Surgical resection apparatus

Abstract

Surgical cutting apparatus having a treatment channel and a measurement channel for conveying microwave energy from a source to an antenna at a cutting edge. The measurement channel operates at lower power than the treatment channel for determining when higher energy can be safely applied. The apparatus may deliver microwave radiation at differing frequencies to one or more antennas at the cutting edge, e.g. to provide different treatment effects. The source may generate an output for an antenna whose frequency can be selected e.g. for most efficient operation. Selection may be automatic based on detected magnitude and phase of reflected signals during a frequency sweep of a forward signal. Power delivered to tissue via the cutting element may be manually boosted to deal with large blood vessels. The apparatus may include a reflected power monitor for recognising behaviour in reflected signals received from the antenna to trigger automatic pre-emptive action.

Claims

1. A surgical cutting apparatus having: a microwave radiation source arranged to generate a microwave radiation signal; a surgical instrument for cutting biological tissue, the surgical instrument comprising an antenna connected to the microwave radiation source and arranged to emit a substantially uniform microwave radiation field; a reflected radiation detector connected between the microwave radiation source and the antenna to detect signals reflected back from the antenna; a reflected power monitor arranged to detect a signature event in the reflected signals detected by the reflected radiation detector during a cutting process, wherein the signature event is a detectable behaviour in the reflected signals and is at least one of the following: a certain rate of change of reflected power for a certain time slot; a certain rate of change of reflected power for a certain duration; a constant level of reflected power for a certain time slot; a constant level of reflected power for a certain duration; a constant voltage for a certain duration; or a voltage spike in the reflected signal; a power level adjuster connected between the microwave radiation source and antenna and arranged to automatically adjust a power level of the microwave radiation signal received by the antenna if the reflected power monitor detects the signature event; and wherein the power level adjustor is arranged to: reduce the power level from a first value to a second non-zero value when the signature event is detected; and automatically ramp the power level back up from the second non-zero value to the first value in a predetermined recovery time period after reducing the power level.

2. The apparatus according to claim 1, wherein the signature event further includes at least one of: (i) a predetermined rate of change of reflected power or a constant level of reflected power detected during a certain time slot or for a certain duration; or (ii) a certain change in a impedance of the tissue derived from changes in a behaviour of the reflected power.

3. The apparatus according to claim 1, wherein the reflected power monitor includes a differentiator arranged to: measure a value of dv/dt (change of voltage with time) for the reflected signals, and compare the measured value to a threshold value, whereby the signature event is a value of dv/dt that is higher than a threshold.

4. A surgical cutting apparatus having: a microwave radiation source arranged to generate microwave radiation signal; a surgical instrument for cutting biological tissue, the surgical instrument having an antenna connected to the microwave radiation source and arranged to emit a substantially uniform microwave radiation field; and an amplification unit between the microwave radiation source and the antenna for amplifying the microwave radiation signal generated by the microwave radiation source, wherein the amplification unit is manually switchable between a first configuration for amplifying the signal to a first non-zero power level for treatment and a second configuration for amplifying the signal to a boosted second power level that is higher than the first power level.

5. The apparatus according to claim 4, wherein the first power level is in a range 10 to 120 W, and the second power level is 20 to 50 W or more and higher than the first power level.

6. The apparatus according to claim 4, wherein the amplification unit includes an amplifier and a feed unit arranged to receive the microwave radiation signal from the microwave radiation source and to generate a drive signal for driving the amplifier, wherein, in the second configuration, the feed unit is arranged to generate the drive signal at a first power level and, in the first configuration, the feed unit is arranged to generate the drive signal at a second power level, the first power level being higher the second power level.

7. The apparatus according to claim 6, wherein the feed unit includes a first signal path for conveying the microwave radiation signal between the source and amplifier in the first configuration and a second signal path for conveying the microwave radiation signal between the source and amplifier in the second configuration, the first and second signal paths being manually selectable to switch the amplification unit between the first and second configurations.

8. The apparatus according to claim 4, including a reflected radiation detector arranged to receive signals reflected back from the antenna and an impedance adjustor on a first signal path, wherein the detector is arranged to detect a magnitude and phase of the reflected signal and the impedance adjustor has an adjustable complex impedance that is controllable based on the detected magnitude and phase of the signals, and wherein the apparatus has a control system arranged to automatically switch the apparatus to the second power level if high perfusion is sensed by the detector during operation at the first power level.

9. The apparatus according to claim 8, wherein the antenna is selectively connectable to the source via a first channel which includes the amplification unit for providing a microwave signal at the first or second power level for treatment and a second channel which bypasses the amplification unit for conveying a microwave signal at a lower power level for measurement, wherein the antenna is connected to the detector via a signal transfer unit which is arranged to route signals reflected from the antenna along the second channel directly to the detector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the aspects outlined above are described in detail below with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic system diagram showing components of surgical cutting apparatus with a treatment channel and a measurement channel for radiation from a source, and is an embodiment of the first aspect of the invention;

(3) FIG. 2A is a schematic system diagram showing components of surgical cutting apparatus capable of delivering microwave radiation at two frequencies, and is an embodiment of both the first and second aspects of the invention;

(4) FIG. 2B is a schematic system diagram showing components of a surgical cutting apparatus capable of delivering microwave radiation at two frequencies which is another embodiment of the second aspect of the invention;

(5) FIG. 3A is a schematic system diagram showing components of surgical cutting apparatus in which the frequency of microwave radiation delivered by the source is variable, and is an embodiment of the third aspect of the invention;

(6) FIG. 3B is a schematic diagram of components in a frequency synthesiser;

(7) FIG. 4 is a side view of a surgical instrument having a blade and two antennas, and is an embodiment of the second aspect of the invention;

(8) FIG. 5 is a partial cross-sectional side view of another surgical instrument having a blade and two antennas, and is another embodiment of the second aspect of the invention;

(9) FIG. 6 is a side view of yet another surgical instrument having a blade and two antennas, and is another embodiment of the second aspect of the invention;

(10) FIG. 7 is a schematic system diagram showing components of surgical cutting apparatus in which a treatment power level can be boosted, and is an embodiment of the first and fourth aspects of the invention;

(11) FIG. 8 is a schematic system diagram showing components of surgical cutting apparatus in which an analogue differentiator is provided to detect a signature event in the reflected power signal, and is an embodiment of the fifth aspect of the invention; and

(12) FIG. 9 is a chart showing how the power delivered to the antenna in the apparatus shown in FIG. 8 is altered depending on events detected in the reflected signal.

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES

(13) Selectable Channels

(14) FIG. 1 shows surgical cutting apparatus 100 e.g. suitable for use in surgical resection procedures (e.g. liver resection) which is an embodiment of the first aspect of the invention. Many of the individual components are similar to those used in the apparatus disclosed in UK patent application 0620060.4. A main difference is the provision of a splitter 106 which separates the output of the source 102 into two channels A, B for conveying microwave radiation from a source 102 to an antenna (not shown) on surgical instrument 104. The channels deliver radiation to the surgical instrument at different power levels. In this aspect, there is a treatment channel A for delivering radiation at a power level which will seal or cauterise blood vessels that are cut open by the blade and a measurement (or sensing) channel B for delivering radiation at a lower power level which will not substantially affect tissue at the blade but which can be used to obtain information about that tissue.

(15) In detail, FIG. 1 shows a source 102 (e.g. an oscillator source such as a VCO or DRO) which outputs a low power signal (e.g. between 0 dBm and 10 dBm) having a stable frequency. The frequency may be any suitable frequency above 10 GHz. For example the frequency may be 14.5 GHz, 24 GHz or more.

(16) The output from the source 102 is split into two parts by power splitter 106, which may be a −3 dB coupler, a 3 dB power splitter, or a directional coupler. The device may be realised in a waveguide, microstrip, or co-axial arrangement. One part is directed along treatment channel A and the other part along measurement channel B.

(17) On treatment channel A, the signal drives the input to power amplifier unit 108, which in this embodiment comprises a preamplifier 110 and a power amplifier 112. The amplifiers 110, 112 may be any of a travelling wave tube (TWT), a magnetron, a Klystron, a semiconductor amplifier or the like that is able to generate power levels of between 1 W and 500 W at frequencies in the range of between 10 GHz and 40 GHz. In this embodiment, the amplifiers may have a gain of 20 or more, e.g. 20 and 30 respectively. A microwave power module, e.g. comprising a series combination of a solid state driver amplifier and mini-TWT, may be used in the power amplifier unit 108. It may be desirable to combine a plurality of microwave power modules using a low loss waveguide or microstrip power combiner to produce the desired power level. The configuration of the power amplifier unit 108 is determined by a control signal C3 provided by microprocessor/DSP unit 116.

(18) An adjustable signal attenuator 114 is located on the treatment channel A between the splitter 106 and the amplifier unit 108. The function of the attenuator 114 is to reduce the amplitude of the signal from the splitter 106 to enable the output power produced by the amplifier unit 108 to be controlled. The attenuator 114 is adjustable according to a control signal C.sub.1 from a microprocessor/DSP unit 116, which is discussed below. The attenuator 114 may be a PIN diode attenuator, and is preferably arranged to provide a range of attenuation which enables the amplifier unit 108 to be driven into saturation when the attenuation level is a minimum value and the power to be backed off sufficiently when the attenuation is set to a maximum value, i.e. a level may be set whereby the system enables cauterisation or coagulation to occur in not such highly perfused tissue, or where the power level does not cause the blood to coagulate. In the former case, this high level of control enables coagulation to occur without causing unnecessary collateral damage, or damage to healthy tissue structures adjacent to the cut.

(19) The output from the power amplifier unit 108 is fed into the input (first) port of a microwave circulator 118 whose function is to protect the amplifier unit 108 against high levels of reflected power being returned to the output stage of the amplifier unit, which may cause damage to the amplifier unit, or cause the amplifier to behave like an oscillator due to the impedance mismatch seen at the output stage. The circulator 118 operates to allow power flow in a clockwise direction only. The power from the output of amplifier unit 108 is thus diverted to the second port of power circulator 118 where it is directed towards the surgical instrument 104 via directional couplers 120, 122, waveguide switch 124 and transmission cable 126. The third port of the circulator 118 is connected to a power dump load 128 whose function is to absorb reflected power returned back along transmission cable 126 that may enter the second port of power circulator 118. Any reflected power received into the second port is diverted to the third port and into the power dump load 128. The impedance as seen at the third port of circulator 118 is arranged to be the same as that as seen at the input to the dump load 128. This ensures that there is no power returned back to the first port of power circulator 118. In practice, the third port of circulator 118 is well matched with the input impedance of the dump load and a negligible amount of power is transferred or transported from port three to port one of circulator 118. It is normal practice for the impedance of the dump load to be 50 Q.

(20) The output power from the second port of the circulator 118 is fed into the input to forward power directional coupler 120, which is configured to measure the forward power by sampling a portion, i.e. 10% or 1%, of the forward going power. The coupled port of forward directional coupler 120 is connected to a detector 130 which converts the microwave power sampled by the coupler 120 into a DC level or lower frequency AC level. The detector 130 may include any suitable diode, e.g. a zener diode, a zero bias Schottky diode, or a tunnel diode. Alternatively, a homo/heterodyne detection unit may be employed in the place of the detector 130. In the latter embodiment, both phase and magnitude can be measured.

(21) The output V.sub.1 from detector 130 is fed into an analogue to digital converter 132 where it is converted into a digital signal so that it can be manipulated or used by microprocessor/DSP unit 116.

(22) The output power from forward power directional coupler 120 is fed into the input port of reverse power directional coupler 122, which is configured to measure the reflected power by sampling a portion of the power returned along cable 126 due to a mismatch between the distal end of surgical instrument 104 and biological tissue, i.e. the reflection coefficient is either greater than or more negative than zero, e.g. 0.5 or −0.5, but is within the bounds of −1 to +1. The actual value is dependent upon whether the load impedance is greater or less than the characteristic impedance of the cable and blade/transformer assembly. The coupled port of reverse power directional coupler 122 is connected to a detector 134 which converts the microwave power sampled by the backward directional coupler 122 into a DC level (or lower frequency AC signal). The detector 134 may be a diode detector which includes any suitable diode, e.g. a zener diode, a zero bias Schottky diode, or a tunnel diode. Alternatively, a homo/heterodyne detection unit may be employed in the place of the detector 134. The output V.sub.2 from detector 134 is fed into the analogue to digital converter 132 where it is converted into a digital signal so that it can be manipulated or used by microprocessor/DSP unit 116. The value of the detected signal is used to determine any action that will (or needs to be taken by the system, i.e. it may be necessary to increase the output power from the amplifier to compensate for any impedance mismatch between the blade and the tissue.

(23) The output power from reverse power directional coupler 122 is connected to a first port S.sub.A of a waveguide switch 124. The waveguide switch 124 is arranged to connect either the (high power) treatment channel A or the (low power) measurement channel B to the cable 126 which feeds surgical instrument 104. In FIG. 1, the treatment channel is selected, i.e. first port S.sub.A is connected to output port S.sub.C. In this embodiment, the waveguide switch 124 is a single-pole-two-throw (SP2T) switch, where the first port S.sub.A and second port S.sub.B are selectively connectable to the output port S.sub.C. The common contact (output port S.sub.C) is connected to cable 126. Other switch types may be used, e.g. a coaxial switch or a high power PIN/varactor switch.

(24) The configuration of the waveguide switch 124 (i.e. position of movable waveguide section within waveguide switch 124 to provide connection path S.sub.A.fwdarw.S.sub.C or S.sub.B.fwdarw.S.sub.C) is determined by a control signal C.sub.2 provided by microprocessor/DSP unit 116.

(25) In this embodiment the transmission cable 126 is a flexible/twistable waveguide assembly, but a low loss coaxial cable assembly may be used instead. It is preferable to cover the flexible/twistable waveguide with a rubber jacket, i.e. a neoprene rubber may be used.

(26) The surgical instrument 104 comprises a blade structure which has the basic form of a scalpel, where two sharp angled cutting edges are machined at one end of a rectangular block of material, e.g. alumina, sapphire or the like. The sides of the rectangular block (i.e. the side surfaces and top and bottom surfaces) are metallized. However, the faces which meet at the cutting edges are not metallized; the alumina is exposed at this position to form a radiating portion.

(27) The dimensions for the blade structure may be obtained based on information about the overall structure and configuration (e.g. wavelength of operation) of the surgical instrument, e.g. by performing microwave field simulations.

(28) In the low power measurement or detection mode, the second port S.sub.B of waveguide switch 124 is connected to the output port S.sub.C to enable the (low power) measurement signal from measurement channel B to be transmitted to the distal radiating tip of surgical instrument 104.

(29) On measurement channel B, the signal from source 102 is input to a low noise, low power amplifier 136. In some embodiments low power amplifier 136 may be omitted because the signal generated by source 102 and split by splitter 106 has a high enough power such that a portion of the transmitted signal that is reflected at the distal end of surgical instrument 104 has an amplitude that is high enough to be detectable by a reflected power detector 138. The reflected power detector may be a magnitude detector, e.g. a diode detector as shown or any other suitable magnitude detector. Alternatively, the detector 138 may be a homodyne or heterodyne receiver arranged to extract both magnitude and phase information from the reflected signal. Herein a detectable signal is a signal with high enough amplitude to enable a valid measurement to be made, i.e. it is possible to discern the signal component from the noise components. The low power amplifier 136 may be a low noise semiconductor amplifier (e.g. a GaAs device, HEMT, MMIC or the like) capable of producing an output power level of up to 20 dBm and beyond. If it is not required to boost the measurement signal then it may be preferable for the low noise amplifier to be omitted from the design since any additional active component in the receiver line-up will introduce a component of noise into the measured signal.

(30) The output from the low power amplifier unit 136 is fed into the input (first) port of a microwave circulator 140, whose function is to direct reflected power from the surgical instrument 104 directly to reflected power detector 138. The circulator 140 operates to allow power flow in a clockwise direction only. The power from the output of low power amplifier 136 is therefore diverted to the second port of the circulator 140 where it is directed towards the surgical instrument 104 via waveguide switch 124 and transmission cable 126. The third port of the circulator 140 is connected to the reflected power detector 138. Any reflected power received into the second port is diverted to the third port and is therefore received by the detector 138. Since substantially all the reflected signal itself is provided to the detector 138 (i.e. it is not coupled), a lower power input signal can be used, which can reduce or minimize the risk of the radiation causing damage to tissue due to higher than necessary power levels emanating from the surgical instrument 104.

(31) The signal output from the third port of the circulator 140 is a function of the degree of impedance mismatch between the radiating blade of the surgical instrument 104 and the biological tissue or air.

(32) In an alternative embodiment (not shown) the signal at the first port of the circulator 140 is sampled in order to compare the difference between the reflected signal and the incident signal. Another optional feature is a carrier or forward signal cancellation circuit (also not shown) which may be implemented between the first and third ports of circulator 140 in order to remove any breakthrough signal that occurs between those ports.

(33) The reflected signal measured using reflected power detector 138 is fed into the analogue to digital converter 132, where the analogue voltage level is digitised and processed using microprocessor/DSP unit 116. Power level adjustments can therefore be made to the treatment channel A (e.g. via control signals C.sub.1 and C.sub.3) based on the detected measurement signal transmitted along measurement channel B before any high power radiation is delivered by the device. This may provide safe control of the emitted radiation field.

(34) Microwave power delivery into tissue is manually activated using footswitch 142, which may be a single pedal. The footswitch 142 is connected to the microprocessor/DSP unit 116 via isolation circuit 144, whose function is to create DC isolation (or galvanic isolation) between the footswitch 142 that is attached to the user/surgeon and the apparatus 100 to effectively break any DC path that would otherwise exist and form a part of the circuit. The isolation circuit 144 may also condition the signal such that it is suitable for processing by the microprocessor/DSP unit 116, i.e. a press of the footswitch pedal may be converted into a voltage pulse of +5 V amplitude.

(35) The microprocessor/DSP unit 116 controls the operation of the system by sending suitable control signals C.sub.1, C.sub.2 and C.sub.3 to various components as discussed above. A user interface 146 communicates with the microprocessor/DSP unit 116 to enable a user to enter instructions, e.g. power level demand, duration, energy delivery, etc., and to provide a display of the status of the operation of the system or instrument.

(36) In another alternative embodiment, the apparatus 100 may be adapted to provide dynamic impedance matching as described in WO 2004/047659. Thus, another pair of power couplers and a tuning filter may also be provided on the treatment channel A, whereby the impedance of the tuning filter is adjustable, e.g. by signals sent from microprocessor/DSP unit 116 based on signals from the couplers to match that of the tissue at the distal end of the surgical instrument 104. The tuning filter may be a stub tuner comprising of a plurality of tuning rods or posts, or may comprise of an arrangement of varactor diodes where the reactance is changed by adjustment of the voltage across the diodes.

(37) Selectable Frequencies—Apparatus

(38) FIG. 2A shows apparatus 200 that is an embodiment of the first and second aspects of the invention. The apparatus 200 has two microwave sources 102, 202, each of which are connected to a surgical instrument 104 by a two channel (high power treatment and low power measurement) arrangement that corresponds to the apparatus 100 shown in FIG. 1. Components in the line-up from the first source 102 are given the same reference number as components in FIG. 1 which provide the same function. The components in the line-up from the second source 202 are given similar reference numbers, except that they commence with a 2, e.g. splitter 206 performs a similar function to splitter 106.

(39) The sources 102, 202 in the apparatus 200 shown in FIG. 2A generate microwave energy at different frequencies. The first source 102 generates energy at a higher frequency than the second source 202. For example, source 102 may provide a frequency of 10 GHz or more, e.g. between 10 GHz and 40 GHz. In this example 14.5 GHz or 24 GHz are preferred. The second source 202 is arranged to provide energy that will produce a large depth of penetration into the tissue to enable large blood vessels that may not be dealt with effectively using the first (higher microwave) frequency to be coagulated or sealed in an efficient manner to limit or prevent bleeding. The frequency may be less than 5 GHz, e.g. between 100 MHz and 5 GHz. In this example 2.45 GHz or 925 MHz are preferred.

(40) The apparatus 200 shown in FIG. 2A effectively consists of two microwave circuits that are identical in construction except that they use components that operate at the different frequencies that are provided by their respective sources.

(41) Thus, the first circuit corresponds to the two channels A, B discussed with reference to FIG. 1 and is not described again. For clarity, the connection between analogue to digital converter 132 and microprocessor/DSP unit 116 is indicated by control signal C.sub.4.

(42) The second circuit also has a treatment channel C and measurement channel D, and is arranged in a similar fashion to the apparatus shown in FIG. 1. It comprises a frequency source 202, power splitter 206, variable attenuator 214 (controlled by control signal C.sub.5 from microprocessor/DSP unit 116), power amplifier unit 208 (including preamplifier 210 and power amplifier 212) controlled by control signal C.sub.6 from microprocessor/DSP unit 116, circulator 218, 50Ω power dump load 228, forward power coupler 220, reflected power coupler 222, forward power detector 230 (delivering output V.sub.3 to analogue to digital converter 232), reflected power detector 234 (delivering output V.sub.4 to analogue to digital converter 232), waveguide switch 224 controlled by control signal C.sub.7 from microprocessor/DSP unit 116, low power amplifier 236, low power circulator 240, detector 238 and cable assembly 226.

(43) In both circuits, the signals from the three detectors 130, 134, 138, 230, 234, 238 are fed into respective analogue to digital converters 132, 232 and interfaced to a common microprocessor/DSP unit 116 (indicated by control signals C.sub.4 and C.sub.8 respectively). However, the invention may not be limited to this arrangement. For example, the apparatus 200 may use a common (e.g. single) analogue to digital converter for the two circuits, or the analogue to digital converters 132, 232 may form an integral part of microprocessor/DSP unit 116.

(44) In the apparatus shown in FIG. 2A, the treatment channel C may be ‘switched on’ automatically using the information provided by the four detectors to deliver high levels of power at the second frequency. Alternatively, the waveguide switch 224 may be activated manually by the surgeon when he/she encounters a large bleed. In the latter case, the footswitch 142 may include two pedals to enable the surgeon to bring in (or turn on) the energy generated at the second frequency on demand. An arrangement comprising two pedals arranged side by side and mounted inside a single case may be provided with e.g. a blue pedal and a yellow pedal. Another embodiment may permit energy generation at the second frequency through the activation of a push button switch connected to the surgical instrument. The switch may be controlled by the surgeon as he/she maneuvers the blade inside the tissue.

(45) The energy developed at the second frequency may be delivered using a half wavelength dipole, a quarter wavelength monopole, a half wavelength loop or a microstrip antenna arrangement. FIG. 2A shows the energy being delivered using a coaxial cable 226 which runs along the bottom edge of the surgical instrument 104 with the centre conductor feeding a microstrip structure 250 that is fabricated onto one of the (unmetallized) surfaces of the radiating blade. Blade structures for implementing the second aspect of the invention are discussed in more detail below with reference to FIGS. 4, 5 and 6.

(46) Another embodiment of the second aspect of the invention is shown in FIG. 2A. Features in common with FIG. 2A are given the same reference numbers and are not described again. In this embodiment a single analogue to digital converter 132 is used to convert the signals V1, V2, V3 and V4 received from the first and second circuits. In this embodiment each circuit only comprises a treatment channel.

(47) The main difference between the embodiments shown in FIGS. 2A and 2B is the use of a common signal path 127 and filtering arrangement in FIG. 2B in place of the waveguide switches 124, 224 and separate signal paths 126, 226 in FIG. 2A. Thus, the amplified microwave signals from the first and second circuit are combined in power combiner 156 and transmitted to the respective antennas on surgical instrument 104 via common signal path 127, which may be a low loss coaxial cable. The first and second circuits have a first band pass filter 154 and a second band pass filter 254 respectively, which are arranged to transmit (or pass) energy at the frequency of their respective circuit and block energy at the frequency of the other circuit. Thus, the filters ensure that the reflected signals measured on each circuit are only those having the desired frequency of that circuit.

(48) The first and second circuits can be activated and deactivated using simple switches 152, 252 e.g. controlled by footswitch 142 in the manner described above.

(49) Variable Treatment Frequency

(50) FIG. 3A shows apparatus 300 that is an embodiment of the third aspect of the invention. The apparatus 300 has a similar line-up to the apparatus 100 shown in FIG. 1, and the same components may be used to provide the corresponding functions. Thus, apparatus 300 comprises the following line-up between a frequency source 302 and surgical instrument 304: variable attenuator 314 (controlled by control signal C.sub.2 from microprocessor/DSP unit 316), power amplifier unit 308 (including preamplifier 310 and power amplifier 312) controlled by control signal C.sub.3 from microprocessor/DSP unit 316, circulator 318, 50Ω power dump load 328, forward power coupler 320, reflected power coupler 322, forward power detector 330 (delivering an output to analogue to digital converter 332), reflected power detector 334 (delivering an output to analogue to digital converter 332), and cable assembly 326. Similarly to FIG. 1, the apparatus 300 is controllable by a footswitch 342 connected to the microprocessor/DSP unit 316 via isolation circuit 344. A user interface 346 permits manipulation of the settings for the apparatus 300.

(51) The third aspect of the invention is the provision of a single wideband power generation system. The system comprises a variable frequency source 302, which may be a voltage controlled oscillator or a frequency synthesiser which may contain a plurality of voltage controlled oscillators, whose output frequency is controlled based on a control signal C.sub.1 from microprocessor/DSP unit 316; this signal may in fact be plurality of digital control lines, e.g. 8 lines, 16 lines or 32 lines. The source may be capable of generating any stable frequency in the range of interest, e.g. from 500 MHz to 24 GHz or more and it is desirable to be able to use the source to sweep over a range of frequencies within this band, i.e. between 1 GHz and 10 GHz.

(52) In one embodiment, the source includes a frequency synthesiser. FIG. 3B is a schematic diagram of components in a source 302 that is a frequency synthesiser Here the source includes a reference oscillator 360, e.g. a stable crystal oscillator, a phase comparator 362, a low pass filter 364, a voltage controlled oscillator (VCO) 366 and a programmable ‘divide by N’ divider 368 connected in a phase locked loop (PLL) arrangement.

(53) The output frequency f.sub.0 of the VCO 366 is a function of the applied voltage, i.e. the voltage on its varactor diode. The output from the phase comparator 362 is a voltage that is proportional to the phase difference between the signals at its two inputs; this controls the frequency of the VCO 366 so that the phase comparator input from the VCO via the divider 368 remains at a constant phase difference with the reference input f.sub.r, i.e. so that those input frequencies are equal. The output frequency f.sub.0 is thus maintained at Nf.sub.r. The size of N may be variable e.g. based on the control signal C.sub.1. The synthesiser may therefore be able to output a series of discrete frequencies across a range corresponding to different values of N. Adjacent frequencies in the series are separated by f.sub.r.

(54) Examples of commercially available frequency synthesisers that can be used in this embodiment include the LMPL-GSP range of dual frequency phase locked frequency synthesisers from GED. These products can produce frequencies over the range of between 100 MHz and 7 GHz. For higher frequencies, the VMESG series of broad bandwidth synthesisers from Elcom Technologies may be used. Devices in this series can operate up to 20 GHz. One product within this series provides a frequency range of between 50 MHz and 20 GHz with a 1 Hz resolution.

(55) Power amplification unit 308 is arranged to be capable of delivering microwave power of up to and in excess of 300 W over a frequency range which lies between 500 MHz and 24 GHz, e.g. a range from 8 to 16 GHz. Table 2 lists devices manufactured by Thales Electronic Devices which may be suitable for this purpose:

(56) TABLE-US-00002 TABLE 2 Amplifier components for wideband apparatus Operational Saturated output Saturated Product No range (GHz) power (W) gain (dB) High power CW TWTs TL10055 6-18 150 30 TL10058 7.5-18.sup.  200 30 Mini/Micro TWTs TH4430S 6-18 140 30 TH4430C 6-18 160 30

(57) In this embodiment, the transmission cable 326 is a low loss coaxial cable. This can achieve the desired bandwidth without the possibility of the occurrence of moding. Waveguides may also be used, but generally have a more limited bandwidth than coaxial cables. Ridge waveguide structures may be considered as a means of increasing the frequency bandwidth from that achievable using standard rectangular waveguide.

(58) It is desirable for apparatus 300 to have both a forward and reflected power coupler 320, 322 to enable the microprocessor/DSP unit 316 to calculate either magnitude, phase, or phase and magnitude information relating to the reflected power from the detected signals. This information can be used to enable selection of a suitable frequency for the energy delivered to the tissue, i.e. frequency is selected based on a detected condition of the tissue load, for example, it may be desirable to search for a null in reflected power in order to establish the optimum operating frequency that should be used.

(59) In a preferred embodiment, the variable frequency of the source 302 may be scanned (swept) across a range. The forward and reflected power couplers 320, 322 and their respective detectors 330, 334 can record the response of the tissue across the frequency range, and can enable the microprocessor/DSP unit 316 to obtain information e.g. about the return loss of the apparatus 300 across the frequency range. Based on this information, an operating frequency of the source may be automatically selected. For example, the frequency at which an energy absorption peak occurs in a particular tissue type (or another material) may be selected in this manner. This arrangement may be advantageous in that the apparatus can be used with a variety of surgical instruments which may respond differently at different frequencies. Indeed, if the surgical instrument is a disposable item, this aspect of the invention may compensate for minor differences between instruments, which occur as part of the manufacturing process, or through temperature variations.

(60) Selectable Frequencies—Surgical Instrument

(61) The second aspect of the invention provides an apparatus where microwave energy having two different frequencies can be emitted from the same surgical cutting instrument. This can be achieved by providing two radiating structures, e.g. two antennas, on the surgical instrument.

(62) FIG. 4 shows a first embodiment of a surgical instrument 400 with two radiating structures. The surgical instrument 400 is a rectangular block of waveguide (i.e. dielectric) material whose end is formed into a scalpel shape, with upper and lower angled sharp edges 402, 404 meeting at a point 406. The lower angled edge 404 is longer than the upper angled edge and forms a main blade of the surgical instrument.

(63) The block of waveguide is coupled directly to the transmission cable of the apparatus that carries microwave energy at a first (higher) frequency. Metallization 408 is provided on the surfaces of the block of waveguide except at a narrow region 410 adjacent to the main blade (i.e. around lower angled edge 404). The unmetallized region 410 therefore acts as an antenna (e.g. radiating blade) for the microwave energy at the first frequency.

(64) A coaxial cable 412 is mounted along the bottom of the block of waveguide. This coaxial cable 412 is the transmission cable of the apparatus that carries microwave energy at a second (lower) frequency. The centre conductor 414 of the coaxial cable is connected and feeds the microwave energy to a microstrip structure 416 which acts as an antenna for the microwave energy at the second frequency. In this embodiment, the microstrip structure 416 is mounted on a strip of dielectric material 418 provided on the layer of metallization 408 towards the lower angled edge 404. Thus, the field emitted by the microstrip structure 416 also emanates from the radiating blade of the surgical instrument. However, since it has a lower frequency, the depth of penetration of the field from the microstrip structure 416 is greater than that from the unmetallized region 410 itself.

(65) In this embodiment, the layer of metallization 408 that forms a part of the radiating blade antenna used to deliver energy at the first frequency also acts as the ground plane for the energy produced at the second frequency. Thus, the dielectric material 418 lies between the layer of metallization 408 (acting as a first conductor or ground plane of the second antenna) and a second layer of metallization 416 which acts as a second (active) conductor and provides the microstrip design (not shown).

(66) The centre conductor 414 of the coaxial cable is attached to the second conductor 416 using a solder contact/joint or other conductive mechanical means. The dielectric layer 418 may be a spray-on dielectric material that exhibits a low loss at the frequency of interest, or may be a sheet of dielectric material attached to the metallized portion of the radiating blade structure, for example, a sheet of Kapton may be used.

(67) FIG. 5 shows a second embodiment of a surgical instrument 500 capable of launching energy into tissue at two different microwave frequencies. Similarly to the instrument shown in FIG. 4, surgical instrument 500 comprises a block of waveguide 501 whose end is formed into a scalpel shape having upper and lower angled sharp edges 502, 504 which meet at a point 506. The lower angled edge 504 is longer and provides the main cutting blade of the instrument 500. A layer of metallization 508 is provided on the surfaces of the block of waveguide 501 except at a region 510 adjacent to the lower angled edge 504. Similarly to FIG. 4, the block of waveguide is coupled directly to the transmission cable (waveguide) 520 of the apparatus that carries microwave energy at the first (higher) frequency. The unmetallized region 510 therefore acts as an antenna (e.g. radiating blade) for the microwave energy at the first frequency.

(68) In this embodiment, the entire layer of metallization 508 is used as a second antenna to radiate energy at the second frequency into the biological tissue. The energy at the second frequency is provided via a coaxial cable 524, whose inner conductor 526 is connected and feeds energy at the second frequency to the layer of metallization 508. Thus, the surgical instrument 500 provides a monopole-type antenna structure with the whole outer portion of the block of waveguide 501 acting as a radiator or aerial. To enable the block of waveguide 501 to act as a radiator, an isolation layer 522 is inserted between the body of the transmission cable 520 and the block of waveguide 501 to provide electrical isolation between those components at the second (lower) frequency energy. The isolation layer 522 may be a dielectric material such as a ceramic material. The isolation layer 522 does not prevent radiation at the first frequency from being transmitted from the transmission cable 520 to the block of waveguide 501. The centre conductor 526 of the coaxial cable penetrates the isolation layer 522.

(69) In alternative embodiments, it may be desirable to prevent or limit radiation of a microwave field at the second frequency from entering or propagating on/in particular sections or portions of the block of waveguide 501. This can be achieved by attaching a layer of insulating material to those regions. For example, a ceramic material or radiation absorbing material may be used.

(70) FIG. 6 shows a third embodiment of a surgical instrument 600 capable of launching energy into tissue at two different microwave frequencies. Similarly to the instrument shown in FIG. 4, surgical instrument 600 comprises a block of waveguide 601 whose end is formed into a scalpel shape having upper and lower angled sharp edges 602, 604 which meet at a point 606. The lower angled edge 604 is longer and provides the main cutting blade of the instrument 600. A layer of metallization 608 is provided on the surfaces of the block of waveguide 601 except at a region 610 adjacent the lower angled edge 604. Similarly to FIG. 4, the block of waveguide is coupled directly to the transmission cable (not shown) of the apparatus that carries microwave energy at the first (higher) frequency. The unmetallized region 610 therefore acts as an antenna (e.g. radiating blade) for the microwave energy at the first frequency.

(71) In this embodiment, a self-contained patch antenna 611 is mounted on layer of metallization 608 adjacent to the unmetallized region 610. Thus, a region of the surface of the block of waveguide 601 is covered with a first dielectric material 612 that is attached to the blade by a suitable means (e.g. adhesive or the like), followed by a first layer of metallization 614 to act as the ground plane, followed by a second dielectric layer 616 to act as the medium through which the fields are propagated, followed by a second layer of metallization 618.

(72) A coaxial cable 620 is mounted along the bottom of the block of waveguide 601. This coaxial cable 620 is the transmission cable of the apparatus that carries microwave energy at a second (lower) frequency. The centre conductor 622 of the coaxial cable is connected and feeds the microwave energy to the patch antenna 611 which therefore acts as an antenna for the microwave energy at the second frequency. The centre conductor 622 of the coaxial cable 620 is attached to the second layer of metallization and the outer conductor 624 of the coaxial cable is attached to the first layer of metallization 614. In this embodiment, the fields emanating from the edges of the second layer of metallization are used to cauterise or ablate the tissue structure.

(73) Power Level Boost

(74) FIG. 7 shows surgical cutting apparatus 700 that is an embodiment of the first and fourth embodiments of the invention. The apparatus 700 has a microwave source 702 which is connected to a surgical instrument 704 by a two channel (high power treatment and low power measurement) arrangement that corresponds to the apparatus 100 shown in FIG. 1. Components in the line-up between the source 702 and surgical instrument 704 which perform the same function as corresponding components in apparatus 100 are given similar reference numbers, except that they commence with a 7, e.g. splitter 706 performs a similar function to splitter 106.

(75) Thus, the line-up comprises a frequency source 702, power splitter 706, variable attenuator 714 (controlled by control signal C.sub.1 from microprocessor/DSP unit 716), power amplifier unit 708 (including preamplifier 710 and power amplifier 712) controlled by control signal C.sub.3 from microprocessor/DSP unit 716, circulator 718, 50Ω power dump load 728, forward power coupler 720, reflected power coupler 722, forward power detector 730 (delivering output V.sub.1 to analogue to digital converter 732), reflected power detector 734 (delivering output V.sub.2 to analogue to digital converter 732), waveguide switch 724 controlled by control signal C.sub.2 from microprocessor/DSP unit 716, user interface 746, low power amplifier 736, low power circulator 740, detector 738 and cable assembly 726. The functions of these elements are discussed above with respect to the first aspect and are not repeated here.

(76) The fourth aspect of the invention is an adaptation of the apparatus whereby perfuse bleeding caused by large blood open vessels can be addressed by driving the amplification unit 708 hard to produce maximum power at the same frequency as used for normal operation.

(77) In this embodiment, the apparatus 700 includes an overdrive signal path which bypasses the variable attenuator and boosts the input to the amplification unit 708 to drive the amplification unit 708 at full power. A pair of single-pole-two-throw switches 760, 762 is connected on treatment channel A on either side of the variable attenuator 714. The switches 760, 762 may be PIN switches and are arranged to adopt either a first configuration where the signal is directed through the variable attenuator 714 (‘normal’ operation) or a second configuration where the signal bypasses the variable attenuator 714 and is directed through a boost amplifier 764, which may be a low power amplifier (‘boosted’ operation). The switches 760, 762 are operated via control signals C.sub.4, C.sub.5 received from the microprocessor/DSP unit 716.

(78) Thus, in normal operation the signal generated by frequency source 702 is connected to the input of variable attenuator 714 by connecting the common contact S.sub.x of first switch 760 to its first port S.sub.y, and the output signal from variable attenuator 714 is connected to the amplification unit 708 by connecting the common contact S.sub.x′ of second switch 762 to its first port S.sub.y′. Thus, an attenuated version of the signal from the source 702 is used to drive amplification unit 708. This corresponds to the operation of treatment channel A discussed with reference to FIG. 1 above.

(79) In boosted or ‘overdrive’ operation, switches 760, 762 adopt their second configuration following receipt of corresponding control signals C.sub.4 and C.sub.5 from the microprocessor/DSP unit 716. In the second configuration, the signal generated by source 702 is connected to the input of boost amplifier 764 by connecting the common contact S.sub.x of first switch 760 to its second port S.sub.z, and the output signal from boost amplifier 764 is connected to the amplification unit 708 by connecting the common contact S.sub.x′ of second switch 762 to its second port S.sub.z′. The signal produced by source 702 is therefore re-routed such that it is amplified using low power amplifier 764 and the amplified signal used to drive amplification unit 708 into saturation or to enable it to produce maximum power at its output port.

(80) The low power amplifier 764 may be optional. For example, if the amplitude of the signal produced by source 702 is of high enough amplitude to drive amplification unit 708 into saturation without additional gain being required, the low power amplifier 764 may be omitted from the line-up. In this instance second port S.sub.z of first switch 760 may be directly connected to second port S.sub.z of second switch 762. The variable attenuator 714 is bypassed to remove its insertion loss, which can be in excess of 1 dB even when its attenuation is set to a minimum value.

(81) In an alternative embodiment the frequency source 702 produces a high enough power level to enable the second stage of amplification unit 708 to be driven into saturation when all (or a substantial amount) of the attenuation introduced by variable attenuator 714 is removed. Thus, the manually activated boost in this embodiment may be achieved by sending a control signal to the variable attenuator to instantly reduce the attenuation. In this embodiment, it is possible to omit the first and second switches 760 and 762 respectively, together with boost amplifier 764, from the microwave line-up shown in FIG. 7.

(82) Similarly to the apparatus 100 shown in FIG. 1, a user operates the apparatus 700 using a footswitch arrangement 742, which is attached to the microprocessor/DSP unit 716 via an isolation circuit 744. In this embodiment, the footswitch arrangement comprises two pedals 743, 745. The first pedal 743 is arranged to control waveguide switch 724, i.e. to control switching between the treatment channel A and measurement channel B. The second pedal 745 is arranged to permit the user (e.g. surgeon) to select the configuration of the switches 760, 762 on the treatment channel, i.e. to select normal treatment or to drive the amplifier at full power (‘boosted’ treatment). Boosted treatment may be desirable when the user visually encounters a large bleed that cannot be dealt with effectively using the power level delivered during normal treatment.

(83) Event Monitor

(84) FIG. 8 shows the relevant parts of surgical cutting apparatus 800 that is an embodiment of the fifth aspect of the invention. The apparatus 800 has a microwave source 802 (e.g. oscillator) which is connected to a surgical instrument 804 by an arrangement that may correspond to the apparatus 100 shown in FIG. 1. Components in the line-up between the source 802 and surgical instrument 804 which perform the same function as corresponding components in apparatus 100 are given similar reference numbers, i.e., amplifier 808 performs a similar function as amplifier 108, forward power directional coupler 820 performs a similar function as forward power directional coupler 120, and variable attenuator 814 performs a similar function as variable attenuator 114.

(85) According to the fifth aspect of the invention, the apparatus 800 includes a monitoring arrangement which is arranged to communicate a trigger signal C.sub.3 to the microprocessor/DSP unit 816 if a certain event is detected in the reflected power signal obtained from reflected power coupler 822 and detected by detector 834. In this embodiment, the monitoring arrangement is an analogue implementation capable of monitoring the value of dv/dt of the detected reflected signal and generating a trigger signal when the monitored value exceeds a set threshold.

(86) In detail, the detected signal (e.g. voltage V.sub.r) from detector 834 is provided to a differentiator 850 via a buffer amplifier 848. The buffer amplifier 848 is interposed between the main apparatus line-up and the differentiator 850 to prevent the differentiator 850 from presenting an undesirable load to the detector 834. The differentiator circuit includes a capacitor 852 with a capacitance value C and a resistor 854 with resistance R arranged such that the output from differentiator 850 is

(87) $-\mathrm{RC}\frac{{\mathrm{dV}}_r}{\mathrm{dt}}.$
This output is provided to a comparator 856, which is arranged to switch its output (e.g. to generate a step-like trigger signal 860) if the value of

(88) $-\mathrm{RC}\frac{{\mathrm{dV}}_r}{\mathrm{dt}}$
(effectively the value of dV.sub.r/dt since that is the only variable) exceeds a threshold. In this embodiment, the comparator 856 compares

(89) $-\mathrm{RC}\frac{{\mathrm{dV}}_r}{\mathrm{dt}}$
to the output from a potentiometer 858. The potentiometer 858 enables the threshold to be varied.

(90) In this embodiment, the trigger signal 860 is generated if dV.sub.r/dt exceeds a certain value. A high value for dV.sub.r/dt (e.g. 5000 V/s) may indicate that a spitting event (e.g. violent ejection of tissue from the treatment site) is about to occur. The apparatus 800 is arranged to react to the trigger signal 860 to prevent the spitting event from occurring. If a trigger signal C.sub.3 is received by the microprocessor/DSP unit 816, a response control signal C.sub.4 is immediately sent to the variable attenuator 814, which instantly increases attenuation to reduce the power level delivered to the tissue to prevent the spitting event.

(91) Reducing the power level to prevent the spitting event also stops the treatment from being as effective. It is therefore desirable for the response signal C.sub.4 to operate the variable attenuator to ramp the power back up to a normal treatment level promptly after it is reduced to prevent the spitting event.

(92) The microprocessor/DSP unit 816 may also be arranged to send control signals C1 and C2 to operate reset switches 862, 864 (e.g. MOSFET switches) which reset the differentiator after an event is detected. This ensures that the initial voltage across the capacitor 852 and resistor 866 is set to zero at the start of a new event.

(93) In the embodiment discussed above, the detector 834 needs to be sensitive to the changes in the reflected signal which represent the monitored behaviour. In this case, the detector may need to sense a rapid change in dV.sub.r/dt. Thus, if a diode detector is used, its rise/fall time must be short, e.g. 1 μs or less. For example, a tunnel diode based detector with a very fast pulse response may be used, e.g. product number ACTP1505N from Advanced Control Systems.

(94) In use, the apparatus may deliver microwave radiation having frequency of 14.5 GHz or 24 GHz at 100 W during normal treatment, and the threshold value for dV.sub.r/dt at with the trigger signal is generated may be set to 4000 V/s. Thus, when a dV.sub.r/dt value of 5000 V/s is detected (e.g. corresponding to a rise of 5V in 1 ms in the reflected power signal), the power level is instantly reduced to 10 W, then ramped back up to 100 W over the following 100 ms. An overall treatment time may be set by a user before treatment commences. The apparatus may automatically compensate for the ‘downtime’ caused by preventing spitting events, e.g. so that a treatment time of 10 s may in fact take up to 100 s when regular power level reductions to prevent spitting are taken into account.

(95) FIG. 9 is a graphical representation of how the power delivered by the apparatus can react to the detected reflected signal using the apparatus of the fifth aspect of the invention. The upper plot shown in FIG. 9 is the output from detector 834. There are three sharp voltage spikes 870 which indicate that a spitting event is about to occur and a gradual increase in voltage 872 which indicates a mismatch between the antenna and tissue, which may be an indication that treatment is effective. The lower plot uses the same time scale and shows the power delivered into the tissue. At positions corresponding to each of the voltage spikes 870, there are instant power drops 874 from 100 W to 10 W followed by relatively gradual ramp ups 876. When the mismatch occurs, the power delivered falls away gradually 878 as the mismatch prevents full power from being coupled into the tissue.

(96) The fifth aspect of the invention may also be used to detect other signature events, and therefore control other devices in the microwave line-up. For example, the monitoring arrangement may determine when the amplifier is to be driven into saturation or if a second frequency source is to be connected to the blade. In these cases, the monitoring arrangement may look for signature events associated with large open blood vessels. This particular signature may take the form of a constant level of voltage for a duration of time (time slot) that is greater than the average time for the system to produce a cut/coagulation over a predetermined distance in tissue. The size of each time slot can be established by experiment.