Electrosurgical instruments with non-liquid heat transfer

Abstract

Various embodiments provide an electrosurgical instrument comprising: a flexible coaxial transmission line arranged to transmit microwave energy; a radiating tip connected to a distal end of the flexible coaxial transmission line to receive microwave energy, the distal coaxial transmission line for transmitting microwave energy; and a needle tip mounted to the distal end of the distal coaxial transmission line, the needle tip configured to deliver microwave energy to biological tissue; and a heat sink mounted at an interface between the flexible coaxial transmission line and the radiating tip. The heat sink is in thermal communication with the proximal end of the distal coaxial transmission line and is configured to draw thermal energy from the radiating tip. Also disclosed is a related electrosurgical system.

Description

[Technical Field]

[0001] The present invention relates to an electrosurgical instrument for delivering electromagnetic energy to biological tissue to ablate or coagulate target tissue. The electrosurgical instrument may be part of an electrosurgical instrument system that includes an electrosurgical generator for supplying RF and / or microwave energy, where the electrosurgical instrument is configured to receive and deliver microwave and / or RF energy to the target tissue. The electrosurgical instrument may be configured to ablate or coagulate, or ablate and coagulate, tissue such as a tumor, cyst, or other lesion. In the case of coagulation, microwave energy may be used to create a plug that cuts off the blood supply to the tumor. Once the supply is cut off, it may be desirable to also ablate the tumor mass. The electrosurgical instrument may be particularly suited for treating pancreatic, lung, kidney, brain, or liver tissue. [Background technology]

[0002] Electromagnetic (EM) energy, particularly microwave and radio frequency (RF) energy, has proven useful in electrosurgery because it can cut, coagulate, and ablate body tissue. Devices for delivering EM energy to body tissue generally include a generator with an EM energy source 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 a patient's body. However, percutaneous placement of the instrument within the body can be difficult, for example, when the target site is in a moving lung or a thin-walled section of the gastrointestinal (GI) tract. Other electrosurgical instruments can be delivered to the target site through a surgical scoping device (e.g., an endoscope) that can navigate internal body passages such as the airway or the lumen of the esophagus or colon. This allows for minimally 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 primarily composed of water. Human soft organ tissue typically has a water content of 70% to 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 rotate and move in response to forces generated by applying a time-varying electric field, aligning their electric dipole moment with the polarity of the applied field. At microwave frequencies, rapid molecular vibrations cause frictional heating, resulting in the dissipation of field energy in the form of heat. This is known as dielectric heating. Because water (the main component of blood) has a much higher dipole moment than adipose tissue, heating of water molecules in blood occurs more rapidly than heating of fat molecules for the same electric field.

[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 target tissue, resulting in tissue coagulation and cell death. Microwave-emitting probes are known to be used 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.

[0005] One challenge faced when delivering microwave energy to a treatment site inside the body is how to prevent undesirable effects caused by losses in the cables that transmit the microwave energy to the treatment site. These losses often manifest as heating of the cables, which can then heat and damage living tissue.

[0006] This heating effect can be improved by cooling the cable. Typically, this is done by circulating a liquid coolant. However, the space required for circulating the coolant within the cable presents a barrier to further miniaturization of the cable itself and any distal probes that may also require cooling. On the other hand, it is desirable to make the cable and probe as small as possible, for example, to access treatment sites in the finer parts of the bronchial tree of the lungs. Summary of the Invention [Problem to be solved by the invention]

[0007] Most generally, the present invention provides an electrosurgical instrument having a non-liquid thermal energy transfer mechanism that operates to draw heat away from its distal end. The thermal energy transfer mechanism may provide a temperature gradient in the instrument that provides a preferential path for thermal energy transfer. The temperature gradient may be provided by a heat sink (or thermal mass) located at the distal end of the coaxial cable that transmits the microwave energy. The heat sink may be made of a material that has a higher thermal conductivity than the distal instrument tip. The heat sink may be actively cooled by providing a thermally conductive connection to a cooling device or coolant source at the proximal end of the cable (i.e., away from the treatment site).

[0008] In one aspect, the present invention provides an electrosurgical instrument comprising: a flexible coaxial transmission line arranged to transmit microwave energy; a radiating tip connected to a distal end of the flexible coaxial transmission line to receive microwave energy, the distal coaxial transmission line for transmitting microwave energy; and a needle tip mounted to the distal end of the distal coaxial transmission line, the needle tip configured to deliver microwave energy to biological tissue; and a heat sink mounted at an interface between the flexible coaxial transmission line and the radiating tip, the heat sink being in thermal communication with the proximal end of the distal coaxial transmission line and configured to draw thermal energy from the radiating tip, the radiating tip having a maximum outer diameter smaller than the outer diameter of the flexible coaxial transmission line. Thus, the heat sink operates to draw thermal energy of the radiating tip (i.e., heat generated by losses in the distal coaxial transmission line) in a proximal direction, away from the radiating tip. This technique prevents heat loss from concentrating around the radiating tip, avoiding unwanted damage to surrounding tissue without adversely affecting the delivered microwave energy.

[0009] The heat sink may be solid, and therefore, in contrast to known fluid-based cooling systems, the instrument does not require space within the flexible shaft for fluid delivery and extraction, allowing the cooling effect to be achieved with a much smaller diameter device.

[0010] A solid body is disposed between the outer conductor of the distal coaxial transmission line and the outer conductor of the flexible coaxial transmission line. Preferably, there is a physical connection between the outer conductor and the heat sink, whereby the heat sink forms part of a continuous heat transfer path away from the radiating tip.

[0011] The heat sink may be an annular body mounted around the proximal end of the distal coaxial transmission line. The heat sink may be formed from a material with high thermal conductivity, for example, a metal such as copper or silver.

[0012] The instrument may further include an insulating cap mounted on the interface between the flexible coaxial transmission line and the radiating tip. Thermal insulation can be provided to isolate the heat sink from surrounding biological tissue. This can further help direct a preferential path for heat flow away from the radiating portion by restricting heat flow from the distal end of the flexible shaft. The insulating cap may also be useful in situations where the heat sink is actively cooled via a heat transfer element (described in more detail below). In these instances, the insulating cap may inhibit the cooling effect of the heat sink from adversely affecting the ablation effect of the electric field emitted from the antenna and may also prevent the cooling effect from damaging surrounding tissue.

[0013] The insulating cap may be formed from epoxy or another suitable insulating material that may be molded onto the distal end of the flexible shaft.

[0014] The maximum outer diameter of the radiating tip is 1.0 mm or less. For example, the radiating tip may be 19 gauge. In some embodiments, the maximum outer diameter may be 0.95 mm, 0.9 mm, or less. The maximum outer diameter may refer to the largest outer diameter of the radiating tip along its length. Thus, the instrument may be able to access deeper regions of the lung than conventional ablation devices.

[0015] The distal coaxial transmission line may be a half-wave transformer to facilitate the transfer of microwave energy to the antenna. Configuring the distal needle tip as a half-wave transformer has the advantage of minimizing reflections at interfaces between components, such as the interface between the coaxial transmission line and the distal coaxial transmission line, and the interface between the distal coaxial transmission line and the 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 the reflection coefficient at the interface between the distal coaxial transmission line and the tissue. The impedance of the distal 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. The radiating tip may have a length of 30 mm or more, e.g., 40 mm. In this manner, the radiating tip may be long enough to allow the distal needle tip to reach the treatment site without the need to insert a portion of the coaxial transmission line into tissue. In some cases, the radiating tip may have a length of 140 mm or more.

[0016] The instrument may further include a heat transfer element disposed along the flexible coaxial transmission line, the heat transfer element creating a thermal gradient that draws thermal energy away from the radiating tip. The heat transfer element is preferably actively cooled (e.g., exposed to a coolant source or forcedly cooled by a refrigerator or thermoelectric cooling effect) at its proximal end, e.g., the proximal end of the instrument. In one example, the heat transfer element may be a sleeve of thermally conductive material mounted around the outer conductor of the flexible coaxial transmission line. The sleeve may be braided, e.g., made of a metal such as copper or gold. In one example, the heat transfer element may be the outer conductor of the flexible coaxial transmission line. In another example, the heat transfer element may be separated from the outer conductor by a thermal insulating layer, e.g., a layer of PTFE or other suitably flexible insulating material. In another example, the heat transfer element can be made from yttrium-barium-copper-oxide or a similar compound, which the inventors have found to be very effective in transferring the cooling effect of a proximal coolant source, such as liquid nitrogen or liquid helium, by conduction to the distal end of the instrument.

[0017] A distal portion of the heat transfer element may be in thermal communication with the heat sink and draw thermal energy proximally along the flexible coaxial transmission line. In other words, the heat transfer element actively cools the heat sink at the interface between the flexible coaxial transmission line and the distal coaxial transmission line. This may act to maintain a preferential flow path for thermal energy proximally away from the radiating tip through the instrument (rather than through the surrounding tissue).

[0018] The heat transfer element comprises a solid, in other words, different from the fluid-based coolant circulation systems of conventional devices and therefore does not require the same volume within the fixture.

[0019] In another aspect, the present invention provides an electrosurgical system including an electrosurgical generator configured to generate microwave energy for ablating biological tissue; an electrosurgical instrument having a heat transfer element as described above, connected to receive microwave energy from the electrosurgical generator; and a cooling device arranged to forcefully cool a proximal portion of the heat transfer element of the electrosurgical instrument. Any suitable means may be used to cool the heat transfer element. The cooling device may be, for example, a thermoelectric cooler. In other examples, the heat transfer element may be kept cool by thermal contact with a cold body, such as a source of liquid nitrogen, liquid helium, or the like. For example, the heat transfer element may be immersed in or sprayed with liquid nitrogen or liquid helium. In such examples, forced cooling of the heat transfer element may not be necessary. Cooling may occur as the system attempts to find thermal equilibrium. In such examples, the temperature of the proximal end of the heat transfer element may be below −50°C, e.g., −100°C or lower.

[0020] The system may further include a surgical scoping device having a flexible instrument cord for insertion into the patient's body, the flexible insertion cord having an instrument channel extending along its length, the electrosurgical instrument being sized to be received within the instrument channel. Because the shaft inserted into the instrument channel does not need to include a fluid-based coolant circulation system, the instrument may be used in an instrument channel with a smaller diameter than conventional instruments.

[0021] The system may further include a handpiece having a housing for receiving the proximal end of the electrosurgical instrument. The handpiece may include a control mechanism configured to move the electrosurgical instrument relative to the housing to deploy the distal end of the electrosurgical instrument at the distal end of the electrosurgical instrument. The handpiece may be adapted to combine the control mechanism, a feed cable for supplying microwave energy from the electrosurgical generator, and input from a cooling device within the housing, thereby combining the flexible coaxial transmission line and heat transfer element into a single flexible shaft insertable into and slidable relative to the instrument channel of the scoping device.

[0022] As used herein, the term "inner" means radially closer to the center (e.g., axis) of the instrument channel and / or coaxial cable. The term "outer" means radially farther from the center (axis) of the instrument channel and / or coaxial cable.

[0023] As used herein, the term "conductive" means electrically conductive, unless the context dictates otherwise.

[0024] 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.

[0025] As used herein, "microwave" may be used broadly to refer to the 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.

[0026] The term "radio frequency" or "RF" is sometimes used to refer to frequencies between 300 kHz and 400 MHz.

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic diagram of an electrosurgical system for tissue ablation, an embodiment of the present invention; [Figure 2] 1 is a schematic cross-sectional view of an instrument cord for an endoscope that can be used with the present invention. [Figure 3] 3 is a schematic side cross-sectional view of the instrument cord of FIG. 2 with a flexible shaft of an electrosurgical instrument according to an embodiment of the invention passing through the instrument channel. [Figure 4] 1 is a schematic side cross-sectional view of a distal assembly of an electrosurgical instrument according to an embodiment of the present invention; [Figure 5] 3 is a schematic side cross-sectional view of the instrument cord of FIG. 2 with a flexible shaft of an electrosurgical instrument according to another embodiment of the present invention passing through its instrument channel. [Figure 6] 1 is a schematic side cross-sectional view of a handpiece of an electrosurgical system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] FIG. 1 is a schematic diagram of an electrosurgical system 100 according to an embodiment of the present invention. The electrosurgical system 100 can deliver microwave energy to the distal end of an invasive electrosurgical instrument to perform tissue ablation. The electrosurgical system can also deliver a fluid, such as a liquid medication 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. The electrosurgical generator is configured to deliver pulsed microwave energy. A suitable generator for this purpose is described in WO 2012 / 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 the optimal delivery power level.

[0030] Electrosurgical system 100 further includes an interface joint 106 connected to electrosurgical generator 102 via an interface cable 104. Interface joint 106 may also be connected to a fluid delivery device 108, such as a syringe, via a fluid flow line 107, although this is not required. In some examples, the system may additionally or alternatively be configured to aspirate fluid from the treatment site. In this scenario, fluid flow line 107 can carry fluid from interface joint 106 to a suitable collector (not shown). An aspiration mechanism can be connected to the proximal end of fluid flow line 107.

[0031] The interface joint 106 can house an instrument control mechanism 109 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 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.

[0032] In this example, the electrosurgical system 100 further includes an active cooling device 130 configured to cool the flexible, elongated heat-transfer element 148, as described in more detail below. The active cooling device 130 can be any device suitable for providing a thermal cooling effect. For example, it can be a refrigerator or can operate using thermoelectric cooling, such as a Peltier cooler. In other examples, the cooling device 130 can be a cooling body, such as liquid nitrogen or liquid helium, with which the heat-transfer element 148 is brought into contact, so that the cooling “effect” of the cooling body is transferred by conduction along the length of the heat-transfer element 148 as it attempts to reach thermal equilibrium.

[0033] The function of the interface joint 106 is to couple inputs from the generator 102, fluid delivery device 108, cooling system 130, and instrument control mechanism to a single flexible shaft 112 (which may be part of the electrosurgical instrument discussed herein), which extends from the distal end of the interface joint 106.

[0034] The electrosurgical system 100 further includes a surgical scoping device 114, which in this example includes an ultrasonic endoscopic device, although it should be understood that the present invention can be used with any type of surgical scoping device 114 or flexible catheter (i.e., an insertable tube without scoping capabilities).

[0035] The flexible shaft 112 is insertable through the entire length of the instrument (working) channel of the surgical scoping device 114 .

[0036] The surgical scoping device 114 includes a body 116 having several 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 components 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 illuminate the distal end or to collect images from the distal end. The body 116 may include an eyepiece 122 for viewing the distal end.

[0037] Endoscopic ultrasound devices typically include 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 down 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 so 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.

[0038] The flexible shaft 112 has a distal assembly 118 (not drawn to scale in FIG. 1 ) configured to pass through an instrument channel of the surgical scoping device 114 and to project (e.g., into the patient's body) at the distal end of the instrument cord. The distal assembly 118 may also be referred to herein as a radiating tip.

[0039] 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 1.0 mm or less, e.g., less than 0.95 mm or 0.90 mm. The length of the flexible shaft may be 1.2 m or more.

[0040] The body 116 includes an input port 128 for connection 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. Exemplary coaxial cables that can physically fit into the instrument channel of an EUS device are available in outer diameters of 1.19 mm (0.047 inch), 1.35 mm (0.053 inch), 1.40 mm (0.055 inch), 1.60 mm (0.063 inch), and 1.78 mm (0.070 inch). Custom-sized coaxial cables (i.e., made to order) can also be used.

[0041] To control the position of the distal end of instrument cord 120, body 116 may further include a control actuator mechanically coupled to the distal end of instrument cord 120 by one or more control wires (not shown) extending through 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 rotatable knob, or any other known catheter manipulation device. Manipulation of instrument cord 120 may be software-assisted, for example, using a virtual three-dimensional map combined with computed tomography (CT) images.

[0042] One example use of the present invention is in the treatment of the pancreas. To reach a target site in the pancreas, the instrument cord 120 may need to be guided through the mouth, stomach, and duodenum. The electrosurgical instrument is positioned to access the pancreas by passing through the wall of the duodenum.

[0043] Another example use of the present invention is in the treatment of the lungs. To reach a target site in the lungs, the instrument cord 120 may need to be guided through the patient's airways (through the nose or mouth) and into the bronchial tree. Electrosurgical instruments may be deployed from the distal end of the instrument cord 120 to treat tissue within the bronchial tree.

[0044] 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 may be other lumens, such as for control wires or fluid delivery or aspiration. Alternatively, the instrument cord 120 may be a simple flexible catheter defining a single lumen for the flexible shaft.

[0045] FIG. 3 is a schematic side cross-sectional view of an instrument cord 120. An instrument channel 132 has a flexible shaft 112 extending therethrough. The flexible shaft 112 includes a coaxial transmission line 140 formed from a longitudinally extending inner conductor 146 surrounded by and separated from an outer conductor 142 by a dielectric material 144. The coaxial transmission line 140 may be, for example, a commercially available coaxial cable available from Huber + Suhner under the Sucoform brand. The outer conductor may have an outer diameter of 2.0 mm or less. For example, it may have any of the following diameters: 1.19 mm (0.047 inch), 1.35 mm (0.053 inch), 1.40 mm (0.055 inch), 1.60 mm (0.063 inch), and 1.78 mm (0.070 inch).

[0046] The flexible shaft 112 also includes a flexible, elongated heat transfer element 148, which in this example is a thermally conductive sleeve mounted over the outer conductor 142. The sleeve may be made of a braided metal such as copper or silver to maintain flexibility.

[0047] As discussed above, the proximal end of the heat transfer element 148 is in thermal communication with the cooling device 130. The heat transfer element 148 is configured to provide a thermal gradient along the length of the flexible shaft 112, which draws heat preferentially away from the distal assembly 118 in a direction along the shaft.

[0048] The cooling device 130 can operate to forcefully cool the proximal end of the heat-transfer element 148 to a temperature below 0° C., such as below −50° C., such as −100° C. The heat-transfer element 148 can then act to cool the coaxial transmission line 140 along its length while simultaneously providing a temperature gradient to draw heat away from the distal assembly 118.

[0049] In one example, a thermal insulating layer (not shown) may be provided between the outer conductor and the heat-transfer element 148. This may limit the transfer of thermal energy from the coaxial transmission line 140 to the heat-transfer element 148 in order to optimize or maximize the temperature gradient along the length of the flexible shaft 112. In other words, providing this layer increases the cooling effect available to the distal assembly 118. The thermal insulating layer may be made of PTFE or other suitable flexible insulator.

[0050] 4 is a schematic side cross-sectional view of a distal assembly 118 (i.e., radiation tip) of an electrosurgical instrument according to an embodiment of the present invention. The distal tip assembly 118 is disposed at the distal end of the flexible shaft 112. The distal tip assembly 118 comprises an elongated rigid probe having an outer diameter smaller than the outer diameter of the coaxial transmission line 140. The elongated rigid probe includes a distal coaxial transmission line 150 formed from an inner conductor 156 separated from an outer conductor 152 by a dielectric material 154. The inner conductor 156 is electrically connected to the inner conductor 146 of the coaxial transmission line 140 within the flexible shaft 112. In this example, the inner conductor 156 within the distal coaxial transmission line 150 has a smaller outer diameter than the inner conductor 146 of the coaxial transmission line 140 within the flexible shaft 112.

[0051] The dielectric material 154 of the distal coaxial transmission line 150 may be the same as or different from the dielectric material 144 of the coaxial transmission line 140 in the flexible shaft 112. In one example, the dielectric material 154 has a stiffness greater than that of the dielectric material 144 to facilitate insertion of the elongated probe into tissue.

[0052] The elongated probe may further include a distal-most tip element 158 ​​formed, for example, from a rigid dielectric (electrically insulating) material. The tip element 158 ​​may have a pointed end, as shown in Figure 4, for penetrating tissue. In other examples, the end may be rounded, for example, hemispherically.

[0053] The inner conductor 156 extends beyond the distal end of the outer conductor 152 and the dielectric material 154 into the tip element 158 ​​to form an antenna for radiating microwave energy received from the coaxial transmission line 140 in the flexible shaft 112. The outer conductor 152 may extend over a portion of the outer surface of the tip element 158. This helps secure the tip element 158 ​​to the distal assembly 118 and can help ensure that the field emitted by the antenna is approximately spherical around the distal tip.

[0054] The length of the distal coaxial transmission line 150 may be selected to ensure efficient transfer of microwave energy from the coaxial transmission line 140 to the antenna within the flexible shaft 112. In one example, the distal coaxial transmission line 150 may be configured as a half-wave transformer.

[0055] In an embodiment of the present invention, the interface between the flexible shaft 112 and the distal assembly 118 is configured to direct thermal energy away from the elongate probe, and in particular away from the distal coaxial transmission line 150. The solution shown in Figure 4 has two aspects.

[0056] The first aspect is to provide a heat sink at the distal end of the elongated probe. In this example, the heat sink is a ring 160 formed from a material with a higher thermal conductivity than the surrounding biological tissue. The material may be, for example, copper or silver. The ring 160 is in direct physical contact with the outer conductor 152 of the distal coaxial transmission line 150. The heat sink may function as an absorptive thermal mass. In other words, the thermal mass of the ring 160 (i.e., the ring's ability to absorb thermal energy) is greater than the thermal mass of the elongated probe (particularly the distal coaxial transmission line 150). Therefore, to achieve thermal equilibrium, heat generated in the coaxial transmission line 150 tends to flow back into the ring 160. The heat sink does not have to be in the form of a ring. For example, it could be a conductive layer formed on the flexible shaft 112 or the distal section of the coaxial transmission line 140. In one example, the coaxial transmission line 140, or a distal portion thereof, may be formed from tin-coated copper Sucoform 86 cable.

[0057] The second aspect is provided by heat transfer element 148. In this example, heat transfer element 148 is in physical contact with the outer surface of ring 160. The effect is that thermal energy is drawn away from ring 160 by heat transfer element 148, thereby increasing the thermal energy absorption capacity of this component.

[0058] The first embodiment can be implemented alone, i.e., heat transfer away from the elongate probe can be provided by a distal heat sink. In this example, no separate cooling device is required. However, the cooling effect of the ring 160 can be enhanced by providing a cooling device and heat transfer element 148.

[0059] To prevent the cooling effect from the heat transfer element 148 or ring 160 from affecting biological tissue that may be present at the distal end of the flexible shaft 112, an insulating cap 162 may be provided on the interface between the flexible shaft 112 and the distal assembly 118. The cap 162 may be made from an epoxy or other material that has a much lower thermal conductivity than the ring 160.

[0060] The insulating cap 162 may also prevent the cooling effect of the ring 160 and the heat transfer element 148 from affecting the shape of the field emitted by the antenna.

[0061] 5 is a schematic side cross-sectional view of the instrument cord of FIG. 2 with a flexible shaft 112 of an electrosurgical instrument, another embodiment of the present invention, passing through its instrument channel. In this embodiment, the heat transfer element 148 is formed from a conductive material that also serves as the outer conductor of the coaxial transmission line 140. The transfer of heat away from the distal assembly in this example is achieved by forced cooling of the distal end of the outer conductor of the coaxial transmission line. In an additional example, the cooling effect can be further enhanced by forced cooling of the inner conductor 146.

[0062] 6 is a schematic side cross-sectional view of a handpiece 180 of an electrosurgical system according to an embodiment of the present invention. Handpiece 180 can perform the function of interface joint 106 described above in that it couples to a single flexible shaft 112 input from cooling device 130, an electrosurgical generator (via interface cable 104), and a control mechanism 109.

[0063] The control mechanism 109 includes a slider 182 that is movable back and forth relative to a housing 184 of the handpiece 180. The slider 182 is connected to a conductive bar 170 that moves within the housing 184 within a first signal transmission element 168. In this example, the first signal transmission element 168 is a conductive sleeve within which the bar 170 slides. The bar 170 is in electrical contact with the sleeve, which is in turn connected to the inner conductor of the interface cable 104 via a connector 166. The conductive bar 170 is connected at its distal end to the proximal end of the coaxial transmission line 140. The conductive bar 170 is electrically connected to the inner conductor 146 of the coaxial transmission line 140. The proximal end of the coaxial transmission line 140 is slidably received in a second signal transmission element 172, which is in electrical contact with a proximal portion 174 of the outer conductor of the coaxial transmission line 140. The second signal transmission element 172 is electrically connected to the outer conductor of the interface cable 104 via the connector 166 .

[0064] By the above mechanism, the coaxial transmission line 140 can be slid longitudinally by the control mechanism 109 and simultaneously receives microwave power from the interface cable 104 .

[0065] In this example, the heat transfer element 148 is a sleeve formed and fixed or otherwise secured over the coaxial transmission line 140. A proximal portion 174 of the outer conductor of the coaxial transmission line 140 extends proximally beyond the proximal end of the heat transfer element 148 for receipt by the second signal transfer element 172. In turn, the proximal portion of the heat transfer element 148 is slidably received within the cooling jacket 164, which is an annular cooling element in thermal communication with the cooling device 130. The cooling device 130 operates to draw heat from the cooling jacket 164, which in turn draws heat from the heat transfer element 148, thus cooling the heat transfer element 148.

Claims

1. 1. An electrosurgical system comprising: an electrosurgical generator configured to generate microwave energy for ablating biological tissue; 1. An electrosurgical instrument comprising: a flexible coaxial transmission line arranged to transmit microwave energy; a radiating tip connected to a distal end of the flexible coaxial transmission line and configured to receive the microwave energy, a distal coaxial transmission line for transmitting said microwave energy; the radiating tip comprising: a needle tip mounted to a distal end of the distal coaxial transmission line, the needle tip configured to deliver the microwave energy to biological tissue; a heat sink attached to the interface between the flexible coaxial transmission line and the radiating tip; a heat transfer element disposed along the flexible coaxial transmission line, the heat transfer element providing a thermal gradient that draws thermal energy away from the radiating tip, the heat transfer element being a sleeve of thermally conductive material mounted around an outer conductor of the flexible coaxial transmission line; the heat sink is in thermal communication with the proximal end of the distal coaxial transmission line and is configured to draw thermal energy from the radiating tip; a maximum outer diameter of the radiating tip is smaller than an outer diameter of the flexible coaxial transmission line; the electrosurgical instrument, wherein the thermal mass of the heat sink is greater than the thermal mass of the radiating tip; the electrosurgical instrument is connected to receive the microwave energy from the electrosurgical generator; The electrosurgical system further includes a cooling device positioned to force cooling of a proximal portion of the heat transfer element of the electrosurgical instrument.

2. The electrosurgical system of claim 1 , wherein the heat sink is solid.

3. The electrosurgical system according to claim 2 , wherein the solid is disposed between the outer conductor of the distal coaxial transmission line and the outer conductor of the flexible coaxial transmission line.

4. The electrosurgical system according to any preceding claim, wherein the heat sink is an annular body mounted around the proximal end of the distal coaxial transmission line.

5. The electrosurgical system according to any preceding claim, further comprising a thermal insulating cap mounted on the interface between the flexible coaxial transmission line and the radiating tip.

6. The electrosurgical system of claim 5 , wherein the insulating cap is formed from epoxy.

7. The electrosurgical system of any preceding claim, wherein the emitting tip has a maximum outer diameter of 1.0 mm or less.

8. The electrosurgical system according to any preceding claim, wherein the distal coaxial transmission line is a half-wave transformer.

9. The electrosurgical system according to claim 1 , wherein the sleeve is made from braided metal.

10. The electrosurgical system of claim 1 , wherein a distal portion of the heat transfer element is in thermal communication with the heat sink to draw thermal energy proximally along the flexible coaxial transmission line.

11. The electrosurgical system of claim 1 , wherein the heat transfer element comprises a solid.

12. The electrosurgical system according to any one of claims 1 to 11, wherein the cooling device is a thermoelectric cooler.

13. 13. The electrosurgical system of claim 1, further comprising a surgical scoping device having a flexible instrument cord for insertion into a patient's body, the flexible instrument cord having an instrument channel extending along its length, the electrosurgical instrument being dimensioned to be received within the instrument channel.

14. 14. The electrosurgical system according to claim 13, further comprising a handpiece having a housing for receiving a proximal end of the electrosurgical instrument, the handpiece comprising a control mechanism configured to move the electrosurgical instrument relative to the housing to deploy the distal end of the electrosurgical instrument at the distal end of the instrument channel.

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