Electrosurgical instrument

Abstract

An electrosurgical instrument for delivering microwave energy to biological tissue includes a pair of conductive tuning elements mounted on the tip of the emitting instrument to shape the instrument's microwave radiation profile, thereby constraining the radiation profile around the tip of the instrument. Such tuning elements can produce a radiation profile that is substantially spherical around the tip of the instrument, providing a well-defined ablation volume. The tuning elements act to improve the efficiency with which microwave energy can be delivered to the target tissue.

Description

Technical Field

[0001] The present invention relates to an electrosurgical instrument for delivering microwave energy to biological tissue to excise tissue. The instrument may include a probe that can be inserted through the channel of an endoscope or catheter, or can be used in laparoscopic or open surgery. This instrument can be used in pulmonary or gastrointestinal applications, but is not limited thereto.

Background Art

[0002] Electromagnetic (EM) energy, particularly microwave energy, has been found to be useful in electrosurgery because of its ability to excise biological tissue. Typically, a device for delivering EM energy to body tissue includes a generator that includes an EM energy source and an electrosurgical instrument connected to the generator for delivering the energy to the tissue.

[0003] Conventional electrosurgical instruments are often designed to be inserted percutaneously into a patient's body. However, for example, when the target site is in a thin cross-section of the lung or gastrointestinal (GI) tract that moves, it may be difficult to position the instrument percutaneously within the body. Other electrosurgical instruments can be delivered to the target site by a surgical scoping device (e.g., an endoscope) that can extend through a path within the body such as the airway or the lumen of the esophagus or colon. This enables minimally invasive treatment, reducing the patient's mortality rate and the complication rate during and after surgery.

[0004] Tissue ablation using microwave EM energy is based on the fact that biological tissue is mainly composed of water. Human soft organ tissue usually has a water content of 70% - 80%. Water molecules have a permanent electric dipole moment, which means there is a charge imbalance across the molecule. Due to this charge imbalance, when the molecule rotates to align its electric dipole moment with the polarity of the applied electric field, the molecule moves in response to the force generated by applying a time-varying electric field. At microwave frequencies, rapid molecular vibrations cause frictional heating, and as a result, the electric field energy is dissipated in the form of heat. This is known as dielectric heating.

[0005] This principle is utilized in microwave ablation therapy, where by applying a local electromagnetic field at microwave frequencies, the water molecules in the target tissue are rapidly heated, resulting in tissue coagulation and cell death. It is known to use microwave emission probes to treat various diseases in the lungs and other organs. For example, in the lungs, microwave radiation can be used to treat asthma and excise tumors or lesions.

Summary of the Invention

Means for Solving the Problems

[0006] Most generally, the present invention provides an electrosurgical instrument for delivering microwave energy to biological tissue, using a pair of conductive tuning elements to shape the microwave radiation profile of the instrument, whereby the radiation profile (also referred to as the "ablation profile") is confined around the tip of the instrument. The inventors have discovered that using such tuning elements can result in a radiation profile that is substantially spherical around the tip of the instrument, providing a well-defined ablation volume. The inventors have also discovered that the tuning elements can act to improve the efficiency of delivering microwave energy to the target tissue.

[0007] In accordance with a first aspect of the present invention, there is provided an electrosurgical instrument, the electrosurgical instrument comprising a coaxial power supply cable for transmitting microwave energy, the coaxial power supply cable having an inner conductor, an outer conductor, and a dielectric material separating the inner conductor and the outer conductor; a radiating tip disposed at a distal end of the coaxial power supply cable for receiving microwave energy, the radiating tip being electrically connected to the inner conductor and extending longitudinally to form a microwave radiator; a proximal tuning element electrically connected to the elongated conductor within a proximal region of the radiating tip; a distal tuning element electrically connected to the elongated conductor within a distal region of the radiating tip; and a dielectric disposed around the elongated conductor, the proximal tuning element, and the distal tuning element. The proximal tuning element and the distal tuning element are longitudinally spaced apart such that a microwave field emitted by the microwave radiator is created around the dielectric.

[0008] The instrument may be operative to excise target tissue within the body. The device is particularly suitable for excising lung tissue, but may also be used to excise tissue of other organs (e.g., the uterus or the digestive tract). In order to efficiently excise the target tissue, the radiating tip should be positioned as close as possible (and in many cases, inside) the target tissue. In order to reach the target tissue (e.g., within the lung), the device may need to be guided through a passageway (e.g., an airway) and around obstacles. This means that it is desirable for the instrument to be as flexible as possible and to have a small cross-sectional area. In particular, the device needs to be fairly flexible near its tip and it may be necessary to maneuver the device along narrow passageways such as narrow bronchioles that may be narrow and tortuous.

[0009] The coaxial power supply cable can be a conventional low-loss coaxial cable that can be connected to an electrosurgical generator at one end. In particular, the inner conductor can be an elongated conductor extending along the longitudinal axis of the coaxial power supply cable. The dielectric material can be disposed around the inner conductor. For example, the first dielectric material can have a channel in which the inner conductor extends. The outer conductor can be a sleeve made of a conductor material disposed on the surface of the dielectric material. The coaxial power supply cable can further include an external protective sheath for insulating and protecting the cable. In some embodiments, the protective sheath can be made of, or coated with, a non-stick material to prevent tissue from adhering to the cable. The radiation tip is located at the distal end of the coaxial power supply cable and serves to deliver the EM energy transmitted along the coaxial power supply cable to the target tissue. The radiation tip can be permanently attached to the coaxial power supply cable, or the radiation tip can be removably attached to the coaxial power supply cable. For example, a connector can be provided at the distal end of the coaxial power supply cable configured to receive the radiation tip and form the necessary electrical connection.

[0010] The radiation tip can generally be cylindrical. The dielectric can be attached to the distal end of the coaxial power supply cable. In some embodiments, the dielectric can include a protruding portion of the dielectric of the coaxial power supply cable that extends beyond the distal end of the coaxial power supply cable. This can simplify the structure of the radiation tip and avoid reflection of EM energy at the boundary between the radiation tip and the coaxial power supply cable. In other embodiments, a second dielectric material different from the dielectric material of the coaxial power supply cable can be used to form the dielectric. To improve the efficiency of delivering microwave energy to the target tissue, the second dielectric material can be selected to improve impedance matching with the target tissue. The radiation tip can also include portions of a plurality of different dielectric materials selected and configured to shape the radiation profile in a desired manner.

[0011] The elongated conductor is electrically connected to the inner conductor of the coaxial feed cable and extends into the dielectric such that the elongated conductor functions as a microwave radiator. In other words, microwave energy transmitted from the coaxial feed cable to the radiation tip can be radiated from the elongated conductor. The outer conductor may terminate at the distal end of the coaxial feed cable such that the elongated conductor extends beyond the distal end of the outer conductor. Thus, the radiation tip can function as a microwave monopole antenna. Accordingly, microwave energy transmitted to the radiation tip can be radiated from the elongated conductor to the surrounding target tissue. The elongated conductor may extend, for example, within a channel of the dielectric. The elongated conductor can be any suitable conductor having an elongated shape. For example, the elongated conductor can be a wire, rod, or strip of conductor material extending within the dielectric.

[0012] The proximal tuning element can be a portion of a conductor material (e.g., metal) located near the proximal end of the radiation tip. The distal tuning element can be a portion of a conductor material (e.g., metal) located near the distal end of the radiation tip. Thus, the distal tuning element can be further away from the distal end of the coaxial feed cable than the proximal tuning element. Both the proximal tuning element and the distal tuning element are electrically connected to the elongated conductor. For example, the proximal tuning element and the distal tuning element can be disposed on or around the elongated conductor, respectively. The proximal tuning element and the distal tuning element can be electrically connected to the elongated conductor by any suitable means. For example, the proximal tuning element and the distal tuning element can be welded or soldered to the elongated conductor. In another example, the proximal tuning element and the distal tuning element can be connected to the elongated conductor using a conductive adhesive (e.g., conductive epoxy). Alternatively, one or both of the proximal tuning element and the distal tuning element can be formed integrally with the elongated conductor (e.g., they can be manufactured together as a single piece). The proximal tuning element and the distal tuning element are longitudinally spaced apart by the length of the elongated conductor. In other words, the section of the elongated conductor is disposed between the proximal electrode and the distal electrode. The proximal tuning element and the distal tuning element can be covered by a portion of the dielectric, thereby isolating / protecting them from the environment.

[0013] Multiple inventors have discovered that a radiation tip having the configuration as described above can reduce the impedance mismatch between the radiation tip and the surrounding target tissue. This can reduce the amount of microwave energy reflected back behind the coaxial feed cable at the radiation tip (which is caused by the impedance mismatch between the radiation tip and the target tissue). As a result, the efficiency of delivering microwave energy to the target tissue can be improved. This may make it possible to reduce the amount of energy that needs to be transmitted under the coaxial feed cable to excise the target tissue. Next, this can reduce the heating effect due to the transmission of microwave energy along the coaxial feed cable, whereby the electrosurgical instrument can be used for a longer period of time.

[0014] Also, multiple inventors have discovered that the proximal tuning element and the distal tuning element can produce a more desirable radiation profile of the radiation tip. In particular, the tuning element can shape the radiation profile so that it concentrates around the radiation tip and reduce the tail of the radiation profile that extends rearward along the coaxial feed cable. In this way, the microwave energy transmitted to the radiation tip is emitted from the radiation tip and can excise the surrounding target tissue in a well-defined volume around the radiation tip. The excised volume (i.e., the volume of tissue excised by the emitted microwave energy) can be approximately spherical. The shape, size, and location of the tuning element can be selected to obtain the desired microwave radiation profile.

[0015] The proximal tuning element and the distal tuning element can be arranged symmetrically with respect to the longitudinal direction. For example, the proximal tuning element and the distal tuning element can be cylindrical, for example, having a central axis that is collinear with the longitudinal axis of the elongated conductor. The longitudinal axis of the elongated conductor is the axis along the length of the elongated conductor. For example, the proximal tuning element can be a cylindrical portion of a conductor material that is disposed around the elongated conductor and is coaxial with the elongated conductor. This can improve the axial symmetry of the radiation profile of the radiation tip.

[0016] In some embodiments, the proximal matching element can be spaced longitudinally from the distal end of the coaxial feed cable. For example, the dielectric can include a spacer positioned between the distal end of the coaxial feed cable and the proximal matching element. The inventors have discovered that spacing the proximal matching element from the distal end of the coaxial feed cable can introduce a phase shift in the instrument. The phase shift can improve the impedance matching between the radiating tip and the target tissue, thereby improving the efficiency of microwave energy delivery to the target tissue. The phase shift can be determined by the distance between the distal end of the coaxial feed cable and the proximal end of the proximal matching element.

[0017] In some embodiments, the proximal matching element can include a channel for receiving the elongate conductor. The channel can serve to position the proximal matching element relative to the elongate conductor and improve the connection between the proximal matching element and the elongate conductor. The channel can also allow the proximal matching element to be positioned at a desired location on the elongate conductor before fixing the proximal matching element to the elongate conductor, thereby facilitating the assembly of the radiating tip. The channel can be a closed channel (e.g., a tunnel) passing through the proximal matching element. In this way, the proximal matching element can be disposed around the elongate conductor. This can improve the axial symmetry of the radiation profile of the radiating tip. For example, if the proximal matching element has a cylindrical shape, the channel can extend along the central axis of the cylinder. Alternatively, the channel can be an open channel, for example, the channel can be a groove extending along the surface of the proximal matching element. The proximal matching element can be electrically connected to the elongate conductor within the channel of the proximal matching element. For example, the walls of the channel can be in direct contact with the outer surface of the elongate conductor. Additionally or alternatively, the proximal matching element can be fixed to the elongate conductor within the channel (e.g., using a conductive adhesive, soldering, or welding).

[0018] Similarly, the distal matching element can include a channel for receiving the elongate conductor. The channel of the distal matching element can have any of the characteristics described above in relation to the channel of the proximal matching element. In particular, the channel can be open or closed, and the distal matching element can be electrically connected and / or fixed to the elongate conductor within the channel of the distal matching element.

[0019] In some embodiments, the distal matching element may be located at the distal end of the elongate conductor. Thus, the distal matching element may be located at the end of the elongate conductor that is furthest from the coaxial feed cable. This may help to concentrate the radiation profile around the distal end of the radiating tip. This may result in a more spherical radiation pattern. For example, the elongate conductor may terminate at or near the distal matching element. In some examples, the elongate conductor may not protrude beyond the distal end of the distal matching element. If the distal matching element includes a channel, the elongate conductor may terminate inside or at the distal end of the channel, such that the elongate conductor does not protrude from the distal end of the channel. In some cases, the channel may not extend along the entire length of the distal matching element, such that the elongate conductor terminates within the distal matching element. In this way, the distal matching element may form a cap at the distal end of the elongate conductor.

[0020] In some embodiments, the length of the longitudinal distal matching element may be greater than the length of the longitudinal proximal electrode. The longitudinal direction corresponds to the direction in which the elongate conductor extends. This may help to concentrate the radiation around the distal end of the radiating tip, thereby resulting in a more spherical radiation pattern. For example, the distal matching element may be twice as long as the longitudinal proximal matching element.

[0021] In some embodiments, the elongate conductor may be the distal portion of the inner conductor that extends beyond the distal end of the coaxial feed cable. In other words, the inner conductor may extend into the dielectric beyond the distal end of the coaxial feed cable to form the elongate conductor. This may facilitate forming the radiating tip at the distal end of the coaxial feed cable by eliminating the need to connect another conductor to the distal end of the inner conductor.

[0022] In some embodiments, the dielectric may include a dielectric spacer between the proximal matching element and the distal matching element. The dielectric spacer may include a channel in which a portion of the elongate conductor located between the proximal matching element and the distal matching element extends. The dielectric spacer may include a proximal surface that contacts the proximal matching element and a distal surface that contacts the distal matching element.

[0023] In some embodiments, the dielectric further comprises a dielectric sheath surrounding the outer surfaces of the proximal matching element and the distal matching element. The dielectric sheath may provide an outer protective layer for protecting the radiation tip from the environment. For example, the dielectric sheath may be made of a non-stick material (e.g., PTFE) or coated therewith, whereby tissue does not adhere to the dielectric. The outer surface of the dielectric sheath may be coplanar with the outer surface of the coaxial feed cable at the interface between the coaxial feed cable and the radiation tip.

[0024] As described above, the proximal matching element may be spaced from the distal end of the coaxial feed cable. The dielectric element may be disposed between the proximal matching element and the distal end of the coaxial feed cable. The dielectric element may be the distal portion of the dielectric material of the coaxial feed cable that protrudes beyond the distal end of the outer conductor. This can assist in ensuring a smooth and safe physical and electrical connection between the coaxial feed cable and the radiation tip. However, it is not necessary. The dielectric element may be, for example, another element made of a material different from the dielectric material of the coaxial feed cable.

[0025] In some embodiments, the radiation tip may further include a distal tip mounted on the distal end of the elongated conductor, and the distal tip is made of a dielectric material. The distal tip may be made of the same dielectric material as the dielectric. Alternatively, the distal tip may be made of a dielectric material different from the rest of the dielectric. The dielectric material of the distal tip may be selected to improve impedance matching between the radiation tip and the target tissue. The distal tip may be pointed to facilitate insertion of the radiation tip into living tissue. In other cases, the distal tip may be rounded. The distal tip may include a non-stick material (e.g., PTFE) on its outer surface to prevent tissue from adhering thereto.

[0026] In some embodiments, the electrosurgical instrument may further include a conductive field-forming element disposed at the distal end of the coaxial power cable, and the field-forming element is electrically connected to the outer conductor. The field-forming element can help reduce the reverse propagation of microwave energy down the coaxial power cable. This can reduce the tail of the radiation profile that extends along a portion of the coaxial power cable. As a result, the radiation profile can be concentrated around the radiation tip. The inventors have discovered that the tail of the radiation profile can be more prominent in electrosurgical instruments having a larger diameter. Thus, the field-forming element can be particularly useful for electrosurgical instruments having a larger outer diameter (e.g., an outer diameter greater than 2.0 mm).

[0027] The field-forming element can be made of any suitable conductive material. The field-forming element can be disposed on the surface of the outer conductor (e.g., the outer or inner surface of the outer conductor). The field-forming element can be electrically connected to the outer conductor by any suitable means (e.g., by conductive epoxy, or by soldering or welding connections). In some cases, the field-forming element can be integrally formed with the distal portion of the coaxial power cable.

[0028] The field-forming element can help increase the effective thickness of the outer conductor at the distal portion of the outer conductor. In some cases, the field-forming element can be configured symmetrically with respect to the longitudinal direction. This can help provide an axially symmetric radiation profile. For example, the field-forming element can be an annular sleeve of conductive material disposed around the outer surface of the outer conductor.

[0029] In some embodiments, the field-forming element can be formed by a distal portion of the outer conductor having a greater thickness compared to the proximal portion of the outer conductor. In other words, the thickness of the outer conductor can be greater at the distal portion than at the proximal portion.

[0030] In some embodiments, the field forming element may have a longitudinal length that matches a quarter wavelength of the microwave energy. In other words, the field forming element may extend along the distal portion of the outer conductor having a length corresponding to a quarter wavelength of the microwave energy transmitted by the coaxial feed cable. This may help minimize the reverse propagation of microwave energy down the coaxial feed cable and improve the efficiency of energy delivery by the radiating tip.

[0031] The electrosurgical instrument described above may form part of a complete electrosurgical device for treating biological tissue. For example, the device may include an electrosurgical generator configured to supply microwave energy. And the electrosurgical instrument of the present invention may be connected to receive microwave energy from the electrosurgical generator. The electrosurgical device may further include a surgical scoping device (e.g., an endoscope) having a flexible insertion cord for insertion into a patient's body, the flexible insertion cord having an instrument channel extending along its length, and the electrosurgical instrument being dimensioned to fit within the instrument channel.

[0032] As used herein, the term "microwave" may be used broadly to denote a frequency range of 400 MHz to 100 GHz, although a range of 1 GHz to 60 GHz is preferred. 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.

[0033] As used herein, the terms "proximal" and "distal" refer, respectively, to the end of the electrosurgical instrument that is farther from the treatment site and the end of the electrosurgical instrument that is closer to the treatment site. Thus, during use, the proximal end of the electrosurgical instrument is closer to the generator for providing RF and / or microwave energy, while the distal end is closer to the patient's treatment site (i.e., the target tissue).

[0034] As used herein, the term "conductive" is used to mean conductive unless otherwise indicated by context.

[0035] As used below, the term "longitudinal" refers to the direction along the length of the electrosurgical instrument parallel to the axis of the coaxial transmission line. The term "inner" means closer radially to the center (e.g., axis) of the instrument. The term "outer" means further radially away from the center (axis) of the instrument.

[0036] The term "electrosurgery" is used in connection with instruments, devices, or tools that are used during surgery and utilize microwave and / or high frequency electromagnetic (EM) energy.

[0037] Embodiments of the present disclosure will be described below with reference to the accompanying drawings.

Brief Description of the Drawings

[0038]

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Mode for Carrying Out the Invention

[0039] FIG. 1 is a schematic view of a complete electrosurgical system 100 capable of supplying microwave energy to the distal end of an invasive electrosurgical instrument. The system 100 includes a generator 102 for controllably supplying microwave energy. A suitable generator for this purpose is described in WO2012 / 076844 which is incorporated herein by reference. The generator can be configured to monitor the reflected signal received so as to be returned from the instrument in order to determine an appropriate power level for delivery. For example, the generator can be configured to calculate the impedance seen at the distal end of the instrument in order to determine the optimal delivery power level. The generator can be configured to deliver power in a series of pulses that are modulated to match the patient's respiratory cycle. This enables power delivery when the lungs contract.

[0040] The generator 102 is connected to the interface joint 106 by the interface cable 104. Optionally, the interface joint 106 can accommodate an instrument control mechanism operable by sliding the trigger 110, for example, to control the longitudinal (front - to - back) movement of one or more control lines or push rods (not shown). If there are multiple control lines, 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 and the instrument control mechanism to a single flexible shaft 112 extending from the distal end of the interface joint 106. In other embodiments, other types of inputs can also be connected to the interface joint 106. For example, in some embodiments, a fluid supply can be connected to the interface joint 106, whereby fluid can be delivered to the instrument.

[0041] The flexible shaft 112 is insertable through the entire length of the instrument (working) channel of the endoscope 114.

[0042] The flexible shaft 112 passes through the instrument channel of the endoscope 114 and has a distal assembly 118 (not drawn to scale in FIG. 1) shaped to project at the distal end of the endoscope's tube (e.g., into the patient's body). The distal - end assembly includes an active tip for delivering microwave energy to biological tissue. The configuration of the tip is described in more detail below.

[0043] The structure of the distal assembly 118 can be configured to have a maximum outer diameter suitable for passing through the working channel. Typically, the diameter of the working channel in a surgical scoping device such as an endoscope is less than 4.0 mm, for example, any one of 2.0 mm, 2.8 mm, 3.2 mm, 3.7 mm, 3.8 mm. The length of the flexible shaft 112 can be 0.3 m or more (for example, 2 m or more). In other embodiments, the distal assembly 118 can be mounted on the distal end of the flexible shaft 112 after the shaft is inserted through the working channel (and before the instrument cord is introduced into the patient's body). Alternatively, the flexible shaft 112 can be inserted into the working channel from the distal end before making its proximal connection. In these configurations, the distal end assembly 118 can possibly have dimensions larger than the working channel of the surgical scoping device 114.

[0044] The system described above is one way to introduce an instrument into a patient's body. Other techniques are possible. For example, the instrument can also be inserted using a catheter.

[0045] Figure 2 shows a cross-sectional side view of an electrosurgical instrument 200 according to an embodiment of the present invention. The distal end of the electrosurgical instrument may correspond to, for example, the distal assembly 118 described above. The electrosurgical instrument 200 includes a coaxial feed cable 202 that can be connected to a generator (such as generator 102) at its proximal end to transmit microwave energy. The coaxial feed cable 202 may be the boundary surface cable 104 described above that passes through the flexible shaft 112. The coaxial feed cable 202 includes an inner conductor 204 and an outer conductor 206 separated by a dielectric material 208. The coaxial feed cable 202 is preferably low-loss with respect to microwave energy. A choke (not shown) is provided to the coaxial feed cable 204 to suppress the reverse propagation of microwave energy reflected from the distal end, and thus limit the reverse heating along the device. The coaxial feed cable 202 further includes a flexible outer sheath 210 disposed around the outer conductor 206 to protect the coaxial feed cable 204. The outer sheath 210 may be made of an insulating material for electrically insulating the outer conductor 206 from around it. The outer sheath 210 may be made of, or coated with, a non-stick material such as PTFE to prevent tissue from adhering to the instrument.

[0046] The radiation tip 212 is formed at the distal end 214 of the coaxial feed cable 202. The dashed line 215 in Figure 2 indicates the boundary surface between the coaxial feed cable 202 and the radiation tip 212. The radiation tip 212 is configured to receive the microwave energy transmitted by the coaxial feed cable 202 and deliver that energy to the biological tissue. The outer conductor 206 of the coaxial feed cable 202 terminates at the distal end 214 of the coaxial feed cable 202, i.e., the outer conductor 206 does not extend into the radiation tip 212. The radiation tip 212 includes a distal portion 216 of the inner conductor 204 that extends beyond the distal end of the coaxial feed cable 202. In particular, the distal portion 216 of the inner conductor 204 extends beyond the distal end of the outer conductor 206.

[0047] The proximal tuning element 218 made of a conductive material (e.g., metal) is electrically connected to the distal portion 216 of the inner conductor 204 near the proximal end of the radiation tip 212. The proximal tuning element 218 has a cylindrical shape and includes a channel 220 through which the distal portion 216 of the inner conductor 204 passes. The diameter of the channel 220 is substantially the same as the outer diameter of the inner conductor 204 such that the inner conductor 204 contacts the proximal tuning element 218 inside the channel 220. Further, the proximal tuning element 218 can be fixed to the inner conductor 204 using, for example, a conductive adhesive (e.g., conductive epoxy), or by soldering or welding. The proximal tuning element 218 is centered on the inner conductor 204. In other words, the central axis of the cylindrical proximal tuning element 218 is collinear with the longitudinal axis of the inner conductor 204. Thus, the proximal tuning element 218 is disposed around the distal portion 216 of the inner conductor 204 in a manner that is symmetric with respect to the longitudinal axis of the inner conductor 204.

[0048] The distal tuning element 222 made of a conductive material (e.g., metal) is electrically connected to the distal portion 216 of the inner conductor 204 near the distal end of the radiation tip 212. Thus, the distal tuning element 222 is positioned further along the inner conductor 204 than the proximal tuning element 218. The distal tuning element 222 is spaced from the proximal tuning element by the length of the distal portion 216 of the inner conductor 204. Similar to the proximal tuning element 218, the distal tuning element has a cylindrical shape and includes a channel 224. As can be seen in FIG. 2, the distal portion 216 of the inner conductor 204 extends into the channel 224. The distal portion 216 of the inner conductor 204 terminates at the distal end of the channel 224, i.e., it does not project beyond the distal tuning element 222. Thus, the distal end of the inner conductor 204 is in the same plane as the distal face of the distal tuning element 222. The diameter of the channel 224 is substantially the same as the outer diameter of the inner conductor 204 such that the inner conductor 204 contacts the distal tuning element 222 inside the channel 224. Further, the distal tuning element 222 can be fixed to the inner conductor 204 using, for example, a conductive adhesive (e.g., conductive epoxy), or by soldering or welding. Similar to the proximal tuning element 218, the distal tuning element 222 is mounted such that it is centered on the inner conductor 204.

[0049] Both the proximal matching element 218 and the distal matching element 222 have the same outer diameter. The outer diameters of the proximal matching element 218 and the distal matching element 222 can be slightly smaller than the outer diameter of the electrosurgical instrument 200. In the illustrated embodiment, the distal matching element 222 is longer than the proximal matching element 218 in the longitudinal direction of the instrument. In other words, the length of the inner conductor 204 of the channel 224 of the distal matching element 222 is greater than the length of the inner conductor 204 of the channel 220 of the proximal matching element 218. For example, the distal matching element 222 can be approximately twice as long as the proximal matching element 218. By making the distal matching element 222 longer than the proximal matching element 218, it is possible to concentrate the emission of microwaves around the distal end of the radiation tip 212.

[0050] The distal portion 226 of the dielectric material 208 extends into the radiation tip 212 beyond the distal end 214 of the coaxial feed cable 202. The distal portion 226 of the dielectric material 208 functions as a spacer between the proximal matching element 218 and the distal end 214 of the coaxial feed cable 202. In some embodiments (not shown), the dielectric material 208 can terminate at the distal end 214 of the coaxial feed cable 202, and another spacer can be provided between the distal end 214 of the coaxial feed cable 202 and the proximal matching element 218. The dielectric spacer 228 is provided within the radiation tip 212 between the proximal matching element 218 and the distal matching element 222. The dielectric spacer 228 is a cylindrical portion of the dielectric material and has a central channel extending therethrough. Thus, the dielectric spacer 228 can be a tube of dielectric material. The distal portion 214 of the inner conductor 204 extends through the channel within the dielectric spacer 228. The proximal face of the dielectric spacer 228 contacts the proximal matching element 218, and the distal face of the dielectric spacer 228 contacts the distal matching element 222. The dielectric spacer 228 has approximately the same outer diameter as the proximal matching element 218 and the distal matching element 222.

[0051] The protective sheath 230 is provided outside the radiation tip 212. The protective sheath 230 covers the dielectric spacer 228, the proximal tuning element 218, and the distal tuning element 222, and forms the outer surface of the radiation tip 212. The protective sheath 230 can be a tube made of an insulating material. The protective sheath 230 can serve to insulate the radiation tip 212 and protect it from the environment. The protective sheath 230 can be made of, or coated with, a non-stick material (e.g., PTFE) to prevent tissue from adhering to it. The outer diameter of the protective sheath 230 is substantially the same as the outer diameter of the coaxial feed cable 202, such that the instrument has a smooth outer surface, i.e., the radiation tip 212 has an outer surface that is coplanar with the outer surface of the coaxial feed cable 202 at the interface 215. In some embodiments (not shown), the protective sheath 230 can be an extension of the outer sheath 210 of the coaxial feed cable 202. At the same time, the distal portion 226 of the dielectric material 208, the dielectric spacer 228, and the protective sheath 230 form the dielectric of the radiation tip 212.

[0052] The radiation tip 212 further includes a distal tip 232 located at its distal end. The distal tip 232 can be sharpened to facilitate insertion of the radiation tip 212 into the target tissue. However, in other embodiments (not shown), the distal tip can be rounded or flat. The distal tip 232 can be made of, for example, the same dielectric material as the dielectric material 208. In some embodiments, the material of the distal tip 232 can be selected to improve impedance matching with the target tissue to improve the efficiency of delivering EM energy to the target tissue. The distal tip 232 can be made of, or covered with, a non-stick material (e.g., PTFE) to prevent tissue from adhering to it.

[0053] The following are examples of the dimensions of the electrosurgical instrument 200. - Distance from the interface 215 to the distal end of the distal portion 216 of the inner conductor 204: 5.75 mm, - Outer diameter of the proximal tuning element 218 and the distal tuning element 222: 1.5 mm, - Length of the proximal tuning element 218: 0.5 mm, - Length of the distal matching element 222: 1.0 mm, - Spacing between the proximal matching element 218 and the distal matching element 222: 3.75 mm, - Spacing between the proximal matching element 218 and the boundary surface 215: 0.5 mm, and - Outer diameter of the electrosurgical instrument 200: 1.85 mm.

[0054] When microwave energy is transmitted to the radiation tip 212, the radiation tip 212 can function as a microwave monopole antenna. In particular, the microwave energy can be radiated from the distal portion 216 of the inner conductor 202, whereby the microwave energy can be delivered to the surrounding biological tissue. The proximal matching element 218 and the distal matching element 222 act to shape the radiation profile of the radiation tip 212 and improve the impedance matching between the instrument and the surrounding target tissue, as will be described below.

[0055] FIG. 3 shows a simulation of the microwave radiation profile of the target tissue of the electrosurgical instrument 200 shown in FIG. 2. The radiation profile was simulated for a microwave frequency of 5.8 GHz using finite element analysis software. The radiation profile shows the shape resulting from the tissue excised by the microwave energy. As can be seen in FIG. 3, the radiation profile is concentrated around the radiation tip, defining a substantially spherical region. Thus, the tissue can be excised within a substantially spherical region around the radiation tip. The boundary surface 215 between the radiation tip and the coaxial feed cable is shown to assist in visualizing the location and shape of the field with respect to the tip of the instrument.

[0056] FIG. 4 shows a graph of the simulation of the S-parameter (input reflection coefficient S 11 or also known as "reflection attenuation") of the electrosurgical instrument 200 with respect to the frequency of the microwave energy. As is well known in the art, the S-parameter is a criterion for evaluating the reflection attenuation of microwave energy due to impedance mismatch, and thus the S-parameter indicates the degree of impedance mismatch between the target tissue and the radiation tip. The S-parameter is given by the equation PI =SP R can be defined by, where P I is the transmission power of the instrument towards the tissue, and P R is the power reflected from the tissue, and S is the S parameter. As shown in FIG. 4, the S parameter has a value of -25.58 dB at 5.8 GHz, meaning that very little microwave energy is reflected from the tissue at this frequency. This indicates that the impedance matching at the operating frequency of 5.8 GHz is good, and the microwave energy is efficiently delivered from the radiation tip to the tissue at this frequency.

[0057] FIG. 5 shows a simulation of the impedance Smith chart of the electrosurgical instrument 200. The Smith chart is simulated for a reference plane located at the interface 215 between the distal end and the radiation tip of the coaxial feed cable. As is well known in the art, the Smith chart is a graphical representation of the S parameter (reflection coefficient) in the complex plane. The S parameter can be defined by the following equation.

[0058]

Equation

[0059] Here, Z = Z / Z0, where Z is the impedance of the radiation tip in contact with the target tissue and Z0 is the normalization factor. In this case, a normalization factor of 50 ohms was used. This is because it is the normal characteristic impedance of the coaxial power cable, the interface cable (e.g., interface cable 104), and the electrosurgical generator (e.g., generator 102). In FIG. 5, the marker (label "1") indicates the value of the S-parameter at 5.8 GHz. As can be seen, the value of the S-parameter is near the unity mark (i.e., the point where Z = 1). This indicates good impedance matching between the generator, the interface cable, the coaxial power cable, and the antenna in contact with the target tissue. In other words, microwave energy can be efficiently delivered from the radiation tip to the target tissue. The value of the impedance Z at 5.8 GHz is shown in the legend of FIG. 5 and is (54.9 + i2.9) ohms. The solid circle (black circle) and the open circle (white circle in the middle) next to the marker in FIG. 5 indicate the points at 6 GHz and 5.6 GHz, respectively. The values of the impedance Z at these points are shown in the legend of FIG. 5.

[0060] Here, referring to the comparative examples shown in FIGS. 6 to 13, the effects of the proximal tuning element and the distal tuning element are shown in more detail. FIG. 6 shows an electrosurgical instrument 600 which is the first comparative example, and FIG. 7 shows an electrosurgical instrument 700 which is the second comparative example. The electrosurgical instrument 600 is similar to the electrosurgical instrument 200 except that the electrosurgical instrument 600 does not include a proximal tuning element. All other mechanisms of the electrosurgical instrument 600 (including the distal tuning element) are the same as those of the electrosurgical instrument 200. The electrosurgical instrument 700 is similar to the electrosurgical instrument 200 except that the electrosurgical instrument 700 does not include a proximal tuning element or a distal tuning element (i.e., neither tuning element). All other mechanisms of the electrosurgical instrument 700 are the same as those related to the electrosurgical instrument 200. The reference numbers used in FIG. 2 are used in FIGS. 6 and 7 and indicate mechanisms corresponding to the mechanisms described above in relation to FIG. 2.

[0061] Figure 8 shows a simulation of the microwave radiation profile of the target tissue of the electrosurgical instrument 600 shown in Figure 6. The radiation profile was simulated for a microwave frequency of 5.8 GHz using finite element analysis software. Except for the absence of the proximal tuning element, the dimensions of the electrosurgical instrument 600 used in the calculation were the same as those used to calculate the radiation profile of the electrosurgical instrument 200 shown in Figure 3. As can be seen by comparing Figures 3 and 8, the radiation profile of the electrosurgical instrument 600 is less spherical than that of the electrosurgical instrument 200. In particular, the radiation profile of the electrosurgical instrument 600 includes a tail that extends behind a longer portion of the coaxial feed cable than the tail of the radiation profile of the electrosurgical instrument 200. Thus, the proximal tuning element acts to make the radiation profile more spherical and reduce the tail that extends behind the coaxial feed cable. Such a tail may be undesirable as it can cause heating of the coaxial feed cable and / or cause resection of tissue outside the target zone.

[0062] Figure 9 shows a graph of the simulation of the S-parameter versus the frequency of the microwave energy of the electrosurgical instrument 600. The graph in Figure 9 was calculated in the same manner as the graph in Figure 4 for the electrosurgical instrument 200. As shown in Figure 9, the S-parameter has a value of -10.18 dB at 5.8 GHz. This represents a significantly larger amount of reflection attenuation compared to the electrosurgical instrument 200, for which the S-parameter was found to have a value of -25.58 dB. Thus, the proximal tuning element helps to improve impedance matching. Thus, microwave energy can be delivered to the target tissue more efficiently using the electrosurgical instrument 200 than using the electrosurgical instrument 600.

[0063] FIG. 10 shows a simulation of the impedance Smith chart of the electrosurgical instrument 600. This is calculated in the same way as the Smith chart of the electrosurgical instrument 200 shown in FIG. 5. The marker (label "1") in FIG. 10 indicates the value of the S-parameter at 5.8 GHz. As can be seen, the marker is further away from the unity mark compared to FIG. 5. This indicates that the impedance matching between the generator, the interface cable, the coaxial power supply cable, and the antenna in contact with the target tissue is not good compared to the electrosurgical instrument 200. By comparing FIGS. 5 and 10, it can be seen that the effect of adding the proximal tuning element is that the marker moves downward towards the unity mark. This indicates that the proximal tuning element introduces additional capacitance into the system. The shift of the marker closer to the unity mark in FIG. 5 may also be related to the phase shift associated with the distance between the distal end of the coaxial power supply cable and the proximal end of the proximal tuning element. The value of the impedance Z of the electrosurgical instrument 600 at 5.8 GHz is shown in the legend of FIG. 10 and is (40.2 + i27.5) ohms. The solid circle (black circle) and the open circle (white circle inside) next to the marker in FIG. 10 indicate the points at 6 GHz and 5.6 GHz, respectively. The values of the impedance Z of these points are shown in the legend of FIG. 10.

[0064] FIG. 11 shows a simulation of the microwave radiation profile of the target tissue of the electrosurgical instrument 700 shown in FIG. 7. The radiation profile was simulated for a microwave frequency of 5.8 GHz using finite element analysis software. Except for the absence of the proximal tuning element and the distal tuning element, the dimensions of the electrosurgical instrument 700 used in the calculation were the same as those used to calculate the radiation profile of the electrosurgical instrument 200 shown in FIG. 3. As can be seen by comparing FIGS. 3, 8, and 11, the radiation profile of the electrosurgical instrument 700 is less spherical and more elongated than the radiation profile of the electrosurgical instrument 600. In particular, the radiation profile of the electrosurgical instrument 700 does not concentrate much around the distal tip of the instrument and has a longer tail extending behind the coaxial feed cable. Thus, the distal tuning element acts to make the radiation profile more spherical and reduce the tail extending behind the coaxial feed cable.

[0065] FIG. 12 shows a graph of the simulation of the S-parameters of the electrosurgical instrument 700 with respect to the frequency of the microwave energy. The graph of FIG. 12 was calculated in the same manner as the graph of FIG. 4 for the electrosurgical instrument 200. As shown in FIG. 12, the S-parameter has a value of -5.66 dB at 5.8 GHz. This shows a considerably large amount of reflection attenuation compared to the electrosurgical instruments 200 and 600 for which the S-parameters were found to be -25.58 dB and -10.18 dB, respectively. Thus, the distal tuning element helps to improve impedance matching.

[0066] FIG. 13 shows a simulation of the impedance Smith chart of the electrosurgical instrument 700. This is calculated in the same way as the Smith chart of the electrosurgical instrument 200 shown in FIG. 5. The marker (label "1") in FIG. 13 indicates the value of the S-parameter at 5.8 GHz. As can be seen, the marker is further away from the unity mark compared to FIG. 5. This indicates that the impedance matching between the generator, the interface cable, the coaxial power supply cable, and the antenna in contact with the target tissue is not good compared to the electrosurgical instrument 200. The marker in FIG. 13 is also further away from the unity mark compared to FIG. 10, indicating that the impedance matching is not good. The value of the impedance Z of the electrosurgical instrument 700 at 5.8 GHz is shown in the legend of FIG. 13 and is (20.5 - i25.7) ohms. The solid circle (black circle) and the empty circle (white circle in the middle) next to the marker in FIG. 13 indicate the points at 6 GHz and 5.6 GHz, respectively. The values of the impedance Z of these points are shown in the legend of FIG. 13.

[0067] In summary, the comparative example shows that the presence of both the proximal tuning element and the distal tuning element within the radiation tip helps to enhance the radiation profile of the radiation tip by making the radiation profile more spherical and reducing the tail extending behind the coaxial power supply cable. The comparative example also shows that the proximal tuning element and the distal tuning element help to improve the impedance matching, which can improve the efficiency of delivering microwave energy to the target tissue.

[0068] Multiple inventors have discovered that as the outer diameter of an electrosurgical instrument increases, the tail of the radiation profile extending behind the coaxial power supply cable increases. This is shown in FIG. 14, which shows a simulation of the microwave radiation profile of the target tissue of an electrosurgical instrument according to an embodiment of the present invention. The electrosurgical instrument of FIG. 14 is similar to the electrosurgical instrument 200 described above, except that it has an outer diameter of 2.6 mm (whereas the electrosurgical instrument 200 has an outer diameter of 1.85 mm). The radiation profile was simulated for a microwave frequency of 5.8 GHz using finite element analysis software. The dashed line indicated by the numeral 215 in FIG. 14 shows the position of the interface between the coaxial power supply cable and the radiation tip. As can be seen by comparing FIG. 14 with the radiation profile of the electrosurgical instrument 200, the tail extending behind the coaxial power supply cable is larger for the electrosurgical instrument of FIG. 14 (i.e., the electrosurgical instrument having a larger outer diameter).

[0069] Multiple inventors have discovered that by including a field-forming element at the distal end of the coaxial power supply cable, the tail of the radiation profile can be suppressed. FIG. 15 shows a cross-sectional side view of an electrosurgical instrument 900 according to an embodiment of the present invention. The electrosurgical instrument 900 is similar to the electrosurgical instrument 200 described above, except that it includes a field-forming element 902 and has an outer diameter of 2.6 mm. The reference numerals used in FIG. 2 are used in FIG. 15 and show mechanisms corresponding to the mechanisms described above in relation to FIG. 2.

[0070] The field forming element 902 is an annular sleeve of conductive material disposed around the outer surface of the outer conductor 206. The field forming element 902 is located at the distal end of the coaxial feed cable 202 and extends from the boundary surface 215 along the length of the coaxial feed cable 202. The length of the field forming element 902 corresponds to a quarter wavelength of the microwave energy transmitted by the coaxial feed cable 202. When the microwave energy is 5.8 GHz, the length of the field forming element 902 can be about 9 mm. The inner surface of the field forming element 902 contacts the outer surface of the outer conductor 206, whereby the field forming element 902 is electrically connected to the outer conductor 206 along its length. The electrical connection between the field forming element 902 and the outer conductor 206 can be ensured by fixing the field forming element 902 to the outer conductor 206, for example, using a conductive epoxy or by soldering or welding them. In some embodiments (not shown), the field forming element 902 can be integrally formed with the outer conductor 206. The field forming element 902 acts to increase the effective thickness of the outer conductor 206 within the distal region of the coaxial feed cable 202.

[0071] FIG. 16 shows a simulation of the microwave radiation profile of the target tissue of the electrosurgical instrument 900 shown in FIG. 15. The radiation profile was simulated for a microwave frequency of 5.8 GHz using finite element analysis software. As can be seen by comparing FIG. 16 and FIG. 14, the radiation profile of FIG. 16 has a smaller tail that extends behind the coaxial feed cable. The radiation profile of FIG. 16 also appears more spherical and is more concentrated around the radiation tip. The only difference between the electrosurgical instrument of FIG. 14 and the electrosurgical instrument 900 is the presence of the field forming element 902 within the electrosurgical instrument 900. Thus, the field forming element 902 serves to reduce the tail of the radiation profile and concentrate the emission of microwave energy around the radiation tip.

Claims

Claim 1. An electrosurgical instrument, comprising: A coaxial power supply cable for transmitting microwave energy, said coaxial power supply cable having an inner conductor, an outer conductor, and a dielectric material separating said inner conductor and said outer conductor; said coaxial power supply cable; A radiation tip disposed at a distal end of said coaxial power supply cable for receiving said microwave energy, said radiation tip comprising: An elongated conductor electrically connected to said inner conductor and extending longitudinally to form a microwave radiator; A proximal tuning element electrically connected to said elongated conductor within a proximal region of said radiation tip; A distal tuning element electrically connected to said elongated conductor within a distal region of said radiation tip; A dielectric disposed around said elongated conductor, said proximal tuning element, and said distal tuning element; said radiation tip; Said proximal tuning element and said distal tuning element are spaced apart in said longitudinal direction, whereby a microwave field emitted by said microwave radiator is formed around said dielectric; The length of said distal tuning element in said longitudinal direction is greater than the length of said proximal tuning element in said longitudinal direction; said electrosurgical instrument. Claim 2. The electrosurgical instrument according to claim 1, wherein said proximal tuning element and said distal tuning element are symmetric with respect to said longitudinal direction. Claim 3. The electrosurgical instrument according to claim 1, wherein said proximal tuning element and said distal tuning element are cylindrical and have a central axis that is collinear with the longitudinal axis of said elongated conductor. Claim 4. The electrosurgical instrument according to any one of claims 1 to 3, wherein said proximal tuning element is spaced apart from said distal end of said coaxial power supply cable in said longitudinal direction. Claim 5. The electrosurgical instrument according to any one of claims 1 to 4, wherein said proximal tuning element and said distal tuning element each include a channel in which said elongated conductor extends. Claim 6. The electrosurgical instrument according to any one of claims 1 to 5, wherein said distal tuning element is located at the distal end of said elongated conductor. Claim 7. The electrosurgical instrument according to any one of claims 1 to 6, wherein said elongated conductor is a distal portion of said inner conductor that extends beyond the distal end of said outer conductor. Claim 8. The electrosurgical instrument according to any one of claims 1 to 7, wherein said dielectric includes a dielectric spacer between said proximal tuning element and said distal tuning element. Claim 9. The dielectric body includes a dielectric sheath that surrounds the outer surfaces of the proximal tuning element and the distal tuning element. The electrosurgical instrument according to any one of claims 1 to 8.

10. The outer surface of the dielectric sheath is in the same plane as the outer surface of the coaxial power supply cable at the interface between the coaxial power supply cable and the radiation tip. The electrosurgical instrument according to claim 9.

11. The electrosurgical instrument according to claim 4, including a dielectric element mounted between the proximal tuning element and the distal end of the coaxial power supply cable.

12. The dielectric element includes a distal portion of the dielectric material of the coaxial power supply cable that protrudes beyond the distal end of the outer conductor. The electrosurgical instrument according to claim 11.

13. The radiation tip further includes a distal tip mounted at the distal end of the elongated conductor, and the distal tip is made of a dielectric material. The electrosurgical instrument according to any one of claims 1 to 12.

14. The distal tip is pointed. The electrosurgical instrument according to claim 13.

15. The electrosurgical instrument according to any one of claims 1 to 14, further including a conductive field forming element disposed at the distal end of the coaxial power supply cable, and the field forming element is electrically connected to the outer conductor.

16. The field forming element is formed by a distal portion of the outer conductor having a greater thickness compared to the proximal portion of the outer conductor. The electrosurgical instrument according to claim 15.

17. The field forming element has a longitudinal length corresponding to a quarter wavelength of the microwave energy. The electrosurgical instrument according to claim 15 or 16.

18. An electrosurgical device for treating biological tissue, comprising: an electrosurgical generator configured to supply microwave energy; and the electrosurgical instrument according to any one of claims 1 to 17, connected to receive the microwave energy from the electrosurgical generator. The electrosurgical device.

19. The electrosurgical device according to claim 18, further comprising a surgical scoping device including a flexible insertion cord having an instrument channel, and the electrosurgical instrument is dimensioned to fit within the instrument channel.

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