpire et al., 2002). Though our results demonstrate that electric fields and sham heat application did not cause an increase in the lung temperatures, they did raise the temperature of the peripheral organs of the treated mice, by at least 2 degrees (the normal skin temperature of mice is 34-35° C. while in the present study the electrodes temperature was set to 37° C.). Hanson (1993) demonstrated that mature primary T-cells response is strongly regulated by temperature changes in the range of 29° to 37° C., which corresponds to the peripheral tissue temperature elevation during febrile episodes. This finding provides a possible explanation for the sham heat inhibitory effect reported in the present study. Since application of electric fields is always associated with heat production it is reasonable to assume that the enhanced efficacy of the fields reported in the present study compared to our previous report (Giladi et al., 2008) is in part due to elevated temperatures of the peripheral tissue. 
     Thus, electric fields can be an effective and safe antibacterial treatment modality which could be applied in cases of both superficial and deep infections, either as a sole treatment or in combination with antibiotics, for both  P. aeruginosa  pathogens and other types of bacteria. Such treatments will involve placement of insulated electrodes on the skin surrounding the infected organs, and generating electric fields by applying the appropriate AC voltages to those electrodes. 
     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made without departing from the spirit and scope of the invention.