U.S. patent application number 10/374097 was filed with the patent office on 2003-08-14 for electrosurgery system.
This patent application is currently assigned to Gyrus Medical Ltd.. Invention is credited to Amoah, Francis E., Goble, Colin C.O., Goble, Nigel M..
Application Number | 20030153908 10/374097 |
Document ID | / |
Family ID | 27269667 |
Filed Date | 2003-08-14 |
United States Patent
Application |
20030153908 |
Kind Code |
A1 |
Goble, Colin C.O. ; et
al. |
August 14, 2003 |
Electrosurgery system
Abstract
An electrosurgery system includes an electrosurgical generator
(10) coupled to or part of an electrosurgical instrument, the
generator being operable to generate electrosurgical power in low
frequency (typically at 1 MHz) and high frequency bands (typically
at 2.45 GHz) either simultaneously or individually. The generator
includes a load-responsive control circuit which, in one mode,
causes power to be generated predominantly at 1 MHz when the load
impedance is high and predominantly at 2.45 MHz when it is low.
This allows automatic switching between cutting and coagulation
operation. In one embodiment, the instrument includes a gas plasma
generator operating such that an ionisable gas is energised in a
gas supply passage by the 2.45 GHz component to form a plasma
stream which acts as a conductor for delivering the 1 MHz component
to a tissue treatment outlet of the passage.
Inventors: |
Goble, Colin C.O.; (Penarth,
GB) ; Amoah, Francis E.; (Cardiff, GB) ;
Goble, Nigel M.; (Cardiff, GB) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
Gyrus Medical Ltd.
|
Family ID: |
27269667 |
Appl. No.: |
10/374097 |
Filed: |
February 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10374097 |
Feb 27, 2003 |
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09517631 |
Mar 3, 2000 |
|
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6582427 |
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60141261 |
Jun 30, 1999 |
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Current U.S.
Class: |
606/41 ; 606/34;
606/45; 606/49 |
Current CPC
Class: |
A61B 2018/0066 20130101;
A61B 18/12 20130101; A61B 18/1206 20130101; A61B 18/14 20130101;
A61B 18/042 20130101 |
Class at
Publication: |
606/41 ; 606/45;
606/49; 606/34 |
International
Class: |
A61B 018/14; A61B
018/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 5, 1999 |
GB |
9905210.2 |
Claims
1. An electrosurgery system comprising an electrosurgical
generator, a feed structure and an electrode assembly, the
electrode assembly having at least one active electrode and at
least one adjacent return electrode, each of which is coupled to
the generator via the feed structure, wherein the generator and
feed structure are capable of delivering radio frequency (r.f.)
power to the active and return electrodes in lower and upper
frequency ranges, the upper range containing frequencies at least
three times the frequencies of the lower frequency range.
2. A system according to claim 1, wherein the lower frequency range
is 100 kHz to 100 MHz and the upper frequency range is 300 MHz to
10 GHz.
3. A system according to claim 2, wherein upper frequency range is
above 1 GHz and the operating frequencies in the said upper and
lower ranges have a frequency ratio of 5:1 or greater.
4. A system according to claim 2, wherein the generator is arranged
such that the r.f. power delivered in the upper frequency range is
at a fixed frequency which is at least ten times the frequency of
r.f. power delivered in the lower frequency range.
5. A system according to claim 4, wherein the fixed frequency is
fixed to the extent that it remains within 50 MHz of 2.45 GHz.
6. A system according to claim 1, wherein the generator and feed
structure are arranged to deliver r.f. power to the electrodes in
the lower and upper frequency ranges simultaneously.
7. A system according to claim 1, wherein the generator includes a
control circuit responsive to electrical load and operable to cause
the delivered power to have a predominant frequency component in
the lower frequency range when the load impedance is in an upper
impedance range and to have a predominant frequency component in
the upper frequency range when the load impedance is in a lower
impedance range.
8. A system according to claim 1, comprising a supply unit, a
handpiece, and a cable connecting the handpiece to the supply unit,
wherein: the electrode assembly is mounted in the handpiece, the
generator has first and second stages for generating power in the
lower and upper frequency ranges respectively, both stages being
contained in the supply unit, and the supply unit and the cable are
configured such that power is supplied to the handpiece in both the
lower and the upper frequency range via the cable.
9. A system according to claim 1, comprising a supply unit, a
handpiece, and a cable connecting the handpeice supply unit,
wherein the electrode assembly is mounted in the handpiece, and the
generator has first and second stages for generating power in the
lower and upper frequency ranges respectively, the fir stage being
contained in the supply unit and the second stage being contained
in the combination of the handpiece and the electrode assembly.
10. A system according to claim 1, wherein the feed structure
comprises: a rigid or resilient coaxial feed supporting the
electrodes at a distal end, the coaxial feed having an inner supply
conductor and an outer supply conductor, and an isolating choke
element in the form of a conductive sleeve connected to the outer
supply conductor in the region of the said distal end, and having
an axial length which is an odd number multiple (1, 3, 5, . . . )
of a quarter wavelength at an operating frequency of the generator
in the upper frequency band.
11. A system according to claim 1, wherein the return electrode
comprises a conductive sleeve.
12. A system according to claim 11, wherein: the active electrode
comprises a rod projecting from the conductive sleeve; the feed
structure comprises a rigid or resilient coaxial feed; and the
active electrode and the return electrode are connected to the
inner and outer conductors respectively of the feed at its distal
end, and extend respectively distally and proximally with respect
to the said connection to form a dipole at an operating frequency
of the generator in the upper frequency range.
13. A system according to claim 1, wherein the return electrode is
covered with a electrically insulative layer.
14. A system according to claim 1, wherein the electrode assembly
includes a gas supply passage and the active electrode is located
in the passage to act as a gas iodising electrode.
15. A system according to claim 6, wherein the electrode assembly
includes a gas supply passage and the active electrode is located
in the passage to act as a gas ionising electrode, and wherein the
active electrode is an elongate conductor having an electrical
length in the region of a quarter wavelength at the operating
frequency of the generator in the upper frequency range.
16. A system according to claim 14, wherein the active electrode is
capacitively coupled to the return electrode.
17. A method of operating an electrosurgical instrument having an
electrode assembly with an active electrode and a return electrode,
comprising delivering to the electrodes radio frequency (r.f.)
power at frequencies in both a lower frequency range and an upper
frequency range, the upper frequency range containing frequencies
which are at least three times the frequencies of the lower
frequency range.
18. A method according to claim 17, wherein the lower frequency
range is 100 kHz to 100 MHz and the upper frequency range is 300 M
to 10 GHz, power being delivered to the electrodes at upper and
lower operating frequencies which have a frequency ratio of at
least 5:1.
19. A method according to claim 18, wherein the r.f. power
delivered in the upper frequency range is at a fixed frequency
which is at least ten times the frequency of power delivered in the
lower frequency range.
20. A method according to claim 19, wherein the fixed frequency is
in the region of 2.45 GHz.
21. A method according to claim 17, comprising delivering r.f.
power to the electrodes in the lower and upper frequency ranges
simultaneously.
22. A method according to claim 19, wherein the r.f. power is
delivered in the lower and upper frequency ranges via a common
feed.
23. A method according to claim 17, including automatically
controlling the delivered power in response to electrical load
impedance such that the delivered power has a predominant frequency
component in the lower frequency range when the load impedance is
in an upper impedance range and a predominant frequency component
in the upper frequency range when the load impedance is in a lower
impedance range.
24. A method according to claim 17, in which an ionisible gas is
passed through a passage containing the active electrode, the gas
is ionised by delivering power to the electrodes in the said upper
frequency range to form a gas plasma in the passage, and causing
the gas plasma to emerge at a treatment outlet of the passage.
25. A method according to claim 24, in which r.f. power is
delivered to the electrodes simultaneously in both the upper and
the lower frequency ranges, the emerging gas plasma generated by
power in the upper frequency range acting as a conductor to the
outside for treatment current in the lower frequency range.
26. A method according to claim 17, wherein the return electrode
acts as a capacitive non-tissue-contacting electrosurgical current
return element.
27. A method according to claim 21, in which the amplitudes of the
delivered r.f. power in the lower and upper frequency ranges are
varied with respect to each other.
28. A dual frequency electrosurgical system for cutting living
tissue, the system being arranged to operate normally in a low
frequency cutting or vaporisation mode, but to operate in a UHF
coagulation mode in response to detection of a lower than normal
load impedance as would typically be encountered when a blood
vessel is severed.
29. A system according to claim 28, wherein the system comprises an
electrosurgical generator, an electrode assembly and at least fist
and second supply conductors coupling the electrode assembly to the
generator, the electrode assembly comprising at least one active
electrode and a capacitive return element adjacent the active
electrode, and the active electrode and the return element being
coupled to the generator by the first and second supply conductors
respectively.
30. A system according to claim 28, arranged to operate
predominantly at a first frequency in the range of from 100 kHz to
40 MHz when in the low frequency cutting mode and predominantly at
a second frequency above 300 MHz when in the UHF coagulation
mode.
31. A system according to claim 30, wherein the first frequency is
less than 10 MHz and the second frequency is greater than 1
GHz.
32. A method of electrosurgically treating tissue using an
electrosurgical instrument having an electrode assembly with an
active electrode and an adjacent return element set back from the
active electrode, wherein electrosurgical cutting or vaporisation
is performed by supplying electrosurgical energy to the assembly in
a lower frequency range and electrosurgical coagulation is
performed by supplying electrosurgical energy to the assembly in an
upper frequency range, the upper frequency range containing
frequencies which are at least three times the frequencies of the
lower frequency range.
33. A method of electrosurgically treating tissue using an
electrosurgical instrument having a electrode assembly with an
active electrode and an adjacent return element set back from the
active electrode, wherein the active electrode is applied to the
tissue to be treated and manipulated whilst r.f. electrosurgical
energy is supplied to the assembly predominantly in a lower
frequency range at a voltage level sufficient to cause cutting or
vaporisation of the tissue until the load impedance drops to a
predetermined degree at which time the energy is supplied
predominantly in an upper frequency range to cause coagulation of
the tissue, the supplied energy reverting predominantly to the
lower frequency range when the load impedance rises again, and
wherein the upper frequency range contains frequencies which are at
least three times the frequencies of the lower frequency range.
34. A method according to claim 33, wherein treatment in the lower
and upper frequency ranges is performed respectively with and
without arcing in a current path between the active electrode and
the return element.
35. A method according to claim 33, wherein the lower frequency
range is from 100 kHz to 40 MHz and the upper frequency range is
from 300 M to 10 GHz.
36. A method according to claim 33, wherein the predominant
frequency of the r.f. electrosurgical energy associated with said
coagulation is at least ten times the predominant frequency of the
r.f. electrosurgical energy associated with said cutting or
vaporisation.
37. A dual frequency electrosurgical system configured to perform
electrosurgical cutting or vaporisation at a first frequency within
a lower frequency range and electrosurgical coagulation at a second
frequency within an upper frequency UHF range.
38. A system according to claim 37, wherein the first frequency is
within the range of from 100 kHz to 5 MHz and the second frequency
is within the range of from 300 MHz to 10 GHz.
39. An electrosurgical system comprising an electrode assembly with
at least a pair of electrodes for receiving radio-frequency
electrosurgical power, and a gas supply passage containing at least
one of the said electrodes, the arrangement of the electrodes and
the passage being such that when the electrodes are energised with
sufficient radio frequency power at a frequency in the range of
from 300 MHz to 10 GHz, and when an ionisable gas is passed through
the passage, a gas plasma is formed in the passage.
40. A system according to claim 39, wherein the passage terminates
in a distal nozzle downstream of the said at least one
electrode.
41. A system according to claim 39, wherein the electrode assembly
is part of a sterilised electrosurgical device.
42. A system according to claim 39, including a generator coupled
to the electrodes and operable to generate electrosurgical power at
a frequency in the range of from 300 MHz to 10 GHz.
43. A method of operating an electrosurgical instrument having at
least a pair of electrodes, at least one of which is located in a
gas supply passage, comprising delivering to the electrodes radio
frequency power at a frequency in the range of from 300 GHz to 10
GHz and passing an ionisable gas through the passage to form a gas
plasma in the passage.
44. A method according to claim 42, fisher comprising causing the
gas plasma to emerge at a treatment outlet of the passage.
Description
[0001] This invention relates to a radio frequency electrosurgery
system and a method of operating an electrosurgical instrument at
UHF frequencies.
[0002] It is known to use a needle or narrow rod electrode for
cutting tissue in monopolar electrosurgery at frequencies in the
range of 300 kHz to 3 MHz. An electrosurgical signal in this
frequency range is applied to the electrode, and the electrical
current path is completed by conduction through tissue to an e ng
plate secured to the patients body elsewhere. The voltage applied
to the electrode must be sufficiently high to cause arcing and
consequent thermal rupture so that tissue adjacent the needle is
ablated or vaporised.
[0003] At lower power levels, coagulation of the tissue can be
achieved, i.e. without arcing, due to thermal dissipation of energy
in the tissue adjacent the electrode. However, with a narrow
electrode as commonly used for tissue cutting, desiccation of the
tissue immediately adjacent the electrode and build-up of
desiccated material on the electrode itself constitutes a
high-impedance barrier to further coagulation. Spatula-shaped
electrodes have been produced to overcome the difficulty in
providing a dual-purpose electrode, i.e. one suitable for both
cutting and coagulation. The designer's intention is that the edge
of the electrode is used for cutting, whereas the flat surface is
used for coagulation. However, coagulation with such an electrode
tends to be imprecise due to the size of the flat surface, with the
result that a large thermal margin is produced.
[0004] It is an object of the invention to provide a means of
achieving both tissue cutting and coagulation with a single
electrode assembly.
[0005] According to this invention, to is provided an
electrosurgery system comprising an electrosurgical generator, a
feed structure and art electrode assembly, the electrode assembly
having at least one active electrode and at least one adjacent
return electrode each of which is coupled to the generator via the
feed structure wherein the generator and feed structure capable of
delivering radio frequency (r.f.) power to the active and return
electrodes in lower and upper frequency ranges, the upper range
containing frequencies at least three times the frequencies of the
lower frequency range. The lower frequency range may extend from
100 kHz to 100 MHz, preferably 300 kHz to 40 MHz, and the upper
frequency range may extend from 300 MHz to 10 GHz, preferably above
1 GHz, with operating frequencies in the upper and lower ranges
having a frequency ratio of 5:1 or greater. Typically, the
generator is arranged such that the r.f. power delivered in the
upper fluency range is at a fixed frequency which is at least ten
times the frequency of power delivered in the lower frequency
range. Indeed, a fixed frequency of 2.45 GHz in the upper frequency
range is preferred.
[0006] The preferred system allows simultaneous delivery of lower
and upper frequency range components to the electrodes to provide a
combination of medium or low frequency tissue cutting, vaporisation
or ablation together with coagulation of surrounding tissue to a
degree dependent upon the amplitude of the component in the upper
frequency range.
[0007] For tissue cutting, vaporisation or ablation the system
preferably operates in a monopolar mode with a separate earthing
electrode applied to the outside of the patient's body, whilst
coagulation occurs in a quasi-bipolar mode whereby the return
current path in the upper frequency range runs from the tissue
adjacent the operation site to the return electrode of the
electrode assembly due to capacitive coupling. It will be
understood that the system may allow selection of power delivery
either in the lower frequency range or the upper frequency range
depending upon the kind of treatment required. This selection may
be performed manually by the surgeon or automatically in the manner
to be described below. In addition, power may be supplied in both
frequency ranges simultaneously to obtain a blended cutting and
coagulation effect, the two components being linearly added or
otherwise combined in a single signal feed structure.
[0008] In a particularly preferred embodiment of the invention, the
generator includes a control circuit responsive to electrical load
and operable to cause the delivered power to have a predominant
frequency component in the lower frequency range when the load
impedance is in an upper impedance range, and to have a predominant
frequency component in the upper frequency range when the load
impedance is in a lower impedance range. In this way, it is
possible to cut, ablate or vaporise living tissue (i.e. causing
cell rupture) with the lower frequency range component but also to
bring about efficient coagulation when a very low load impedance is
detected, indicating the presence of electrolytic fluid such as
blood from a blood vessel, requiring coagulation. The system
reverts to predominantly low frequency operation once the impedance
has risen above a predetermined threshold following
coagulation.
[0009] When electrical load impedance is used as the control
stimulus, a signal representative of load impedance being compared
with a reference signal, the reference signal may have different
levels depending on whether the generator is to be switched from a
predominant low frequency component to a predominant high frequency
component or vice versa. In other words, different load impedance
thresholds may be selected when operating in the lower frequency
range or the upper frequency range respectively.
[0010] A composite signal having components from both frequency
ranges may be produced by combining (e.g. adding) the signals from
two generator stages, one operating in the region of, say, 1 MHz
and the other operating at 2.45 GHz. Both generator stages may be
in a single supply unit coupled to al electrosurgical instrument
which consists of a handpiece mounting the electrode assembly so
that, for instance, the two frequency components are fed from the
supply unit to the handpiece by common delivery means such as a low
loss flexible coaxial cable. Alternatively, the generator stage
producing the UHF frequency component may be located in the
handpiece to reduce transmission losses and radiated interference,
the signal combination being performed within the handpiece as
well.
[0011] For dual-purpose operation, i.e. cutting and coagulation, an
electrode assembly having a needle-like active electrode is
preferred.
[0012] Typically, the electrode assembly is at the distal end of a
rigid or resilient coaxial feed forming the above-mentioned feed
structure. To reduce extraneous UHF radiation, an isolating choke
element in the form of a conductive quarter-wave stub or sleeve may
be mounted to the outer supply conductor of the coaxial feed in the
region of the distal end. As stated above, the active electrode may
take the form of a rod or pin projecting from the coaxial feed
distal end. The return electrode may be a conductive sleeve, plate
or pad connected to the outer supply conductor at the feed distal
end and extending proximally over the outer conductor but spaced
from the latter so that the active electrode rod and the return
electrode sleeve, plate or pad together form an axially oriented
dipole at the operating frequency of the generator in the upper
frequency range. Alternatively, the return electrode simply takes
the form of a distal end portion of the feed outer conductor
located distally of the choke. The return electrode may be covered
with an electrically insulative layer in order that, when the
active electrode is applied to tissue, the return electrode, being
set back from the active electrode so as normally to be spaced from
the tissue, acts as a capacitive element forming part of a
capacitive return path between the treated tissue and the return
supply conductor of the feed.
[0013] In an alternative embodiment in accordance with the
invention, the electrode assembly includes a gas supply passage and
the active electrode is located within the passage where it acts as
a gas-ionising electrode. In this case, the active electrode acts
as a low- to high-impedance transformer at the operating frequency
of the generator in the upper frequency range, producing an intense
electric field in the space between the distal end portion of the
active electrode and the return electrode. Accordingly, when there
is an ionisable gas in the passage, the major part of the power
delivered to the electrode assembly in the upper frequency range is
dissipated in the passage. In the lower frequency range no
transforming effect occurs and the frequency component in the lower
frequency range is, instead, delivered to the tissue to be treated
by the ionised gas plasma which, in effect, acts as a monopolar
gaseous electrode. Use of a UHF frequency component as a plasma
generator and a lower frequency component for electrosurgery allows
independent control of plasma generation and electrosurgical power
delivery, thereby avoiding the disadvantage of known single r.f.
source gas plasma electrosurgery devices. Typically, in such a
prior device the ability of the source to deliver current through
the plasma is severely hampered due to the requirement for high
peak voltages when using low frequencies (i.e. typically, less than
1 MHz).
[0014] The invention will now be described by way of example and
with reference to the drawings in which:
[0015] FIG. 1 is a diagram showing an electrosurgical system in
accordance with the invention;
[0016] FIG. 2 is a diagrammatic cut away perspective view of an
electrode assembly and associated feed structure;
[0017] FIG. 3 is a diagram showing a simulation of the electric
field pattern obtainable with the electrode assembly of FIG. 2;
[0018] FIG. 4 is an electrical block diagram of the system of FIG.
1;
[0019] FIG. 5 is a circuit diagram of a low frequency part of the
generator used in the system of FIG. 4;
[0020] FIG. 6 is a graph showing the variation of delivered power
and voltage obtained from the generator part of FIG. 5;
[0021] FIG. 7 is a circuit diagram of a generator control
circuit,
[0022] FIG. 8 is a microstrip layout for a mixer holding the
signals obtained from the low and high frequency part of the
generator;
[0023] FIG. 9 is a circuit diagram for a power control circuit
forming a portion of the high frequency generator part;
[0024] FIG. 10 is a cross-section diagram of an alternative
electrode assembly configured for gas plasma generation; and
[0025] FIG. 11 is a cross-section diagram of a further alternative
electrode assembly configured for gas plasma generation.
[0026] The preferred embodiments of the present invention are
applicable mainly to the performance of electrosurgery upon tissue
in a gaseous environment using a dual electrode instrument having
active and return electrodes situated at the distal end of an
instrument shaft. The active electrode is applied directly to the
tissue. The return electrode does not contact the tissue being
treated, but is normally adjacent the tissue surface where it is
capactively coupled to the tissue at UHF frequencies.
[0027] A system incorporating such an instrument is shown in FIG.
1. Referring to FIG. 1, the system has a electrosurgical supply
unit 10 with an output socket 10S providing a radio frequency
(r.f.) output for the electrosurgical instrument 12 via a flexible
cable 14. Instrument 12 has a handpiece 12A and, mounted to the
handpiece, all instrument shaft 12B having an electrode assembly 16
at its distal end. A patient U pad 17 is also connected to the
supply unit 10. Activation of the supply unit may be performed from
the handpiece 12A via a control connection in cable 14, or by means
of a foot switch 18 connected separately to the rear of the supply
unit 10 by a foot switch connection cable 20.
[0028] Instrument shaft 12B constitutes a feed structure for the
electrode assembly 16 and takes the form of a rigid coaxial feed
having an inner conductor and an outer supply conductor made with
rigid material cons as a resilient metal tube or as a plastics tube
with a metallic coating. The distal end of the feed structure
appears in FIG. 2 from which it will be seen that the inner
conductor 22 has an extension which projects beyond the outer
conductor 24 as a rod 26 forming an axially extending active
electrode of a diameter typically less than 1 mm. Where they are
surrounded by the outer supply conductor 24, the inner supply
conductor 22 and the active electrode 26 are encased in a coaxial
ceramic or high-temperature polymer sleeve 28 acting as an
insulator and as a dielectric defining the characteristic impedance
of the transmission line formed by the coaxial feed.
[0029] The return electrode is formed as a coaxial conductive
sleeve 30 surrounding a distal end portion of the outer supply
conductor 24 with an intervening annular space 31. An connection
between the return electrode 30 and the outer supply conductor 24
is formed as an annular connection 30A at one end only, here the
distal end, of the return electrode 30 such that the projecting
portion of the active electrode 26 and the return electrode 30
together constitute an axially extending dipole with a feed point
at the extreme distal end of the coaxial feed. This dipole 26, 30
is dimensioned to match the load represented by the tissue and air
current path to the characteristic impedance of the feed at or near
2.45 GHz.
[0030] Located proximally of the electrode assembly formed by
active electrode 26 and return electrode 30 is an isolating choke
constituted by a second conductive sleeve 32 connected at one of
its ends to the outer supply conductor 24 by an annular connection
32A. In this instance, the annular connection is at the proximal
end of the sleeve. The sleeve itself has an electrical length which
is a quarter-wavelength (.lambda./4) at 2.43 GHz or thereabouts,
the sleeve thereby acting as an balun promoting at least an
approximately balanced feed for the dipole 26, 30 at that
frequency.
[0031] The projecting part of the active electrode 26 has a length
in the region of 10 mm while the return electrode 30 is somewhat
greater than 10 mm in length. The reason for this difference in
length is that the relative dielectric constant of living tissue is
higher than that of air, which tends to increase the electrical
length of the active electrode for a given physical length. The
electrode assembly 16 and choke 32 are configured to provide an
electrical impedance match with the tissue being treated and
advantageously, a mismatch to the impedance of free space, so that
power transmission from the electrode assembly is minimised when
the active electrode is removed from tissue whilst an
electrosurgical voltage is still being applied at 2.45 GHz.
[0032] Sleeve 32 has an important function insofar as it ac as an
isolating trap isolating the outer supply conductor 24 of the feed
structure from the return electrode 30, largely eliminating r.f.
currents at 2.45 GHz on the outside of the outer supply conductor
24. This also has the effect of constraining the electric field
which results from the application of a voltage at 2.45 GHz between
the active electrode and the return electrode, as seen in FIG.
3.
[0033] FIG. 3 is a computer-generated finite element simulation of
the electric (E) field pattern produced by the electrode assembly
16 and choke 32 of FIG. 2 when energised via the coaxial feed 12B
at 2.45 GHz. It should be noted that the components of the
electrode assembly and the sleeve 32 are shown quartered in FIG. 3
(i.e. with a 90.degree. sector cross-section). The active electrode
26 is shown with its tip in contact with a body 40 of tissue. The
pattern 42 of E-field contours in a plane containing the axis of
the electrode assembly illustrates the marked concentration of
E-field in the space 44 surrounding the active electrode 26 and the
distal part of the return electrode 30 immediately adjacent the
tissue surface 40S. Proximally of this space, the E-field intensity
is much reduced, as will be seen by the relatively wide spacing of
the contours. (It should be noted that the region 44 of greatest
intensity appears as a white area in the drawing. In this region
and the immediately surrounding region the contour lines are too
closely spaced to be shown separately.) The presence of an intense
E-field region between the distal end of the return electrode 30
and the tissue surface 40S is also indicative of capacitive
coupling between these two surfaces at the frequency of operation
(which is 2.45 GHz in the simulation of FIG. 3). Localisation of
the E-field in this manner also has the effect of reducing radiated
loss in comparison with an arrangement in which intense field
regions exist further from the tissue surface 40S, with the effect
that radiated loss is minimised.
[0034] Referring back to FIG. 2, it will be understood that the
feed structure makes use of a coaxial feed rather than a waveguide
to transmit power to the electrode assembly from the handpeice and,
indeed, as shown in FIG. 1, there is a flexible cable between the
handpiece 12 and the electrosurgical supply unit 10. Use of coaxial
feeders rather than waveguides in both cases allows the
transmission of voltage components of widely spaced frequencies in
a single transmission line. This also provides the advantage of a
flexible connection between the handpiece 12 and the supply unit
10. Dielectric losses in the cable 14 are mitigated by selection of
a cable with a low density, partly air-filled dielectric structure.
A further reduction in dielectric loss can be obtained by
increasing the diameter of the cable. Such increased diameter need
not be used over the whole length of the cable 14. Indeed, a
smaller diameter may be retained near the handpiece to retain
flexibility of movement
[0035] The ability to feed different voltage components at
different frequencies from the supply unit to the handpiece in a
single transmission line has advantages related to the main aspect
of the present invention which is the provision of means for
delivering r.f. power to the electrode assembly in lower and upper
frequency ranges, the upper range containing frequencies at least
five times the frequencies of the lower frequency range. Thus, the
supply unit may include generator parts generating electrosurgical
signals at, for instance, 1 MHz and 2.45 GHz respectively to suit
different operation site conditions and surgical requirements. In
the preferred embodiments of the invention, these different
components are supplied simultaneously through cable 14 to the
handpiece 12 and electrode assembly 16.
[0036] Details of the electrosurgical generator for delivering
electrosurgical power in this way will now described with reference
to FIGS. 4 to 9.
[0037] Referring to FIG. 4, the supply unit 10 contains separate 1
MHz and 2.54 GHz synthesisers 50, 52 the output signals of which
are summed in an adder stage 54 having low- and high-pass filters
coupled to inputs arranged to receive the 1 MHz and 2.45 GHz
signals respectively, as shown. A circulator 56 connected in series
between the 2.45 GHz synthesiser 52 and the adder 54 serves to
provide a 50 ohm source impedance for synthesiser 52 under
conditions of varying load impedance, reflected power being
dissipated in a 50 ohm reflected energy sink or dump 58, also
connected to the circulator 56.
[0038] At the output of the adder 54 a composite signal consisting
principally of the two frequency components at 1 MHz and 2.45 GHz
is delivered to the output socket 10S of the supply unit and thence
via cable 14, which is typically in the region of three metres
long, to the handheld instrument, represented in FIG. 4 by an
impedance transformer 60 operable at 2.45 GHz, and thereafter to
the tissue 40 under treatment.
[0039] Referring to FIG. 5, the 1 MHz synthesiser has a push-pull
output stage 64 which drives an output transformer 66 via a current
limiting inductor 67 of 3 .mu.H and a series coupling capacitor 68
of 1 .mu.F. Included in the primary circuit of the transformer 66
is a shunt current transformer 70 having an output winding (not
shown) for monitoring the output current of the synthesiser at 1
MHz. The transformer secondary winding is coupled to the output 10S
through a toning inductance 72 of 840 .mu.H which resonates with
the capacitance of the cable 14 and other components on the
secondary side of the transformer 66. In this example the cable has
an inherent shunt inductance of about 80 .mu.H and the series
capacitance 78 between the return electrode and the tissue being
treated is in the region of 30 pF. The tissue is shown as a
resistance 40. Those skilled in the art will understand that at 1
MHz, series inductance 72 and capacitance 78 can resonate so as to
act as a short circuit, thereby coupling the load (tissue
resistance 40) directly to the transformer secondary under matched
conditions. The effect of the series inductance 67 in the primary
circuit is to limit the secondary current at 1 MHz typically to 50
mA. The capacitance 78 is larger than 30 pF of the patient-attached
return pad 17 (se FIG. 1) is used such that, at 1 MHz, the system
is used in a monopolar mode.
[0040] It will be understood that the filter/adder circuitry shown
in FIG. 4 has been omitted from FIG. 5 for clarity.
[0041] As will be seen from the graph of FIG. 6, the arrangement
described above with reference to FIG. 5 yields maximum power
transfer to the tissue when the tissue impedance is in the region
of 10 k ohms. At 1 k ohm and below, both the delivered power and
the output voltage are comparatively low, representing a stall
condition. Stalling occurs, typically, when the electrode assembly
encounters an electrolyte, such as when a blood vessel is cut. This
condition is detected in a manner which will now be described.
[0042] Referring to FIG. 7, a 1 MHz stall detector, forming part of
the 1 MHz synthesiser 50 shown in FIG. 4, has voltage and current
inputs 80 and 82 respectively. In the first instance, the stall
detector applies the voltage from the pr y winding of the
transformer 66 (see FIG. 5) to a pulse width modulation chip 84 to
produce a pulsed output signal having a pulse width which varies
according to the voltage supplied at input 90. At input 82, a
voltage proportional to the current in the primary winding of
transformer 66, as sensed by the current transformer 70, is
supplied to a potential divider 88A, 88B, the tap of the divider
being connected to the output line 86 of the pulse width modulation
chip 84. Accordingly, the voltage applied to buffer circuit 90,
smoothed by capacitor 89, is equivalent to the pule width
modulation output on output line 86, scaled according to the level
of the transformer primary current. In other words, the signal
applied to buffer 90 represents the product of the transformer
primary voltage and primary current, i.e. the delivered power at 1
MHz.
[0043] Thus, the signal at the output of buffer 90 is proportional
to power, and is delivered to one input of an OR-gate formed by
diodes 92, 94 which receives, at its other input, the voltage
applied to input 80. Accordingly, the signal at the output 98 of
the OR-gate is low only when both the delivered power at 1 MHz and
the output voltage at 1 MHz are low, i.e. in accordance with the
power and voltage characteristics show in FIG. 6 when the load
impedance is less than a few kilohms, and typically less than 1 k
ohm. An output comparator circuit 100 is used to compare the output
voltage from the OR-gate 92, 94 with a reference voltage applied to
input 102, representing a reference value of the voltage obtained
from the push-pull pair 64 (See FIG. 5) in open-circuit conditions.
The resulting output at the detector output 104 is a control signal
for enabling the 2.45 GHz synthesiser 52 shown in FIG. 4.
[0044] The adder 54 is formed as a microstrip device, as shown in
FIG. 8. This is a 3-port device having a first input port 104 for
the UHF signal from the 2.45 GHz generator part and a second input
port 106 for the low frequency signal from the 1 MHz generator
part. The device allows the UHF signal to be transmitted to an
output port 108 with little loss whilst being isolated from the low
frequency input port 106. Similarly, the low frequency signal
applied to port 106 is transmitted to the output port 108 with low
loss whilst being isolated from the UHF input port 104 a quarter
wave (.lambda./4) short circuit stub 110 and series capacitor 111
at the UHF input port 104 are transparent to the signal applied at
input port 104, which is thereby transmitted to the output port 108
via an output limb 112. Between the output limb 112 and the low
frequency input 106 are three .lambda./4 open circuit stabs 114,
116, 118, the first 114 of these being spaced from the output limb
112 by a series .lambda./4 section 120. These open circuit stubs
114, 116, 118 reactively attenuate the 2.45 GHz signal to isolate
it from the low frequency input 106. The base of the output limb
122 constitutes a sum injunction 112 and the .lambda./4 length of
the line section 120 extends from this junction 112 to the base 124
of the first open circuit stub 114.
[0045] The open circuit stubs 114, 116, 118 are transparent to the
1 MHz signal, whereas the series capacitor 111 and the short
circuit stub 110 reactively attenuate the 1 MHz signal in order to
isolate the UHF input port 104 at 1 MHz.
[0046] It will be appreciated that the .lambda./4 components
described above may have an electrical length which is any
odd-number multiple of .lambda./4. Here, .lambda. is the wavelength
of the applied UHF (2.45 GHz) signal in the microstrip medium
[0047] The 2.45 GHz synthesiser includes a power control circuit as
shown in FIG. 9. Referring to FIG. 9, the power control circuit has
two inputs 130, 132 coupled to the input and the "reflected" power
output of the circulator 56 (see FIG. 4) respectively. The
reflected voltage applied to input 132 is subtracted from the input
voltage supplied to 130 in comparator 134 and the resulting
difference value compared with a reference voltage set by
potentiometer 136 in an output comparator 138 to produce a
switching signal for limiting the power output to a threshold value
set by the user (or set automatically using a microprocessor
controller forming part of the supply unit). Different power
settings may be used depending upon the size of the electrode
assembly connected to the handpiece and environment
[0048] It will be appreciated that electrosurgical power may be
delivered from the supply unit 10 shown in FIG. 1 either
exclusively at 1 MHz or exclusively at 2.45 GHz for predominantly
tissue vaporisation or thermal tissue coagulation respectively. In
addition, power may be delivered at both frequencies simultaneously
on the basis of a user-defined combination depending upon the
characteristics of the tissue being treated A third mode of
operation is an auto-detection mode using the stall detection
circuit described above with reference to FIG. 6, such that either
of the two components predominate in a composite output voltage
waveform, according to tissue impedance. In the latter case, the
user typically selects a tissue vaporisation mode for predominant
tissue cleaving or vaporisation, in which mode the 2.45 GHz
component is enabled only when the tissue being treated presents a
very low impedance. As mentioned above, this typically indicates
the presence of an electrolyte such as blood from a blood vessel.
Under these circumstances, the UHF component (i.e. the 2.45 GHz
component) of the composite voltage waveform provides coagulation
and/or desiccation of the tissue in the region of blood loss the
generator continuing in that mode until the detected tissue
impedance rises again, whereupon the UHF component is disabled and
treatment continues again exclusively at 1 MHz.
[0049] As described above, detection of low tissue impedance in
these circumstances can be achieved by comparison of voltage and
current amplitudes at the output of the 1 MHz source, prior to the
adder 54 shown in FIG. 4. To avoid a low impedance detection output
occurring as a result of reactive loading between the generator and
the tissue being treated, the detector circuit may be modified to
generate a signal representative of (V cos .phi.)/I, where V is the
magnitude of the 1 MHz voltage component, I is the magnitude of the
1 MHz current component, and .phi. the phase angle between the said
voltage and current.
[0050] It should be noted that detection of low power delivery at 1
MHz as described above with reference to FIG. 7 makes use of a
signal representative of the real power delivered to the load,
scaled by the voltage that would be obtained from the 1 MHz
synthesiser with an open circuit output.
[0051] In an alternative embodiment, not shown in the drawings the
UHF (2.45 GHz) synthesiser 52 shown in FIG. 4 may be installed in
the handpiece 12 together with the circulator 56, energy dump 58,
and adder 54. This has the advantage that the cable 14 (see FIG. 1)
between the supply unit and the headpiece 12 may be an inexpensive
smaller diameter component A d.c. power supply for the UHF
synthesiser is also required, and may be provided by an additional
cable or additional wires in the 1 MHz feed together with, when
necessary, a further line for control functions. The composite
output voltage is, in this case, fed directly from the adder 54 to
the feeder structure represented by the instrument shaft.
[0052] It will be appreciated that losses at UHF are much reduced
with this embodiment, to the extent that the power output of the
UHF synthesiser may be reduced. Drawbacks include the additional
bulk and weight of the handpiece and the possible need for forced
fluid cooling of the UHF synthesiser, depending on the required
power output. Such cooling could take place by evacuating air from
the operation site into a passage at the distal end of the
electrode shaft through a filter element to the UHF synthesiser,
performing the dual functions of cooling the synthesiser and
removing smoke or vapour from the operation site to enhance
visibility.
[0053] The ability to supply electrosurgical voltages at widely
spaced frequencies also has application in a further alternative
embodiment making use of a gas plasma electrode, as will now be
described with reference to FIG. 10.
[0054] It is well known to use an inert gas such as argon, ionised
using an r.f voltage and fed via a nozzle, typically having a
diameter in excess of 1 mm, to produce a hot plasma "bcam".
Directing this gas plasma onto the tissue being t causes
coagulation through transfer of thermal energy.
[0055] The behaviour of the argon plasma depends upon the incident
energy. The higher the temperature of the argon, the greater its
electrical conductivity. Paradoxically, the more energy initially
imparted to the plasmas the less is the energy absorbed by the
plasma due to its lower electrical impedance.
[0056] Supplying upper and lower frequency components
simultaneously to a plasma-generating electrode assembly has the
advantage that formation of the plasma can be performed
independently of the conduction of energy along the plasma beam. As
described above with reference to FIGS. 1 to 9, the tipper and
lower components typically have frequencies of 2.45 GHz and 1 MHz
respectively.
[0057] Referring to FIG. 10, the preferred electrode assembly
consists of a ceramic nozzle body 200 attached to the end of a
coaxial feed structure which has the same configuration as the feed
structure in the embodiment described above with reference to FIGS.
1 to 9. Nozzle body 200 has an axial gas supply chamber 202 with a
communicating lateral gas inlet 204. The nozzle body 200 is tapered
distally to form a narrow tube 206 with an axial bore 208 providing
an outlet from the chamber 202, the exit nozzle having an internal
diameter in the region of 50 to 300 .mu.m. Situated axially within
the gas supply chamber 202 and the nozzle bore 208 is a whisker
electrode 210 coupled to the inner supply conductor 22 of the
coaxial feed. As shown in FIG. 10, the whisker electrode 210 is
coiled within the chamber 202 and has an extension extending
axially into bore 208 so that the total electrical length of the
electrode 210 is about .lambda./4 at the frequency of the upper
component.
[0058] Plated on the lateral exterior she of the ceramic nozzle
body 200 is a conductive return electrode 212 adjacent to the outer
supply conductor 24 of the feed structure 12B and spaced from the
supply conductor 24 by a gap 213.
[0059] Essentially then, the plasma generator comprises a whisker
antenna within a ceramic tube having a metallised shroud. The
capacitance between the whisker electrode 210 and the return
electrode 212 is typically in the region of 0.5 to 5 pF. Clearly,
this is a relatively low impedance at 2.45 GHz but a very high
impedance at 1 MHz. This, coupled with the fact that the .lambda./4
length of the electrode 210 causes the electrode 210 to act as an
impedance transformer producing a high voltage at the tip of the
electrode, means that the 2.45 GHz component is dissipated within
the plasma chamber when an ionisable gas is introduced via inlet
204 (causing plasma generation in bore 208) whereas the low
frequency component at 1 MHz is conducted along the plasma beam to
target tissue and to earth via the return pad attached to the
patient (see FIG. 1).
[0060] The plasma generator is highly efficient at UHF frequencies,
which means that the plasma may be generated with sufficient flow
to absorb as much as 100 watts. The ionised gas is pumped from the
chamber 202 through bore 208 which may have a bore as small as 0.1
mms. Since the majority of the power is dissipated within the
chamber, little or no power at UHF is conducted to the nozzle
outlet by the plasma. Instead, the UHF current component flows from
the whisker electrode 210 via capacitive coupling to the return
electrode 212, and thence via further capacitive coupling to the
outer conductor 24 of the feed structure 12B.
[0061] Using the UHF source alone, the plasma beam acts as a
powerful tissue coagulation tool, the depth and area of the
coagulation effect being determined by the dispersion of the gas
beyond the nozzle which depends, in turn, upon the distance the
nozzle is held from the tissue surface. This is a purely thermal
effect.
[0062] As described above, when both lower and upper frequency
components are supplied, the lower frequency component at medium
frequencies such as 1 MHz (a range of 100 kHz to 5 MHZ is
applicable in this instance) results in power being conducted along
the plasma beam to the target tissue and thence to earth,
vaporising the tissue.
[0063] Since the 1 MHz component is not coupled in plasma
generation, its voltage can be comparatively low, at typically 300
volts to 1000 volts rms. It follows that the ability of the low
frequency source to support significant current delivery at low
power is superior to that achievable in known prior systems.
[0064] The ionising ability of the UHF source is such that gases
other than argon may be used. Argon has tended to be used in the
prior art because it has a low ionisation potential, it is an inert
gas, and it is the most abundant of the noble inert gases and
consequently the cheapest. However, when using the described
electrode assembly, with the plasma beam acting as an active
electrode conveying electrosurgical tissue vaporising power at 1
MHz, a significant amount of residual carbon can be produced. This
is the result of vaporising the tissue in an oxygen-free
environment.
[0065] Use of an oxidising gas plasma by supplying oxygen or an
oxide of nitrogen, gases which are both readily available in an
operating theatre, counters the formation of carbon. Such gases
have a considerably higher ionisation potential than argon with the
result that considerably higher temperatures are attained with
sufficiently conductive plasma streams, to the extent that the gas
delivery rate has to be correspondingly reduced. An oxidising gas
can be mixed with the argon before plasma generation, and
introduced directly via inlet 204. Alternatively, the oxidising gas
may be mixed with the argon plasma using an electrode assembly
having a second gas inlet, as shown in FIG. 11. The embodiment
shown in FIG. 11 makes use of a ceramic body 200 with a second
lateral gas inlet 214 communicating with the bore 208 of the nozzle
tube 206.
[0066] The whisker electrode 210 is preferably tungsten or tantalum
due to the high melting point of these metals. Where an oxidising
gas is introduced into the plasma generating chamber, a platinum or
platinum-coated electrode is more appropriate, in order to avoid
electrode oxidisation. The electrode may also be constructed from a
thoriated alloy such as a thorium-toungsten alloy to improve
electron emission and to promote predictable ionisation.
[0067] Dual frequency operation of a gas plasma electrode assembly
as described above avoids the difficulties created by generating
the plasma and the tissue effects from the same electrical source.
Consequently, the difficulty in generating a plasma from a voltage
which varies due to large variations in load impedance is avoided,
and the lower frequency r.f. source can be used to deliver current
through the plasma without relatively high peak voltages when using
low frequencies, which places high power demands upon the r.f.
generator.
[0068] Narrow jet diameters, as disclosed above, as allowed by high
excitation voltages and low impedance, result in higher current
density upon tissue contact, giving the opportunity to perform
rapid but fine tissue vaporisation.
* * * * *