4/23/24, 2:10 PM
`
`Espacenet- Bibliographic data
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`
`https://worldwide.espacenet.com/publicationDetails/biblio?II
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`D&date=20090617&CC
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`4/23/24, 2
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`Espacenet- Bibliographic data
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`D&date=2009061 7&CC=EP&NR=2069.
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`

` {13} Vergifentlichungsaummer:
`
`{11} Publication number:
`
`{13} Numére de publication:
`
`EP 2 069 0714 AG
`
`internationale Anmeldung veréfientlicht durch die
`
`Weltorganisation fur geistiges Eigentum unter der Nummer:
`
`WO 2008/043999 (Art. 153(3) EPU).
`
`international application published by the World
`
`intellectual Property Organization under number:
`
`WO 2008/043999 (Art. 153(3) EPC).
`
`Demande internationale publiée par POrganisation
`
`Mondiale de la Propriéte Intellectuelle sous le numero:
`
`WO 2008/043999 (art. 153(3) CBE).
`
`

`

`(12) INTERNATIONAL APPLICATION PUBLISHED UNDER TRE PATENT COOPERATION TREATY (PCT)
`
`
`
`
`
`(10) Intermational Publication Neamber
`WO 2008/043999 A2
`
`(19) World Intellectual Property Organization
`international Bureau
`‘
`
`(43) International Publication Date
`17 April 2008 17.04.2008)
`
`(54) Tatermational Patent Classification:
`AGEN 5/62 (2006.01)
`AGIB 18/48 2005.01)
`
`(2%) Taterrational Application Number:cr
`AQ97
`4,
`PCT/GB2007003827
`(22) International Fling Date: 10 October 2007 (18.10.2007)
`
`(25) Filing Language:
`
`(26) Publication Language:
`.
`Dyak
`Cds
`sp
`tecne
`(30) Priority Data:
`O620064.6
`717030.4
`
`English
`
`English
`
`10 October2606 (10.10.2006)
`;
`31 August 2007 (31.08.2007)
`
`GB
`GB
`
`(7a) Agents: JOHNSGN, Richard et al.; Mewburn Hitis LLP,
`York House, 23 Kingsway, London Greater London WC2B
`GHP (GB).
`:
`:
`:
`a
`.
`(gy) Designated States (uniess otherwise indicated, for every
`kind of national protection availabley AE, AG, AL. AM,
`AT, AU, AZ, BA, BB, BG, BH, BR, BW, BY, BZ, CA, CH,
`CN, CO, CR, CU, CZ, DE, DK, DM, DO, DZ, EC, EE, BG,
`ES, FL, GB, GD, GE, GH, GM, GT, HIN, HR, HU, ID, IL,
`IN, 18, JP, KE, KG, KM, KN. KE KR, K%, LA, LC, LK,
`DR, LS, UP LU, LY, MA, MD, ME, MG, ME, MN, MW,
`MX, MY, MZ, NA, NG, NE, NO, NZ, OM, PG, PHL PL,
`:
`:O,
`RS,
`RU, SC,
`SP, SE, SG, SK, SL,
`SM,
`SY, SY,
`PE, RO, RS, RU, SC, SD, SH, SG, SK, SL, SM, S¥, SY,
`ETM, PN, PR, ‘PL UY, UA, UG, US, U4 VC, VN, ZA,
`EM, ZW.
`
`(72) Applicant Gor olf designated States except US}: MED-
`ICAL DEVICE INNOVATIONS LIMITED [GB/GH],
`Daresbury Innovation Centre Limited, Daresbury Science
`and Innovation Campus, Plalton Cheshire WA4 4B(GB).
`
`72}
`)
`
`
`
`Inventors; and
`BANCOCK,
`US only:
`(for
`Inventors/Applicants
`Christopher Paul [GB/GE!; 61 Bryants Hull, St George,
`Bristol Avon BSS 807% (GB). WHITE, Maicobn
`[GBAGKE: ‘Lhe Arches, Phe Grove, Coleford, Radstock,
`Bath And North Bast Somerset BA3 SLW (GB). BISHOP,
`Published:
`Jebu [GB/GRB]; 12 Metford Road, Redland, Bristol Avon
`5S6 7LE (GB). BOOTOR, Martie Wynford (GR/GB], —- without international search repart and to be republished
`Cardamine, Dulcote, Wells Somerset BAS 3P7, (GR).
`upon receipt of that report
`
`(84) Designated States (uniess otherwise indicated, forevery
`
`Kind of regional provection available}: ARIPO (BW, GH,
`OM, KE, LS, MW, M4, NA, SD, SL, S54, PZ, UG, 34M,
`ZW), Burasian CAM, AZ, BY, RG, KZ, MD, RU, TS, TM),
`Duropean (AT, BE, BG, CH, CY, CZ, DE, DE, EEL ES, Te,
`PROGR. GR, AU, LEIS, TP UP LO, LV, MO, MP NL, PL,
`FT, RO, SH, ST, SK, TR), OAPI GE, BI, CE CG, CL, CM,
`GA, GN, GQ, GW, ML, MR, NE, 5N, TD, TG).
`
`($4) Title: APPARATUS POR TREATING TISSUE WITH MICROWAVE RADIATION AND ANTUNNA CALIBRATION SYS-
`TEM AND METHOD
`
`
`
`ey
`<f
`
`
`
`Hae
`aB
`
`(87) Abstract: A calibration method and apparatus for surgical antennas which are arranged to deliver microwave radiation (e.g.
`having a treatment frequency of SOQ MHz to 100 GHz) into biological tissue is disclosed. An emitting region of the antenna is
`exposed to a plurality of calibration standards each having a different complex impedanceat the treatment frequency. In one embod-
`iment the calibration standards are created in a short-circuit-terminated waveguide cavity of variable length. In another embodiment,
`cLeaY
`each calibration standard is a different mixture of two or moreliquids. Measurementofthe magnitude and phase ofsignals reflected
`omthe emitting region when exposed to the calibration standard can permit calibration ofthe antenna, ¢.g. by generating a mapping
`function based on the measured values and knownor reference values forthe calibration standards, Also disclosedis tissue treatment
`
`
`apparatus having an ablation channel for conveying microwave radiation fo a surgical antenna at a high power level and a separate
`measurement channel for conveying microwave radiationto a surgical antenna at a low powerlevel, wherein the measurement chan-
`nel bypasses noisy corsponents on the ablation channel. A surgical antenna having an impedance transformerfor matching an e.g.
`coaxial feed structure which terminates in one or more radiating elements wilh Ossue to be treated is also disclosed.
`
`y=©— 3
`
`sS=aW
`
`o:
`
`

`

`WO 2608/043999
`
`POCT/GB2007/803827
`
`APPARATUS FORTREATING TISSUEWITH MICROWAVE
`
`ANTENNA CALIBRATION SYSTEM AND METHOD
`
`TECANICAL FIELD
`
`The invention relates to the treatment of biological
`
`tissue using microwave radiation.
`
`In particular aspects,
`
`the
`
`invention concerns a surgical antenna for delivering microwave
`
`radiation to tissue, a tissue treatment system for carrying
`
`out ablation or measurement of tissue using microwave
`
`radiation from such an antenna, and a system and method of
`
`calibrating an antenna for use in such a system.
`
`An electrosurgical system that is arranged to
`
`controllably ablate a tumour and/or measure information
`
`concerning the tumour and surrounding healthy tissue is known.
`
`Such a system may use two channels: a first channel
`
`toa perform
`
`controllacd tissue ablation, and a second channel
`sensitive tissue state {dielectric} measurements.
`
`to perform
`The general
`
`principles relating to the operation of such a system are
`
`disclosed in WO 2004/047659 and WO 2005/115235.
`
`This disclosure comprises three main aspects.
`
`The first
`
`aspect relates to a system and method for calibrating surgical
`antennas at
`the point of radiation (the aerial), and in
`
`particular to performing the calibration routine automatically
`
`when the calibration systems are used in conjunction with an
`
`electrosurgical system @.g. of the known type.
`
`The second
`
`aspect relates to further improvements to the known treatment
`system, which improvements offer significant advantages in
`terms of enhanced measurement sensitivity and reduced power
`
`levels required in the measurement mode due to the use of a
`
`cn
`
`ts
`
`(si
`
`tal
`
`sad on
`
`

`

`WO 2603/043999
`
`PCT/GB2007/003827
`
`10
`
`L5
`
`separate low power transmitter and receiver {transceiver}.
`
`The third aspect relates to surgical antennas that may be used
`
`with the calibration system to enable said antennas to be
`
`calibrated at the distal and (the aerial) thereby to enable
`Said antennas to be used to perform tissue state measurements
`or to be used to ablate tissue where it is desirable to
`
`perform dynamic impedance matching between the distal tip of
`
`the antenna (the aerial) and the biclogical tissue lead.
`
`Calibration System and Procedure
`
`At its most general,
`
`the first aspect of the invention
`
`May provide calibration apparatus for an antenna that is
`
`arranged to emit microwave radiation from an emitting region
`
`thereof,
`
`the apparatus having:
`
`a loading arrangement adapted
`
`to subject the emitting region of the antenna to a plurality
`of impedances, each impedance having a known value for a
`predetermined frequency of microwave radiation, a detector
`
`arranged to measure the magnitude and phase of microwave
`radiation having the predetermined frequency that is emitted
`
`from the antenna and reflected from the loading arrangement,
`
`and a processing unit configured to generate calibration data
`
`for the antenna, wherein,
`
`if the antenna is used subsequently
`
`to measure magnitude and phase of microwave radiation having
`
`the predetermined frequency with an unknown load at the
`
`emitting region of the antenna,
`
`the calibration data is usable
`
`to convert the measured magnitude and phase to be
`
`representative of the unknown load.
`
`Praferably,
`
`the loading arrangement
`
`includes a
`
`wa
`
`ubstantially lossless waveguide cavity between a first end
`
`adapted to receive the emitting region of the antenna and a
`
`second end, and wherein a distance between the first end and
`
`the second end is variable.
`
`For example,
`
`the second end may
`
`be slidable relative to the first end, e.g. under the action
`
`of a linear actuator.
`
`

`

`WO 2603/043999
`
`PCT/GB2007/003827
`
`Preferably,
`
`the cavity is electrically connectable to the
`
`antenna and the second end electrically connected to the
`
`cavity.
`
`Phe electrical connection between the cavity and
`
`antenna and/or between the cavity and the second end may be
`
`through a radio frequency (RF) choke.
`
`Preferably,
`the plurality of impedances include 9 ©
`{short circuit) and ~ Q {open circuit}.
`Preferably,
`the loading arrangement is adapted to permit
`
`generation of calibration data for two or more different
`
`frequencies of microwave radiation.
`
`the first aspect of the invention
`in another expression,
`may provide a combination of calibration apparatus according
`to any preceding claim and an antenna arranged to emit
`
`microwave radiation from an emitting region thereof, wherein
`
`at least the emitting region of the antenna and the loading
`
`arrangement are packaged together in a sterile environment.
`
`In yet another expression,
`
`the first aspect of the
`
`invention may provide a method of calibrating an antenna that
`is arranged to emit microwave radiation from an emitting
`region thereof,
`the method comprising: subjecting the emitting
`region to a plurality of impedances, each impedance having a
`
`known value for a predetermined frequency of microwave
`
`for each impedance: emitting microwave radiation
`yadiation,
`having the predetermined frequency through the antenna;
`measuring the magnitude and phase of the emitted microwave
`
`radiation that is reflected from the loading arrangement; and
`
`generating calibration data for the antenna from the magnitude
`and phase measured for each of the plurality of impedances,
`whereby,
`if the antenna is used subsequentiy to measure
`magnitude and phase of microwave radiation having the
`predetermined frequency with an unknown load at the emitting
`region of the antenna,
`the calibration data is usable to
`convert the measured magnitude and phase to be representative
`of the unknown load.
`
`The ability to effectively perform antenna calibration at
`the emitting region (e.g. distal tip) may enable efficient
`
`wn
`
`16
`
`bo Cit
`
`30
`
`Ww FV
`
`

`

`WO 2603/043999
`
`PCT/GB2007/003827
`
`Microwave energy transfer into biological tissue, where the
`impedance presented to the distal tip of the surgical anterna
`
`changes as the treatment process progresses. Once the antenna
`
`structure has been calibrated, 1t is then possible to perform
`
`accurate dynamic tuning adjustment to enable the distal tip of
`
`the antenna structure to be impedance matched with the
`
`changing impedance of the biclogical tissue. Fhe ability to
`
`perform impedance matching between the distal tip of the
`fen
`
`surgical antenna and the biological
`
`tissue can prevent
`
`reflection of energy due to impedance mismatch, which can
`
`cause excessive heating of antenna and cable assemblies and
`
`increase the time required to perform ablation of a volume of
`
`tissue.
`
`In applications where the antenna is used in minimally
`
`imvasive surgery this heating may cause te collateral damage
`
`i
`
`5
`
`to healthy tissue structures.
`
`A further advantage is that the
`
`dosage of energy delivered into biological tissue can be
`controlled with greater accuracy than that possible using a
`
`system where unquantifiable reflections due to impedance
`
`mismatches cannot be compensated for.
`
`For the implementation
`
`of this feature it is preferable for this invention to be used
`
`with a method of performing dynamic impedance matching.
`
`A
`
`system to perform such impedance matching using a three stub
`
`waveguide cavity tuner, where the stubs are automatically
`
`moved using three linear motors and a suitable control system
`
`has been disclosed in WO 2004/047659.
`
`Fhe ability to effectively perform antenna calibration at
`the distal tip may also enable the surgical antenna to be used
`as a useful tool for measurement of dielectric information
`
`relating to
`
`the
`
`properties of the biological tissue. Effective
`
`calibration at the distal tip of the surgical antenna enables
`
`the measurement reference plane to be moved to the exact site
`
`{or location} where the measurement is to be performed,
`
`for
`
`example at the periphery between healthy tissue and cancerous
`
`tissue, er inside the cancerous tissue. The ability to
`
`calibrate surgical antennas in this way can enable optimal
`
`measurement sensitivity to be achieved.
`
`2
`
`5
`
`Ud
`
`Co
`
`on
`
`

`

`WO 2603/043999
`
`PCT/GB2007/003827
`
`in
`
`Therefore,
`
`the current invention can be used to enable
`
`dynamic impedance matching to be performed, and can be used to
`
`enable sensitive and repeatable dielectric measurements to be
`
`made.
`
`The current invention relates primarily to the
`
`5
`
`calibration of surgical antennas, but the invention is not
`
`Limited to calibrating these devices.
`
`‘The calibration system disclosed herein effectively
`
`conmects the distal tip of the antenna to a plurality of load
`impedances between open circuit (infinite impedance) and short
`circuit
`(zero impedance} values to enable the antenna to have
`
`10
`
`the capability of being able to measure or be sensitive to a
`
`range of impedances between the two extremes.
`
`The distal tip
`
`of the antenna may be automatically subjected to a range of
`
`~
`
`impedances. Methods of automating the measurements are
`
`15
`
`disclosed herein.
`
`Preferably,
`
`the antenna calibration system uses a sliding
`
`short with the antenna fixed in position. RF chokes may be
`
`included to enable the antenna and the sliding short to bs
`
`loosely fitted inside the cavity.
`
`26
`
`In this specification microwave means the frequency range
`
`of between 506 MHz and 100 GHz. However, frequencies between
`
`14 GHz and 15 GHz are preferred, and a spot frequency of 14.5
`
`GHz is used in some embodiments discussed below.
`
`Although the primary purpose of the invention is to
`
`25
`
`calibrate antennas for use in tissue ablation and measurement,
`
`the invention is not limited to this application.
`
`Indeed,
`
`the
`
`invention. may be used wherever the measurement location is at
`
`the distal tip of an antenna arrangement. Put
`
`in another way,
`
`the invention may permit all systematic errors that are
`
`30
`
`present between the distal tip of the antenna (the aerial} and
`
`the digital signal processing unit to be cancelled out,
`
`thus
`
`enabling the tissue load to be effectively connected ta the
`
`digital signal processing unit. This may take into account
`
`variations in the components within the microwave transceiver,
`
`35
`
`for example,
`
`thermal noise or short noise produced by low
`
`

`

`WO 2603/043999
`
`PCT/GB2007/003827
`
`noise amplifiers, driver amplifiers, microwave frequency .
`
`mixers and PIN diode switches and attenuators,
`
`it may be desirable to calibrate at more than one
`
`frequency where a first frequency is used for controlled
`
`ablation and a second frequency is used to perform dielectric
`
`measurements (tissue type/s tate, etc). For example, it may be
`
`desirable to calibrate an antenna structure over a frequency
`
`range of +/- 50 MHz around a spot frequency of 14.5 GHz or ait
`
`
`may be desirable to use other frequencies within the microwave
`or RF region of the electromagnetic spectrum. The dimensions
`ef the calibration system {or assembly} can be adjusted to
`
`accommodate any practicable frequency {or range of
`
`frequencies) where the underlying theory related to the
`
`current
`
`invention remains valid. Bue to the dynamic tuning
`
`mechanism used in the system (e.g. of the type described in WO
`
`2004/047659}, it may be necessary to calibrate at the ablation
`
`frequency.
`
`In this mode of operation,
`
`information concerning
`
`the state of the ablated tissue is used to automatically
`
`the impedance matching mechanism to ensure that
`control
`maximum power
`(or the demanded power)
`is delivered into the
`
`tissue Load seen by the distal tip of the antenna.
`In a
`particular arrangement given in WoO 2004/0 7659,
`four
`directional couplers are used to measure the forward and
`
`reflected power signals and this information is used as the
`
`basis upon which the dynamic impedance matching method is
`
`implemented. It may,
`
`for example, be desirable to perform
`
`tissue ablation at 10 GHz and make dielectric measurements at
`
`pod 6 GHz.
`
`In the instance where it is necessary to calibrate the
`fy
`oD 7)
`ry gu Oo ps o ct a fe ct
`system at two or more frequencies, it is desi
`
`bw
`
`the frequencies can propagate inside the microwave structure,
`
`i.e.
`
`in the case of using rectangular or cylindrical
`
`waveguide,
`
`the waves
`
`should not be cut-off. Tt may also be
`
`esirable to include more than one transceiver unit in the
`
`system when more than one frequency is used and there is a
`_large difference between the two frequencies, for example a 10
`GHz difference. Higher order modes may also propagate when the
`
`an
`
`i
`
`8
`
`the
`
`3
`
`iw
`
`st
`
`

`

`WO 2603/043999
`
`PCT/GB2007/003827
`
`wavelength of the calibration frequency signais are small
`
`compared with the size of the waveguide or co-axial
`
`calibration assembly.
`
`These effects may be taken into account
`
`by performing a system analysis to model
`
`the effects of higher
`
`ry
`
`order modes set up in the cavity. This may not be needed when
`
`the same frequency is used for ablation and measurement
`
`because a standard waveguide can be used which enables the
`
`relevant frequency to propagate unimpaired (e.g.
`
`for 14 GHz,
`
`WRE?2
`
`(WG17) may be used}.
`(WGLS} or WRYS
`The tissue ablation/measurement systems disclosed e.g.
`
`in
`
`WG 2004/047659 and WO 2005/115275 provide for impedance (or
`
`energy) matching between the surgical treatment antenna and
`
`the tissue load, and far the antenna to be capable of
`
`measuring smali changes in complex impedance to enable
`
`characterisation of various tissue types,
`tissue states and/or
`stages associated with the growth of cancerous tumours to be
`
`measured. The present invention aims to improve the
`
`operational efficiency of those systems by providing for the
`
`calibration of the surgical antenna to take place at the
`
`distal tip where the antenna will radiate energy into tissue.
`
`In order to ensure that the widest possible range of
`
`impedances can be measured, it is desirable for the
`
`calibration system to be capable of locally presenting the
`
`antenna with a range
`
`of known impedances between open circuit
`
`and short circuit conditions.
`
`Tt is further desirable for the
`
`calibration procedure to be automated.
`
`The antenna may be a surgical antenna or any other type
`of antenna structure, or other device. The invention is of
`
`particular use where the design of said antenna (or other
`
`device} dees not
`
`lend itself to be connected
`
`to a standard co-
`
`a@ co-axial {or
`for example,
`axial calibration arrangement,
`waveguide) 50 Q lead, and/or a co-axial {or waveguide} short
`cireuit, andfor a co-axial
`(or waveguide}, open-circuit,
`
`and/or a co-axial {or waveguide) sliding load. Phe calibration
`
`system described herein enables the reference plane for
`a mu te
`
`ibration to be moved to the distal tip of the antenna and
`
`re un
`
`an
`vas)
`
`Nr cn
`
`Lad =>
`
`35
`
`

`

`WO 2603/043999
`
`PCT/GB2007/003827
`
`wm
`
`takes into account
`
`the shape and geometry .of the antenna
`
`structure to be calibrated.
`
`Preferably, a range of calibration positions can be
`
`obtained by moving a sliding short circuit, connected to an
`electromechanical linear actuator,
`in such a manner that the
`Sliding short
`(or plunger} starts at the short circuit
`position on the Smith chart and as the plunger is withdrawn
`from the waveguide cavity,
`the impedance moves around the
`
`outer circle {assuming a lossless cavity) where one or more
`
`calibration points can be measured.
`
`If the cavity is
`
`substantially lossless then there may be no real component
`
`present and so the complex impedance will either be an
`inductive reactance or a capacitive reactance. Such an
`
`arrangement forms a particular aspect of the current invention
`
`and is addressed in detail below.
`
`‘The calibration can be
`
`represented on a Smith chart or in other forms, ¢.g. a polar
`
`chart, phase/maqgnitude plots or another suitable measurement
`
`plane.
`
`Due to the need to accurately measure both the phase and
`
`magnitude of information in terms of impedance seen at the
`
`distal end of the treatment /measurement antenna, it is
`
`desirable to calibrate the surgical antenna at the point where
`
`tissue state (dielectric) measurements are to be made. TF the
`
`antenna is not calibrated at the distal tip (where it connects
`
`to the tissue load)
`
`then it is more difficult to measure the
`
`value of impedance presented to the distal tip, and it will be
`
`‘Gifficult to make valid and repeatable measurements of tissue
`
`impedances and/or be able to differentiate between various
`
`tissue. types. Phase and magnitude variations associated with
`
`the components that form the transmission path between the
`
`measurement
`
`instrumentation (generator) and the distal tip of
`
`the antenna make it difficuit to theoretically determine the
`exact phase and magnitude of the signal at the distal end of
`
`the antenna seen at the generator end, where the microwave
`
`transceiver and signal
`
`processing circultry is located. The
`
`components in the path may include: microwave connectors and
`
`=
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`WO 2603/043999
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`PCT/GB2007/003827
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`interconnects, a Flexible cable assembly, a Length of rigid
`co-axial cable that forms a part of the antenna (this is
`
`inserted inside the body},
`
`the antenna (aerial) itself,
`
`the
`
`tuning unit,
`
`the microwave signal mixers, various co-axia
`
`couplers,
`
`semi rigid or flexible semi rigid assemblies,
`
`low
`
`noise amplifiers, drive amplifiers, microwave circulators and
`
`other components within the microwave transceiver line-up. Due
`
`to the short wavelengths associated with microwave
`
`frequencies, it is very difficult to calculate or quantify the
`
`be oo
`
`phase at the distal end of the antenna,
`for example the free
`space wavelength at 14.5 GHz is 20.69 mm,
`thus a variation of
`imm caused,
`for example, by a connector not fully tightened,
`
`will cause a phase variation of approximately 17 degrees.
`
`Also, due to limitations on possible manufacturing tolerances,
`
`it may be impossible to build transmission line assemblies of
`
`several thousands of millimetres in length with less than 1 mm
`
`for less than 0.1%) yield variation,
`
`If the above assembly is connected to the measurement
`
`instrumentation (generator) and calibration is performed with
`
`20
`
`the reference plane at the distal tip of the antenna,
`
`then the
`
`a@ifficulties described above can be reduced or eliminat
`
`Therefore,
`
`the invention addresses problems associated with
`
`inferring information regarding a remotely located tissue load
`
`connected to the distal tip.of the antenna. Preferably,
`
`the
`
`able assembly used between the generator and the distal tip
`199)
`fe
`oss
`and a small
`
`of the antenna exhibits a low insertion
`
`variation in phase with random flexure. It is preferable for
`the insertion loss of the complete assembly (flexible cable
`assembly and rigid co-axial antenna)
`to be less than 1.5 dB,
`
`30
`
`and for the phase variation to be less than 2 degrees for any
`
`possible physical
`y
`im
`ssembi
`het
`
`random variation of the flexible cable
`
`The flexible cable assembly may be a co-axial cable
`
`assemoly or a waveguide assembly or a combination of the two,
`for example, one metre of low loss waveguide assembly could be
`ee)
`attached to the cutpur of the electrosurgical unit and a
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`WO 2603/043999
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`PCT/GB2007/003827
`
`10
`
`second metre of flexible co~axial cable could be attached to
`
`the distal end of the waveguide assembly and be used as the
`
`flexible section to ease antenna manipulation. This
`
`arrangement could be particularly suitable where it is
`
`desirable to implement a structure where the treatment antenna
`
`is attached to a mechanical arm that forms a permanent
`structure.
`In this arrangement, a rotary joint may be employed
`to move the fixed arm in one plane. Said waveguida assembly
`
`may be flexible,
`
`twistable, or a combination of the two. The
`
`‘advantages of using a waveguide assembly are the high power
`
`handiing capability and low insertion loss.
`
`In one aspect,
`
`the invention may therefore relate to a
`
`calibration system to enable a surgical antenna arrangement to
`
`be calibrated at the distal tip. Such a calibrated antenna
`
`arrangement may be used to make repeatable measurements of the
`complex impedance of biclogical tissue for the purpose of the
`determination of the type of biclogical tissue and/or the
`
`state of said tissue, and/or for differentiating between
`
`healthy and cancerous tissue. Alternatively or additionaily,
`the calibrated antenna arrangement may be dynamically
`
`impedance matched into a load represented by the changing
`
`state of said bislegical tissue during the treatment
`
`(or
`
`ablation} process to ensure that said energy is efficiently
`launched for matched} inte said bislogical tissue load, hence
`providing a controlled and efficient method of causing tissue
`
`ablation which can avoid the drawbacks associated with
`
`conventional ablation systems.
`
`According to the invention, calibration takes place at
`
`the reference plane where
`i.e.
`the distal tip of the antenna,
`said calibration is to be made is positioned at the distal tip
`of the surgical antenna. During calibration, it is desirable
`
`for the distal tip of the antenna be exposed to a large range
`of impedances. Ideally the range should span from an open
`circuit, where the impedance is infinity,
`to a short circuit,
`where the impedance is zero,
`to make it possible
`for as much
`information as possibl
`regarding the state of the biclogical
`
`i5
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`
`ho an
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`10
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`Me wn
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`WO 2008/043999
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`PCT/GB2007/003827
`
`roy feat
`
`tissue to be available for capture. The calibration system
`
`described in this invention may enable both the calibration
`plane to be located at the distal tip of the antenna and for
`the impedance measurement range to be maximised. It is
`
`reguired to be able to repeatably measure smali changes in
`
`magnitude anc/or phase in order to increase the chance of
`
`being able to differentiate between healthy and cancerous
`
`tissue or between types of cancerous tissue. It is therefore
`preferable to optimise the measurement sensitivity or
`capability. Described generally,
`this can be achieved using a
`
`sliding short circuit
`
`for plunger)
`
`inserted inside a wavequide
`
`cavity that is of large enough geometry to prevent the wave
`
`from being cut-off. The exact location of the antenna and the
`
`overall physical geometry of the calibration system may be
`
`optimised based on the theory set out herein e.g. by using
`
`Computer Simulation Technology (CST) Microwave Studio®
`
`electromagnetic field simulation tool. However,
`
`the design of
`
`the calibration system is not limited to using this simulation
`
`package.
`
`Other suitable electromagnetic field simulation
`
`packages that may be used include Ansoft HFSS and Flomerics
`
`Microstripes.
`
`in an alternative arrangement for performing a multipoint
`
`calibration, a plurality of fixed loads designed to Fit to the
`
`distal tip of the surgical antenna that take into account the
`
`non 50 G impedance environment created by the radiating tip
`
`.(the aerial) could be used. However,
`
`this arrangement may
`
`require each load to be physically connected to the distal tip
`of the antenna. This may
`be particularly important in a
`surgical environment where possible operator error is
`preferably minimised and the time
`available to perform
`surgical procedures is limited. Other possible calibration
`arrangements include:
`a threaded arrangement whereby the load
`is moved by twisting a rod inside a cavity containing a moving
`load (short), or an arrangement whereby a load is moved using
`
`a biased, 6.q. spring loaded, ratchet mechanism (e.g. similar
`
`to that used in retractable pens}.
`
`In the latter arrangement,
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`WO 2603/043999
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`PCT/GB2007/003827
`
`12
`
`for example,
`
`the pressed state (where the spring is
`
`compressed} may cause the movable load to be in the short
`
`circuit position, and the released state (where the spring is
`released) may cause the movable load to be in the open circuit
`position, i.e. the movement between the pressed and released
`
`states may be an exact multiple of an odd number of quarter
`wavelengths at. the frequency of operation to enable the
`impedance transformation from an open circuit to a short
`
`circuit or vice versa.
`
`In another aspect,
`
`the invention may relate to a method
`
`of connecting a transmission assembly to a calibration system
`
`to perform an automated calibration using measurement
`
`instrumentation located away from the calibration site.
`
`In a
`
`preferred ambodiment,
`
`the transmission assembly is 1.62 metres
`
`15
`
`in length and comprises:
`
`a co-axial connector
`
`(preferably N-
`
`type}, a flexible transmission cable of length 1.5 metres, and
`an antenna assembly of Length @.12 metres comprising itself of
`
`a section of rigid co-axial cable with an outer jacket made
`
`from a composition of stainless steel and copper
`
`or silver
`
`{the inner of the outer jacket shail be copper
`
`(or silver
`
`plated)
`
`to provide low conductor loss for the electromagnetic
`
`field), and a distal tip made from a low loss ceramic material
`
`that forms an impedance transformation circuit, and also
`
`provides the desired hardness and sharpness to enable the
`antenna to be directly inserted through human tissue. This
`
`invention is not Limited to the use of co-axial transmission
`
`assemblies, or co~asial anterna structures. For example,
`
`the
`
`transmission line may comprise a waveguide assembly (solid,
`
`flexible or flexible/twistable} and a ceramic antenna
`
`structure may be coupled directly into said waveguide
`
`Gy
`structure. The transmission assembly may be greater than 1.5
`
`The length may be Limited by the insertion
`metres in length.
`5
`ce orwo @
`&Os
`be
`3 of the cable assembly and the antenna structure since
`
`Q of the system is limited by the insertion loss and it. is
`
`required for the 9 to be as high as possible to enable 4
`resonant cavity to be set-up between the tuner and the digital
`
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`WO 2603/043999
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`PCT/GB2007/003827
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`13
`
`tip of the antenna.
`
`For conventional
`
`low less co-axial cable
`
`the length may be limited to 3 metres.
`
`In yet another aspect,
`
`the invention may relate to a
`
`method of operating the sliding short to enable the antenna to
`
`be connected to a plurality of calibration impedances.
`
`An
`
`example of calibrating to a specific impedance between the
`
`open anc short
`
`load is as follows: if the sliding short is
`
`moved an electrical distance of three eighths of a wavelength
`
`at the frequency of operation from the short circuit {the
`generator)
`towards the tissue (the load)
`then, assuming that
`
`the impedance
`the transmission loss along said path is zero,
`Will comprise an inductive reactance of value equal
`to the
`characteristic impedance of the transmission line. It should
`be noted that this analysis assumes that a perfect short
`
`circuit
`exists when the sliding short is at the distal tip of
`the antenna. The advantage of using the sliding load
`
`arrangement is that
`
`the varlable