Electrosurgical Systems

Abstract

Various embodiments provide an electrosurgical system for treating biological tissue. The system includes an electrosurgical generator configured to supply pulsed microwave energy and an electrosurgical instrument. The electrosurgical instrument includes a flexible coaxial cable configured to transmit pulsed microwave energy and a radiating tip portion connected to a distal end of the coaxial cable and configured to receive the pulsed microwave energy. The radiating tip portion has a maximum outer diameter of 1.0 mm or less, the maximum outer diameter of the radiating tip portion being smaller than the outer diameter of the coaxial cable. The radiating tip portion also includes a proximal coaxial transmission line for transmitting the pulsed microwave energy and a distal needle tip attached to the distal end of the proximal coaxial transmission line, the distal needle tip being configured to deliver the pulsed microwave energy to biological tissue.

Description

[Technical field]

[0001] The present invention relates to an electrosurgical system for delivering electromagnetic energy to living tissue to ablate the targeted tissue. The electrosurgical system includes an electrosurgical generator for providing microwave energy and an electrosurgical instrument arranged to receive and deliver the microwave energy to the targeted tissue. The electrosurgical instrument may be arranged to ablate tissue such as a tumor, cyst, or other lesion. The system may be particularly suited for treating pancreatic, pulmonary, or hepatic tissue. [Background technology]

[0002] Electromagnetic (EM) energy, and in particular microwave and radio frequency (RF) energy, have proven useful in electrosurgery due to their ability to cut, coagulate, and ablate living tissue. Generally, devices for delivering EM energy to living tissue include a generator with a source of EM energy and an electrosurgical instrument connected to the generator to deliver energy to the tissue. Conventional electrosurgical instruments are often designed to be inserted percutaneously into the patient's body. However, it can be difficult to place the instrument percutaneously within the body, for example, when the target site is in a moving lung or a thin-walled portion of the gastrointestinal (GI) tract. Other electrosurgical instruments can be delivered to the target site by a surgical scope device (e.g., endoscope) that can pass through internal body passages such as the airway or the lumen of the esophagus or colon. This allows for less invasive treatments, reducing patient mortality and intraoperative and postoperative complication rates.

[0003] Tissue ablation using microwave EM energy is based on the fact that biological tissue is composed primarily of water. Human soft organ tissues typically have a water content of 70%-80%. Water molecules have a permanent electric dipole moment, meaning that there is an imbalance of charge throughout the molecule. This charge imbalance causes the molecules to move in response to forces generated by applying a time-varying electric field, as they rotate and their electric dipole moment aligns with the polarity of the applied electric field. At microwave frequencies, the rapid molecular vibrations cause frictional heating, resulting in the dissipation of field energy in the form of heat. This is known as dielectric heating.

[0004] This principle is utilized in microwave ablation therapy, in which the application of a localized electromagnetic field at microwave frequencies rapidly heats water molecules in targeted tissue, resulting in tissue coagulation and cell death. It is known to use microwave emitting probes to treat various conditions in the lungs and other organs. For example, in the lungs, microwave radiation can be used to treat asthma and to ablate tumors or lesions. Summary of the Invention [Means for solving the problem]

[0005] Most generally, the present invention provides an electrosurgical system that is arranged to deliver pulsed microwave energy to biological tissue via a small diameter (e.g., 1.0 mm or less) emitting tip portion. An advantage of using a small diameter emitting tip portion is that the size of the insertion opening made when the emitting tip portion is inserted into the target tissue can be minimized, thereby reducing bleeding and promoting healing. However, a disadvantage of using such a small diameter emitting tip portion is that the transmission of microwave energy through the emitting tip portion can cause excessive heating of the emitting tip portion. Such excessive heating can cause burns and therefore damage to healthy tissue. The inventors have overcome this disadvantage by configuring the electrosurgical system to deliver microwave energy in a pulsed manner. By delivering microwave energy in a pulsed manner, it is possible to avoid excessive heating of the emitting tip portion. This can allow for effective treatment of the target biological tissue with the emitting tip portion while avoiding damage to the surrounding healthy tissue.

[0006] The radiating tip portion of conventional electrosurgical instruments that may be used to treat the liver typically has an outer diameter between 2-3 mm. The inventors have found that the use of such electrosurgical instruments in the liver can cause excessive bleeding that may be difficult to keep under control during a surgical procedure. If the surgeon is unable to control such bleeding during surgery, it may be necessary to remove the electrosurgical instruments and attempt to continue the operation by other means.

[0007] In contrast, the electrosurgical system of the present invention may be particularly suitable for treating tissue in highly vascularized regions of the body (where there may be excessive bleeding, for example, when piercing tissue) because the small insertion hole created by the emitting tip portion may avoid or reduce bleeding. Thus, the combination of a small diameter emitting tip portion and pulsed microwave energy delivery may allow highly vascularized regions of the body to be treated with microwave energy. In particular, the inventors have found that by using a small diameter emitting tip portion of the electrosurgical system of the present invention, excessive bleeding may be avoided when used to treat target tissue in the liver. Thus, the electrosurgical system of the present invention may be particularly suitable for use in treating tissue in the liver. Furthermore, a small diameter emitting tip portion may be beneficial where scarring may be an issue. For example, the electrosurgical instrument of the present invention may allow for reduced scarring when used to resect tumors in the chest.

[0008] In accordance with the present invention, there is provided an electrosurgical system for treating biological tissue comprising an electrosurgical generator configured to supply pulsed microwave energy; and an electrosurgical instrument comprising: a flexible coaxial cable arranged to transmit pulsed microwave energy; and a radiating tip portion configured to connect to a distal end of the coaxial cable to receive the pulsed microwave energy, the radiating tip portion having a maximum outer diameter of 1.0 mm or less, the maximum outer diameter of the radiating tip portion being smaller than an outer diameter of the coaxial cable; the radiating tip portion comprising a proximal coaxial transmission line for transmitting the pulsed microwave energy; and a distal needle tip attached to a distal end of the proximal coaxial transmission line, the distal needle tip arranged to deliver the pulsed microwave energy to biological tissue.

[0009] The inventors have found that by making the maximum outer diameter of the radiating tip portion 1.0 mm or less, bleeding during insertion of the radiating tip portion into the target tissue can be significantly reduced or avoided. As discussed above, the use of pulsed microwave energy can ensure that excessive heat is not generated at the radiating tip portion when microwave energy is delivered to the radiating tip portion. In contrast to delivering microwave energy as a continuous wave, which can cause the radiating tip portion to heat up quickly, pulsed microwave energy can facilitate maintaining the radiating tip portion at an acceptable temperature. Pulsed microwave energy delivery can also allow for a reduction in the total time that microwave energy is delivered to the radiating tip portion, for example, by delivering short, high-power pulses. In this manner, the electrosurgical system can be used to effectively treat (e.g., ablate) the target tissue while avoiding damage to nearby healthy tissue.

[0010] The electrosurgical generator may be any suitable generator for controllably supplying microwave energy. A suitable generator for this purpose is described in WO2012 / 076844, which is incorporated herein by reference. The electrosurgical generator may generate pulsed microwave energy by modulating a microwave energy source to generate a profile (or waveform) having a series of "on" periods (corresponding to microwave pulses) separated by a series of "off" periods. Generally speaking, pulsed microwave energy may be microwave energy having a profile that includes multiple pulses (or bursts) of microwave energy separated by periods of no microwave energy. Pulsed microwave energy may be periodic, for example having a periodic cycle with "on" and "off" periods.

[0011] A variety of pulsed microwave energy profiles can be used. For example, all microwave pulses may be of the same duration or may vary in duration. Similarly, the period between pulses may all be the same or may vary over time. The pulses may have a predefined power profile (i.e., power versus time). In some cases, different pulses may have different power profiles depending on the desired energy delivery profile.

[0012] The electrosurgical instrument can be dimensioned for insertion into an instrument (or working) channel of a surgical scoping device, which can facilitate insertion of the electrosurgical instrument into a patient's body and allow access to a treatment site.

[0013] The flexible coaxial cable may be a conventional low-loss coaxial cable connectable at a proximal end to an electrosurgical generator for receiving pulsed microwave energy. In some cases, the coaxial cable may be permanently connected to the electrosurgical generator. The coaxial cable may have a central conductor separated from an outer conductor by a dielectric material. The coaxial cable may further include an outer protective sheath for insulating and protecting the cable. In some embodiments, the protective sheath may be made of or coated with a non-stick material to prevent tissue from adhering thereto and / or to facilitate insertion of an instrument into an instrument channel of a surgical scope device. The radiating tip portion is located at a distal end of the coaxial cable and is connected to receive the pulsed microwave energy transmitted along the coaxial cable.

[0014] The proximal coaxial transmission line may be electrically connected to the distal end of the coaxial cable to receive and transmit the pulsed microwave energy to the distal needle tip where the pulsed microwave energy is delivered to the target tissue. The material used in the proximal coaxial transmission line may be the same or different from the material used in the coaxial cable. The material used in the proximal coaxial transmission line may be selected to provide a desired flexibility and / or impedance of the proximal coaxial transmission line. For example, the dielectric material of the proximal coaxial transmission line may be selected to improve impedance matching with the target tissue.

[0015] The distal needle tip is formed at the distal end of the proximal coaxial transmission line. The distal needle tip may include an emitter structure configured to receive pulsed microwave energy from the proximal coaxial transmission line and deliver the energy to the target tissue. The emitter structure may be configured to generate a desired ablation profile in the target tissue. For example, the emitter structure may be a monopole or dipole microwave antenna for radiating microwave energy to the surrounding tissue. In some cases, the emitter structure may also be capable of delivering radio frequency energy to the target tissue, either individually or in combination with the pulsed microwave energy.

[0016] The distal needle tip may include a sharpened distal end to facilitate insertion of the emitting tip portion into the target tissue.

[0017] The maximum outer diameter of the radiating tip portion is 1.0 mm or less. For example, the radiating tip portion can be 19 gauge. In some embodiments, the maximum outer diameter can be 0.95 mm, 0.9 mm, or less. The maximum outer diameter can refer to the largest outer diameter of the radiating tip portion along the length of the radiating tip portion.

[0018] The outer diameter of the radiating tip portion is smaller than the outer diameter of the coaxial cable. Using a smaller diameter radiating tip portion allows the radiating tip portion to be more flexible than the coaxial cable, which may make it easier to navigate the distal needle tip to a desired location, for example, when the device needs to be navigated near a sharp bend. An advantage of using a coaxial cable with a larger outer diameter than the radiating tip portion is that heating of the coaxial cable may be reduced, as heating is generally related to the diameter of the coaxial cable.

[0019] The pulse duration of the pulsed microwave energy may be shorter than the thermal response time of the radiating tip portion. This may reduce heating of the radiating tip portion because the radiating tip portion may not be thermally responsive to the magnitude of the pulsed microwave energy within the time frame of the pulse duration. This may improve the efficiency with which microwave energy may be delivered to the distal needle tip because heating effects (e.g., dissipation of microwave energy) along the length of the radiating tip portion may be reduced. This may help improve the overall efficiency with which microwave energy may be delivered to the target tissue.

[0020] The pulse duration may correspond to the duration of a pulse of microwave energy in the pulsed microwave energy supplied by the electrosurgical generator. The thermal response time may correspond to the time it takes for the temperature of the radiating tip portion to react (e.g., change by a given amount) when microwave energy of a given power level is delivered to the radiating tip portion. The thermal response time of the radiating tip portion may depend on the thermal capacity of the radiating tip portion, e.g., the greater the thermal capacity, the longer the thermal response time. To determine an appropriate pulse duration, the thermal response time of the radiating tip portion can be measured experimentally.

[0021] In some embodiments, the electrosurgical generator may be configured to deliver pulsed microwave energy at a duty cycle of 25% or less. Having a duty cycle of the pulsed microwave energy of 25% or less may avoid or reduce heating effects of the radiating tip portion. For example, a duty cycle of 25% or less may ensure that the microwave pulse is short enough so that the radiating tip portion does not have enough time to thermally react to the pulse. As used herein, a duty cycle may refer to a portion of the period of pulsed microwave energy during which microwave energy is delivered by the electrosurgical generator (the remainder of the period may correspond to an "off" period during which microwave energy is not delivered). Thus, a duty cycle of 25% or less may not deliver microwave energy for at least 75% of the period of the pulsed microwave energy. This may ensure that the pause between pulses of microwave energy is long enough so that there is little or no buildup of thermal effects over multiple pulses.

[0022] The pulse duration of the pulsed microwave energy may be between 10 ms and 200 ms. The inventors have found that by using a pulse duration between 10 ms and 200 ms, it may be possible to avoid or reduce heating effects at the radiating tip portion, so that the radiating tip portion can be maintained at an acceptable temperature. A pulse duration between 10 ms and 200 ms in combination with a duty cycle of 25% or less may further ensure that heating effects are avoided or reduced.

[0023] In some embodiments, the pulsed microwave energy may be delivered according to one of the following cycles: a) Pulse duration 10 ms, pulse interval 90 ms. b) Pulse duration 10 ms, pulse interval 50 ms. c) Pulse duration 10 ms, pulse interval 30 ms. d) Pulse duration 100 ms, pulse interval 900 ms. e) Pulse duration 100 ms, pulse interval 500 ms. f) Pulse duration 100 ms, pulse interval 300 ms. g) Pulse duration 200 ms, pulse interval 800 ms.

[0024] Cycles a) and d) correspond to a 10% duty cycle, cycles b) and e) correspond to a 16.67% duty cycle, cycles c) and f) correspond to a 25% duty cycle, and cycle g) corresponds to a 20% duty cycle. These duty cycles may allow for effective treatment of the target tissue while maintaining the emitting tip at an acceptable temperature during treatment of the target tissue.

[0025] In some embodiments, the length of the radiating tip portion may be 140 mm or more. Coaxial cables commonly used in electrosurgical instruments (e.g., Sucoform 86 coaxial cable) often have a thickly tinned exterior to allow longitudinal movement of the cable. However, this can make the coaxial cable relatively stiff, which requires a large force to bend the coaxial cable. This can cause a large amount of friction as the device moves through a bend, for example, in the instrument channel of a surgical scope device. This can prevent control of the position of the radiating tip portion. The inventors have found that having a long radiating tip portion can facilitate bending of the instrument near its distal end, as the radiating tip portion can have greater flexibility compared to the coaxial cable. Having a radiating tip portion of 140 mm or more can allow for avoiding the need to move the coaxial cable through a curved distal portion of a surgical scope device. This can facilitate deployment of the radiating tip portion, for example, when the distal portion of the surgical scope device is deflected. This configuration can be particularly beneficial for use in the pancreas, where the distal portion of the instrument may need to be deflected.

[0026] In some embodiments, the proximal coaxial transmission line can include an inner conductor extending from a distal end of a flexible coaxial cable and electrically connected to a center conductor of the flexible coaxial cable, a proximal dielectric sleeve mounted about the inner conductor, and an outer conductor mounted about the proximal dielectric sleeve, the distal needle tip including a distal dielectric sleeve mounted about the inner conductor, a distal portion of the outer conductor overlapping a proximal portion of the distal dielectric sleeve, the distal dielectric sleeve can be secured such as by crimping.

[0027] The outer conductor may be, for example, a conductive tube formed from Nitinol, a material that exhibits sufficient longitudinal stiffness to transmit forces capable of penetrating target tissue. Preferably, the conductive tube also exhibits suitable lateral flexure to allow instruments to travel through the instrument channel of a surgical scope device. Advantageously, Nitinol may provide sufficient longitudinal stiffness to penetrate the duodenal wall, allowing treatment of pancreatic tissue, while still providing a high degree of lateral flexibility. The distal needle tip may be substantially rigid to facilitate insertion into biological tissue.

[0028] The inner conductor may be formed from a highly conductive material, for example, silver. The inner conductor may have a diameter smaller than that of the central conductor of the flexible coaxial cable. This may facilitate bending of the radiating tip portion. For example, the diameter of the inner conductor may be 0.25 mm. The preferred diameter may take into account that the primary parameter determining the loss (and heating) along the radiating tip portion is the conductor loss, which is a function of the diameter of the inner conductor. Other relevant parameters are the dielectric constants of the distal and proximal dielectric sleeves and the diameter and material used for the outer conductor. The dimensions of the components of the proximal coaxial transmission line may be selected to provide an impedance that is the same as or close to that of the flexible coaxial cable (e.g., about 50 Ω).

[0029] The radiating tip portion may be secured to the flexible coaxial cable by a collar attached over the junction therebetween. The collar may be electrically conductive and may be formed from brass, for example. The collar may electrically connect the outer conductor with the outer conductor of the flexible coaxial cable.

[0030] The distal end of the distal dielectric sleeve can be sharpened, for example, so that it can taper to a point. Alternatively, a separate pointed tip element can be attached to the distal end of the distal dielectric sleeve. This can facilitate insertion of the instrument into the target tissue, for example through the duodenal or gastric wall and into the pancreas.

[0031] The distal dielectric sleeve may be made of a different material than the proximal dielectric sleeve. The proximal dielectric sleeve may be made of the same material as the dielectric material of the flexible coaxial cable, such as PTFE. In contrast, the distal dielectric sleeve may be made of either ceramic, polyetheretherketone (PEEK), or glass-filled PEEK. These materials may exhibit desirable stiffness and may be sharpened. It may also allow for the physical length of the radiating tip portion to be controlled (e.g., reduced or optimized) while maintaining its electrical length. Thus, the distal dielectric sleeve may have a higher stiffness than the proximal dielectric sleeve. The higher stiffness of the distal dielectric sleeve may facilitate insertion of the radiating tip portion into the target tissue, while the greater flexibility of the proximal dielectric sleeve may facilitate manipulation of the radiating tip portion, for example, around bends.

[0032] In some embodiments, the proximal end of the distal dielectric sleeve can include a protrusion disposed about the inner conductor, which can be received in a complementary shaped cavity in the distal end of the proximal dielectric sleeve. Such a configuration can improve the mechanical connection between the proximal and distal dielectric sleeves. Additionally, the protrusion can help increase the breakdown voltage of the radiating tip portion at the junction between the proximal and distal dielectric sleeves, thereby improving the electrical safety of the radiating tip portion.

[0033] The distal needle tip may be configured to act as a half-wave transformer for delivering microwave energy from the distal needle tip. An advantage of configuring the distal needle tip as a half-wave transformer may be to minimize reflections at interfaces between components, for example, between the coaxial cable and the proximal coaxial transmission line, and between the proximal coaxial transmission line and the distal needle tip. The reflection coefficient at the latter interface is typically large due to the large impedance variation. The half-wave configuration may minimize these reflections so that the dominant reflection coefficient is that of the interface between the proximal coaxial transmission line and the tissue. The impedance of the proximal coaxial transmission line may be selected to be the same as or close to the expected tissue impedance to provide a good match at the frequency of the microwave energy.

[0034] In some embodiments, the electrosurgical system may further include a surgical scope device having a flexible insertion cord for insertion into a patient's body, the flexible insertion cord having an instrument channel extending along its length, the electrosurgical instrument being dimensioned to be received within the instrument channel.

[0035] The electrosurgical systems discussed herein may also be suitable for treating difficult to reach treatment sites, such as pancreatic or pulmonary tissue, due to the small diameter of the emitting tip.

[0036] As used herein, the term "surgical scope device" may refer to any surgical device with an insertion cord, which is a rigid or flexible (e.g., steerable) conduit introduced into a patient's body during an invasive procedure. The insertion cord may include an instrument channel and an optical channel (e.g., for transmitting light to illuminate a treatment site at a distal end of the insertion tube and / or capture an image of the treatment site). The instrument channel may have a diameter suitable for receiving an invasive surgical tool. The diameter of the instrument channel may be 5 mm or less. In an embodiment of the invention, the surgical scope device may be an ultrasound-enabled endoscope. For example, the surgical scope device may be an ultrasound-enabled bronchoscope, with the insertion cord adapted to be inserted through a patient's airway into the bronchial tree. The bronchoscope may include one or more ultrasound transducers at a distal end of the insertion cord. The ultrasound transducers may be operable to aid in the insertion and placement of electrosurgical instruments. In particular, they may be positioned to generate ultrasound images of the emitting tip as it extends from the distal end of the instrument channel (and beyond the catheter) and penetrates tissue on its way to the treatment site.

[0037] As used herein, the term "inner" means radially closer to the center (e.g., axis) of the instrument channel and / or coaxial cable, and the term "outer" means radially farther from the center (axis) of the instrument channel and / or coaxial cable.

[0038] As used herein, the term "conductive" means electrically conductive, unless the context indicates otherwise.

[0039] As used herein, the terms "proximal" and "distal" refer to the ends of an elongate instrument. In use, the proximal end is closer to a generator for providing RF and / or microwave energy, while the distal end is farther from the generator.

[0040] As used herein, "microwave" may be used broadly to refer to a frequency range of 400 MHz to 100 GHz, but preferably refers to the range of 1 GHz to 60 GHz. Preferred spot frequencies of microwave EM energy include 915 MHz, 2.45 GHz, 3.3 GHz, 5.8 GHz, 10 GHz, 14.5 GHz, and 24 GHz. 5.8 GHz may be preferred. Devices may deliver energy at more than one of these microwave frequencies.

[0041] The term "high frequency" or "RF" may be used to indicate frequencies between 300 kHz and 400 MHz. The term "low frequency" or "LF" may mean frequencies in the range of 30 kHz to 300 kHz.

[0042] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. [Brief description of the drawings]

[0043] [Figure 1] 1 is a schematic diagram of an electrosurgical system for tissue ablation, one embodiment of the present invention; [Diagram 2] 1 is a schematic cross-sectional view through an instrument cord of an endoscope that can be used in the present invention. [Diagram 3] 1 is a schematic side view of an electrosurgical instrument that can be used in the electrosurgical system of the present invention; [Figure 4] FIG. 4 is a cross-sectional view of the electrosurgical instrument of FIG. 3 with the outer conductor omitted for purposes of illustration. [Diagram 5] 4 is a cross-sectional view of a distal portion of the electrosurgical instrument of FIG. 3. [Figure 6] 1 is a graph illustrating the power delivery profile of pulsed microwave energy supplied by an electrosurgical generator that is part of the electrosurgical system of the present invention. [Figure 7] 1 is a schematic cross-sectional view of a radiating tip portion that can be used in the electrosurgical system of the present invention [Figure 8a] 1 is a schematic cross-sectional view of a radiating tip portion that can be used in the electrosurgical system of the present invention [Figure 8b] FIG. 8b is a perspective view of the distal tip of the radiating tip portion of FIG. 8a. [Figure 9a] 1 is a schematic cross-sectional view of a radiating tip portion that can be used in the electrosurgical system of the present invention. [Figure 9b] FIG. 9b is a schematic cross-sectional view of the distal portion of the radiating tip portion of FIG. 9a. [Figure 10] 1 is a schematic cross-sectional view of a radiating tip portion that can be used in the electrosurgical system of the present invention. [Figure 11] 1 is a schematic cross-sectional view of a radiating tip portion that can be used in the electrosurgical system of the present invention. [Figure 12] 12A-12C show plots of simulated return loss for electrosurgical instruments having the radiating tip portions of FIGS. 8, 8a, 9a, 10 and 11. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] FIG. 1 is a schematic diagram of an electrosurgical system 100 according to one embodiment of the present invention. The electrosurgical system 100 can deliver microwave energy to a distal end of an invasive electrosurgical instrument to perform tissue ablation. The electrosurgical system can also deliver a fluid, such as a liquid drug or a coolant, to the distal end of the invasive electrosurgical instrument. The system 100 includes an electrosurgical generator 102 for controllably delivering microwave energy. As discussed in more detail below, the electrosurgical generator is configured to deliver pulsed microwave energy. A suitable generator for this purpose is described in WO2012 / 076844, which is incorporated herein by reference. The electrosurgical generator 102 can be configured to monitor a reflected signal received back from the instrument to determine an appropriate power level for delivery. For example, the generator 102 can be configured to calculate the expected impedance at the distal end of the instrument to determine an optimal delivery power level.

[0045] The electrosurgical system 100 further includes an interface joint 106 connected to the electrosurgical generator 102 via an interface cable 104. The interface joint 106 is also connected to a fluid delivery device 108, such as a syringe, via a fluid flow line 107. In some embodiments, the system may additionally or alternatively be configured to aspirate fluid from the treatment site. In this scenario, the fluid flow line 107 may carry the fluid from the interface joint 106 to a suitable collector (not shown). An aspiration mechanism may be connected to the proximal end of the fluid flow line 107.

[0046] The interface joint 106 can house an instrument control mechanism for controlling the position of the electrosurgical instrument. The control mechanism can be used to control the longitudinal position of the electrosurgical instrument and / or the bending of the distal end of the electrosurgical instrument. The instrument control mechanism can be operated by sliding a trigger to control the longitudinal (back and forth) movement of one or more control wires or push rods (not shown). If there are multiple control wires, there can be multiple sliding triggers at the interface joint to provide complete control. The function of the interface joint 106 is to couple the inputs from the generator 102, fluid delivery device 108 and instrument control mechanism to a single flexible shaft (or electrosurgical instrument) 112, which extends from the distal end of the interface joint 106.

[0047] The electrosurgical system further includes a surgical scope device 114, which in an embodiment of the invention may comprise an endoscopic ultrasound device. The flexible shaft 112 is insertable through the entire length of the instrument (working) channel of the surgical scope device 114.

[0048] The surgical scope device 114 includes a body 116 having a number of input ports and an output port from which an instrument cord 120 extends. The instrument cord 120, shown in more detail in FIG. 2, includes an outer jacket surrounding multiple lumens. The multiple lumens transport various things from the body 116 to the distal end of the instrument cord 120. One of the multiple lumens is the instrument channel discussed above. Other lumens may include channels for transmitting optical radiation, for example, to provide illumination at the distal end or to collect images from the distal end. The body 116 may include an eyepiece 122 for viewing the distal end.

[0049] Endoscopic ultrasound devices typically provide an ultrasound transducer at the distal tip of the instrument cord, beyond the exit lumen of the instrument channel. Signals from the ultrasound transducer may be transmitted by a suitable cable 126 back up the instrument cord to a processor 124, which may generate images in a known manner. An instrument channel may be formed in the instrument cord such that an instrument exiting the instrument channel may be directed through the field of view of the ultrasound system to provide information regarding the position of the instrument at the target site.

[0050] The flexible shaft 112 passes through an instrument channel of the surgical scope device 114 and has a distal assembly 118 (not drawn to scale in FIG. 1) shaped to protrude (e.g., into the patient) at the distal end of the instrument cord.

[0051] The structure of the distal assembly 118 discussed below may be specifically designed for use with an endoscopic ultrasound (EUS) device. The maximum outer diameter of the distal assembly 118 is less than 1.0 mm, e.g., less than 0.95 mm or 0.90 mm. The length of the flexible shaft may be 1.2 m or more.

[0052] The body 116 includes an input port 128 for connecting to the flexible shaft 112. As described below, the proximal portion of the flexible shaft may comprise a conventional coaxial cable capable of transmitting pulsed microwave energy from the electrosurgical generator 102 to the distal assembly 118. Examples of coaxial cables that can physically fit into the instrument channel of an EUS device are available in outer diameters of 0.047 inches, 0.053 inches, 0.055 inches, 0.063 inches, and 0.070 inches. Custom sized coaxial cables (i.e., made to order) can also be used.

[0053] To control the position of the distal end of the instrument cord 120, the body 116 may further comprise a control actuator mechanically coupled to the distal end of the instrument cord 120 by one or more control wires (not shown) extending through the instrument cord 120. The control wire may move within the instrument channel or may move within its own dedicated channel. The control actuator may be a lever or a rotatable knob, or any other known catheter manipulation device. Manipulation of the instrument cord 120 may be software assisted, for example, using a virtual three-dimensional map combined with computed tomography (CT) images.

[0054] The present invention may be particularly suitable for treatment of the pancreas. To reach a target site in the pancreas, the instrument cord 120 may need to be navigated through the mouth, stomach, and duodenum. The electrosurgical instrument is positioned to access the pancreas by passing through the wall of the duodenum. The present invention may also be particularly suitable for treatment of liver tissue.

[0055] 2 is a view looking down the shaft of the instrument cord 120. In this embodiment, there are four lumens within the instrument cord 120. The largest lumen is the instrument channel 132 through which the flexible shaft 112 is received. Other lumens include an ultrasound signal channel 134, an illumination channel 136, and a camera channel 138, although the invention is not limited to this configuration. For example, there could be other lumens, such as for control wires or fluid delivery or aspiration.

[0056] An electrosurgical instrument 300 that may be part of the electrosurgical system of the present invention will now be described with reference to Figures 3 and 4. Figures 3 and 4 show a side view of a distal portion of electrosurgical instrument 300, which may correspond to distal assembly 118 described above. The electrosurgical instrument 300 includes a flexible coaxial cable 302 and a radiating tip portion 304 connected to a distal end of the coaxial cable 302. The coaxial cable 302 may be a conventional flexible 50 Ω coaxial cable suitable for transmitting microwave energy. The coaxial cable includes a center conductor and an outer conductor separated by a dielectric material. The coaxial cable 302 is connectable at a proximal end to a generator, for example, generator 102, for receiving microwave energy.

[0057] The radiating tip portion 304 includes a proximal coaxial transmission line 306 and a distal needle tip 308 formed at a distal end of the proximal coaxial transmission line 306. The proximal coaxial transmission line 306 is electrically connected to the distal end of the coaxial cable 302 to receive electromagnetic energy from the coaxial cable 302 and transmit the electromagnetic energy to the distal needle tip 308. The distal needle tip 308 is configured to deliver the received electromagnetic energy to a target biological tissue. In this embodiment, the distal needle tip 308 is configured as a half-wave transformer to deliver microwave energy to the target biological tissue to ablate the target tissue. In other words, the electrical length of the distal needle tip 308 may correspond to a half wavelength (e.g., 5.8 GHz) of microwave energy. When microwave energy is delivered to the distal needle tip 308, it can radiate the microwave energy along its length to the surrounding biological tissue.

[0058] An inner conductor 310 of the proximal coaxial transmission line 306 is electrically connected to the center conductor of the coaxial cable 302. The radiating tip portion 304 is secured to the coaxial cable 302 via a collar 312 that is attached over the junction between the coaxial cable 302 and the radiating tip portion 304. The collar 312 is made of a conductive material (e.g., brass) and electrically connects the outer conductor of the coaxial cable 302 to the outer conductor 314 of the proximal coaxial transmission line 306. The outer conductor 314 is formed of a tube of Nitinol that is flexible and provides sufficient longitudinal stiffness to penetrate tissue (e.g., the duodenal wall). For purposes of illustration, the outer conductor 314 has been omitted from FIG. 4 to reveal the internal structure of the radiating tip portion 304. Also, for purposes of illustration, a length of the proximal coaxial transmission line 306 has been omitted from FIGS. 3 and 4, as indicated by dashed line 307.

[0059] The proximal coaxial transmission line 306 includes a proximal dielectric sleeve 320 disposed about the inner conductor 310 and spacing the inner conductor 310 from the outer conductor 314. The outer conductor 314 is formed on an outer surface of the proximal dielectric sleeve 320. A distal dielectric sleeve 322 is disposed about a distal portion of the inner conductor 310 to form a distal needle tip 308. The distal needle tip 308 further includes a point 324 at its distal end to facilitate insertion of the radiating tip portion into a target tissue. The distal dielectric sleeve 322 may be made of a different dielectric material as compared to the proximal dielectric sleeve 504. In one embodiment, the proximal dielectric sleeve 504 may be made of PTFE (e.g., a PTFE tube) and the distal dielectric sleeve may be made of PEEK. Particular examples of materials that may be used in the radiating tip portion 304 are described below in connection with FIGS. 7-11.

[0060] A distal portion of the outer conductor 314 overlaps a proximal portion of the distal dielectric sleeve 322. In this manner, the distal portion of the proximal coaxial transmission line 306 includes the proximal portion of the distal dielectric sleeve 322. The materials of the proximal and distal dielectric sleeves and the length of overlap between the outer conductor 314 and the distal dielectric sleeve 322 may be selected to adjust the electrical length of the radiating tip portion 308 and the impedance match with the target tissue.

[0061] The collar 312 includes a substantially cylindrical body 316 that is attached to the distal end of the coaxial cable 302 and electrically connected to the outer conductor of the coaxial cable 302. The collar 312 further includes a distal portion 318 that extends from the body 316 of the collar 312 to the proximal end of the outer conductor 314 of the proximal coaxial transmission line 306. The distal portion 318 of the collar 312 includes a rounded distal surface, which may reduce friction between the electrosurgical instrument 300 and the instrument channel of the surgical scope device as the electrosurgical instrument 300 moves along the channel by eliminating sharp edges at the interface between the coaxial cable 302 and the radiating tip portion 304. This may also facilitate moving the electrosurgical instrument along the channel when the channel is deflected.

[0062] The maximum outer diameter of the radiating tip portion 304 is indicated by arrow 326 in FIG. 3. In this example, the maximum outer diameter of the radiating tip portion 304 corresponds to the outer diameter of the outer conductor 314, since the outer conductor 314 is the component of the radiating tip portion 304 that has the maximum outer diameter. The maximum outer diameter of the radiating tip portion 304 is 1.0 mm or less. For example, it may be 1.0 mm, 0.95 mm, or 0.90 mm. This may ensure that the size of the insertion hole created by the radiating tip portion 304 when it is inserted into the target tissue is small, which may minimize bleeding. This may make the electrosurgical instrument 300 particularly suitable for use in highly vascularized areas of the body, such as the liver, where excessive bleeding may be a problem.

[0063] The outer diameter of the coaxial cable 302 is indicated by arrow 328 in FIG. 3. The outer diameter of the coaxial cable 302 is greater than the maximum outer diameter of the radiating tip portion 304. For example, the outer diameter of the coaxial cable 302 may be between 1.19 mm and 2.0 mm, or it may be greater than 2.0 mm. By providing the radiating tip portion 304 with a smaller maximum outer diameter than the coaxial cable, it is possible to increase the flexibility of the radiating tip portion 304 relative to the coaxial cable 302. This may make it easier to manipulate the radiating tip portion 304 to a particular treatment location. At the same time, by providing the coaxial cable 302 with a larger diameter, transmission losses (e.g., due to heating) in the coaxial cable 302 may be reduced, as transmission losses are generally related to the diameter of the coaxial cable 302. This may allow microwave energy to be more efficiently transferred along the coaxial cable 302 to the radiating tip portion 304.

[0064] In some embodiments, the electrosurgical instrument 300 may be housed in a catheter (not shown). The electrosurgical instrument 300 may be movable relative to the catheter so that the emitting tip portion 304 can be retracted into the catheter when not in use. This may help protect the emitting tip portion and prevent it from getting caught on the instrument cord when inserted into the instrument cord of a surgical scope device.

[0065] The radiating tip portion 304 may have a length of 30 mm or more, for example 40 mm. In this manner, the radiating tip portion 304 may be long enough for the distal needle tip 308 to reach the treatment site without having to insert a portion of the coaxial cable 302 into tissue. In some cases, the radiating tip portion 304 may have a length of 140 mm or more. The inventors have found that this may facilitate insertion of the electrosurgical instrument 300 into an instrument cord having a curved distal portion of the instrument cord, as it may be unnecessary to push a stiffer coaxial cable 302 through the distal portion of the instrument cord.

[0066] FIG. 5 shows the interface between the proximal dielectric sleeve 320 and the distal dielectric sleeve 322 in more detail. FIG. 5 shows a cross-sectional view of the distal portion of the radiating tip portion 304. For purposes of illustration, the outer conductor 314 has been omitted from FIG. 5. The proximal end of the distal dielectric sleeve 322 includes a protrusion 502 extending from the proximal end of the distal dielectric sleeve 322. The protrusion 502 is generally cylindrical with an outer diameter smaller than the outer diameter of the distal dielectric sleeve 322 and is disposed about the inner conductor 310. The proximal dielectric sleeve 320 includes a cavity having a shape complementary to the shape of the protrusion 502, in which the protrusion 502 is received. Thus, the proximal dielectric sleeve 320 moves around the protrusion 502. When the protrusion 502 of the distal dielectric sleeve 322 is received in the proximal dielectric sleeve 320, this helps to provide a strong mechanical connection between the distal and proximal dielectric sleeves. Additionally, the protrusions 502 may help increase the breakdown voltage of the radiating tip portion 304 at the interface between the distal dielectric sleeve 322 and the proximal dielectric sleeve 320. This may improve the electrical safety of the radiating tip portion 304.

[0067] Because the radiating tip portion 304 of the electrosurgical instrument has a small diameter (i.e., 1.0 mm or less), it can heat up quickly when microwave energy is delivered to it. This can make the delivery of microwave energy to the distal needle tip inefficient. Heating of the radiating tip portion 304 can also damage healthy surrounding tissue. The inventors have overcome this drawback by configuring the electrosurgical generator (e.g., electrosurgical generator 102) of the electrosurgical system of the present invention to deliver microwave energy in pulses. The inventors have found that the pulsed delivery of microwave energy can avoid or reduce heating effects at the radiating tip portion, such that the radiating tip portion can be maintained at an acceptable temperature during a surgical procedure.

[0068] To avoid heating of the radiating tip portion during application of microwave energy, the pulse duration of the microwave pulse can be set to be longer than the thermal response time of the radiating tip portion. In this way, the radiating tip portion may not have time to thermally respond to the pulsed microwave energy on the time scale of the microwave pulse. The thermal response time of the radiating tip portion can be experimentally measured by determining the time it takes for the temperature of the radiating tip portion to increase by a given amount (e.g., 5°C) when microwave energy is delivered to the radiating tip portion at a given power level (e.g., a power level used during electrosurgical procedures). The pulse duration can then be set accordingly to ensure that the temperature of the radiating tip portion remains at an acceptable temperature over the course of the electrosurgical procedure.

[0069] The inventors have found that by configuring the electrosurgical generator to deliver pulsed microwave energy at a duty cycle of 25% or less, the heating effects of the radiating tip portion can be avoided or reduced so that it can be maintained at an acceptable temperature during use. The electrosurgical generator can be configured to deliver microwave energy according to one of the following exemplary cycles: a) Pulse duration 10 ms, pulse interval 90 ms. b) Pulse duration 10 ms, pulse interval 50 ms. c) Pulse duration 10 ms, pulse interval 30 ms. d) Pulse duration 100 ms, pulse interval 900 ms. e) Pulse duration 100 ms, pulse interval 500 ms. f) Pulse duration 100 ms, pulse interval 300 ms. g) Pulse duration 200 ms, pulse interval 800 ms.

[0070] Cycles a) and d) correspond to a 10% duty cycle, cycles b) and e) correspond to a 16.67% duty cycle, cycles c) and f) correspond to a 25% duty cycle, and cycle g) corresponds to a 20% duty cycle.

[0071] FIG. 6 illustrates a power delivery profile according to cycle a) above. The power delivery profile of FIG. 6 illustrates the power of microwave energy delivered by the electrosurgical generator versus time. The power delivery profile includes a series of microwave pulses 600, each having a duration of 10 milliseconds. The microwave pulses 600 are separated by intervals 602, each having a duration of 90 milliseconds. Each of the microwave pulses 600 has a power P, as shown in FIG. 6. During the intervals 602, no microwave energy is delivered by the electrosurgical generator (i.e., the power delivered is 0 W). Each of the pulses 600 is identical and includes a constant power level. It should be noted that the power delivery profile of FIG. 6 is not drawn to scale. In other embodiments, the power level of the microwave pulses may vary over the course of the pulse depending on the desired energy delivery profile. In some cases, a microwave pulse cycle may include pulses having different durations and / or power levels.

[0072] Specific examples of radiating tip portions of electrosurgical instruments that can be used in the electrosurgical system of the present invention will now be described with reference to Figures 7-11. The radiating tip portions described below may be used, for example, in place of radiating tip portion 304 of electrosurgical instrument 300 described above. Each of radiating tip portions 700, 800, 900, 1000, and 1100 described below have a similar overall configuration. Like radiating tip portion 304, each of radiating tip portions 700, 800, 900, 1000, and 1100 has an inner conductor electrically connected to a central conductor of a coaxial cable (not shown) and an outer conductor electrically connected to the outer conductor of the coaxial cable. Each of radiating tip portions 700, 800, 900, 1000, and 1100 further includes proximal and distal dielectric sleeves disposed about the inner conductor to form a proximal transmission line and a distal needle tip as discussed above with respect to radiating tip portion 304.

[0073] FIG. 7 shows a cross-sectional view of a distal portion of a radiating tip portion 700. A proximal dielectric sleeve 706 of the radiating tip portion 700 may be made of a flexible insulating material, such as PTFE. A distal dielectric sleeve 708 of the radiating tip portion 700 is made of a cylindrical piece of zirconia. A distal tip 710 of the distal dielectric sleeve 708 is sharpened to facilitate insertion of the radiating tip portion 700 into tissue. Making the distal dielectric sleeve 708 of zirconia can provide the radiating tip portion 700 with a rigid distal needle tip, which can facilitate puncturing tissue. The use of zirconia can also allow for a reduction in the physical length of the radiating tip portion while maintaining a desired electrical length.

[0074] Example dimensions of the radiating tip portion 700 are shown in FIG. 7. The dimension indicated by reference numeral 712, which corresponds to the length of the proximal dielectric sleeve 706, may be 37 mm. Note that the overall length of the proximal dielectric sleeve 706 is not shown in FIG. 7. The dimension indicated by reference numeral 714, which corresponds to the length of the overlap between the outer conductor 704 and the distal dielectric sleeve 708 of the radiating tip portion 700, may be 3.6 mm. The dimension indicated by reference numeral 716, which corresponds to the length of the inner conductor 702 of the radiating tip portion 700 that protrudes beyond the distal end of the outer conductor 704, may be 1.5 mm. The dimension indicated by reference numeral 718, which corresponds to the length of the distal tip 710, may be 1.5 mm. The maximum outer diameter of the radiating tip portion 700, which is indicated by reference numeral 720, is equal to or less than 1.0 mm. The joint between the distal dielectric sleeve 708 and the proximal dielectric sleeve may be crimped, for example, around the outer surface of the outer conductors 704, 706 to strengthen the connection between the distal dielectric sleeve 708 and the remainder of the device.

[0075] FIG. 8a shows a cross-sectional view of a distal portion of the radiating tip portion 800. A proximal dielectric sleeve 806 of the radiating tip portion 800 may be made of a flexible tube of insulating material, such as PTFE. A distal dielectric sleeve 808 of the radiating tip portion 800 is made of a cylindrical piece of zirconia. The distal dielectric sleeve 808 includes a bore in which an inner conductor is received. A distal tip 810 made of zirconia is attached to the distal end of the distal dielectric sleeve 808. A perspective view of the distal tip 810 is shown in FIG. 8b. The distal tip 810 has a cone 812 that forms a pointed tip to facilitate insertion of the radiating tip portion 800 into tissue. The distal tip 810 includes a protrusion 814 extending from a proximal face 816 of the cone 812. The protrusion of the distal tip 810 is received in the bore of the distal dielectric sleeve 808 where it is fixed in place. The tip may be secured using an adhesive. Additionally or alternatively, the tip may be secured by crimping the distal end.

[0076] Exemplary dimensions of the radiating tip portion 800 are shown in FIG. 8a. The dimension indicated by reference numeral 818, corresponding to the length of the proximal dielectric sleeve 806, may be 37 mm. Note that the overall length of the proximal dielectric sleeve 806 is not shown in FIG. 8a. The dimension indicated by reference numeral 820, corresponding to the length of the overlap between the outer conductor 804 and the distal dielectric sleeve 808 of the radiating tip portion 800, may be 3.6 mm. The dimension indicated by reference numeral 822, corresponding to the length of the distal dielectric sleeve 808 that protrudes beyond the distal end of the outer conductor 804, may be 2.0 mm. The dimension indicated by reference numeral 824, corresponding to the length of the cone 812 of the distal tip 810, may be 1.5 mm. The dimension indicated by reference numeral 826, corresponding to the length of the protrusion 814, may be 0.5 mm. The maximum outer diameter of the radiating tip portion 800, indicated by reference numeral 828, is equal to or less than 1.0 mm.

[0077] 9a shows a cross-sectional view of a distal portion of a radiating tip portion 900. A proximal dielectric sleeve 906 of the radiating tip portion 900 may be made of a flexible tube of insulating material, for example, PTFE. A distal dielectric sleeve 908 of the radiating tip portion 900 is made of a cylindrical piece of polyetheretherketone (PEEK). The distal dielectric sleeve 908 includes a cavity at its distal tip into which a distal tip 910 made of zirconia is received. A "press-fit" connection may be formed between the distal tip 910 and the distal dielectric sleeve 908.

[0078] FIG. 9b shows the connection between the distal tip 910 and the distal dielectric sleeve 908 in more detail. The distal tip includes a body 912 that is received in a cavity of the distal dielectric sleeve 908. The body 912 includes bumps 914 on its outer surface that are arranged to press outwardly against the distal dielectric sleeve 908 to retain the distal tip 910 within the cavity. Thus, the distal tip 910 may be automatically retained within the cavity once it is inserted into the cavity. The distal tip 910 may be further secured within the cavity using an adhesive. The distal tip 910 further includes a conical portion 916 that forms a pointed tip at the distal end of the radiating tip portion 900. The outer surface of the distal dielectric sleeve 908 tapers at an angle that matches the taper angle of the conical portion 916, such that the outer surface of the radiating tip portion 900 is smooth. Because zirconia may have a higher stiffness than PEEK, making the distal tip 910 out of zirconia may allow for a sharper distal tip to be provided.

[0079] Exemplary dimensions of the radiating tip portion 900 are shown in FIG. 9a. The dimension indicated by reference numeral 918, corresponding to the length of the proximal dielectric sleeve 906, may be 37 mm. Note that the overall length of the proximal dielectric sleeve 906 is not shown in FIG. 9a. The dimension indicated by reference numeral 920, corresponding to the length of overlap between the outer conductor 904 and the distal dielectric sleeve 908 of the radiating tip portion 900, may be 7.0 mm. The dimension indicated by reference numeral 922, corresponding to the length of the inner conductor 902 of the radiating tip portion 900 that protrudes beyond the distal end of the outer conductor 904, may be 5.0 mm. The dimension indicated by reference numeral 924, corresponding to the length of the distal tip 910, may be 2.0 mm. The maximum outer diameter of the radiating tip portion 900, indicated by reference numeral 926, is equal to or less than 1.0 mm.

[0080] 10 shows a cross-sectional view of a distal portion of a radiating tip portion 1000. A proximal dielectric sleeve 1006 of the radiating tip portion 1000 may be made of a flexible tube of insulating material, such as PTFE. A distal dielectric sleeve 1008 of the radiating tip portion 1000 is made of a cylindrical piece of PEEK. Similar to the radiating tip portion 800, the radiating tip 1000 includes a distal tip 1010 made of zirconia attached to the distal end of the distal dielectric sleeve 1008. The distal tip 1010 has a similar configuration to the distal tip 810 shown in FIG. 8b, i.e., it includes a cone and a protrusion 1014 that is received in a bore of the distal dielectric sleeve 1008.

[0081] Exemplary dimensions of the radiating tip portion 1000 are shown in FIG. 10. The dimension indicated by reference numeral 1018, corresponding to the length of the proximal dielectric sleeve 1006, may be 37 mm. Note that the overall length of the proximal dielectric sleeve 1006 is not shown in FIG. 10. The dimension indicated by reference numeral 1020, corresponding to the length of the overlap between the outer conductor 1004 and the distal dielectric sleeve 1008 of the radiating tip portion 1000, may be 6.0 mm. The dimension indicated by reference numeral 1022, corresponding to the length of the distal dielectric sleeve 1008 that protrudes beyond the distal end of the outer conductor 1004, may be 5.5 mm. The dimension indicated by reference numeral 1024, corresponding to the length of the cone of the distal tip 810, may be 1.5 mm. The dimension indicated by reference numeral 1026, corresponding to the length of the protrusion 1014, may be 0.5 mm. The maximum outer diameter of the radiating tip portion 1000, indicated by reference numeral 1028, is equal to or less than 1.0 mm.

[0082] 11 shows a cross-sectional view of a distal portion of the radiating tip portion 1100. The proximal dielectric sleeve 1106 of the radiating tip portion 1100 may be made of a flexible tube of insulating material, such as PTFE. The distal dielectric sleeve 1108 of the radiating tip portion 1100 is made of a cylindrical piece of PEEK. The distal tip 1110 of the distal dielectric sleeve 1108 is sharpened to facilitate insertion of the radiating tip portion 1100 into tissue.

[0083] Exemplary dimensions of the radiating tip portion 1100 are shown in FIG. 11. The dimension indicated by reference numeral 1118, corresponding to the length of the proximal dielectric sleeve 1106, may be 37 mm. Note that the overall length of the proximal dielectric sleeve 1106 is not shown in FIG. 11. The dimension indicated by reference numeral 1120, corresponding to the length of the overlap between the outer conductor 1104 and the distal dielectric sleeve 1108 of the radiating tip portion 1000, may be 6.0 mm. The dimension indicated by reference numeral 1122, corresponding to the length of the inner conductor 1102 of the radiating tip portion 1100 that protrudes beyond the distal end of the outer conductor 1004, may be 5.5 mm. The dimension indicated by reference numeral 1024, corresponding to the length of the distal tip 1110, may be 1.5 mm. The maximum outer diameter of the radiating tip portion 1100, indicated by reference numeral 1028, is equal to or less than 1.0 mm.

[0084] 12 shows a simulated plot of S-parameters (also known as "return loss") versus frequency of microwave energy for electrosurgical instruments having radiating tips 700, 800, 900, 1000 and 1100 described above. As is well known in the art, S-parameters are a measure of the return loss of microwave energy due to impedance mismatch and, therefore, the S-parameters indicate the degree of impedance mismatch between the target tissue and the radiating tip. The S-parameters are calculated according to the formula P I =SP R where P I is the power delivered to the tissue in the instrument, P R is the power reflected from the tissue, and S is the S-parameter. In Figure 12, curve 1200 corresponds to a simulation for radiating tip portion 700, curve 1202 corresponds to a simulation for radiating tip portion 800, curve 1204 corresponds to a simulation for radiating tip portion 900, curve 1206 corresponds to a simulation for radiating tip portion 1000, and curve 1208 corresponds to a simulation for radiating tip portion 1100. Note that curves 1200 and 1202 are so close to each other that they appear to overlap.

[0085] 12, at a microwave energy frequency of 5.8 GHz, the S-parameters are −19.2 dB for radiating tip section 700, −19.3 dB for radiating tip section 800, −26.7 dB for radiating tip section 900, −33.5 dB for radiating tip section 1000, and −30.4 dB for radiating tip section 1100. This means that for each of these radiating tip sections, very little microwave energy is reflected from the tissue at 5.8 GHz. This indicates that there is a good impedance match between the radiating tip and biological tissue at the operating frequency of 5.8 GHz, and microwave energy can be efficiently delivered from the radiating tip to the tissue at this frequency.

Claims

1. 1. An electrosurgical system for treating living tissue, comprising: an electrosurgical generator configured to deliver pulsed microwave energy; an electrosurgical instrument configured to receive the pulsed microwave energy from the electrosurgical generator; Equipped with The electrosurgical instrument includes: a flexible coaxial cable having an inner conductor, an outer conductor, and a dielectric material separating the inner conductor and the outer conductor, the flexible coaxial cable being positioned to transmit the pulsed microwave energy; a radiating tip portion configured to connect to a distal end of the coaxial cable to receive the pulsed microwave energy, the radiating tip portion having a maximum outer diameter of 1.0 mm or less, the maximum outer diameter of the radiating tip portion being less than an outer diameter of the coaxial cable; Equipped with The radiating tip portion a proximal coaxial transmission line for transmitting the pulsed microwave energy; a distal needle tip attached to a distal end of the proximal coaxial transmission line, the distal needle tip emitting the pulsed microwave energy into biological tissue; Equipped with The proximal coaxial transmission line includes: an inner conductor extending from a distal end of the flexible coaxial cable and electrically connected to the inner conductor of the flexible coaxial cable; a proximal dielectric sleeve mounted about the inner conductor of the proximal coaxial transmission line; an outer conductor mounted about the proximal dielectric and electrically connected to an outer conductor of the flexible coaxial cable; Equipped with an inner conductor of the proximal coaxial transmission line extending longitudinally within the radiating tip portion, the inner conductor being a distal portion of the proximal coaxial transmission line, the inner conductor being a length that is not covered by the outer conductor of the proximal coaxial transmission line.

2. 2. The electrosurgical system of claim 1, wherein a pulse duration of the pulsed microwave energy supplied by the surgical generator is less than a thermal response time of the radiating tip portion, the thermal response time corresponding to the time it takes for a temperature of the radiating tip portion to change a given amount when microwave energy of a given power level is delivered to the radiating tip portion.

3. The electrosurgical system of claim 1 or 2, wherein the electrosurgical generator is configured to deliver the pulsed microwave energy at a duty cycle of 25% or less.

4. The electrosurgical system of claim 3 , wherein the pulsed microwave energy has a pulse duration between 10 milliseconds and 200 milliseconds.

5. The pulsed microwave energy comprises: a) Pulse duration 10 ms, pulse interval 90 ms; b) pulse duration 10 ms, pulse interval 50 ms; c) pulse duration 10 ms, pulse interval 30 ms; d) pulse duration 100 ms, pulse interval 900 ms; e) pulse duration 100 ms, pulse interval 500 ms; f) pulse duration 100 ms, pulse interval 300 ms; g) pulse duration 200 ms, pulse interval 800 ms; The electrosurgical system of claim 4 , wherein the pulse is delivered according to one of the following cycles:

6. The electrosurgical system of any preceding claim, wherein the radiating tip portion has a length of 140 mm or greater.

7. the distal needle tip comprises a distal dielectric sleeve mounted about the inner conductor; The electrosurgical system of any preceding claim, wherein a distal portion of the outer conductor overlaps a proximal portion of the distal dielectric sleeve.

8. The electrosurgical system of claim 7 , wherein the distal dielectric sleeve is made from a different material as compared to the proximal dielectric sleeve.

9. a proximal end of the distal dielectric sleeve including a protrusion disposed about the inner conductor; The electrosurgical system according to claim 8 , wherein the protrusion is received in a complementarily shaped cavity in a distal end of the proximal dielectric sleeve.

10. The electrosurgical system of any preceding claim, wherein the distal needle tip operates as a half-wave transformer for delivering the microwave energy from the distal needle tip.

11. a surgical scope device having a flexible insertion cord for insertion into a patient's body; the flexible insertion cord having an instrument channel extending along its length; The electrosurgical system of any preceding claim, wherein the electrosurgical instrument is dimensioned to be received within the instrument channel.

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