Tissue ablation systems

"ELECTROSURGICAL ABLATION PROBE AND SYSTEM COMPRISING THE SAME"

FUNDAMENTALS OF THE INVENTION

1. Field of the Invention. The present invention relates to electrosurgical devices and related methods for rapid and controlled tissue ablation. More particularly, the present invention relates to treating tissue with a radiofrequency current supplied through an electrically non-conductive gas, which is ionized to capacitively couple with the surrounding tissue through a thin dielectric layer surrounding the gas.

The treatment of diseased organs, such as the uterus and gallbladder, by ablation of an endometrial or mucosal layer surrounding the organ's interior, has long been proposed. Such internal surface ablation can be achieved by heating the surface, treating the surface with microwave energy, treating the surface with cryoablation, and supplying radiofrequency energy to the surface. Of particular interest to the present invention, a variety of radiofrequency ablation structures have been proposed, including solid electrodes, balloon electrodes, metallized tissue electrodes, and the like. Although often effective, most earlier electrode designs have suffered from one or more shortcomings, such as relatively long treatment times, incomplete treatments, non-uniform ablation depths, and the risk of damaging adjacent organs.

For these reasons, it should be desirable to provide methods and apparatus for radiofrequency ablation of internal tissue surfaces that are rapid, provide uniform ablation depths, ensure complete ablation over the entire targeted surface, and reduce the risk of damaging adjacent organs. At least some of these objectives will be satisfied by the inventions described below.

2. Fundamentals of the Art. US Patent No. 4,979,948 describes a balloon loaded with an electrolytic solution to deliver radiofrequency current to a mucosal layer via capacitive coupling. US 2008/097425, having common invention with the present application, describes the supply of a pressurized flow of a liquid medium carrying a radiofrequency current to the tissue, where the liquid is ignited within a plasma as it passes through flow orifices. US 5,891,134 describes a radiofrequency heater within an enclosed balloon. US 6,041,260 describes radiofrequency electrodes distributed across the outer surface of a balloon, which is inflated into a body cavity to be treated. US 7,371,231 and US 2009/054892 describe a conductive balloon having an outer surface that acts as an electrode for performing endometrial ablation. US 5,191,883 describes bipolar heating of a medium within a balloon for thermal ablation.

US patents 6,736,811 and 5,925,038 show an inflatable conductive electrode.

BRIEF SUMMARY OF THE INVENTION

The present invention provides apparatus and device systems for treating patient tissue. The treatment generally comprises supplying a radiofrequency current to the tissue in order to heat and generally remove the tissue by ablation at a desired depth. The current is supplied to the tissue from a radiofrequency power source through a first dielectric medium and a second dielectric medium in series with the first medium. The first dielectric medium will generally comprise an electrically non-conductive gas, which can be ionized to form a plasma, typically by applying a high-voltage radio frequency voltage, but optionally by applying direct heat to the gas, or even optionally by applying both high-voltage radio frequency voltage and heat to the gas. The second dielectric medium will separate the first medium from the target tissue, typically comprising a thin dielectric material, such as silicone or a silicone-based material, more typically comprising a thin dielectric wall, which defines an inner chamber containing the electrically non-conductive gas. The radiofrequency current 5 is thus supplied to the tissue by applying a radiofrequency voltage across the first and second dielectric media, so that the first dielectric becomes ionized, typically forming a gas plasma, and the second dielectric allows current flow to the tissue via capacitive coupling.

The systems and apparatus for supplying radiofrequency current to tissues comprise a body having a support end, a working end, and an inner chamber. A thin dielectric wall surrounds at least part of the inner chamber and has an outer surface disposed at the working end of the body. A gas inlet will be provided to connect to the chamber for supplying an electrically non-conductive gas in a continuously flowing mode or in a static mode. A first electrode structure is provided, which has a surface exposed to the inner chamber or the gas inlet. A second electrode structure is also provided and has a surface adapted to contact tissue, typically being somewhere on the body, most typically being on a part of the handle or rod of the device. The apparatus further includes a connected radiofrequency power supply to apply a radiofrequency voltage across the first and second structures, where the voltage is sufficient to initiate ionization of the gas within a plasma inside the chamber. The voltage will still be sufficient to capacitively couple the current in the plasma, through the dielectric wall, and into the tissue adjacent to the outer surface.

The specific structure of the body can vary. In one example, the dielectric wall might comprise a rigid material,^tlplacamente Selected from the group consisting of ceramics, glass, and polymer, the rigid material can be formed into a variety of geometries including a tube, sphere, or similar. Generally, the dielectric wall will have a thickness in the range of about 0.0051 to 0.254 cm, usually from 0.013 to 0.13 cm.

In alternative embodiments, the dielectric wall may comprise a conformable material, typically a silicone. Such conformable dielectric walls will typically have a thickness in the range of about 0.010 cm to 0.076 cm, generally 0.020 cm to 0.038 cm. The conformable wall may be non-expandable or it may be elastic, so that the wall structure can be inflated. For non-expansive or elastic dielectric walls, the device may further comprise a structure that supports the conformable material, generally where the structure can be expanded and contracted to open and close the dielectric wall.

The apparatus of the present invention will typically also include a rod or other handle structure connected to the supporting end of the body. Generally, the rod will have a lumen extending into the gas inlet of the body, to supply electrically non-conductive gas to the chamber. The rod or handle may also include at least a second lumen, 20 to remove electrically non-conductive gas from the chamber, so that the gas can be recirculated in a continuous flow. Frequently, the first electrode will be at least partially in the first lumen of the device, although it may also be inside the chamber, or inside both the first lumen and the chamber. The second electrode will generally be disposed at least partially on an external surface of the device, typically on the stem, although in certain systems the second electrode could be disposed on a separate scattering mandrel.

The apparatus according to the present invention will have an internal chamber volume in the range of 0.01 ml to 20 ml, typically from 1 ml to 10 ml. The dielectric wall will have an area in the range of 1 mm².² 100 mm², typically 5 mm² 50 mm²The first electrode surface will have an area in contact with the electrically non-conductive gas in the range of 0.01 mm².² 10 mm², typically 1 mm² 5 mm²Additionally, the second electrode structure 5 will have an area available for tissue contact in the range of 0.5 mm.² 50 mm², usually 1 mm² 10 mm².

Radiofrequency power supplies can be of general construction, as is often used in electrosurgery. The power supply will typically be configured to supply a voltage in the range of 500 V (rms) to 2500 V (rms), usually 600 V (rms) to 1200 V (rms), typically at a current in the range of 0.1 A to 1 A, typically 0.2 A to 0.5 A, and at a frequency in the range of 450 kHz to 550 MHz, usually 480 kHz to 500 MHz.

Devices useful for treating patient tissue 15 comprise containing an electrically non-conductive gas in a chamber within an applicator, having a thin dielectric wall surrounding at least part of the inner chamber. An outer surface of the thin dielectric wall is contacted with a target region of the tissue, and a radiofrequency voltage is applied across the gas and thin wall, wherein the voltage is sufficient to ionize the gas to initiate a plasma in the gas and to capacitively couple the current in the gaseous plasma through the dielectric wall and into the contacted tissue.

The electrically non-conductive gas may be statically retained within the chamber, but more frequently it will be actively flowing through the applicator chamber. The flow rate of the non-conductive gas will typically be in the range of about 1 ml/sec to 50 ml/sec, preferably 5 ml/sec to 30 ml/sec. The inner chamber will have a volume in the range of 0.01 ml to 100 ml, typically 2 ml to 10 ml. Generally, the electrically non-conductive gas will be argon or another noble gas or mixture of noble gases.

The dielectric wall of the applicator can assume a variety of configurations. In a first embodiment, the dielectric wall will have a generally fixed shape that will remain constant, regardless of the internal pressurization of the contained gas. Alternatively, the dielectric wall may be elastic, conformable, loose, or otherwise have a variable shape that can conform to the surface of the contacted tissue. In some examples, the thin dielectric wall will comprise a balloon or other inflatable structure, which is expanded by increasing the internal pressure of the electrically non-conductive gas or other medium. Alternatively, a separate structure, cage, spring, or other mechanical unfolding structure may be provided within a thin, conformable elastic or non-elastic dielectric wall. In the latter case, the structure or other structure can be configured and "configured" to conform to the thin dielectric wall, when desired in the method.

Voltage is applied to the tissue by providing a first electrode surface coupled to the non-conductive gas and a second electrode surface coupled to the patient's tissue. A radiofrequency voltage is then applied across the first and second electrodes in order to both ionize the electrically non-conductive gas (forming a plasma) within the inner chamber and capacitively couple the charged plasma to the tissue through the thin dielectric wall.

The voltage applied to the first and second dielectric media will depend on the distance between the first electrode surface and the dielectric wall 25, as well as the resistance between the dielectric wall and the second electrode, which is in contact with the tissue, typically being in the range between 500V (rms) and 2500V (nns). In exemplary embodiments, the first electrode surface will generally be within or on the inner chamber or in a gas flow path leading to the inner chamber, and the second electrode surface will be located..._m contact with, in the patient's tissue, often being placed on a rod or other external surface of the treatment device.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the invention and to see how it can be implemented in practice, some preferred embodiments are described below, by way of non-limiting examples only, with reference to the attached drawings, where similar reference features indicate corresponding aspects, consistently across the 10 similar embodiments of the attached drawings.

Fig. 1 is a schematic view of an ablation system corresponding to the invention, including an electrosurgical ablation probe, RF power source and controller.

Fig. 2A is a view of the ablation probe of Fig. 1, 15 configured with a sharp tip for ablation of a tumor.

Fig. 2B is another view of the probe from Fig. 2A, after it has been inserted into the tumor.

Fig. 3 is an enlarged schematic view of the working end of the probe of Fig. 1, which provides a gas electrode within the interior 20 of a thin-walled dielectric structure.

Fig. 4A is a cross-sectional view of a thin-walled cylindrical dielectric structure, in which supporting elements are formed within the dielectric structure.

Fig. 4B is a cross-sectional view of a portion of another 25 thin-walled planar dielectric structure, in which the supporting elements are in a waffle-like configuration.

Fig. 5A is a cross-sectional view of a portion of another thin-walled, flat dielectric structure, wherein the supporting elements comprise post-like elements.

THE^F.g· ^{5B c one} A cross-sectional view of one end of a probe rod in which a thin-walled dielectric structure with post-like support elements is provided around the core electrode.

Fig. 6 is_one Block diagram of the components of an electrosurgical system corresponding to the invention.

Fig. 7 is a block diagram of the gas flow components of an electrosurgical system corresponding to the invention.

^AF‘⁸’ ^{8 it's llma v}'This schematic of a cut-out of a working end as in Fig. 3 illustrating a step of a method of the invention, in which the current is coupled to the fabric, via capacitive coupling, through a thin-walled dielectric structure.

Fig. 9A is an enlarged schematic view of an aspect of the method in Fig. 3 illustrating the step of positioning an ionized gas electrode 5 and thin-walled dielethane in contact with tissue.

Fig. 9B is a schematic view of a subsequent step of applying RF energy to create an arc through a gas and capacitive coupling through the thin-walled dielectric, to cause current flow in a discrete path in the tissue.

Fig. 9C is a schematic view similar to Fig. 9B representing the flow sweep of content for another random projection in the tissue.

Fig. 9D is a schematic view similar to Figs. 9A-9C, representing the thermal diffusion of the plurality of current flows swept' 25 in the tissue.

Fig. 10 is a circuit diagram showing the electronic aspects and components of the power supply mode.

Fig. 1 IA and a cross-sectional view of the working end of Fig. 3, positioned in the tissue, illustrate one step of a method of utilizing the working end, in which the current is coupled to the tissue via an ionized gas and capacitive coupling through a thin-walled dielectric structure.

Fig. 11B is a sectional view similar to that in Fig. 1 IA 5, illustrating another step in the method where the volume of tissue removed by ablation is shown.

Fig. 12 is a sectional view of an alternative working end, similar to that in Fig. 3, of a method of use, the dielectric structure having a central support member functioning as (i) an electrode and as (ii) a gas flow direction means.

Fig. 13 is a block diagram of a method corresponding to the invention.

Fig. 14 is a block diagram of another method corresponding to the invention.

Fig. 15 is a block diagram of another method corresponding to the invention.

Fig. 16 is a block diagram of another method corresponding to the invention.

Fig. 17 is a block diagram of another method 20 corresponding with the invention.

Fig. 18A is a plan view of an alternative ablation probe carrying a plurality of expandable needle-like ablation elements in a sheath, each element having a dielectric structure with varying dielectric parameters for directional control of capacitive coupling and thus directional control of ablation.

Fig. 18B is another view of the ablation probe of Fig. 18A, with the plurality of extendable needle ablation elements extended from the sheath.

Fig. 19 is an enlarged view of one end of the ablation probe working on Fis. 18A - 18B, with a volume of tissue targeted for ablation and excision.

Fig. 20 is a cross-sectional view of scanned tissue using the working end of Fig. 19 showing the directional capacitive coupling 5 and directional ablation.

Fig. 21 is a schematic view of a tumor ablation method using a plurality of working ends, similar to those in Figs. 19-20, for targeted capacitive coupling and targeted ablation.

^Flg' ^{22 and a view in}Design of an alternative working end, similar to that in Figs. 3 and 12, with a non-uniform thickness dielectric structure for directional control of capacitive coupling and thus directional control of ablation.

Fig. 23 is a cross-sectional view of a 15-inch non-uniform thickness dielectric structure for directional capacitive coupling control for fabric.

Fig. 24 is a cross-sectional view of a uniform thickness dielectric structure with different materials for directional control of capacitive coupling for fabric.

Fig. 25A is a cross-sectional view of a working end of an ablation probe similar to that in Fig. 12 with a thin-walled dielectric structure that is extensible in an unextended condition.

Fig. 25B is a sectional view of the working end of Fig. 25A with the extensible thin-walled dielectric structure in an extended condition in soft tissue; the structure configures expansion by gas inflation pressure.

Fig. 25C is another sectional view, as in Fig. 25B, showing the capacitive energy coupling to the tissue of a plasma contained within the expandable dielectric structure.

Fig. 25D is another sectional view, similar to Fig. 25B, showing the region of tissue removed by ablation after energy delivery.

Fig. 26 is another cross-sectional view of the expandable dielectric structure 5 in an unextended condition, folded within a translatable sheath.

Fig. 27 is a cutaway schematic view of a heart and a working end of another ablation probe similar to that in Fig. 25 A, with an expandable thin-walled dielectric structure configured for ablation around a pulmonary vein to treat atrial fibrillation, with the structure configured for expansion by gas inflation pressure.

Fig. 28 is a schematic enlarged cross-sectional view of the working end of Fig. 27 removing a pulmonary vein by ablation.

Y 29 is a schematic cropped view of a heart and the flexible working end of another ablation probe configured to remove a lesion by ablation to treat atrial fibrillation.

Fig. 30 is a schematic perspective view of the flexible working end of Fig. 29, illustrating an elongated dielectric structure 20.

Fig. 31 is a cross-sectional view of the flexible working end and dielectric structure of Fig. 30 illustrating an internal electrode.

Fig. 32 is a perspective view of another end of a 25 flexible working tool, similar to that in Figs. 30-31, for creating a circumferential lesion to treat atrial fibrillation.

Fig. 33 is a schematic cutaway view of an esophagus and working end of another ablation probe, similar to that in Fig. 27, with an expandable thin-walled dielectric structure configured for expansion by a skeletal frame.

Fig. 34 is a cutaway view of the [expandable] thin-walled dielectric structure of Fig. 33, showing the internal skeletal support structure which optionally functions as an electrode.

Fig. 35 is a cutaway view of another expandable dielectric structure similar to Fig. 34, showing an alternative internal skeletal support structure.

Fig. 36 is a schematic sectional view of one working end of another ablation probe, comprising first 10 and second opposing grippers contacting the tissue, with each gripper contacting the surface including a thin-walled dielectric structure, the grippers configured to seal or coagulate the tissue trapped between them.

Fig. 37 is a schematic view of the working end of another embodiment with a thin, dielectric, expandable, walled structure, with a plurality of chambers carrying plasma to perform another form of bipolar ablation.

Fig. 38 is a schematic cross-sectional view of the working end of Fig. 37, taken along line 38-38 of Fig. 37 rotated 90°, showing the current flow in the tissue.

²⁰ DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of ablation systems, useful for performing an electrosurgical method corresponding to the present invention, are shown in the drawings. In general, each of these embodiments uses an ionized gas in a first polarity and contained within a thin-walled dielectric envelope, which provides capacitive coupling of the RF current from the gas with a target tissue in contact with an electrode in a second polarity and spaced apart from each other, and external to the dielectric envelope. The embodiments of the system typically include an instrument with a working end, including a thin-walled dielectric envelope containing an ionizable gas. Current flow to the tissue begins when sufficient voltage is applied to ionize the contained gas into a plasma, and contemporaneous capacitive coupling occurs through the surrounding dielectric structure. The invention thus provides a voltage-based electrosurgical effect that is capable of removing tissue by ablation at a controlled depth, from 1 mm to 5 mm or more, very quickly, wherein the ablation depth is very uniform around the entire surface of the dielectric sheath. The working end and dielectric sheath of the instrument may have a variety of forms, including, but not limited to, an elongated rod portion of a needle ablation device, a dielectric expandable structure, a hinged member, a flexible member, or at least a gear surface of an electrosurgical gripper structure. The embodiments and methods of the system can be used for ablation of 15 interstitial tissue, ablation of intraluminal tissue, or ablation of topical tissue.

The embodiments of the system described herein utilize a thin-walled dielectric structure or wall at one working end of the instrument, which contains an electrically non-conductive gas as a dielectric. The thin-walled dielectric structure may be a polymer, ceramic, or glass with a surface configured to contact tissue. In one embodiment, an internal chamber within the thin-walled dielectric structure carries a circulating neutral gas or static neutral gas, such as argon. An RF power source provides current, which is coupled to the flow of neutral gas or static gas volume by an electrode disposed within the working end. The gas flow, or static gas contained within the dielectric envelope, is of a non-conductive type until it is transformed into a conductive plasma by voltage breakdown. The threshold voltage for gas breakdown will vary with variations in several parameters, including gas pressure, gas flow velocity, gas type, and the distance from the inner electrode through the inner chamber to the dielectric structure. As will be seen in some of the embodiments, voltage and other operating parameters can be modulated during operation by feedback mechanisms.

The gas, which is ionized by contact with a conductive electrode at the working end of the instrument, functions as a switching mechanism that only allows current flow into the target tissue when the voltage, through the combination of the gas, the dielectric structure, and the contacted tissue, reaches a predetermined threshold potential that causes capacitive coupling through the dielectric structure. By allowing current flow only at a high threshold voltage that capacitively couples the current to the tissue, the invention enables a substantially uniform tissue effect throughout the tissue in contact with the dielectric structure. Furthermore, the invention allows ionized gas to be created concurrently with the application of energy to the tissue by converting a non-conductive gas into a plasma.

In one embodiment of the apparatus, the ionized gas functions as an electrode and comprises a gas flow that can conduct current through a contained internal volume of gas within a dielectric structure, typically an electrode inside a working end in contact with the gas flow. The gas flow is configured for the purpose of coupling energy with the dielectric structure uniformly across the surface of the dielectric structure; however, this will only conduct such energy when the non-conductive gaseous medium has been transformed into a conductive plasma 5, by being increased to a threshold voltage.

Definitions

Plasma. In general, this description can use the terms "plasma" and "ionized gas" interchangeably. A plasma consists of a state of matter in which electrons in a neutral gas are extracted or "ionized" from its molecules or atoms. Such plasmas can be formed by applying an electric field or by high temperatures. In a neutral gas, electrical conductivity is non-existent or very low. Neutral gases act as a dielectric or insulator until the electric field reaches a breakdown value, releasing electrons from the atoms in a collapse process, thus forming a plasma. Such a plasma provides mobile electrons and positive ions, acts as a conductor that carries electric currents, and can form a spark or arc. Due to their lower mass, electrons in a plasma accelerate more rapidly in response to an electric field than heavier positive ions, and therefore carry the charge of the current.

Dielectric and dielectric loss. The term dielectric is used in its usual sense, meaning a material that resists the flow of electric current, that is, a non-conductive substance. An important property of a dielectric is its ability to withstand an electrostatic field while dissipating minimal energy in the form of heat. The lower the dielectric loss (the proportion of energy lost as heat), the more effective a dielectric material is.

Dielectric constant or relative permittivity. The dielectric constant (k) or relative static permittivity of a material under given conditions is a measure of the extent to which electrostatic flux lines are concentrated, or alternatively, it is a number relative to the material's ability to carry alternating current compared to the ability of a vacuum to carry alternating current. The capacitance created by the presence of a material is directly related to its dielectric constant. In general, a material or medium having a high dielectric constant breaks down more easily when subjected to an intense electric field than materials with low dielectric constants. For example, air or another neutral gas may have a low dielectric constant, and when it undergoes dielectric breakdown—a condition in which the dielectric begins to conduct current—the breakdown is not permanent. When the excessive electric field is removed, the gas returns to its normal dielectric state.

Dielectric breakdown. The phenomenon called dielectric breakdown occurs when an electrostatic field applied to a material reaches a critical threshold and is sufficiently intense so that the material will suddenly conduct current. In a gaseous or liquid dielectric medium, this condition is reversed if the voltage decreases below the critical point. In solid dielectrics, such a dielectric breakdown can also occur and couple energy through the material. As used herein, the term dielectric breakdown medium refers to both solid and gaseous dielectrics that allow current flow through the medium at a critical voltage.

Q^rau—of—ionization. The degree of ionization describes the proportion of atoms in the plasma that have lost (or gained) electrons, and is primarily controlled by temperature. For example, it is possible for an electric current to create a degree of ionization ranging from less than 0.001% to more than 50.0%. Even a partially ionized gas, in which as little as 0.1% or 1.0% of the particles are ionized, can have the characteristics of a plasma, that is, it can strongly respond to magnetic fields and can be highly electrically conductive. For the purposes of this description, a gas can begin to behave as a conductive plasma when the degree of ionization reaches approximately 0.1%, 0.5%, or 1.0%. The temperature of a plasma volume also relates to the degree of ionization. In particular, plasma ionization can be determined by the electron temperature relative to the ionization energy. A plasma is sometimes referred to as "hot" if it is almost completely ionized, or "cold" or a "technological plasma" if only a small fraction (e.g., less than 5% or less than 1%) of the gas molecules are ionized. Even in such a cold plasma, the electron temperature can still be different by thousands of degrees Celsius. In systems according to the present invention, plasmas are cold in this sense because the percentage of ionized molecules is very low. Another phrase used here to describe a “cold” plasma is the plasma's “mass-average temperature,” which refers to the degree of ionization versus non-ionized gas and which determines the average temperatures of the two volumetric components of the gas. For example, if 1% of a gas volume is ionized with an electronic temperature of 10,000 °C and the remaining 99% has a temperature of 150 °C, then the average temperature of the mass will be 149.5 °C. It was found that measuring the plasma temperature of 10 can be done to determine an approximate degree of ionization, which can be used to control the applied energy feedback, and with a protection mechanism to prevent unwanted high temperatures within an FMA wall dielectric structure.

Referring to Fig. 1, a first embodiment of a tissue ablation system 100 using principles of the present invention is shown. The system 100 includes a probe 110, having a proximal handle 112 and an elongated rod or extension member 114, which extends along the geometric axis 115. The handle 110 is made of an electrically insulating material, such as a plastic, ceramic, glass or combinations thereof. The extension member 114 has a proximal end 116 coupled to the handle 112. The extension member 114 extends into a working end 120, which includes a dielectric member or structure 122, which is configured to contact tissue that is targeted by ablation.

In the embodiment shown in Fig. 1, the working end

120 The dielectric structure 122 is elongated and cylindrical, with a cross-section ranging from about 0.5 mm to 5 mm or more, and a length ranging from about 1 mm to 50 mm. The cross-section of the working end 120 may be round, oval, polygonal, rectangular, or any other cross-section. As can be seen in Figs. 2A-2B, in one embodiment, the working end 120 has a sharp tip 124 for penetrating tissue, to perform an ablation procedure, such as removing by ablation a tumor indicated in 125 in a tissue volume 130. In another embodiment, the distal tip of a working end 120 may be blunt. In yet another embodiment, the entire working end may have a guide channel in it to advance the working end through a guide wire.

Now returning to Fig. 3, an enlarged view of the working end 120 of Figs. 1, 2A and 2B is shown. It can be seen that the dielectric structure 122 has a thin wall 132, which provides an enclosure around an inner chamber 135 containing a gaseous medium indicated by 140 in Fig. 3. In one embodiment, the dielectric structure 122 may comprise a ceramic (e.g., alumina) having a dielectric constant ranging from about 3 to 4. The wall thickness 132 can vary from 0.0051 cm to 0.254 cm, depending on the diameter, or more typically, 0.013 cm to 0.13 cm in a diameter ranging from 1 to 4 mm. In another embodiment shown in Fig. 4A, the dielectric structure 122 may comprise a ceramic, glass, or polymer in a molded form with stiffening support parts 142 or ribs, terminating axially, radially, helically, or a combination thereof. The supporting parts 142 may alternatively comprise members that are independent of a thin wall 132 of a dielectric material. In one such embodiment (Fig. 4A), as will be described below, the thin-walled parts 144 of the dielectric structure 122 allow capacitive current coupling to the tissue, while the supporting parts 142 provide structural resistance to the thin-walled parts 144. In another embodiment, a part, of which is shown in Fig. 4B, the dielectric structure 122 has supporting parts 142 in a waffle-like configuration, wherein thin-walled parts 144 are supported by thicker-walled supporting parts 142. The waffle-like structure may be substantially flat, cylindrical, or have any other configuration suitable for containing a gaseous dielectric in a chamber, indicated by 135, on one side of the dielectric structure 122. In another embodiment of Figs. In Figures 5A and 5B, the dielectric structure 122 may have supporting parts 142 comprising posts supporting thin-walled parts 144 over another supporting member 145. The flat dielectric structure 122 may be used, for example, in flat gripper members, to apply RF energy to seal fabric. In another example, Fig. 5B shows a blunt-tipped cylindrical thin-wall 132 of a dielectric structure 122 supported by a core supporting member 145. In the embodiment of Fig. 5B, the inner chamber 135, which can contain a plasma, comprises a space between the thin-walled parts 144 and the core support member 145.

Referring again to Fig. 3, the extension member 114 is made of an electrically non-conductive material, such as polymer, ceramic, glass, or a metal with an insulating coating. The dielectric structure 122 can be bonded to the extension member 114 by glues, adhesives, or the like, to provide a sealed, fluid-tight inner chamber 135. In one embodiment, a gas source 150 may comprise one or more compressed gas cartridges (Figs. 1 and 6). As will be described below (Fig. 6), the gas source is coupled to a microcontroller 155, which includes a gas circulation subcontroller 155A that controls a pressure regulator 158 and also controls an optional negative pressure source 160, adapted to assist in gas circulation. The RF and control box 162, in Fig. 1. They may include a monitor 164 and input controls 165 to determine and control operating parameters such as treatment time intervals, gas flows, energy levels, etc. Suitable gases for use in the system include argon, other noble gases and their mixtures.

Referring to Fig. 3, the gas source 150 provides a flow of gaseous medium 140 through a flexible conduit 166, to a first flow channel 170 in the extension member 114, which communicates with at least one inflow orifice 172 interfacing with the inner chamber 135. The inner chamber 135 also interfaces with an efflux orifice 174 and a second flow channel 180 in the extension member 114, thereby allowing a circulating flow of gaseous medium 140 within the interior of the dielectric structure 122.

Referring again to Fig. 3, a first-polarity electrode 185 is arranged around the flow channel 170, close to the influx orifice 172, thus being in contact with a flow of gas medium 140. It should be noted that the electrode 185 can be positioned anywhere closer to the channel 170 in contact with the gas flow, or the electrode 185 can be inside the inner chamber 135 of the dielectric structure 122. Electrode 185 is electrically coupled to a conductor or wire 187, which extends through the extension member and loop 112, and is coupled to a first pole of a high-frequency RF generator 200, which is controlled by the controller 155 and RF subcontroller 155B. An electrode of opposite polarity 205 is disposed on the outer surface of the extension member 114 and is electrically coupled by wire 207 to a second pole of the RF generator 200.

The box diagrams in Figs. 6 and 7 schematically represent the system, subsystems, and components of an embodiment configured to supply electrosurgical ablation energy to the tissue. In the box diagram of Fig. 6, it can be seen that an RF 200 power source and circuit is controlled by the RF 155B subcontroller. The feedback control subsystems (described below) based on probe pressure feedback, probe temperature feedback, and/or gas flow velocity feedback, are also operatively coupled to the controller 155. The system can be activated by a foot switch 208 or other suitable switch. Fig. 7 shows a schematic of the flow control components relating to the flow of the gas medium through the system and probe 110. It can be seen that a pressurized gas source 150 is connected with a downstream pressure regulator 158, a proportional inflow valve 210, a flowmeter 212, and a normally closed solenoid valve 220. The valve 220 is actuated by the system operator, which then allows a flow of gas medium 140 to circulate through a flexible conduit 166 and probe 110. The gas efflux side of the system includes a normally open solenoid valve 225, proportional efflux valve 226, and flowmeter 228 that communicate with the negative pressure source 160. The gas exhaust can be within the environment or within a cooling system. A temperature sensor 230 (e.g., thermocouple) is shown in Fig. 7 to monitor the temperature of the efflux gases.

Figures 8 and 9A-9D schematically illustrate a method of the invention in which (i) the dielectric structure 122 and (ii) the contained neutral gas volume 140 function contemporaneously to provide first and second dielectric media which cooperatively function as independent mechanisms to optimize the supply of very high voltage current to contacted tissue volumes. The two dielectric components can be characterized as having complementary voltage threshold levels where only the high voltage current can couple through a filament 235 of a plasma 240 within the chamber 135 and capacitively couple through the thin-walled dielectric 132, to allow a current to still pass through a minimal resistive path 245 in the contacted tissue. In Fig. 8, the contacted tissue is assumed to be surrounding the dielectric structure 122 and is transparent. In the embodiment of Fig. 8, the electrode 185 also functions as a gas supply sleeve, wherein a neutral gas 140 can exit from the orifices 250 in the chamber 135. The high-voltage current paths 245 in the tissue are effectively “swept” through and around the inner surface 252 of the dielectric structure 122 and within the contacted tissue, to cause a maximized form of electrosurgical ablation voltage. Fig. 8 provides a schematic view of what is meant by the term “swept”, wherein high intensity electric fields are produced in the inner chamber 135 of the dielectric structure 122 by capacitive coupling through the dielectric wall 132 until a voltage threshold is reached in the neutral gas medium 140 to convert the gas within into a plasma 240 (see Fig. 8) which, in turn, allows plasma filaments 235 to form within the chamber 135 that randomly bounce or sweep around the inner surface 248 of the dielectric wall. The random jumping of plasma filaments 235 within the dielectric chamber 135 (from electrode 185 to inner surface 248 of the dielectric wall 132) occurs where there is a reversible, transient voltage breakdown in a localized part 252 of the dielectric wall 132, which is determined by a transient higher conduction path 240 in the tissue contacted with the second polarity electrode 205 (Fig. 3). An instant after the current flows through plasma 240 and path 245 into the tissue, the localized part 252 dissipates the electric field and another capacitive coupling occurs through another plasma filament 235' and current path 245' in the tissue, to cause electrosurgical ablation at another random discrete location.

Figures 9A-9D are enlarged schematic illustrations of the electrosurgical ablation method in Figure 8, which depicts other aspects of the ablation method. In Fig. 9A, it can be seen that the system and method are generalized to clearly show the first and second mechanisms of dielectric current transmission characterized by voltage parameters selected to cause an electronic collapse in the gas and capacitive coupling in the thin-wall envelope, to optimize and maximize a form of high-voltage current supply to an exemplary fabric 260. As previously described, the voltage threshold or dielectric breakdown mechanisms occur within (i) the volume of gaseous dielectric or neutral gas 140, which is contained within an inner chamber 135 of the dielectric structure 122 and (ii) the non-gaseous dielectric or structure 122 shown as a plane in Figs. 9A-9D.

Fig. 9A illustrates the components of the working end and tissue 260 before actuation and power supply to the tissue. It can be seen that the gaseous medium 140 is neutral and not yet ionized. The first polarity electrode 185, positioned in the inner chamber 135 in contact with the neutral gas 140, is shown schematically. The second polarity electrode 205 in contact with the tissue is also shown schematically, however the illustration represents another aspect of the invention in which the second electrode 205 may have a small surface area compared to the surface areas of the return/ground electrodes as in conventional electrosurgical systems. It was found that the capacitively coupled power supply mechanism of the invention does not cause tissue heating on or around the surface of the second polarity electrode 205 as would be expected in a conventional electrosurgical device. As will be described below, it is believed that the constant flow in the current paths, initiated by voltage breakdown and initiated by capacitive coupling in tissue 260, greatly reduces the accumulation of heat in or around the return electrode 205.

Figure 9B illustrates the components of the working end and tissue 260 at a given instant in time, immediately after the operator activates the system and supplies power to the working end of the probe. Several aspects of the voltage-initiated disruption ablation method are represented in Fig. 9B, including (i) in one aspect of the instant in time, the neutral gas 140 is converted into a plasma 240 by the potential between the first and second electrodes 185 and 205; and, contemporaneously, (ii) the current flow defines a minimum resistive path 245 in the tissue 260; (iii) a 'part 252 of the dielectric structure 122, adjacent to the current path 245, allows capacitive coupling to the tissue; (iv) the plasma filament arcs 253, through a high intensity plasma current 262 between the electrode 185 and part 252 of the dielectric structure. In other words, 5 when a selected voltage potential is reached, the voltage breakdown of the gas 140 and, capacitively, coupling through the dielectric 122, cause a high voltage current to follow through the path 245 in the tissue 260. Finally, the thermal diffusion indicated by arrows 265 causes thermal effects in a tissue volume 270a outside the path of transient current 245. The thermal effects in and around path 245 increase the tissue impedance, which thus causes the system to push a conductive path to another random location.

Fig. 9C illustrates the components of the working end and tissue 260 an instant after that of Fig. 9B, when the continuous voltage potential causes voltage breakdown in the plasma filament 235' along with capacitively coupling through the dielectric 122 to provide another high voltage current through the path 245', after which heat diffusion 265' causes thermal effects indicated in 270b. The “scanning” aspect of the ablation method can be understood from Figs. 9A-9B, in which the plasma filaments 235, 235' and current paths jump or sweep very rapidly around the inner chamber 135 in order to supply current in a path of minimum resistance 245, 245' in the tissue 260.

Now returning to Fig. 9D, another schematic is shown in power supply intervals where a multiplicity of 25 current paths, through the pre-existing plasma and dielectric 122, have provided diffuse thermal effects through a multiplicity of regions indicated in 270a270f. By this method, it was found that ablation depths of 3 mm to 6 mm can be performed very quickly in, for example, 30 seconds to 90 seconds, depending on the voltage selected.

In one aspect of the invention, Fig. 10 is a circuit diagram representing the steps of the method in Figs. 9A-9D, which explain the discovery that the return electrode 205 can have a small surface area and not be subjected to significant heating. In Fig. 10, it can be seen that the voltage potential can increase until a dielectric breakdown occurs in both the neutral gas 140 and the dielectric structure 122, which causes a high voltage current through path PI to electrode 205, followed by that path preventing exit, thus causing the current to change to current path P2, then current path P3 to infinity to the current path indicated in Pn. The fabric 260 in Fig. 10, therefore, is shown as a variable resistor in each current path, when the current path is in continuous flow based on the path increasing in resistance.

Figures 11A and 11IB are enlarged schematic illustrations of the method of using the embodiment of Figure 3, to capacitively couple current to the tissue with a gas dielectric 140 in the inner chamber 135 (i.e., plasma indicated in 240). Referring to Figure 11A, the system is activated, for example, by a foot switch 208 (Fig. 1) coupled to RF power source 200 and controllers 155A and 155B, which initiate a gas flow from source 150 to provide circulating flow through the first channel (inflow) 170, internal chamber 135 and the second channel (outflow) 180. For convenience, embodiments using such a circulating gas flow will be described here as using a preferred gas, which is argon. In one embodiment, the gas flow rate can be in the range of 1 ml/sec to 50 ml/sec, more typically 5 ml/sec to 30 ml/sec. In Fig. 11A, the working end 120 of the probe is introduced into tissue 260, for example, to remove a tumor by ablation as in Figs. 2A-2B. The dielectric structure 122 is positioned at a desired location to remove adjacent tissue by ablation. The activation of the system simultaneously applies RF energy to electrode 185 and to the gas flow, which instantly converts the non-conductive argon 140 into a plasma indicated by 240 in Fig. 11 A. The threshold voltage at which argon becomes conductive (i.e., partially converted into a plasma) is dependent on a number of factors controlled by the controller, including the argon gas pressure, the volume of the inner chamber 135, the gas flow rate 140, the distance between the electrode 185 and the inner surfaces of the dielectric surface 122, the dielectric constant of the dielectric structure 122, and the selected voltage applied by the RF power source 200. It should be noted that activating the system may cause gas flows for a period of 0.1 to 5 seconds before the RF generator switches on, to ensure circulating gas flows.

Fig. 11A schematically represents the current indicated at 280 being capacitively coupled, through the wall 132 of the dielectric structure 122, to the tissue 260, with the electric field lines indicating that high energy densities do not occur around the electrode 205. Instead, as described above, the high resistance developed in the tissue around the dielectric structure of the current path 122 rapidly causes changes in the current paths and ohmic heating. In one aspect of the invention, capacitive coupling allows for rapid and uniform ablation of tissue adjacent to the dielectric structure. Fig. 11B schematically represents the tissue after the RF energy supply is terminated, resulting in the tissue removed by ablation indicated in 285.

Now returning to Fig. 12, an alternative working end 120' is shown in a method of use. In this embodiment, the dielectric structure 122 is similar to that of Fig. 3, except the working end 120' includes a central support member 290, which extends from the extension member 214 to a distal tip portion 292. In this embodiment, the central support member 290 may contain, or carry, a conductive electrode surface, indicated in 295, to supply energy to the gas 140 in the inner chamber 135 to create the plasma. The embodiment of Fig. 12 It also includes concentric gas influx and efflux channels, 170 and 180, wherein the first channel (influx) 170 comprises a lumen in the supporting member 290 that communicates with a plurality of outflow outlets 250 in a distal part of the inner chamber 135. The gas efflux orifice 174 is again disposed in a proximal part of the inner chamber 135. The placement of the gas influx and efflux ports at opposite ends of the inner chamber allows for efficient gas circulation, which helps maintain a predetermined plasma quality. In Fig. 12, ablative currents and ohmic heating of the tissue are indicated at 200.

In another aspect of the invention, Fig. 12 illustrates that at least one temperature sensor, for example, thermocouples 300A and 300B, are provided within or adjacent to the inner chamber 135 to monitor the plasma temperature. The temperature sensors are coupled to controllers 155A and 155B to allow feedback control of operating parameters, such as supplied RF power, neutral gas influx rate, and negative pressure assisting efflux. By measuring the average temperature of the medium mass in chamber 135, the degree of ionization of the ionized gas 240 can be determined. In one aspect of the invention, the temperature measured inside chamber 135 during operation can provide feedback to the gas circulation controller to thereby modulate the neutral gas flow to maintain a degree of ionization between 0.01% and 5.0%. In another aspect of the invention, the temperature measured inside chamber 135 during operation can provide feedback to modulate the neutral gas flow to maintain a temperature of less than 200 °C, 180 °C, 160 °C, 140 °C, 120 °C, or 100 °C. In various embodiments of polymeric dielectric structures, it is important to maintain a cold or technological plasma to avoid damage to the dielectric. In another aspect of the invention, the operating parameters of the system can be modulated to maintain the average temperature of the mass within a selected range, for example, a range of 5 °C, a range of 10 °C, or a range of 20 °C around a selected temperature for the duration of a tissue treatment interval. In another aspect of the invention, the system's operating parameters can be modulated to maintain a degree of ionization with less than 5% variability, less than 10% variability, or less than 20% variability from a target "degree of ionization" value selected for a tissue treatment range. Although Fig. 12 Show thermocouples inside the inner chamber 135; another embodiment may position such temperature sensors on the outside of the wall 132 of the dielectric structure to monitor the wall temperature. It should also be noted that multiple electrodes may be provided in the inner chamber to measure the impedance of the gaseous medium to provide additional feedback signals.

In another embodiment similar to Fig. 12, the working end 15 or flow channel in communication with the inner chamber 135 may carry at least one pressure sensor (not shown) and the pressure measurement may provide feedback signals to modulate at least one operating parameter such as supplied RF power, neutral gas influx rate, negative pressure assisting efflux, plasma ionization degrees, or plasma temperature. In another aspect of the invention, the operating parameters of the system can be modulated to maintain a pressure within the inner chamber 135 with less than 5% variability, less than 10% variability, or less than 20% variability from a selected target pressure over a tissue treatment range of 25.

In general, Fig. 13 This represents the steps of a method corresponding to an aspect of the invention comprising containing a non-conductive gas inside an enclosure having a dielectric wall, a contacting surface external to the dielectric wall in contact with a target region of the tissue, and applying a radiofrequency voltage across the gas and the dielectric wall wherein the voltage is sufficient to initiate a plasma in the gas and capacitively coupling the current in the gas plasma. through the dielectric wall and into the contacted tissue. This method involves the use of a first-polarity electrode in contact with the gas inside the thin dielectric wall, and a second-polarity electrode in contact with the patient's tissue.

Fig. 14 depicts aspects of a related method corresponding to the invention, comprising positioning a dielectric structure on a fabric surface containing a non-conductive ionizable gas within the dielectric structure, and applying RF voltage across the gas and fabric to ionize the gas and supply current through the dielectric structure to the fabric, to ohmically heat the fabric.

In general, Fig. 15 represents the steps of a method corresponding to another aspect of the invention, which comprises providing a working end or electrosurgical applicator with a first gas dielectric and a second non-gas dielectric in a series circuit, contacting the non-gas dielectric with the tissue, and applying sufficient RF voltage across the circuit to cause dielectric breakdown in the gas dielectric in order to thereby apply ablative energy to the tissue. The ablative energy application step involves capacitively coupling the RF current to the tissue through the second non-gas dielectric medium.

Fig. 16 represents steps of another aspect of the invention, which comprises positioning a dielectric structure including an internal chamber in contact with the bleached fabric, providing a gaseous medium inside the chamber having a degree of ionization of at least 0.01%, and applying RF current through the gaseous medium to cause capacitive coupling of energy through the dielectric structure to modify the fabric. In this aspect of the invention, it should be noted that an ionized gas can be provided for influx into chamber 135, for example, with a neutral gas converted into the ionized gas medium before its flow into chamber 135. The gas can be ionized anywhere along a gas influx channel, intermediate between the gas source 150 and the inner chamber 135, by an RF energy source, a photonic energy source, or any other suitable electromagnetic energy source.

Fig. 17 This represents the steps of another method of the invention, which comprises positioning a dielectric structure encompassing a gaseous medium in contact with bleached fabric, and applying RF current through the gaseous medium and dielectric structure to apply energy to the fabric, and measuring the temperature and/or impedance of the ionized gas medium to provide feedback signals to thereby modulate an operational parameter of the system, such as supplied RF energy, neutral gas influx rate, and/or negative pressure that assists gas efflux.

Now returning to Figs. 18A-22, other embodiments of the electrosurgical working ends are shown, which are adapted to apply energy to the tissue, as described above, except that the dielectric structures have differing dielectric parts, each having a different relative permittivity to thus cause differential effects (greater or lesser capacitive coupling) in the tissue regions in contact with the different parts of the dielectric structure. In one embodiment of probe 400, shown in Figs. 18A-18B, a working end carries multiple tissue penetration elements 405, which are similar to the needle-like working end 120 of Figs. 1-3. The tissue penetration elements 405 can be extended from a shaft 410 of an endoscopic instrument 412 by actuation of lever 414. Each tissue penetration element 405 has a working end with a dielectric structure 422 as described above and one or more return electrodes indicated by 425. As can be seen in Fig. 19, the *

* Tissue penetration elements 405 are adapted to penetrate tissue 260, such as a liver, on the side of a target line 430 which is to be an excision line or plane. Thus, the tissue penetration elements 405 can coagulate tissue on the side of the line 430, and then the tissue can be cut and bleeding will be avoided or reduced. Such an instrument 412 can be used in liver excisions, lung excisions and the like. Fig. 20 This illustrates a cross-section of the multiple tissue penetration elements 405 of Fig. 19 in the tissue, where it can be seen that the wall 432 of the dielectric structure varies from a thin-walled part 435 to a thicker-walled part 436, with each part extending axially along the length of the dielectric structure. As can easily be understood, the thin-walled portion 435 allows for greater current coupling in the adjacent tissue 260, when compared to the thicker-walled portion 436. For this reason, the depth of the ablative or cauterized tissue regions 440 will vary depending on whether it is adjacent to the thin-walled portion 435 or the thicker-walled portion 436. Thus, the instrument can control the ablation depth by varying the volume resistivity of the dielectric wall. For example, the thin-walled section 435 can have a volume resistivity in the range of 1 x 10¹⁴ Ohm/cm, 20 as described above, which can then transition to a thicker wall section 438, having a volume resistivity in the range of 1.5X, 2X or 3X, three times the range of 1 x 10¹⁴ Ohm/cm. As shown in Fig. 20, the energy supply converges to remove by ablation or cauterize regions 440 internally towards line 430 which is targeted for cutting.

At the extreme end of the 430 line, there is less collateral damage due to reduced ohmic heating.

Fig. 21 illustrates a plurality of probes 450A-450D demonstrating a similar use of “directional” dielectric structures 422 for directional control of energy supply to the tissue, in this case to provide ablation convergence regions for ablation removal of tumor 452 when at the working ends of the device in Fig. 18A-20. In this embodiment, it can be seen that the probe loops include an indicator mark 455 that indicates the orientation of the thin-walled part 435 or thick-walled part 436 in order to selectively direct the RF energy supply. In another embodiment, it should be noted that the proximal and distal ends of a dielectric structure 422 can be marked with any suitable image-forming marker, for example, radiopaque markers. In another aspect of the invention shown in Fig. 20, any probe carries at least one thermocouple, for example, thermocouples 456a and 456b, at locations proximal and distal to the dielectric structure 422, to measure tissue temperatures to provide a saturation point to terminate the power supply. The thermocouples provide a signal to controllers 155A and 155B to terminate the ablation procedure. The 15 ablation probes 450A-450D can each carry a return electrode as at the working end in Fig. 19 or, alternatively, they can be a remote return electrode as indicated at 458 in Fig. 21.

Fig. 22 illustrates another embodiment of the electrosurgical working end 460, wherein the wall 432 of the dielectric structure 422' varies from a thin-walled portion 435' to thicker-walled proximal and distal portions 436', with each portion extending radially around the dielectric structure. As can be easily understood, as shown in Fig. 22, the central thin-walled portion 435' thus allows greater current coupling adjacent to tissue 260, to cause deeper ablative tissue 440', when compared with the thicker-walled portions 436' at the ends of the dielectric structure (cf. ablative tissue in Fig. 11B). In all other respects, the working end 460 operates as previously described in the embodiments.

At the working ends of electrosurgical ablation of the *

Figs. 19-21 above, the dielectric structures 422 and 422' provide differential or energy transmissibility by means of varying thicknesses of a dielectric, such as silicon. A portion of an exemplary dielectric wall 470, with thicknesses varying 435' and 436', is shown in Fig. 23, which represents the dielectric of Fig. 22. In other words, a wall of varying thickness with a uniform dielectric constant or volume resistivity of the material can provide varying RF current coupling to the tissue around the surface of the dielectric. It should be noted that an objective of the invention is controlled ablation depth, which can be achieved equally well by having a dielectric of uniform thickness, but varying the electrical properties of the material. Fig. 24 This illustrates a dielectric wall of constant thickness 475 with first and second dielectric materials 477 and 480, which provide higher capacitive coupling through material 480. The number of layers of 15 materials, or material parts, and their dielectric properties can vary from two to ten or more. Furthermore, combinations of varying material thickness and dielectric properties can be used to control the capacitive coupling of the current through the dielectric.

Figures 25A-25D illustrate another embodiment of the electrosurgical system 500 and working end 520 and method of use, which is similar to the device of Fig. 12, except that the dielectric structure 522 of Figs. 25A-25D is made of a thin-walled dielectric that can be moved from an initially unexpanded condition to an expanded condition. In Fig. 25A, the working end is shown with a distally extended sheath 524, which may be made of plastic or metal. A first step of such a method comprises introducing the working end into the tissue interstitially or into a body lumen with the sheath protecting the dielectric structure 522. The dielectric structure 522 is then expanded by gas influxes that cause compression of surrounding tissue and increase the surface area of ​​the thin dielectric wall in contact with the tissue. As can be seen in Fig. 25A, the expandable dielectric 522 can be manufactured from a swellable or non-swellable material, such as a stretchable silicone or a braided, reinforced non-stretchable silicone. The wall thickness of a silicone structure can vary from 0.010 cm to 0.076 cm, and more typically from 0.020 cm to 0.038 cm with an internal volume ranging from less than 5 ml to more than 100 ml. The dielectric structure can have any suitable shape, such as cylindrical, axially tapered, or flattened with internal baffles or restrictions. Fig. 26 shows a section of sheath 524 and a non-expandable expandable dielectric 522 with a thin dielectric wall folding method.

Fig. 25B illustrates multiple subsequent steps of the method, in which the sheath 524 is retracted and the physician activates the gas source 150 and controller to expand the expandable dielectric structure 522. The structure 522 or balloon can be expanded to any predetermined dimension or pressure in soft tissue or in any body lumen, cavity, space, or passage. Radiopaque markings on the dielectric structure (not shown) can be observed fluoroscopically to determine their expanded dimensions and location. The 155A gas circulation controller can circulate gas flow after a predetermined pressure has been reached and maintained.

Fig. 25C represents a subsequent step in the method where the physician activates the RF power source 200 and controller 155B to develop a high voltage potential between the central support electrode 295 and the return electrode 205 which, as previously described, can cause a voltage breakdown in the gaseous dielectric 140 (Fig. 25B) to create plasma 240 and, simultaneously, capacitively couple current to the tissue 260, as indicated by current flows 530. 25D represents the termination of the RF power supply, so that the resulting voltage breakdown and plasma are extinguished - leaving uniform ablative tissue 540 similar to that shown in Fig. 11B.

In one embodiment, the 522 dielectric structure was made of NuSil MED-6640 silicone material, commercially available from NuSil Technology LLC, 1050 Cindy Lane, Carpinteria, California 93013. The 522 dielectric structure was fabricated by immersion to provide a length of 6 cm and a uniform wall thickness of 0.020 cm, thereby providing a relative permittivity in the range of 3 to 4. The structural ends were attached to a rod with a diameter of approximately 4 mm, with the expanded structure having an internal volume of 4.0 cc. The gas used was argon, supplied in a pressurized cartridge available from Leland Limited, Inc., Post Office Box 466, South Plainfield, NJ 07080. The argon was circulated at a flow rate varying between 10 ml/sec and 30 ml/sec. The pressure in the dielectric structure was maintained between 0.984 kg/cm².² and 1.055 kg/cm² with zero or negative differential pressure between the gas influx source 150 and the negative pressure (efflux) source 160. The RF power source 200 had a frequency of 480 kHz, and electrical power was provided within the range of 600 Vrms to about 1200 Nrms and about 0.2 Amps to 0.4 Amps and an effective power of 40W to 80W.

Figures 27 and 28 illustrate another embodiment of the electrosurgical system 600 comprising a catheter having a working end 610 for treating atrial fibrillation by ablation around the pulmonary veins PV. Several methods of using conventional RF catheters for such treatments are known. The catheter 610 is configured with a guide wire channel 612 and can be navigated to a site shown in Figures 27-28. The working end of catheter 620 is included in an expandable dielectric structure 622, similar to that in Figs. 25A-25D, which can be expanded to apply pressure between the balloon wall and the tissue to then create a circumferential lesion in a pulmonary vein (PV). Fig. 28 This is a schematic illustration that again shows the gas source 150 and gas circulation controller 155A which can expand in chamber 635, in the thin-walled dielectric structure 622, to contact the pulmonary vein wall PV. In the embodiment of Fig. 28, it can be seen that the dielectric wall 622 includes a first (smaller) energy-transmissible region 636 and a second (larger) energy-transmissible region 638, thus allowing focused circumferential ablation—which corresponds to the dielectric wall configuration shown in Fig. 24. Next, the RF energy source 200 and controller 155B can be activated to convert the neutral gas flow into plasma 240 and, simultaneously, remove indicated tissue by ablation at 640. In this embodiment, a first-polarity electrode 645 is provided on the catheter rod in the chamber 635, which may cooperate with a second-polarity electrode on the remote balloon catheter rod 622 or any other type of ground support may be used (not shown). In all other considerations, the method of the invention for cardiac tissue ablation follows the steps described above. The balloon may have radiopaque markers, and the system may be operated by an algorithm to expand the 622 dielectric structure or balloon to a predetermined pressure, then supply RF energy and terminate the supply automatically. It should be noted that additional electrodes may be provided on the balloon surface (not shown) for conducting mapping in cardiac tissue.

Although Figs. Figures 27-28 illustrate an expandable dielectric 622 for treating cardiac tissue; it should be noted that the scope of the invention includes using a similar apparatus and method to controllably apply ablative RF energy to any body lumen, vessel, cavity, or body space, such as in a stomach, gallbladder, esophagus, intestine, joint capsule, airways, sinuses, a blood vessel, an arteriovascular malformation, heart, lung, uterus, vaginal canal, bladder, or urethra.

Figures 29-31 schematically illustrate another embodiment of the electrosurgical system 700 and catheter, having a working end 710, for treating atrial fibrillation with linear lesions within a heart chamber, to block anomalous conduction pathways. The catheter may have a guide wire channel (not shown) and may be navigated to perform an elongated ablation in a heart chamber, as in Fig. 29. In this embodiment, the working end of the catheter 720 has a flexible shaft portion 721, which is included in a thin-walled dielectric extending axially 722 onto a tissue-contacting surface, to provide a linear lesion as represented in Fig. 31. The catheter shaft 721 is flexible by means of a pull wire 728, which can be actuated from a catheter handle. Fig. 30 This is another schematic illustration showing the gas source 150 and gas circulation controller 155A, which can provide gas circulation within the inner chamber 735, inside the thin-walled dielectric 722. The RF power source 200 is coupled to a wire 738 and the first-polarity electrode 740 is elongated in the inner chamber 735. The RF 200 power source and 155B controller can be activated to convert the neutral gas flow into a plasma and, simultaneously, remove contacted tissue by dielectric 722, as described above. The second polarity electrode can be provided on the catheter rod remote from the dielectric 722, or any type of ground support can be used (not shown). In all such considerations, the invention's method for cardiac tissue ablation follows the steps described above. The working end may have radiopaque markers, and the system can be operated according to algorithms. It should be noted that additional electrodes can be provided on the working end of the catheter (not shown) for conducting pre- and post-ablation heart mapping.

Fig. 32 illustrates another working end of catheter 720', which is similar to that of Figs. 29-31, which is flexible by a push wire 738, to provide all or part of the circumferential lesion in a pulmonary vein (see Figs. 28-29). In this embodiment, the thin-walled dielectric 722 extends around the outer surface of the articulated working end.

Figures 33 and 34 illustrate another embodiment of the electrosurgical system 800, comprising a catheter having a working end 810 for treating an esophagus 811, for example, for ablating Barrett's esophagus, for applying energy to the lower esophageal sphincter, or for other conditions. The system operates, as previously described in Figures 25A-28, in embodiments having an expandable dielectric structure. In the dielectric structure 822 of Figs. 33-34, the expansion of the structure is provided by a skeletal support member, such as a spring-like member, with an optional pushable cable actuation mechanism. As can be seen in Fig. 34, a helical support member 825 is provided, which is capable of a cross-section (axially stretched) or an expanded cross-section in the chamber 835, which is assisted by a central push cable 828 on the catheter shaft 830. In this embodiment, the dielectric may again comprise a thin-walled silicon, as described above. In this embodiment, it has been found that the support member 825 may be of a conductive metal and coupled to the RF power source to function as a first-polarity electrode 840. The second-polarity electrode (not shown) may be located elsewhere on the catheter, in a tissue-contact location, or a ground support may be used.

Fig. 35 illustrates another embodiment of the electrosurgical system 800', which is similar to that of Fig. 34, with a dielectric structure 822 that is supported in an expanded condition by a plurality of outwardly bent skeletal support members 825', which are assisted by a push cable 828. In this embodiment, the part of the push cable, inside the chamber 835, functions as a first polarity electrode 840'. In the operation, in any of the embodiments described above, it was found that the first-polarity electrode can provide sufficient voltage to create a substantially uniform plasma in an inner chamber (see Figs. 2, 8, 11A, 28, 30, 34, 35) of a non-expandable or expandable dielectric, when the electrode surface is less than 15 mm, less than 10 mm, or less than 5 mm from the inner wall of the dielectric. This maximum dimension of the dielectric wall up to electrode 840' is indicated by D in Fig. 35. It was also found that, in operation, the first polarity electrode can provide voltage to create a substantially uniform plasma in an inner chamber of a non-expandable or expandable dielectric wall, when the electrodes contact the surface of the dielectric 822, as in Fig. 34, however the electrode surface must contact less than about 10% of the inner surface of the dielectric wall. If the first-polarity electrode contacts more than about 10% of the inner surface of the dielectric wall, then the “flow” of energy supply through the tissue, as schematically represented in Fig. 8, will be reduced, and greater capacitive coupling may occur around the regions of the electrode(s) in contact with the wall, which may reduce the uniformity of tissue ablation.

Fig. 36 illustrates another embodiment of the electrosurgical system 900, wherein the working end 910 comprises first and second opposing grippers 912A and 912B, which are adapted for gripping tissue for coagulation, sealing, or tissue welding 914. In one embodiment, both grippers have a tissue contact surface, which comprises a dielectric structure 922A, 922B, which is similar in function to all other such dielectric structures described above. 36 This is a schematic illustration that again shows the gas source 150 and gas circulation controller 155A, which can supply gas to chambers 935A, 935B in the grippers. The RF power source 200 and controller 155B can be activated to convert the neutral gas flows in chambers 935A, 935B within the plasma 240 and, simultaneously, apply energy to the contacted tissue 914. In this embodiment, the clamps carry first and second electrodes of polarity 945A and 945B, respectively, thus enabling the clamp to function by means of a contained ionized gas and capacitive coupling, which differs from previous embodiments. It should be noted that a clamp may comprise a single electrode surface when opposite the plasma-initiated capacitive coupling system of Fig. 36. The dielectric structure of Fig. 36 is of the type described in Figs. 4B and 5A, in which the thin-walled dielectric material is supported by support columns, posts, and channels thereof.

Figures 37 and 38 illustrate another embodiment of the electrosurgical system 1000, again including a catheter or probe rod 1002 extending at a working end 1010 that carries an expandable dielectric structure 1022. In this embodiment, the dielectric structure 1022 includes a plurality of internal chambers, for example, first and second chambers 1024A and 1024B. The expansion of the dielectric structure 1022 can be provided by skeletal support members, such as internal spring-like members as described above, or by fluid pressure expansion from gas influxes or a combination thereof. Each chamber is configured to carry a flexible inner electrode, with adjacent chambers having inner electrodes of opposite polarity, such as electrodes 1040A and 1040B, indicated by polarities (+) and (-) in Figs. 37 and 38, to allow another form of bipolar ablation. In this embodiment, the electrodes and supporting members may comprise the same members. As can be seen in Fig. 37, the outer wall of the dielectric structure 1022 has thin-walled parts 1032A and 1032B, to capacitively couple energy to the tissue, and a thicker-walled part 1042, which isolates and separates the first and second chambers 1024A and 1024B. Flexible electrodes 1040A and 1040B are operatively coupled to power source RF 200. Gas influx source 150 and negative pressure source 160 are coupled to the influx and efflux channels communicating with each internal chamber, 1024A and 1024B, independently. In the cross-sectional view of Fig. 38, the open terminations 1046 and 1048 of the influx and efflux channels can be seen in each internal chamber, 1024A and 1024B. Thus, each chamber is provided with a circulating gas flow (indicated by arrows in Fig. 37), similar to that described in previous embodiments with respect to the single-chamber working ends.

Fig. 38 is a schematic sectional view of the dielectric structure 1022 developed in a bleached fabric 1050. It can be understood that the system can be driven to circulate gas in chambers 1024A and 1024B, which is then converted into plasma 240 in each chamber, as described previously. In this embodiment and method of use, capacitive coupling occurs through the thin dielectric walls 1032A and 1032B in the current flow paths indicated at 280 in Fig. 38. While previous embodiments illustrate a single chamber containing a plasma that capacitively couples current to a non-gas electrode, the embodiment of Figs. 37 and 38 represents the use of at least two contained plasma electrodes and capacitive coupling between them. It should be noted that the number of adjacent chambers carrying electrodes of opposite polarity can be used in a thin-walled dielectric structure, for example, 2 to 10 or more, with the chambers having any suitable dimensions or relative orientations to each other.

Although particular embodiments of the present invention have been described above in detail, it will be understood that this description is merely for illustrative purposes and the above description of the invention is not exhaustive. Specific aspects of the invention are shown in some drawings and not in others, and this is for convenience only, and any aspects may be combined with each other in accordance with the invention. Numerous variations and alternatives will be evident to a person possessing common skills in the art. Such alternatives and variations are intended to be included within the scope of the claims. Particular aspects that are presented in the dependent claims may be combined and fall within the scope of the invention. The invention also encompasses embodiments in which dependent claims were alternatively written in a multiple dependent claim format, with reference to other independent claims.