Electrosurgical snare

Abstract

An electrosurgical snare, e.g. suitably sized for insertion down the instrument channel of an endoscope, arranged to radiate microwave frequency energy (e.g. having a frequency greater than 1 GHz) from an elongate conductive element within an area encircled by a retractable loop. The elongate conductive element and retractable loop may be independently slidable relative to a snare base at a distal end of a sleeve to provide an appropriate device configuration. By controlling the shape of the emitted microwave field, the risk of collateral thermal damage can be reduced.

Claims

1. A surgical snare comprising: a retractable loop for encircling an area containing biological tissue; a radiating structure arranged to radiate microwave frequency energy into the area encircled by the retractable loop; a coaxial cable for conveying the microwave frequency energy to the radiating structure, the coaxial cable comprising an inner conductor, an outer conductor surrounding and coaxial with the inner conductor, and a dielectric material separating the inner conductor and the outer conductor; and a snare base at a distal end of the coaxial cable, wherein the retractable loop is retractable relative to the coaxial cable towards the snare base, and wherein the radiating structure consists of a curved conductive portion partially bounding the area encircled by the retractable loop, the curved conductive portion being connected to the inner conductor of the coaxial cable and electrically insulated from the outer conductor of the coaxial cable to act as a radiating microwave monopole antenna, wherein the curved conductive portion comprises a guide for the retractable loop, and wherein the guide comprises an opening, the retractable loop extending through the opening and a length of the retractable loop that protrudes from the opening being adjustable.

2. A surgical snare according to claim 1, wherein the curved conductive portion extends between two ends, which are spaced at equal distances from a connection point at which the inner conductor of the coaxial cable is connected to the curved conductive portion.

3. A surgical snare according to claim 2, wherein an electrical length between the ends of the curved conductive portion is $\frac{(2 n - 1) λ_{L}}{4},$ where λ.sub.L is a wavelength of the microwave frequency energy when propagating through the biological tissue, and n is a positive integer.

4. A surgical snare according to claim 2, wherein an electrical length of the curved conductive portion is 10 mm or more.

5. A surgical snare according to claim 1, wherein the curved conductive portion comprises a pair of flexible prongs extending from the distal end of the coaxial cable.

6. A surgical snare according to claim 5 having a tubular end cap mounted at the distal end of the coaxial cable, wherein the curved conductive portion and tubular end cap are movable relative to each other between: a stored configuration in which the curved conductive portion is surrounded by the tubular end cap, and a deployed configuration in which the curved conductive portion protrudes beyond a distal end of the tubular end cap.

7. A surgical snare according to claim 6, wherein the tubular end cap has an outer diameter less than 2.6 mm.

8. A surgical snare according to claim 1, wherein the guide comprises a hollow tubular section with the opening at one end thereof, wherein the retractable loop extends along the hollow tubular section and through the opening.

9. A surgical snare according to claim 8, wherein the opening of the hollow tubular section is at a first end of the curved conductive portion and wherein the retractable loop includes a wire that is fixed to a second end of the curved conductive portion.

10. Electrosurgical apparatus comprising: a microwave signal generator for outputting microwave frequency energy having a frequency of 1 GHz or more, and a surgical snare according to claim 1 connected to receive the microwave frequency energy and deliver it through the coaxial cable to be emitted as a microwave frequency field by the curved conductive portion.

11. A surgical snare comprising: a retractable loop for encircling an area containing biological tissue; a radiating structure arranged to radiate microwave frequency energy into the area encircled by the retractable loop; a coaxial cable for conveying the microwave frequency energy to the radiating structure, the coaxial cable comprising an inner conductor, an outer conductor surrounding and coaxial with the inner conductor, and a dielectric material separating the inner conductor and the outer conductor; and a snare base at a distal end of the coaxial cable, wherein the retractable loop is retractable relative to the coaxial cable towards the snare base, wherein the radiating structure consists of a conductive portion formed in or on the retractable loop, the conductive portion being connected to receive microwave power from the coaxial cable and configured to radiate the received microwave frequency energy into the area encircled by the retractable loop, wherein the conductive portion comprises a guide for the retractable loop, and wherein the guide comprises an opening, the retractable loop extending through the opening and a length of the retractable loop that protrudes from the opening being adjustable.

12. A surgical snare according to claim 11, wherein an electrical length of the conductive portion around the retractable loop is $\frac{(2 n - 1) λ_{L}}{4},$ where λ.sub.L is a wavelength of the microwave frequency energy when propagating through the biological tissue, and n is a positive integer.

13. A surgical snare according to claim 11, wherein the retractable loop comprises a wire having a first end fixed at the distal end of the coaxial cable, and a second end whose position relative to the distal end of the coaxial cable is adjustable, and wherein the conductive portion extends around the retractable loop from the first end.

14. A surgical snare according to claim 11, wherein the conductive portion comprises a length of coaxial cable that is shorted at its distal end and along which portions of the outer conductor are periodically removed to permit radiation therefrom.

15. Electrosurgical apparatus comprising: a microwave signal generator for outputting microwave frequency energy having a frequency of 1 GHz or more, and a surgical snare according to claim 11 connected to receive the microwave frequency energy and deliver it through the coaxial cable to be emitting as a microwave frequency field by the conductive portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIGS. 1A and 1B show a schematic cross-sectional view of a surgical snare that is a first embodiment of the invention, in a deployed and retracted position respectively;

(3) FIGS. 2A and 2B show a schematic cross-sectional view of a surgical snare that is a second embodiment of the invention, in a deployed and retracted position respectively;

(4) FIGS. 3A and 3B show a schematic cross-sectional view of a surgical snare that is a third embodiment of the invention, in a deployed and retracted position respectively;

(5) FIG. 4 is a perspective view of a model surgical snare used to simulate the microwave delivery performance of the invention;

(6) FIG. 5 is a graph showing return loss (impedance match) into blood for the model surgical snare shown in FIG. 4;

(7) FIG. 6 is a plan view of the model surgical snare of FIG. 4 showing power loss density into blood;

(8) FIG. 7 is a graph showing return loss (impedance match) into blood for the model surgical snare of FIG. 4 with different tip diameters;

(9) FIG. 8 is a plan view of the model surgical snare of FIG. 4 showing power loss density into blood with minimal protrusion of the probe into the area encircled by the retractable loop;

(10) FIG. 9 is a graph showing return loss (impedance match) into blood for the model surgical snare of FIG. 8;

(11) FIG. 10 is a graph showing return loss (impedance match) into blood for the model surgical snare of FIG. 8 with different loop diameters;

(12) FIG. 11 shows four plan views of the model surgical snare of FIG. 8 showing power loss density into blood for four different loop diameters;

(13) FIGS. 12A, 12B and 12C show a schematic cross-sectional view of a surgical snare that is a fourth embodiment of the invention, in a polyp capture position, a deployed antenna position and a retracted position respectively;

(14) FIG. 13A shows a schematic cross-sectional view of a distal portion of a surgical snare that is a fifth embodiment of the invention; and

(15) FIG. 13B is a perspective view of a cap used in the surgical snare shown in FIG. 13A.

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES

(16) FIG. 1A shows a cross-sectional view through a surgical snare 100 that is an embodiment of the invention. The drawing is schematic and not to scale. In particular, the relative length of the device is shortened substantially. In practice, the largest width (diameter) of the device is less than 2.6 mm in order to make it suitable for passing through the instrument channel of an endoscope. The total length of the device, meanwhile, may be 2 m or more.

(17) The surgical snare 100 comprises a coaxial cable 102, comprising an inner conductor 104, an outer conductor 106 and a dielectric material 108 separating the inner conductor 104 from the outer conductor 106. A microwave connector 110 (e.g. a QMA connector or the like) is mounted at a proximal end of the coaxial cable 102 for connecting to a microwave signal generator (not shown). A snare base 112 (e.g. a disc of a suitable insulator, e.g. a low loss microwave ceramic, PTFE, PEEK, Nylon or the like, is mounted at a distal end of the coaxial cable 102.

(18) The coaxial cable 102 is encased in a sleeve 114. The sleeve 114 has a pair of passages for conveying a pair of pull wires 116 from the proximal end of the device to the distal end. Each pull wire 116 passes through the snare base 112 via a feed channel (i.e. a passageway formed in the snare base). The pair of pull wires 116 are each connected at their distal end to a respective end 117 of a length of wire 118 that forms a loop for the snare. The pair of pull wires 116 are each connected at their proximal end to a slider mechanism 120 which is movable relative to the sleeve 114. The slider mechanism 120 can be operated by the user to adjust the length of wire 118 that protrudes from the sleeve 114, thereby controlling the diameter of the loop formed by the length of wire 118 at the distal end of the device. The length of wire 118 may have a shape retaining property which allows it to deform in order to enter the passages in the sleeve, but recover its loop shape when drawn out again. FIG. 1A shows the loop in a fully deployed position. FIG. 1B shows the device with the loop partly withdrawn into the sleeve 114.

(19) In this embodiment, the inner conductor 104 of the coaxial cable 102 protrudes through and beyond the snare base 112 to form an elongate conductive member 122. The function of the elongate conductive member 122 is as a microwave antenna (preferably a radiating monopole antenna) to radiate microwave frequency energy supplied to it through the coaxial cable 102. The elongate conductive member 122 may or may not penetrate the biological tissue that is encircled by the loop of the snare (e.g. the stem of a polyp), depending on its length. The elongate conductive member 122 includes a proximal portion that runs alongside the pull wires 116 in the snare base 112. Microwave energy delivered to the elongate conductive member 122 is coupled to set up a travelling wave in the pull wires 116 at this location, from where it is conveyed into and radiates from the wire loop 118. The strength of the radiated field is at a maximum at the distal end of the loop, where the travelling waves from each of the pull wires meet.

(20) The microwave energy delivered to the elongate conductive member is radiated into the tissue, where it will promote coagulation and therefore assist in the removal of the biological tissue or prevent bleeding which would otherwise occur if mechanical action only was employed. It may be preferable to deliver microwave radiation continuously when a mechanical force is applied to the polyp stalk. Alternatively, the microwave source may be activated based on the measurement of a physical force, e.g. measured using a mechanical to electrical transducer, such as a piezoelectric transducer force sensor or the like.

(21) The microwave energy may be delivered as a sequence of pulses or a burst of microwave energy, whereby the mechanical force follows or is embedded within the burst of microwave coagulation energy. For example, one activation profile may comprise applying 10 W of microwave power for 10 seconds, and applying the mechanical force for shorter periods within that 10 second time frame, i.e. the mechanical and microwave energy are delivered together and microwave energy is always applied, but mechanical energy is applied at intervals within the window of application of the microwave energy.

(22) It may also be desirable to deliver the microwave energy based on the detection of a change in the reflected signal caused by a change in the impedance of the tissue that makes contact with the radiating monopole (or other) antenna, i.e. only deliver the microwave energy when the impedance of blood is detected. In addition, the delivery of the microwave energy may cease when a change of impedance is detected, i.e. the impedance of coagulated blood is detected. The measurement information may be magnitude only or magnitude and phase or phase only. To achieve this function effectively, the electrical length of the elongate conductive member 122 is determined based on a knowledge of the dielectric constant ε.sub.r of the biological tissue to be treated, the equivalent dielectric properties of the structure surrounding the elongate conductive member 122 in the snare base 112, and the frequency f of the microwave frequency energy that will be provided through the coaxial cable. This information is used to calculate a wavelength λ.sub.L of the microwave energy as it propagates through the biological tissue. The electrical length of the elongate conductive member 122 is set to be an odd number of quarter wavelengths, i.e.

(23) $\frac{(2 n - 1) λ_{L}}{4},$
where

(24) $λ_{L} = \frac{c}{f \sqrt{{.Math.}_{r}}}$
and c is the speed of light at the frequency of choice.

(25) To avoid damaging the elongate conductive member 122 as the device is inserted along the instrument channel of an endoscope, a slidable tubular cover 124 is mounted at the distal end of the sleeve 114. A pull wire 126 extends from the tubular cover 124 to a handle 128 at the proximal end of the snare. The handle 128 may be operated by the user to slide the cover 124 over the elongate conductive member 122 (as shown in FIG. 1B). In use, the cover 124 is slid back over the sleeve 114 to expose the elongate conductive member 122.

(26) The wire loop 118 may be rotated by turning a handle 125 that is attached to the sleeve 114. The sleeve may include a braided cable which facilitates accurate torque transfer to allow the rotation of the wire loop to be controlled precisely.

(27) FIG. 2A shows a cross-sectional view through a surgical snare 200 that is another embodiment of the invention. Similarly to FIGS. 1A and 1B, the drawing is schematic and not to scale. Features in common with FIGS. 1A and 1B are given the same reference numbers and are not described again. The handle 125 is omitted for clarity.

(28) In FIG. 2A the inner conductor 104 of the coaxial cable 102 is connected to a curved conductive portion 130 which comprises a pair of curved prongs which extend symmetrically away from the feed point 132 at which they are connected to the inner conductor 104. Each prong may be a flexible elongate conductor, e.g. a wire or tube. In this embodiment, the length of wire 118 that forms a loop for the snare is fixed at one end to a distal end 134 of one of the prongs. The other end of the length of wire 118 is connected to the distal end 136 of a pull wire 116. The proximal end of the pull wire 116 is connected to the slider 120, which operates in the same manner as discussed above with reference to FIGS. 1A and 1B.

(29) However, in this embodiment, the pull wire 116 and length of wire 118 forming the loop for the snare are arranged to pass through a guide passage formed in one of the prongs. Thus, upon exiting the passage in the sleeve 114, the pull wire 116 or wire 118 pass through a rear opening 138 on one of the prongs, through a hollow guide passage in that prong, to exit through a front opening 140 at the distal end of that prong.

(30) The function of the curved conductive portion 130 is the same as the elongate conductive element 122 discussed above: it is a radiating microwave monopole antenna for radiating microwave frequency energy supplied to it through the coaxial cable 102. In use, the curved conductive portion 130 will contact the biological tissue that is encircled by the loop of the snare (e.g. the stem of a polyp). The microwave energy will therefore be radiated into the tissue, where it will promote coagulation and therefore assist in the removal of the biological tissue. To achieve this function effectively, the electrical length of the curved conductive portion 130 is therefore determined in a similar way to the elongate conductive element 122 discussed above, i.e. it is determined based on a knowledge of the dielectric constant ε.sub.r of the biological tissue to be treated and the frequency f of the microwave frequency energy that will be provided through the coaxial cable. This information is used to calculate a wavelength λ.sub.L of the microwave energy as it propagates through the biological tissue. The electrical length of the curved conductive member 130 is thus set to be an odd number of quarter wavelengths, i.e.

(31) $\frac{(2 n - 1) λ_{L}}{4},$
where

(32) $λ_{L} = \frac{c}{f \sqrt{{.Math.}_{r}}}$
and c is the speed of light.

(33) However, as the curved conductive portion 130 does not penetrate tissue, it can be made longer than the elongate conductive element 122. In order to fit down the instrument channel of an endoscope, the prongs of the curved conductive portion 130 preferably deform when the cover 124 is slid over them, as shown in FIG. 2B. The prongs may be resiliently deformable so that they regain their original position when the cover 124 is slid back over the sleeve 114.

(34) FIG. 3A shows a cross-sectional view through a surgical snare 300 that is another embodiment of the invention. Similarly to FIGS. 1A and 1B, the drawing is schematic and not to scale. Features in common with FIGS. 1A and 1B are given the same reference numbers and are not described again.

(35) In FIG. 3A the inner conductor 104 of the coaxial cable is connected to a conductive portion 142 which is mounted on the wire 118 that forms the loop for the snare. The wire 118 in this embodiment is made from a non-conductive material (e.g. nylon).

(36) Similarly to the other embodiments discussed above, the function of the conductive portion 142 is the same as the elongate conductive element 122 is as a radiating microwave monopole antenna for radiating microwave frequency energy supplied to it through the coaxial cable 102. In use, the conductive portion 142 will contact the biological tissue that is encircled by the loop of the snare (e.g. the stem of a polyp). The microwave energy will therefore be radiated into the tissue, where it will promote coagulation and therefore assist in the removal of the biological tissue. To achieve this function effectively, the electrical length of the conductive portion 142 is therefore determined in a similar way to the elongate conductive element 122 discussed above, i.e. it is determined based on a knowledge of the dielectric constant ε.sub.r of the biological tissue to be treated and the frequency f of the microwave frequency energy that will be provided through the coaxial cable. This information is used to calculate a wavelength λ.sub.L of the microwave energy as it propagates through the biological tissue. The electrical length of the conductive member 142 is thus set to be an odd number of quarter wavelengths, i.e.

(37) 0 $\frac{(2 n - 1) λ_{L}}{4},$
where

(38) $λ_{L} = \frac{c}{f \sqrt{{.Math.}_{r}}}$
and c is the speed of light. It should also be noted that the conductivity and the dielectric constant of the biological tissue are a function of the frequency of the microwave energy, and these parameters, together with the physical geometry of the antenna and the power lever (or energy delivery profile) determine the depth of penetration of the electric field into the tissue structure, e.g. polyp stem, mucosa, etc., which determines the profile of the focussed heat.

(39) Alternatively, however, the conductive member 142 may itself be a coaxial cable with an inner conductor electrically connected to the inner conductor 104 of the coaxial cable 102 and a ground outer conductor. The inner and outer conductors may be connected together at the distal end 144 of the conductive portion 142, e.g. where it connected to the wire 118. This structure may be made to radiate by removing periodically spaced sections of the outer conductor. The sections may be s aced by an odd number of quarter wavelengths, i.e.

(40) $\frac{(2 n - 1) λ_{L}}{4} .$
This structure is also known as a ‘leaky feed’.

(41) In this embodiment, the length of wire 118 that forms a loop for the snare is fixed at one end to a distal end 144 of the conductive portion 132. The other end of the length of wire 118 is connected to the distal end 136 of a pull wire 116. The proximal end of the pull wire 116 is connected to the slider 120, which operates in the same manner as discussed above with reference to FIGS. 1A and 1B.

(42) The conductive element 142 may be deformable in a manner similar to that shown in FIGS. 2A and 2B when the cover 124 is slid forward as shown in FIG. 3B. The conductive portion 142 or the wire 118 may be resiliently deformable so that they regain their original position when the cover 124 is slid back over the sleeve 114.

(43) FIG. 4 depicts a representative model 400 of a surgical snare according to the invention that was modelled using CST MICROWAVE STUDIO®, and the performance simulated as various modifications were made to the structure to improve the return loss (impedance match into tissue load model) and power density in the tissue.

(44) In order to allow room for the mechanism to mechanically operate the snare, the coaxial cable 402 required to feed microwave energy down the endoscope channel is selected to have a diameter that is around 1.2 mm in diameter. Sucoform 47 (made by Huber+Suhner) is a suitable cable that is 1.2 mm in diameter and is flexible enough to allow full manipulation of the endoscope with the cable within its channel. Sucoform 86 cable, with an outside diameter of around 2.2 mm may also be a suitable candidate for implementing the microwave snare.

(45) The retractable loop 404 of the snare was modelled as a circular loop of square cross section wire of thickness 0.5 mm. For most of the simulations the internal diameter of the loop was 3.6 mm. This implies that the length of the antenna that will radiate into the stalk of the polyp is around 11 mm. Referring to FIG. 11, the loop was filled with a cylinder of tissue which for most of the simulations was given the microwave properties of blood. The loop is connected to two wires 406 which run beside the outer conductor of the coaxial cable 402, and overlap it by one wire thickness. No further wire length was modelled. The inner conductor and dielectric covering 408 were extended from the end of the coaxial cable 402 to project into the loop, and the end of the centre conductor was connected to a spherical metal dome 410.

(46) The structure of FIG. 4 was the result of some preliminary modelling, during which it was found that the return loss could be improved by moving the loop further from the end of the coaxial cable, and extending the inner conductor and dielectric covering 408.

(47) The power density inside the loop is higher if the end of the centre conductor is exposed than if it is covered with dielectric. However, if the end of the centre conductor is kept at its original radius the power density close to its end is extremely high. Thus, placing a conducting dome on the end of the centre conductor increases the power density in the loop and results in less concentrated power close to the conductor.

(48) FIG. 5 shows the return loss for the configuration shown in FIG. 4, with a long cylinder of blood completely filling the loop. The dielectric properties of blood used in this simulation were as follows:

(49) TABLE-US-00001 Pene- Conductivity Relative Loss Wavelength tration [S/m] permittivity tangent [m] depth [m] Blood 6.5057 52.539 0.38376 0.0070075 0.006019

(50) FIG. 6 shows the power loss density in the plane of the loop. Here it has been assumed that the specific heat capacity of blood is about 4.2 J/(g.Math.K), which is the specific heat capacity of water, and that the density of tissue is about 1 g/cm.sup.3, which is the density of water, so that the volumetric heat capacity of tissue is about 4.2 J/(cm.sup.3.Math.K).

(51) Most of the area surrounding by the loop has a power absorption of around 67 dBW/m.sup.3, which is equivalent to 5 W/cm.sup.3, for a 1 W input power. Thus, for a 10 W input power the power absorption would be 50 W/cm.sup.3. This is enough to raise the temperature of the tissue in the loop by 12 Ks.sup.−1. Close to the spherical dome the temperature rise will be considerably faster.

(52) FIG. 7 illustrates the effect on the return loss of changing the diameter of the spherical tip. Line 412 represents a diameter of 0.6 mm. Line 414 represents a diameter of 0.8 mm. Line 416 represents a diameter of 1.0 mm. Line 418 represents a diameter of 1.2 mm. Smaller tip diameters give better return loss. However a larger diameter gives a better heat distribution and minimises the risk of perforation. A diameter of 0.8 mm was chosen for further simulations.

(53) FIG. 8 shows the results of a simulation carried out on a structure where there is minimal protrusion of the spherical tip into the loop. In this arrangement it is intended for only the metal sphere to protrude into tissue captured by the loop. FIG. 8 shows the power loss density for the structure. It is slightly lower than with the fully protruding tip of FIG. 4. The central region of the loop in this arrangement has a power absorption level of around 64 dBW/m.sup.3. FIG. 9 shows the return loss for the same structure.

(54) FIGS. 10 and 11 illustrate the effect of changing the diameter of the loop using the configuration of FIG. 8. FIG. 10 shows the return loss for six different diameters: 4 mm, 3.5 mm, 3 mm, 2 mm, 1.5 mm and 1 mm, represented by lines 420, 422, 424, 426, 428 and 430 respectively. At 5.8 GHz the return loss for each diameter is as follows:

(55) TABLE-US-00002 Loop diameter (mm) Return loss (dB) 1.0 −2.789259 1.5 −2.2937289 2.0 −2.1571845 3.0 −2.4899045 3.5 −3.2297901 4.0 −3.8561229

(56) As the loop diameter reduces, at first the return loss worsens, but for diameters less than 2 mm the return loss begins to improve again (the higher the magnitude of the return loss, the better the impedance match into tissue or the more power will be delivered into the tissue).

(57) FIG. 11 shows the power densities in the cylinder of blood enclosed in the loop for four loop diameters: 4 mm, 3 mm, 2.5 mm, 2 mm, and 1.5 mm. (The power density for a loop diameter of 3.6 mm is already shown in FIG. 8). These results show that the microwave power is adequate for loop diameters out to 4 mm and beyond. Given the stability of the profile, there is tolerance of loop shape too, i.e. the loop may take a large variety of shapes without disturbing the power absorption profile. For smaller diameters, even though the return loss get worse, the power density rises, particularly in the centre of the loop, which means that the microwave heating becomes stronger as the loop tightens. Thus, the power density in the central region of the 4 mm loop is around 60 dBW/m.sup.3, whereas in the central region of the 2 mm loop it is around 67 dBW/m.sup.3.

(58) The Sucoform 47 cable has an attenuation of about 3 dB/m at 5.8 GHz. This has an impact on the power that can be delivered to the end of the cable. The Sucoform 47 cable needs to be slightly longer than the endoscope channel, i.e. just over 2 m long, and so has an attenuation of about 7 dB. If the power available at the proximal end of the cable is 50 W (47 dBm), the maximum power than can be delivered at the distal end of the cable is about 10 W (40 dBm).

(59) FIG. 12A shows a cross-sectional view through a surgical snare 500 that is another embodiment of the invention. Similarly to FIGS. 1A and 1B, the drawing is schematic and not to scale. Features in common with FIGS. 1A and 1B are given the same reference numbers and are not described again.

(60) This embodiment differs from the arrangement shown in FIGS. 1A and 1B in that instead of having a sliding cover, the coaxial cable 102 is slidable within the sleeve 114 to cause the elongate conductive member 122 to protrude into the area encircled by the retractable loop 118. This embodiment therefore comprises a housing 502 at the proximal end of the device. The housing 502 has a tapered distal tip 504 which is attached, e.g. adhered or otherwise secured, to the proximal end of the sleeve 114. The housing 502 has a passageway therethrough for receiving the coaxial cable 102 in a manner that permits the coaxial cable 102 to slide relative to the housing 502 (and therefore the sleeve 114).

(61) A handle 506 for operating the retractable loop 118 independently of the elongate conductive member 122 is slidably mounted on the housing 502 and connected to a proximal end of a push rod 508. The push rod 508 extends through the sleeve 114 and is attached at its distal end to a first end of the retractable loop 118.

(62) This embodiment comprises a snare base 512 that is fixed, e.g. adhered or otherwise secured, to the distal end of the sleeve 114. As shown in the expanded cross-sectional view of FIG. 12B, the snare base 512 has two longitudinal passageways therethrough. A first passageway 514 is for conveying the push rod 508. The distal end 117 of the push rod 508 that is connected to the first end of the retractable loop 118 is located within the first passageway 514 in this view. A second passageway 516 is for conveying the coaxial cable 102. The snare base 512 also receives the second end 518 of the retractable loop 118. The second end 518 is attached to the snare base 512.

(63) FIG. 12A shows the surgical snare 500 of this embodiment in a configuration where the elongate conductive member is retracted but the retractable loop 118 is extended. This may correspond to a polyp capture position, where the retractable loop is open to fit over a polyp.

(64) FIG. 12B shows the surgical snare 500 of this embodiment in a configuration where the elongate conductive member 122 is extended into the area encircled by the retractable loop 118. This may correspond to a deployed antenna position in which the elongate conductive member 122 may deliver microwave frequency energy into tissue captured within the retractable loop 118. To arrive in this configuration from the polyp capture configuration shown in FIG. 12A, the coaxial cable 102 is moved distally (to the right as shown in FIG. 12B by arrow 522). In this embodiment, the elongate conductive member 122 has a rounded conductive tip 520 mounted thereon. The rounded conductive tip 520 may be formed from silver wire wrapped around and soldered to elongate conductive member 122, i.e. to the protruding portion of the inner conductor 104.

(65) FIG. 12C shows the surgical snare 500 of this embodiment in a configuration where both the retractable loop 118 and the elongate conductive member 122 are fully retracted. This may correspond to a retracted position, e.g. for use when moving the device through the instrument channel of an endoscope. To arrive in this configuration from the polyp capture configuration shown in FIG. 12A, the handle 506 is moved proximally (to the left as shown in FIG. 12C by arrow 524).

(66) The process of retraction may be used to assist cutting of biological tissue (e.g. a polyp stem) encircled by the retractable loop 118. The retractable loop may force the encircled tissue against the distal surface of the snare base 512, which thus forces a reaction surface to assist cutting. the distal surface of the snare base may be shaped to assist cutting, e.g. by being curved in a convex manner. The retractable loop 118 may have a roughened or sharpened surface (e.g. on the inside thereof) to assist cutting.

(67) FIG. 13A shows a schematic cross-sectional view of a distal portion of a surgical snare 600 that is another embodiment of the invention. This embodiment may use the same deployment mechanism (housing 502 and handle 506) as FIG. 12A, and so these feature are omitted for clarity. Features in common with FIGS. 1A and 1B and FIGS. 12A, 12B and 12C are given the same reference numbers and are not described again. Similarly to FIGS. 1A and 1B, the drawing is schematic and not to scale.

(68) Similarly to the embodiment discussed with reference to FIGS. 12A, 12B and 12C above, in the embodiment of FIG. 13A the coaxial cable 102 is slidable with the sleeve 114 in order to extend and retract the elongate conductive member 122. Similarly, the retractable loop 118 is operated via the slidable push rod 508 in the same way as discussed above.

(69) However, the configuration of the snare base in FIG. 13A is different from FIGS. 12A, 12B and 12C. In this embodiment, the snare base comprises a cap 602 that is secured to the end of the sleeve 114. As shown in FIG. 13B, the cap 602 has a top hat shape, with an annular flange 604 that provides the distal surface thereof which mounted in use. The annular flange 604 may thus provide the reaction surface during mechanical cutting using the retractable loop 118. The cap has a passageway 606 therethrough for conveying the coaxial cable 102 and the push rod 508 or retractable loop 118.

(70) Within the sleeve 114, a collar 608 is attached (e.g. adhered or soldered or otherwise affixed) to the outer surface (e.g. outer conductor 106) of the coaxial cable 102. The collar 608 thus moves with the coaxial cable 102 within the sleeve 114. The collar 608 has a larger diameter than the coaxial cable 102 and therefore leaves a space between its inner surface and the outer surface of the coaxial cable on a side of the coaxial cable that is opposite to the location at which the collar is attached to the coaxial cable. The push rod 508 passes through this space and is thus free to move relative to the coaxial cable 102.

(71) The inner diameter of the flange 604 is smaller than the diameter of the collar 608 to act as a stop to limit the extent to which the elongate conductive member 122 can protrude out of the sleeve 114.

(72) In this embodiment the other end 518 of the retractable loop 518 is attached (e.g. soldered) to the collar 608, e.g. to the outer surface of the collar 608. This means that the attachment point of the retractable loop 118 lies inside the sleeve 114, which may assist in complete retraction of the loop. Moreover, since the collar 608 is movable with the coaxial cable 102 within the sleeve 114, both ends of the retractable loop 118 are effectively movable within the sleeve, which can ensure that the loop is fully retractable.

Electrosurgical snare

Assignee

Inventors

Cpc classification

Classification Explorer

A61B2018/144

HUMAN NECESSITIES

Classification Explorer

A61B2017/2212

HUMAN NECESSITIES

Classification Explorer

A61B17/221

HUMAN NECESSITIES

Classification Explorer

A61B2018/00607

HUMAN NECESSITIES

Classification Explorer

A61B2018/1853

HUMAN NECESSITIES

Classification Explorer

A61B2018/00494

HUMAN NECESSITIES

Classification Explorer

A61B2018/1407

HUMAN NECESSITIES

Classification Explorer

A61B2018/00589

HUMAN NECESSITIES

Classification Explorer

A61B17/32056

HUMAN NECESSITIES

Classification Explorer

A61B18/1815

HUMAN NECESSITIES

Classification Explorer

A61B18/1402

HUMAN NECESSITIES

Classification Explorer

A61B2018/1861

HUMAN NECESSITIES

Classification Explorer

A61B2018/141

HUMAN NECESSITIES

Classification Explorer

A61B2018/00875

HUMAN NECESSITIES

International classification

Classification Explorer

A61B18/14

HUMAN NECESSITIES

Classification Explorer

A61B17/3205

HUMAN NECESSITIES

Classification Explorer

A61B18/18

HUMAN NECESSITIES

Classification Explorer

A61B17/221

HUMAN NECESSITIES

Classification Explorer

A61B18/00

HUMAN NECESSITIES

Abstract

Claims

Description