ELECTROSURGICAL APPARATUS FOR TREATING BIOLOGICAL TISSUE WITH MICROWAVE ENERGY

Abstract

Various embodiments provide an electrosurgical apparatus for treating biological tissue with microwave energy. The apparatus comprises: a microwave energy signal generator for generating a microwave energy waveform; an electrosurgical instrument arranged to deliver the microwave energy waveform from a distal end thereof for tissue treatment; and a controller in communication with the microwave energy signal generator. The microwave energy signal generator is configured to deliver the microwave energy waveform as one microwave energy signal pulse. The controller is configured to control the profile of the one microwave energy signal pulse to cause ablation or coagulation of the biological tissue and to substantially prevent the one pulse from causing heat to build-up in the electrosurgical instrument.

Claims

1.-33. (canceled)

34. An electrosurgical apparatus for treating biological tissue with microwave energy, the apparatus comprising: a microwave energy signal generator for generating a microwave energy waveform; an electrosurgical instrument arranged to deliver the microwave energy waveform from a distal end thereof for tissue treatment; a controller in communication with the microwave energy signal generator; the microwave energy signal generator being configured to deliver the microwave energy waveform as one microwave energy signal pulse, and the controller being configured to control the profile of the one microwave energy signal pulse to cause ablation or coagulation of the biological tissue and to substantially prevent the one pulse from causing heat to build-up in the electrosurgical instrument, wherein the controller is configured to control the profile of the one pulse such that a peak power of the one pulse is maintained at or above a peak power minimum which is set to cause ablation or coagulation of the biological tissue during the one microwave energy signal pulse, the peak power minimum being 500 W, and wherein at least one of the following applies: (a) the controller is configured to control the profile of the one pulse such that a duration of an ON portion of the one pulse is maintained at or below an ON portion duration limit which is set to substantially prevent the microwave energy waveform from causing dielectric heating of the electrosurgical instrument during the one pulse, the ON portion duration limit being 1 s; (b) the controller is configured to control the profile of the one pulse such that a duty cycle of the one pulse is maintained at or below a duty cycle limit which is set such that heat which the microwave energy waveform causes to be built up in the electrosurgical instrument during an ON portion of the one pulse substantially dissipates during an OFF portion of the one pulse.

35. The electrosurgical apparatus of claim 34, wherein the controller is configured to control the profile of the one pulse such that an energy of the one microwave energy signal pulse is maintained at or above an energy minimum which is set to cause ablation or coagulation of the biological tissue during the one microwave energy signal pulse.

36. The electrosurgical apparatus of claim 35, wherein the energy minimum is 1 kJ.

37. The electrosurgical apparatus of claim 34, wherein the peak power minimum is any one of the following: 1 kW, 10 kW, 1 MW, 5 MW.

38. The electrosurgical apparatus of claim 34, wherein the ON portion duration limit is any one of the following: 0.1 s, 1 ms, 0.2 ms.

39. The electrosurgical apparatus of claim 34, wherein at least one of the following applies: (a) the duty cycle limit is 10%, (b) the ON portion has a duration of between 10 μs to 200 μs.

40. The electrosurgical apparatus of claim 37, wherein the energy minimum is 1 kJ, and wherein: the microwave energy signal generator is configured to deliver the microwave energy waveform as a plurality of microwave energy signal pulses, and the controller is configured to control the profile of the plurality of microwave energy signal pulses to form a plurality of bursts of pulses, wherein an energy of each burst is maintained at or above the energy minimum.

41. The electrosurgical apparatus of claim 40, wherein at least one of the following applies: (a) each burst has a burst duty cycle of up to 40%, (b) each burst has a burst ON portion duration of up to 200 ms.

42. The electrosurgical apparatus of claim 34, wherein the electrosurgical instrument comprises: a coaxial cable for conveying the microwave energy waveform, the coaxial cable having an inner conductor, an outer conductor, and a first dielectric material separating the inner conductor and the outer conductor; and a radiating tip portion disposed at a distal end of the coaxial cable to receive the microwave energy waveform from the coaxial cable and to radiate a localized microwave field for tissue treatment.

43. The electrosurgical apparatus of claim 42, wherein the radiating tip portion comprises: a dielectric tip, and a distal conductive portion of the inner conductor, which extends longitudinally into the dielectric tip.

44. The electrosurgical apparatus according to claim 43, wherein the outer diameter of the coaxial cable and radiating tip portion is equal to or less than 2.5 mm.

45. The electrosurgical apparatus of claim 42, wherein the radiating tip portion comprises two conductive elements separated by an insulator, and wherein one conductive element is connected to the inner conductor of the coaxial cable and the other conductive element is connected to the outer conductor of the coaxial cable.

46. The electrosurgical apparatus of claim 42, wherein the radiating tip portion comprises a helical antenna.

47. The electrosurgical apparatus of any of claim 42, wherein the radiating tip portion is arranged to act as a quarter wave impedance transformer to match an input impedance to a tissue load impedance.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0047] Examples of the invention are described in more detail below with reference to the accompanying drawings, in which:

[0048] FIG. 1A is a schematic diagram of an electrosurgical apparatus with which the present invention can be used;

[0049] FIG. 1B is a graphical representation of a microwave energy waveform in accordance with an embodiment;

[0050] FIG. 1C is a graphical representation of a microwave energy waveform in accordance with another embodiment;

[0051] FIG. 2 is a schematic system diagram of an electrosurgical system in accordance with an embodiment;

[0052] FIG. 3 is a longitudinal cross section of an electrosurgical instrument that can be used in embodiments of the invention;

[0053] FIG. 4A is a longitudinal cross section of a simulation of the radiation absorption pattern produced by the electrosurgical instrument of FIG. 3;

[0054] FIG. 4B is an axial cross section of a simulation of the radiation absorption pattern produced by the electrosurgical instrument of FIG. 3;

[0055] FIG. 5 is a longitudinal cross section of an electrosurgical instrument that is another embodiment of the invention; and

[0056] FIG. 6 is a longitudinal cross section of a simulation of the radiation absorption pattern produced by the electrosurgical instrument of FIG. 5; and

[0057] FIG. 7 is a flow diagram illustrating a method of treating a tumour by controlling microwave energy delivered from an electrosurgical instrument into a biological tissue in accordance with an embodiment.

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES

[0058] FIG. 1A is a schematic diagram of a complete electrosurgery apparatus 100 that is capable of supplying microwave energy to the distal end of an invasive electrosurgical instrument. The apparatus 100 may also be capable of supplying fluid, e.g. cooling fluid, to the distal end. The apparatus 100 comprises a generator 102 for controllably supplying microwave energy. A suitable generator for this purpose is described in WO 2012/076844, which is incorporated herein by reference. The generator may be arranged to deliver a microwave energy waveform as one or more microwave energy signal pulses. A controller in communication with the generator is configured to control the profile of the one or more microwave energy signal pulses such that, firstly, the pulses cause ablation or coagulation of biological tissue, that is, the one or more pulses have sufficient energy to cause ablation or coagulation. Also, secondly, the controller is configured to control the profile of the one or more microwave energy signal pulses to substantially prevent the or each pulse from causing heat to build-up in the electrosurgical instrument, that is, each pulse is shaped so that it does not leave an appreciable amount of unwanted heat in the instrument once the pulse is complete. A power amplifier of the generator 102 may be specifically selected to enable the generator to deliver such pulses, for example, the power amplifier may be a power amplifier usually used in radar applications. The controller may form part of the generator 102 or may be housed in the same physical unit as the generator 102.

[0059] The generator 102 is connected to an interface joint 106 by an interface cable 104. The interface joint 106 may also be connected to receive a fluid supply 107 from a fluid delivery device 108, such as a syringe. If needed, the interface joint 106 can house an instrument control mechanism that is operable by sliding a trigger 110, e.g. to control longitudinal (back and forth) movement of one or more control wires or push rods (not shown). If there is a plurality of control wires, there may be multiple sliding triggers on the interface joint to provide full control. The function of the interface joint 106 is to combine the inputs from the generator 102, fluid delivery device 108 and instrument control mechanism into a single flexible shaft 112, which extends from the distal end of the interface joint 106.

[0060] The fluid delivery device 108, the interface cable 104, and the instrument control mechanism are optional.

[0061] The flexible shaft 112 is insertable through the entire length of an instrument (working) channel of a scoping device 114 (e.g. a bronchoscope, endoscope, or laparoscope).

[0062] The flexible shaft 112 has a distal assembly 118 (not drawn to scale in FIG. 1A) that is shaped to pass through the instrument channel of the scoping device 114 and protrude (e.g. inside the patient) at the distal end of the scoping device's tube. The distal end assembly includes an active tip for delivering or radiating microwave energy into biological tissue. The tip configuration is discussed in more detail below.

[0063] The structure of the distal assembly 118 discussed below may be particularly designed for use with a conventional steerable flexible scoping device, whereby the maximum outer diameter of the distal assembly 118 is equal to or less than 2.5 mm, and preferably less than 1.9 mm (and more preferably less than 1.5 mm or even more preferably less than 1 mm) and the length of the flexible shaft can be equal to or greater than 1.0 m, e.g. 1.5 m, 2 m, 2.5 m, etc.

[0064] The apparatus described above is one way of introducing the instrument. Other techniques are possible. For example, the instrument may also be inserted using a catheter.

[0065] The invention seeks to provide an instrument that can travel inside a blood vessel (e.g. vein or artery) and deliver microwave energy to tissue from within the blood vessel, particularly to tissue at a region where a tumour joins to the blood vessel or to tissue inside the tumour itself. For example, the instrument may be used to treat (e.g. ablate or coagulate) tissue at a join or junction between the blood vessel and the tumour to cut-off blood supply to the tumour and, possibly, to detach the tumour from the blood vessel. Additionally or alternatively, the instrument may be used to enter inside the tumour from inside the blood vessel and to deliver microwave energy when inside the tumour. In order for side effects to be reduced and the efficiency of the instrument to be maximised, the transmitting antenna should be located as close to the target tissue as possible. In order to reach the target site, the instrument will need to be guided through the airways and around obstacles. This means that the instrument will ideally be flexible and have a small cross section. Particularly, the instrument should be very flexible near the antenna where it needs to be steered along blood vessels which can be narrow and winding. The size of the antenna part of the instrument should also be reduced where possible to allow the antenna to work properly in small locations and increase flexibility of the instrument when components of the antenna are rigid. The instrument may comprise two coaxial transmission lines arranged in series, with a proximal coaxial transmission line having a greater outer diameter than a distal coaxial transmission line. The outer diameter of the proximal coaxial transmission line may be equal to or greater than 2 mm and the outer diameter of the distal coaxial transmission line may be equal to or less than 1.5 mm, e.g. 1.2 mm. The proximal coaxial transmission line may extend along the majority of the flexible shaft. For example, proximal coaxial transmission line may have a length of 1 m or more and the distal coaxial transmission line may have a length equal to or less than 0.3 m. This arrangement can ensure that more microwave power is delivered into the tissue without the proximal coaxial transmission line getting too hot.

[0066] As mentioned above, the generator 102 is controlled (e.g. by a controller) to deliver one or more microwave energy signal pulses which cause ablation or coagulation of biological tissue, wherein the or each pulse is arranged to substantially prevent or avoid causing heat to build-up in the electrosurgical instrument. Two different techniques for avoiding this heat build-up will now be described with reference to FIGS. 1B and 1C.

[0067] As seen in FIG. 1B, the generator 102 can be controlled to deliver microwave energy as one or more microwave energy signal pulses. FIG. 1B only illustrates a single pulse, but it is to be understood that in some other embodiments multiple pulses may be combined into a series or train of pulses. Specifically, a profile of the one or more microwave energy signal pulses is controlled (i) to cause ablation or coagulation of the biological tissue, and (ii) to substantially prevent the or each pulse from causing heat to build-up in the electrosurgical instrument. Regarding requirement (i), where only a single pulse is provided (e.g. as in FIG. 1B), the pulse profile is controlled so that the energy delivered by this single pulse is at or above an energy minimum which is set to cause ablation or coagulation of the biological tissue during that pulse. This energy minimum may be 1 kJ. Since energy is a function of power and time, in order to achieve this energy minimum, a peak pulse power of the pulse may be maintained at or above a peak power minimum which is set to cause ablation or coagulation of the biological tissue during that pulse. Additionally or alternatively, an ON portion of the pulse may be maintained at or above an ON portion duration minimum which is set to cause ablation or coagulation of the biological tissue during the pulse. On the other hand, where multiple pulses are provided (e.g. a series of the pulse shown in FIG. 1B) the multiple pulses as a whole combine to deliver energy at or above the energy minimum, i.e. enough energy to cause ablation or coagulation, but each individual pulse on its own may not deliver enough energy to cause ablation or coagulation. Therefore, where multiple pulses are used the peak power minimum (and ON portion duration minimum) per pulse may be less than a case where a single pulse is used because the minimum energy requirement can be spread over multiple pulses rather than being provided by a single pulse. Regarding requirement (ii), regardless of whether or not a single pulse or multiple pulses are used, the profile of each pulse is controlled so that a duration of the ON portion of that pulse is maintained at or below a first ON portion duration limit which is set to substantially prevent that pulse from causing dielectric heating of the electrosurgical instrument. Therefore, for a single pulse to satisfy requirements (i) and (ii), the energy delivered by that single pulse must be greater than or equal to the energy minimum to cause ablation or coagulation, but the ON portion of that single pulse must be shorter than the first ON portion duration limit so as to avoid dielectric heating of the instrument. On the other hand, for a series of pulses to satisfy requirements (i) and (ii), the combined energy delivered by the series of pulses must be greater than or equal to the energy minimum so that the series of pulses as a whole cause ablation or coagulation, but the ON portion of each pulse in the series must be shorter than the first ON portion duration limit so as to avoid dielectric heating of the instrument.

[0068] In an embodiment, the energy minimum is 1 kJ. Also, the peak power minimum and first ON portion duration limit, respectively, may be any of the following: 1 kW and 1 s; 10 kW and 0.1 s; 1 MW and 1 ms; and, 0.2 ms and 5 MW.

[0069] As seen in FIG. 10, the generator 102 can be controlled to deliver the microwave energy as multiple microwave energy signal pulses. It is to be understood that in some embodiments (e.g. as shown in FIG. 10), the microwave energy may be delivered as one or more bursts of pulses, i.e. where the multiple pulses are grouped into bursts (or burst periods) having an burst ON portion (with pulse ON portions) and a burst OFF portion (without pulse ON portions). However, in some other embodiments, the microwave energy may be delivered as a single series or train of pulses (which may be analogous to a single burst ON portion, as shown in FIG. 10). It is to be understood, that each burst and the series/train of pulses can be made up of any number of pulses, including a single pulse. In any case, a profile of each pulse is controlled to keep the combined energy delivered by the multiple microwave energy signal pulses at or above an energy minimum which causes ablation or coagulation of the biological tissue during the multiple microwave energy signal pulses. As before, each pulse may be controlled based on a peak power minimum and/or an ON portion duration minimum to ensure that the multiple pulses deliver at least the energy minimum. For instance, the energy of all the pulses in a single burst (or the complete series/train of pulses) combine together to meet or exceed the energy minimum such that each burst (or the complete series/train of pulses) causes ablation or coagulation, but each individual pulse within that burst (or complete series) may not have sufficient energy to cause ablation or coagulation. Also, the profile of each pulse (i.e. each pulse in the burst or each pulse in the series/train) is controlled to keep a duty cycle of that pulse at or below a duty cycle limit which is set such that heat which the microwave energy waveform causes to be built up in the electrosurgical instrument during an ON portion of that pulse substantially dissipates during an OFF portion of that pulse. It is to be understood that heat dissipation includes the process by which an object that is hotter than other objects is placed in an environment where the heat of the hotter object is transferred to the colder objects and the surrounding environment. Heat dissipation can include conduction, convention and/or radiation.

[0070] In an embodiment, instead of or in addition to controlling the duty cycle, the profile of each pulse is controlled to keep the ON portion duration of that pulse at or below a second ON portion duration limit which is set such that heat which the microwave energy waveform causes to be built up in the electrosurgical instrument during the ON portion of that pulse is substantially dissipated during the OFF portion of that pulse. Also, instead of controlling the ON portion duration (via the second ON portion duration limit), the profile of each pulse is controlled such that a pulse period of the or each pulse is maintained at or below a pulse period limit which is set such that heat which the microwave energy waveform causes to be built up in the electrosurgical instrument during the ON portion of that pulse is substantially dissipated during the OFF portion of that pulse.

[0071] Accordingly, by controlling the duty cycle (and/or ON portion duration limit or pulse period) a profile of the one or more microwave energy signal pulses is controlled (i) so that the one or more pulses cause ablation or coagulation of the biological tissue, and (ii) to substantially prevent the or each pulse from causing heat to build-up in the electrosurgical instrument. Compared to the embodiment of FIG. 1B, the mechanism by which unwanted heat build-up in the instrument is avoided is different. That is, in FIG. 1B, unwanted heat build-up of the instrument is avoided because the ON portion duration of the or each pulse is below a threshold at which appreciable dielectric heating of the instrument occurs. On the other hand, in FIG. 1C, unwanted heat build-up of the instrument is avoided because the duty cycle (and/or ON portion duration limit or pulse period) is configured so that any unwanted heat which builds up in the instrument during the pulse ON portion (e.g. due to dielectric heating) dissipates during the pulse OFF portion.

[0072] In one example, as diagrammatically represented by FIG. 1C, the microwave energy is delivered with a pulse duty cycle of 10% (e.g. a duty cycle limit of 10%). Also, each pulse has a 2 ms pulse period consisting of a 200 μs ON portion and a 1800 μs OFF portion. In this manner, the ON portion duration limit is 200 μs. Hence, the individual pulses have a relatively low duty cycle, i.e. the ON portion duration is small compared to the OFF portion duration. Also, the microwave energy can be delivered such that each ON portion has a power of 1 kW (e.g. a peak power minimum of 1 kW). In this way, each pulse delivers 0.2 J of energy, and in 1 second, 500 pulses are delivered which combine to deliver 100 J of energy. Hence, the ON portion of individual pulses has a high power relative to typical electrosurgical applications (i.e. the pulse has a high peak power), but the average pulse power is much lower (e.g. only 10% of the peak power). The high peak power enables ablation or coagulation to occur, but the lower average power ensures that unwanted equipment and patient heat damage is avoided because heat built-up during each pulse ON portion dissipates during that pulse's OFF portion. Furthermore, the pulses may be arranged into bursts, having a burst period made up from a burst ON portion and a burst OFF portion. In an example, the burst period is 25 ms with a burst ON portion of 10 ms and a burst OFF portion of 15 ms (i.e. a burst duty cycle of 40%). In this way, each burst ON portion contains 5 pulses so that each burst delivers 1 J of energy. However, it is to be understood that in different embodiments, the burst period and burst duty cycle may be different. An advantage of the bursts is that the burst OFF portion further limits unwanted thermal heating in the electrosurgical instrument and patient caused by the microwave energy. It is to be understood, that a single burst may deliver enough energy to cause coagulation, but multiple bursts may be required to deliver enough energy to cause ablation.

[0073] In summary, there are many advantages of delivering power as described above with reference to FIGS. 1B and 1C. Firstly, one or more microwave energy signal pulses may be delivered to biological tissue to cause ablation or coagulation in the tissue. Secondly, each pulse may be specially configured so as to avoid causing unwanted heat to build up in the electrosurgical instrument by avoiding dielectric heating of the instrument. Thirdly, each pulse may be specially configured so as to avoid causing unwanted heat to build up in the electrosurgical instrument by ensuing that any unwanted heat generated in the electrosurgical instrument during the ON portion of that pulse is dissipated during the OFF portion of that pulse. As such a result of these advantages, ablation and coagulation can be performed at the treatment site without causing significant temperature rises elsewhere in the patient's body, and without requiring active cooling mechanisms. This is particularly important when the distal assembly and its cable are intended to be located inside a blood vessel, where even small amounts of heating can have a negative impact on patient wellbeing.

[0074] The cable for delivering the microwave radiation to the target site should be low-loss, have a small cross-section and be flexible. The cable should be low loss to avoid or reduce heating during treatment and so that there is enough power at the distal end to produce the desired radiation from the antenna.

[0075] If the cable is not separated from the body by the use of a sealed scoping device, catheter or other protective sheath, then the cable should be made of, or be coated with, a biologically inert material to avoid unwanted interaction with the body.

[0076] A preferred cable type is a coaxial cable which is made up of an inner conductor axially surrounded by a dielectric sheath which is in turn axially surrounded by an outer conductor. The radiating portion in an antenna produced from such a cable may be made up of a section of inner conductor and dielectric sheath which protrudes from the end of the outer conductor of the coaxial cable.

[0077] In an embodiment, the outer conductor of the coaxial cable may be as physically thick as possible to increase its thermal mass and heat capacity. In this way, all or a majority of the heat generated in the cable due to conveying microwave energy can be held within the structure of the cable rather than, for example, being leaked inside the patient. In an embodiment, the outer conductor may be 0.5 mm thick.

[0078] The invention also seeks to provide an antenna with a well-defined radiation pattern. It is desirable that a practitioner would be able to select an instrument for the treatment of a specific area of tissue, such that the radiation of target tissue is maximised and the radiation of healthy tissue is minimised. For example, in some circumstances it can be desirable to produce a generally spherically symmetric radiation pattern with a substantially uniform power absorption distribution, so that the amount of radiation received by an area of tissue can be more easily controlled by the practitioner.

[0079] It is also preferable that the instrument can be operated alongside other instruments to enable practitioners to receive information from the target site. For example, a scoping device may aid the steering of the instruments around obstacles within a patient's body. Other instruments may include a thermometer or camera.

[0080] In the following description, unless stated otherwise, the length of a component refers to its dimension in the direction parallel to the longitudinal axis of the coaxial cable.

[0081] FIG. 2 shows an overall system diagram for an electrosurgical apparatus 20 that is an embodiment of the invention. The apparatus 20 comprises a microwave line-up 22 which forms part of a microwave channel.

[0082] The microwave line-up 22 contains components for generating and controlling a microwave frequency electromagnetic signal at a power level suitable for treating (e.g. coagulating or ablating) biological tissue. The microwave line-up 22 of FIG. 2 may form part of the generator 102 of FIG. 1A. In this embodiment, the microwave line-up 22 includes a phase locked oscillator 24, a signal amplifier 26, an adjustable signal attenuator (e.g. an analogue or digital diode attenuator) 28, an amplifier unit (here a driver amplifier 30 and a power amplifier 32), a forward power coupler 34, a circulator 36 and a reflected power coupler 38. The circulator 36 isolates the forward signal from the reflected signal to reduce the unwanted signal components present at the couplers 34, 38, i.e. it increases the directivity of the couplers. Optionally, the microwave line-up 22 includes an impedance matching sub-system having an adjustable impedance. Furthermore, the frequency of the microwave source may be varied around the centre frequency, e.g. 2.45 GHz+/−50 MHz (2.4 GHz to 2.5 GHz) or 5.8 GHz+/−100 MHz (5.7 GHz to 5.9 GHz) or 24.125 GHz+/−125 MHz (24 GHz to 24.25 GHz).

[0083] It is to be understood that the power amplifier 32 is configured to enable generation of pulsed waveforms, as described above with reference to FIGS. 1B and 1C. For example, the power amplifier 32 may be a high-power pulsed radar RFPA unit, such as those sold by RFHIC Corporation. That is, the inventors have surprisingly discovered that using an amplifier designed for radar applications enables to the aforementioned advantages in medical applications.

[0084] The microwave line-up 22 is in communication with a controller 40, which may comprise signal conditioning and general interface circuits 42, a microcontroller 44, and watchdog 46. The controller 40 may form part of the generator 102 of FIG. 1A. The watchdog 46 may monitor a range of potential error conditions, which could result in the apparatus not performing to its intended specification, i.e. the apparatus delivers the wrong dosage of energy into patient tissue due to the output or the treatment time being greater than that demanded by the user. Such a capability is particularly important where a high peak pulse power (e.g. at least 500 W or 1 kW) is being delivered because if this is delivered for longer than intended it could cause damage to the electrosurgical system and the patient. The watchdog 46 comprises a microprocessor that is independent of the microcontroller 44 to ensure that microcontroller is functioning correctly. The watchdog 46 may, for example, monitor the voltage levels from DC power supplies or the timing of pulses determined by the microcontroller 44.

[0085] The controller 40 is operable to accurately enforce a preset pulse duration of microwave energy provided to the instrument (e.g. cable 52 and/or probe 54) and to shut off the microwave energy supply to the instrument at the end of this pulse duration. In an embodiment, the controller 40 may include a shut-off circuit that performs this operation. For example, the shut off circuit may include an integrator coupled to a comparator. In operation, the comparator compares an output from the integrator with a preset threshold that corresponds to a given pulse duration. As the integrator's output accumulates over time this output is compared to the threshold by the comparator and the comparator output changes when the integrator's output reaches the threshold. The microwave supply can be shut off by the controller 40 based on the comparator output. In this way, a mechanism is provided for accurately shutting off the microwave supply at the end of the pulse duration. In an embodiment, the integrator may be clamped, for example, to 5 V. In an embodiment, the shut-off circuit may be part of the watchdog 46.

[0086] The controller 40 is arranged to communicate control signals to the components in the microwave line-up 22. In this embodiment, the microprocessor 44 is programmed to output a microwave control signal C.sub.M for the adjustable signal attenuator 28. This control signal is used to set the energy delivery profile of the microwave EM radiation output from the microwave line-up 22. In particular, the adjustable signal attenuator 28 is capable of controlling the power level of the output radiation. Moreover, the adjustable signal attenuator 28 may include switching circuitry capable of setting the waveform (e.g. pulse energy, pulse peak power, pulse period, pulse duty cycle, pulse ON portion, pulse OFF portion, burst energy, burst period, burst duty cycle, burst ON portion, etc.) of the output radiation. Therefore, the controller 40 can use the control signal C.sub.M to cause the system 20 to deliver a microwave energy waveform according to FIG. 1B or 1C discussed above.

[0087] The microprocessor 44 may be programmed to output the microwave control signal C.sub.M based on forward and reflected power couplers 34, 38. In this embodiment, the microwave generator may be controlled by measurement of phase information only, which can be obtained from the microwave channel (from sampled forward and reflected power information). The forward power coupler 34 outputs a signal S.sub.M1 indicative of the forward power level and the reflected power coupler 38 outputs a signal S.sub.M2 indicative of the reflected power level. The signals S.sub.M1, S.sub.M2 from the forward and reflected power couplers 34, 38 are communicated to the signal conditioning and general interface circuits 42, where they are adapted to a form suitable for passing to the microprocessor 44.

[0088] It is to be understood that outputting the microwave control signal C.sub.M based on forward and reflected power couplers 34, 38 is optional. For example, in some other embodiments, the microprocessor 44 may be programmed to output the microwave control signal C.sub.M in an open loop manner, i.e. without consideration of the forward and reflected power.

[0089] A user interface 48, e.g. touch screen panel, keyboard, LED/LCD display, membrane keypad, footswitch or the like, communicates with the controller 40 to provide information about treatment to the user (e.g. surgeon) and permit various aspects of treatment (e.g. the amount of energy delivered to the patient, or the profile of energy delivery) to be manually selected or controlled, e.g. via suitable user commands. The apparatus may be operated using a conventional footswitch 50, which is also connected to the controller 40. In an embodiment, the user interface 48 and the foot switch 50 may form part of the controller 40.

[0090] The microwave signals produced by the microwave line-up 22 are input to a cable assembly 52 (e.g. a coaxial cable) an onwards to a probe 54 (or applicator). The probe 54 of FIG. 2 may provide the distal assembly 118 of FIG. 1A. The cable assembly 52 allows energy at microwave frequencies to be transmitted to the probe 54, from which it is delivered (e.g. radiated) into the biological tissue of a patient. Example structures of the probe 54 are discussed below.

[0091] The cable assembly 52 also permits reflected energy, which returns from the probe 54, to pass into the microwave line-up 22, e.g. to be detected by the detectors contained therein. The apparatus may include a high pass filter 56 on the microwave channel, so that only a reflected microwave signal enters the microwave line-up 22.

[0092] Finally, the apparatus includes a power supply unit 58 which receives power from an external source 60 (e.g. mains power) and transforms it into DC power supply signals V.sub.1, V.sub.2, V.sub.4, V.sub.5, and V.sub.6 for the components in the apparatus. Thus, the user interface receives a power signal V.sub.1, the microprocessor 110 receives a power signal V.sub.3, the microwave line-up 22 receives a power signal V.sub.4, the signal conditioning and general interface circuits 42 receive a power signal V.sub.5, and the watchdog 46 receives a power signal V.sub.6.

[0093] As mentioned above, a suitable generator for controllably supplying microwave energy is described in WO 2012/076844 and, therefore, the apparatus 20 presents only one possible implementation for generating microwave energy and the other implementations described in WO 2012/076844 are also applicable. However, it is to be understood that the power amplifier of the generator must be capable of generating waveforms in accordance with the present invention (e.g. as per FIG. 1B or 1C).

[0094] FIG. 3 is a longitudinal cross section taken along the axis of a coaxial cable which forms an electrosurgical instrument or tissue ablation antenna 10. The tissue ablation antenna 10 may include the distal assembly 118 of FIG. 1A, or the probe 54 and cable 52 of FIG. 2. The tissue ablation antenna 10 may therefore be used to deliver a microwave energy waveform according to FIGS. 1B and 10 discussed above. The tissue ablation antenna 10 comprises a radiating portion 12. The inner conductor 14 is radially surrounded by a dielectric sheath 16 which is in turn radially surrounded by the outer conductor 18. The inner conductor 14 and the insulating sheath 16 extend beyond a distal end 19 of the outer conductor 18 and the protruding section of inner conductor and insulating sheath forms the radiating portion 12. In this example, the inner conductor 14 is shorter than the insulating sheath 16 so that the end of the insulating sheath 16 forms a cap over the inner conductor 14.

[0095] FIGS. 4A and 4B show longitudinal and axial cross-sections respectively of a radiation pattern simulation for the antenna 10 shown in FIG. 3. It can be seen that the pattern covers an elongated region near the end of the outer conductor 18. It is axially symmetric and is generally strongest at the distal end 19 of the outer conductor 18.

[0096] FIG. 5 is a cross-sectional view of the distal end of an electrosurgical instrument 200 that is an embodiment of the invention. The electrosurgical instrument 200 may include the distal assembly 118 of FIG. 1A, or the probe 54 and cable 52 of FIG. 2. The electrosurgical instrument 200 may therefore be used to deliver a microwave energy waveform according to FIGS. 1B and 10 discussed above. The electrosurgical instrument 200 comprises a coaxial cable 202 that is connected at its proximal end to an electrosurgical generator (not shown) in order to convey microwave energy. The coaxial cable 202 comprises an inner conductor 206, which is separated from an outer conductor 208 by a first dielectric material 210. The coaxial cable 202 is preferably low loss for microwave energy. A choke (not shown) may be provided on the coaxial cable to inhibit back propagation of microwave energy reflected from the distal end and therefore limit backward heating along the device.

[0097] The device may include a temperature sensor at the distal end. For example, in FIG. 5 a thermocouple 230 is mounted on the outer conductor to transmit a signal back to the proximal end that is indicative of temperature at the distal end of the instrument.

[0098] Other techniques for temperature monitoring can be used. For example, one or more micromechanical structures whose physical configuration is sensitive to temperature may be mounted in the distal portion of the device, e.g. in or on the outer sheath discussed below. These structures can be interfaced with an optical fibre, whereby changes in a reflected signal caused by movement of the structure can be indicative of temperature changes.

[0099] The coaxial cable 202 terminates at its distal end with a radiating tip section 204. In this embodiment, the radiating tip section 204 comprises a distal conductive section 212 of the inner conductor 206 that extends beyond a distal end 209 of the outer conductor 208. The distal conductive section 212 is surrounded at its distal end by a dielectric tip 214 formed from a second dielectric material, which is different from the first dielectric material 210. The length of the dielectric tip 214 is shorter than the length of the distal conductive section 212. An intermediate dielectric sleeve 216 surrounds the distal conductive section 212 between the distal end of the coaxial cable 202 and the proximal end of the dielectric tip 214. The intermediate dielectric sleeve 216 is formed from a third dielectric material, which is different from the second dielectric material but which may be the same as the first dielectric material 210.

[0100] In this embodiment, the coaxial cable 202 and radiating tip section 204 have an outer sheath 218 formed over their outermost surfaces. The outer sheath 218 may be formed from a biocompatible material. The outer sheath 218 has a thickness that is small enough to ensure that it does not significantly interfere with the microwave energy radiated by the radiating tip section 204 (i.e. radiating pattern and return loss). In an embodiment, the sheath is made from PTFE, although other materials are also appropriate. The thickness of the wall of the sheath is selected to withstand breakdown voltages equal to or greater than 200 kV/m.

[0101] The purpose of the dielectric tip 214 is to alter the shape of the radiated energy. The second dielectric material is selected to reduce the wavelength of the microwave energy, which results in the radiated energy exhibiting a more spherical radiation pattern. To do this, the second dielectric material preferably has a large dielectric constant (relative permittivity ε.sub.r). The dielectric constant of the second dielectric material is preferably chosen to enable the length of the dielectric tip 214 to be minimised whilst still constituting a non-negligible portion of a wavelength of the microwave energy when it propagates through the second dielectric material. It is desirable for the dielectric tip 214 to be as short as possible in order to retain flexibility in the device, especially if the second dielectric material is rigid. In an embodiment, the dielectric tip 214 may have a length equal to or less than 2 mm. The dielectric constant of the second dielectric material may be greater than 80, and is preferably 100 or more at the frequency of the microwave energy. The second dielectric material may be TiO.sub.2 (titanium dioxide).

[0102] The wavelength of radiation in a material becomes shorter as the dielectric constant of the material increases. Therefore a dielectric tip 214 with a greater dielectric constant will have a greater effect on the radiation pattern. The larger the dielectric constant, the smaller the dielectric tip 214 can be while still having a substantial effect on the shape of the radiation pattern. Using a dielectric tip 214 with a large dielectric constant means that the antenna can be made small and so the instrument can remain flexible. For example the dielectric constant in TiO.sub.2 is around 100. The wavelength of microwave radiation having a frequency of 5.8 GHz is about 6 mm in TiO.sub.2 compared to around 36 mm in PTFE (which may be the material used for the first and/or third dielectric materials). A noticeable effect on the shape of the radiation pattern can be produced in this arrangement with a dielectric tip 214 of approximately 1 mm. As the dielectric tip 214 is short, it can be made from a rigid material whilst still maintaining flexibility of the antenna as a whole.

[0103] The dielectric tip 214 may have any suitable distal shape. In FIG. 5 it has a dome shape, but this is not necessarily essential. For example, it may be cylindrical, conical, etc. However, a smooth dome shape may be preferred because it increases the mobility of the antenna as it is maneuvered through small channels (e.g. inside blood vessels). The dielectric tip 214 may be coated with a non-stick material such as Parylene C or Parylene D, or PFTE to prevent the tissue from sticking to the instrument. The whole instrument can be coated in this way.

[0104] The properties of the intermediate dielectric sleeve 216 are preferably chosen (e.g. through simulation or the like) so that the radiating tip section 204 forms a quarter wave impedance transformer for matching the input impedance of the generator into a biological tissue load in contact with the radiating tip section 204.

[0105] A longitudinal cross section of a simulation of the absorption pattern of an antenna having the configuration shown in FIG. 5 is shown in FIG. 6. The pattern produced is more uniform and more spherical than the pattern shown in FIGS. 4A and 4B. The pattern in FIG. 6 is axially symmetric and more of the radiation is concentrated around the radiating portion rather than spreading down the cable as occurs in FIGS. 4A and 4B. This means that, when in use, an area of tissue may be radiated more uniformly, meaning there is less chance of damage to healthy tissue. The radiation is also less spread out, allowing the practitioner to more accurately radiate target tissue and reduce radiation of or damage to healthy tissue. The pear drop shape of radiation pattern shown in FIG. 6 may also be particularly useful for treating fibroids.

[0106] During treatment, the surrounding tissue absorbs the radiated energy. The volume of tissue into which the energy is delivered depends on the frequency of the microwave energy.

[0107] It is to be understood that in some other embodiments the structure of the radiating tip portion 204 may be different and may not include a dielectric tip 214. For example, the radiating tip portion may include two conductive elements (e.g. disks) separated by an insulator, wherein one of the conductive elements is connected to the inner conductor 206 of the coaxial cable 202 and the other one of the conductive elements is connected to the outer conductor 208 of the coaxial cable 202. Alternatively, the radiating tip portion may include a helical antenna. For example, an insulator or dielectric element may have two helical electrodes arranged on its surface, wherein one of the helical electrodes is connected to the inner conductor 206 of the coaxial cable 202 and the other of the helical electrodes is connected to the outer conductor 208 of the coaxial cable 202. Alternatively, other radiating tip portion structures may include slotted antennas.

[0108] FIG. 7 illustrates a method of controlling microwave energy delivered from an electrosurgical instrument into a biological tissue at the distal end of the electrosurgical instrument, an accordance with an embodiment. The method may be implemented using the electrosurgical apparatuses described above with reference to FIGS. 1A, 2, 3 and 5. Furthermore, the method can be used to treat tumours which are joined to blood vessels.

[0109] The method begins at block 300. At block 300, an electrosurgical instrument is inserted into a blood vessel (e.g. vein or artery) within a patient. For example, the electrosurgical instrument may be as shown in FIG. 3 or 5. The instrument is moved through the blood vessel until it reaches a target site. In an embodiment, the target site is at or near to where a tumour joins to the blood vessel. The tumour may be connected to or may grow from (e.g. branch off of) the blood vessel such that the tumour receives a blood supply from the blood vessel. In another embodiment, the target site may be elsewhere inside the blood vessel. Once the electrosurgical instrument is at the target site, processing flows to block 302.

[0110] At block 302, optionally, the electrosurgical instrument is pushed through a junction between the blood vessel and the tumour so that the distal end of the electrosurgical instrument enters inside the tumour (e.g. a centre of the tumour). At block 304, the electrosurgical instrument is activated to radiate microwave energy from the distal end (e.g. as per the above-described pulse profile of FIG. 1B or 1C) in order to treat (e.g. ablate or coagulate) biological tissue inside the tumour. In this way, the tumour may be destroyed or killed from the inside. Further details of what constitutes activation of the electrosurgical instrument are included below.

[0111] In addition to blocks 302 and 304, or as an alternative to blocks 302 and 304, at block 306, the electrosurgical instrument is positioned at the junction between the blood vessel and the tumour (i.e. the target site) and is activated to treat (e.g. ablate or coagulate) the biological tissue which forms the junction. In this way, the biological tissue at the junction is destroyed so as to cut-off a blood supply to starve the tumour of blood and to kill the tumour.

[0112] In addition to blocks 302 to 306, or as an alternative to blocks 302 to 306, at block 308, the electrosurgical instrument is positioned at the junction between the blood vessel and the tumour (i.e. the target site) and is activated to treat (e.g. coagulate) the biological tissue at an opening between the tumour and the blood vessel so as to form a plug (e.g. a solid mass of cells) in the tumour which seals the opening shut. Next, the electrosurgical instrument is activated to treat (e.g. ablate) the biological tissue at the junction to detach the tumour from the blood vessel. A consequence of detaching the tumour from the blood vessel is that the tumour's blood supply is cut-off thereby starving the tumour of blood and killing the tumour. The detached tumour may be left to travel around the patient's body because, since its blood supply has been cut-off, the detached tumour can no longer grow or spread around the body. It is noted that the act of forming a plug which seals shut the tumour opening where it once joined to the blood vessel avoids tumour cells leaking out of the detached tumour.

[0113] In an embodiment, the method includes each of blocks 300 to 308. However, in some other embodiments, the method may involve only blocks 300, 302 and 304, or only blocks 300 and 306, or only blocks 300 and 308, or only blocks 300, 306 and 308, or only blocks 300, 302, 304 and 308. This is indicated on FIG. 7 by various arrows between the blocks.

[0114] Also, block 300 may involve inserting a guiding device (e.g. a guide catheter or a scoping device) through the lumen of the patient's blood vessel and positioning a distal end of the catheter at or near to the target site. Then, the electrosurgical instrument may be positioned at or near to the target site by inserting the instrument through a lumen of the guiding device. In an embodiment, the guiding device may be stopped before reaching the target site, so that the electrosurgical instrument can protrude from an opening at a distal end of the guiding device to directly reach the target site.

[0115] It is to be understood that the process of activating the electrosurgical instrument to treat biological tissue involves the operations performed by, for example, the electrosurgical apparatus of FIGS. 1A, 2, 3 and 5, as discussed above. That is, the electrosurgical instrument may be controlled to deliver a microwave energy waveform according to FIG. 1B or 1C, discussed above. Generally, these operations include: generating a microwave energy waveform; conveying the microwave energy waveform along a microwave channel to the electrosurgical instrument; delivering the microwave energy waveform into biological tissue from the distal end of the electrosurgical instrument as one or more microwave energy signal pulses; controlling the profile of the one or more microwave energy signal pulses to cause ablation or coagulation of the biological tissue and to substantially prevent the or each pulse from causing heat to build-up in the electrosurgical instrument. In this way, the profile of the one or more microwave energy signal pulses is controlled to cause ablation or coagulation of the biological tissue but each pulse is arranged such that heat does not to build-up in the electrosurgical instrument. A more detailed explanation of the one or more microwave energy signal pulses in accordance with different embodiments are described above with reference to FIGS. 1B and 1C.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] Throughout this specification, including the claims which follow, unless the context requires otherwise, the words “have”, “comprise”, and “include”, and variations such as “having”, “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.

[0120] 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%.

[0121] The words “preferred” and “preferably” are used herein refer to embodiments of the invention that may provide certain benefits under some circumstances. It is to be appreciated, however, that other embodiments may also be preferred under the same or different circumstances. The recitation of one or more preferred embodiments therefore does not mean or imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the disclosure, or from the scope of the claims.