System and method for microwave ablation of tissue

Abstract

Systems and methods for microwave ablation of tissue. The probe includes a transmission line, and the electrical shorting provides a choke with a tube. The sheath may be coaxially disposed on the tube and define a fluid port with the distal infusion path in fluid communication with the proximal infusion path through an aperture in the tube. The choke may be floating with the shorted conductive tube disposed coaxially with the non-conductive tube. The probe may be a dual slot architecture in which the choke is located proximal to the proximal slot. A method may include providing a real-time estimate of tissue condition and / or lesion size. A frequency scan may be performed, whereby a relative dielectric constant of the tissue may be determined. A distance to a reflection point of the tissue boundary may be determined in the time-domain spectrum, from which a feature of the ablation procedure may be provided on a display.

Description

[0001] Priority claim

[0002] This application claims priority to and all benefits of U.S. Provisional Patent Application No. 63 / 414,962, filed on October 11, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0003] Microwave ablation procedures use electromagnetic energy in the microwave frequency range to heat and destroy tissue. In the oncology context, tissue is typically composed of tumors that typically assume a spherical shape. Microwave energy is transmitted from a microwave generator to the tissue via a microwave probe (commonly referred to as an antenna). The energy in the near-field region of the probe interacts strongly with the tissue surrounding the probe tip. Due to the nature of microwave heating, tissue properties affect the performance of the probe. For example, heating, dehydration, and charring of tissue can change its electrical properties, particularly its relative dielectric constant at a given frequency of microwave energy. These changes, if not adequately addressed, may affect the efficiency and burn pattern of the probe and may result in uncontrolled and / or non-spherical lesions or ablations. The construction of a probe with a cooling circuit is complex, thereby increasing the complexity and cost of manufacturability. In addition, a large amount of heat is effectively drawn away, which otherwise could have been used to ablate the tissue.

[0004] Because ablation occurs within anatomical structures, it is difficult to obtain real-time information about the ablation, especially the size of the lesion. Large changes in the electrical properties of the tissue during ablation can be detrimental to microwave probe performance and may result in uncontrolled ablation. Uncertainty in ablation size may result in insufficient destruction of tumor margins, or collateral damage to healthy tissue near the tumor. Therefore, there is a need in the art for systems and methods to mitigate large changes in tissue electrical properties during ablation, and further to achieve improved real-time estimates of lesion size or other aspects of ablation procedures. Summary of the invention

[0005] Certain aspects of the present disclosure are intended to mitigate changes in the relative dielectric constant of tissue by infusing the tissue with an infusion liquid. The infusion liquid may have a higher relative dielectric constant to balance the dehydration of the tissue during the ablation procedure. The infusion liquid passes through the shaft of the probe before being infused into the tissue. Ohmic heating in the shaft can preheat the infusion liquid, which is ultimately transferred to the tissue. In this way, there is no waste of thermal energy in the system. In addition, the infusion liquid can change state (i.e., from liquid to gas) near the tip of the probe to improve heat transfer. In particular, when the gas molecules return to liquid form, latent heat energy can be deposited in the tissue. Since the dielectric properties of the tissue are actively maintained without wicking away a large amount of thermal energy, this enables the ablation area to be faster, larger and more consistent. In addition, by adjusting the flow rate to ensure consistent electrical properties in the tissue adjacent to the tissue, the performance of the probe can be optimized, and thus the optimal ablation zone is achieved. Certain aspects of the present disclosure are also intended to provide improved real-time estimates of tissue conditions and tissue boundaries, as well as corresponding visualization of ablation and / or control of the system. Other advantages will be easily understood from the systems and methods described herein.

[0006] The system may include a console, a probe, and an optional liquid reservoir. The console may include a pump arranged in fluid communication with the liquid reservoir. The console may include a controller in electronic communication with the pump. The probe is configured to be arranged in fluid communication with the liquid reservoir. The probe is also configured to be arranged in operative communication with a microwave generator of the console. The microwave generator is in electronic communication with the controller. The controller is configured to operate the microwave generator to emit microwave energy at a desired frequency and power.

[0007] The probe includes a hub and a shaft extending distally from the hub to a tip. The shaft can be sufficiently rigid, and the tip is sharp enough to allow the probe to penetrate and be guided through soft tissue to reach a target location within the anatomical structure. The transmission line of the probe can extend from the hub into the shaft. The transmission line includes an outer conductor and an inner conductor coaxially arranged within the outer conductor. An insulating layer is coaxially arranged between the outer conductor and the inner conductor. The transmission line can include a proximal section, an intermediate section, and a distal section. The inner conductor can extend through the proximal section and the intermediate section, and optionally through the distal section. The distal section and the intermediate section can define a first axial slot, and the intermediate section and the proximal section can define a second axial slot. Such an arrangement can be considered as a double slot architecture. Alternatively, the probe can have a monopole architecture, or other architectures including a single slot, a dipole, a triaxial, and a sleeve.

[0008] The probe includes a choke, which may include a tube formed of a conductive material and coaxially disposed on a portion of a transmission line. In some embodiments, the tube may be coaxially spaced from the transmission line along its length. The electrical short may provide electrical connectivity between the transmission line and the tube. The electrical short is formed of a conductive material and is in direct contact with each of the outer conductor and the tube. The choke insulation layer is disposed between the tube and the transmission line. The length of the choke defined between the distal end and the electrical short may be one-quarter of the effective wavelength of microwaves at 2.45 GHz in the material forming the choke insulation layer, or more specifically one-quarter of the microwave field in the choke insulation layer.

[0009] In another embodiment, the choke may not be shorted to the outer conductor of the transmission line. The inner choke layer may be floating and otherwise spaced apart from the transmission line. The non-conductive tube is coaxially disposed on a portion of the transmission line. The choke includes an inner choke layer, an outer choke layer, and an optional electrical shorting portion. The inner choke layer includes a first conductive tube coaxially disposed between the non-conductive tube and the outer conductor of the transmission line. The outer choke layer includes a second conductive tube coaxially disposed on the non-conductive tube so that an area of ​​the non-conductive tube forms a choke insulation layer. The area of ​​the non-conductive tube may be thinned to define a recess. The second conductive tube forming the outer choke layer may be disposed within the recess. The length of the area is based on the relative dielectric constant of the material forming the sheath. The length of the area of ​​the non-conductive tube may be approximately equal to one-quarter of the effective wavelength of the drive frequency in the material of the non-conductive tube.

[0010] The electrical short may be a conductive element compressed between the outer choke layer and the inner choke layer. The conductive element may be a wire or a ring. The conductive element may be formed of a suitable conductive material such as gold, or alternatively, solder may form the conductive element. The distal end of the inner choke layer terminates at a position proximal to the second axial slot. The distal end of the outer choke layer terminates at a position proximal to the second axial slot.

[0011] The probe includes a dielectric housing coupled to the transmission line and defining a tip at the distal end of the probe. The dielectric housing can be coupled to the transmission line and include an outer diameter that is at least substantially equal to the outer diameter of the tube. The proximal end of the dielectric housing can abut the distal end of the choke at the interface. The dielectric housing can be coaxially disposed on the proximal segment and more specifically shaped to contact the outer conductor along its length. The dielectric housing is formed of a material having a relative dielectric constant and other material properties required for percutaneous deployment into the anatomical structure.

[0012] The probe is configured to deliver an infusion liquid to tissue surrounding an active tip of the probe, which can be defined at any point along the probe distal to the choke. The probe can include a sheath coaxially disposed on at least a portion of the tube and the dielectric housing. The sheath can be sized to be disposed proximally above the tube and the dielectric housing to define a distal infusion path therebetween. The tube defines a proximal infusion path and an orifice. The orifice can be a single hole, a plurality of holes radially arranged around the tube, and the like. The orifice provides fluid communication between the proximal infusion path and the distal infusion path to define the infusion path as a whole. The orifice can be positioned proximal to the electrical shorting portion. An optional barrier can be disposed between the sheath and the tube and proximal to the electrical shorting portion to avoid backflow of the infusion liquid.

[0013] The sheath defines a fluid port that is in fluid communication with the distal infusion path. The fluid ports can have any suitable number and be arranged in any suitable configuration around the active tip of the shaft, as described herein. The fluid ports or their higher distribution density can be set at a position associated with maximum heating in the ablation zone within the active tip, also referred to as the "hot spot" of the probe. Specifically, the position can be proximal to the first axial groove, and / or distal to the second axial groove. Additionally or alternatively, the higher distribution density of fluid ports can be positioned adjacent to the choke, rather than away from the choke, because the choke may be a hot spot. The fluid ports can have any suitable size or shape.

[0014] The controller operates the pump to control the characteristics of delivering the infusion liquid into the tissue through the probe. Additionally or alternatively, the controller can operate the pump based on the probe type, and more specifically based on the tip type corresponding to the characteristics of the fluid port. Additionally or alternatively, the controller operates the pump based on the reflected power sensed by the microwave generator. The system can also provide real-time estimates of tissue conditions, as well as real-time estimates of ablation size (or lesion size). The system can also estimate or determine the lesion size in real time. This real-time determination of the lesion size can be used to control the flow rate of the infusion liquid, control the delivery of microwave energy, facilitate the correct placement of the probe, and provide data-rich output on a display.

[0015] Thus, a first aspect of the present disclosure relates to a probe for ablating tissue using microwave energy. The probe includes a transmission line including an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor. The transmission line defines a first axial slot and a second axial slot proximal to the first axial slot. A non-conductive tube is coaxially disposed on a portion of the transmission line, and an electrical choke is coupled to the non-conductive tube. The electrical choke includes an inner choke layer, an outer choke layer, and an electrical shorting portion. The inner choke layer includes a first conductive tube coaxially disposed between the non-conductive tube and the outer conductor of the transmission line. The inner choke layer has a distal end that terminates at a position proximal to the second axial slot. The outer choke layer includes a second conductive tube coaxially disposed on the non-conductive tube so that a region of the non-conductive tube forms a choke insulating layer. The outer choke layer has a distal end that terminates at a position proximal to the second axial slot. The electrical shorting portion provides electrical communication between the inner choke layer and the outer choke layer.

[0016] A second aspect of the present disclosure relates to a probe for ablating tissue using microwave energy. The probe includes a transmission line, which includes an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor. A non-conductive tube is coaxially disposed on a portion of the transmission line. An area of ​​the outer surface of the non-conductive tube defines a recess. An electrical choke is connected to the non-conductive tube and includes an inner choke layer, an outer choke layer, and an electrical short. The inner choke layer includes a first conductive tube coaxially disposed between the non-conductive tube and the outer conductor of the transmission line. The outer choke layer includes a second conductive tube, which is disposed within the recess so that a portion of the non-conductive tube forms a choke insulating layer. The electrical short provides electrical connectivity between the inner choke layer and the outer choke layer.

[0017] A third aspect of the present disclosure relates to a probe for ablating tissue using microwave energy. The probe includes a transmission line, the transmission line including an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor. The transmission line defines a first axial slot and a second axial slot located proximal to the first axial slot. A non-conductive tube is coaxially disposed on a portion of the transmission line. An electrical choke is coupled to the non-conductive tube and includes an inner choke layer, an outer choke layer, and an electrical shorting portion. The inner choke layer is coaxially disposed between the non-conductive tube and the outer conductor of the transmission line. The outer choke layer is coaxially coupled to the outer surface of the non-conductive tube so that a region of the non-conductive tube forms a choke insulating layer. The outer choke layer has a distal end that terminates at a position proximal to the second axial slot. The electrical shorting portion provides electrical communication between the inner choke layer and the outer choke layer. At least one of the inner choke layer, the outer choke layer, and the electrical shorting portion is formed by conductive foil and / or electroplating.

[0018] A fourth aspect of the present disclosure relates to a probe for ablating tissue using microwave energy. The probe includes a transmission line including an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor. A non-conductive tube is coaxially disposed on a portion of the transmission line. An electrical choke is coupled to the non-conductive tube and includes an inner choke layer and an outer choke layer. The inner choke layer includes a first conductive tube coaxially disposed between the non-conductive tube and the outer conductor of the transmission line. The inner choke layer is spaced apart from the outer conductor of the transmission line. The outer choke layer includes a second conductive tube such that a region of the non-conductive tube forms a choke insulating layer.

[0019] A fifth aspect of the present disclosure relates to a probe for ablating tissue using microwave energy. The probe includes a transmission line, the transmission line including an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor. A conductive tube is coaxially disposed on a portion of the transmission line. An electrical short provides electrical communication between the tube and the outer conductor of the transmission line to define a choke, wherein the choke insulating layer is disposed between the outer conductor and the tube. The tube defines a proximal infusion path and an orifice, the proximal infusion path being configured to be arranged in fluid communication with an infusion liquid source. A sheath is coaxially disposed on the tube. The sheath defines a distal infusion path that is fluidly connected to the proximal infusion path through the orifice, and a fluid port that is fluidly connected to the distal infusion path.

[0020] A sixth aspect of the present disclosure relates to a probe for ablating tissue using microwave energy. The probe includes a transmission line, the transmission line including an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor. The transmission line defines a first axial slot and a second axial slot located proximal to the first axial slot. A tube is coaxially disposed on a portion of the transmission line. An electrical short provides electrical communication between the tube and the outer conductor of the transmission line to define a choke, wherein the choke insulating layer is disposed between the outer conductor and the tube. A sheath is coaxially disposed on the tube and defines an infusion path, the infusion path being configured to be arranged in fluid communication with an infusion liquid source, and the sheath further defines a fluid port positioned between the first axial slot and the second axial slot.

[0021] Other aspects of the present disclosure relate to embodiments of probes, instrument consoles for ablating tissue using microwave energy, and methods of performing ablation procedures using microwave energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a perspective view of a microwave ablation system including a console, fluid reservoir, and probe.

[0023] Figure 2 is a front view of the probe.

[0024] Figure 3 yes Figure 2 A cross-sectional elevation view of one embodiment of a probe taken along line 3-3.

[0025] Figure 4 yes Figure 2 A cross-sectional elevation view of another embodiment of a probe taken along line 4-4.

[0026] Figure 5A is an enlarged cross-sectional elevational view of the probe, wherein the infusion flow path includes a proximal flow path and a distal flow path.

[0027] Figure 5B is another enlarged cross-sectional elevational view of the probe, wherein the infusion flow path further includes a distal fluid port.

[0028] Figure 6 is a schematic diagram of the electronic aspects of the system, wherein a switch provides electrical communication between the probe and one of the generator and analyzer.

[0029] Figure 7 is a graph of S11 and the resonant frequency of the probe at several points during an ablation procedure.

[0030] Figure 8 is a schematic representation of a console configured to display a real-time estimate of organizational boundaries.

[0031] Fig. 9 is a front view of another embodiment of a probe.

[0032] Fig.10 yes Fig. 9 A cross-sectional elevation view of a variation of the probe taken along line 10-10.

[0033] Fig.11 yes Fig. 9 A cross-sectional elevation view of another variation of the probe taken along line 11-11.

[0034] Fig. 12A yes Figure 2 A cross-sectional elevation view of another embodiment of a probe taken along line 12A-12A.

[0035] Fig. 12B yes Figure 2 A cross-sectional elevation view of another embodiment of a probe taken along line 12B-12B.

[0036] Fig.13 is a front view of another embodiment of a probe with an inflatable member coupled to a shaft.

[0037] Fig.14 yes Fig.13 A cross-sectional elevation view of a variation of the probe taken along line 14-14.

[0038] Fig.15 yes Fig.13 Another variation of the probe is a cross-sectional elevation view taken along line 15-15. DETAILED DESCRIPTION

[0039] Figure 1 , a system 30 for microwave ablation is shown in FIG. 3 , wherein a console 32 is configured to supply microwave energy to a probe 34. The console 32 may include a pump 36 configured to be arranged in fluid communication with a liquid reservoir 38 to deliver cooling liquid or infusion liquid to the probe 34. The console 32 may include a box receiver 40 configured to removably receive a flushing box 42 to provide a single-use sterile barrier between the console 32 and the probe 34. In one example, the flushing box 42 includes tubing, and the pump 36 is a peristaltic pump. The console 32 includes a controller 44 in electronic communication with the pump 36. The controller 44 is configured to operate the pump 36 to control the cooling and / or infusion liquid to be delivered through the probe 34 in a manner to be described. Alternatively, the liquid reservoir 38 may be directly coupled to the probe 34 and may be operated by manual input or by an electromechanical device (such as an inline peristaltic pump coupled to an appropriate tubing). In one example, the infusion liquid is liquid saline, but the infusion liquid may be sterile water or another suitable liquid of a known relative dielectric constant.

[0040] The probe 34 is configured to be arranged in fluid communication with the liquid reservoir 38. For example, the probe 34 may include a fluid coupling 53 configured to be coupled to an outflow conduit extending from the flushing box 42. The probe 34 is also configured to be arranged to operably communicate with the microwave generator 46 of the console 32. The console 32 may include a port 48 for removably receiving an energy coupling 55 associated with the transmission line 50 of the probe 34. The microwave generator 46 is in electronic communication with the controller 44. The controller 44 is configured to operate the microwave generator 46 so as to transmit microwave energy at a desired frequency and power. In one example, the microwave generator 46 transmits microwave energy of approximately 2.45 gigahertz (GHz) and at least 150 watts. The microwave generator 46 may include a circuit configured to continuously and simultaneously transmit microwave energy on at least two channels. Other operating parameters (e.g., frequency, power, channel, etc.) of the microwave generator 46 are considered to be within the scope of the present disclosure.

[0041] Reference now Figure 2, the probe 34 includes a hub 52 and a shaft 54 ​​extending distally from the hub 52 to a tip 56. The hub 52 may include a fluid coupler 53 and an energy coupler 55. The shaft 54 ​​may be sufficiently rigid and the tip 56 may be sufficiently sharp to allow the probe 34 to penetrate and be guided through soft tissue to a target location within the anatomical structure. For example, treatment of a liver lesion may indicate that the probe 34 is guided into the liver by piercing the abdominal muscle system. The markings on the shaft 54 ​​may be arranged at fixed or variable intervals to provide information about the depth of penetration of the tip 56 into the tissue.

[0042] Figure 3 An embodiment of a probe 34 including a double slot architecture with a choke is shown. The transmission line 50 of the probe 34 can extend from within the hub 52 to within the shaft 54. The transmission line 50 can be a semi-rigid coaxial cable. The transmission line 50 includes an outer conductor 58 and an inner conductor 60 coaxially disposed within the outer conductor 58. An insulating layer (not identified) is coaxially disposed between the outer conductor 58 and the inner conductor 60. The transmission line 50 can include a proximal segment 62, an intermediate segment 64, and a distal segment 66. The inner conductor 60 can extend through the proximal segment 62 and the intermediate segment 64, and optionally through the distal segment 66. In this way, the inner conductor 60 extends beyond at least the distal end 72 of the proximal segment 62 of the outer conductor 58. The distal segment 66 can be a stub-shaped portion of the transmission line 50 (i.e., the outer and inner conductors 58, 60 have an insulating layer disposed therebetween), wherein the inner conductor 60 is shorted to the outer conductor 58. For example, the exposed distal end of the inner conductor 60 can be deformed and joined to the outer conductor 58 by welding, swaging or other suitable joining processes. The distal segment 66 of the transmission line 50 can have a length in the range of about 2 to 4 millimeters, and more specifically has a length of about 3 millimeters. Alternatively, the distal segment 66 can be an end cap formed of a conductive material and fixedly joined to the inner conductor 60. Another variation is envisioned in which the distal segment 66 can include a stub-like portion of the transmission line 50 to which the end cap is fixedly joined to short the inner conductor 60 to the outer conductor 58.

[0043] The distal segment 66 and the intermediate segment 64 may define a first axial slot 68 characterized by the absence of the outer conductor 58, and the intermediate segment 64 and the proximal segment 62 may define a second axial slot 70 characterized by the absence of the outer conductor 58. In other words, the segments 62, 64, 66 can be formed by stripping or removing portions of the outer conductor 58 (and optionally the insulation) from the inner conductor 60. The sizes and axial positions of the first and second axial slots 68, 70 and thus the associated sizes and axial positions of the segments 62, 64, 66 are adjusted to give the probe 34 the desired performance characteristics. The sizes of the first and second axial slots 68, 70 may be the same or different. The first axial slot 68 may have a length in the range of 0.5 to 1.5 millimeters, and more specifically a length of about one millimeter. The second axial slot 70 may have a length in the range of 0.5 to 1.5 millimeters, and more specifically a length of about one millimeter.

[0044] The probe 34 includes a choke 74 to shape the near field characteristics to facilitate obtaining a desired ablation shape, preferably a spherical or near-spherical shape. The choke 74 also prevents the wave from propagating backward along the axis 54 to limit or prevent undesirable heating of tissue in locations other than the target location. The choke 74 may include a tube 76 formed of a conductive material and coaxially disposed on a portion of the transmission line 50. For example, the tube 76 may be a hypodermic tube. Continued reference Figure 3 , the tube 76 can extend from the hub 52 to the distal end 78 of the choke 74. The tube 76 can be coaxially spaced from the transmission line 50 along its length. The electrical short 80 provides electrical communication between the transmission line 50 and the tube 76. More specifically, the electrical short 80 is formed of a conductive material and is in direct contact with each of the outer conductor 58 and the tube 76. The electrical short 80 can be annular and extends annularly between the outer conductor 58 and the tube 76. It should be understood that the portion of the tube 76 that provides the choke is distal to the electrical short 80, and the tube 76 does not have to extend back to the hub 52. Alternatively, the tube 76 can have a length equal to the length of the choke 74, and another tube can extend from the hub 52 to provide an infusion path to be described. A choke insulation layer 82 is provided between the tube 76 and the transmission line 50. The choke insulation layer 82 is formed of a non-conductive material and is configured to prevent electrical communication between the tube 76 and the outer conductor 58 (except via the electrical short 80). The non-conductive material has a known relative dielectric constant. An example of a suitable non-conductive material is polytetrafluoroethylene (PTFE), which has a relative dielectric constant of about 22. The choke insulation layer 82 is disposed distally of the electrical short 80, and the choke insulation layer 82 may be coterminous with the tube 76 at the distal end 78 of the choke 74.

[0045] The proximal section 62 can be defined between the distal end 78 of the choke 74 and the second axial slot 70, and the intermediate section 64 can be defined between the first and second axial slots 68, 70. As described above, the size of the sections 62, 64, 66 is adjusted to give the probe 34 the desired performance characteristics. In some embodiments, the length of each of the proximal section 62 and the intermediate section 64 is a quarter of the effective wavelength of microwaves at a frequency of 2.45 gigahertz (GHz) in the tissue being ablated. Alternatively, the relative lengths of the proximal section 62 and the intermediate section 64 can be different. The resonant length of the intermediate section 64 can be in the range of about 8 mm to 23 mm, and more specifically in the range of about 8 mm to 12 mm. The length of the choke 74 defined between the distal end 78 and the electrical shorting portion 80 can be a quarter of the effective wavelength of microwaves at 2.45 GHz in the PTFE or other materials forming the choke insulation layer 82, or more generally a quarter of the microwave field in the choke insulation layer 82.

[0046] The probe 34 includes a dielectric housing 84 coupled to the transmission line 50 and defining a tip 56 at the distal end of the probe 34. The dielectric housing 84 can be coupled to the transmission line 50 and include an outer diameter that is at least substantially equal to the outer diameter of the tube 76. The proximal end of the dielectric housing 84 can abut the distal end 78 of the choke 74 at the interface. The abutting relationship and the complementary outer diameters provide a smooth transition across the interface. The interface can include a lap joint arrangement in which the dielectric housing 84 defines a recess at the interface for receiving PTFE or another adhesive. An optional seal can be provided at the interface.

[0047] The dielectric housing 84 can be coaxially disposed on the proximal segment 62 and more specifically shaped to contact the outer conductor 58 of the first segment 62 along its length. Similarly, the dielectric housing 84 can be coaxially disposed on each of the intermediate segment 64 and the distal segment 66 and more specifically shaped to contact the outer conductor 58 (or end cap) of these segments 64, 66 along their length. In addition, an inward flange 88 can surround the inner conductor 60 in each of the first and second axial grooves 68, 70. In other words, the contour of the dielectric housing 84 can be designed to conform to the contour of the portion of the transmission line 50 distal to the choke 74. The dielectric housing 84 can be tapered to define the tip 56. Certain features of the probe 34 can be disposed within the dielectric housing 84 near the tip 56, for example, a sensor for temperature sensing and / or a transmitter for intraoperative navigation. In an alternative embodiment, the dielectric housing 84 is tubular with a tapered tip.

[0048] The dielectric shell 84 is formed of a material having a relative dielectric constant and other material properties (e.g., stiffness, hardness, ductility, thermal conductivity, electrical conductivity, etc.) required for percutaneous deployment into an anatomical structure. An exemplary material is ceramic, and another suitable material is fiberglass. The ceramic can have a profile that conforms to the transmission line 50 as described, or the ceramic can be a tube with a thickness sufficient to prevent rupture. The dielectric shell 84 can be formed of a single material or more than one material. Layers of different materials can be arranged to produce different relative dielectric constants at different axial locations along the axis 54, thereby further shaping the near-field characteristics to facilitate achieving the desired ablation shape.

[0049] The probe 34 is configured to deliver an infusion fluid to tissue surrounding an active tip of the probe 34 , which may be defined at any point along the probe 34 distal to the choke 74 . Figure 5A and 5B yes Figure 3 34 to more clearly illustrate the infusion path through the probe 34. The probe 34 includes a sheath 90 coaxially disposed on the tube 76 and at least a portion of the dielectric housing 84. The size of the sheath 90 can be set to be closely disposed on the tube 76 and the dielectric housing 84 to define a distal infusion path (arrow 92) therebetween. In one example, the sheath 90 is polymeric, such as formed by PTFE, wherein the sheath 90 is heat shrunk to the tube 76 and the dielectric housing 84. PTFE is biocompatible, non-stick, and has a melting point above 300 degrees Celsius, and is therefore very suitable for ablation surgery. In addition, in the tubular form, the wall thickness of the PTFE can be selected based on other parameters of the probe 34 design to adjust the relative dielectric constant of the probe 34. In another example, the sheath 90 can be a fiberglass tube.

[0050] Continue to refer Figure 5A and Figure 5B , the tube 76 defines a proximal infusion path (arrow 94) and an orifice 96. The orifice 96 can be a single hole, a plurality of holes arranged radially around the tube 76, etc. The orifice 96 provides fluid communication between the proximal infusion path 92 and the distal infusion path 94 to generally define the infusion path. The orifice 96 can be positioned proximal to the electrical shorting 80. An optional barrier 98 can be provided between the sheath 90 and the tube 76 and proximal to the electrical shorting 80 to avoid backflow of the infused liquid. The barrier 98 can be a discrete structure or a location where the sheath 90 is joined to the tube 76.

[0051] The infusion fluid directed from the liquid reservoir 38 to the probe 34 travels along the proximal infusion path 94, through the orifice 96 and along the distal infusion path 92 to be discharged through the fluid port 100 to be described. The advantages of the infusion path of the probe 34 are easy to understand. First, the proximal infusion path 94 is also defined between the tube 76 and the outer conductor 58 of the transmission line 50. Therefore, when the fluid travels along the proximal infusion path 94, it cools the transmission line 50 (i.e., takes away heat from the transmission line 50). Potential damage to the probe 34 by ohmic heating is minimized. In addition, any ohmic heating in the transmission line 50 is used to preheat the infusion liquid and ultimately transfer it to the tissue. In this way, the heat energy wasted is minimized. Further, by implementing an open-loop system in which the infusion liquid is directed to the tissue, the effect of latent heat is optionally utilized, and the probe 34 can be effectively cooled with a reduced fluid flow (i.e., by utilizing the latent heat of vaporization during the cooling process). Still further, the infusion preserves the functionality of the choke 74, which otherwise might be compromised if the relative dielectric constant of the tissue becomes too low. These advantages are achieved in a manner that limits the overall size (i.e., outer diameter) of the shaft 54. More specifically, certain structures of the probe 34 (e.g., the choke 74 and the dielectric housing 84) are coaxially arranged around the transmission line 50, which would otherwise interrupt the travel of the infused liquid around the transmission line 50 toward the distal end of the probe 34. By providing an orifice 96 through the tube 76, particularly in combination with a sheath 90 that closely conforms to the outer diameter of the tube 76, cooling of the transmission line 50 is achieved while still accommodating the other structures of the probe 34 in a space-conscious manner. In other words, it is conceivable to design the proximal and distal flow paths 94, 92 with a series of coaxial rigid tubing types, but the resulting shaft size is too large for practical applications. In one example, the shaft 54 ​​of the probe 34 can be fourteen or seventeen gauge, but smaller or larger sizes are conceivable.

[0052] The sheath 90 defines fluid ports 100 that are in fluid communication with the distal infusion pathway 92. The fluid ports 100 may be provided in any suitable number and arranged in any suitable configuration about the active tip of the shaft 54. Figure 2 Fluid ports 100 are shown arranged equiangularly around the sheath 90 at two axial positions. Additionally or alternatively, the fluid ports 100 can be concentrated on one side of the shaft 54, such as the upper and / or lower side of the shaft 54, based on, for example, common approach angles to target anatomical structures for certain surgeries. Additionally or alternatively, there may be one, two (as shown), three, four, five, ten or twenty or more "rings" of fluid ports 100 spaced at regular and / or irregular intervals. The fluid ports 100 can be disposed throughout the active tip or a portion thereof. In one example, the fluid ports 100 may be evenly distributed radially around the sheath 90, such as along the distal two centimeters of the shaft 54. Figure 5B A distal fluid port 102 defined by the distal end of the sheath 90 is shown for draining infusion fluid not drained by the fluid port 100 . Figure 5A A distal barrier 102 is shown that is configured to prevent infusion fluid from escaping from near the tip 56.

[0053] The fluid ports 100 or a higher distribution density thereof can be disposed at a location within the active tip that is associated with maximum heating within the ablation zone, also referred to as a "hot spot" of the probe 34. In particular, the location can be proximal to the first axial slot 68, and / or distal to the second axial slot 70. Additionally or alternatively, the location can be distal to the first axial slot 68, and / or proximal to the second axial slot 70. Additionally or alternatively, the location can be axially aligned with the first and second axial slots 68, 70. Additionally or alternatively, the location can be between the first and second axial slots 68, 70, such as near the center of the middle section 64 of the transmission line 50. Additionally or alternatively, the location can be along the choke 74. For example, the higher distribution density of fluid ports 100 can be located adjacent to the choke 74, rather than away from the choke 74, because the choke 74 may be a hot spot. The fluid ports 100 can have any suitable size or shape. In one example, the fluid ports 100 can be relatively large, with a diameter of one millimeter or less. In another example, the fluid ports 100 are formed as perforations in the sheath 90 formed of a polymer material. The fluid ports 100 may be micropores of sufficiently small size that the shaft 54 ​​may be considered to "leak" the infusion fluid. Finally, the fluid ports 100 may have the same or different sizes. For example, the fluid ports 100 between the first and second axial grooves 68, 70 may be larger than the fluid ports 100 elsewhere.

[0054] In another embodiment, the fluid port 100 can be disposed at one or more of the locations described herein, and a membrane or filter layer (not shown) can be disposed on the sheath 90. The filter layer is configured to disperse the infusion liquid discharged from the fluid port 100. The filter layer can provide uniform dispersion or focal dispersion at the hot spot of the probe 34.

[0055] Reference now Figure 4, another embodiment of the probe 34 is shown, in which the shaft 54 ​​includes a choke monopole architecture. Like numbers represent like parts, and the inner conductor 60 also extends beyond the distal end 72 of the outer conductor 58. A distal segment 66 (such as an end cap) can be fixedly joined to the inner conductor 60. In other words, the transmission line 50 may not include an intermediate segment 64. The length of the inner conductor 60 between the proximal segment 62 and the distal segment 66 can be a quarter effective wavelength of the tissue being ablated. In addition, the length of the proximal segment 62 can be a quarter effective wavelength of the tissue being ablated. The length of the choke 74 can be a quarter effective wavelength of the PTFE. The choke 74 and the dielectric housing 84 can be similar to the previously described embodiments in other ways.

[0056] Likewise, the sheath 90 of the present embodiment provides an infusion path for cooling the transmission line 50 and preheating the infusion liquid. The fluid port 100 can be positioned proximal to the distal segment 66 and / or distal to the proximal segment 62. Additionally or alternatively, the fluid port 100 can be disposed at one or more of the positions previously described herein. Therefore, it should be understood that infusion-related concepts can be extended to antenna types other than dual slot and monopole architectures. The present disclosure may be included on other antenna types, such as single slots, dipoles, triaxes, and sleeves. In addition, the choke 74 may be an optional feature, wherein the orifice 96 is defined proximal to the dielectric housing 84 within the tube 76 to guide the infusion liquid from the proximal infusion path to the distal infusion path.

[0057] The controller 44 operates the pump 36 to control the characteristics of the delivery of the infusion liquid into the tissue through the probe 34. The characteristics of the delivery can be a volume flow rate, a fluid pressure, a delivery interval, etc. The console 32 may include a user interface in communication with the controller 44, such as a display 104 that is also configured to receive input from the user. Thus, in some embodiments, the user can input a desired flow rate for the infusion liquid, and the controller 44 operates the pump 36 based on the input. For example, the user can input a desired flow rate (in cubic centimeters per minute), and the controller 44 can cause the peristaltic pump to rotate at a calibrated speed to produce the flow rate.

[0058] Additionally or alternatively, the controller 44 can operate the pump 36 based on the probe type, and more specifically based on the tip type corresponding to the characteristics of the fluid port 100. In other words, the flow rate can be based on the number and / or size of the fluid ports 100 through which the infusion liquid is discharged. For example, the larger the number or the larger the size of the fluid ports 100, the more infusion liquid can be discharged per unit time. The flow rate for one or more tip types can be stored as calibration data. The user can enter the tip type into the display 104 (or the tip type can be automatically detected in other ways), and the controller 44 operates the pump 36 based on the calibration data. Force feedback on the roller of the peristaltic pump can be sensed, and / or the pressure from the pump 36 can be sensed, and the speed of the pump 36 operation can be adjusted accordingly in real time during the ablation procedure. Additionally or alternatively, the controller 44 operates the pump 36 based on the reflected power sensed by the microwave generator 46 in a manner to be described. The response control of the controller 44 to the pump 36 can be considered as active fluid delivery.

[0059] In another embodiment, a device for passive fluid delivery (not shown) may be provided. The device may include a mechanism configured to discharge an infusion liquid at a predetermined and constant flow rate. The mechanism may be a spring-loaded plunger, a solenoid valve, or the like. The mechanism may be actuated at or near the start of an ablation procedure, after which the device may typically discharge the infusion liquid at a constant flow rate without other user input. If desired, the flow of the infusion liquid may be paused or terminated, for example, by closing a valve or clamping an infusion line. It is also contemplated that the system 30 may provide active fluid delivery in combination with passive fluid delivery. The device may provide a constant flow rate of a low level of infusion liquid, and the controller 44 may replenish the low level with additional infusion liquid in real time based on parameters sensed during the ablation procedure or otherwise indicated by the user.

[0060] The advantages of discharging the infusion liquid into the tissue are easy to understand. First, while the closed-loop cooling system can only affect the tissue in the immediate vicinity of the probe by conduction, the infusion allows the properties of the tissue to be directly affected. For example, the effects of dehydration and carbonization are offset, thereby maintaining the relative dielectric constant of the tissue at a value that the probe 34 can be optimized to. Secondly, the liquid molecules within the tissue can be excited by the microwave energy from the probe 34. The result can be that the infusion liquid adjacent to the probe 34 becomes a functional part of the active tip. Third, the infusion liquid can be fully heated by microwave energy to change the state and generate steam. The steam is guided into the tissue to provide an additional heat transfer mechanism, which can promote faster realization of the desired ablation zone and / or achieve a larger ablation zone. Fourth, the irrigation fluid is guided to the ablation site by the ablation probe, and the irrigation fluid acts as a coolant to ensure the integrity of the semi-rigid coaxial cable used for high-power transmission. As previously described, this effectively preheats the irrigation fluid before the irrigation fluid is deposited into the tissue, and realizes an efficient system that utilizes the heat lost in the coaxial cable.

[0061] The present disclosure also provides real-time estimation of tissue condition, and real-time estimation of ablation size (or lesion size). Real-time estimation can be used to control infusion fluid, and / or be presented to the user as output on display 104. For any probe with a fixed resonant length, the resonant frequency is determined by the average relative dielectric constant of the material interacting with the near field. This includes the non-conductive layer of probe 34 and the tissue surrounding probe 34. Although the relative dielectric constant of the probe material will remain substantially constant throughout the ablation process, the relative dielectric constant of the tissue may change dramatically as the tissue changes from a well-hydrated state at body temperature to an ablated and dehydrated state. Therefore, if probe 34 is designed to resonate for ablated tissue, it may not resonate for unablated or partially ablated tissue. The relationship between the resonant frequency of a simple probe designed to resonate at a quarter wavelength and the average relative dielectric constant of the surrounding medium can be defined by Equation 1:

[0062]

[0063] Where f is the resonant frequency, ε ris the average relative dielectric constant of the surrounding medium, and K is a constant equal to c / 4L, where c is the speed of light and L is a length equal to one-quarter wavelength of the tissue being ablated. Thus, in the manner to be described, performing a frequency scan in which the S11 parameter is determined for at least two frequencies, the location of the resonant frequency can be identified, and the average relative dielectric constant of the tissue can be determined (because the relative dielectric constant of the probe 34 is fixed). The S11 parameter is based on the reflected power reflected back to the microwave generator 46, which can be sensed and quantified. Changes in the average relative dielectric constant can inform the user of the condition of the tissue and whether more or less infusion fluid should be provided. In addition, in combination with the reflection of microwaves from tissue interfaces sensed in the time domain spectrum, the lesion size or lesion progression of an ablation procedure can be estimated or determined in real time. Now referring to Figure 1 and Figure 6 , the console 32 includes a switch 110 and an analyzer 112. The switch 110 and the analyzer 112 are in electronic communication with the controller 44. The switch 110 can be a high power, high isolation switch rated for frequencies up to 20 GHz. The switch 110 is configured to selectively establish electronic communication between the probe 34 and one of the microwave generator 46 and the analyzer 112. More specifically, the switch 110 can be configured to quickly move the probe 34 between a high power ablation mode in which tissue is ablated and a low power sensing mode in which the probe 34 is used as a sensor to extract information about tissue conditions and lesion size. The analyzer 112 can be a vector network analyzer configured to analyze signals in both the time domain spectrum and the frequency domain spectrum. In one example, the switch can be a quasi-DC MOSFET, but other switches can be envisioned. Alternatively, a filter including passive components or distributed filter elements can be used.

[0064] Figure 7 1 shows the traces of the S11 parameter as a function of frequency for the probe 34 of one embodiment at several points during an ablation procedure (i.e., each trace represents a different point in the procedure). Specifically, trace A may represent a state or situation at the beginning of an ablation procedure, where the resonant frequency is less than 2 GHz. When microwave energy is delivered to tissue using the probe 34, the tissue is ablated and loses water, resulting in an average relative permittivity (ε r ) decreases. Because the resonant frequency is proportional to the inverse square root of the average relative permittivity (see Equation 1), the resonant frequency shifts accordingly from lower frequencies to higher frequencies, as reflected in traces B, C, and D. Since it is preferred to radiate microwave energy into the tissue rather than reflect it back to the microwave generator 46, it is expected that the resonant frequency matches the drive frequency (e.g., trace D is at approximately 2.3 GHz) during most of the ablation time.

[0065] The method of performing the procedure includes delivering microwave energy from microwave generator 46 to probe 34 to ablate tissue. Memory 111 in electronic communication with controller 44 stores a plurality of "power curves" (e.g. Figure 7 The power curve may include calibration data for the probe 34 (trajectory of the power curve). Each power curve may include data indicating the resonant frequency associated with each different known value of the average relative permittivity of the designed probe 34. The average relative permittivity may be a weighted average relative permittivity because the tissue near the probe 34 has a greater effect on the average relative permittivity than the tissue away from the probe 34. The switch 110 may be in a first position, in which electronic communication is established between the microwave generator 46 and the probe 34. The measured S11 parameter 113 may be determined based on the reflected power sensed by the microwave generator 46 at the effective or driving frequency. The controller 44 may actuate the switch 110 to a second position, in which electronic communication is established between the probe 34 and the analyzer 112. In doing so, the probe 34 may move from a high-power ablation mode, in which microwave energy is delivered to the probe 34 at a first wattage, to a low-power sensing mode, in which a frequency sweep is performed at a second wattage less than the first wattage. The frequency sweep is performed by the microwave generator 46 within its operable range, or by the analyzer 112, wherein the sensed S11 parameter is determined for at least two frequencies within the frequency range. By actuating the switch 110 to the analyzer 112, the frequency range can be outside the operable range of the microwave generator 46, thereby providing robust data points for analysis. Figure 7 Two examples of frequencies (f1, f2) are marked to identify the frequency range.

[0066] At least two data points of the sensed S11 parameter are determined, each of which is associated with a corresponding one of the two frequencies. The two data points of the sensed S11 parameter are evaluated based on the calibration data of the probe 34. Based on the two data points of the sensed S11 parameter, one of the power curves can be selected as an indication of the state of the ablation procedure. In other words, the two data points can uniquely correspond to one of the power curves. For example, at the beginning of the ablation procedure, two data points 114a, 114b of the sensed S11 parameter can be determined, and the controller 44 determines that trajectory A represents the weighted average relative dielectric constant of the medium (i.e., the probe 34 in the tissue) before and after that moment based on the performance of the probe 34 in the medium. Only one data point may not be sufficient to select an appropriate power curve because more than one of these power curves may be associated with certain data points.

[0067] The method may include determining the slope of the data point. The slope may be positive or negative. Given the properties of the power curve, the slope may indicate whether the resonant frequency of the corresponding power curve (also referred to herein as the probe resonant frequency) is lower than, equal to, or higher than the drive frequency. The determination may provide features of the ablation procedure based on the measured S11 parameter 113 and the frequency sweep. More specifically, the determined features may inform the system 30 whether the tissue condition is progressing as expected, or whether the tissue has begun to dehydrate, dry, or char, so that the controller 44 should start or increase the flow rate of the infusion fluid (and / or adjust the delivery of microwave energy). In addition, the extent to which the frequency of the measured S11 parameter 113 is lower than, equal to, or higher than the resonant frequency may indicate the magnitude of the correction or corresponding measures that should be taken.

[0068] As an example and for continued reference Figure 7 , two data points 114a, 114b of track A include a positive slope. Due to the general shape of the power curve, since the determined slope is positive, it can be assumed that the probe resonant frequency is less than the drive frequency, and therefore the weighted average relative permittivity is too high to allow the probe 34 to operate optimally at the drive frequency. Simply put, the determined feature can be that the tissue is in a non-ablative state. In this way, the controller 44 can operate the pump 36 to reduce the flow rate of the infusion liquid provided to the tissue (and / or adjust the delivery of microwave energy). In addition, the magnitude of the difference between the measured S11 parameter 113 and the current resonant frequency can be determined, and the controller 44 can operate the pump 36 based on the determined magnitude. In one example, the controller 44 may not start or increase the flow rate of the infusion liquid until the probe resonant frequency matches the drive frequency. In another example, the controller 44 may start, reduce or increase the flow rate of the infusion liquid to a degree proportional to the difference between the probe resonant frequency and the drive frequency, so that overly dehydrated tissue receives the infusion liquid faster. The tissue condition can be displayed on the display 104 quantitatively or qualitatively. For example, quantitative output may include displaying the relative dielectric constant of the tissue, and qualitative output may include displaying color coding or other indicia indicating the condition of the tissue.

[0069] Depending on the selected power curve, if the slope of the determined data point is positive, the control algorithm may forgo initiating or increasing the flow rate of the infusion fluid. An example may be where the probe resonant frequency is less than the drive frequency of the probe 34. In such an example, the weighted average relative permittivity of the selected power curve may be too high (relative to the weighted average relative permittivity designed for the probe 34). In other words, the probe 34 is optimized to place the tissue in an ablation state with some tissue dehydration. Figure 7In the illustrated example of FIG. 4 , track A may provide such a scenario. The resonant frequency of track A is less than the driving frequency, so the S11 parameter at the driving frequency is too high, resulting in too much microwave energy being reflected to the microwave generator 46. Therefore, if the selected power curve is track A, if the two data points 114a, 114b associated with track A have a positive slope, the controller 44 may reduce the pump 36 operation to drive the power curve toward tracks B, C, and / or D.

[0070] The determined slope of the two data points of the sensed S11 parameter may be negative. Figure 7 The trace D of FIG. 4 includes two data points 120 a, 120 b at two frequencies of the frequency sweep. Based on the negative slope, the controller 44 can operate the pump 36 to increase the flow rate of the infusion fluid provided to the tissue (and / or adjust the delivery of microwave energy). With further delivery of microwave energy and infusion of more infusion fluid, the dehydration of the tissue can be reversed, so that the weighted average relative permittivity of the medium increases to correspond to the weighted average relative permittivity designed for the probe 34. Eventually, the probe resonant frequency will approach or be equal to the drive frequency of the microwave generator 46, which corresponds to minimum reflected power and optimal operation of the probe 34. If the probe resonant frequency is equal to the drive frequency of the microwave generator 46, the controller 44 can operate the pump 36 to maintain the flow rate of the infusion fluid (or increase or decrease it if otherwise necessary).

[0071] In addition to tissue conditions, it may be desirable to estimate or determine lesion size in real time. Such real-time determination of lesion size can be used to control the flow rate of infusion fluid, control the delivery of microwave energy, facilitate the correct placement of probe 34, and provide data-rich output on display 104, as well as other advantages. As mentioned, analyzer 112 can be configured to analyze signals in both time domain spectrum and frequency domain spectrum. The method may include transforming a frequency sweep from a frequency domain spectrum to a time domain spectrum. The time domain spectrum can be considered to display a time-varying response to a Gaussian-like electrical pulse, and the frequency domain spectrum decomposes the waveform into separate frequency components. The step of transforming a frequency sweep from a frequency domain spectrum to a time domain spectrum may include applying Fourier transform.

[0072] Interfaces between tissues of different electrical properties in the time domain spectrum reflect microwave energy. Exemplary interfaces include lesion boundaries, tumor boundaries, and boundaries of the liver, veins, arteries, and other anatomical structures. Measuring reflections in the time domain spectrum can be used to determine lesion size, and therefore the progress of the ablation procedure. The relationship between the group velocity of electromagnetic radiation in a medium and the relative dielectric constant of the medium is shown in Equation 2:

[0073]

[0074] where c is the speed of light, ε ris the average relative permittivity of the surrounding medium, and c eff is the effective speed of the microwaves in the tissue. As the weighted average relative permittivity of the medium decreases, the effective speed of the microwaves increases. The increase in the effective speed of the microwaves reduces the time it takes for the microwaves to be emitted by the probe 34, reflected by any given interface in the tissue, and returned to the probe 34. When an interface is formed or shifted between ablated tissue and non-ablated tissue (e.g., coagulated tissue and non-coagulated tissue), the change in reflection time can be sensed and determined.

[0075] The exemplary method includes a step of determining a weighted average relative permittivity based on the resonant frequency of the medium, for example, in the manner previously described. The speed of the microwaves can then be determined based on the weighted average relative permittivity and the time at which the sensed microwaves are reflected in the tissue. As described above, changes in the weighted average relative permittivity determined by the frequency sweep affect the speed at which the microwaves pass through the medium. Changes in the speed of the microwaves can then be determined by frequency domain data. Based on the speed and resonant frequency of the microwaves, reflection points from the interface can be determined or "visualized." In other words, the distance from the probe 34 to the interface can be determined. The distance can be compared with the previously determined distance to determine whether one or more of the reflection points exist or do not exist. For example, the presence of a new reflection point can indicate that a new interface is formed or shifted at the boundary of the lesion. It should also be understood that a combination of signals in the frequency domain and time domain spectra can also be used to determine the average relative permittivity along the path of the microwave energy, which is a measure of tissue ablation.

[0076] Based on the determined distance, the size of the lesion can be approximated. Based on the size of the lesion and other parameters of the ablation procedure, the controller 44 can react in a corresponding manner. For example, if it is determined that the probe 34 is at or has passed through the tumor boundary and entered into adjacent healthy tissue, the delivery of microwave energy can be terminated. Additionally or alternatively, the controller 44 can operate the pump 36 to increase or decrease the flow rate of the infusion liquid.

[0077] According to the above method, a data-rich output can be provided on the display 104. For example, an indication can be displayed to warn the user that the probe 34 has passed through the interface between the tumor and the adjacent tissue to facilitate the placement of the probe 34 or to warn of improper placement. Additionally or alternatively, a graphic can be displayed on the display 104 in which a representation of the estimated lesion size is provided. The representation can be two-dimensional, three-dimensional, or animated, and additional visual representations can include lines or shapes for virtually mapping the placement of the probe 34 and the corresponding ablation zone. Figure 8One such example is shown in which a representation of the estimated lesion size (L) is superimposed on preoperative imaging, such as a computed tomography (CT) scan in which a tumor (t) and other tissue boundaries can be identified. As described above, the distance (d) from the probe 34 to the interface can be determined based on the reflection point. In addition, the CT scan can be segmented to extract features, and the controller 44 can associate the reflected signal with the features extracted from the CT scan. Based on the correlation and real-time estimation of tissue condition and / or lesion size, the controller 44 can adjust the operation of the system 30 accordingly (e.g., increase or decrease the infusion fluid and / or microwave energy). In addition, the CT scan can be digitally analyzed, thereby automatically determining the initial parameters of the ablation procedure. Based on the initial parameters and real-time estimation, the controller 44 can adjust the operation of the system 30 accordingly. In other words, if the ablation procedure deviates too much or progresses differently than planned, the controller 44 can coordinate the current parameters with the initial parameters during the operation.

[0078] The embodiments of the probe 34 discussed thus far discharge an infusion fluid into the tissue. Additionally or alternatively, certain embodiments of the probe may be configured to circulate a fluid, which may be considered a cooling fluid. Referring now to Figure 9-11 , shows an embodiment of a probe 134, wherein like numbers plus one hundred represent like parts. The probe 134 includes a hub 152 and a shaft 154 extending distally from the hub 52 to a tip 156. The tip 156 can be a short, independent structure that is only coupled to the sheath 190, as shown, or can be formed by a dielectric housing disposed around the transmission line 150, similar to the previously described embodiments. The hub 152 can include a fluid coupling 153 and an energy coupling 155. Fig.10 and Fig.11 A schematic diagram of a hub 152 is shown, wherein the fluid coupler 153 includes a fluid inlet 157 and a fluid outlet 159, and the energy coupler 155 is a joint.

[0079] The hub 152 may include an outer housing 161 and a fluid barrier 151 disposed within the outer housing 161. The fluid barriers 151 are axially spaced apart from each other and coupled to certain subcomponents of the probe 134, as will be described, to define an inflow path and an outflow path fluidly separated from the inflow path. Each fluid barrier 151 may include at least one sealing member 163 fixed to the inner surface of the outer housing 161, and a seal 165 such as an O-ring. More specifically, a first fluid barrier 151a of the fluid barriers may be positioned adjacent to the fluid outlet 159 and configured to prevent fluid from flowing out through the connector 155. A second fluid barrier 151b of the fluid barriers may be positioned between the fluid outlet 159 and the fluid inlet 157. The second fluid barrier 151b defines a hole through which the transmission line 150 extends so that the transmission line 150 is electrically connected to the connector 155. The distal surface of the second fluid barrier 151b may be coupled to a tube 176 coaxially disposed around the transmission line 150 and extending into the shaft 154. The tube 176 can be formed of polyamide or other suitable materials. The second fluid barrier 151b can fluidly separate the inflow path and the outflow path. The third fluid barrier 151c of the fluid barriers can be positioned distal to the fluid inlet 157. The third fluid barrier 151c can define one or more holes through which the transmission line 150 extends and through which the tube 176 extends. The distal surface of the third fluid barrier 151c can be connected to a sheath 190 coaxially arranged around the transmission line 150 and the tube 176. The sheath 190 can be PTFE, as described above, or a fiberglass tube. The fourth fluid barrier 151d of the fluid barriers can be positioned distal to (or away from) the fluid inlet 157 and is configured to prevent fluid from flowing out through the outer housing 161 adjacent to the shaft 154.

[0080] Fig.10 The antenna type is shown as a monopole architecture. The tube 176 extends from the hub 152 to the distal end 179 of the tube 176. The distal end 179 of the tube 176 can be axially positioned proximal to the distal end 167 of the transmission line 150. Alternatively, the distal end 179 can be flush with the distal end 167 of the transmission line 150 or axially positioned distal to the distal end 167 of the transmission line 150. Cooling liquid is introduced through the fluid inlet 157 into the annular space defined between the tube 176 and the sheath 190. The cooling liquid can occupy the space around the transmission line 150 proximal to the tip 156. Because the inflow path is spaced apart from the transmission line 150 until closer to its distal end 167, the maximum cooling effect is provided to the portion of the transmission line 150 that ablates the tissue. The tissue itself is also cooled, thereby providing a degree of control over the electrical properties of the tissue. The cooling liquid is directed through an outflow path also defined between the tube 176 and the transmission line 150 , and then through the fluid outlet 159 of the hub 152 .

[0081] Fig.11 The antenna type is shown as a double slot architecture. The distal end 179 of the tube 176 is axially positioned flush with the distal end 167 of the transmission line 150. Alternatively, the distal end 179 may be axially positioned proximal or distal to the distal end 167 of the transmission line 150, and more specifically positioned proximal to the first axial slot 168, the second axial slot 170, or any position therebetween. As previously described, the first axial slot 168 and the second axial slot 170 are defined between the proximal, intermediate, and distal segments 162, 164, 166. The cooling liquid is directed through the fluid inlet 157 into the annular space defined between the tube 176 and the sheath 190, and is further directed through an outflow path also defined between the tube 176 and the transmission line 150. It is contemplated that the inflow and outflow paths may be provided conversely, wherein cooling liquid is directed through fluid inlet 157 into the annular space defined between tube 176 and jacket 190 and then directed through an outflow path also defined between tube 176 and transmission line 150. It is also contemplated that certain features from other embodiments of probe 34 may be provided, such as a choke.

[0082] Fig. 12A and 12B An alternative embodiment of the probe 134 is shown, which includes a choke double slot structure in which the choke 174 is fixed to the jacket 190. The choke 174 may not be shorted to the outer conductor 158 of the transmission line 150. In other words, the inner choke layer 177 may be floating (i.e., not grounded) and otherwise spaced apart from the transmission line 150 to optionally provide a reference-like Fig.11 The transmission line 150 may include a proximal segment 162, an intermediate segment 164, and a distal segment 166. The inner conductor 160 may extend through the proximal segment 162 and the intermediate segment 164, and optionally through the distal segment 166. The distal segment 166 and the intermediate segment 164 may define a first axial slot 168, and the intermediate segment 164 and the proximal segment 166 may define a second axial slot 170. Figure 3 The number (plus 100) and Fig.11 Like numerals in FIG. 1 denote like parts, and the corresponding disclosures are incorporated herein by reference.

[0083] The jacket 190 is a non-conductive tube coaxially disposed on a portion of the transmission line 150. In one example, the non-conductive tube is formed of fiberglass. The choke 174 includes an inner choke layer 177, an outer choke layer 175, and an electrical short 180. The inner choke layer 177 may be a first conductive tube coaxially disposed between the non-conductive tube and the outer conductor 158 of the transmission line 150. The first conductive tube may be a hypodermic tube of a biocompatible metal. Fig. 12A1 shows a first variation in which a first conductive tube extends proximally from the active tip to a hub (not shown) to provide mechanical support and stiffness to the shaft 154 of the probe 134. The outer choke layer 175 may include a second conductive tube coaxially disposed on a portion of the non-conductive tube such that a region 183 of the non-conductive tube forms a choke insulation layer. The electrical short 180 provides electrical communication between the inner choke layer 177 and the outer choke layer 175. Fig. 12B 170 is a second variation in which a second conductive tube forming the outer choke layer 175 extends proximally from the active tip to the hub to provide mechanical support and stiffness to the shaft 154. In the second variation, the inner choke layer 177 can be one of a conductive tube extending proximally to the hub, a conductive tube segment as shown, or a plating layer to be described. In a third variation, each of the outer choke layer 175, the inner choke layer 177, and the electrical short 180 is formed by a continuous plating layer.

[0084] In some embodiments, a region 183 of the non-conductive tube is thinned to define a recess. A second conductive tube forming the outer choke layer 175 can be disposed within the recess. This arrangement facilitates secure engagement of the second conductive tube and provides a smooth profile to the outer diameter of the shaft 154. The length of region 183 is based on the relative dielectric constant of the material forming the jacket 190. In other words, the length of region 183 of the non-conductive tube can be approximately equal to one-quarter effective wavelength of the drive frequency in the material of the non-conductive tube. For example, the relative dielectric constant of glass fiber can determine the length of the choke 174, particularly the length of region 183. Region 183 (e.g., the thinned region) effectively becomes a waveguide with infinite impedance at the distal end of the choke 174 defined by the distal end 181 of the second conductive tube forming the outer choke layer 175.

[0085] In some embodiments, the electrical short 180 can be a conductive element compressed between the outer choke layer 175 and the inner choke layer 177. In one example, the conductive element is a wire or a ring. The conductive element can be formed of a suitable conductive material such as gold, or alternatively, solder can form the conductive element. Alternatively, as described above, the electrical short 180 can be formed by electroplating. The electrical short 180 can be optional because it is contemplated that the choke effect can be provided without providing a separate component that provides electrical connectivity between the inner choke layer 175 and the outer choke layer 177. In a variation where the outer choke layer 175 is not electrically connected to the inner choke layer 177, a sleeve can be formed over the inner choke layer 177, wherein the length of the sleeve is one quarter of the wavelength of the drive frequency, or other integer multiples of this value.

[0086] Continue to refer Fig. 12A and Fig. 12B, the distal end 178 of the inner choke layer 177 terminates at a position proximal to the second axial slot 170. Similarly, the distal end 181 of the outer choke layer 175 terminates at a position proximal to the second axial slot 170. The distance between the second axial slot 170 and one or both of the distal ends 178, 181 can be selectively adjusted to impart desired performance characteristics to the probe 134. In the illustrated embodiment, the distal end 178 of the inner choke layer 177 is at a position distal to the distal end 181 of the outer choke layer 175. In another embodiment, the distal ends 178, 181 of the inner and outer choke layers 175, 177 are flush. It should be understood that the first conductive tube forming the inner choke layer 177 may not be shorter than the second conductive tube forming the outer choke layer 175. In other words, the distal end 178 of the inner choke layer 177 may not be located at a position proximal to the distal end 181 of the outer choke layer 175.

[0087] According to certain exemplary methods of assembly of the shaft 154 of the probe 34, the outer choke layer 175 is formed by a second conductive tube extending to and fixed to the hub 152. The inner choke layer 177 is formed by a plated layer on a non-conductive tube or another dielectric member. The plated layer can be a section or can extend proximally to the hub 152. Alternatively, the outer choke layer 175, the inner choke layer 177 and the electrical shorting portion 180 are formed by a continuous plated layer on a non-conductive tube or another dielectric member. The plated tip assembly can be connected to the hypodermic injection tube via a welding process, and / or joined by an adhesive or other suitable manufacturing technology. Such variations including electroplating may include a plated layer having a thickness of at least two microns. An embodiment including a plated layer can eliminate the need for a recessed portion of the non-conductive tube.

[0088] Another assembly method includes plastically deforming one or both of the first and second conductive tubes that respectively form the inner choke layer 177 and the outer choke layer 175. For example, the plastic deformation may be facilitated by a swaging or crimping process, wherein the inner choke layer 177 and / or the outer choke layer 175 are plastically deformed into close contact or direct contact with each other, thereby forming the electrical short 180. Additional fastening means (e.g., solder, conductive adhesive, etc.) may be applied at the contact point to improve the conductivity of the electrical short 180.

[0089] It is easy to understand the functional advantage of the distal end 181 of the choke 174 terminating at a position proximal to the second axial slot 170. As previously described, the choke 174 is configured to prevent waves from propagating backward along the axis 154. The benefits of the choke 174 itself may not be fully realized over the entire range of the relative dielectric constant of the tissue. For example, the effect of the choke 174 may not be optimal in highly ablated tissue. The dual-slot architecture combines with the choke 174 to achieve significant synergy. The dual-slot architecture concentrates energy at appropriate locations along the axis 154 and accommodates highly ablated tissue. In summary, the choke 174 is configured to prevent reverse current propagation initially in unablated (e.g., "original") tissue, and the dual-slot architecture is configured to constrain the field when the tissue is severely ablated. The combination of the choke 174 and the dual-slot architecture helps to achieve a near-spherical shape of the near-field region over an improved range of the relative dielectric constant of the tissue when the tissue is ablated.

[0090] In certain embodiments, the probe 34, 134 can be configured to cool the transmission line 50, 150 with a cooling liquid and discharge the infused liquid into the tissue. In other words, the probe 34, 134 can be a hybrid of the above methods, wherein at least a portion of the liquid is infused into the tissue and the remainder is circulated to the pump 36 (or liquid reservoir 38). Based on the characteristics of the probe 34, 134 (e.g., the size and / or number of fluid ports 100, the expected operating pressure, and the filter layer on the sheath 90, 190, etc.), the ratio of liquid infused into the tissue to the liquid circulated can be fixed. Alternatively, the probe 34, 134 may include an infusion flow path that is separate from the cooling flow path fluid. For example, the probe 34, 134 may include another subcutaneous injection tube coaxially disposed within the tube 76, 176 and extending to near the tip 56, 156. The tube 76, 176 and the subcutaneous injection tube are arranged in a manner similar to Fig.10 and Fig.11The inflow path and outflow path of the cooling flow path are defined in a manner, and the annular space between the tubes 76, 176 and the sheaths 90, 190 defines an infusion flow path. The pump 36 may include a valve, or a valve may be provided in other ways, so that the controller 44 independently controls the flow rate of the infusion liquid through the infusion flow path and the cooling liquid through the cooling flow path. The controller 44 can operate the system 30 in an infusion mode, in which the infusion liquid is guided through the infusion flow path, but the guiding of the cooling liquid in the cooling flow path is suspended (e.g., the valve is selectively opened and closed). The controller 44 can operate the system 30 in a cooling mode, in which the cooling liquid is guided through the cooling flow path, but the infusion liquid is suspended from being guided in the infusion flow path. In addition, the controller 44 can operate the system 30 in a combination mode, in which the flow rates of the infusion liquid and the cooling liquid are independently controlled in a simultaneous manner. The selective operation of the system 30 in one of the infusion mode, the cooling mode, and the combination mode can be selected by the user on the display 104, or automatically started or terminated in real time based on the characteristics of the ablation procedure determined in the manner previously described. Finally, certain embodiments of probe 134 (e.g., Fig.10 and Fig.11 ) may provide an infusion only mode, in which the inflow and outflow paths do not necessarily have to be separated, and thus tube 176 may be optional.

[0091] The probe 34, 134 and control aspects described herein can be used for channel ablation, that is, ablation is performed during the process of withdrawing the probe 34, 134 from the channel through which the probe 34, 134 is guided. Channel ablation can burn tissue and reduce the risk of tumor implantation. However, the characteristics of the ablated channel depend on the surgeon's technique. The system 30 of the present disclosure can provide channel ablation in an automatic and consistent manner without bringing cognitive burden to the surgeon. In some embodiments, the probe 34, 134 may include a temperature sensor along the axis 54, 154 or another suitable position to sense the temperature of the tissue in the channel. The system 30 can be configured to ensure that the temperature is sufficiently increased during the channel ablation to ensure cell death. As described above, the pump 36 is operated to control the flow rate of the cooling fluid, and reversible flow can also be provided. In such an arrangement, the cooling liquid can initially flow along the outflow path for the portion of the tissue desired to be cooled in the ablation, and then reverse to allow the cooling liquid to be heated by the active antenna area of ​​the axis 54, 154. For example, the initial flow rate can be adjusted so that the cooling fluid on the inflow path can heat the shaft 54, 154 instead of cooling the shaft 54, 154. During the first part of the ablation, the cooling fluid is pumped at a slow rate by the pump 36 to keep the probe 34, 134 cool enough to avoid damage, but hot relative to the tissue temperature sensed by the temperature sensor. This allows the heated cooling liquid to flow along the outflow path of the probe 34, 134. The outer wall of the shaft 54, 154 promotes heat transfer, thereby providing a short period of time during which the heated cooling liquid transfers heat along the shaft 54, 154 to effectively perform automatic channel ablation. This arrangement is particularly suitable for the dual-slot architecture of the probe 34, 134 described herein, in which the tissue reaches the ablated stage more quickly, and the probe 34, 134 becomes self-choked during the ablation stage. When the probe 34, 134 reaches the self-choked condition, the controller 44 can operate the pump 36 to increase the flow rate. The increased flow rate of the heated cooling fluid helps maintain the self-choking condition and terminates the automatic channel ablation to prevent excessive damage to the tissue surrounding the probe 34, 134.

[0092] Reference now Figure 13-15 , shows a variation of the shaft 254 of the dual slot architecture, wherein the probe includes an inflatable member 281. The inflatable member 281 can be coupled to the dielectric housing 284 and is in fluid communication with at least the inflow path. For example, Fig.14The inflatable member 281 is shown in fluid communication with the distal infusion path through a fluid port 200 defined in the sheath 190. As such, the inflatable member 281 is in fluid communication with the proximal infusion path through an orifice 196 defined by the tube 176, which provides fluid communication around the choke 174 as previously described. A sleeve 283 can be coaxially disposed on the sheath 190, and the inflatable member 281 can be coupled to the sleeve 283 at any suitable axial position to achieve a desired ablation zone. In the example shown, the inflatable member 281 is axially positioned proximate the first and second slots 168, 170, which may be particularly advantageous for positioning a volume of liquid proximate the location of maximum microwave energy transfer.

[0093] The inflatable member 281 can be formed of a non-compliant material. This prevents over-expansion during inflation, so that the volume of liquid within the inflatable member 281 can be reliably known. Advantageously, inflation of the inflatable member 281 engages the tissue to limit or eliminate "pull-out" of the probe from the tissue, e.g., over-pushing. In addition, as described above, positioning the liquid volume within the ablation zone can provide improved control over the ablation shape. The inflatable member 281 can be spherical or ellipsoidal, such as Figure 13-15 As generally shown in FIG. 254 , an eccentric shape may be utilized to promote a desired heating pattern (or distribution) adjacent to the active tip. It is also contemplated that multiple inflatable members may be provided along the axis 254. For example, Fig.14 A second inflatable member 281' is shown (shown in phantom) positioned axially about the choke 274. In one variation, the second inflatable member 281' is included and the inflatable member 281 is optional.

[0094] The inflatable member 281 may include fenestrations, perforations, or other suitable pores configured to facilitate infiltration of infusion fluid into tissue. Because of the number and / or size (e.g., porosity) of the fenestrations, the infusion fluid maintains the inflatable member 281 in an inflated state. The size and / or number of the fenestrations can be specifically designed to allow infusion of the infusion fluid at a desired flow rate while also maintaining the inflatable member 281 at a minimum or predetermined pressure. Additionally or alternatively, the microporosity of the inflatable member 281 can be provided by the inflatable member 281 becoming fully inflated or slightly stretched. Infusion fluid that seeps out of the inflatable member 281 into adjacent tissue can be heated by microwaves and produce steam. As described above, steam can advantageously provide an additional heat transfer mechanism. The generation of steam can be further facilitated by preheating the infusion fluid, which can be achieved during infusion. Fig.14 If any infusion liquid evaporates within the inflatable member 281, the vapor can simply be discharged through the fenestrations and / or micropores without problems.

[0095] Fig.15Another variation of the shaft 254 of the probe is shown in which inflow and outflow paths for cooling are provided. The tube 276 is coaxially positioned within the sheath 290, and its distal end 279 is axially positioned flush with (or proximal or distal to) the distal end 267 of the transmission line 250. The cooling liquid is directed through the annular space defined between the tube 276 and the sheath 290, and further directed through the outflow path also defined between the tube 276 and the transmission line 250 (or vice versa). The inflatable member 281 is coupled to the sleeve 283, which defines an inflation flow path with the sheath 290 therebetween. The inflation flow path can be arranged to be in fluid communication with the inflow path, the inflation flow path receives a portion of its fluid from the inflow path, or the inflation flow path can be fluidly separated from the inflow path. The controller 44 can operate the pump 36 (and / or the second pump) to independently control the flow rates of the inflation liquid and the cooling liquid in a simultaneous manner. In another embodiment, the inflatable member 281 includes fenestrations, perforations, micropores, etc., wherein the inflation flow path can be considered an infusion flow path. The controller 44 can operate the system 30 in a cooling mode, an infusion mode, a combination mode, or an inflation mode, in which the inflatable member 281 is inflated and other fluid delivery is suspended.

[0096] Certain inventive aspects of the present disclosure are understood with reference to the following exemplary clauses.

[0097] Item 1 - A probe for ablating tissue using microwave energy, the probe comprising: a transmission line, the transmission line comprising an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor; a dielectric shell, the dielectric shell connected to the transmission line and defining a distal tip of the probe; a sheath, the sheath coaxially disposed over the outer conductor and at least a portion of the dielectric shell, the sheath defining an infusion path configured to receive an infusion fluid; and an inflatable member, the inflatable member connected to the dielectric shell and in fluid communication with the infusion path and defining micropores or fenestrations, wherein the inflatable member is configured to be inflated with the infusion fluid so that the infusion fluid seeps into the tissue through the micropores or fenestrations.

[0098] Clause 2 - The probe of clause 1, further comprising any embodiment of the choke described and disclosed herein.

[0099] Clause 3 - The probe of clause 1, further comprising any embodiment of the choke described and disclosed herein.

[0100] Item 4 - A method for performing an ablation procedure in which a probe is connected to a generator to ablate tissue and to an analyzer, the method comprising: delivering microwave energy to the probe to ablate tissue; determining a measured S11 parameter based on reflected power sensed by the generator at a driving frequency; performing a frequency scan in which the sensed S11 parameter is determined for at least two frequencies; determining characteristics of the ablation procedure based on the measured S11 parameter and the frequency scan; and at least one of: (i) controlling the delivery of an infusion fluid, (ii) controlling the flow rate of a cooling fluid, and (iii) controlling the delivery of microwave energy based on the determined characteristics.

[0101] Clause 5 - The method of clause 4, further comprising evaluating the sensed S11 parameter based on calibration data of the probe over a frequency range of different known average relative permittivity values.

[0102] Clause 6 - A method according to clause 5, wherein the calibration data further comprises a plurality of power curves, each power curve being associated with one of said different known average relative permittivity values, the method further comprising selecting one of the power curves based on the sensed S11 parameter.

[0103] Clause 7 - A method according to clause 6, wherein each of the power curves includes a resonant frequency, the method further comprising: determining a slope of a data point associated with the sensed S11 parameter, wherein the slope is positive or negative; and determining whether the resonant frequency is greater than or less than the drive frequency based on the slope.

[0104] Clause 8 - The method of clause 7, further comprising initiating, increasing or decreasing infusion fluid provided to the tissue if the measured resonant frequency is less than the drive frequency and if the determined slope is positive.

[0105] Clause 9 - The method of clause 8, further comprising initiating or increasing infusion of fluid to the tissue by an amount proportional to the difference between the resonant frequency and the drive frequency.

[0106] Clause 10 - The method of clause 7, further comprising maintaining, reducing or terminating the infusion fluid being delivered to the tissue if the measured S11 parameter is equal to the designed resonant frequency of the probe.

[0107] Clause 11 - A method according to any of clauses 4-10, wherein the characteristic determined is a weighted average relative permittivity.

[0108] Clause 12 - The method according to any one of clauses 4-11, further comprising: transforming the frequency scan from a frequency domain spectrum to a time domain spectrum; determining an average relative dielectric constant of the tissue; determining a change in the velocity of the microwaves, wherein the change indicates a change in the electrical properties of the tissue; and providing an indication on a display regarding a feature or status of the ablation procedure.

[0109] Item 13 - A method for determining characteristics of an ablation procedure, wherein a probe is connected to a generator to ablate tissue, the method comprising: delivering microwave energy to the probe to ablate the tissue; performing a frequency scan; transforming the frequency scan from a frequency domain spectrum to a time domain spectrum; determining a speed of the microwaves based on the moment when the sensed microwaves are reflected from the tissue; determining a change in the speed of the microwaves, wherein the change indicates a change in the electrical properties of the tissue; and providing an indication on a display regarding a characteristic or status of the ablation procedure.

[0110] Clause 14 - The method of clause 13, further comprising providing a warning on the display that the probe has passed through an interface between the lesion and adjacent tissue.

[0111] Clause 15 - The method according to clause 14, further comprising: determining a change in an average relative dielectric constant based on a frequency sweep, wherein a speed of the microwaves is based on the average relative dielectric constant; and compensating for the change in the average relative dielectric constant when determining a change in the speed of the microwaves.

[0112] Clause 16 - The method according to any of clauses 13-15, further comprising: determining a distance to a reflection point associated with the interface based on a speed of the microwaves; estimating a lesion size based on the determined distance; and providing a virtual representation of the lesion size on a display.

[0113] Item 17 - A method for determining characteristics of an ablation procedure in which a probe is connected to a generator to ablate tissue, the method comprising: delivering microwave energy to the probe to ablate tissue; performing a frequency scan in a frequency domain spectrum; determining an average relative dielectric constant based on the frequency scan; and transforming the frequency scan from the frequency domain spectrum to a time domain spectrum; determining the absence or presence of a reflection point in the time domain spectrum; determining a distance to the reflection point based on a speed of the microwaves; comparing the distance to a previously determined distance; and providing an indication of a boundary between ablated tissue and non-ablated tissue on a display if the distance indicates that the reflection point is a new reflection point.

[0114] Clause 18 - A method according to any of clauses 4-17, wherein the step of delivering microwave energy to ablate tissue is performed in a high power mode of a first wattage and the step of performing the frequency sweep is performed in a low power mode of a second wattage less than the first wattage.

[0115] Clause 19 - A method according to any of clauses 4-18, wherein the generator comprises a controller and a pump in communication with the controller, the method further comprising operating the pump to control delivery of the infusion fluid.

[0116] Item 20 - An instrument console configured to be removably connected to a probe to perform any of the methods of items 4-19, the instrument console comprising: a microwave generator configured to generate microwave energy of a first wattage; a vector network analyzer configured to generate microwave energy of a second wattage less than the first wattage and to perform analysis in a frequency domain spectrum and a time domain spectrum; a switch configured to selectively establish communication between the microwave generator and one of the probe and the vector network analyzer; and a controller in communication with the microwave generator and the switch, wherein the controller is configured to control the switch to establish communication between the microwave generator and the probe to ablate tissue in a high power mode at the first wattage, or to establish communication between the probe and the vector network analyzer to perform a frequency scan in a low power mode at the second wattage.

[0117] Clause 21 - The instrument console of Clause 20, further comprising a pump in communication with the controller, wherein the controller is configured to operate the pump based on data received from the vector network analyzer.

[0118] Clause 22 - The instrument console of clause 20 or 21, further comprising a probe according to any of clauses 1-3 and / or any embodiment of the probe described and disclosed herein.

[0119] The foregoing disclosure is not intended to be exhaustive or to limit the present invention to any particular form. The terms used are intended to have the nature of descriptive terms rather than restrictive terms. According to the above teachings, many modifications and variations are possible, and the present invention can be practiced in a manner different from that specifically described.

Claims

1. A probe for ablating tissue using microwave energy, the probe comprising: a transmission line comprising an outer conductor, an inner conductor coaxially disposed within the outer conductor, an insulating layer coaxially disposed between the outer conductor and the inner conductor, wherein the transmission line defines a first axial slot and a second axial slot proximal to the first axial slot; a non-conductive tube coaxially disposed on a portion of the transmission line; an electric choke coupled to the non-conductive tube and comprising: an inner choke layer comprising a first conductive tube coaxially disposed between the non-conductive tube and the outer conductor of the transmission line, wherein the inner choke layer has a distal end terminating at a location proximal to the second axial slot; an outer choke layer comprising a second conductive tube coaxially disposed on the non-conductive tube such that a region of the non-conductive tube forms a choke insulation layer, wherein the outer choke layer has a distal end terminating at a location proximal to the second axial slot; and An electrical short provides electrical communication between the inner choke layer and the outer choke layer. 2 . The probe of claim 1 , wherein the non-conductive tube defines a recess, the second conductive tube being coaxially disposed within the recess. 3 . The probe according to claim 1 , wherein the distal end of the inner choke layer is distal to the distal end of the outer choke layer.

4. The probe according to claim 1 or 2, wherein the distal end of the inner choke layer is flush with the distal end of the outer choke layer.

5. A probe for ablating tissue using microwave energy, the probe comprising: A transmission line comprising an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor; a non-conductive tube coaxially disposed on a portion of the transmission line, wherein a region of an outer surface of the non-conductive tube defines a recess; an electric choke coupled to the non-conductive tube and comprising: an inner choke layer, the inner choke layer comprising a first conductive tube coaxially disposed between the non-conductive tube and the outer conductor of the transmission line; an outer choke layer, the outer choke layer comprising a second conductive tube disposed within the recess such that a portion of the non-conductive tube forms a choke insulation layer; and An electrical short provides electrical communication between the inner choke layer and the outer choke layer.

6. The probe according to any one of claims 1-5, wherein the electrical shorting portion is formed by plastic deformation of the first conductive tube and the second conductive tube and direct contact between the first conductive tube and the second conductive tube; and optionally, wherein the plastic deformation is formed by a swaging process.

7. The probe of claim 6, further comprising solder or conductive adhesive at a direct contact point between the first conductive tube and the second conductive tube.

8. The probe according to any one of claims 1 to 7, wherein the electrical short is a conductive element compressed between the inner choke layer and the outer choke layer.

9. The probe of claim 8, wherein the conductive element is a wire or a ring.

10. The probe according to claim 9, wherein the conductive element is formed of gold or solder.

11. A probe for ablating tissue using microwave energy, the probe comprising: a transmission line comprising an outer conductor, an inner conductor coaxially disposed within the outer conductor, an insulating layer coaxially disposed between the outer conductor and the inner conductor, wherein the transmission line defines a first axial slot and a second axial slot proximal to the first axial slot; a non-conductive tube coaxially disposed on a portion of the transmission line; an electric choke coupled to the non-conductive tube and comprising: an inner choke layer coaxially disposed between the non-conductive tube and the outer conductor of the transmission line; an outer choke layer coaxially coupled to an outer surface of the non-conductive tube such that a region of the non-conductive tube forms a choke insulation layer, wherein the outer choke layer has a distal end terminating at a location proximal to the second axial slot; and an electrical short providing electrical communication between the inner choke layer and the outer choke layer, At least one of the inner choke layer, the outer choke layer and the electrical shorting portion is formed by conductive foil and / or electroplating.

12. The probe of claim 11, wherein the inner choke layer, the outer choke layer and the electrical short are formed by continuous electroplating layers to form a plated tip assembly with the non-conductive tube; and optionally, wherein the plated tip assembly is fixed to a subcutaneous injection tube.

13. The probe of any one of claims 1-12, wherein the length of the region of the non-conductive tube forming the choke insulation layer is approximately equal to one quarter of the effective wavelength of the drive frequency in the material forming the non-conductive tube.

14. The probe of any one of claims 1-13, further comprising an additional non-conductive tube coaxially disposed between the transmission line and the inner choke layer, wherein the additional non-conductive tube defines an inflow fluid path and an outflow fluid path.

15. The probe of claim 14, wherein the distal end of the additional non-conductive tube is positioned axially proximal to the distal end of the transmission line.

16. The probe of claim 14, wherein a distal end of the additional non-conductive tube is flush with a distal end of the transmission line.

17. A probe for ablating tissue using microwave energy, the probe comprising: A transmission line comprising an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor; a non-conductive tube coaxially disposed on a portion of the transmission line; an electric choke coupled to the non-conductive tube and comprising: an inner choke layer, the inner choke layer comprising a first conductive tube coaxially disposed between the non-conductive tube and the outer conductor of the transmission line, wherein the inner choke layer is spaced apart from the outer conductor of the transmission line; and The outer choke layer includes a second conductive tube, so that a region of the non-conductive tube forms a choke insulation layer.

18. The probe of claim 17, further comprising an electrical short providing electrical communication between the inner choke layer and the outer choke layer.

19. A probe for ablating tissue using microwave energy, the probe comprising: A transmission line comprising an outer conductor, an inner conductor coaxially disposed within the outer conductor, and an insulating layer coaxially disposed between the outer conductor and the inner conductor; an electrically conductive tube coaxially disposed over a portion of the transmission line, wherein an electrical short provides electrical communication between the tube and the outer conductor of the transmission line to define a choke, wherein a choke insulation layer is disposed between the outer conductor and the tube, wherein the tube defines a proximal infusion path and an orifice, the proximal infusion path being configured to be disposed in fluid communication with a source of an infusion fluid; and A sheath is coaxially disposed on the tube, wherein the sheath defines a distal infusion path in fluid communication with the proximal infusion path through the aperture and a fluid port in fluid communication with the distal infusion path.

20. The probe of claim 19, wherein the orifice is located proximal to the electrical short such that at least a portion of the transmission line is cooled with the infusion fluid prior to passing through the orifice.

21. The probe of claim 19 or 20, wherein the proximal infusion path is further defined between the tube and the outer conductor.

22. The probe of any one of claims 19-21, wherein the fluid port is positioned to an active tip of the probe, the active tip being axially defined between the choke and the distal end of the tip of the probe.

23. The probe of claim 22, wherein the fluid ports are evenly spaced along the length of the active tip.

24. The probe of any one of claims 19-23, wherein the fluid ports are evenly distributed radially around the sheath.

25. The probe of any one of claims 19-24, wherein a distal fluid port is defined at a distal end of the sheath.

26. The probe of any one of claims 19-25, wherein the sheath is polymeric.

27. The probe according to claim 26, wherein The fluid ports are microscopic holes in the polymer sheath.

28. The probe of any one of claims 19-27, further comprising an end cap coupled to the inner conductor and defining a first axial slot with the outer conductor of the transmission line, wherein the fluid port is positioned proximal to the first axial slot.

29. The probe of claim 28, wherein the outer conductor of the transmission line further defines a second axial slot positioned proximal to the first axial slot, wherein the first axial slot and the second axial slot are separated by a middle section of the outer conductor having a quarter effective wavelength of the tissue.

30. A probe for ablating tissue using microwave energy, the probe comprising: a transmission line comprising an outer conductor, an inner conductor coaxially disposed within the outer conductor, an insulating layer coaxially disposed between the outer conductor and the inner conductor, wherein the transmission line defines a first axial slot and a second axial slot proximal to the first axial slot; a tube coaxially disposed on a portion of the transmission line, wherein an electrical short provides electrical communication between the tube and the outer conductor of the transmission line to define a choke, wherein a choke insulation layer is disposed between the outer conductor and the tube; as well as A sheath is coaxially disposed on the tube and defines an infusion path configured to be placed in fluid communication with an infusion fluid source and further defines a fluid port positioned between the first axial slot and the second axial slot.

31. The probe of claim 30, further comprising an end cap coupled to the inner conductor, wherein the first axial slot is defined between the end cap and the outer conductor.

32. The probe of claim 31 wherein the second axial groove is positioned proximal to the fluid port.

33. The probe of any one of claims 30-32, wherein a distribution density of the fluid ports positioned between the first axial groove and the second axial groove is higher than a distribution density of the fluid ports distal to the first axial groove or proximal to the second axial groove.

34. The probe of any one of claims 30-33, wherein fluid ports located proximal to the choke are distributed at a higher density than fluid ports located distal to the choke.

35. The probe of any one of claims 30-34, wherein the first axial groove and the second axial groove are each about one millimeter in length.

36. The probe of any one of claims 30-35, wherein the transmission line further comprises a proximal segment of the outer conductor positioned distally of the choke, wherein the length of the proximal segment is one quarter of the effective wavelength of the tissue.

37. The probe according to any one of claims 30-36 further includes a dielectric shell at least partially disposed within the sheath, wherein a choke length of the choke defined between the electrical shorting portion and the interface between the outer conductor and the dielectric shell is configured to be one-quarter of the effective wavelength of the microwave field in the choke insulation layer.

38. The probe of any one of claims 30-37, further comprising a dielectric shell at least partially disposed within the sheath, and an inflatable member coupled to the dielectric shell and in fluid communication with the infusion path, wherein the inflatable member is configured to be inflated with the infusion fluid to prevent movement of the probe within the tissue.

39. The probe of any one of claims 30-38, further comprising an inflatable member coupled to the sheath to define an inflation flow path, wherein the probe defines an inflow path and an outflow path, the inflow path and the outflow path being fluidly separated from the inflation flow path and configured to circulate a cooling fluid.

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