Electrosurgical instrument

Abstract

Various embodiments provide an electrosurgical instrument comprising: a coaxial feed cable having an inner conductor, an outer conductor, and a dielectric material separating the inner conductor and the outer conductor, the coaxial feed cable being for conveying a microwave signal The instrument further comprises a radiating tip disposed at a distal end of the coaxial feed cable to receive the microwave signal. The radiating tip comprises: an elongate element electrically connected to the inner conductor and extending in a longitudinal direction, and a looped element electrically connected to the elongate element, wherein the looped element is wound around at least a portion of the elongate element. 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] 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.

[0011] 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. The ability to reduce the size of the instrument tip has therefore previously been limited by the need for efficient energy transfer. In addition, it should be noted that lower microwave frequencies require a greater electrical length in order to efficiently deliver energy to tissue due to their longer wavelength.

[0012] According to a first aspect of the present invention, there is provided an electrosurgical instrument comprising: a coaxial feed cable having an inner conductor, an outer conductor, and a 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 (e.g., mounted to) a distal end of the coaxial feed cable to receive the microwave signal, wherein the radiating tip comprises: an elongate element electrically connected (either directly or indirectly) to the inner conductor and extending in a longitudinal direction, and a looped element which is wound (e.g. directly wound) around at least a portion of the elongate element. It will be appreciated that the elongate element and the looped element are insulated from each other, except at one or more points of electrical connection or electrical contact. For example, one or each of the elongate element and the looped element may comprise a layer of insulation (such as an enamel material, a varnish, or the like), or the radiating tip may comprise additional insulation which allows the elongate element and the looped element to be in close proximity to one another (e.g., in physical contact) without an unwanted electrical connection. The layer of insulation or additional insulation may have a thickness which is less than a thickness / diameter of the elongate element and / or the looped element so as to provide the necessary insulation without significantly increasing a thickness / diameter of the radiating tip. For example, a maximum thickness / diameter of the radiating tip may be less than a maximum thickness / diameter of the coaxial feed cable. For example, where a layer of insulation is provided on or around the elongate element, a thickness of that layer of insulation may be less (e.g. at least an order of magnitude less) than a thickness of the dielectric material of the coaxial feed cable. For example, where a layer of insulation is provided on or around the conductive element which is wound to form the looped element, a thickness of that layer of insulation may be less (e.g. at least an order of magnitude less) than a thickness of the dielectric material of the coaxial feed cable. For example, where additional insulation is provided, a thickness of that additional insulation may be less (e.g. at least an order of magnitude less) than a thickness of the dielectric material of the coaxial feed cable. It is to be understood that the looped element (with or without a layer of insulation) may be wound “directly” around the elongate element (with or without a layer of insulation) meaning that there are no intervening elements, e.g. no intervening dielectric body, in-between the looped element and the elongate element. The insulation may be arranged to maintain a desired electrical length of the radiating portion. By being wound around at least a portion of the elongate element, at least part of the looped element may be in physical contact with that portion (and this may differ from the point of electrical contact). The elongate element and the looped element may be referred to together as a conductive element, or as conductive elements. The terms elongate element and elongate conductor, and looped element and looped conductor, may be used interchangeably herein. The looped element may be a wound element, such as a helical element or the like, and may comprise at least one loop around the elongate element. In embodiments of the present invention where the looped element comprises a plurality of loops, turns or coils, each loop may have different dimensions (e.g., radius, length) and the spacing between each loop may be uniform or may differ. The inventors have found that the electrosurgical instrument as set out according to the first aspect of the present invention increases the effective electrical length of the radiating element such that the electrosurgical instrument can have a reduced physical size whilst retaining effectiveness at low microwave frequencies, and the instrument can also be used to deliver energy into tissue at a plurality of microwave frequencies. The frequencies at which the instrument is effective can be tuned by altering dimensions of the radiating element as described herein.

[0013] It will be appreciated that the radiating tip is arranged to act as a microwave monopole antenna, radiating microwave energy, when the microwave signal is delivered thereto, in order to perform tissue treatment.

[0014] Embodiments may therefore allow the physical size (e.g. length, diameter) of the instrument, particularly the radiating tip, to be made smaller than prior art arrangements, whilst maintaining the ability to efficiently deliver the same working signal into tissue (e.g. a microwave frequency signal), since the provision of a looped element on an elongate element can increase the electrical length of the instrument and thereby offset any decreases in electrical length which would otherwise occur when decreasing the physical size of the instrument.

[0015] 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

[0016] 2 2 2 / V£e / / effective dielectric constant of the planar body. 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. Optionally, the elongate element may comprise a distal portion of the inner conductor that extends beyond a distal end of the outer conductor.

[0017] Optionally, the looped element may comprise an insulated wire, such as an enamelled wire (e.g., a copper wire, or other metal wire, comprising an insulating varnish or the like). For example, the insulation may be arranged to insulate a portion (e.g., a middle portion or a length) of the looped element from the elongate element, which may be particularly advantageous in embodiments where the looped element is in physical contact with (e.g., wound on) the elongate element. In an embodiment, insulation surrounds all of the looped element except end portions or end faces, or one or more surfaces where the looped element is in electrical contact with the elongate element.

[0018] Optionally, an outer diameter of the radiating tip may be less than 5 mm, for example less than 2 mm. As explained above, the present invention is able to provide sufficient electrical length to operate at one or more microwave frequencies while having a narrow diameter, which is not the case for prior art arrangements.

[0019] Optionally, the looped element is also electrically connected to the outer conductor of the coaxial feed cable.

[0020] Optionally, the looped element may be spaced from a distal end of the outer conductor by a first distance. For example, the first distance may be between 1 mm and 5 mm, though in some embodiments the first distance may be 0 mm (i.e. , the looped element may be positioned adjacent to the outer conductor, for example to be electrically connected thereto). Adjusting the first distance may allow the radiating tip to be tuned to operate at a predetermined or desired microwave frequency.

[0021] Optionally, the looped element may be spaced from a distal end of the elongate element by a second distance. For example, the second distance may be between 1 mm and 5 mm, though in some embodiments the second distance may be 0 mm (i.e., the looped element may be positioned adjacent to the distal end of the elongate element, for example to be electrically connected thereto). Adjusting the second distance may allow the radiating tip to be tuned to operate at a predetermined or desired microwave frequency.

[0022] Optionally, the looped element may have at least five coils (e.g., at least five turns, loops, or windings etc.). Adjusting the number of coils may allow the radiating tip to be tuned to operate at a predetermined or desired microwave frequency. For example, the looped element may have 20 coils or more. However, it will be appreciated that some embodiments of the present invention may comprise fewer coils, such as 2, 3, or 4 coils.

[0023] Optionally, the looped element may be tightly wound around the elongate element such that adjacent coils of the looped element are in contact with one another. This may help to increase the electrical length of the radiating tip while maintaining small dimensions (e.g., length) of the radiating tip. In other embodiments, adjusting the distance or gap between adjacent coils may allow the radiating tip to be tuned to operate at a predetermined or desired microwave frequency. In some examples, the gaps may be uniform, though it will be appreciated that in other examples the gaps may vary in length in order to suit a predetermined or desired operating frequency.

[0024] Optionally, the looped element may be electrically connected to the elongate element at either a proximal end of the looped element; or a distal end of the looped element. Adjusting the electrical connection point (feed point) of the looped element to the elongate element may allow further adjustment of the electrical length and properties of the radiating tip to operate at a predetermined or desired microwave frequency. Optionally, the looped element may be electrically connected to the elongate element at a distal end of the elongate element.

[0025] Optionally, the radiating tip may further comprise a second looped element, wherein the second looped element is wound around a different portion of the elongate element to the looped element, and is electrically connected to the elongate element. Parameters and dimensions of the second looped element may be configured in the same manner as described herein for the looped element, though they may be adjusted independently in order to be tuned to operate at a predetermined or desired microwave frequency. In one example, the first looped element may be electrically connected to the elongate element at a proximal end of the first looped element, and the second looped element may be electrically connected to the elongate element at a distal end of the second looped element, wherein the first looped element is positioned distally of the second looped element. For completeness, it is noted that the second looped element is insulated from the other components, such as the elongate element and the looped element, except at one or more points of electrical connection or electrical contact, for example in a similar manner as described above.

[0026] In certain embodiments, the radiating tip may further comprise an intermediate element which is electrically connected (e.g., directly or indirectly) between the elongate element and the looped element. For completeness, it is noted that the intermediate element is insulated from the other components, such as the elongate element and the looped element, except at one or more points of electrical connection or electrical contact, for example in a similar manner as described above. For example, the intermediate element may be electrically connected to the elongate element at a distal end of the elongate element and / or at a distal end of the intermediate element. Alternatively, the intermediate element may be electrically connected to the elongate element at a distal end of the intermediate element and spaced from a distal end of the elongate element by a third distance (wherein the third distance may be between 1 mm and 5 mm, for example). In one embodiment, the intermediate element may be electrically connected to the looped element at a distal end of the looped element.

[0027] Optionally, the intermediate element may have a length of between 3 mm and 20 mm.

[0028] Optionally, the intermediate element may include at least one fold, and the looped element is wound around at least a portion of the intermediate element. For example, both the elongate element and the intermediate element may be located within one or more coils of the looped element. This may further increase the electrical length of the radiating tip while ensuring that the dimensions of the radiating tip can be minimised.

[0029] Optionally, the intermediate element may be unitary with the looped element. For example, both the intermediate element and the looped element may be made from a single length of wire, such as an insulated wire.

[0030] Optionally, the electrosurgical instrument may further comprise an insulating membrane that surrounds the radiating tip to prevent moisture and / or tissue ingress. This may help to ensure that the radiating tip operates as designed. In some embodiments, the membrane may also surround at least a distal portion of the coaxial feed cable.

[0031] Optionally, an outer diameter of the coaxial cable may be 5 mm or less, such as 2 mm or less.

[0032] 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) 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. 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.

[0033] 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.

[0034] The term “conductive” is used herein to mean electrically conductive, unless the context dictates otherwise.

[0035] 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.

[0036] 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.

[0037] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0038] Summary of the Figures

[0039] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0040] Figure 1 is a schematic diagram of an electrosurgical system for tissue ablation that is an embodiment of the invention;

[0041] Figure 2 is a schematic cross-section of an electrosurgical instrument that is an embodiment of the invention;

[0042] Figure 3 is a schematic cross-section of an electrosurgical instrument that is a second embodiment of the invention;

[0043] Figure 4 is a schematic cross-section of an electrosurgical instrument that is a third embodiment of the invention;

[0044] Figure 5 is a schematic cross-section of an electrosurgical instrument that is a fourth embodiment of the invention;

[0045] Figure 6 is a schematic cross-section of an electrosurgical instrument that is a fifth embodiment of the invention; Figure 7 is a schematic cross-section of an electrosurgical instrument that is a sixth embodiment of the invention;

[0046] Figure 8 shows a graph plotting return loss against frequency for the electrosurgical instrument of Fig. 2; and

[0047] Figure 9 is a schematic cross-section of an electrosurgical instrument that is a seventh embodiment of the present invention.

[0048] Detailed Description of the Invention

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The flexible shaft 112 is insertable through the entire length of an instrument (working) channel of an endoscope 114.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Fig. 2 shows a cross-sectional side view of an electrosurgical instrument 200 that is an embodiment of the invention. The distal end of the electrosurgical instrument may correspond, for example, to the distal assembly 118 discussed above. The electrosurgical instrument 200 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 and an outer conductor 204 which are separated by a dielectric material 206. 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. In some embodiments, the coaxial feed cable 202 may further include a flexible outer sheath disposed around the outer conductor 204 to protect the coaxial feed cable 202. The outer sheath may be made of an insulating material to electrically isolate the outer conductor 204 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.

[0057] The coaxial cable 202 has an outer diameter 205 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 205 is 1 .4 mm, in order to fit through a working channel having a diameter of 2 mm. A radiating tip 210 is formed at the distal end of the coaxial feed cable 202. The dashed line 211 in Fig. 2 illustrates an interface between the coaxial feed cable 202 and the radiating tip 210. The radiating tip 210 is arranged to receive microwave energy conveyed by the coaxial feed cable 202, and deliver the energy into biological tissue. The outer conductor 204 of the coaxial feed cable 202 terminates at the distal end of the coaxial feed cable 202, i.e. the outer conductor 204 does not extend into the radiating tip 210. The radiating tip 210 includes a distal portion 212 of the inner conductor which extends beyond the distal end of the coaxial feed cable 202. In particular, the distal portion 212 of the inner conductor extends beyond a distal end of the outer conductor 204 to form an elongate element of the radiating tip 210.

[0058] A protective sheath 230 is provided on the outside of the radiating tip 210. The protective sheath 230 is an insulating membrane that forms an outer surface of the radiating tip 210 to prevent moisture and / or tissue ingress. The protective sheath 230 thereby serves to insulate the radiating tip 210 and protect it from the environment. The protective sheath 230 may be made of or coated with a non-stick material (e.g. polytetrafluoroethylene, PTFE) to prevent tissue from sticking to it. The protective sheath 230 also covers at least a distal portion of the coaxial feed cable 202, so that the instrument has a smooth outer surface. The thickness and material of the protective sheath 230 may, in addition to the dimensions and other parameters of the radiating tip 210 as discussed below, impact the return loss exhibited by the electrosurgical instrument 200, and so may be chosen such that the radiating tip 210 effectively delivers energy into tissue at a predetermined or desired operating frequency. For example, in the embodiment shown, the protective sheath 230 is made of PTFE with a thickness of 0.1 mm (100 microns), and extends along substantially the entire length of the coaxial cable 202 such that the outer diameter of the coaxial cable 202 and the protective sheath 230 together is around 1 .6 mm.

[0059] The radiating tip 210 may act as a microwave monopole antenna when microwave energy is conveyed to the radiating tip 210. In order to reduce the dimensions of the radiating tip 210 and yet still enable the radiating tip 210 to effectively operate at low microwave frequencies such as 915 MHz, the radiating tip 210 is configured to have an increased electrical length. In particular, in addition to the elongate element formed by the distal portion 212 of the inner conductor, the radiating tip 210 comprises a looped element 214 which is wound about a portion of the elongate element and is electrically connected to the elongate element. In particular, in this embodiment the looped element 214 is wound directly on the elongate element. By providing the radiating tip 210 with a looped element 214 in this way, the electrical length of the radiating 210 is increased despite the restrictions imposed by the small diameter of the device, which allows the radiating tip 210 to effectively deliver microwave energy at a range of microwave frequencies, in particular including low microwave frequencies of around 915 MHz, into tissue. In this example, the looped element 214 comprises an enamelled copper wire (that is, a copper wire which is coated in an insulating varnish), which allows the looped element 214 to be tightly wound on and in physical contact with the elongate element along its length. In some examples, adjacent coils are in contact with one another to further help increase the electrical length of the radiating tip 210. It will be appreciated that the elongate element 212 and the looped element 214 are insulated from each other, except at the electrical contact 218, by the enamel coating of the looped element 214. In other embodiments, for example, the elongate element 212 may comprise such a coating, or the radiating tip 210 may comprise additional insulation which allows the elongate element 212 and the looped element 214 to be in close proximity to one another (e.g., in physical contact) without an unwanted electrical connection.

[0060] Specific examples of dimensions are parameters associated with the radiating tip 210 will now be described, but it will be appreciated that these dimensions are parameters may be adjusted in various embodiments of the present invention to allow the radiating tip 210 to effectively operate as a microwave monopole antenna to match energy into tissue at one or more predetermined or desired microwave frequencies, including (but not limited to) 433MHz, 915 MHz, 2.45 GHz, 3.3 GHz, 5.8 GHz, 10 GHz, 14.5 GHz and 24 GHz.

[0061] The distal portion 212 of the inner conductor forms an elongate element having a length 215 of 10.6 mm, and the diameter of the distal portion 212 is 0.6 mm. That is, the inner conductor of the coaxial cable 202 extends beyond the outer conductor 204 by 10.6 mm to form the elongate element. The looped element 214 is spaced from the proximal end of the elongate element (and thereby spaced from the distal end of the outer conductor of the coaxial cable 205) by a distance 216 of 2.8 mm, and spaced from the distal end of the elongate element (and thereby spaced from the distal end of the radiating tip 210) by a distance 217 of 1 .8 mm. The looped element 214 therefore has a length 219 of 6 mm. The outer diameter 220 of the looped element 214 is 1 .6 mm. The number of turns of the looped element 214 may also be adjusted to match return loss of the radiating tip 210 to a desired microwave operating frequency. For example, the looped element 214 may comprise 13 turns of 0.35 mm diameter enamelled copper wire. The looped element 214 is electrically connected to the distal portion 212 of the inner conductor by an electrical contact 218. For example, the electrical contact 218 may comprise a solder or other electrical joint. However, it will be appreciated that the looped element 214 may be electrically connected to the distal portion 212 of the inner conductor at other positions to alter the return loss exhibited by the radiating tip 210, for example as described with reference to further embodiments below.

[0062] Fig. 3 is a schematic cross-section of an electrosurgical instrument 300 that is a second embodiment of the present invention. Many features of the electrosurgical instrument 300 are the same as described above for the electrosurgical instrument 200 shown in Fig. 2, and so description of those features is not repeated and only the differences are described in detail below. In particular, the radiating tip of the electrosurgical instrument 300 differs in that the looped element 214 is electrically connected to the elongate element 212 at its proximal end and not at the distal end. The electrical contact 318 which connects the looped element 214 to the elongate element 212 is thereby positioned nearer to the coaxial cable than to the distal end of the radiating tip, as shown in Fig. 3. Adjusting the position of the electrical connection between the looped element 214 and the elongate element 212 allows the electrosurgical instrument to be tuned to effectively deliver microwave energy into tissue at a predetermined or desired operating frequency.

[0063] Fig. 4 is a schematic cross-section of an electrosurgical instrument 400 that is a third embodiment of the present invention. Many features of the electrosurgical instrument 400 are the same as described above for the electrosurgical instrument 200 shown in Fig. 2, and so description of those features is not repeated and only the differences are described in detail below. In this embodiment, the electrosurgical instrument 400 further comprises an intermediate element 412 which is electrically connected between the elongate element 212 and the looped element 214. That is, the looped element 214 is not directly electrically connected to the elongate element 212 as is the case with the embodiments described with respect to Figs. 2 and 3, but is electrically connected to the elongate element 212 via the intermediate element 421 . The intermediate element 421 comprises an enamelled copper wire which is connected at a first end to the distal tip of the elongate element 212 by an electrical contact 418 and at a second end to a distal end of the looped element 214 (e.g., by a further electrical contact such as a solder). By providing an intermediate element 421 in this way, the electrical length of the radiating tip can be further increased in order to provide a desired return loss characteristic for delivering microwave energy of a desired or predetermined frequency into tissue. In the example shown in Fig. 4, the enamelled copper wire which forms the intermediate element 421 is bent or folded and arranged such that the length of the wire passes from the distal tip of the elongate element 212 towards the coaxial cable through the coils of the looped element 214, to the distal end of the looped element 214, then passes back through the coils of the looped element 214 to the proximal end of the looped element 214 where a second electrical contact is positioned to electrically connect the intermediate element 421 with the looped element 214. That is, the looped element 214 is wound around both the intermediate element 421 and the elongate element 212. In this way, the electrical length of the radiating tip is increased by more than twice the length covered by the looped element 214. For example, using the dimensions given above for the radiating tip described above with respect to Fig. 3, the intermediate element 421 has a total length of 13.8 mm.

[0064] Fig. 5 is a schematic cross-section of an electrosurgical instrument 500 that is a fourth embodiment of the present invention. Many features of the electrosurgical instrument 500 are the same as described above for the electrosurgical instrument 400 shown in Fig. 4, and so description of those features is not repeated and only the differences are described below. In particular, in this embodiment the intermediate element 521 does not extend to the distal tip of the elongate element 212, but is arranged to terminate at a distance short of the distal tip. This distance may be adjusted according to the frequency of microwave energy which the electrosurgical instrument 500 is intended to deliver to tissue. The electrical contact 518 which electrically connects the intermediate element 521 to the elongate element 212 is therefore spaced from the distal tip of the elongate element 212. The intermediate element 521 comprises a bent or folded wire and is electrically connected with a distal end of the looped element 214, in generally the same manner as described above.

[0065] Fig. 6 is a schematic cross-section of an electrosurgical instrument 600 that is a fifth 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 Fig. 2, and so description of those features is not repeated and only the differences are described in detail below. In particular, the electrosurgical instrument 600 comprises two looped elements 614a, 614b which are each wound about a portion of the elongate element 212 and are electrically connected to the elongate element 212.

[0066] Specifically, a first looped element 614a is positioned proximally of a second looped element 614b. An electrical contact 618 is positioned between the first looped element 614a and the second looped element 614b to electrically connected the two looped elements 614a, 614b to the elongate element 212. As a result, the first looped element 614a is electrically connected to the elongate element 212 at its distal end, and the second looped element 614b is electrically connected to the elongate element 212 at its proximal end. The dimensions and parameters of the two looped elements 614a, 614b may be configured independently according to the frequency of microwave energy which the electrosurgical instrument 600 is intended to deliver to tissue. For example, the length of the two looped elements 614a, 614b, the number of turns, outer diameter etc. - any of the dimensions or parameters described above in relation to Fig. 2.

[0067] Fig. 7 is a schematic cross-section of an electrosurgical instrument 700 that is a sixth 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 Fig. 2, and so description of those features is not repeated and only the differences are described in detail below. In particular, in this embodiment the looped element 714 is electrically connected to the elongate element 212 and also to the outer conductor 204 of the coaxial feed cable. At its distal end, the looped element 714 is electrically connected to the elongate element 212, at a position which is spaced away from the distal tip of the elongate element 212, by a first electrical contact 718a. At its proximal end, the looped element 714 is electrically connected to the outer conductor 204 by a second electrical contact 718b.

[0068] Fig. 8 shows a graph 800 plotting return loss against frequency for an electrosurgical instrument according to an embodiment of the present invention, specifically the electrosurgical instrument 200 described above with respect to Fig. 2. The dimensions and parameters of the radiating tip 210 have been selected to exhibit a suitable return loss (that is, a return loss below a predetermined threshold, in this case less than -10 dB) at three microwave frequencies indicated by the lines 801 , 802, 803. A first frequency, indicated by line 801 , is 915 MHz; a second frequency, indicated by line 802, is 2.45 GHz; a third frequency, indicated by line 803, is 5.8 GHz. However, it will be appreciated by inspection of the graph 800 that the radiating tip 210 also exhibits suitable return losses at other frequencies.

[0069] Fig. 9 is a schematic cross-section of an electrosurgical instrument 900 that is a seventh embodiment of the present invention. Many features of the electrosurgical instrument 900 are the same as described above for the electrosurgical instrument 200 shown in Fig. 2, and so description of those features is not repeated and only the differences are described in detail below. In particular, in this embodiment, the looped element 914 is tightly coiled such that there is no spacing or gap between adjacent coils, turns, or loops of the wire. This may help to provide a compact radiating tip 910 with sufficient electrical length to operate at a predetermined frequency, for example including 433 MHz. It will be appreciated that the looped element 914 comprises an insulated metal wire as before (i.e., an enamelled copper wire) such that, although the coils are in physical contact with adjacent coils, they are not in electrical contact.

[0070] As suggested above, the return loss characteristics of the electrosurgical tip can be altered by adjusting the dimensions and parameters of the radiating tip. For example, increasing the number of turns of the looped element may generally act to move the ‘nulls’ (minima) of the return loss chart leftwards (i.e., to lower frequencies). As another example, increasing the length of the looped element (e.g., by increasing the distance between adjacent turns) may generally act to move nulls above about 4 GHz rightwards (i.e., to higher frequencies). Increasing the proximal gap length (i.e., the distance between the distal end of the outer conductor and the proximal end of the looped element) may generally act to move nulls below about 5 GHz leftwards (i.e., towards lower frequencies). The return loss exhibited by the electrosurgical tip as a result of any changes to parameters or dimensions may be confirmed by simulation, in order to ensure that a suitable return loss (e.g., less than -10 dB) is present at the predetermined or desired operating frequency or frequencies.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0075] 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.

[0076] 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 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 element electrically connected to the inner conductor and extending in a longitudinal direction, and a looped element electrically connected to the elongate element, wherein the looped element is wound around at least a portion of the elongate element.

2. The electrosurgical instrument of claim 1 , wherein the elongate element comprises a distal portion of the inner conductor that extends beyond a distal end of the outer conductor.

3. The electrosurgical instrument of claim 1 or claim 2, wherein the looped element comprises an insulated wire.

4. The electrosurgical instrument of any preceding claim, wherein an outer diameter of the radiating tip is less than 5 mm.

5. The electrosurgical instrument of any preceding claim, wherein the looped element is also electrically connected to the outer conductor of the coaxial feed cable.

6. The electrosurgical instrument of any preceding claim, wherein the looped element is spaced from a distal end of the outer conductor by a first distance.

7. The electrosurgical instrument of claim 6, wherein the first distance is between 1 mm and 5 mm.

8. The electrosurgical instrument of any preceding claim, wherein the looped element is spaced from a distal end of the elongate element by a second distance.

9. The electrosurgical instrument of claim 8, wherein the second distance is between 1 mm and 5 mm.

10. The electrosurgical instrument of any preceding claim, wherein the looped element has at least five coils.11 . The electrosurgical instrument of any preceding claim, wherein the looped element is tightly wound around the elongate element such that adjacent coils of the looped element are in contact with one another.

12. The electrosurgical instrument of any preceding claim, wherein the looped element is electrically connected to the elongate element at either: a proximal end of the looped element; or a distal end of the looped element.

13. The electrosurgical instrument of any preceding claim, wherein the looped element is electrically connected to the elongate element at a distal end of the elongate element.

14. The electrosurgical instrument of any preceding claim, wherein the radiating tip further comprises a second looped element, wherein the second looped element is wound around a different portion of the elongate element to the looped element, and is electrically connected to the elongate element.

15. The electrosurgical instrument of any one of claims 1 to 11 , wherein the radiating tip further comprises an intermediate element which is electrically connected between the elongate element and the looped element.

16. The electrosurgical instrument of claim 15, wherein the intermediate element is electrically connected to the elongate element at a distal end of the elongate element and / or at a distal end of the intermediate element.

17. The electrosurgical instrument of claim 15, wherein the intermediate element is electrically connected to the elongate element at a distal end of the intermediate element and is spaced from a distal end of the elongate element by a third distance.

18. The electrosurgical instrument of claim 17, wherein the third distance is between 1 mm and 5 mm.

19. The electrosurgical instrument of any one of claims 15 to 18, wherein the intermediate element is electrically connected to the looped element at a distal end of the looped element.

20. The electrosurgical instrument of any one of claims 15 to 19, wherein the intermediate element has a length of between 3 mm and 20 mm.

21. The electrosurgical instrument of any one of claims 15 to 20, wherein the intermediate element includes at least one fold, and the looped element is wound around at least a portion of the intermediate element.

22. The electrosurgical instrument of any one of claims 15 to 21 , wherein the intermediate element is unitary with the looped element.

23. The electrosurgical instrument of any preceding claim, further comprising an insulating membrane that surrounds the radiating tip to prevent moisture and / or tissue ingress.

24. The electrosurgical instrument of any preceding claim, wherein an outer diameter of the coaxial feed cable is 5 mm or less.

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

26. An electrosurgical apparatus according to claim 25, 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.

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