Electrosurgical instrument and system

Abstract

Various embodiments provide an electrosurgical instrument for delivering electromagnetic (EM) energy to biological tissue The instrument comprises a transmission line for conveying microwave EM energy, and an instrument tip at a distal end of the transmission line. The instrument tip comprises a bipolar antenna structure configured to receive the microwave EM energy from the transmission line and emit the microwave EM energy into biological tissue. The bipolar antenna structure comprises a first electrode and a second electrode, and a reactive unit electrically connected between the first electrode and the second electrode. Some other embodiments provide an electrosurgical system including a generator and the electrosurgical instrument.

Description

[0001] ELECTROSURGICAL INSTRUMENT AND SYSTEM

[0002] Field of the Invention

[0003] The present invention relates to an electrosurgical instrument and system for delivering electromagnetic energy (e.g. microwave and / or radiofrequency energy) to biological tissue. For example, the invention may be applied to instruments sized to be suitable for insertion through the instrument channel of a standard surgical endoscope.

[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 biological (e.g. body) 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. In some cases, the electrosurgical instrument can include a pair of jaws at a distal end so that EM energy can be delivered to tissue located between the jaws.

[0006] Conventional electrosurgical instruments are often designed to be inserted percutaneously into the patient’s body. 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. 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] 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), 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. RF coagulation operates by applying a different waveform to the tissue, whereby instead of being vaporised, the cell contents are heated to (e.g. to around 65°C). This dries out the tissue by desiccation and also denatures the proteins.

[0010] The present invention has been devised in light of the above considerations.

[0011] Summary of the Invention

[0012] At its most general, the present invention provides an electrosurgical instrument having an instrument tip with a bipolar antenna structure for delivering microwave EM energy into biological tissue, the bipolar antenna structure having a first electrode and a second electrode, and a reactive unit electrically connected between the first electrode and the second electrode. The inventors have found that providing a reactive unit in the bipolar antenna structure as described enables an energy delivery profile of the bipolar antenna structure to be controlled, so as to achieve a desired treatment effect along the bipolar antenna structure. In particular, a reactance value of the reactive unit and / or a position at which the reactive unit is connected between the first and second electrodes can be selected to provide a desired energy delivery profile along the bipolar antenna structure.

[0013] When microwave EM energy is conveyed to the bipolar antenna structure, the bipolar antenna structure may act as a leaky (lossy) transmission line, so that the microwave EM energy can be emitted into tissue contacting the instrument tip. The bipolar antenna structure may be operated in a travelling wave mode, where all of microwave EM energy is delivered into tissue as it travels along the length of the bipolar antenna structure. Typically however, there may be some power remaining when the microwave signal reaches a distal end of the bipolar antenna structure, resulting in reflection of the remaining power at the distal end of the bipolar antenna structure. This may be because, for example, tissue may not be continuously in contact along the length of the instrument tip. Interaction between incident and reflected microwave EM energy can thus produce a standing wave in the bipolar antenna structure. This may be referred to as a standing wave mode.

[0014] In the standing wave mode, an energy delivery profile of the microwave EM energy will vary along the length of the bipolar antenna structure, due to variations in magnitude of the standing wave along the length of the bipolar antenna structure. This may result in different rates of treatment at different positions along the instrument tip. Indeed, a treatment effect caused by the microwave EM energy is generally proportional to a square of a strength of the electric field. An effect of connecting the reactive unit in the bipolar antenna structure is to shift positions of maxima and minima of the microwave energy delivery profile along the bipolar antenna structure. Thus, for example, by selecting an appropriate reactance value and / or location of the reactive unit in the bipolar antenna structure, the electrical length of the bipolar antenna structure can be adjusted so as to enhance a uniformity of the energy delivery profile along the bipolar antenna structure. As another example, the reactive unit may be arranged to provide the energy delivery profile with a maximum at a desired location, so as to enhance the treatment effect at the desired location.

[0015] According to a first aspect of the invention, there is provided an electrosurgical instrument for delivering electromagnetic (EM) energy to biological tissue, the instrument comprising: a transmission line for conveying microwave EM energy; and an instrument tip at a distal end of the transmission line, the instrument tip comprising a bipolar antenna structure configured to receive the microwave EM energy from the transmission line and emit the microwave EM energy into biological tissue; wherein the bipolar antenna structure comprises a first electrode and a second electrode, and a reactive unit electrically connected between the first electrode and the second electrode.

[0016] The transmission line may be any suitable transmission line (e.g. cable) for conveying microwave EM energy from an electrosurgical generator to the instrument tip. The transmission line may be connectable at one end to an electrosurgical generator. The transmission line may also be referred to as a feed cable.

[0017] The transmission line may comprise a coaxial transmission line, including an inner conductor, an outer conductor, and a dielectric material separating the inner conductor and the outer conductor. The inner conductor may be an elongate conductor extending along a longitudinal axis of the coaxial transmission line. The dielectric material may be disposed around the inner conductor, e.g. the dielectric material may have a channel through which the inner conductor extends. The outer conductor may be a sleeve made of conductive material that is disposed on the surface of the first dielectric material.

[0018] The transmission line may include an outer protective sheath for insulating and protecting the cable. In some examples, the protective sheath may be made of or coated with a non-stick material to prevent tissue from sticking to the cable.

[0019] The instrument tip is located at the distal end of the transmission line. The instrument tip may be permanently attached to the transmission line, or it may be removably attached to the transmission line. For example, a connector may be provided at the distal end of transmission line, which is arranged to receive the instrument tip and form the required electrical connections.

[0020] The instrument tip may include a dielectric material. The bipolar antenna structure may be provided in and / or on the dielectric material. The dielectric material may form a body of the instrument tip, e.g. the dielectric material may act as a support for at least part of the bipolar antenna structure. For example, the dielectric material may act as a support for the first electrode and / or the second electrode.

[0021] The dielectric material of the instrument tip may comprise any suitable electrically insulating (isolating) material. The dielectric material of the instrument tip may be the same as, or different from, the dielectric material in the coaxial transmission line. In some cases, the dielectric material of the instrument tip may be selected to improve impedance matching with target tissue, in order to improve the efficiency with which the microwave energy is delivered into target tissue.

[0022] The first electrode and the second electrode form the bipolar antenna structure for emitting (delivering) microwave energy into tissue. In this manner, microwave EM energy received from the transmission line is emitted (or radiated) from the bipolar antenna structure into tissue at the instrument tip. This may serve, for example, to ablate, cut, and / or coagulate the tissue, e.g. depending on a profile of the received microwave EM energy.

[0023] The first electrode and the second electrode are electrically connected to the transmission line, to receive the microwave EM energy from the transmission line. For example, where a coaxial transmission line is used, the first electrode may be connected to the inner conductor of the coaxial transmission line, and the second electrode may be connected to the outer conductor of the coaxial transmission line.

[0024] The first electrode and the second electrode may extend alongside (i.e. next to) one another in a longitudinal direction of the instrument tip. Here, the longitudinal direction is a direction linking a proximal end and a distal end of the instrument tip. The longitudinal direction of the instrument tip may be aligned with a longitudinal axis of the transmission line. Accordingly, the first electrode and the second electrode extend along at least part of a length of the instrument tip.

[0025] The first electrode and the second electrode may be spaced apart (e.g. in a direction normal to the longitudinal axis) and electrically isolated from one another by the dielectric material of the instrument tip.

[0026] The first electrode and the second electrode may each have an elongate shape that extends in the longitudinal direction. As an example, the first electrode and the second electrode may each comprise a respective strip of conductive material that extends in the longitudinal direction.

[0027] The first electrode and the second electrode may be substantially parallel to one another.

[0028] The first electrode and the second electrode may be configured as a leaky (lossy) transmission line for the microwave EM energy. In this manner, microwave EM energy can be emitted into biological tissue as it travels along the first and second electrodes.

[0029] The reactive unit is electrically connected between the first electrode and the second electrode. The reactive unit may be considered as part of the bipolar antenna structure. The reactive unit may comprise one or more electrical components having a reactance, e.g. having a capacitance and / or an inductance. For example, the reactive unit may comprise a capacitor and / or an inductor, as discussed in more detail below. The one or more electrical components of the reactive unit are distinct (separate) from the first electrode and the second electrode. Thus, the reactance provided by the reactive unit may be in addition to any reactance of the first and second electrodes themselves.

[0030] The reactive unit may also be referred to as a reactive element, or a reactive assembly.

[0031] In line with the discussion above, an effect of the reactive unit connected between the first and second electrodes is to shift the longitudinal positions of maxima and minima in the microwave energy delivery profile with respect to the instrument tip when in standing wave mode, e.g. as compared to an equivalent instrument tip where no such reactive unit is provided. This is believed to arise because the reactive unit affects boundary conditions for the standing wave in the instrument tip, with the boundary conditions determining locations of maxima and minima in the standing wave pattern. Moreover, the reactive unit may affect an electrical length (i.e. number of wavelengths) of the bipolar antenna structure at the frequency of the microwave EM energy. Accordingly, the value of the reactance and / or the position of the reactance in the bipolar antenna structure can be selected to achieve a desired effect on the energy delivery profile. For example, the reactive unit may be arranged to increase a uniformity of the energy delivery profile along the length of the bipolar antenna structure. As another example, the reactive unit may be arranged to increase (or reduce) an energy delivery rate at a particular location on the instrument tip.

[0032] The electrosurgical instrument may further comprise an instrument shaft through which the transmission line extends. The instrument shaft may be dimensioned to fit within an instrument channel of a surgical scoping device. The surgical scoping device may be a laparoscope or an endoscope. Surgical scoping devices are typically provided with an insertion tube that is a rigid or flexible (e.g. steerable) conduit that is introduced into a patient’s body during an invasive procedure. The insertion tube may include the instrument channel and an optical channel (e.g. for transmitting light to illuminate and / or capture images of a treatment site at the distal end of the insertion tube). The instrument channel may have a diameter suitable for receiving invasive surgical tools. The diameter of the instrument channel may be equal to or less than 13 mm, preferably equal to or less than 10 mm, and more preferably, especially for flexible insertion tubes, equal to or less than 5 mm.

[0033] The transmission line may be flexible to facilitate insertion into the instrument channel of the scoping device. Likewise, the instrument shaft may be flexible. Further, the transmission line may be arranged within a lumen of the shaft. The instrument shaft may cover and / or shield the transmission line. The transmission line may extend from a distal end to a proximal end of the electrosurgical instrument.

[0034] The reactive unit may be connected between the first electrode and the second electrode in a distal end region of the bipolar antenna structure. An effect of connecting the reactive unit in the distal end region may be to move a maximum of the energy delivery profile away from the distal end and towards a middle of the bipolar antenna structure. This may contribute to improve treatment efficiency and uniformity towards the middle of the bipolar antenna structure. In contrast, in an equivalent bipolar antenna structure where no reactive unit is provided, the maximum in the energy delivery profile may be located at the distal end of the bipolar antenna structure.

[0035] Here, the distal end region of the bipolar antenna structure corresponds to a region at (or near) the distal end of the bipolar antenna structure. The distal end of the bipolar antenna structure is the end furthest from the connection to the transmission line.

[0036] In some cases, the reactive unit may be connected to a distal end of the first electrode and / or a distal end of the second electrode.

[0037] The reactive unit may be connected to one of the first electrode and the second electrode at (or near) a distal end of the bipolar antenna structure, and to another one of the first electrode and the second electrode at a location spaced in the longitudinal direction from the distal end of the bipolar antenna structure. In this manner, the reactive unit may be connected between longitudinally spaced points in the bipolar antenna structure, such that the reactive unit extends at least partially in the longitudinal direction. Such an arrangement of the reactive unit may facilitate integrating the reactive unit within a width of the instrument tip, as well as contribute to reducing a diameter of the instrument tip by reducing a dimension of the reactive unit in a direction normal to the longitudinal direction.

[0038] As an example, where the reactive unit comprises an inductor in the form of an inductive wire, the wire may be arranged to extend at least partially along the longitudinal direction of the instrument tip. This may facilitate integrating the inductive wire within the width of the instrument tip.

[0039] The reactive unit may be connected between the first electrode and the second electrode within an eighth of a wavelength of the microwave EM energy from a distal end of the bipolar antenna structure. In other words, the electrical connections between the reactive unit and each of the first and second electrodes may be located within eighth of a wavelength from the distal end of the bipolar antenna structure. Thus, the distal end region mentioned above may correspond to a region that is within an eight of a wavelength from the distal end. The inventors have found that such a positioning of the reactive unit allows effective control of the energy delivery profile. In particular, in this position the reactive unit can be used to effectively set a boundary condition for the standing in the instrument tip, so as to reliably control the energy delivery profile.

[0040] Herein, the wavelength of the microwave EM energy corresponds to its wavelength in the bipolar antenna structure. As such, the wavelength may depend on electrical properties of the bipolar antenna structure and a dielectric constant of the dielectric material in the instrument tip.

[0041] The wavelength A of the microwave EM energy in the bipolar antenna structure may approximated as: where c is the speed of light, f is the frequency of the microwave EM energy, and seffis an effective dielectric constant of the bipolar antenna structure. The effective dielectric constant may depend on the shape, arrangement and material(s) of the bipolar antenna structure, including the first and second electrodes and dielectric material(s) of the instrument tip. The effective dielectric constant may vary along the length of the bipolar antenna structure, and therefore using one value for ceffin this formula may be an approximation.

[0042] The reactive unit may be arranged to provide a short circuit between the first electrode and the second electrode. The inventors have found that this results in a maximum of the energy delivery profile being located approximately one quarter of a wavelength away from the location of the short circuit between the two electrodes. For instance, the reactive unit may be connected between the first electrode and the second electrode in the distal region of the bipolar antenna structure (e.g. at the distal end). Then, a local maximum of the energy delivery profile may be located approximately one quarter of a wavelength away from the distal end region (e.g. distal end), with a local minimum being located in the distal end region (e.g. distal end). Thus, the effect of the reactive unit may be to shift the maximum in a proximal direction, closer to a middle of the bipolar antenna structure.

[0043] The reactance value of the reactive unit may be selected so as to provide the short circuit between the first electrode and the second electrode. For example, a relatively high capacitance and / or a relatively low inductance may be used. Here, a short circuit may refer to a null or negligible voltage drop across the reactive unit. The reactance value of the reactive unit may provide the short circuit at the frequency of the microwave EM energy.

[0044] The reactive unit may be arranged to provide an open circuit between the first electrode and the second electrode. The inventors have found that this results in a local maximum of the energy delivery profile being located by the reactive unit, with the energy delivery profile dropping to a minimum a quarter of a wavelength away from the reactive unit. For instance, the reactive unit may be connected between the first electrode and the second electrode in the distal region of the bipolar antenna structure (e.g. at the distal end). Then, a local maximum of the energy delivery profile may be located in the distal end region (e.g. at the distal end), with a local minimum being located approximately one quarter of a wavelength away from the distal end region (e.g. distal end). Thus, the effect of the reactive unit may be to provide a maximum of the energy delivery profile towards the distal end of the bipolar antenna structure.

[0045] The reactance value of the reactive unit may be selected so as to provide the open circuit between the first electrode and the second electrode. For example, a relatively low capacitance and / or a relatively high inductance may be used. Here, an open circuit may refer to a large voltage drop across the reactive unit. The reactance value of the reactive unit may provide the open circuit at the frequency of the microwave EM energy. The reactive unit may comprise an inductor. This enables positions of maxima and minima of the energy delivery profile to be adjusted. An inductance value of the inductor may be selected to achieve a desired effect. Any suitable type of inductor may be used. As an example, the inductor may comprise a conductive wire. A length and diameter of the wire may be adapted to provide a desired inductance. The wire may in some cases be coiled, e.g. to increase its inductance. For instance, the inductor may be connected between the first electrode and the second electrode in the distal region of the bipolar antenna structure (e.g. at the distal end).

[0046] In line with the above, the inductor may be arranged to provide a short circuit between the first electrode and the second electrode. To provide a short circuit between the first electrode and the second electrode, the inductance value of the inductor may be relatively low. For example, the inductance value may be 100 pH or less. A suitably low inductance L may be selected as L < 0.1 x R / (2nf , where R is the impedance of the bipolar antenna structure.

[0047] Alternatively, the inductor may be arranged to provide an open circuit between the first electrode and the second electrode. To provide an open circuit between the first electrode and the second electrode, the inductance value of the inductor may be relatively high. For example, the inductance value may be 10 nH or more. A suitably high inductance L may be selected as L > 10 x R / (2nf).

[0048] The inductor may comprise a wire extending in the longitudinal direction of the instrument tip. As discussed above, this may facilitate fitting the inductor within a width of the instrument tip, and / or contribute to reducing the width of the instrument tip.

[0049] The first electrode may comprise a first side portion and a second side portion extending in the longitudinal direction, and the wire may extend within a gap (or slot) between the first side portion and the second side portion. This may facilitate integrating the inductor into the instrument tip, and minimising a width of the instrument tip. In particular, by fitting the wire between the first and second side portions of the first electrode, the wire can be located within a width of the first electrode.

[0050] The first side portion and the second side portion may extend alongside one another in the longitudinal direction, with a gap between them. The first side portion and the second side portion may be electrically connected, so as to form the first electrode. In some cases, the first side portion and the second side portion may be integrally formed as a single piece of material, where the gap is formed by cutting out a portion of the material.

[0051] Where the inductor is connected between the first electrode and the second electrode in the distal region of the bipolar antenna structure, the gap between the first and second side portions may be located in the distal region. The first and second portions of the first electrode may then be connected together in a proximal region of the first electrode. The reactive unit may comprise a capacitor. This enables positions of maxima and minima of the energy delivery profile to be adjusted. A capacitance value of the capacitor may be selected to achieve a desired effect. Any suitable type of capacitor may be used.

[0052] The capacitor may be connected between the first electrode and the second electrode in the distal region of the bipolar antenna structure (e.g. at the distal end).

[0053] In line with the above, the capacitor may be arranged to provide a short circuit between the first electrode and the second electrode. To provide a short circuit between the first electrode and the second electrode, the capacitance value of the capacitor may be relatively high. For example, a capacitance of the capacitor may be equal to or greater than 100 pF.

[0054] More generally, to provide a short circuit between the first and second electrode, the capacitance C of the capacitor may be set such that:

[0055] C > l / (0.1 x R x 2nf) where R is the impedance of the bipolar antenna structure.

[0056] Alternatively, the capacitor may be arranged to provide an open circuit between the first electrode and the second electrode. To provide an open circuit between the first electrode and the second electrode, the capacitance value of the capacitor may be relatively low. For example, the capacitance value may be 1 pF or less. A suitably low capacitance C may be selected as C < 1 / (10 x R x 2TT ).

[0057] Where the reactive unit comprises an inductor and a capacitor, the inductor and the capacitor may be connected in series between the first electrode and the second electrode.

[0058] Advantageously, providing the capacitor in series with the inductor enables use of the instrument with lower frequency signals (e.g. radiofrequency (RF) EM energy), as the capacitor provides some isolation between the two electrodes. In particular, whilst the inductor acts to shift the microwave energy delivery profile as discussed above, the capacitor enables use of the instrument with lower frequency energies. In this manner, the electrosurgical instrument may be used to deliver microwave EM energy and / or RF EM energy to biological tissue. Accordingly, the same instrument can be used to perform different electrosurgical procedures involving microwave energy and / or RF EM energy.

[0059] Thus, where the reactive unit comprises an inductor in series with a capacitor, the transmission line may convey microwave EM energy and / or RF EM energy.

[0060] Where the capacitor is connected in series with the inductor, the capacitor may tend to reduce an effect of the inductor on the microwave energy delivery profile. Increasing the capacitance value reduces the capacitor’s impact on the effect of the inductor on the microwave energy delivery profile. Thus, in some cases, a relatively high capacitance capacitor may be used (e.g. equal to or greater than 100 pF). Likewise, the inductance of the inductor can be increased to compensate for the effect of the capacitor. Where the inductor comprises a wire extending in the longitudinal direction, the capacitor may be connected to an end of the wire. For example, a distal end of the wire may be connected to a distal end of one of the first and second electrodes, a proximal end of the wire may be connected to a first end of the capacitor, and a second end of the capacitor may be connected to another one of the first and second electrodes.

[0061] The capacitor may have a self-resonant frequency below a frequency of the microwave EM energy. In this manner, when the microwave EM energy is conveyed to the bipolar antenna structure, the capacitor may operate above its self-resonant frequency. Operating the capacitor above its self-resonant frequency results in an inductive effect which shifts the microwave energy delivery profile in line with the above discussion, whilst providing low-frequency isolation to enable use of the instrument with lower frequency energy (e.g. RF EM energy). Indeed, above the self-resonant frequency, the capacitor will have an increased inductive effect and may tend to act as an inductor. This enables the reactive unit to be simplified and made smaller, as there may be no need to use a separate inductor in this case. For example, a capacitor having a self-resonant frequency below a microwave frequency range may be selected for this purpose.

[0062] The self-resonant frequency of the capacitor may, for example, be between 10% and 90% of the frequency of the microwave EM energy. For instance, the self-resonant frequency may be around 50% of the frequency of the microwave EM energy. An inductive reactance of the capacitor increases in a set manner above the self-resonant frequency, determined by the frequency and impedance of the resonator. The capacitance C and the inductance L of the capacitor (resonator) can be estimated using the resonator impedance and self-resonant frequency, e.g. L = Z / 2nfo), and C where Z is the impedance of the resonator and fois the self-resonant frequency.

[0063] The reactive unit may have a variable reactance. This enables the microwave energy delivery profile to be adjusted, by adjusting (varying) the reactance of the reactive unit. For example, this may enable a maximum of the microwave energy delivery profile to be positioned at a desired location on the instrument tip, to optimise treatment at the desired location. This may also enable the maximum of the microwave energy delivery profile to be swept back and forth along the length of the bipolar antenna structure, so as to effectively treat tissue along the length of the bipolar antenna structure. For instance, the maximum of the energy delivery profile can act as a microwave blade that can be swept along the length of the bipolar antenna structure to cut tissue.

[0064] The variable reactance of the reactive unit may be controllable at a proximal end of the electrosurgical instrument. In this manner, a user may control the reactance during use of the instrument, i.e. when the instrument tip is located inside a patient. For example, a control wire may extend between the instrument tip and the proximal end of the instrument, to enable control of the reactance. The control wire may extend along a instrument shaft of the instrument. A proximal end of the control wire may be connected to a handpiece or other suitable user interface, which enables the user to set (select) the reactance value. A distal end of the control wire may be connected to the reactive unit, such that the reactance of the reactive unit is controlled in response to an input from the user at the proximal end.

[0065] The reactive unit may comprise a variable inductor. Thus, the inductance can be varied to control a position of a maximum of the microwave energy delivery profile relative to the bipolar antenna structure. For instance, the inductance may be varied between a first value where a maximum of the microwave energy delivery profile is located at the distal end of the bipolar antenna structure, and a second value where the maximum of the microwave energy delivery profile is spaced from the distal end in a proximal direction. The first value of the inductance (which may correspond to the ‘open circuit’ arrangement discussed above) may be higher than the second value of the inductance (which may correspond to the short circuit arrangement discussed above). As an example, the variable inductor may have an inductance that is variable in a range between 0.1 nH to 10 nH.

[0066] Additionally or alternatively, the reactive unit may comprise a variable capacitor. For example, a varactor diode may be used. Thus, the capacitance can be varied to control a position of a maximum of the microwave energy delivery profile relative to the bipolar antenna structure. For instance, the capacitance may be varied between a first value where a maximum of the microwave energy delivery profile is located at the distal end of the bipolar antenna structure, and a second value where the maximum of the microwave energy delivery profile is spaced from the distal end in a proximal direction. The first value of the capacitance (which may correspond to the ‘open circuit’ arrangement discussed above) may be lower than the second value of the capacitance (which may correspond to the short circuit arrangement discussed above). As an example, the variable capacitor may have a capacitance that is variable in a range between 1 pF to 100 pF.

[0067] A length of the bipolar antenna structure may correspond (approximately) to a quarter wavelength of the microwave EM energy or less. Thus, a quarter wavelength of the microwave EM energy may fit within the length of the bipolar antenna structure. This may contribute to increasing a uniformity of the microwave energy delivery profile along the bipolar antenna structure, as at most one maximum or minimum of the microwave energy delivery profile may be located along the length of the bipolar antenna structure. In some cases, the length of the bipolar antenna structure may be in a range of 40% to 120% of a quarter wavelength of the microwave EM energy. In other words, the length of the bipolar antenna structure may be up to 60% shorter than a quarter wavelength, and up to 20% longer than a quarter wavelength.

[0068] Where the length of the bipolar antenna structure is less than a quarter of the wavelength of the microwave EM energy, this may enable increased uniformity of the energy delivery profile along the length of the bipolar antenna structure. For example, the reactive unit may be arranged such that a maximum of the microwave energy delivery profile is located toward a middle of the bipolar antenna structure, e.g. one eighth of a wavelength from the distal end (half-way along the bipolar antenna structure with a length of a quarter wavelength). This may produce a relatively uniform microwave energy delivery profile along the quarter wavelength bipolar antenna structure. This may be achieved, for instance, by providing an inductor in the distal end region (e.g. at the distal end) of the bipolar antenna structure. The inductance of the inductor may be selected to be relatively low, in line with the discussion above. For the maximum of the microwave energy to be located one eighth of a wavelength from the distal end, the reactance of the reactive unit may be set to equal an impedance of the bipolar antenna structure. Thus, the sum of the inductance and capacitance of the reactive unit may be equal to the impedance of the bipolar antenna structure.

[0069] The second electrode may form a conductive shell of the instrument tip. This may facilitate integrating the second electrode into the structure of the instrument tip, and contribute to providing a more uniform energy delivery profile around the instrument tip. The conductive shell may define at least part of an outer surface of the instrument tip. The conductive shell may define a channel (or groove or inner space) in which at least a portion of the dielectric material of the instrument tip is located. The first electrode may then be provided on and / or in the portion of the dielectric material located in the channel of the conductive shell.

[0070] The reactive unit may be embedded in the dielectric material of the instrument tip. This may facilitate integrating the reactive unit into a space between the first electrode and the second electrode, and contribute to a compactness of the instrument tip. The dielectric material may also serve to protect the reactive unit, e.g. by avoiding contact between the reactive unit and body tissue or fluids, as well as improve electrical isolation of the reactive unit. The reactive unit may be sealed within the dielectric material.

[0071] The instrument tip may comprise a first jaw and a second jaw; the first jaw and the second jaw may be movable between an open position, in which biological tissue can be inserted between the first surface and the second surface, and a closed position, in which the first and second surfaces are brought together to clamp the biological tissue therebetween; and the bipolar antenna structure may be provided on (or in) the first jaw. In this manner, the jaws can be used to hold and / or clamp tissue, which may facilitate treating tissue with the bipolar antenna structure. The bipolar antenna structure may be arranged to emit the microwave EM energy into biological tissue located between the first jaw and the second jaw.

[0072] The first jaw and / or the second jaw may be movable relative to the distal end of the transmission line. The first jaw and / or the second jaw may be attached to the distal end of the transmission line, and / or a distal end of the instrument shaft, via a joint (or hinge). The joint may include a pivot axis around which the first jaw and / or the second jaw may rotate. The first jaw and / or the second jaw may be activated by one or more actuation rods or control wires respectively connected to the first jaw and / or the second jaw. The one or more actuation rods or control wires may extend within the instrument shaft to a proximal end of the electrosurgical instrument. The one or more actuation rods may be connected to a handle (handpiece) with which the first and / or second jaws can be actuated, e.g. opened and / or closed. The electrosurgical instrument may comprise an actuation mechanism which converts a back-and- forth movement of the actuation rod(s) or control wire(s) into a rotational movement of the first jaw and / or the second jaw.

[0073] For example, both jaws can be movable, e.g. rotatable around a (common) pivot axle. In another embodiment, one of the jaws is fixed to the shaft and the other jaw is movable relative to the one jaw.

[0074] In the open position, the first jaw and the second jaw are (maximally) spaced apart so that there is a free space (gap) between inner surfaces of the two jaws. In this way, tissue can be inserted between the jaws in the open position. Usually, the first jaw and the second jaw are moved towards the tissue such that the tissue is pushed into the space between the inner surfaces of the jaws in the open position of the first jaw and the second jaw.

[0075] By moving the first jaw and / or the second jaw from the open position to the closed position, the tissue between the first surface and the second surface can be grasped and / or clamped between the first jaw and the second jaw. In this way, the tissue can be fixed between the inner surfaces of the first and second jaws in the closed position.

[0076] The electrosurgical instrument may further comprise a second antenna structure on the second jaw. The second antenna structure may be any suitable antenna structure, e.g. having one or more electrodes. In some cases, the second antenna structure may be a second bipolar antenna structure. The second bipolar antenna structure may have an analogous arrangement to the bipolar antenna structure described above, and may include any of the features described in relation to the bipolar antenna structure.

[0077] The second antenna structure may be configured to deliver microwave EM energy and / or RF EM energy to tissue located between the jaws.

[0078] The second antenna structure may be electrically isolated from the bipolar antenna structure. Thus, the second antenna structure may not be connected to the transmission line. This may enable EM energy to be delivered independently via the antenna structures on each jaw. Additionally, it has been found that providing an isolated antenna structure on the second jaw enables coupling between the antenna structures on the two jaws when microwave EM energy is emitted by the bipolar antenna structure on the first jaw, which can enhance efficiency of energy delivery into tissue located between the jaws. For example, microwave EM energy may be conveyed to the bipolar antenna structure in the first jaw, with no separate microwave signal being conveyed to the second antenna structure. Coupling between the two antenna structures between the jaws then contributes to enhanced energy delivery to tissue between the jaws. In some cases, the instrument may comprise a second transmission line, which is connected to the second antenna structure, so that microwave EM energy and / or RF EM energy can be conveyed to the second antenna structure. The second transmission line may have any of the features described above in relation to the (first) transmission line. The second transmission line may be electrically isolated from the (first) transmission line.

[0079] Alternatively, the transmission line may be connected to the bipolar antenna structure and the second antenna structure, such that the antenna structure in both jaws are arranged to receive the microwave EM energy from the same transmission line.

[0080] According to a second aspect of the invention, there is provided an electrosurgical system for delivering electromagnetic (EM) energy to biological tissue, the system comprising: a generator for generating microwave EM energy; and the electrosurgical instrument of the first aspect of the invention, wherein the transmission line is configured to convey the microwave EM energy from the generator to the bipolar antenna structure. Any of the features described above in relation to the first aspect of the invention may be shared with the second aspect of the invention (and vice versa).

[0081] The generator may be configured to generate an electrosurgical signal comprising microwave EM energy and / or RF EM energy. The generator may be configured to generate electromagnetic energy of a fixed single frequency or of a plurality of fixed single frequencies. Alternatively or additionally, the generator may be tuneable to generate electromagnetic energy of various frequencies, for example in a continuous range of frequencies between a minimum frequency and a maximum frequency. The generator unit may be connected to a power supply which provides the energy for generating the radiofrequency electromagnetic energy and / or microwave electromagnetic energy.

[0082] The generator may be electrically and / or electronically (directly or indirectly) connected to the transmission line.

[0083] The microwave EM energy (generated by the generator) may have a frequency between 400 MHz and 15 GHz. It has been found that frequencies in this range provide a highly effective tissue sealing performance with a bipolar antenna structure. Moreover, using suitable instrument tip dimensions, this frequency range facilitates controlling the microwave energy delivery profile to provide a more uniform delivery profile along the bipolar antenna structure, and to avoid points of null energy delivery along the bipolar antenna structure. For example, at 2.45 GHz, the wavelength of the microwave EM energy may be approximately 70 mm in the instrument tip. The bipolar antenna structure can then have a length around one quarter of a wavelength (around 17.5 mm), with the reactive unit being arranged to set a position of a maximum of the energy delivery profile within the length of the bipolar antenna structure. For instance, an inductor may be connected at the distal end of the bipolar antenna structure to provide the maximum approximately one eighth of a wavelength away from the distal end, thus avoiding nulls in the energy delivery profile along the bipolar antenna structure and enhancing uniformity of the energy delivery profile along the length of the bipolar antenna structure.

[0084] In some cases, the microwave EM energy may have a frequency between 2 GHz and 6 GHz.

[0085] As a particular example, the microwave EM energy may have a frequency of (approximately) 2.45 GHz. As another example, the microwave EM energy may have a frequency of (approximately) 5.8 GHz.

[0086] Other spot frequencies that may be used include (but are not limited to) 433 MHz, 915 MHz, and 14.5 GHz.

[0087] Herein, the terms “proximal” and “distal” refer to the ends of the electrosurgical instrument, the instrument tip, the bipolar antenna structure, the jaws, the shaft and / or the transmission line further from and closer to a treatment site, respectively. Thus, in use the proximal end is closer to a generator for providing the microwave (and / or RF) energy, whereas the distal end is closer to the treatment site, e g. in the patient.

[0088] The term “conductive” is used herein to mean electrically conductive, unless the context dictates otherwise. The terms “isolating” or “insulating” used herein may mean electrically isolating or insulating.

[0089] The term “longitudinal” used herein refers to a direction along the instrument channel parallel to the axis of the (coaxial) transmission line. In the context of the instrument tip (including the pair of jaws), the term “longitudinal” refers to the direction linking a proximal end of the instrument tip to a distal end of the instrument tip. Where the instrument tip is curved, the longitudinal “axis” may be considered as a line extending from a proximal end to a distal end of the instrument tip, and which is centred about a width of the instrument tip.

[0090] The term “lateral” refers to a direction that is perpendicular to the longitudinal direction. In the context of the instrument tip, the later direction may extend along a direction of a width of the instrument tip.

[0091] The term “inner” may mean radially closer to the centre (e.g. axis) of the instrument channel. The term “outer” may mean radially further from the centre (axis) of the instrument channel.

[0092] The term “electrosurgical” is used in relation to an instrument, apparatus or tool which is used during surgery and which utilises radiofrequency (RF) electromagnetic (EM) energy and / or microwave electromagnetic energy.

[0093] Herein, radiofrequency electromagnetic energy may mean a stable fixed frequency in a range 10 kHz to 300 MHz, preferably in a range from 100 kHz to 5MHz, and more preferably in a range from 360 to 440 kHz. Microwave electromagnetic energy may mean electromagnetic energy having a stable fixed frequency in the range 300 MHz to 100 GHz. The radiofrequency electromagnetic energy should have a frequency high enough to prevent the energy from causing nerve stimulation. In use, the magnitude of the radiofrequency electromagnetic energy and the duration for which it is applied may be selected to prevent the energy from causing tissue blanching or unnecessary thermal margin or damage to the tissue structure. Preferred spot frequencies for the microwave electromagnetic energy include 915 MHz, 2.45 GHz, 5.8 GHz, 14.5 GHz, 24 GHz. 2.45 GHz and / or 5.8 GHz may be preferred. Preferred spot frequencies for the radiofrequency electromagnetic energy include any one or more of: 100 kHz, 250 kHz, 400 kHz, 500 kHz, 1 MHz, 5 MHz.

[0094] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0095] Summary of the Figures

[0096] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0097] Fig. 1 is a schematic diagram of an electrosurgical system according to an embodiment of the invention;

[0098] Fig. 2 is a schematic cross-sectional diagram of an electrosurgical instrument according to an embodiment of the invention;

[0099] Fig. 3 is a graph of a microwave energy delivery profile of an electrosurgical instrument according to an embodiment of the invention;

[0100] Fig. 4 is a graph of a microwave energy delivery profile of an electrosurgical instrument according to an embodiment of the invention;

[0101] Fig. 5 is a schematic perspective view of an instrument tip of an electrosurgical instrument according to an embodiment of the invention;

[0102] Fig. 6 is a schematic perspective view of a first jaw of the instrument tip of Fig. 5;

[0103] Fig. 7 is a schematic perspective view of the first jaw of Fig. 6, where a dielectric material of the first jaw is omitted;

[0104] Fig. 8 is a schematic side sectional view of the first jaw of Fig. 6; and

[0105] Fig. 9 is a schematic front sectional view of the first jaw of Fig. 6.

[0106] Detailed Description of the Invention

[0107] 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.

[0108] Fig. 1 is a schematic diagram of an electrosurgical system 10 that is an embodiment of the invention. The electrosurgical system 10 is arranged to treat biological tissue using microwave electromagnetic (EM) energy delivered from an electrosurgical instrument 12. In some cases, the system 10 may further be configured to treat biological tissue using radiofrequency (RF) EM energy. The electromagnetic energy emitted by the electrosurgical instrument 12 into a treatment zone can be used to coagulate, cut, and / or ablate tissue in the treatment zone.

[0109] The electrosurgical system 10 further comprises a generator unit 14 which can controllably supply microwave electromagnetic energy and / or RF EM energy to the electrosurgical instrument 12. Where the generator unit 14 is arranged to supply both microwave and RF energy, the generator unit 14 may in some cases include a first generator for supplying microwave EM energy and a second generator for supplying RF EM energy. Suitable generators for this purpose are described in WO 2012 / 076844, which is incorporated herein by reference. The generator unit 14 may be arranged to monitor reflected signals received back from the electrosurgical instrument 12 in order to determine an appropriate power level for delivery. For example, the generator unit 14 may be arranged to calculate an impedance seen at the electrosurgical instrument 12 in order to determine an optimal delivery power level.

[0110] The electrosurgical system 10 further comprises a surgical scoping device 18, such as a bronchoscope, endoscope, gastroscope, laparoscope or the like. The scoping device 18 may include a handpiece 20 and a flexible shaft 22. The handpiece 20 may include means for guiding the flexible shaft 22 through a cavity of a body. For example, the handpiece 20 can include means for moving a distal end of the flexible shaft 22 to change direction of the distal end of the flexible shaft 22. This helps manoeuvring the flexible shaft 22 through the cavity of the body. The flexible shaft 22 may include a working channel through which elongated structures can be moved and, thus, positioned at the treatment zone within the cavity of the body.

[0111] The electrosurgical instrument 12 includes a transmission line 28, and an instrument tip 32 connected at a distal end of the transmission line 28. The transmission line 28 is electrically connected to the generator unit 14, to convey EM energy from the generator unit 14 to a bipolar antenna structure in the instrument tip 32. The transmission line 28 may comprise, for example, a flexible coaxial cable. The bipolar antenna structure in the instrument tip 32 is configured to emit microwave EM energy into tissue located at the instrument tip 32, in order to treat the tissue, e.g. coagulate, cut, and / or ablate the tissue. The bipolar antenna structure may also be configured to deliver RF EM energy to the tissue. Example structures of the instrument tip 32 are discussed in more detail below. The electrosurgical instrument 12 may be insertable through the entire length of an instrument (working) channel in the flexible shaft 22 of the scoping device 18, so that the instrument tip 32 protrudes from the distal end of the flexible shaft 22. The transmission line 28 and the instrument tip 32 may therefore be dimensioned to be insertable through the instrument channel in the flexible shaft 22. For example, the instrument tip 32 may 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 22 can be equal to or greater than 0.3 m, e.g. 2 m or more.

[0112] In other examples, the instrument tip 32 may be mounted at the distal end of the transmission line 28 after the transmission line 28 has been inserted through the working channel of the flexible shaft 22 (and before the instrument cord is introduced into the patient). Alternatively, the transmission line 28 can be inserted into the working channel from the distal end before making its proximal connections. In these arrangements, the instrument tip 32 can be permitted to have dimensions greater than the working channel of the flexible shaft 22.

[0113] In some cases, one or more control wires or actuation rods may extend within the flexible shaft 22, between the handpiece 20 and the instrument tip 32. For example, the instrument tip 32 may comprise a pair of jaws which can be opened and closed to grip tissue therebetween. The control wire may be arranged to transmit movement of a handle in the handpiece 20 to the instrument tip 32, in order to open or close the jaws.

[0114] The system 10 described above is one way of introducing the instrument 12 into a patient’s body. Other techniques are possible. For example, the instrument 10 may also be inserted using a catheter.

[0115] Fig. 2 shows a schematic cross-sectional view of an electrosurgical instrument 200 according to an embodiment of the invention. The electrosurgical instrument 200 may, for example, correspond to the instrument 12 described above. The electrosurgical instrument 200 comprises a transmission line in the form of a coaxial feed cable 202, that is connectable at its proximal end to a generator (such as generator unit 14) in order to convey microwave EM energy and / or RF EM energy. The coaxial feed cable 202 comprises an inner conductor 204 and an outer conductor 206 which are separated by a dielectric material 208. The coaxial feed cable 202 is preferably low loss for microwave energy. A choke (not shown) may be provided on the coaxial feed cable 202 to inhibit back propagation of microwave energy reflected from the distal end on the outside of the cable and therefore limit backward heating along the outside of the coaxial cable 202. The coaxial cable further includes a flexible outer sheath 210 disposed around the outer conductor 206 to protect the coaxial cable. The outer sheath 210 may be made of an insulating material to electrically isolate the outer conductor 206 from its surroundings. The outer sheath 210 may be made of, or coated with, a non-stick material such as PTFE to prevent tissue from sticking to the instrument.

[0116] An instrument tip 212 is provided at a distal end of the coaxial feed cable 202. The instrument tip 212 comprises a bipolar antenna structure formed by a first electrode 214 and a second electrode 216 which extend alongside one another in a longitudinal direction of the instrument tip 212. The first electrode 214 and the second electrode 216 are separated by a dielectric material 218 of the instrument tip 212, such that they are electrically isolated from one another. The first electrode 214 and the second electrode 216 may be formed by respective elongate conductors, such as strips or wires of conductive material. Other elongate shapes may also be used for the first and second electrodes 214, 216. The first and second electrodes 214, 216 may be located on and / or in the dielectric material 218. For example, the first and second electrodes 214, 216 may be embedded within the dielectric material 218. In other cases, the first and second electrodes 214, 216 may be exposed on an outer surface of the dielectric material 218. Where the first and second electrodes 214, 216 are exposed on an outer surface of the dielectric material 218, they may be used to deliver RF EM energy to tissue. The dielectric material 218 may form at least part of a tip body of the instrument tip 218. Any suitable electrically insulating material may be used as the dielectric material 218, such as a ceramic material (e.g. alumina) or silicone.

[0117] The first electrode 214 is electrically connected to the inner conductor 204, and the second electrode is electrically connected to the outer electrode 206. In this manner, EM energy conveyed by the coaxial feed cable 202 is received by the bipolar antenna structure comprising the first and second electrodes 214, 216, with the bipolar antenna structure being arranged to deliver the EM energy to tissue located at the instrument tip 212. In the example shown, the instrument tip 212 and bipolar antenna structure are provided directly at the distal end of the coaxial feed cable 202. However in other examples a connection interface may be provided between the distal end of the coaxial feed cable 202 and the instrument tip 212, to facilitate mounting the instrument tip 212 on the distal end of the coaxial feed cable 202 and forming the required electrical connections.

[0118] The first electrode 214 and the second electrode 216 are configured as a leaky (lossy) transmission line for microwave EM energy, such that microwave EM energy can be emitted along the length of the bipolar antenna structure into tissue contacting the instrument tip 212. In this manner, when the instrument tip contacts target tissue, microwave EM energy received from the coaxial feed cable 202 travels along the first and second electrodes 214, 216, and a portion of the energy is absorbed by the target tissue. The instrument 200 may be operated in a travelling wave mode, where all of the microwave EM energy is emitted (used up) by the time the microwave signal reaches the distal end of the first and second electrodes 214, 216. Alternatively, the instrument 200 may be operated in a standing wave mode where there is some energy remaining when the microwave signal reaches a distal end of the bipolar antenna structure, resulting in reflection of the remaining power at the distal end of the bipolar antenna structure. For example, tissue may only contact part of the length of the instrument tip 212, such that not all of the microwave EM energy may be absorbed by the tissue before the energy reaches the distal end. Interaction between incident and reflected microwave EM energy can thus produce a standing wave in the bipolar antenna structure. Such a standing wave in the instrument tip 212 results in variations in the microwave energy delivery profile along the length of the instrument tip 212.

[0119] The instrument tip 212 further includes a reactive unit 220 electrically connected between the first electrode 214 and the second electrode 216. In the example shown, the reactive unit 220 includes an inductor 222 and a capacitor 224 connected in series between the first electrode 214 and the second electrode 216. However, in other examples, only the inductor 222 or the capacitor 224 may be provided. The reactive unit 220 is connected in a distal end region of the bipolar antenna structure, near distal ends of the first and second electrodes 214, 216. In some cases, the reactive unit 220 may be connected at the distal end of one or both of the first and second electrodes 214, 216. The reactive unit 220 serves to control the microwave energy delivery profile of the instrument tip 212, as discussed further below.

[0120] Figs. 3 and 4 show examples of microwave energy delivery profiles in standing wave mode along the length of the bipolar antenna structure in the instrument tip 212 of the instrument 200. The graphs in Figs. 3 and 4 show a proportion of power from the microwave signal absorbed by tissue contacting the instrument tip 212, as a function of longitudinal position along the bipolar antenna structure (i.e. along the length of the first and second electrodes 214, 216). The bipolar antenna structure has a length L. The microwave EM energy conveyed to the instrument tip may be in the form of a pure sine wave, e.g. in a frequency range between 2 GHz and 3 GHz. In the examples of Figs. 3 and 4, the length L of the bipolar antenna structure corresponds to approximately a quarter of a wavelength A of the microwave EM energy. For example, where the microwave EM energy has a frequency of 2.45 GHz, the wavelength in the bipolar antenna structure may be approximately 70 mm (depending on the dielectric constant and shape of the dielectric material 218). Accordingly, the bipolar antenna structure may have a length L of approximately 17.5 mm.

[0121] Fig. 3 shows an example of the microwave energy delivery profile where the reactive unit 220 is arranged to appear as an open circuit in the distal end region between the first electrode 214 and the second electrode 216. This may be achieved, for example, using a relatively high inductance inductor 222 (e.g. 10 nH or more), and / or using a relatively low capacitance capacitor 224 (e.g. 1 pF or less). In this manner, the reactive unit 220 may produce an open circuit between the first and second electrodes 214, 216 at low frequencies. Alternatively, a similar effective could be provided by omitting the reactive unit 220, with the dielectric material 218 providing the open circuit between the first and second electrodes 214, 216.

[0122] As shown in Fig. 3, where the reactive unit 220 is arranged to appear as an open circuit between the distal ends of first and second electrodes 214, 216, there is a maximum in the proportion of power absorbed at the distal end (position L in the graph) of the bipolar antenna structure. The proportion of power absorbed decreases away from the distal end, to a minimum at the proximal end of the bipolar antenna structure (which is a quarter wavelength away from the distal end). Accordingly, a treatment effect of the microwave EM energy will be highest at the distal end, as that is where a largest proportion of the microwave EM energy is absorbed by tissue. In contrast, the treatment effect will be lower towards the proximal.

[0123] Fig. 4 shows an example, of the microwave energy delivery profile where the reactive unit 220 presents a reactance equal in magnitude to the impedance of the bipolar antenna structure formed by the first and second electrodes 214, 216. As shown, an effect of such an arrangement is to shift the maximum of the energy delivery profile away from the distal end and towards the proximal end. In the example of Fig. 4, the capacitance and / or inductance of the reactive unit are selected to shift the position of the maximum of the energy delivery profile approximately an eighth of the wavelength A from the distal end of the bipolar antenna structure, such that the maximum is located near a middle of the bipolar antenna structure (with respect to the longitudinal direction). As a result, the treatment effect of the microwave EM energy will be highest towards the middle of the bipolar antenna structure, and lowest towards the proximal and distal ends. Overall, uniformity of the energy delivery profile is increased compared to the configuration shown in Fig. 3. In particular, the configuration of Fig. 4 enables microwave energy to be absorbed by tissue along the entire length of the bipolar antenna structure.

[0124] To shift the position of the maximum of the energy delivery profile approximately an eighth of the wavelength A from the distal end of the bipolar antenna structure, the reactance of the reactive unit 220 is set to equal the impedance of the bipolar antenna structure. Thus, the sum of the inductive and capacitive reactances of the reactive unit 220 is equal to the impedance of the bipolar antenna structure. For example, the inductance L and capacitance C of the reactive unit 220 can be determined using the equation 2nfL - Z, where f is the frequency of the microwave EM energy and Z is the impedance of the bipolar antenna structure.

[0125] As another example, where the reactive unit 220 is arranged to appear as a short circuit in the distal end region between the first electrode 214 and the second electrode 216, the energy delivery profile may be shifted relative to that shown in Fig. 3. In particular, such an arrangement would result in an energy delivery profile that is a left-right reflection of the one shown in Fig. 3, i.e. such that there is a minimum at the distal end and a maximum at the proximal end. In other words, the energy delivery profile would be shifted by a quarter wavelength in the distal direction relative to Fig. 3.

[0126] In some cases, the reactive unit 220 may have a variable reactance, which enables the position of the maximum in the microwave energy delivery profile to be moved along the length of the bipolar antenna structure, as indicated by the arrows in Fig. 4. In particular, by varying the reactance of the reactive unit 220, the microwave energy delivery profile may be continuously adjusted between the profiles illustrated in Figs. 3 and 4. This enables uniformity of the microwave energy delivery profile to be adjusted. Moreover, the maximum of the microwave energy delivery profile can be swept along the length of the bipolar antenna structure, so as to provide effective treatment of tissue along the entire length of the bipolar antenna structure. As an example, the reactive unit 220 may comprise a variable inductor and / or a variable capacitor (e.g. a varactor diode). The reactive unit 220 may be connected to a control wire which extends along the coaxial feed cable 202 (e.g. within the instrument channel of the flexible shaft 22) to a proximal end of the instrument. In this manner, a control signal may be transmitted along the control wire for controlling (adjusting) the reactance of the reactive unit 220. For example, the control wire may transmit a control voltage for setting a capacitance of a varactor diode. The control wire may, for example, be connected to the handpiece 20 or other suitable interface, which enables a user to adjust the value of the reactance, in order to adjust the microwave energy delivery profile. Where a varactor diode is used, it may also be possible to control the capacitance using a low frequency (nominally DC) control signal applied to the first and second electrodes 214, 216, such that a separate control wire may not be needed.

[0127] As noted above, the reactive unit 220 may include one or both of the inductor 222 and the capacitor 224. Where the capacitor 224 is used, this may enable the instrument 200 to further be used for delivering RF EM energy to tissue. In particular, the capacitor 224 may serve to prevent conduction of RF EM energy between the first and second electrodes 214, 216 via the reactive unit 220. In this manner, when RF EM energy is delivered to the first and second electrodes 214, 216, an RF current can be passed through tissue contacting the first and second electrodes 214, 216.

[0128] The capacitor 224 may be selected to have a self-resonant frequency below the frequency of the microwave EM energy. For example, the capacitor 224 may have a self-resonant frequency below 2 GHz. In this manner, when microwave EM energy is conveyed to the bipolar antenna structure, the capacitor 224 is operated above its self-resonant frequency. When the capacitor 224 is operated above its self-resonant frequency, it has an increased inductive effect and so may effectively act as a combination of an inductor and a capacitor. In this manner, the capacitor 224 provides low-frequency isolation to enable use of the instrument with RF EM energy, whilst also providing an inductive effect to shift the position of the maximum of the energy delivery profile. Accordingly, where the capacitor 224 is operated above its self-resonant frequency, the inductor 222 may not be needed. When the capacitor 224 is operated above its self-resonant frequency, an inductance value of the capacitor 224 will depend on its capacitance value, its self-resonant frequency, and a ratio of the self-resonant frequency to the frequency of the microwave EM energy.

[0129] Figs. 5 to 9 illustrate an electrosurgical instrument 500 according to an embodiment of the invention. The electrosurgical instrument 500 includes a transmission line in the form of a coaxial feed cable 502, which may be configured as described above in relation to the coaxial feed cable 202. An instrument tip comprising a first jaw 504 and a second jaw 506 is mounted at a distal end of coaxial feed cable 502. Fig. 5 shows a perspective view of the instrument tip with the first jaw 504 and the second jaw 506; and Fig. 6 shows a perspective view of instrument 500, where the second jaw 506 is omitted for illustration purposes.

[0130] The first jaw 504 and the second jaw 506 are movable relative to one another between an open position and a closed position. The first jaw 504 and / or the second jaw 506 may pivotably mounted relative to the distal end of the coaxial feed cable 502. For example, the first and second jaws 504, 506 may be arranged such that they can be pivoted relative to one another. In some embodiments, the one of the first and second jaws 504, 506 may be a static jaw that is fixed relative to the distal end of the coaxial feed cable 502, with the other jaw being pivotable or rotatable. Alternatively, both jaws may be pivotably mounted relative to the distal end of the coaxial feed cable 502. A pivot axle (not shown) may be connected to the distal end of the coaxial cable 502, to define a pivot axis. The first jaw 504 and / or the second jaw 506 can pivot around the pivot axis or pivot axle. Any other suitable mechanism for enabling relative movement between the jaws may be used.

[0131] A control wire or actuation rod which extends along the instrument 500 between a proximal end and a distal end may be used for controlling opening and closing of the jaws. The instrument 500 may comprise a converting mechanism which converts longitudinal back-and-forth movement of the control wire or actuation rod into a rotational movement of the first jaw 504 an / or second jaw 506, to enable opening and closing of the jaws. For example, the control wire or actuation rod may extend from the instrument tip to the handpiece 20, which include an handle (or other suitable actuator) for causing longitudinal movement of the control wire or actuation rod.

[0132] The first jaw 504 and the second jaw 506 include inner surfaces which face each other across a gap between the jaws. The first jaw 504 and the second jaw 506 can be used to grip biological tissue (e.g. a blood vessel) therebetween. The first jaw 504 and the second jaw 506 can be used to apply pressure to the biological tissue between the opposing inner surfaces of the jaws and deliver energy from the coaxial feed cable 502 into the tissue.

[0133] The first jaw 504 comprises a bipolar antenna structure with a first electrode 508 and a second electrode 510 that extend alongside one another in a longitudinal direction of the first jaw 504. The first and second electrodes 508, 510 are separated and electrically isolated from one another by a dielectric material 512 in the first jaw 504. The first electrode 508 is electrically connected to the inner conductor of the coaxial feed cable 502, and the second electrode 510 is electrically connected to the outer conductor of the coaxial feed cable 502. Fig. 7 shows a perspective view of the first jaw 504 where the dielectric material 512 is omitted for illustration purposes. Fig. 8 shows a sectional side view of the first jaw 504, where a section is taken in a plane parallel to a longitudinal axis of the first jaw 504 and along a centreline of the first jaw 504. Fig. 9 shows a sectional front view of the first jaw 504, where a section is taken in a plane normal to the longitudinal axis of the first jaw 504. The section of Fig. 9 is taken at a position 515 on the first jaw 504 indicated in Fig. 7.

[0134] As shown in Figs. 7 and 8, and inductor 514 and a capacitor 516 are connected in series between the first electrode 508 and the second electrode 510 in a distal end region of the bipolar antenna structure. Thus, the inductor 514 and the capacitor 516 form a reactive unit similar to the reactive unit 220 described above. The inductor 514 is formed by a piece of conductive wire, such as a silver-coated copper wire (other wire materials may also be used). As an example, the conductive wire may have an outer diameter of about 0.25 mm, and a length of the wire may be about 7 mm. The inductor 514 may, for example, have an inductance around 2.7 nH. A length and diameter of the conductive wire may be selected to provide a desired inductance. The wire may also be coiled to increase its inductance. The conductive wire forming the inductor 514 is connected at a first end to a distal end of the first electrode 508, and at a second end to the capacitor 516. The conductive wire extends in the longitudinal direction of the first jaw 504, in a gap formed between a first side portion 508a and a second side portion 508b of the first electrode. The first and second side portions 508a, 508b of the first electrode 508 extend alongside one another along the inner surface of the first jaw 504, and are joined together by an intermediate portion 508c of conductive material towards a proximal end of the first jaw 504. A gap is formed in a distal region of the first electrode 508 between the first and second side portions 508a, 508b, e.g. by omitting or removing the intermediate portion 508c in the distal region, to accommodate the inductor 514.

[0135] The capacitor 516 is connected between the second end of the inductor 514, and the second electrode 510. As an example, the capacitor may have a capacitance of 3 pF. A position at which the capacitor 516 is connected to the second electrode is spaced in the longitudinal direction from the distal end of the first electrode 508 (where the inductor 514 is connected). Thus, the reactive unit (made up of the inductor 514 and the capacitor 516) extends in the longitudinal direction, which may contribute to minimising an extend of the reactive unit in a lateral direction.

[0136] As shown in Fig. 9, the second electrode 510 is in the form of a conductive shell, defining a channel (or groove). The dielectric material 512 fills the channel and the space between the first and second electrodes 508, 512, such that the inductor 514 and the capacitor 516 are embedded within the dielectric material 512. The dielectric material 512 may also be arranged to cover part of an outer surface of the conductive shell, so that the conductive shell is partly embedded within the dielectric material 512. As an example, the dielectric material 512 may be a silicone material which is moulded around parts of the first and second electrodes 508, 512. As shown, the first electrode 508 may include a series of holes 518 which are filled with the dielectric material 512, so as to enhance a grip between the dielectric material and the first electrode 508. Similar holes may also be provided in the second electrode 510. The first electrode 508 and the second electrode 510 form a bipolar antenna structure which acts as a leaky (lossy) transmission line for microwave EM energy. The bipolar antenna structure of the instrument 500 therefore operates in an analogous manner to the bipolar antenna structure of the instrument 200 described above. In particular, the reactive unit (made up of the inductor 514 and the capacitor 516) acts to control the microwave energy delivery profile, e.g. by shifting a maximum of the energy delivery profile. For instance where the first jaw 504 has a length of approximately one quarter of a wavelength (around 17.5 mm at 2.45 GHz), and using around 2.7 nH for the inductor 514 and 3 pF for the capacitor 516, a maximum of the energy delivery profile may be shifted towards a middle of the first jaw 504 (e.g. as illustrated in Fig. 4).

[0137] Furthermore, in line with the above discussion, the capacitor 516 may be a variable capacitor (e.g. varactor diode). Additionally, the inductor 514 may be implemented using a variable inductor instead of the conductive wire shown.

[0138] In some cases, a second antenna structure (not shown) may be provided on the second jaw 506. The second antenna structure may have a similar structure to the bipolar antenna structure on the first jaw 504, or alternatively a different antenna structure may be used. The second antenna structure may be electrically isolated from the bipolar antenna structure on the first jaw 504. For instance, the second antenna structure may not be connected the coaxial feed cable 502. This may result in coupling of microwave EM energy from the first jaw 504 with the second antenna structure in the second jaw 506, which can improve effectiveness of microwave energy delivery to tissue located between the jaws 504, 506. The second antenna structure may not be connected to any transmission line for receiving EM energy from a generator. Alternatively, a second coaxial feed cable (not shown) may be connected to the second antenna structure, to enable delivery of EM energy from both jaws 504, 506. Otherwise, the antenna structures in both jaws may be connected to receive EM energy from the same coaxial feed cable 502.

[0139] 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.

[0140] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0141] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0142] 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. 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 for delivering electromagnetic (EM) energy to biological tissue, the instrument comprising: a transmission line for conveying microwave EM energy; and an instrument tip at a distal end of the transmission line, the instrument tip comprising a bipolar antenna structure configured to receive the microwave EM energy from the transmission line and emit the microwave EM energy into biological tissue; wherein the bipolar antenna structure comprises a first electrode and a second electrode, and a reactive unit electrically connected between the first electrode and the second electrode.

2. The electrosurgical instrument of claim 1 , wherein the reactive unit is connected between the first electrode and the second electrode in a distal end region of the bipolar antenna structure.

3. The electrosurgical instrument of claim 2, wherein the reactive unit is connected to one of the first electrode and the second electrode at a distal end of the bipolar antenna structure, and to another one of the first electrode and the second electrode at a location spaced in a longitudinal direction from the distal end of the bipolar antenna structure.

4. The electrosurgical instrument of claim 2 or 3, wherein the reactive unit is connected between the first electrode and the second electrode within an eighth of a wavelength of the microwave EM energy from a distal end of the bipolar antenna structure.

5. The electrosurgical instrument of any preceding claim, wherein the reactive unit comprises an inductor.

6. The electrosurgical instrument of claim 5, wherein the inductor comprises a wire extending in a longitudinal direction of the instrument tip.

7. The electrosurgical instrument of claim 6, wherein the first electrode comprises a first side portion and a second side portion extending in the longitudinal direction, and the wire extends within a gap between the first side portion and the second side portion.

8. The electrosurgical instrument of any preceding claim, wherein the reactive unit comprises a capacitor.

9. The electrosurgical instrument of claim 8 and one of claims 5 to 7, wherein the inductor and the capacitor are connected in series between the first electrode and the second electrode.

10. The electrosurgical instrument of claim 8 or 9, wherein the capacitor has a self-resonant frequency below a frequency of the microwave EM energy.

11. The electrosurgical instrument of one of claims 8 to 10, where a capacitance of the capacitor is equal to or greater than 100 pF.

12. The electrosurgical instrument of any preceding claim, wherein the reactive unit has a variable reactance.

13. The electrosurgical instrument of any preceding claim, wherein a length of the bipolar antenna structure corresponds to a quarter wavelength of the microwave EM energy or less.

14. The electrosurgical instrument of any preceding claim, wherein the second electrode forms a conductive shell of the instrument tip.

15. The electrosurgical instrument of any preceding claim, wherein the reactive unit is embedded in the dielectric material of the instrument tip.

16. The electrosurgical instrument of any preceding claim, wherein: the instrument tip comprises a first jaw and a second jaw; the first jaw and the second jaw are movable between an open position, in which biological tissue can be inserted between the first surface and the second surface, and a closed position, in which the first and second surfaces are brought together to clamp the biological tissue therebetween; and the bipolar antenna structure is provided on the first jaw.

17. The electrosurgical instrument of claim 16, further comprising a second antenna structure on the second jaw.

18. An electrosurgical system for delivering electromagnetic (EM) energy to biological tissue, the system comprising: a generator for generating microwave EM energy; and the electrosurgical instrument according to any preceding claim, wherein the transmission line is configured to convey the microwave EM energy from the generator to the bipolar antenna structure.

19. An electrosurgical system according to claim 18, wherein the microwave EM energy has a frequency between 400 MHz and 15 GHz.

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