Electrosurgical instrument

Abstract

Various embodiments provide an electrosurgical instrument comprising a coaxial feed cable having an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor and the outer conductor, the coaxial feed cable being for conveying a microwave signal. The instrument further comprising a radiating tip disposed at a distal end of the coaxial feed cable to receive the microwave signal. The radiating tip comprises: an elongate conductor electrically connected to the inner conductor and extending in a longitudinal direction; a dielectric body disposed on at least a first portion of the elongate conductor, the dielectric body comprising a second dielectric material having a higher dielectric constant than the first dielectric material; and, a conductive body disposed on at least a second portion of the elongate element, the second portion being different from the first portion. Some other embodiments provide an electrosurgical apparatus including the instrument.

Description

[0001] ELECTROSURGICAL INSTRUMENT

[0002] Field of the Invention

[0003] The invention relates to an electrosurgical instrument for delivering microwave energy to biological tissue in order to ablate the tissue. The instrument may comprise a probe that is insertable through a channel of an endoscope or catheter, or may be used in laparoscopic surgery or open surgery. The instrument may be used in pulmonary or gastrointestinal applications, but is not limited to such.

[0004] Background

[0005] Electromagnetic (EM) energy, and in particular microwave energy, has been found to be useful in electrosurgical operations for its ability to ablate biological tissue. Typically, apparatus for delivering EM energy to body tissue includes a generator comprising a source of EM energy, and an electrosurgical instrument connected to the generator, for delivering the energy to tissue.

[0006] Conventional electrosurgical instruments are often designed to be inserted percutaneously into the patient’s body. However, it can be difficult to locate the instrument percutaneously in the body, for example if the target site is in a moving lung or a thin walled section of the gastrointestinal (Gl) tract. Other electrosurgical instruments can be delivered to a target site by a surgical scoping device (e.g. an endoscope) which can be run through channels in the body such as airways or the lumen of the oesophagus or colon. This allows for minimally invasive treatments, which can reduce the mortality rate of patients and reduce intraoperative and postoperative complication rates.

[0007] Tissue ablation using microwave EM energy is based on the fact that biological tissue is largely composed of water. Human soft organ tissue is typically between 70% and 80% water content. Water molecules have a permanent electric dipole moment, meaning that a charge imbalance exists across the molecule. This charge imbalance causes the molecules to move in response to the forces generated by application of a time varying electric field as the molecules rotate to align their electric dipole moment with the polarity of the applied field. At microwave frequencies, rapid molecular oscillations result in frictional heating and consequential dissipation of the field energy in the form of heat. This is known as dielectric heating.

[0008] This principle is harnessed in microwave ablation therapies, where water molecules in target tissue are rapidly heated by application of a localised electromagnetic field at microwave frequencies, resulting in tissue coagulation and cell death. It is known to use microwave emitting probes to treat various conditions in the lungs and other organs. For example, in the lungs, microwave radiation can be used to treat asthma and ablate tumours or lesions.

[0009] Summary of the Invention

[0010] At its most general, the present invention provides an electrosurgical instrument for delivering microwave energy to biological tissue, in which a radiating tip comprises a dielectric body comprising a dielectric material having a higher dielectric constant than a dielectric material used in a coaxial cable for supplying a microwave signal to the radiating tip. The inventors have found that using such a dielectric body in the radiating tip allows the effective electrical length of the radiating tip to be increased without increasing the physical length of the radiating tip.

[0011] It is generally desirable to reduce the size of an electrosurgical instrument, e.g. by making it thinner and / or shorter. A compact arrangement may provide several advantages. For example, a compact arrangement may allow the instrument to be used within narrower scoping devices and / or in smaller biological structures, may enable the instrument to be more easily manoeuvred, and / or may help to improve the control and precision at the instrument tip.

[0012] However, it is difficult to reduce the size of the instrument whilst retaining its functionality. In particular, in order to efficiently transfer energy into tissue, an instrument tip may be configured with a physical length that corresponds to a particular electrical length (i.e. number of wavelengths) at a desired frequency of energy. For example, in order to provide efficient energy transfer at 5.8 GHz microwave energy, the physical length of the instrument tip may be selected to correspond to a half wavelength at that frequency (taking into account the dielectric constant of the material), for the instrument tip to act as a halfwavelength resonator. However, since the physical length of the instrument tip is selected to provide a particular electrical length (i.e. to correspond to a certain number of wavelengths at the desired frequency), the physical length of the instrument tip cannot be reduced whilst retaining the desired electrical properties. Instead, as the physical length is reduced, the electrical length will also be reduced, resulting in destructive reflections at the interface with biological tissue at the desired frequency (e.g. 5.8 GHz), and causing reduced efficiency of energy delivery through the instrument tip.

[0013] According to a first aspect of the invention, there is provided an electrosurgical instrument comprising a coaxial feed cable having an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor and the outer conductor, the coaxial feed cable being for conveying a microwave signal, and a radiating tip disposed at a distal end of the coaxial feed cable to receive the microwave signal; wherein the radiating tip comprises an elongate conductor electrically connected (either directly or indirectly) to the inner conductor and extending in a longitudinal direction; a dielectric body disposed on at least a first portion of the elongate conductor, the dielectric body comprising a second dielectric material having a higher dielectric constant than the first dielectric material; and a conductive body (for example, made of a metal material) disposed on at least a second portion of the elongate element, the second portion being different from the first portion. In this way, the radiating tip comprises a microwave radiator which is formed of the elongate conductor and the conductive body, wherein the radiating tip may thereby act as a microwave monopole antenna where microwave energy delivered to the radiating tip is radiated from the elongate conductor and the conductive body into surrounding target tissue. The conductive body may be in electrical contact with the elongate conductor along a majority or an entirely of the length of the conductive body.

[0014] The instrument may operate to ablate target tissue in the body. The device is particularly suited to the ablation of tissue in the lungs, however it may be used to ablate tissue in other organs (e.g. the uterus or the Gl tract). In order to efficiently ablate target tissue, the radiating tip should be located as close as possible (and in many cases inside) the target tissue. In order to reach the target tissue (e.g. in the lungs), the device may need to be guided through passageways (e.g. airways) and around obstacles. This means that the instrument will ideally be as flexible as possible and have a small cross section. Particularly, the device should be very flexible near its tip, where it may need to be steered along narrow passageways such as bronchioles which can be narrow and winding.

[0015] By providing a dielectric body which uses a second dielectric material having a higher dielectric constant than the first dielectric material used in the coaxial cable, the effective electrical length of the radiating tip is increased compared a radiating tip of the same physical length which uses the same dielectric material in the radiating tip as in the coaxial cable. This means that a tip according to this new configuration can operate at the same frequency as an existing instrument, but with a shorter physical length - which may thereby be easier to guide to target tissue (for example, allowing a reduced radius of curvature relative to known arrangements). The coaxial feed cable used in embodiments of the present invention may be a conventional low loss coaxial cable that is connectable at one end to an electrosurgical generator. It should be noted that a coaxial cable needs to be long (e.g., 1 metre or more in length) in order to ensure that target tissue can be reached, and so it is desirable to use a dielectric material having a relatively low dielectric constant (e.g., relative to the radiating tip) in order to minimise energy losses through the coaxial cable. In addition, the choice of material for the coaxial cable is restricted by flexibility requirements, and it may not be possible to select a high dielectric material that is suitably flexible. However, due to the relative short length of the radiating tip (as described in more detail herein), this is less of a concern for the radiating tip according to an embodiment.

[0016] The ablation volume (i.e., a volume of tissue that is ablated by the radiated microwave energy) of the instrument may be approximately spherical. The shape of the ablation volume may be affected by the shape, size and location of the dielectric body and the conductive body. For example, increasing the length of the dielectric body may, in some examples, increase the length of the ablation volume along the longitudinal axis of the instrument.

[0017] As used herein, the phrase “electrical length” may refer to a length of the instrument tip as calculated using the working signal’s wavelength A, i.e., it may refer to the length of the instrument tip as “seen” by the working signal. The electrical length may be calculated as a fraction or multiple of wavelengths. For example, in order to act as a half wave resonator, the instrument tip may have an electrical length of approximately -A. This can be calculated as -A = - ,c, where c is the speed of light and Eetr is the

[0018] 2 2 2 / V£e / / effective dielectric constant of the radiating tip. The effective dielectric constant may depend on the dimensions of the conductive element, and the material surrounding the conductive element. The effective dielectric constant may vary along the length of the conductive element (i.e., along the length of the radiating tip), and therefore using one value for Eetr in this formula may be an approximation.

[0019] The radiating tip may be generally cylindrical. The dielectric body and the conductive body be cylindrical, e.g. having a central axis that is collinear with a longitudinal axis of the elongate conductor. The longitudinal axis of the elongate conductor is an axis along the length of the elongate conductor. This may improve the axial symmetry of the radiation profile of the radiating tip. Optionally, the conductive body may have a diameter which is less than that of the coaxial cable and, optionally, less than that of the outer conductor of the coaxial cable. In an embodiment, the conductive body has a diameter which is substantially the same as that of the dielectric material of the coaxial cable. The diameter of the conductive body also changes the effective electrical length of the radiating tip (e.g., increasing the diameter of the conductive body serves to increase the effective electrical length of the radiating tip), and so providing a conductive body which is of a similar diameter to the coaxial cable may be useful to provide an increase in effective electrical length. However, if the conductive body is wider than the coaxial cable, the radiating tip may be more difficult to manoeuvre to the target treatment site, for example, it may cause an increase in the maximum outer diameter of the radiating tip.

[0020] Optionally, an outer diameter of the radiating tip may be less than 5 mm, for example less than 2 mm, such as 1 .5 mm or less.

[0021] Optionally, the conductive body may have a length in the longitudinal direction of 7 mm or less, for example the conductive body may have a length in the longitudinal direction of between 2 mm and 4 mm. It has been found that, as the conductive body is typically made of a metal material and so is a generally rigid structure, providing the conductive body with a length of 7 mm or less ensures that the radius of curvature of the radiating tip may is still in a range which is suitable for reaching desired tissue treatment sites (e.g., in a patient’s lung).

[0022] Optionally, the dielectric body may have a length in the longitudinal direction of 14 mm or less. It has been found that, as materials having higher dielectric constants may generally be less flexible and more rigid than materials having low dielectric constants, providing a dielectric body with a length of 14 mm or less ensures that the radius of curvature of the radiating tip may is still in a range which is suitable for reaching desired tissue treatment sites (e.g., in a patient’s lung). A dielectric body with a length in a range of 1 mm to 7 mm may be particularly suitable for delivering energy at a frequency of 5.8 GHz, and a dielectric body with a length in a range of 6 mm to 14 mm may be particularly suitable for delivering energy at a frequency of 2.45 GHz, for example.

[0023] Optionally, the length of the dielectric body in the longitudinal direction may be less than the length of the conductive body in the longitudinal direction. It has surprisingly been found that such an arrangement may have an electrical length which is suitable for delivering energy into tissue with frequencies at 2.45 GHz and 5.8 GHz, but which also provides a radiating tip with a short physical length, and which generates an ablation zone with a short length in the longitudinal direction leading to a highly spherical ablation zone. An electrosurgical instrument configured in this way is therefore a good arrangement to balance the matching of energy into tissue at these frequencies while still generating a spherical, and thus predictable, ablation pattern. For instance, a clinician may find working with a spherical ablation zone simpler than a tear-shaped ablation zone because the length and the width of a spherical zone are substantially the same (whereas the length of a tear-shaped zone is different, i.e. longer, than the width) and so the spherical ablation zone may be easier to predict when being moved through different orientations in 3D space. For example, the length of the dielectric body may be between 1 mm and 3 mm, and the length of the conductive body may be between 2 mm and 4 mm. The dimensions of the radiating tip may therefore allow the electrosurgical instrument to be used to treat target tissue in a patient's lungs.

[0024] Optionally, the conductive body may be positioned at a distal end of the elongate conductor. In other embodiments, the elongate conductor may extend distally beyond the distal end of the conductive body, which may provide a more spherical ablation zone in use. For example, the elongate conductor may extend distally beyond the distal end of the conductive body by a length of 1 mm to 3 mm, such as 2 mm.

[0025] Optionally, the conductive body may be provided as a plurality of conductive rings which are fitted over the elongate conductor, wherein the plurality of conductive rings are electrically connected to each other (e.g., adjacent conductive rings may be in physical and electrical contact with one another). By providing the conductive body in the form of a plurality of rings (for example, rather than as a single block of material), the conductive body is provided with a degree of flexibility as adjacent rings are able to move relative to one another. However, as adjacent conductive rings are electrically connected, they act (or are ‘seen’) as a single body when a microwave signal is delivered to the radiating tip. For example, each conductive ring may have a length, in the longitudinal direction, of 0.5 mm. Providing the conductive body as a plurality of conductive rings may also help to tune the tip to a predetermined operating frequency during manufacture (e.g., by allowing conductive rings to be easily added or removed to adjust the matching at the predetermined frequency), and allow adjustment of the ablation zone shape.

[0026] Optionally, the dielectric body may be provided as a plurality of dielectric rings which are fitted over the elongate conductor. By providing the dielectric body in the form of a plurality of rings (for example, rather than as a single block of material), the dielectric body is provided with a degree of flexibility as adjacent rings are able to move relative to one another. This may be particularly suitable where a rigid material, such as a ceramic material, is chosen as the second dielectric material. For example, each dielectric ring may have a length, in the longitudinal direction, of 0.5 mm. Providing the dielectric body as a plurality of dielectric rings may also help to tune the tip to a predetermined operating frequency during manufacture (e.g., by allowing dielectric rings to be easily added or removed to adjust the matching at the predetermined frequency), and allow adjustment of the ablation zone shape.

[0027] Optionally, the radiating tip may further comprise a dielectric sheath that surrounds an outer surface of the dielectric body and the conductive body, wherein the dielectric sheath is formed into a pointed tip at its the distal end. The dielectric sheath may provide an outer protective layer for protecting the radiating tip from the environment. For example, the dielectric sheath may be made of or coated with a non-stick material (e.g. PTFE), so that tissue does not stick to the dielectric body. An outer surface of the dielectric sheath may be flush with an outer surface of the coaxial feed cable at an interface between the coaxial feed cable and the radiating tip. The distal tip may be pointed to facilitate insertion of the radiating tip into biological tissue, e.g., for piercing tissue. In other cases, the distal tip may be rounded. The dielectric sheath may be made of a biocompatible material, since it may penetrate biological tissue in use.

[0028] Optionally, the electrosurgical instrument may further include a conductive field shaping element disposed at a distal end of the coaxial feed cable, the field shaping element being electrically connected to the outer conductor. The field shaping element may serve to reduce back-propagation of microwave energy down the coaxial feed cable. This may reduce a tail of the radiation profile that extends along a portion of the coaxial feed cable. As a result, the radiation profile may be concentrated around the radiating tip, with an ablation zone which is closer to spherical (i.e., where the length of the ablation zone is similar or equal to the diameter of the ablation zone). The field shaping element may be made of any suitable conductive material. The field shaping element may be disposed on a surface of the outer conductor, e.g. on an outer surface or an inner surface of the outer conductor. The field shaping element may be electrically connected to the outer conductor via any suitable means, e.g. via a conductive epoxy, or via a soldered or welded connection. In some cases, the field shaping element may be integrally formed with a distal portion of the coaxial feed cable. In some embodiments, the field shaping element may have a length in the longitudinal direction corresponding to a quarter wavelength of the microwave energy. The field shaping element may comprise a balun or choke.

[0029] Optionally, the dielectric constant of the second dielectric material may be in the range of 2.5 to 4. For example, the second dielectric material may be polyethylene terephthalate (PET). PET may be suitable for this purpose as it is flexible but has a higher dielectric constant than polytetrafluoroethylene (PTFE) which may typically be used in the coaxial cable. For example, PET has a dielectric constant of around 3.0 to 3.5, and PTFE has a dielectric constant of 2.0 to 2.1 . Of course, other materials may be considered including, in some embodiments, a ceramic material.

[0030] The electrosurgical instrument discussed above may form part of a complete electrosurgical apparatus for treating biological tissue. For example, the apparatus may include an electrosurgical generator arranged to supply microwave energy; and the electrosurgical instrument of the invention may be connected to receive the microwave energy from the electrosurgical generator. The electrosurgical apparatus may further include a surgical scoping device (e.g. an endoscope or bronchoscope) having a flexible insertion cord for insertion into a patient’s body, wherein the flexible insertion cord has an instrument channel running along its length, and wherein the electrosurgical instrument is dimensioned to fit within the instrument channel.

[0031] In this specification “microwave” may be used broadly to indicate a frequency range of 400 MHz to 100 GHz, but preferably the range 1 GHz to 60 GHz. Preferred spot frequencies for microwave EM energy include: 433MHz, 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.

[0032] Herein, the terms “proximal” and “distal” refer to the ends of the electrosurgical instrument further from and closer to the treatment site, respectively. Thus, in use, the proximal end of the electrosurgical instrument is closer to a generator for providing the RF and / or microwave energy, whereas the distal end is closer to the treatment site, i.e. target tissue in the patient.

[0033] The term “conductive” is used herein to mean electrically conductive, unless the context dictates otherwise.

[0034] The term “longitudinal” used below refers to the direction along the length of the electrosurgical instrument, parallel to the axis of the coaxial transmission line. The term “inner” means radially closer to the centre (e.g. axis) of the instrument. The term “outer” means radially further from the centre (axis) of the instrument. The term “electrosurgical” is used in relation an instrument, apparatus or tool which is used during surgery and which utilises microwave and / or radiofrequency electromagnetic (EM) energy.

[0035] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0036] Summary of the Figures

[0037] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0038] Figure 1 is a schematic diagram of an electrosurgical system for tissue ablation that is an embodiment of the invention;

[0039] Figure 2a is a schematic cross-section of an electrosurgical instrument that is an embodiment of the invention;

[0040] Figure 2b is a photograph of an electrosurgical instrument as shown in Figure 2a;

[0041] Figure 3 shows a graph plotting return loss against microwave signal frequency for the electrosurgical instrument of Figs. 2a and 2b;

[0042] Figure 4 shows a plot of the simulated power loss density showing approximate energy deposition into tissue for the electrosurgical instrument of Figs. 2a and 2b;

[0043] Figure 5a is a schematic cross-section of an electrosurgical instrument that is a second embodiment of the invention;

[0044] Figure 5b is a photograph of an electrosurgical instrument as shown in Figure 5a;

[0045] Figure 6 is a schematic cross-section of an electrosurgical instrument that is a third embodiment of the invention; and

[0046] Figure 7 is a schematic cross-section of an electrosurgical instrument that is a fourth embodiment of the invention.

[0047] Detailed Description of the Invention

[0048] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0049] Fig. 1 is a schematic diagram of a complete electrosurgical system 100 that is capable of supplying microwave energy to the distal end of an invasive electrosurgical instrument. The system 100 comprises a generator 102 for controllably supplying microwave energy. A suitable generator for this purpose is described in WO 2012 / 076844, which is incorporated herein by reference. The generator may be arranged to monitor reflected signals received back from the instrument in order to determine an appropriate power level for delivery. For example, the generator may be arranged to calculate an impedance seen at the distal end of the instrument in order to determine an optimal delivery power level. The generator may be arranged to deliver power in a series of pulses which are modulated to match a patient’s breathing cycle. This will allow for power delivery to occur when the lungs are deflated.

[0050] The generator 102 is connected to an interface joint 106 by an interface cable 104. If needed, the interface joint 106 can house an instrument control mechanism that is operable by sliding a trigger 110, e.g. to control longitudinal (back and forth) movement of one or more control wires or push rods (not shown). If there is a plurality of control wires, there may be multiple sliding triggers on the interface joint to provide full control. The function of the interface joint 106 is to combine the inputs from the generator 102 and instrument control mechanism into a single flexible shaft 112, which extends from the distal end of the interface joint 106. In other embodiments, other types of input may also be connected to the interface joint 106. For example, in some embodiments a fluid supply may be connected to the interface joint 106, so that fluid may be delivered to the instrument.

[0051] The flexible shaft 112 is insertable through the entire length of an instrument (working) channel of an endoscope 114.

[0052] The flexible shaft 112 has a distal assembly 118 (not drawn to scale in Fig. 1) that is shaped to pass through the instrument channel of the endoscope 114 and protrude (e.g. inside the patient) at the distal end of the endoscope’s tube. The distal end assembly includes a radiating tip for delivering microwave energy into biological tissue. The tip configuration is discussed in more detail below.

[0053] The structure of the distal assembly 118 may be arranged to have a maximum outer diameter suitable for passing through the working channel. Typically, the diameter of a working channel in a surgical scoping device such as an endoscope is less than 4.0 mm, e.g. any one of 2.0 mm, 2.8 mm, 3.2 mm, 3.7 mm, 3.8mm. The length of the flexible shaft 112 can be equal to or greater than 0.3 m, e.g. 2 m or more. In other examples, the distal assembly 118 may be mounted at the distal end of the flexible shaft 112 after the shaft has been inserted through the working channel (and before the instrument cord is introduced into the patient). Alternatively, the flexible shaft 112 can be inserted into the working channel from the distal end before making its proximal connections. In these arrangements, the distal end assembly 118 can be permitted to have dimensions greater than the working channel of the surgical scoping device 114.

[0054] The system described above is one way of introducing the instrument into a patient’s body. Other techniques are possible. For example, the instrument may also be inserted using a catheter.

[0055] Fig. 2a shows a cross-sectional side view of an electrosurgical instrument 200 that is an embodiment of the invention. A photograph of the electrosurgical instrument 200 is shown in Fig. 2b. The distal end of the electrosurgical instrument 200 may correspond, for example, to the distal assembly 118 discussed above. The electrosurgical instrument includes a coaxial feed cable 202 that is connectable at its proximal end to a generator (such as generator 102) in order to convey microwave energy. The coaxial feed cable 202 may be the interface cable 104 discussed above, which passes through the flexible shaft 112. The coaxial feed cable 202 comprises an inner conductor 204 and an outer conductor 206 which are separated by a first dielectric material 208. The coaxial feed cable 202 is preferably low loss for microwave energy. A choke (not shown) may be provided on the coaxial feed cable 202 to inhibit back propagation of microwave energy reflected from the distal end and therefore limit backward 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 202. The outer sheath 210 is made of an insulating material to electrically isolate the outer conductor 206 from its surroundings. The outer sheath may be made of, or coated with, a non-stick material such as PTFE to prevent tissue from sticking to the instrument.

[0056] The coaxial cable 202 has an outer diameter selected to fit through the working channel of a surgical scoping device (e.g., a surgical scoping device as described above with respect to Fig. 1). In particular, the outer diameter is 1 .4 mm, in order to fit through a working channel having a diameter of 2 mm.

[0057] A radiating tip 212 is formed at the distal end of the coaxial feed cable 202. The dashed line 21 illustrates an interface between the coaxial feed cable 202 and the radiating tip 212. The radiating tip 212 is arranged to receive microwave energy conveyed by the coaxial feed cable 202, and deliver the energy into biological tissue. The outer conductor 206 of the coaxial feed cable 202 terminates at the distal end of the coaxial feed cable 202, i.e., the outer conductor 206 does not extend into the radiating tip 212. The radiating tip 212 includes a distal portion 214 of the inner conductor 204 which extends beyond the distal end of the coaxial feed cable 202. In particular, the distal portion 214 of the inner conductor 204 extends beyond a distal end of the outer conductor 206 to form an elongate conductor of the radiating tip 212. In other embodiments, the elongate conductor may comprise an additional conductive element (e.g., a conductive wire) which is electrically connected (e.g., by solder or a conductive adhesive) to the distal end of the inner conductor 204 (which does not extend into the radiating tip in such embodiments).

[0058] The outer sheath 210 also extends over the outside of the radiating tip 212, providing an insulating membrane that forms an outer surface of the radiating tip 212 to prevent moisture and / or tissue ingress. The protective sheath 210 thereby serves to insulate the radiating tip 212 and protect it from the environment. A distal end 216 of the outer sheath 214 is formed into a pointed tip in order to assist penetration of the radiating tip 212 into tissue where treatment is to take place.

[0059] A dielectric body 218 made of a dielectric material having a dielectric constant than that of the first dielectric material 208 is disposed on a first portion of the inner conductor 204 in the radiating tip 212. In particular, in this embodiment the dielectric body 218 is made of PET, while the first dielectric material 208 is PTFE. The dielectric body 218 has a cylindrical shape and includes a channel through which the distal portion 214 of the inner conductor 204 passes. A diameter of the channel is substantially the same as an outer diameter of the inner conductor 204 to provide a secure fit. However, the dielectric body 218 may be further secured to the inner conductor 204, for example, using an adhesive. The dielectric body 218 is centred on the inner conductor 204. In other words, a central axis of the dielectric body 218 is collinear with the longitudinal axis of the inner conductor 204. In this manner, the dielectric body 218 is disposed around the distal portion 214 of the inner conductor 204 in a manner that is symmetrical about the longitudinal axis of the inner conductor 204.

[0060] Positioned distally of the dielectric body 218 on the inner conductor 204, the radiating tip 212 further comprises a conductive body 220. The conductive body 220 is made of a metal material, and is electrically connected to the inner conductor 204. The conductive body 220 is disposed on a second portion of the inner conductor 204 in the radiating tip 212, different from the first portion, and extends from a distal end of the dielectric body 220 to a distal end of the inner conductor 204. The conductive body 220 has a cylindrical shape and includes a channel through which the distal portion 214 of the inner conductor 204 passes. A diameter of the channel is substantially the same as an outer diameter of the inner conductor 204 to provide a secure fit and to provide an electrical connection to the inner conductor 204 along the length of the conductive body 220. However, the conductive body 220 may be further secured to the inner conductor 204, for example, using a conductive adhesive, soldering or welding. The conductive body 220 is centred on the inner conductor 204. In other words, a central axis of the conductive body 220 is collinear with the longitudinal axis of the inner conductor 204. In this manner, the conductive body 220 is disposed around the distal portion 214 of the inner conductor 204 in a manner that is symmetrical about the longitudinal axis of the inner conductor 204.

[0061] Both the dielectric body 218 and the conductive body 220 have the same outer diameter. The outer diameter of the dielectric body 218 and the conductive body 220 may be slightly less than the outer diameter of the electrosurgical instrument 200, and in particular slightly less than the outer diameter of the coaxial cable 202. In particular, the dielectric body 218 and the conductive body 220 have the same outer diameter as the first dielectric material 208 of the coaxial cable 202.

[0062] In this embodiment, the length of the dielectric body 218 in the longitudinal direction (i.e., the length of the dielectric body 218 between the distal end of the coaxial cable 202 and the proximal end of the conductive body 220) is less than the length of the conductive body 220 (i.e., the length of the conductive body 220 between the distal end of the dielectric body 218 and the distal end of the inner conductor 204). In particular, the length of the dielectric body 218 is 2 mm and the length of the conductive body 220 is 3 mm (the total length of the distal portion 216 as the elongate conductor is 5 mm). As described in more detail below, such an arrangement provides an electrical length which provides a good impedance match of the radiating tip 210 into tissue at frequencies of 2.45 GHz and 5.8 GHz, while maintaining a short physical length of the radiating tip 210 which allows the radius of curvature of the electrosurgical instrument 200 to be suitable for delivering the radiating tip 210 to difficult treatment areas, such as lung tissue. In addition, the physical length of the radiating tip 210 ensures that the ablation zone is approximately a spherical pattern which provides ease of use of the electrosurgical instrument 200.

[0063] Fig. 3 shows a graph 300 plotting return loss against frequency for an electrosurgical instrument according to an embodiment of the invention, specifically the electrosurgical instrument 200 described above with respect to Figs. 2a and 2b. As explained above, the dimensions of the dielectric body 218, the conductive body 220 and the elongate conductor (i.e., the distal portion 214 of the inner conductor 204) have been selected to exhibit return losses at frequencies of 2.45 GHz (indicated at 301) and 5.8 GHz (indicated at 302) which allows the electrosurgical instrument 200 to be suitable for performing electrosurgery (e.g., ablation) at those frequencies. It will be appreciated that alternative dimensions and geometries may be selected (e.g., as described herein) in order to provide suitable return losses at a desired microwave frequency.

[0064] Fig. 4 shows a plot 400 of the simulated power loss density showing approximate energy deposition (i.e., a simulated microwave radiation profile) in target tissue for the electrosurgical instrument 200 illustrated in Figs. 2a and 2b. The radiation profile was simulated for a microwave frequency of 5.8 GHz, using finite element analysis software. The radiation profile is indicative of the resultant shape of tissue ablated by the microwave energy. As can be seen in Fig. 4, the radiation profile is concentrated around the radiating tip, and defines an approximately spherical region. In this manner, tissue may be ablated in an approximately spherical region around the radiating tip 210. The interface 211 between the radiating tip and coaxial feed cable is shown to aid visualisation of the location and shape of the field relative to the tip of the instrument.

[0065] Fig. 5a is a schematic cross-section of an electrosurgical instrument 500 that is a second embodiment of the present invention. A photograph of the electrosurgical instrument 500 is shown in Fig. 5b. Many features of the electrosurgical instrument 500 are the same as described above for the electrosurgical instrument 200 shown in Figs. 2a and 2b, and so description of those features is not repeated and only the differences are described in detail below. Reference numerals used in Figs. 2a and 2b are used in Figs. 5a and 5n to indicate features corresponding to those discussed above in relation to Figs. 2a and 2b.

[0066] In this embodiment, the dielectric body 518 is provided as a plurality of dielectric rings 518a-518d which are fitted over the distal portion 214 of the inner conductor 204. Each of the dielectric rings 518a-518d is made of a dielectric material having a higher dielectric constant than that of the first dielectric material 208. For example, each of the dielectric rings 518a-518d may be made of PET. Each dielectric ring 518a- 518d has a cylindrical shape and includes a channel through which the distal portion 214 of the inner conductor 204 passes. A diameter of the channel is substantially the same as an outer diameter of the inner conductor 204 to provide a secure fit. However, each dielectric ring 518a-518d may be further secured to the inner conductor 204, for example, using an adhesive. Each dielectric ring 518a-518d is centred on the inner conductor 204. In other words, a central axis of the dielectric body 518 is collinear with the longitudinal axis of the inner conductor 204. In this manner, the dielectric body 518 is disposed around the distal portion 214 of the inner conductor 204 in a manner that is symmetrical about the longitudinal axis of the inner conductor 204.

[0067] Additionally, the conductive body 520 is provided as a plurality of conductive rings 520a-520f which are fitted over the distal portion 214 of the inner conductor 204. Each of the conductive rings 520a-520f is made of a metallic material, which may, for example, be the same material as the inner conductor 204, as is electrically connected to the distal portion 214 of the inner conductor 204 and to adjacent rings. In this way, the conductive body 520 acts substantially as a unitary body when microwave energy is delivered through the coaxial cable. Each conductive ring 520a-520f has a cylindrical shape and includes a channel through which the distal portion 214 of the inner conductor 204 passes. A diameter of the channel is substantially the same as an outer diameter of the inner conductor 204 to provide a secure fit. However, each conductive ring 520a-520f may be further secured to the inner conductor 204, for example, using a conductive adhesive, or by soldering or welding. Each conductive ring 520a-520f is centred on the inner conductor 204. In other words, a central axis of the conductive body 520 is collinear with the longitudinal axis of the inner conductor 204. In this manner, the conductive body 520 is disposed around the distal portion 214 of the inner conductor 204 in a manner that is symmetrical about the longitudinal axis of the inner conductor 204.

[0068] Although in the electrosurgical instrument 500 both the dielectric body 518 and the conductive body 520 are provided as a plurality of rings of material, it will be appreciated that in other embodiments only one of the dielectric body 518 or the conductive body 520 may be provided as a plurality of such rings.

[0069] By providing the dielectric body 518 as a plurality of dielectric rings 518a-518d and the conductive body 520 as a plurality of conductive rings 520a-520f, adjustment and tuning of the radiating tip 510 to be suitable for delivering energy at a predetermined frequency during manufacture of the electrosurgical instrument 500 may be easier, for example by allowing individual rings to be added or removed as required, whereas such fine adjustment of the length is not possible if the dielectric body 518 and / or the conductive body 520 are provided as single blocks of material. In addition, such an arrangement may help to decrease the radius of curvature of the radiating tip 510, as providing the dielectric body 518 and / or the conductive body 520 as a plurality of individual rings of material provides the dielectric body 518 and / or the conductive body 520 with a degree of flexibility which would not be present if they are provided as single blocks of material as each ring is able to move slightly relative to adjacent rings when the radiating tip 510 is bent. This may be useful in helping the electrosurgical instrument 500 be delivered to certain areas of the body (e.g., being delivered to a treatment site through a patient’s airways).

[0070] Fig. 6 is a schematic cross-section of an electrosurgical instrument 600 that is a third embodiment of the present invention. Many features of the electrosurgical instrument 600 are the same as described above for the electrosurgical instrument 200 shown in Figs. 2a and 2b, and so description of those features is not repeated and only the differences are described in detail below. Reference numerals used in Figs. 2a and 2b are used in Fig. 6 to indicate features corresponding to those discussed above in relation to Figs. 2a and 2b.

[0071] The electrosurgical instrument 600 is similar to electrosurgical instrument 200 discussed above, except that it includes a field shaping element 902, and the lengths of the dielectric body 618 and the conductive body 620 are changed. In particular, in this embodiment the dielectric body 618 is longer than the conductive body 620. The dielectric body 618 has a length in the longitudinal direction of 6 mm, and the conductive body 620 has a length in the longitudinal direction of 3 mm. This arrangement provides a match into tissue at both 2.45 GHz and 5.8 GHz. In another example, the dielectric body 618 may have a length of 12 mm, and the conductive body may have a length of 2 mm, which provides a radiating tip which is particularly suited for delivering energy into tissue at a frequency of 2.45 GHz.

[0072] The field shaping element 622 is an annular sleeve of conductive material disposed around an outer surface of the outer conductor 206. The field shaping element 622 is located at the distal end of the coaxial feed cable 202, and extends from the interface 211 along a length of the coaxial feed cable 202 towards its proximal end (towards the generator to which the coaxial cable 202 is connected). The length of the field shaping element 622 corresponds to a quarter wavelength of the microwave energy to be conveyed by the coaxial feed cable 202. For example, in the case where microwave energy is at 5.8 GHz, the length of the field shaping element 622 may be approximately 9 mm. An inner surface of the field shaping element 622 is in contact with the outer surface of the outer conductor 206, so that the field shaping element 622 is electrically connected to the outer conductor 206 along its length. Electrical connection between the field shaping element 622 and the outer conductor 206 may be ensured by securing the field shaping element 622 to the outer conductor 206, e.g., using conductive epoxy, or by soldering or welding them together. In some embodiments (not shown) the field shaping element 622 may be integrally formed with the outer conductor 206. The field shaping element 622 acts to increase an effective thickness of the outer conductor 206 in a distal region of the coaxial feed cable 202. The field shaping element 622 serves to reduce the tail in the radiation profile (the ablation zone) which extends along the coaxial cable 202, and to concentrate emission of microwave energy around the radiating tip 610, providing a more spherical ablation zone. This may be particularly useful in embodiments where the dielectric body 618 is longer, as increasing the length of the dielectric body 618 serves to increase the length of the tail in the radiation profile, and so providing a field shaping element 622 may help reduce this effect.

[0073] Fig. 7 is a schematic cross-section of an electrosurgical instrument 700 that is a fourth embodiment of the present invention. Many features of the electrosurgical instrument 700 are the same as described above for the electrosurgical instrument 200 shown in Figs. 2a and 2b, and so description of those features is not repeated and only the differences are described in detail below. Reference numerals used in Figs. 2a and 2b are used in Fig. 7 to indicate features corresponding to those discussed above in relation to Figs. 2a and 2b.

[0074] In this embodiment, the distal portion 214 of the inner conductor 204 extends distally beyond the distal end of the conductive body 720. The dielectric body is therefore provided in a first portion 718a which is disposed proximally of the conductive body 720 on the distal portion 214 of the inner conductor 204, and a second portion 718b which is disposed distally of the conductive body 720 on the distal portion 214 of the inner conductor 204. In particular, the first portion 718a of the dielectric block has a length in the longitudinal direction of 2 mm, the conductive body 720 has a length in the longitudinal direction of 7 mm, and the second portion 718b of the dielectric body has a length in the longitudinal direction of 2 mm. Such an arrangement is particularly suited for delivering energy into tissue at a frequency of 5.8 GHz. In addition, extending the distal portion 214 of the inner conductor 204 distally beyond the distal end of the conductive body 720 helps to shape the ablation zone to provide a more generally spherical pattern.

[0075] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0076] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0077] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0078] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0079] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:1 . An electrosurgical instrument comprising: a coaxial feed cable having an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor and the outer conductor, the coaxial feed cable being for conveying a microwave signal, and a radiating tip disposed at a distal end of the coaxial feed cable to receive the microwave signal; wherein the radiating tip comprises: an elongate conductor electrically connected to the inner conductor and extending in a longitudinal direction; a dielectric body disposed on at least a first portion of the elongate conductor, the dielectric body comprising a second dielectric material having a higher dielectric constant than the first dielectric material; and a conductive body disposed on at least a second portion of the elongate element, the second portion being different from the first portion.

2. The electrosurgical instrument of claim 1 , wherein the conductive body has a diameter which is less than that of the coaxial cable, and optionally, than that of the outer conductor of the coaxial cable.

3. The electrosurgical instrument of claim 1 or claim 2, wherein the conductive body has a length in the longitudinal direction of 7 mm or less.

4. The electrosurgical instrument of any preceding claim, wherein the dielectric body has a length in the longitudinal direction of 14mm or less.

5. The electrosurgical instrument of any preceding claim, wherein the length of the dielectric body in the longitudinal direction is less than the length of the conductive body in the longitudinal direction.

6. The electrosurgical instrument of claim 5, wherein the length of the dielectric body is between 1 mm and 3 mm, and the length of the conductive body is between 2 mm and 4 mm.

7. The electrosurgical instrument of any preceding claim, wherein the conductive body is positioned at a distal end of elongate conductor.

8. The electrosurgical instrument of any one of claims 1 to 6, wherein the elongate conductor extends distally beyond the distal end of the conductive body.

9. The electrosurgical instrument of any preceding claim, wherein the conductive body is provided as a plurality of conductive rings which are fitted over the elongate conductor, wherein the plurality of conductive rings are electrically connected to each other.

10. The electrosurgical instrument of any preceding claim, wherein the dielectric body is provided as a plurality of dielectric rings which are fitted over the elongate conductor.11 . The electrosurgical instrument of any preceding claim, wherein the radiating tip further comprises a dielectric sheath that surrounds an outer surface of the dielectric body and the conductive body, wherein the dielectric sheath is formed into a pointed tip at its the distal end.

12. The electrosurgical instrument of any preceding claim, further including a conductive field shaping element disposed at a distal end of the coaxial feed cable, the field shaping element being electrically connected to the outer conductor.

13. The electrosurgical element of any preceding claim, wherein the dielectric constant of the second dielectric material is in the range of 2.5 to 4.

14. The electrosurgical instrument of claim 13, wherein the second dielectric material is polyethylene terephthalate, PET.

15. An electrosurgical apparatus for treating biological tissue, the electrosurgical apparatus comprising: an electrosurgical generator arranged to supply a microwave signal; and an electrosurgical instrument according to any preceding claim, connected to receive the microwave signal from the electrosurgical generator.

16. The electrosurgical apparatus of claim 15, further comprising a surgical scoping device that comprises a flexible insertion cord having an instrument channel, wherein the electrosurgical instrument is dimensioned to fit within the instrument channel.

Images