Electrosurgical instrument

Abstract

Various embodiments provide an electrosurgical instrument for applying radiofrequency (RF) electromagnetic (EM) energy and / or microwave frequency EM energy to biological tissue. The electrosurgical instrument comprises a coaxial feed cable for conveying a working signal comprising a microwave frequency signal and / or RF signal, the coaxial feed cable having an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor and the outer conductor. The electrosurgical instrument comprises an instrument tip disposed at a distal end of the coaxial feed cable to receive the working signal. The instrument tip comprises an energy delivery structure for delivering the working signal into biological tissue, the energy delivery structure comprising a first electrode that is electrically connected to the inner conductor and a second electrode that is electrically connected to the outer conductor. The instrument tip comprises a dielectric body comprising a second dielectric material separating the first electrode and the second electrode. The instrument tip comprises an impedance adjustor comprising a third dielectric material separating the first dielectric material of the coaxial feed cable and the dielectric body of the instrument tip. The third dielectric material has a dielectric constant which is different from the dielectric constants of the first and second dielectric materials. Some other embodiments provide an electrosurgical system comprising an electrosurgical generator and the instrument.

Description

[0001] ELECTROSURGICAL INSTRUMENT

[0002] Field of the Invention

[0003] The invention relates to an electrosurgical instrument for delivering microwave energy and / or radiofrequency energy to biological tissue to ablate the tissue. For example, the instrument may be inserted through a channel of an endoscope or catheter, or may be used in laparoscopic surgery or open surgery.

[0004] Background

[0005] Electromagnetic (EM) energy, and in particular microwave and radiofrequency (RF) energy, has been found to be useful in electrosurgical operations, for its ability to cut, coagulate, and ablate body tissue. Typically, an 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. 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.

[0006] 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.

[0007] 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.

[0008] RF EM energy can be used for cutting and / or coagulation of biological tissue. The method of cutting using RF energy operates based on the principle that as an electric current passes through a tissue matrix (aided by the ionic contents of the cells, i.e. sodium and potassium), the impedance to the flow of electrons across the tissue generates heat. When a pure sine wave is applied to the tissue matrix, enough heat is generated within the cells to vaporise the water content of the tissue. There is thus a large rise in the internal pressure of the cell that cannot be controlled by the cell membrane, resulting in the cell rupturing. When this occurs over a wide area it can be seen that tissue has been transected.

[0009] RF coagulation operates by applying a less efficient waveform to the tissue, whereby instead of being vaporised, the cell contents are heated to around 65°C. This dries out the tissue by desiccation and also denatures the proteins in the walls of vessels and the collagen that makes up the cell wall. Denaturing the proteins acts as a stimulus to a coagulation cascade, so clotting is enhanced. At the same time, collagen in the cell wall is denatured from a rod like molecule to a coil, which causes the vessel to contract and reduce in size, giving the clot an anchor point, and a smaller area to plug.

[0010] Some electrosurgical instruments may be used with a fluid delivery system for delivering a fluid (e.g. liquid and / or gas) to a treatment site. In some cases, the fluid delivery system may be used to administer liquid medication to a treatment site. For example, it is known to administer adrenaline to the site of a bleed in order to constrict blood vessels during severe bleeds.

[0011] As another example, the fluid delivery system may be used to deliver argon gas to a treatment site, to perform argon plasma coagulation (APC). APC is a surgical technique for controlling bleeding in a manner that does not require physical contact between the electrosurgical instrument and the target tissue. In APC, a jet of argon is ionised with the microwave and / or RF energy delivered by the electrosurgical instrument, to cause coagulation and control bleeding.

[0012] WO 2020 / 070113 A provides an electrosurgical instrument for performing haemostasis by radiating microwave energy from a distal tip. The electrosurgical instrument comprises: a coaxial feed cable for conveying microwave energy and / or radiofrequency energy, the coaxial feed cable having an inner conductor, an outer conductor, and a dielectric material separating the inner conductor and the outer conductor; an instrument tip disposed at a distal end of the coaxial feed cable to receive the microwave energy and / or the radiofrequency energy; and a fluid channel for conveying fluid to the instrument tip; wherein the instrument tip comprises: an energy delivery structure for delivering the microwave energy and / or the radiofrequency energy into biological tissue; and a hollow needle in fluid communication with the fluid channel, the hollow needle being arranged to deliver fluid from the fluid channel to a treatment site, wherein the energy delivery structure comprises a radiating structure for radiating the microwave energy into biological tissue, and wherein the hollow needle is electrically connected to the outer conductor to ground the hollow needle.

[0013] The present invention has been devised in light of the above considerations.

[0014] Summary of the Invention

[0015] The present invention provides a development to the concepts discussed in WO 2020 / 070113 A.

[0016] According to a first aspect of the invention, there is an electrosurgical instrument for applying radiofrequency (RF) electromagnetic (EM) energy and / or microwave frequency EM energy to biological tissue, the electrosurgical instrument comprising: a coaxial feed cable for conveying a working signal comprising a microwave frequency signal and / or RF signal, the coaxial feed cable having an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor and the outer conductor; and an instrument tip disposed at (e.g. mounted to) a distal end of the coaxial feed cable to receive the working signal, the instrument tip comprising: an energy delivery structure for delivering the working signal into biological tissue, the energy delivery structure comprising a first electrode that is electrically connected to the inner conductor and a second electrode that is electrically connected to the outer conductor; a dielectric body comprising a second dielectric material separating the first electrode and the second electrode; and an impedance adjustor (e.g. an impedance adjustment structure) comprising a third dielectric material separating the first dielectric material of the coaxial feed cable and the dielectric body of the instrument tip; wherein the third dielectric material has a dielectric constant which is different from the dielectric constants of the first and second dielectric materials.

[0017] The second dielectric material may isolate (e.g. physically and / or electrically) the first electrode from the second electrode. This arrangement avoids a short circuit between the first and second electrodes.

[0018] The combined dielectric constants of the impedance adjustor and dielectric body may together set an electrical length of the instrument tip to correspond to (e.g. match or be close to) a fraction or multiple of wavelengths (e.g. quarter wavelength) of the working signal. As used herein, the phrase “electrical length” may refer to a length of the instrument tip as calculated using the working signal’s wavelength, i.e. it may refer to the length of the instrument tip as “seen” by the working signal. This may be represented by a number of wavelengths n. By setting the electrical length to correspond to a set number of

[0019] 1 1 1 3 wavelengths of the working signal (e.g. matching or close to an integer multiple of - 4, e.g. n = 4 2 4 1, etc), unwanted reflections causing destructive interference of the working signal within the instrument tip can be avoided. In other words, the instrument tip may be a resonator at the frequency of the working signal. By configuring the instrument tip as a quarter wavelength resonator, the amount of energy delivered from the end of the instrument can be at a maximum, thereby efficiently delivering energy into tissue.

[0020] The impedance adjustor and dielectric body may together set an impedance of the instrument tip to substantially match an impedance of the coaxial cable. This helps to reduce or avoid impedance mismatches at the interfaces between different materials (which would result in destructive interference), thereby helping to efficiently deliver energy into tissue.

[0021] The instrument tip (impedance adjustor and dielectric body) may have a physical length which substantially matches or is less than its electrical length at the working signal. For a particular working signal frequency, the desired electrical length may be fixed (e.g. % wavelength). The possible physical sizes of the instrument may be constrained or fixed, e.g. by the size of the anatomical structures and / or scoping devices (endoscopes) within which the instrument is intended to fit. Providing an impedance adjustor allows the instrument tip to be changed (e.g. reduced) in size (compared to arrangements without the impedance adjustor) whilst retaining the desired electrical length.

[0022] Accordingly, embodiments can help to improve the size, cost, and ease of manufacture of the instrument, while balancing this with providing a desired energy efficiency and / or radiation profile. In particular, since the material of the impedance adjustor has a different (e.g. greater) dielectric constant than that of the dielectric body, the impedance adjustor can enable the size of the instrument tip to be modified (e.g. reduced) compared to arrangements that lack an impedance adjustor. The working signal can therefore be transferred efficiently into tissue even at different (e.g. reduced dimensions).

[0023] Further, the dielectric body may be dimensioned (e.g. shaped, sized) to provide desired characteristics to a radiation profile (e.g. by positioning the electrodes in a desired manner). For example, In some embodiments, which will be described further herein, the dielectric body may have grooves for accommodating the first and second electrodes, which may form interdigitated conductive fingers alternatingly arranged around the circumference of the dielectric body. It may be desirable to use a material that is relatively inexpensive and / or convenient to manufacture (e.g. a polymer such as PEEK, PTFE, or silicone) into the necessary shape for the dielectric body. However, such materials may be inefficient at delivering the working signal into tissue. Other, higher dielectric materials (e.g. ceramics such as zirconia or alumina) may provide more efficient energy delivery while allowing the size of the instrument tip to be reduced, but these materials can be more expensive and challenging to manufacture, particularly into the shape of the dielectric body. The provision of an impedance adjustor helps to overcome these constraints, since the impedance adjustor can be formed separately from the dielectric body (e.g. in a simpler shape than the dielectric body) and can thus be formed of a material that may otherwise be difficult to incorporate into the dielectric body itself. Accordingly, the dielectric body can be formed of a material that is easier and / or less expensive to manufacture into its desired dimensions (e.g. shape, size), whilst still providing efficient energy transfer due to the provision of the impedance adjustor.

[0024] As discussed above, the impedance adjustor separates (is located between) the first dielectric material from the dielectric body. In other words, the impedance adjustor can be an intervening element that forms a continuous dielectric pathway together with the first dielectric material and dielectric body. The impedance adjustor may be located directly between the dielectric material of the coaxial cable and the dielectric body of the instrument tip, i.e. without any further intervening elements positioned between the impedance adjustor and the dielectric material or dielectric body.

[0025] The impedance adjustor may be discrete from (not integrally formed with) the first dielectric material and / or dielectric body. The third dielectric material may be different from the second dielectric material. The second and / or third dielectric materials may also be different from (e.g. stiffer than) the first dielectric material.

[0026] Optionally, the dielectric constant of the third dielectric material is greater than the dielectric constant of the first and / or second dielectric materials. The dimensions of the instrument tip can therefore be reduced compared to arrangements that lack such an impedance adjustor. For example, the instrument tip (or one or more components thereof, e.g. the energy delivery structure and / or dielectric body) can be made shorter than arrangements that lack an impedance adjustor, whilst still efficiently delivering the working signal into tissue. This is because increasing the dielectric constant of the impedance adjustor offsets the impact that shortening the dielectric body has on impedance matching. The Instrument may therefore be used within narrower scoping devices and / or in smaller biological structures, can be more easily manoeuvred, and / or can more precisely control energy delivery at the instrument tip (e.g. because less energy is lost within the instrument).

[0027] The effect of the impedance adjustor on the dimensions of the instrument tip can be better understood in view of the following theory.

[0028] The instrument tip may have an electrical length and / or physical length corresponding to (e.g. matching or close to) a fraction or multiple of wavelengths (e.g. quarter wavelength) at the frequency of the working signal. By configuring the instrument tip in this manner, unwanted reflections can be reduced at the interfaces between the instrument tip and coaxial cable and / or tissue, thereby helping to maximise the amount of energy delivery into tissue. Further, if configured e.g. so that the number of wavelengths n = i 4, the instrument tip can transmit the working signal as a standing wave having a maximum at a distal end of the instrument tip, thereby delivering a maximum available amount of energy into tissue at the distal end of the tip.

[0029] In embodiments, a suitable frequency f for the working signal may be, for example, 915 MHz, 2.45 GHz, 5.8 GHz, 14.5 GHz, or 24 GHz. These frequencies may be particularly useful for treating biological tissue. For example, the instrument tip may be configured as a quarter-wave impedance transformer (n = i), e.g. at 5.8 GHz.

[0030] In general, the physical length G of a structure may be calculated as a number n of wavelengths A, as G = nA. The physical length G of the structure can also be related to its dielectric constant s, the frequency f, and the speed of light c, according to the following equation:

[0031] (equation 1)

[0032] As can be understood from equation 1 , if the dielectric constant s is changed (e.g. increased), then its physical length G will also change (e.g. decrease) for a fixed number n and frequency f. This relationship can be exploited to change (e.g. decrease) the physical size of the instrument without substantially affecting the number of wavelengths n, by changing (e.g. increasing) the dielectric constant s to compensate for the effect of the changed physical length on the instrument tip’s electrical length. Embodiments may therefore allow the physical size (e.g. length or diameter) of the instrument tip to be changed (e.g. made smaller) compared to prior art arrangements, whilst maintaining the ability to efficiently deliver the same working signal into tissue, since the impedance adjustor can help offset any changes (e.g. reductions) in electrical length that would otherwise occur when changing (e.g. decreasing) the physical size the instrument tip.

[0033] Another factor to consider is the impedance Z of the dielectric materials in the electrosurgical instrument and tissue. Providing an impedance match to the coaxial feed cable can improve the efficiency of energy transfer, by effectively maximising the amplitude of the working signal within the instrument tip. In use, the efficiency of energy transfer may be affected by the impedance match between the instrument tip and coaxial cable, and the impedance match between the instrument tip and the tissue, since there will be reflections at both interfaces. However, the tissue’s impedance can vary based on the type of tissue being contacted, orthe amount (e.g. width) of tissue being contacted. For example, the impedance of tissue could vary between approximately 20 to 300 ohms. Conversely, the impedance of the coaxial cable could be constant e.g. 50 ohms. It may therefore be particularly useful to provide the instrument tip with an impedance which is matched to that of the coaxial cable. In this way, signal reflections cancel out. For example, reflections from a junction between the tissue and instrument tip may cancel reflections from a junction between the instrument tip and tissue.

[0034] Accordingly, the impedance adjustor may be configured to set an impedance value of the instrument tip to match an impedance value of the coaxial cable. As used herein, an impedance “match” may allow a variation between 1 / 3 (33%) and 3 times (300%) the desired value, or optionally between 70% and 140% of the desired value. The instrument may therefore be very tolerant of varying loads. An impedance match can help to improve the efficiency of energy transfer, by reducing unwanted reflections of energy.

[0035] The dielectric materials (and their dielectric constants) can therefore influence the efficiency of energy transfer in two manners: 1) by affecting the electrical length of the instrument tip (i.e. how well the second and third dielectric materials provide a desired electrical length at the working signal frequency); and 2) by affecting the impedance match between the first, second, and / or third dielectric materials. In general, adjusting the impedance match may be particularly useful when trying to make the instrument tip narrower (since narrowing the instrument tip will not affect electrical length but may affect impedance), and adjusting the electrical length may be particularly useful when trying to make the instrument tip shorter (which may affect electrical length and impedance).

[0036] The dielectric body may be dimensioned in a similar manner as discussed in WO 2020 / 070113 A, which is incorporated herein by reference in its entirety. For example, optionally, the energy delivery structure is formed in and / or on the dielectric body. Optionally, the radiating structure’s first and electrode and second electrode are exposed on an outer surface of the dielectric body. Optionally, the dielectric body includes a first groove in which the first electrode is disposed and a second groove in which the second electrode is disposed. Optionally, the first electrode includes a first set of longitudinally extending conductive fingers disposed around a circumference of the dielectric body. Optionally, the second electrode includes a second set of longitudinally extending conductive fingers disposed around the circumference of the dielectric body, and wherein the first set and second set of conductive fingers are arranged in an interdigitated manner around the circumference of the dielectric body. This configuration may serve to provide a substantially uniform radiation profile around the instrument tip. This may help, for example, tissue to be uniformly ablated or coagulated in a volume around the instrument tip.

[0037] As discussed above, the inventors have identified a challenge in that certain materials which provide efficient energy delivery can be difficult and / or expensive to manufacture into the dimensions of the dielectric body. By providing an impedance adjustor in addition to the dielectric body, the impedance adjustor may be formed of a material that improves or optimises efficiency of energy delivery, and the dielectric body may be formed of a material that is easier and / or less expensive to manufacture into its required shape (e.g. to accommodate the electrodes and / or provide a desired radiation profile). Accordingly, the impedance adjustor may have a shape that is simpler to manufacture than the dielectric body, e.g. having fewer grooves and / or ridges than the dielectric body. Optionally, the impedance adjustor is tubular, e.g. cylindrical. This helps simplify manufacture of the impedance adjustor, even at small sizes for miniaturising the instrument. Due to this simplicity, this tubular shape is also particularly convenient for incorporating certain materials (e.g. ceramics) that may otherwise be difficult or expensive to incorporate into the dielectric body of the instrument tip.

[0038] The impedance adjustor may have substantially the same diameter as the coaxial feed cable, e.g. having an outer surface which is flush with an outer surface of the coaxial feed cable’s outer conductor.

[0039] Optionally, the third dielectric material comprises (e.g. consists of) a ceramic. Ceramics can have relatively high dielectric constants compared to other dielectric materials such as polymers and can therefore facilitate a reduction in size of the instrument tip. However, ceramics can be difficult to manufacture into complex shapes, particularly at small dimensions (with ceramics being processed, for example, by sintering / fusing ceramic powder), whereas polymers can be much easier to manufacture into complex shapes, even at small dimensions (for example, via injection moulding). Accordingly, forming the impedance adjustor from a ceramic can help optimise a balance between improving energy efficiency at a desired instrument size, whilst also being simple to manufacture (due to being implemented in the impedance adjustor rather than in the dielectric body).

[0040] Optionally the ceramic may be zirconia or alumina. The inventors have identified that both of these materials provide good energy performance even at small dimensions. Zirconia has a higher dielectric constant than alumina and therefore can allow even further miniaturisation of the instrument tip.

[0041] For example, zirconia can have a dielectric constant of s = 29 (for Technox 3000). If implemented as a quarter wavelength impedance transformer at f = 5.8 GHz, then this provides an electrical length using

[0042] 1 3xl0 equation (1) ' of G = -8ms 4 5.8 GHzV ■=- 2=19 = 2.4 mm. In another example, alumina can have a dielectric constant of

[0043] 1 3xl0 9.9, providing an electrical length under equation (1) of G = ~5 8 GH8m z s s = ^- g1= 4.1 mm. In comparison, a polymer composite such as glass-filled PEEK may have a dielectric constant of s = 3.6, providing an

[0044] 1 3xl08ms~ electrical length of G = - = = 6.8 mm. Accordingly, it can be seen that zirconia and alumina allow for a shortened length compared to lower-dielectric materials such as glass-filled PEEK.

[0045] Optionally, the second dielectric material (of the dielectric body) comprises (e.g. consists of) a polymer or polymer composite. Such materials can be easily and inexpensively manufactured even at small dimensions and / or special shapes required for the dielectric body (e.g. by injection moulding, compression moulding, extrusion, etc). For example, the second dielectric material may comprise a polymer such as PEEK, PTFE, or silicone. A suitable polymer composite may be, e.g. glass-filled PEEK. As used herein, a polymer composite may refer to a material having both a polymer and a ceramic, with the polymer providing a majority of the material by weight (e.g. 70% or more of the material by weight). The dielectric body may comprise a non-stick coating (e.g. Parylene C), e.g. in combination with a dielectric such as PEEK. Alternatively, the second dielectric material itself may have non-stick properties (e.g. silicone). Optionally, the first dielectric material (of the coaxial cable) has a dielectric constant of up to 2.5, optionally up to 2.2, optionally up to 2.1 , optionally up to 2, optionally up to 1 .8, optionally up to 1 .7, optionally up to 1 .6. For example, the first dielectric material may comprise (e.g. consist of) PTFE. Solid PTFE dielectric may have a dielectric constant of approximately 2. Alternatively, lower density PTFE may have a dielectric constant of approximately 1 .6.

[0046] Optionally, the third dielectric material (of the impedance adjustor) has a dielectric constant of greater than or equal to 5, optionally greater than 8, optionally greater than 10, optionally greater than 15, optionally greater than 20, optionally greater than 25.

[0047] The dielectric body and / or impedance adjustor may comprise one or more engagement features for mutually engaging (mating) with each other. Optionally, the dielectric body and the impedance adjustor may form a plug-and-socket type connection. For example, the dielectric body may comprise a socket for mating with (mounting onto) the impedance adjustor. Accordingly, optionally the dielectric body comprises a socket opening toward a proximal end of the instrument tip, and the impedance adjustor is mounted in the socket. This provides a convenient structure for connecting the dielectric body and the impedance adjustor, by slotting the dielectric body and impedance adjustor into place. The socket may have a complementary shape to a distal end of the impedance adjustor, e.g. having a tubular (e.g. cylindrical) internal shape for accommodating a tubular (e.g. cylindrical) distal end of the impedance adjustor.

[0048] Optionally, the first electrode is integrally connected to (integrally formed with) an inner conductive sleeve that extends through the impedance adjustor and is electrically connected to the inner conductor of the coaxial feed cable. This provides a unitary structure (in the form of the first electrode and inner conductive sleeve) that extends through the impedance adjustor, thereby helping to reinforce a mechanical connection between the energy delivery structure and impedance adjustor. The inner conductive sleeve may be connected to the first electrode at a distal end of the instrument tip.

[0049] Optionally, the inner conductor of the coaxial feed cable extends through the inner conductive sleeve (beyond a distal end of the coaxial feed cable’s outer conductor and / or dielectric material) to electrically connect to the first electrode (e.g. via electrical connection with the inner conductive sleeve).

[0050] Accordingly, the inner conductor of the coaxial feed cable can protrude beyond the coaxial feed cable’s first dielectric material and / or outer conductor, such that a portion (“protruding portion”) of the inner conductor extends through at least a portion of the inner conductive sleeve. The protruding portion of the inner conductor can extend through the impedance adjustor, and optionally further through the dielectric body, e.g. to a distal end of the dielectric body. This further reinforces the mechanical connection between the instrument tip and the coaxial cable, and provides an arrangement that is simple to manufacture.

[0051] Optionally, the second electrode is integrally connected to (integrally formed with) an outer conductive sleeve that extends over (e.g. extends around an outer surface of) the impedance adjustor and is electrically connected to the outer conductor of the coaxial feed cable. This provides a unitary structure (in the form of the second electrode and outer conductive sleeve) that extends over the impedance adjustor, thereby helping to reinforce a mechanical connection between the energy delivery structure and impedance adjustor.

[0052] The outer conductive sleeve may be distinct from (not integrally formed with) the outer conductor of the coaxial feed cable. Optionally, the outer conductive sleeve extends over (overlays) an outer surface of the coaxial feed cable’s outer conductor to electrically connect to the outer conductor. This helps further reinforce a connection between the instrument tip and the coaxial feed cable.

[0053] Additionally, these arrangements can also help to simplify manufacture since the inner and outer conductive sleeves can form relatively rigid elements (e.g. compared to the coaxial feed cable) that can be easily slotted into place to connect the energy delivery structure to the impedance adjustor and / or coaxial feed cable.

[0054] The impedance adjustor may be considered to form part of an “intervening portion” or “intermediate portion” of the electrosurgical instrument located between a “proximal portion” of the instrument (that comprises the coaxial feed cable), and a “distal portion” or “exposed portion” of the instrument (that comprises the energy delivery structure and the dielectric body). In addition to having the impedance adjustor, the intervening portion may further comprise an inner conductive segment (e.g. the inner conductive sleeve and protruding portion of the coaxial feed cable’s inner conductor) and an outer conductive segment (e.g. the outer conductive sleeve), which are separated (e.g. radially separated) by the third dielectric material of the impedance adjustor. The inner conductive segment electrically connects the first electrode of the instrument tip to the inner conductor of the coaxial cable. The outer conductive segment electrically connects the second electrode of the instrument tip to the outer conductor of the coaxial cable.

[0055] Optionally, the instrument further comprises a flexible sleeve overlying the coaxial feed cable and extending beyond (e.g. distally beyond) a distal end of the coaxial feed cable, over a (proximal) portion of the instrument tip. The flexible sleeve therefore extends across a junction connecting the instrument tip and the coaxial feed cable, helping to reinforce their connection.

[0056] Optionally, the flexible sleeve may overlie (at least a proximal portion of) the outer conductive sleeve (if present). This further strengthens the connection between the coaxial feed cable and instrument tip, since both the flexible sleeve and the outer conductive sleeve overlap the junction between the instrument tip (e.g. impedance adjustor thereof) and the coaxial feed cable from opposite directions. In other words, the junction between the instrument tip and the coaxial feed cable can be located (in a longitudinal direction) between a distal end of the flexible sleeve and a proximal end of the outer conductive sleeve.

[0057] The flexible sleeve may comprise a heat-shrink material, e.g. fluorinated ethylene propylene (FEP). This helps to provide strong reinforcement while also having a small profile. The flexible sleeve may be made of or coated with a biocompatible non-stick material, to prevent tissue from sticking to the instrument. This may assist with lubricious insertion of the instrument into the body. Optionally, the energy delivery structure is coaxial with (shares a central longitudinal axis with) the coaxial feed cable. The coaxial feed cable can therefore be made larger relative to the energy delivery structure while retaining a same (or smaller) overall diameter of the instrument, compared to previous arrangements in which the coaxial feed cable is offset from a central longitudinal axis of the energy delivery structure (e.g. to accommodate a push rod for a needle). This in turn helps to reduce losses, since smaller diameter cables will typically involve higher losses.

[0058] For example, optionally, an outer diameter (e.g. maximum outer diameter) of the coaxial feed cable is at least than 50% of a diameter (e.g. maximum outer diameter) of the energy delivery structure, optionally at least 60%, optionally at least 70%, optionally at least 80%, optionally at least 90%. By providing a large coaxial feed cable relative to the energy delivery structure, the efficiency of energy transfer can be improved (by reducing losses along the coaxial feed cable) while retaining a small overall size.

[0059] The maximum outer diameter of the coaxial feed cable may be smaller than the maximum outer diameter of the energy delivery structure, e.g. to allow the outer conductive sleeve to extend over the outer conductor of the coaxial feed cable.

[0060] Optionally, the dielectric body and / or impedance adjustor has a central longitudinal axis aligned with the coaxial cable. This can also help simplify connection between the coaxial feed cable and the energy delivery structure. For example, optionally, the dielectric body and / or impedance adjustor comprises a longitudinal channel extending therethrough (e.g. through its centre), and a portion of the inner conductor extends through the longitudinally extending channel to electrically connect to the first electrode.

[0061] Optionally, the instrument tip does not include a retractable needle (or optionally any type of needle) for piercing biological tissue and conveying fluid from the instrument into the biological tissue. Optionally, the flexible sleeve may not include any retractable needle (or optionally any needle) for piercing tissue.

[0062] Accordingly, the instrument (e.g. flexible sleeve) may omit a push rod, control wire, or other means for controlling such a needle. The instrument may therefore have a relatively simple configuration than instruments requiring a retractable needle. Further, the absence of a needle (and associated deployment structure) allows a larger, lower-loss coaxial cable to be used than in instruments having a retractable needle, without requiring an increase in the size of the instrument itself. This in turn further improves upon the efficiency of energy delivery into tissue.

[0063] As used herein, the phrase “needle” may refer to a tube (e.g. metallic tube) having a sharp point at its distal end for piercing tissue. A “retractable needle” may be longitudinally movable relative to a flexible sheath between a stowed configuration and a deployed configuration, e.g. by using control means such as a push rod which extends through the flexible sheath to the needle. When in the stowed configuration, a sharp distal end of the retractable needle may be located proximally to a distal end of the instrument tip, so as not to protrude from the instrument tip. When in the deployed configuration, the sharp distal end may protrude from the instrument tip to pierce the tissue.

[0064] Optionally, the instrument tip has a length of up to 15mm, optionally up to 12mm, optionally up to 10mm, optionally up to 8mm. These sizes are relatively small and easily manoeuvrable. The instrument tip may have a length of at least 2mm, optionally at least 3mm, optionally at least 5mm. An instrument tip having a length of at least 2mm up to 7mm (e.g. at least 3mm up to 5mm) may be particularly convenient for small surgical scoping devices, e.g. a surgical scoping device having a 2.8 mm working channel.

[0065] Optionally, the coaxial feed cable has a length of up to 2.5m, optionally up to 2.2m, optionally up to 2m, optionally 1 ,8m, optionally up to 1 ,5m, optionally up to 1 ,2m, optionally up to 1 m. Although longer coaxial feed cables are possible, a relatively short coaxial cable helps to further reduce losses. Short dimensions may also be particularly useful in combination with needleless arrangements, since it will not be necessary in such arrangements for an interface joint to be accessible by an assistant to selectively deploy the needle / fluid into the instrument.

[0066] Optionally, the instrument has a maximum diameter of up to 2.7mm, e.g. up to 2.5mm, e.g. up to 2.3 mm, e.g. up to 2.2 mm, e.g. up to 2.1 mm. Such instruments may be compatible with a scoping device having a channel (“working channel”) of 2.8 mm or less. An outer diameter of up to 2.2 mm may be advantageous to allow additional instrument channels (e.g. irrigation or suction channels) to be conveyed down the same working channel of the scoping device, alongside the coaxial feed cable. For use with scoping devices having different (e.g. larger) working channels, the instrument may have different dimensions, e.g. up to 4mm.

[0067] The electrosurgical instrument may be implemented in an electrosurgical system for treating biological tissue. Optionally, the electrosurgical system comprises: an electrosurgical generator arranged to supply microwave energy and / or radiofrequency energy; and the electrosurgical instrument connected to receive the microwave energy and / or radiofrequency energy from the electrosurgical generator. Alternatively or additionally, the electrosurgical system may comprise a surgical scoping device 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.

[0068] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0069] Summary of the Figures

[0070] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0071] Figure 1 is a schematic diagram of an electrosurgical system according to an embodiment of the invention.

[0072] Figure 2 is a perspective view of an electrosurgical instrument according to an embodiment of the invention.

[0073] Figure 3 is a perspective cutaway of an electrosurgical instrument according to another embodiment of the invention, showing the internal elements of the instrument. Figures 4 to 7 are perspective views which show different layers of the instrument tip of the electrosurgical instrument of FIG 2 or FIG 3, in which:

[0074] Figure 4 shows the inner conductor of the coaxial cable that extends to a distal end of the instrument tip;

[0075] Figure 5 shows the first electrode of the energy delivery structure that is connected to the inner conductor;

[0076] Figure 6 shows the dielectric body mounted onto the inner conductor and supporting the first electrode;

[0077] Figure 7 shows the impedance adjustor located between the dielectric material of the coaxial cable and the dielectric body; and

[0078] Figure 8 shows the second electrode supported by the dielectric body and integrally connected to a conductive sleeve that extends over the impedance adjustor.

[0079] Figure 9 shows a flow chart of a method for manufacturing an embodiment electrosurgical instrument.

[0080] Detailed Description of the Invention

[0081] 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.

[0082] Figure 1 is a schematic diagram of a complete electrosurgical system 100 that is capable of supplying microwave energy and radiofrequency energy to the distal end of an invasive electrosurgical instrument. The system 100 comprises a generator 102 for controllably supplying microwave and radiofrequency 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.

[0083] The generator 102 is connected to an interface cable 104, which is connected to a flexible shaft 106 of an electrosurgical instrument 108 via an interface joint 110. The interface joint 110 allows removable connection between the interface cable 104 and the electrosurgical instrument 108. This can allow the electrosurgical instrument 108 to be removed and sterilised (or disposed of and replaced) for each patient, while the interface cable 104 (which can be entirely outside a patient’s body in use) can be reused for a plurality of patients. The interface joint 110 may also be configured to adapt for size differences between the interface cable 104 and the flexible shaft 106, e.g. so that the interface cable 104 can be larger than the flexible shaft 106 to maximise energy efficiency, noting that the interface cable 104 will not be subjected to the same size constraints as the electrosurgical instrument 108 which is intended for insertion into the body. The flexible shaft 106 is insertable through the entire length of an instrument (working) channel of an endoscope 112.

[0084] The flexible shaft 106 has a distal assembly 114 (not drawn to scale in Figure 1) that is shaped to pass through the instrument channel of the endoscope 112 and protrude (e.g. inside the patient) at the distal end of the endoscope’s instrument channel. The distal end assembly 114 includes an instrument tip for delivering microwave energy and / or radiofrequency energy into biological tissue. The tip configuration is discussed in more detail below.

[0085] The structure of the distal assembly 114 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 2.8 mm, 3.2 mm, 3.7 mm, 3.8mm. The length of the flexible shaft 106 can be equal to or greater than 0.3 m, e.g. 2 m or more. In other examples, the distal assembly 114 may be mounted at the distal end of the flexible shaft 106 after the shaft has been inserted through the working channel (and before the instrument cord is introduced into the patient). Alternatively, the flexible shaft 106 can be inserted into the working channel from the distal end before making its proximal connections. In these arrangements, the distal end assembly 114 can be permitted to have dimensions greater than the working channel of the surgical scoping device 112.

[0086] 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.

[0087] Figures 2 shows an electrosurgical instrument 200 according to an embodiment of the invention. Figures 4 to 8 (discussed further below) show other view of this same instrument 200. The electrosurgical instrument 200 can be implemented, for example, as the electrosurgical instrument 108 of Figure 1 .

[0088] The electrosurgical instrument includes a coaxial feed cable 216 that extends through a flexible shaft 206. The coaxial feed cable 216 is configured to convey a working signal (e.g. a microwave frequency signal and / or RF signal) to an instrument tip 214 that is mounted at a distal end of the coaxial feed cable 216. Optionally, the flexible shaft 206 may overlay a proximal end of the instrument tip 214, with a distal end of the flexible shaft 206 covering a junction between the coaxial feed cable 216 and the instrument tip 214. The instrument tip 214 therefore includes an exposed distal portion 218 that protrudes beyond a distal end of the flexible shaft 206, and a covered proximal portion 220 (insulated portion, unexposed portion) that protrudes beyond a distal end ofthe coaxial feed cable (i.e. beyond the dielectric material and outer conductor) and is covered by the flexible shaft 206.

[0089] The exposed distal portion 218 of the instrument tip 214 includes an energy delivery structure for delivering the working signal into biological tissue. The energy delivery structure includes a first electrode 222 and a second electrode 224. A distal end of the first electrode 222 defines an aperture 226 for electrically connecting the first electrode 222 to an inner conductor 234 (shown in Figures 3-4) of the coaxial feed cable 216 (e.g. via solder). The exposed distal portion 218 of the instrument tip 214 further includes a dielectric body 228 that separates the first electrode 222 from the second electrode 224. In this embodiment, the first electrode 222 and second electrode 224 are each located within grooves of the dielectric body 228 and lie substantially flush with an outer surface of the dielectric body. The first and second electrodes 222 and 224 form an interdigitated arrangement extending in a longitudinal direction along the dielectric body 228.

[0090] The second electrode 224 is integrally formed with an outer conductive sleeve 226 that extends under the flexible shaft 206 (within the covered portion 220 of the instrument tip 214) and overlies an outer conductor 232 (shown in Figures 3-7) of the coaxial feed cable 216 to electrically connect thereto.

[0091] Further details of possible configurations for the dielectric body 228 and first and second electrodes 222, 224 may be found in WO 2020 / 070113 A (see e.g. FIGs 10a and 10b), which is incorporated herein by reference in its entirety.

[0092] Figure 3 shows an electrosurgical instrument 200’ according to another embodiment of the invention. The electrosurgical instrument 200’ is configured in the same manner as the electrosurgical instrument 200, except where discussed otherwise below.

[0093] The electrosurgical instrument 200’ differs from the electrosurgical instrument 200 in that the electrosurgical instrument 200 includes an insulating coating 230 (shown in Figures 4 to 8) that is applied onto an outer surface of the coaxial feed cable’s 216 outer conductor 232 and is covered by the flexible shaft 206 (shown in Figure 2), whereas the electrosurgical instrument 200’ of Figure 3 omits the insulating coating 230. The electrosurgical instrument 200’ of Figure 3 can therefore have a smaller profile along the length of the flexible shaft 206, since the flexible shaft 206 is applied directly onto the outer conductor 232 rather than onto the insulating coating 230 which adds additional thickness. The insulating coating 230 and / or flexible shaft 206 each function to electrically insulate and protect the coaxial feed cable 216.

[0094] In other respects, the electrosurgical instrument 200’ may be substantially the same as the electrosurgical instrument 200.

[0095] As can be seen from Figure 3, the coaxial feed cable 216 includes an inner conductor 234 which is separated by the outer conductor 232 by a (first) dielectric material 236. The inner conductor 234 protrudes beyond a distal end of the outer conductor 232 and first dielectric material 236, to a distal end of the instrument tip 214.

[0096] An impedance adjustor 238 is located at a distal end of the first dielectric material 236, between the first dielectric material 236 and the dielectric body 228. The impedance adjustor 238 is formed from a different (third) dielectric material than the (first) dielectric material 236 of the coaxial cable 216 and the (second) dielectric material of the dielectric body 228. For example, the impedance adjustor 238 may be formed of a ceramic (e.g. zirconia or alumina), and the dielectric body 228 may be formed of a polymer or polymer composite (e.g. PEEK, silicone, or glass-filled PEEK). The first dielectric material 236 of the coaxial cable 216 may be formed of e.g. PTFE.

[0097] The impedance adjustor 238 has a tubular shape and extends around a portion of the inner conductor

[0098] 234 which protrudes beyond the first dielectric material 236 and outer conductor 232. The dielectric body 228 has a socket 240 at a proximal end thereof, opening towards a proximal end of the instrument tip 214 to secure a distal end of the impedance adjustor 238 therein.

[0099] The first electrode 222 is integrally connected to an inner conductive element in the form of an inner conductive sleeve 242 that extends through the dielectric body 228 and impedance adjustor 238 to abut a distal end of the first dielectric material 236 of the coaxial feed cable 216. The inner conductor 234 extends through the inner conductive sleeve 242, within the impedance adjustor 238 and dielectric body 228, to the aperture 226 at the distal end of the instrument tip 214. The inner conductive sleeve 242 can help to electrically connect and / or physically secure the first electrode 222 to the inner conductor 234.

[0100] Conversely, the second electrode 224 is integrally connected to an outer conductive element in the form of an outer conductive sleeve 244 that is located distally from the dielectric body 228 and extends over the impedance adjustor 238 and over an outer surface of the outer conductor 232 of the coaxial feed cable 216 to electrically connect the second electrode 224 to the outer conductor 232.

[0101] The inner conductive sleeve 242 may be electrically connected to the inner conductor 234 via a soldered or welded connection, or using a conductive adhesive (e.g. conductive epoxy). Likewise, the outer conductive sleeve 244 may be electrically connected to the outer conductor 232 via a soldered or welded connection, or using a conductive adhesive (e.g. conductive epoxy). The electrical connection(s) may be potted, e.g. encased in a solid or gelatinous compound for protection.

[0102] Figures 4 to 8 show perspective views of different layers of the instrument 200 of Figure 2. As noted above, the instrument 200 differs from the instrument 200’ in the configuration of the insulating coating 230 and flexible shaft 206. In other respects, the instrument 200 may be configured in the same manner as the instrument 200’, and so the same reference numerals will be used.

[0103] Figure 4 shows the coaxial feed cable 216 having the inner conductor 234, outer conductor 232, and dielectric material (not visible in Figure 4) separating the inner conductor 234 and outer conductor 232. A distalmost section of the outer conductor 232 and dielectric material has been removed to allow the inner conductor 234 to protrude therefrom. An insulating coating 230 is applied along the length of the outer conductor 232, but terminates proximally of a distal end of the outer conductor 232 so that a distal end of the outer conductor 232 has an uncoated outer surface.

[0104] Figure 5 shows the arrangement of Figure 4, further with the first electrode 222 and its integrated inner conductive sleeve 242 slotted as a unitary element over the inner conductor 234 of the coaxial feed cable 216.

[0105] Figure 6 shows the arrangement of Figure 5, further with the dielectric body 228 overlying the inner conductive sleeve 242 and supporting the first electrode 222 within a set of grooves formed in the dielectric body 228. The annular socket 240 is located at the proximal end of the dielectric body 228, facing proximally towards the dielectric material of the coaxial feed cable 216.

[0106] Figure 7 shows the arrangement of Figure 6, further with impedance adjustor 238 surrounding the inner conductive sleeve 242, and received within the socket 240 of the dielectric body 228. In this position, the impedance adjustor is separating a dielectric material of the coaxial feed cable 216 from the dielectric body 228, thereby forming a continuous dielectric pathway from the dielectric material of the coaxial feed cable, through the dielectric material of the impedance adjustor, and through the dielectric body 28.

[0107] Figure 8 shows the arrangement of Figure 7, further with the second electrode 224 and integrated outer conductive sleeve 244. The second electrode 224 is located within grooves of the dielectric body 228, forming an interdigitated arrangement with the first electrode 222. A proximal end of the second electrode 224 forms an annulus distally of the dielectric body 228 which reduces in diameter (e.g. in a step-wise manner) proximally to the integrally connected outer conductive sleeve 244. The outer conductive sleeve 244 is slotted over the impedance adjustor 238 and over the exposed (non-insulated) portion of the outer conductor 232 of the coaxial feed cable 216 to electrically connect the outer conductor 232 to the second electrode 224.

[0108] The flexible sleeve 206 (e.g. shrink-fit material) may then be formed over the coaxial feed cable 216 and a proximal portion of the instrument tip 214, to provide the instrument shown in Figure 2.

[0109] It will be appreciated that the successive layers of the instrument 200 as shown in Figures 3 to 8 do not necessarily correspond to successive steps in a manufacturing process, but rather are shown to help clearly illustrate the various elements of the device. These may be different from the steps in which the instrument is assembled. Accordingly, Figure 9 shows a flow diagram for a method of assembling the various components to form the electrosurgical instrument. This method may be performed after an initial step of manufacturing the individual components into the desired dimensions, for example after forming the dielectric body (e.g. using a polymer processing technique such as injection moulding or compression moulding) and manufacturing the impedance adjustor (e.g. using a ceramics processing technique).

[0110] The method will be described with reference to the instrument 200 of Figures 3 and 4 to 8 as an example, although it will be appreciated that the method may be performed differently for other embodiments.

[0111] In step 300, the coaxial cable 216 is prepared by removing portions of the coaxial cable’s insulating coating 230, outer conductor 232 and first dielectric material 242, to expose distal portions of the inner conductor 234 and outer conductor 232. This results in the configuration shown in Figure 4.

[0112] In step 302, the impedance adjustor 238 is mounted onto the coaxial cable, e.g. by sliding it over an exposed distal end of the inner conductor 234.

[0113] In step 304, the outer conductive sleeve 244 (which is part of a unitary structure with the second electrode 224) is mounted onto the impedance adjustor 238, e.g. by sliding the outer conductive sleeve 244 over an end of the impedance adjustor. Once mounted, the second electrode 224 protrudes beyond a distal end of the impedance adjustor 238. The outer conductive sleeve 244 is electrically connected to the outer conductor 232 of the coaxial cable 216.

[0114] In step 306, the dielectric body 228 is mounted (e.g. slid) against the second electrode 224. The dielectric body 228 abuts a distal end of the outer conductive sleeve 244. In step 308, the first electrode is mounted onto the dielectric body and is electrically connected to the inner conductor 234 of the coaxial cable 216. In particular, the inner conductive sleeve 242 (which is part of a unitary structure with the first electrode 222) is mounted within the dielectric body 228, e.g. by slidably inserting the inner conductive sleeve 242 into an aperture at a distal end of the dielectric body 228. In doing so, the first electrode 222 slides into grooves within the dielectric body 228. This results in the assembly as shown in Figure 8. The inner conductive sleeve 242 and / or first electrode 222 may be mechanically and electrically fixed to the inner conductor 234 of the coaxial cable 216, e.g. by applying solder within the aperture 226.

[0115] The instrument may be covered in a flexible sleeve 206, e.g. a heat shrink sleeve, for insulation and reinforcement, to form the instrument 200 as shown in Figure 3.

[0116] It will be recognised that this is just one embodiment of forming the instrument. In other embodiments, the instrument may be assembled differently, e.g. by over-moulding the dielectric body over the electrodes.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0121] 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.

[0122] 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%.

[0123] Reference numerals

[0124] 100 System

[0125] 102 Generator

[0126] 104 Interface cable

[0127] 108, 200, 200’ Electrosurgical instrument

[0128] 106, 206 Flexible shaft

[0129] 114, 214 Distal assembly I instrument tip

[0130] 218 Exposed (distal) portion

[0131] 222 First electrode

[0132] 226 Aperture

[0133] 224 Second electrode

[0134] 228 Dielectric body

[0135] 240 Socket

[0136] 220 Covered (proximal) portion

[0137] 238 Impedance adjustor

[0138] 242 Inner conductive sleeve

[0139] 244 Outer conductive sleeve

[0140] 216 Coaxial feed cable

[0141] 230 Insulating coating

[0142] 232 Outer conductor

[0143] 234 Inner conductor

[0144] 236 (First) dielectric material

[0145] 110 Interface joint

[0146] 112 Endoscope

[0147] 300-308 Method

Claims

Claims:1 . An electrosurgical instrument for applying radiofrequency (RF) electromagnetic (EM) energy and / or microwave frequency EM energy to biological tissue, the electrosurgical instrument comprising: a coaxial feed cable for conveying a working signal comprising a microwave frequency signal and / or RF signal, the coaxial feed cable having an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor and the outer conductor; and an instrument tip disposed at a distal end of the coaxial feed cable to receive the working signal, the instrument tip comprising: an energy delivery structure for delivering the working signal into biological tissue, the energy delivery structure comprising a first electrode that is electrically connected to the inner conductor and a second electrode that is electrically connected to the outer conductor; a dielectric body comprising a second dielectric material separating the first electrode and the second electrode; and an impedance adjustor comprising a third dielectric material separating the first dielectric material of the coaxial feed cable and the dielectric body of the instrument tip; wherein the third dielectric material has a dielectric constant which is different from the dielectric constants of the first and second dielectric materials.

2. The electrosurgical instrument of claim 1 , wherein the dielectric constant of the third dielectric material is greater than the dielectric constant of the first and / or second dielectric materials.

3. The electrosurgical instrument of claim 1 or 2, wherein the impedance adjustor is tubular.

4. The electrosurgical instrument of any preceding claim, wherein the third dielectric material comprises a ceramic.

5. The electrosurgical instrument of claim 4, wherein the ceramic is zirconia or alumina.

6. The electrosurgical instrument of any preceding claim, wherein the dielectric body comprises a socket opening toward a proximal end of the instrument tip, and wherein the impedance adjustor is mounted in the socket.

7. The electrosurgical instrument of any preceding claim, wherein the first electrode is integrally connected to an inner conductive sleeve that extends through the impedance adjustor and is electrically connected to the inner conductor of the coaxial feed cable.

8. The electrosurgical instrument of claim 7, wherein the inner conductor of the coaxial feed cable extends through the inner conductive sleeve to electrically connect to the first electrode.

9. The electrosurgical instrument of any preceding claim, wherein the second electrode is integrally connected to an outer conductive sleeve that extends over the impedance adjustor and is electrically connected to the outer conductor of the coaxial feed cable.

10. The electrosurgical instrument of claim 9, wherein the outer conductive sleeve extends over an outer surface of the coaxial feed cable’s outer conductor to electrically connect to the outer conductor.11 . The electrosurgical instrument of claim 10, further comprising a flexible sleeve that overlies the coaxial feed cable and extends beyond a distal end of the coaxial feed cable to overlie the outer conductive sleeve.

12. The electrosurgical instrument of any preceding claim, wherein the energy delivery structure is coaxial with the coaxial feed cable.

13. The electrosurgical instrument of claim 12, wherein an outer diameter of the coaxial feed cable is at least 50% of a diameter of the energy delivery structure, optionally at least 60%, optionally at least 70%, optionally at least 80%, optionally at least 90%.

14. The electrosurgical instrument of any preceding claim, wherein the instrument tip does not include a retractable needle for piercing biological tissue and conveying fluid from the instrument into the biological tissue.

15. The electrosurgical instrument of any preceding claim, wherein the coaxial feed cable has a length of up to 2.5 metres, optionally up to 2.2 metres, optionally up to 2 metres.

16. The electrosurgical instrument of any preceding claim, wherein the instrument tip has a length of up to 15 mm, optionally up to 12 mm, optionally up to 10 mm, optionally up to 8 mm.

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

18. The electrosurgical system according to claim 17, further comprising a surgical scoping device 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.

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