Apparatus for sterilising an instrument channel of a surgical scoping device

Abstract

Sterilisation apparatus comprising a sterilisation instrument configured to be inserted through the instrument channel of a surgical scoping device and a withdrawal device for withdrawing the sterilisation instrument from the instrument channel at a predetermined rate. The sterilisation instrument comprises an elongate probe having a probe tip with a first electrode and a second electrode arranged to produce an electric field from received RF and/or microwave frequency EM energy. In operation the instrument may disinfect an inner surface of the instrument channel by emitting energy whilst being withdrawn through the channel.

Claims

1. A sterilisation apparatus for sterilising an instrument channel of a surgical scoping device, the apparatus comprising: a sterilisation instrument configured to be inserted through the instrument channel of a surgical scoping device, the sterilisation instrument comprising: an elongate probe comprising a coaxial cable for conveying radiofrequency (RF) electromagnetic (EM) energy and/or microwave EM energy, and a probe tip connected at the distal end of the coaxial cable for receiving the RF and/or microwave energy, wherein the coaxial cable comprises an inner conductor, an outer conductor and a dielectric material separating the inner conductor from the outer conductor, wherein the probe tip comprises a first electrode connected to the inner conductor of the coaxial cable and a second electrode connected to the outer conductor of the coaxial cable, and wherein the first electrode and second electrode are arranged to produce an electric field from the received RF and/or microwave frequency EM energy; and a withdrawal device for withdrawing the sterilization instrument from the instrument channel at a predetermined rate, wherein the sterilisation instrument further comprises a gas conduit for conveying gas to the probe tip, wherein the first electrode and second electrode are arranged to produce an electric field from the received RF and/or microwave frequency EM energy across a flow path of gas received from the gas conduit to produce a thermal plasma or a non-thermal plasma, wherein the coaxial cable comprises a layered structure comprising: an innermost insulating layer; an inner conductive layer formed on the innermost insulating layer; an outer conductive layer formed coaxially with the inner conductive layer; and a dielectric layer separating the inner conductive layer and the outer conductive layer, wherein the inner conductive layer, the outer conductive layer and the dielectric layer form a transmission line for conveying RF and/or microwave frequency energy, and wherein the innermost insulating layer is hollow, thereby providing a longitudinal channel within the coaxial cable, and wherein the coaxial cable further comprises: a first terminal that is electrically connected to the inner conductive layer and which extends through the innermost insulating layer into the channel; and a second terminal that is electrically connected to the outer conductive layer and which extends through the dielectric layer and innermost insulating layer into the channel, wherein the first terminal and the second terminal are arrangeable to form electrical connection with the first and second electrodes on the probe tip, wherein the probe tip is insertable in or through the longitudinal channel.

2. The sterilisation apparatus according to claim 1, wherein the sterilisation instrument is further configured to be extendable out of the instrument channel to deliver the RF EM energy and/or the microwave EM energy into biological tissue located at a distal end of the instrument channel.

3. The sterilisation apparatus according to claim 1, wherein the coaxial cable has a lumen extending from a proximal end to a distal end of the cable, wherein the lumen forms the gas conduit for conveying gas through the elongate probe to the probe tip.

4. The sterilisation apparatus according to claim 1, wherein the gas conduit passes through the probe tip.

5. The sterilisation apparatus according to claim 1, wherein the probe tip is a plasma applicator having an enclosed plasma generating region and an outlet for directing plasma out of the plasma generating region towards an inner surface of the instrument channel.

6. The sterilisation apparatus according to claim 1, wherein the probe tip comprises: an extension of the innermost insulating layer of the coaxial cable; the first electrode, comprising an extension of the inner conductive layer of the coaxial cable; a dielectric cylinder placed over the inner conductive layer; and the second electrode, comprising a metal tube which is electrically connected to the outer conductive layer of the coaxial cable.

7. The sterilisation apparatus according to claim 6, wherein the dielectric cylinder comprises a number of holes in the walls of the cylinder.

8. The sterilisation apparatus according to claim 1, wherein the longitudinal channel comprises or contains the gas conduit.

9. The sterilisation apparatus according to claim 1, wherein the gas conduit terminates in a rigid tube or needle.

10. The sterilisation apparatus according to claim 1, wherein the probe tip comprises a single piece of metallised dielectric material.

11. The sterilisation apparatus according to claim 1, wherein the probe tip has a parallel plate structure comprising: a substantially planar body of dielectric material; a first conductive layer on a first surface of the planar body as the first electrode; and a second conductive layer on a second surface of the planar body that is opposite to the first surface, as the second electrode.

12. The sterilisation apparatus according to claim 1 further comprising: a container defining a sterilisation enclosure for the surgical scoping device, and a plasma generating unit for creating a non-thermal plasma or a thermal plasma within the sterilisation enclosure for sterilising an exterior surface of the surgical scoping device.

13. The sterilisation apparatus according to claim 12, wherein the container includes a chamber for receiving a control head of the surgical scoping device, and wherein the plasma generating unit includes an annular body for enclosing an instrument tube of the surgical scoping device.

14. The sterilisation apparatus according to claim 13, wherein the annular body is slidable along the instrument tube.

15. The sterilisation apparatus according to claim 1, wherein the probe tip further comprises a cleaning brush.

16. The sterilisation apparatus according to claim 1, wherein the predetermined rate is less than 10 mm per second.

17. The sterilisation apparatus according to claim 1, wherein the cable coupling element is mountable in a fixed position relative to the surgical scoping device.

18. The sterilisation apparatus according to claim 1, wherein the cable coupling element comprises a plurality of rollers defining a space between them for receiving the elongate probe, the rollers being arranged to grip an exterior surface of the elongate probe whereby rotation of the rollers causes longitudinal movement of the elongate probe.

19. The sterilisation apparatus according to claim 1, wherein the withdrawal device further comprises a drum around which the elongate probe may be wound.

20. The sterilisation apparatus according to claim 1, wherein the motor is disengageable from the cable coupling element.

21. A sterilisation apparatus according to claim 1, wherein the withdrawal device comprises: a cable coupling element operably connected to the elongate probe at a proximal end thereof; and a motor arranged to drive the cable coupling element to cause relative movement between the elongate probe and the instrument channel in a longitudinal direction.

22. A sterilisation apparatus for sterilising an instrument channel of a surgical scoping device, the apparatus comprising: a sterilisation instrument configured to be inserted through the instrument channel of a surgical scoping device, the sterilisation instrument comprising: an elongate probe comprising a coaxial cable for conveying radiofrequency (RF) electromagnetic (EM) energy and/or microwave EM energy, and a probe tip connected at the distal end of the coaxial cable for receiving the RF and/or microwave energy, wherein the coaxial cable comprises an inner conductor, an outer conductor and a dielectric material separating the inner conductor from the outer conductor, wherein the probe tip comprises a first electrode connected to the inner conductor of the coaxial cable and a second electrode connected to the outer conductor of the coaxial cable, and wherein the first electrode and second electrode are arranged to produce an electric field from the received RF and/or microwave frequency EM energy; and a withdrawal device for withdrawing the sterilization instrument from the instrument channel at a predetermined rate, wherein the withdrawal device comprises: a cable coupling element operably connected to the elongate probe at a proximal end thereof; and a motor arranged to drive the cable coupling element to cause relative movement between the elongate probe and the instrument channel in a longitudinal direction, wherein the motor is switchable between a forward mode and a reverse mode of operation, wherein the forward mode is suitable for inserting the elongate probe through the instrument channel and the reverse mode is suitable for withdrawing the elongate probe from the instrument channel.

23. A probe withdrawal device for moving an elongate probe through an instrument channel of a surgical scoping device, the probe withdrawal device comprising: a cable coupling element operably connected to the elongate probe at a proximal end thereof; and a motor arranged to drive the cable coupling element to cause relative movement at a predetermined rate between the elongate probe and the instrument channel in a longitudinal direction, wherein the cable coupling element comprises a plurality of rollers defining a space between them for receiving the elongate probe, the rollers being arranged to grip an exterior surface of the elongate probe whereby rotation of the rollers causes longitudinal movement of the elongate probe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

(2) FIGS. 1A and 1B show a sterilisation apparatus according to a first aspect of the invention;

(3) FIG. 2 shows sterilisation apparatus and an alternative embodiment of a withdrawal device;

(4) FIG. 3A is a cross-sectional view through a distal end of the elongate probe showing the probe tip and coaxial cable;

(5) FIG. 3B shows the probe tip of FIG. 3A alone;

(6) FIG. 3C shows the coaxial cable of FIG. 3A alone;

(7) FIG. 4 is a cross-sectional view through an alternative probe tip embodiment;

(8) FIG. 5 is a cross-sectional view through another alternative probe tip arrangement;

(9) FIG. 6 is a cross-sectional view through yet another embodiment of a probe tip;

(10) FIG. 7 is a longitudinal cross-sectional view through a coaxial plasma applicator (probe tip) that can be used with the present invention;

(11) FIG. 8 is a longitudinal cross-sectional view through a waveguide plasma applicator (probe tip) that can be used with the present invention;

(12) FIG. 9 is a longitudinal cross-sectional view through an integrated microwave cable assembly and plasma applicator probe tip that can be used with the present invention;

(13) FIG. 10 is a longitudinal cross-sectional view through another coaxial plasma applicator (probe tip) that can be used with the present invention;

(14) FIG. 11 is a longitudinal cross-sectional view through another coaxial plasma applicator (probe tip) that can be used with the present invention;

(15) FIG. 12 is a longitudinal cross-sectional view through another elongate instrument 290 that can be used with the present invention;

(16) FIG. 13 is a longitudinal cross-sectional view through another probe tip that can be used with the present invention;

(17) FIG. 14 is a longitudinal cross-sectional view through a withdrawal device that can be used with the present invention;

(18) FIG. 15 is a lateral cross-sectional view through driving components in the withdrawal device of FIG. 14;

(19) FIG. 16 is a longitudinal cross-sectional view through another withdrawal device that can be used with the present invention;

(20) FIGS. 17A to 17C show a sterilisation apparatus in use for sterilising the instrument channel of a scoping device;

(21) FIG. 18 is a schematic view of a probe tip which may be used with the present invention; and

(22) FIG. 19 is an end view of the probe tip of FIG. 18.

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES

(23) FIG. 1A shows a sterilisation apparatus 10 according to a first aspect of the invention. The sterilisation apparatus comprises an elongate probe having a coaxial cable 12 and a probe tip 14 at its distal end. A generator 30 is connected to the coaxial cable at its proximal end. A gas supply 40 is also connected to supply gas to the probe tip 14 through a gas conduit (not shown) in the coaxial cable 12. A withdrawal device 20 is positioned on the coaxial cable 12 in order to withdraw the elongate probe from an instrument channel which runs through the insertion tube 52 of scoping device 50, in a manner which will be explained in more detail below.

(24) FIG. 1B shows the sterilisation apparatus 10 in use. The elongate probe is within the instrument channel of the insertion tube 52, and the withdrawal device 20 is attached to the handle of the scoping device 50. The withdrawal device 20 is switched on to withdraw the coaxial cable 12 from the instrument channel of the insertion tube 52 at a predetermined rate, in a direction indicated by arrow 18. While the withdrawal device 20 is withdrawing the coaxial cable 12 and probe tip (not shown) through the instrument channel, the generator 30 is supplying RF and/or microwave frequency EM energy to the probe tip such that the probe tip is sterilising the instrument channel. The gas supply 40 supplies gas to the probe tip through the gas conduit so that the RF and/or microwave EM energy may be used to generate a non-thermal plasma at the probe tip to destroy or eliminate micro-organisms in the instrument channel of the insertion tube 52.

(25) FIG. 2 shows sterilisation apparatus having an alternative withdrawal device 20. In this arrangement, the withdrawal device additionally comprises a drum 22 around which the coaxial cable 12 is wrapped as it is withdrawn from the instrument channel of the scoping device 50. The generator 30 supplies RF and/or microwave EM energy to the coaxial cable 12 via a connecting wire 32 and a suitable plug on the housing of the withdrawal device 20. Similarly, gas from the gas supply 40 is conveyed to the gas conduit through a connecting tube 42. The withdrawal device 20 is discussed in more detail below.

(26) FIG. 3A is a cross-sectional view through a distal end of the elongate probe showing the probe tip 14 and a layer-structured coaxial cable 12, with a catheter 110 and probe tip 14 inserted in a channel 130 of the coaxial cable 12.

(27) The probe tip 14, which is shown alone in FIG. 3B, used in sterilisation of an instrument channel but may also be suitable for use in electrosurgery. In particular, the probe tip 14 shown in FIGS. 3A and 3B is configured for use as a resection instrument.

(28) The probe tip 14 comprises a connection collar 152 attached to the distal end of the catheter 110, an extension sleeve 154 which extends distally from the connection collar 152, and a sterilisation instrument connected at a distal end of the extension sleeve 154. The sterilisation instrument is formed from a piece of rigid dielectric 144 that has a conductive coating (not shown) on its upper surface 146 and lower surface 148 to form two electrodes, and a smooth tapering dielectric 150 formed below the lower surface 148. The connection collar 152 comprises a short rigid cylindrical portion having a diameter selected to snugly fit in the channel 130 of the coaxial cable so that its outer surface is in physical contact with the surface that defines the channel 130 (i.e. the inner surface of wall 134). The connection collar 152 may have a larger diameter than the catheter 110. A pair of contacts 156, 158 are formed on the outer surface of the connection collar 152. The contacts 156, 158 may extend around all or part of the outer surface. In this embodiment, a back (i.e. proximal) contact 156 is arranged to electrically connect to the inner conductive layer 140 of the layer-structured coaxial cable 12, and a forward (i.e. distal) annular contact 158 is arranged to electrically connect to the outer conductive layer 136 of the layer-structured coaxial cable 12.

(29) To achieve these electrical connections, the coaxial cable 12 has a pair of longitudinally spaced terminals 160, 162 that protrude through the innermost layer 142 at the distal end of the channel 130, as shown in FIG. 3C. The terminals 160, 162 may extend around all or part of the inner surface of the channel 130. In this embodiment, a back (i.e. proximal) terminal 160 extends through the innermost layer 142 from a distal end of the inner conductive layer 140, and a forward (i.e. distal) terminal 162 extends through both the dielectric layer 138 and the innermost layer 142 from a distal end of the outer conductive layer 136. The outer conductive layer 136 extends longitudinally beyond a distal end of the inner conductive layer 140. The inner conductive layer 140 thus terminates at the back terminal 160, i.e. there is a gap 164 (e.g. an air gap or other insulating material) located beyond of the distal end of the inner conductive layer 140 before the forward terminal 162.

(30) A conductive rod 166 extends from the back contact 156 through the extension sleeve 154 to provide an electrical connection for the conductive coating on the upper surface 146 of the piece of rigid dielectric 144. The upper surface 146 is therefore electrically connected to the inner conductive layer 140 of the coaxial cable 14. Similarly, a conductive rod 168 extends from the forward contact 158 through the extension sleeve 154 to provide an electrical connection for the conductive coating on the lower surface 148 of the piece of rigid dielectric 144. The lower surface 148 is therefore electrically connected to the outer conductive layer 136 of coaxial cable 12.

(31) The extension sleeve 154 may be a rigid tube of dielectric material for both protecting and electrically insulating the conductive rods 166, 168. The extension sleeve 154 may have an electric length that corresponds to half a wavelength of the microwave energy that is conveyed by the extension sleeve 154. The conductive rods 166, 168 may be separately enclosed (e.g. coated of otherwise covered) by dielectric, e.g. glue, plastic or some other insulator, to prevent breakdown, especially where they are close together.

(32) A distal end of the connection collar 152 may abut against a stop flange 170 formed at the distal end of the channel 130. The probe tip 14 can therefore be secured in place with an electrical connection between the contacts 156, 158 and terminals 160, 162, e.g. by maintaining a pushing force on the catheter 110. Although in this embodiment the connection collar 152 performs a dual function of electrical connection and physical stop, it is possible for these functions to be performed by separate features, in which case the connection collar 152 may be located further back in the channel 130 and the extension sleeve 154 may be longer.

(33) To prevent material escaping backwards into the channel, a seal 172 may be formed over the entrance to the channel 130.

(34) The catheter 110 may be a hollow tube for conveying a gas conduit or control lines 178 to the probe tip 14. In this embodiment, the gas conduit extends right through to the distal end of the probe tip for delivering argon or another gas for plasma sterilisation. The gas conduit 178 may also be adapted to deliver fluid such as saline to the probe tip 14 for performing electrosurgery

(35) FIG. 4 shows another embodiment of a probe tip 14 which can be used with the layer-structured coaxial cable 12 described above with respect to FIGS. 3A-3C. The probe tip 14 comprises an extension of the innermost layer 142 and inner conductive layer 140. In this embodiment, the innermost layer 142 is a PTFE tube. The inner conductive layer acts as a first electrode of the probe tip 14. The probe tip 14 also comprises a dielectric material 182 which is placed over the first electrode 140, and a second electrode 180 over the dielectric material 182. The dielectric 182 is a MACOR cylinder and the second electrode 180 is formed of a thin wall copper tube. The second electrode 180 is electrically connected to the outer conductive layer 136, which extends beyond the distal end of a sleeve 184 covering the coaxial cable 12. Gas may be supplied to the distal end of the probe tip 14 through the channel 130, which extends through the elongate instrument to its proximal end where gas may be supplied e.g. from a gas canister. The probe tip 14 has an outer diameter of 2.5 mm, the dielectric layer 182 has a wall thickness of 0.325 mm, and the channel 130 a diameter of 1 mm.

(36) FIG. 5 shows an alternative probe tip 14 which can be used with the layer-structured coaxial cable 12 described above with respect to FIGS. 3A-3C. The probe tip 14 comprises a first electrode 186 which is a tube structure inserted into the innermost layer 142, and which defines part of the channel 130. The innermost layer 142 may be a PTFE tube. Dielectric layer 182 is provided over the first electrode 186. Similar to the embodiment shown in FIG. 4, the second conductor 180 is a thin wall copper cylinder connected to the outer conductive layer 136. The first electrode 186 is connected to the inner conductive layer 140 via a metal ring 188 which is gripped between the dielectric material 182 and the innermost layer 142. The outer diameter of the probe tip 14 is 2.5 mm, the channel 130 has a diameter of 0.8 mm and the dielectric 182 has a wall thickness of 0.65 mm. The reduced channel 130 diameter and increased dielectric 182 thickness increases the impedance of the probe tip 14, allowing a lower dielectric constant material to be used for the dielectric layer 182.

(37) Other probe tip embodiments discussed herein may also be used with a ‘conventional’ coaxial cable; i.e. a coaxial cable not having the layered structure described above.

(38) FIG. 6 shows a cross-sectional view through a probe tip which is suitable for generating plasma at the distal end of an elongate instrument. The tip shown may also be used as an electrosurgical instrument. The elongate instrument 500 is cylindrical, and sized to fit down the instrument channel of a scoping device, e.g. an endoscope. The instrument comprises a coaxial cable 502 having an inner conductor 504 and an outer conductor 506 separated from the inner conductor 504 by a dielectric material 508. The outer conductor 506 is exposed around at the outside surface of the coaxial cable 502. At the distal end of the coaxial cable 502, the inner conductor 504 extends beyond the outer conductor 506 and is surrounding by a dielectric cap 510, e.g. made of PEEK or the like. The cap 510 is a cylinder having substantially the same diameter as the coaxial cable 502. The distal end of the cap 510 forms a rounded, e.g. hemispherical dome. The inner conductor 504 terminates at its distal end at a rounded tip 512 which projects beyond the end of the cap 510. The coaxial cable 502 is mounted within a sleeve 514, which preferably includes internal braids (not shown) to impart strength. The sleeve is dimensioned to fit within the instrument channel of a scoping device. There is an annular gap 516 between the inner surface of the sleeve 514 and the outer surface of the coaxial cable 502 (i.e. the exposed outer conductor) which forms a gas conduit for conveying gas introduced at the proximal end of the sleeve 514 to the distal end. A conductive terminal tube 518 is mounted at the distal end of the sleeve 514. For example, the conductive terminal tube 518 may be welded to the sleeve 514.

(39) In the configuration shown in FIG. 6, the rounded tip 512 of the inner conductor 504 forms a first electrode and the conductive terminal tube 518 forms a second electrode. An electric field for striking a plasma in the gas flowing from the annular gap 516 is formed between the first electrode and second electrode by applying suitable energy (e.g. RF and/or microwave frequency energy) to the coaxial cable. The conductive terminal tube 518 is electrically connected to the outer conductor 506 of the coaxial cable 502 by a plurality of radially projecting bumps 520 on the inner surface of the conductive terminal tube 518. There may be two, three, four or more bumps 520 spaced from one another around the inner circumference of the conductive terminal tube 518. Spacing the bumps in this manner permits gas to flow past. An insulating liner 522 is mounted around the inside surface of the conductive terminal tube 518 along a distal length thereof. The insulating liner 522 may be made of polyimide or the like. The purpose of the liner 522 is to provide a suitable dielectric barrier between the first electrode and second electrode to ensure that the applied RF and/or microwave frequency energy results in an electric field with high voltage for striking the plasma. There is a small gap between the liner 522 and the cap 510 to permit gas to flow past.

(40) FIG. 7 is a longitudinal cross-sectional view through a coaxial plasma applicator (probe tip) that can be used in the present invention. The plasma sterilisation apparatus need not be limited to use with this type of structure. Indeed this example is provided to explain the theory behind the use of voltage transformers (or impedance transformers) in the generation of plasma in the applicator. In fact it may be possible to generate the plasma without voltage transformers, especially if an impedance adjustor is present. The plasma applicator 300 shown in FIG. 7 is a coaxial structure comprising three quarter wave impedance transformers, where the diameter of the centre conductor is changed to produce three sections with different characteristic impedances. The impedances are chosen such that the voltage at the distal end of the structure is much higher than the voltage at the proximal (generator) end of the structure.

(41) If the physical length of each section is equal to an odd multiple of the quarter electrical wavelength, i.e.

(42) $L=\frac{\left(2n-1\right)\lambda }{4},$

(43) where L is length in metres, n is an integer, and λ is wavelength at frequency of interest in metres, then the following equation applies
Z.sub.0=√{square root over (Z.sub.LZ.sub.S)},

(44) where Z.sub.0 is the characteristic impedance of the coaxial line in ohms, Z.sub.L is the load impedance seen at the distal end of the section in ohms, and Z.sub.S is the source impedance seen at the proximal end of the section in ohms. By algebraic manipulation of this equation, the load impedance can be expressed as

(45) $Z_L=\frac{Z_0^2}{Z_S}.$

(46) It can therefore be seen that if the characteristic impedance of the transformer section is high and the source impedance is low then the load impedance can be transformed to a very high value. Since the power level at the generator end of the antenna should theoretically be the same as that at the load end, the following can be stated

(47) $P_{\mathrm{in}}=P_{\mathrm{out}}.Math.P_{\mathrm{in}}=\frac{V_L^2}{Z_L},$

(48) which means the voltage at the distal end can be expressed as V.sub.L=√{square root over (P.sub.inZ.sub.L)}. Thus it can be seen that if Z.sub.L can be made as large as possible then the value of the voltage at the distal end of the antenna structure V.sub.L will also be very large, which implies that the electric field will also be high. Since it is required to set up a high electric field in order to strike the plasma, it may be seen that this structure can be used to set-up the correct conditions to strike the plasma.

(49) Considering the structure shown in FIG. 7, the microwave generator 3000 is indicated schematically as having a source impedance (Z.sub.S) 308. The power from the generator 3000 enters the applicator 300 via a coaxial cable (not shown) using microwave connector 340. Connector 340 may be any microwave connector that is capable of operating at the preferred frequency of operation and can handle the power level available at the output of power generator 3000, e.g. N-type or SMA type connectors may be used. Microwave connector 340 is used to launch the microwave power into the plasma generating region, which includes an antenna structure described below.

(50) The first stage of the antenna structure is a 50Ω coaxial section that consists of a centre inner conductor (a first electrode) with an outside diameter b and an outer conductor (a second electrode) with an inside diameter a. The space between the inner and outer conductors contained within the first section is filled with a dielectric material 342, which is labelled here as PTFE. The characteristic impedance of the first section of the antenna is shown here to be the same as that of the generator, i.e. 50Ω, and can be described as follows

(51) $Z_0=Z_S=\frac{138}{\sqrt{{\mathrm{.Math.}}_r}}{\log }_{10}\frac{a}{b}50\Omega ,$

(52) where ε.sub.r is the relative permittivity of the filler material, Z.sub.0 is the characteristic impedance of the first section and Z.sub.S is the source impedance (or the generator impedance). The second section is the first quarter wave impedance transformer 311 whose characteristic impedance Z.sub.01 is higher than that of the first section and can be calculated using

(53) $Z_{01}=138{\log }_{10}\frac{c}{b},$

(54) where c is the inside diameter of the outer conductor 312. Since the second section is filled with air (or at least the gas from gas feed 470), the relative permittivity ε.sub.r is equal to unity and so the square root term disappears from the equation that describes the impedance of a coaxial transmission line. A practical example of the impedance of the second section may be b=1.63 mm and c=13.4 mm. With such dimensions, Z.sub.01 would be 126.258Ω.

(55) The third section is the second quarter wave impedance transformer 310, whose characteristic impedance Z.sub.02 is lower than that of the first section and second sections, and can be calculated using

(56) $Z_{02}=138{\log }_{10}\frac{c}{d},$

(57) where d is the outer diameter of the inner conductor. It is desirable to taper the input and output ends of the centre conductor in order to make the step from the high impedance condition to the low impedance condition more gradual in order to minimise mismatches occurring at the junctions between the two impedances. A suitable angle for the taper is 45°. A practical example of the impedance for the third section may be d=7.89 mm and c=13.4 mm. With such dimensions, Z.sub.02 would be 31.744Ω.

(58) The fourth section is the final section and consists of a third quarter wave impedance transformer 320, whose characteristic impedance Z.sub.03 is higher than that of the third section, and can be calculated using

(59) $Z_{03}=138{\log }_{10}\frac{c}{e},$

(60) where e is the outer diameter of the inner conductor. It is desirable for the distal end of the inner conductor to be sharp and pointed in order to maximise the magnitude of the electric field produced at this point. A practical example of the characteristic impedance for the fourth section may be e=1.06 mm and c=13.4 mm. With such dimensions, Z.sub.03 would be 152.048Ω.

(61) For the arrangement using three quarter wave transformers as shown in FIG. 7, the load impedance Z.sub.L seen at the distal end of the antenna may be expressed as

(62) $Z_L=\frac{Z_{03}^2{Z}_{01}^2}{Z_{02}^2{Z}_S}.$

(63) Using the values of characteristic impedance calculated above for the three transformers, Z.sub.L would be 7,314.5Ω. If the input power is 300 W, then the voltage at the output will be V.sub.L=√{square root over (P.sub.inZ.sub.L)}=1481.33 V. The electric field generated at the end of this structure will thus be

(64) $E=\frac{2V_L}{c}=221094.03{\mathrm{Vm}}^{-1}.$
This large electric field may enable the plasma to be set up using any one of a number of gases and gas mixtures.

(65) The inner conductor may be a single conductor whose diameter changes from b to d to e from the proximal end to the distal end. The outer conductor has the same inner diameter c for the length of the three impedance transformer sections and is reduced to a at the first section. The material used for the inner and outer conductors may be any material or composite that has a high value of conductivity, for example, copper, brass, aluminium, or silver coated stainless steel may be used.

(66) The gas or mixture of gases is fed into the structure via gas conduit 470 and the gas fills the interior (the plasma generating region) of the plasma applicator. The applicator is dimensioned to fit within the instrument channel of a scoping device.

(67) FIG. 8 shows a plasma applicator probe tip 300 in which a waveguide cavity is used to create the field to generate the plasma. In this particular embodiment, an H-field loop 302 is used to transfer the microwave energy from the microwave generator into the waveguide antenna, and the gas mixture is introduced into the structure via gas feed 471, which is connected to gas conduit 470. It may be preferable for H-field loop to have a physical length that is equal to half the wavelength at the frequency of interest or operation, and for the distal end of said loop to be connected to the inside wall of outer conductor. The connection may be made using a weld or solder joint. The H-field loop may be considered a first electrode and the waveguide antenna a second electrode.

(68) Although not illustrated in FIG. 8, impedance transformers may also be introduced into the waveguide embodiment to generate high electric fields at the distal end of the applicator. In other words, the waveguide antenna may comprise of a plurality of sections that have a length equal to an odd multiple of the quarter loaded or unloaded wavelength at the frequency of interest,

(69) 0$i.e.L=\frac{\left(2n-1\right)\lambda }{4}.$
In order to reduce the dimensions of the waveguide (length, width, or diameter) the waveguide may be filled with a dielectric, or magnetic, or composite material where the wavelength is reduced by a function of the inverse of the square root of the relative permittivity, or the relative permittivity, or the product of the two. A number of impedance transformers may be introduced by loading one or a plurality of the sections that form the transformer. In the instance whereby the waveguide structure is loaded with a dielectric or magnetic material (or combination of the two), it may be preferable for the loading material to be porous or have a plurality of holes drilled into it to enable the gas or gas mixture to flow inside the waveguide sections.

(70) In order to change the impedance of the waveguide to produce the desired quarter wavelength transformations within the structure, it is necessary to make adjustments to the geometry of the structure or change the loading material. For a rectangular waveguide, the characteristic impedance of the waveguide cavity may be expressed as

(71) $Z_0=377\frac{b}{a}\sqrt{\frac{{\mu }_r}{{\mathrm{.Math.}}_r}\frac{{\lambda }_g}{\lambda }},\mathrm{where}$$\frac{{\lambda }_g}{\lambda }\mathrm{is}\frac{1}{\sqrt{1-f_{c/2f}}},$

(72) b is the height of the guide (or the length of the short wall), a is the width of the guide (or the length of the long wall), μ.sub.r is the relative permeability of the magnetic loading material, ε.sub.r is the relative permittivity of the dielectric loading material, f.sub.c is the cut off frequency of the guide, and f is the frequency of operation.

(73) In FIG. 8, an additional material 360 is added at the distal end of the waveguide. The additional material 360 may be a quartz tube used to increase the electric field at the distal end of the antenna structure.

(74) FIG. 9 provides a detailed diagram of a probe tip comprising an integrated microwave cable assembly and plasma applicator. In this arrangement, the integrated gas and microwave cable assembly comprises a coaxial arrangement formed using two tubes. The first tube 314 is a relatively thick walled tube made from a flexible dielectric material and is coated with a layer of metal (e.g. a metallization layer of high conductivity, e.g. made from silver, copper or gold) on both the inner and outer walls 318, 319 thereof. The second tube 313 is a relatively thin walled tube made from a flexible material. The first tube 314 is suspended inside the second tube 313 using spacers 312 that may be made from a metallic or dielectric material and must allow gas to flow within and along the channel formed between the outer wall 318 of first tube and the inner wall of second tube 313. The plasma applicator comprises two impedance transformers 310, 320, a gas conduit 315 from centre channel of first tube 314 into the applicator, and a gas extraction passage 316 from the applicator along a channel formed between the outer wall of first tube and the inner wall of second tube. A first section 321 of the inner channel used to feed gas into the applicator is solid to enable the centre pin within microwave connector 340 to be electrically connected to the new microwave cable assembly. The input microwave connector may be any connector suitable for carrying microwave power up to 600 W CW at the frequency of interest, e.g. SMA or N-type connectors may be used. Microwave power is delivered to the connector 340 from a generator.

(75) The centre 311 of the inner conductor 319 used to form the coaxial microwave cable assembly is hollow due to the fact that the microwave field produced at the frequency of interest only requires a small amount of wall thickness to enable the field to efficiently propagate along the cable or waveguide, thus the centre portion 311 of inner conductor 319 may be transparent to the microwave field. Similar criteria apply to the thickness of the outer conductor 318, i.e. it is only a thin layer 318 on the outer surface of the first tube 314 that plays an important part in the microwave field or wave propagation along the wave guiding channel. The first tube 314 should preferably be made from a low loss dielectric material, e.g. low density PTFE, in order to ensure that the power loss along the structure (the insertion loss) is minimised. The integrated applicator or antenna is formed inside second tube 313 and forms an integral part of the cable assembly, aiding insertion of the device through an instrument channel, e.g. of an endoscope. The plasma applicator shown in FIG. 9 consists of two quarter wave impedance transformer sections 310, 320. The first section is a low impedance section whose impedance is determined by the ratio of the diameter of inner conductor (g) and the diameter of outer conductor (.Math.) as described above. The outer conductor may be an extension of outer conductor 318 within the integrated microwave cable assembly used to transport the microwave energy from the generator to the applicator. The gas from within channel 311 is fed into the applicator through a hole, groove, or channel made in inner conductor 311. The second transformer section is a high impedance section whose impedance is determined by the ratio of the diameter of inner conductor (h) and the diameter of outer conductor (I). The material used to form inner conductor may be a material that is able to withstand high temperature without change of physical form or characteristic, e.g. tungsten.

(76) A quartz tube 319 is located at the distal end of the applicator between the inner and outer conductors. The quartz tube reduces the likelihood of arcing and promotes plasma striking in the plasma generating region. Here the plasma plume 1000 is directed out of the open end of the applicator by the flow of gas from the centre channel 311. An annular gap between the quartz tube and outer conductor leads to the outer channel 316. This channel may be connected to a pump for extracting excess or residual gas from the sterilisation site.

(77) FIGS. 10 and 11 show two elongate instrument structures 250, 252 that, in addition to performing sterilisation of an instrument channel, may be used to cut, coagulate, ablate and sterilise biological tissue. The overall diameter of these structures may range from less than 1 mm to greater than 5 mm. In both cases, the instrument structures 250, 252 comprise a coaxial cable 254 having a connector 256 at a proximal end to receive microwave frequency energy and RF energy from a generator (not shown). The coaxial cable 254 has an inner conductor 258 separated from and coaxial with an outer conductor 260 by a suitably low loss dielectric material 262, which may be low density PTFE, a micro-porous material such as Gortex® or the like.

(78) In this embodiment, a distal portion of the inner conductor 258 is hollowed out to form a conduit 264 extending toward the instrument tip 266, 268. It is possible to make inner conductor 258 hollow by making use of the skin effect in conductors that occurs at microwave frequencies.

(79) When a conductive material is exposed to an EM field, it is subjected to a current density caused by moving charges. Good conductors, such as gold, silver and copper, are those in which the density of free charges are negligible and the conduction current is proportional to the electric field through the conductivity, and the displacement current is negligible with respect to the conduction current. The propagation of an EM field inside such a conductor is governed by the diffusion equation, to which Maxwell's equations reduce in this case. Solving the diffusion equation, which is valid mainly for good conductors, where the conduction current is large with respect to the displacement current, it can be seen that the amplitude of the fields decay exponentially inside the material, where the decay parameter (δ) is described using the following equation:

(80) $\delta =\frac{1}{\sqrt{\frac{\omega \mu \sigma }{2}}},$

(81) wherein δ is known as the skin depth and is equal to the distance within the material at which the field is reduced to 1/e (approximately 37%) of the value it has at the interface, σ is the conductivity of the material, μ is the permeability of the material, and w is the radian frequency or 2πf (where f is the frequency). From this, it can be seen that the skin depth decreases when the frequency of the microwave energy increases as it is inversely proportional to the square root of this frequency. It also decreases when the conductivity increases, i.e. the skin depth is smaller in a good conductor than it is in another less conductive material.

(82) For the microwave frequencies of interest and the materials of interest for implementing the structures shown in FIGS. 10 and 11, the skin depth is around 1 μm, hence the inner conductor/first electrode 258 used in the construction of the instruments described here require a wall thicknesses of only about 5 μm to enable most of the microwave field to propagate. This implies that a hollow centre conductor can be used without causing any change to the EM wave propagating along the structure.

(83) A fluid feed inlet 270 is formed through the side of the coaxial feed cable 254 to permit an external fluid (gas and/or liquid) supply to communicate with the conduit 264 to deliver fluid to the probe tip 266, 268. Preferably, the fluid feed does not affect the electromagnetic field that has been set up in the co-axial transmission line structure. EM modelling is performed to determine optimal feed points where the EM field is unaffected.

(84) FIG. 10 is a longitudinal cross-sectional view through a probe tip for delivering plasma, wherein the probe tip has a coaxial structure. In FIG. 10, the probe tip 266 includes an outlet 272 from the conduit, which permits the gas to enter the interior of the probe tip 266 in which the dielectric material 262 is removed, which may form a plasma generation region 274. In this particular arrangement, the outlet 272 comprises a plurality of slots on the inner conductor/first electrode 258 within the plasma generation region 274. In the plasma generation region 274, the electric field set up by the microwave frequency EM energy and/or RF field ionises the gas to produce plasma in the same region. The plasma may be thermal or non-thermal and may be used to sterilise the instrument channel of a scoping device, sterilise tissue, provide a local return path for the RF current, produce surface coagulation and/or assist with tissue cutting. The plasma may be formed in the cavity by initially using energy at the RF frequency to provide the voltage necessary to strike the plasma and then using energy at the microwave frequency to enable the plasma to be sustained. Where the distance between the outer surface of the inner conductor and the inner surface of the outer conductor is very small, i.e. less than 1 mm, the microwave field may be used to strike and maintain plasma. Similarly, it may only be necessary to use the RF field to produce both non-thermal plasma for sterilisation and thermal plasma for surface ablation and/or tissue cutting.

(85) The distal end 276 of the inner conductor/first electrode 258 in the probe tip 266 is a solid pointed section, which may take the form of a sharp needle with a small diameter, i.e. 0.5 mm or less, which may be particularly effective when performing tissue cutting. The distal end 277 of the plasma generation region 274 is open to permit plasma to be delivered out of the elongate instrument.

(86) A quarter wave (or odd multiple thereof) balun 278, comprising a third coaxial conductor that is shorted at its distal end and open at its proximal end is connected to the structure to prevent microwave currents from flowing back along the outer conductor 260 to the coaxial cable 254, which can cause the profile of the microwave energy to become non-optimal.

(87) The composition of gas and its flow rate and delivery profile, together with the power level and profile of the supplied RF EM energy and/or microwave EM energy determines the type of plasma that is set up in plasma generation region 274 of the elongate instrument.

(88) FIG. 11 is a longitudinal cross-sectional view through another coaxial plasma applicator. The elongate instrument 252 in FIG. 11 has a similar probe tip structure to the instrument shown in FIG. 10 except that outer conductor/second electrode 260 has been continued such that it ends closer to the distal end 276 of the inner conductor/first electrode 258 in the probe tip 268. Here the outer conductor 260 takes the form of a pointed cone at the distal end of the probe tip 268. The slope of outer conductor/second electrode may be at the same angle as the slope of the solid pointed section. A jet of plasma may be emitted through a small gap 280 that separates the inner conductor 258 from the outer conductor 260 in this region.

(89) The probe tip may be arranged such that the initial ionisation discharge or breakdown of the gas occurs between the distal end of the outer conductor 260 and the solid pointed section of the inner conductor 258. The solid pointed section may be cone shaped, which is a preferred structure for use as a surgical instrument.

(90) FIG. 12 depicts an elongate instrument 290 suitable for use in the present invention. The probe tip shown is suited for gastrointestinal procedures in addition to instrument channel sterilisation. The elongate instrument 290 comprises a coaxial cable 254 having an inner conductor 258 separated from and coaxial with an outer conductor 260 by a dielectric material 262. A probe tip 292 is connected at the distal end of the coaxial cable 254. A connector 256 is connected to the proximal end of the coaxial cable to receive RF EM energy and microwave frequency EM energy from a generator.

(91) The probe tip 292 is a unitary piece of dielectric material (e.g. low loss Dynallox® Alumina) having two separate layers of metallisation formed thereon to form first and second electrodes. The inner conductor 258 of the coaxial cable 254 extends beyond the distal end of the coaxial cable 254 into the interior of the probe tip 292. From there it is electrically connected to one of the layers of metallisation. The outer conductor 260 of the coaxial cable 254 is connected to the other layer of metallisation. The probe tip 292 is fixed to the coaxial cable 254 by a sleeve 294 (e.g. of stainless steel), which may be crimped to force securing tabs 296 into corresponding notches in the ceramic body of the probe tip 292. The length of the sleeve 294 may be selected to match the impedance of the probe tip 292 to the coaxial cable 254, i.e. it may act as a tuning stub.

(92) The layers of metallisation are provided on the side surfaces of the probe tip 292. The layers are separated from each other by the ceramic so that it effectively forms a planar transmission line. In this embodiment, the layers of metallisation are set back from the side edges and the distal edge of the probe tip except at regions where it is desired to emit an RF EM field. FIG. 12 shows schematically a first layer of metallisation 298 which is set back slightly from the edges of the probe tip except along a region along the bottom edge.

(93) In this embodiment, the probe tip 292 has a hooked shape where one of the edges of the probe tip 292 curves inwards and outwards, i.e. defines a recess. The recess may include a substantially proximally facing surface for facilitating tissue removal, e.g. by permitting tissue to be pulled, scooped or scraped away from the treatment site. The region along the bottom edge (the RF cutting region) to which the first layer of metallisation 298 extends is on the inside of the recess.

(94) The length of the probe tip 292 that extends from the sleeve 294 to deliver RF and microwave energy may be between 3 mm and 8 mm, preferably 4 mm. The width of the probe tip may be similar to the diameter of the coaxial cable, e.g. between 1.1 mm and 1.8 mm, preferably 1.2 mm. The thickness of the distal part of the probe tip 292 may be between 0.2 mm and 0.5 mm, preferably 0.3 mm.

(95) The general shape of the distal end of the instrument is of a spoon or scoop having a radius commensurate with that of the inner region of the vessel (e.g. bowel) in which treatment is to take place. For example, the curved arrangement shown may be suitable for getting underneath a polyp and scooping it out.

(96) The instrument may incorporate a gas conduit (not shown) to provide a gas supply to the probe tip for production of thermal or non-thermal plasma. The conduit may also supply liquid (e.g. saline) for injection capability during use as an electrosurgical instrument.

(97) For example, the gas and/or saline could be introduced along the inner conductor of the coaxial feed line in a manner similar to the embodiments shown in FIGS. 10 and 11, to be injectable out of an aperture formed in the probe tip 292. Alternatively a separate gas conduit may be mounted alongside the coaxial feed line.

(98) An alternative embodiment of a probe tip which is suitable for electrosurgery in addition to instrument channel sterilisation is shown in FIG. 13. The probe tip 402 comprises a dielectric block 416 that has layers of metallisation on its upper and lower surfaces. The inner conductor 418 of the coaxial cable 406 protrudes from the distal end of the coaxial cable 406 and is electrically bonded (e.g. using solder) to the upper layer of metallisation (first electrode). The outer conductor of the coaxial cable 406 is electrically coupled to the lower layer of metallisation (second electrode) by a braid termination 420. The braid termination 420 comprises a tubular part that is electrically bonded to the outer conductor and a distally extending plate part that fits under the dielectric block 416 and is electrically connected to the lower layer of metallisation.

(99) In this embodiment, a shaped piece of dielectric material 422 is attached to the lower surface of the dielectric block 416. It may be secured to the lower layer of metallisation. The shaped piece of dielectric material 422 is curved such that in cross-section its lower surface describes the chord of a circle between the edges of the dielectric block 416. In the longitudinal direction, the shaped piece of dielectric material 422 comprises a proximal part with a constant cross-section and a distal part in which the underside gradually tapers (e.g. in a curved manner) towards the dielectric block 416.

(100) In this embodiment, the gas conduit 408 terminates with a needle 424 (e.g. a hypodermic needle) which has an outer diameter smaller than the gas conduit 408 and which terminates with a sharp point. The needle 424 is retained in a longitudinal bore hole 426 through the shaped piece of dielectric material 422. Longitudinal movement of the gas conduit 408 relative to the dielectric block 416 acts to extend and retract the needle 424 from the probe tip.

(101) A cross-section through the withdrawal device 20 positioned on the handle of a scoping device 50 is shown in FIG. 14. The withdrawal device 20 is able to withdraw a coaxial cable 12 from an instrument channel 54, in a direction shown by arrows 18, at a predetermined rate. The withdrawal device 20 comprises a housing 21 containing a motor (not shown) and two rollers 25, wherein the motor acts to rotate rollers 25 via cogs 23, 24. The first cog 23 may be directly powered by the motor, and transfers rotational movement to the rollers 25 through a second cog 24 on each roller. The coaxial cable 12 is gripped between the rollers 25 such that it is withdrawn from the instrument channel 54 as the rollers 25 rotate.

(102) The withdrawal device 20 is releasably attached to the scoping device 50 by an attachment portion 26. By attaching the withdrawal device 20 directly to the scoping device 50, it is ensured that the rotation of the rollers 25 acts to withdraw the coaxial cable 12 rather than move the device body along the cable. The withdrawal device 20 can therefore be set up to withdraw the coaxial cable without further user interaction during the process.

(103) The withdrawal device 20 can also be configured to run in a ‘reverse’ mode to insert the coaxial cable 12 through the instrument channel 54. The reverse mode may be selected by a user through a switch on the housing 21 of the device. In addition, the rate of withdrawal or insertion is set by the speed of the motor. However, the speed of the motor may be adjustable. For example, the motor may comprise a control device for setting the speed. This may be adjusted by a control knob on the housing of the device. In alternative embodiments, the operation mode (forward/reverse) and speed of the motor may be set by a microcontroller which is part of the control device. The microcontroller may itself receive inputs from an external processing device, e.g. a Raspberry Pi® or Arduino® device.

(104) FIG. 15 shows a cross-section through the motor 27; cogs 23, 24; rollers 25 and instrument cable 12. As can be seen in the figure, the rollers 25 have an hourglass cross-sectional shape which gives a good fit between the rollers and the instrument cable, increasing friction to ensure that the coaxial cable 12 is smoothly pulled by rotation of the rollers 25. The rollers 25 may be made of a silicone material which conforms to the surface shape of the coaxial cable 12. In addition, the rollers 25 are biased towards each other, in a direction shown by arrows 28, to ensure good contact between the rollers 25 and the surface of the coaxial cable 12.

(105) FIG. 16 shows a view of an alternative embodiment of a withdrawal device 20. In this embodiment, the withdrawal device 20 further comprises a drum 22 around which the coaxial cable 12 is wrapped as it is withdrawn from the instrument channel of a scoping device. The drum 22 may have a spring drive mechanism to automatically wind the coaxial cable 12 about the drum as it is withdrawn by action of the rollers 25. Gas and RF and/or microwave EM energy are provided to the coaxial cable 12 via a connecting tube 42 and a connecting wire 32, which may respectively be connected to a gas supply and a generator (not shown). These connections mean that the probe tip at the distal end of the coaxial cable 12 is able to carry out sterilisation of the instrument channel as it is withdrawn by the withdrawal device 20.

(106) The drum 22 may also be used to store the coaxial cable 12 before it inserted into an instrument channel by the same motor and roller mechanism discussed above. The drum and housing may provide a sterile environment, as well as providing a space saving storage place for the cable 12.

(107) FIGS. 17A-17C show a sterilisation apparatus in use for sterilising the instrument channel of a scoping device 50. In FIG. 17A, the scoping device 50 is hung from a stand 60 so that the insertion tube 52 hangs vertically downwards. The coaxial cable 12 of an elongate sterilisation instrument is fully inserted in the instrument channel within the insertion tube. A withdrawal device 20 is attached to the scoping device 50, and is positioned on the coaxial cable 12 towards its proximal end. A generator 30 is configured to provide RF and/or microwave frequency EM radiation to the elongate instrument via connecting wire 32. A gas supply 40 is configured to supply a gas, e.g. Argon, to the elongate instrument via a connecting tube 42.

(108) In FIG. 17B, the motor of the withdrawal device 20 has been switched on to withdraw the coaxial cable 12 from the instrument channel of the scoping device 50 at a predetermined rate. At the same time, a probe tip (not shown) at the distal end of the coaxial cable 12 is generating a non-thermal plasma to sterilise the instrument channel. The plasma is generated at the probe tip by producing an electric field from the received RF and/or microwave frequency EM energy across a flow path of gas received from the gas supply 40. The gas reaches the probe tip through a gas conduit which extends the length of the elongate instrument.

(109) FIG. 17C shows the apparatus when the coaxial cable 12 has been completely withdrawn from the instrument channel. At this point the instrument channel is completely sterilised, requiring no further processing such as rinsing. The coaxial cable 12 and insertion tube 52 both hang vertically downwards from the stand 60, which avoids contamination by contact with other surfaces. The withdrawal device 20 remains attached to the scoping device 50. The generator 30 and gas supply 40 can be switched off as there is no further need for plasma to be produced at the probe tip.

(110) FIG. 18 shows a plan view of a probe tip 600, suitable for sterilisation of an instrument channel, connected to the distal end of a coaxial cable 610. The probe tip is configured to produce a circumferential jet of thermal or non-thermal plasma which can be directed at the wall of the instrument channel as the elongate instrument is withdrawn. In this embodiment, the first electrode 602 is a circular plate of conducting material, such as copper, which is connected to the inner conductor of the coaxial cable 610. The second electrode 604 is a cylinder of conducting material, e.g. copper, connected to the outer conductor of the coaxial cable 610. Between the second electrode 604 and the inner conductor there is a dielectric element, wherein the first electrode 602 is mounted on the end of the dielectric element. There is an annular opening between the first and second electrodes which defines the end of the gas conduit and out of which a thermal or non-thermal plasma is emitted when in use. The elongate instrument comprises a sleeve (not shown) which surrounds the coaxial cable from a proximal to a distal end of the instrument so as to define a gas conduit between the sleeve and the outer surface of the coaxial cable 610.

(111) FIG. 19 shows an end view of the probe tip 600 of FIG. 18 with the first electrode 602 removed. As can be seen in FIG. 19, the dielectric element 606 is positioned between the second electrode 604 and the inner conductor 612 of the coaxial cable 610. There are a number of groove 608 in the outer surface of the dielectric element 606 where gas is subjected to an electric field to produce a thermal or non-thermal plasma which is then emitted from the probe tip 600. The equally spaced grooves 608 help ensure that the plasma is emitted circumferentially and directed at the walls of the instrument channel. The dielectric element 606 may be elongate such that it has a length substantially equal to that of the second electrode 604.