Broadband microwave tissue ablation probe with variable length antenna parameters

Abstract

A variable length microwave ablation probe is provided. The probe is configured to have a range of resonant frequencies. The probe includes a microwave antenna, an outer conductor, and a cap. The probe further includes a radiation window that is at least partially transparent to microwave energy. The distance of the distal boundary of the outer conductor or the proximal boundary of the cap from the distal end of the probe varies. The probe can have a choke length, an arm length, a radiating portion length, and a cap length. Each of these lengths can affect the resonant frequency of the antenna. Some examples provide a variable choke length, a variable arm length, a variable radiating portion length, and / or a variable cap length.

Description

[0001] This application was filed as a PCT international patent application on January 10, 2020 in the name of Boston Scientific Scimed, Inc., a U.S. company, as the applicant in all country designations, and Hong Cao, a U.S. citizen, and Timothy A. Ostroot, a U.S. citizen, as the inventors in all country designations, and claims priority to U.S. Provisional Application No. 62 / 791,276 filed on January 11, 2019 and claims priority to U.S. Patent Application No. 16 / 738,532 filed on January 9, 2020, the contents of which are hereby incorporated by reference in their entirety. Background Art

[0002] Microwave ablation (MWA) is a minimally invasive energy physical therapy for treating many parts of the body, including soft tissue injuries in the liver, kidneys, and lungs. The microwave ablation probe uses an antenna (such as a monopole antenna or a dipole antenna) to radiate microwave energy into the tissue for heating. Unlike radiofrequency ablation, which relies on ion movement and friction for heating, the energy of microwave ablation causes water molecules to rotate due to the polarity of the molecules and generates heat due to magnetic hysteresis. Microwave ablation typically operates in the industrial, scientific, and medical (ISM) radio bands (such as 500MHz to 10GHz), and more specifically can operate at 945MHz or 2.45GHz. Microwave ablation has advantages such as fast heating to allow the probe to operate at high temperatures to produce greater damage, and has gained a market share that exceeds radiofrequency ablation (RFA) in tissue ablation over the past decade. Summary of the invention

[0003] One general aspect includes a microwave ablation probe comprising a probe body, a coaxial cable within the probe body, and a cap. The probe body includes a shielding portion and a radiation window that is at least partially transparent to microwave energy. The coaxial cable includes: a center conductor; a dielectric material, the dielectric material surrounding the center conductor of the cable; and an outer conductor, the outer conductor having an outer conductor distal boundary. The center conductor includes a radiating portion extending beyond the distal boundary of the outer conductor, wherein the radiating portion is configured to emit microwave energy, wherein the radiating portion is aligned with the radiation window. The cap is located at the distal end of the probe and includes a cap proximal boundary, wherein the outer conductor distal boundary or the cap proximal boundary varies in distance from the distal end of the probe.

[0004] Embodiments may include one or more of the following features. The probe wherein the outer conductor distal boundary varies in distance from the probe distal end. The probe wherein the cap comprises a metal material and the cap proximal boundary varies in distance from the probe distal end. The probe wherein the outer conductor distal boundary and the cap proximal boundary vary in distance from the probe distal end. The probe wherein the outer conductor distal boundary or the cap proximal boundary comprises a plurality of discrete segments, wherein adjacent discrete segments are at different distances from the probe distal end. The probe wherein the outer conductor distal boundary or the cap proximal boundary comprises a wavy shape. The probe wherein the outer conductor distal boundary or the cap proximal boundary comprises a sawtooth shape. The probe wherein the outer conductor distal boundary is a consistent distance from the probe distal end. The probe wherein the cap proximal boundary is a consistent distance from the probe distal end. The probe further comprises a choke. The probe wherein the shielding portion of the probe body comprises a metal cannula. The probe further comprises a dielectric layer between the metal cannula and the outer conductor. The probe further includes a choke, the choke including: a choke contact, the choke contact is between the metal cannula and the outer conductor; and a choke length, the choke length extending between the choke contact and the distal end of the metal cannula. The probe wherein the distance of the choke contact or the distal end of the cannula from the distal end of the probe varies. The probe wherein the radiation window includes a portion of the dielectric material of the cable surrounding the radiating portion of the center conductor. The probe wherein the cap further includes a cap tip, the cap tip being configured to pierce tissue at the distal end of the cap. Implementations of the described technology may include hardware, methods or processes, or computer software on a computer-accessible medium.

[0005] One general aspect includes a microwave ablation system, the microwave ablation system including a microwave energy source and a microwave ablation probe. The probe includes a probe body, a coaxial cable within the probe body, a cap at a distal end of the probe, and a choke. The probe body includes a shielding portion and a radiation window that is at least partially transparent to microwave energy. The probe body further includes a metal cannula. The coaxial cable within the probe body is connected to the microwave energy source. The cable includes: a center conductor; a dielectric material, the dielectric material surrounding the center conductor of the cable; and an outer conductor, the outer conductor having an outer conductor distal boundary. The center conductor includes a radiating portion extending beyond the distal boundary of the outer conductor, wherein the radiating portion is configured to emit microwave energy, wherein the radiating portion is aligned with the radiation window. The cap includes a cap tip configured to pierce tissue at the distal end of the cap and a cap proximal boundary. The choke includes: a choke contact, the choke contact between the metal cannula and the outer conductor; and a choke length, the choke length extending between the choke contact and the distal end of the metal cannula. The outer conductor distal boundary or the cap proximal boundary may have a variable distance from the probe distal end. The outer conductor distal boundary may be variable in distance from the probe distal end. Implementations of the described technology may include hardware, methods or processes, or computer software on a computer accessible medium.

[0006] One general aspect includes a method of microwave ablation, the method comprising providing a microwave ablation probe and providing microwave energy to a radiating portion of the probe. The probe includes a probe body, the probe body including a shielding portion and a radiation window that is at least partially transparent to microwave energy. The probe also includes a coaxial cable within the probe body, the coaxial cable including: a center conductor; a dielectric material, the dielectric material surrounding the center conductor of the cable; and an outer conductor, the outer conductor having an outer conductor distal boundary. The center conductor includes a radiating portion extending beyond the distal boundary of the outer conductor, wherein the radiating portion is configured to emit microwave energy, wherein the radiating portion is aligned with the radiation window. The probe includes a cap, the cap is located at the distal end of the probe, the cap includes a cap tip configured to pierce tissue at the distal end of the cap, and a cap proximal boundary. The outer conductor distal boundary or the cap proximal boundary varies in distance from the distal end of the probe. The probe can generate microwave energy at two or more resonant frequencies. Implementations of the described technology may include hardware, methods or processes, or computer software on a computer-accessible medium.

[0007] This summary is a review of some of the teachings of the present application and is not intended to be an exclusive or exhaustive treatment of the subject matter of the present invention. Further details can be found in the detailed description and the appended claims. Other aspects will be clear to those skilled in the art when reading and understanding the following detailed description and viewing the drawings that form a part of the detailed description, each of which is not intended to be limiting. The scope of this article is defined by the appended claims and their legal equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a cross-sectional view of a microwave ablation probe according to some examples.

[0009] Figure 2 is a graph showing the resonant frequency of a microwave ablation probe with different antenna parameters.

[0010] Figure 3 is a graph showing the temperature dependence of the resonant frequency of a microwave ablation antenna.

[0011] Figure 4 is a schematic diagram of a microwave ablation system including a microwave ablation probe according to some examples.

[0012] Figure 5 is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0013] Figure 6 is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0014] Figure 7 is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0015] Figure 8 yes Figure 5 Unfolded cylindrical view of the antenna.

[0016] Fig. 9 yes Figure 6 Unfolded cylindrical view of the antenna.

[0017] Fig.10 yes Figure 7 Unfolded cylindrical view of the antenna.

[0018] Fig.11 is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0019] Fig.12 is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0020] Fig.13is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0021] Fig.14 is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0022] Fig.15 is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0023] Fig.16 is a side view of a microwave ablation antenna with variable parameters according to some examples.

[0024] Fig.17 is a cross-sectional view of a slot microwave antenna.

[0025] Fig.18 is a cross-sectional view of a monopole microwave antenna.

[0026] Fig.19 is a cross-sectional diagram of a dipole microwave antenna.

[0027] Fig. 20 It is a cross-sectional view of a triaxial microwave antenna.

[0028] Fig.21 is a cross-sectional view of a microwave antenna with a choke.

[0029] Fig. 22 is a cross-sectional side view of a microwave ablation probe with variable parameters according to some examples.

[0030] Fig.23 is a cross-sectional perspective view of a microwave antenna with variable parameters according to some examples.

[0031] Fig.24 is a cross-sectional view of an irrigated and cooled microwave ablation probe according to some examples.

[0032] Some of the drawings are schematic in nature and are not drawn to scale. Certain features are shown as being larger than their proportions, and certain features are omitted from some views for ease of illustration. Although the embodiments allow for various modifications and alternative forms, the specific forms of these embodiments have been illustrated with the aid of examples and drawings, and will be described in detail. However, it should be understood that the scope of this article is not limited to the specific aspects described. On the contrary, the present invention will cover modifications, equivalents, and alternatives that fall within the spirit and scope of this article. DETAILED DESCRIPTION

[0033] The present disclosure provides a broadband microwave tissue ablation probe having variable length antenna parameters. The term "variable" is used herein to refer to different portions of the antenna structure having different dimensions compared to adjacent portions.

[0034] Microwave antennas have a resonant frequency. The resonant frequency of the antenna affects the efficiency of the system because when the resonant frequency is properly tuned with the surrounding tissue, a high ratio of energy is transmitted into the tissue relative to the amount of energy that is reflected. When the resonant frequency is not tuned, more energy is reflected, resulting in less energy being transmitted into the patient's tissue.

[0035] Different portions of the antenna having different sizes allow the antenna to have more than one resonant frequency, such as two, three, four or more resonant frequencies. The antenna has multiple portions, each portion having a different resonant frequency. A single antenna acts as if it were multiple antennas in parallel.

[0036] Due to limitations of the microwave antenna within a microwave ablation probe, some of the microwave energy transmitted from the microwave energy source through the probe to the distal portion of the probe is reflected from the distal portion of the probe back toward the proximal portion of the probe. This reduces the efficiency of the probe and may cause self-heating within the antenna. Reducing the amount of reflected energy can help reduce this self-heating.

[0037] Many factors can affect the resonant frequency of the probe. One factor is the length of the various parts of the antenna. Changes in these lengths can significantly affect the resonant frequency. The choke length, arm length, radiating portion length, cap base length, and cap tip length can all affect the resonant frequency. Each of these lengths is described in more detail below. Figure 1 is a cross-sectional view of a microwave ablation probe, showing the parameters that can be varied to affect the resonant frequency of the probe.

[0038] Go to Figure 1 , the probe 112 has a distal portion 102 and a proximal portion 104. As used herein, the words "proximal" and "distal" represent a relationship between two different elements. The element designated as the proximal end is positioned closer to the external portion of the system, that is, the portion that does not enter the patient's body. The element designated as the distal end is positioned closer to the insertion end of the system. In some examples, the probe 112 includes a cannula 113 having a cannula distal boundary 114 adjacent to a radiation window 119. The cannula 113 constitutes a portion of a shielding portion 115 of the probe 112. A cap tip 165 is at the distal portion 102 of the probe 112. The radiation window 119 extends between the distal boundary 114 of the shielding portion 115 and the proximal boundary 166 of the cap tip 165.

[0039] The microwave antenna 152 includes a coaxial cable 151 having a center conductor 121, an outer conductor 131 coaxially surrounding the center conductor 121, and a dielectric 141 surrounding the center conductor 121 and separating the center conductor 121 from the outer conductor 131. Some examples of the technology also include a cap 161 at the distal portion 102 of the antenna 152. In some examples, the cap 161 includes a cap base 163 and a cap tip 165, which is adjacent to the cap base 163 and is at the distal end of the cap base 163. In some examples, the cap tip 165 is a tissue piercing trocar tip. The outer conductor 131 has a distal boundary 133 adjacent to the radiating portion 123 of the antenna 152. The cap 161 has a proximal boundary 164 adjacent to the cap base 163 of the radiating portion 123, which is opposite to the distal boundary 133 of the outer conductor 131. The radiating portion 123 of the antenna 152 includes an exposed portion of the dielectric 141 between the distal boundary 133 of the outer conductor 131 and the proximal boundary 164 of the cap base 163. In some examples, the probe 112 includes a choke 172 that includes a length 171 of the cannula 113 defined between a choke contact 175 and the distal boundary 114 of the cannula 113. The choke contact 175 electrically connects the cannula 113 to the outer conductor 131. For example, the choke contact 175 can be a welded connection. The choke 172 further includes a dielectric 116 between the cannula 113 and the outer conductor 131. The dielectric 116 can be a polymer, or in an alternative example, the dielectric can be an air gap. The choke 172 is designed as a quarter wave reflector and acts as a barrier to prevent microwave energy from traveling back along the coaxial cable 151.

[0040] The ablation probe 112 includes a shield portion 115 surrounding and coaxial with the antenna 152. The radiation window 119 is aligned with the radiating portion 123 of the antenna 152. During the ablation process, microwave energy propagates in a direction 141, with the center conductor 121 and the outer conductor 131 acting as boundary constraints. At the distal end of the coaxial cable, the outer conductor 131 is removed so that the microwave energy can be radiated into the patient's tissue to cause heating.

[0041] Antenna parameters

[0042] The arm length, radiating portion length, and cap length can each affect the resonant frequency of the antenna. As used herein, the term "length" refers to the distance measured along or parallel to the longitudinal axis of the ablation probe. Still referring to Figure 1, arm 135 is a portion of probe 112 wherein center conductor 121 is surrounded by dielectric 141, which is surrounded by outer conductor 131, and wherein outer conductor 131 is surrounded by radiating window 119. Arm 135 has an arm length a defined between distal boundary 114 of cannula 113 and distal boundary 133 of outer conductor 131. Choke 172 has a choke length 171 defined between choke contact 175 and distal boundary 114 of cannula 113. Radiating portion 123 has a radiating portion length r defined between distal boundary 133 of outer conductor 131 and proximal boundary 164 of cap 161. Cap 161 has a cap length C defined between proximal boundary 164 of cap 161 and probe distal end 180. Proximal boundary 164 of cap 161 is also a proximal boundary of cap base 163. The cap base 163 has a length Cb extending from its proximal boundary 164 to the proximal boundary of the cap tip 165. The cap tip 165 has a length Ct extending from the distal end of the cap base 163 to the probe distal end 180. The sum of Cb and Ct is the cap length C. The arm length overlapping the inner conductor and the cap length are parameters that can be varied to change the length of the radiating portion and thereby change the resonant frequency of the antenna 152.

[0043] Go to Figure 2 , graph 200 shows how the resonant frequency of an antenna may change when the dimensions of a particular structure of the antenna change. Graph 200 shows the antenna reflection coefficient |S plotted against frequency (gigahertz) 11 |(dB). A decrease in the reflection coefficient indicates that more energy at that particular frequency will be transmitted to the tissue. Graph 200 is from the article A Minimally Invasive Antenna for Microwave Ablation Therapies: Design, Performances, and Experimental Assessment by Marta Cavagnaro et al. Figure 5(a), IEEE Transactions on Biomedical Engineering, Vol. 58, No. 4, April 2011, at 949, 954, which is incorporated herein by reference in its entirety. The antenna reflection coefficient was experimentally determined in the protein. Reference numeral 201 shows the main resonant frequency of an example of a microwave antenna in a first configuration, wherein the downward peak at about 2.25 GHz represents the main resonant frequency of the antenna configuration. For a total length of 27 mm, the parameters of the first configuration have a choke length of 10 mm, an arm length of 6 mm, a radiating portion length of 1 mm, a cap base length of 5 mm, and a cap tip length of 5 mm. Reference numeral 202 shows the reduction in the resonant frequency of different probes, wherein the radiating portion length of the antenna is increased by 1 mm relative to the first configuration, while the other parameters remain unchanged. Reference numeral 203 shows the increase in the resonant frequency of the third probe, wherein the length of the arm is reduced by 1 mm relative to the first configuration, and reference numeral 204 shows the reduction in the resonant frequency of the fourth probe relative to the original configuration when the length of the arm is increased by 1 mm compared to the first configuration.

[0044] Figure 3 A second graph 300 is shown illustrating the change in resonant frequency of a single configuration of a microwave antenna as the temperature of the patient tissue surrounding the probe increases. Graph 300 also shows the antenna reflection coefficient |S plotted against frequency (GHz). 11 |(dB). Graph 300 is from Erin Coleback and Erdem Topsakal, Ultra-Wideband Microwave Ablation Therapy (UMAT), IEEE MTT-S International Microwave Symposium Digest (2013), which is hereby incorporated by reference in its entirety. Curve 301 shows the primary resonant frequency of the antenna when the surrounding patient tissue is at a temperature of 15°C. Curve 302 shows the increase in the primary resonant frequency of the same antenna when the surrounding patient tissue is at a temperature of 98°C. Figure 3 In the example of , at 15°C, the resonant frequency of the antenna matches the liver tissue at about 2.45 GHz, with 97.5% of the energy transmitted to the tissue and 2.5% reflected. However, at 98.9°C, the resonant frequency of the antenna shifts up to about 2.8 GHz, and only a small portion (about 20% of the energy) is transmitted to the tissue.

[0045] As in Figure 2 and Figure 3As shown in the graph shown in , the resonant frequency of a microwave ablation antenna depends on both the temperature and the size of the antenna's structure. The resonant frequency also depends on the mass of the patient's tissue. When the parameters of the antenna are fixed, the antenna has a higher radiation amplitude at the antenna's resonant frequency. Since the dielectric properties of the tissue change when the tissue is heated to different temperatures, a fixed antenna can only match the tissue's resonant frequency at a given frequency and temperature. A fixed antenna loses efficiency as the tissue heats up.

[0046] Changes in tissue temperature due to heating during the ablation process cause the resonant frequency of the antenna to change, which results in a mismatch between the antenna resonant frequency and the desired operating frequency (915 MHz or 2.45 GHz). The technology herein describes an antenna design with variable antenna parameters. This variable parameter antenna has a wider range of resonant frequencies; although the radiation amplitude of the disclosed variable parameter antenna is reduced relative to the fixed parameter antenna, the resonant frequency of the variable parameter antenna is consistent with the operating frequency (915 MHz or 2.45 GHz) over a wider range of temperatures, so it can effectively radiate microwave energy into the tissue. This is more suitable for different tissue ablation situations and produces better ablation performance.

[0047] The disclosed antenna with variable parameters acts as multiple antennas connected in parallel, each antenna having a different resonant frequency. The antenna with variable parameters has a portion of the antenna whose resonant frequency is at the operating frequency (915 MHz or 2.45 GHz) and transmits energy at a sufficiently high energy amplitude to operate with different tissue types and at different temperatures.

[0048] In various embodiments of the variable length antenna, the length of the radiating portion varies around the circumference of the coaxial cable. For example, the length of the radiating portion can vary between 0.5 mm and 1.5 mm. The antenna behaves as if there are multiple antennas connected in parallel with different resonant frequencies in the range of 2 GHz to 3 GHz. In this way, even when the tissue properties change due to different tissue types and different tissue temperatures, there is always a portion of the antenna that resonates at 2.45 GHz. As will be discussed below, the variable length parameter can be discrete or continuous.

[0049] Microwave Ablation System

[0050] Figure 4401 is a schematic diagram of a microwave ablation system according to some examples. System 401 includes a microwave ablation control unit 403, which includes a microwave energy source 405 that delivers microwave energy to an ablation probe 411. Microwave ablation control unit 403 also includes: a controller 407, which can be a microprocessor that controls the microwave energy source; a user input 402; and a display 404, allowing a physician or other medical professional to monitor and interact with the control unit 403.

[0051] An available microwave ablation generator is the Sairem GMS solid-state generator operating at 200W and 2450MHz manufactured by Sairem of Naylor, France. Alternatively, the Emblation Microwave MSYS245 medical system operating at 100W and 2450MHz manufactured by Emblation Microwave Ltd. of Scotland, UK can be used. These commercial systems and any combination can be used to implement the system described herein.

[0052] Microwave Ablation Probe

[0053] The microwave ablation probe includes a probe body 412 having a radiation window 419 at a distal portion 431 of the ablation probe 411. The elongated probe body 412 may include a cannula 413, which is arranged to have various lengths. The length of the probe body 412 is much greater than its diameter. For example, the length may be 10 times or more of the diameter, 50 times or more of the diameter, 100 times or more of the diameter, or 200 times or more of the diameter. The length may be at least 5 cm or at least 10 cm.

[0054] The probe 411 has a cap tip 415 at a distal portion 431 of the probe 411, which is configured to be inserted into the patient tissue 423. In some examples, the cap tip 415 has a tissue piercing tip configured to percutaneously enter the patient tissue 423. The ablation probe 411 has a shielding portion 417 that prevents microwave energy from entering the patient tissue along the proximal portion 435 of the probe body 412 and a radiation window 419 that is transparent to microwave energy, thereby allowing microwave energy to be transmitted into the patient tissue 423 to form a lesion 421. The radiation window 419 is at least partially transparent to electromagnetic radiation emitted at a frequency of approximately 300 megahertz to 300 gigahertz in the microwave range of the electromagnetic spectrum. The length of the radiation window 419 is based on the specific antenna used in the microwave ablation probe 411. In some examples, the length of the radiation window 419 is at least about 7 mm, at least about 10 mm, or at least about 13 mm. In some examples, the length is at most about 30 mm or at most about 20 mm. In one example, the length is about 15 mm.

[0055] Variable arm length and radial section length

[0056] Figures 5 to 7 is a side view of a variable length antenna according to some examples. Figures 8 to 10 Shows Figures 5 to 7 An expanded cylindrical view of the variable length antenna in FIG. For illustration purposes, Figures 5 to 7 A side view of the distal portion of the coaxial cable antenna and the cap extending beyond the cannula is shown in . The distal portion of the coaxial cable is shown from the distal end to boundary 513 where the coaxial cable meets the cannula distal end or the end of the choke segment. Figures 5 to 7 The cannula and dielectric material that will surround the coaxial cable in the probe have been omitted so that the dimensions of the outer conductor, cap, and radiating portion can be described. Figures 5 to 7 It is not visible in the side view of the , as it is behind the dielectric material in the radiation window section. Figures 5 to 7 In the examples of the embodiment, the cap length (which includes the cap base length and the cap tip length) remains constant. In these examples, the arm length and the radiating portion length are variable due to the change of the distal boundary of the outer conductor.

[0057] exist Figure 5 In the embodiment, the change in antenna shape is a rectangular stepped shape, where adjacent discrete sections of the outer conductor are at different distances from the distal end. Figure 6 In the case of , the change in antenna shape is a sinusoidal wave shape. Figure 7 In some examples, the change in antenna shape is a sawtooth shape. These shapes can be formed, for example, by laser cutting or die cutting the outer conductor. In some examples, the outer conductor of the antenna is copper, and chemical etching is used with a mask to form the variable antenna shape.

[0058] exist Figure 5 In, the coaxial antenna 501 includes an outer conductor 503 having a distal boundary 505. An arm 504 extends from an end 513 of the cannula to the distal boundary 505 of the outer conductor 503. The proximal boundary of the arm 504 is the end 513 of the cannula. The arm proximal boundary is the axial position of the distal end of the cannula on the outer conductor 503. The cap 511 includes a cap base 515 and a cap tip 517. The cap base 515 has a proximal boundary 516. The radiating portion 521 is defined between the distal boundary 505 of the outer conductor 503 and the proximal boundary 516 of the cap base 515. As described herein, the cap 511 has a cap length 551 defined between the probe distal end 531 and the cap proximal boundary 516. In Figure 5 In the example of FIG. 5 , the cap proximal boundary 516 has a constant uniform distance from the probe distal end 531 . The outer conductor distal boundary 505 includes a plurality of discrete segments at different distances from the probe distal end 531 . Figure 8 Shows Figure 5 An expanded cylindrical view of an example of Figure 8 504, a repeating staircase pattern of the distal boundary 505 is disposed around the circumference of the coaxial antenna 501. The distal boundary of the arm 504 is the distal boundary 505 of the outer conductor 503. The distal boundary 505 of the outer conductor has a first distance 553 from the probe distal end 531, which is defined between the probe distal end 531 and a first portion 506 of the outer conductor distal boundary 505. The distal boundary 505 of the outer conductor has a second distance 555 from the probe distal end 531, which is defined between the probe distal end 531 and a second portion 507 of the outer conductor distal boundary 505. The outer conductor distal boundary 505 has a third distance 557, which is defined between the probe distal end 531 and a third portion 508 of the outer conductor distal boundary 505. The difference between the distances 553, 555, and 557 forms the distal boundary 505 having a staircase shape. Arm 504 has a variable length as measured between distal boundary 505 of arm 504 and arm proximal boundary 513. Radiating portion 521 has a different length at each of different portions 506, 507, and 508 of the distal boundary. Each of portions 506, 507, and 508 forms a different resonant frequency of antenna 501.

[0059] Figure 6 A coaxial antenna 601 having a probe distal end 531 and a cap 511 including a cap base 515 and a cap tip 517 are shown. A proximal boundary 516 of the cap 511 maintains a constant consistent distance from the probe distal end 531. An arm 604 of the antenna 601 includes a continuously variable distal boundary 605. The distal boundary 605 has a first length 653 from the probe distal end 531, which is defined between the probe distal end 531 and a first portion 607 of the distal boundary 605. The distal boundary 605 has a second length 655 from the probe distal end 531, which is defined between the probe distal end 531 and a second portion 608 of the distal boundary 605. Figure 6 In the example of FIG. 5 , the distal boundary 605 has a continuously variable length relative to the probe distal end 531 rather than being in discrete segments of varying lengths. In other words, Figure 6 The example of provides a continuously variable length of arm 604. Arm 604 has a variable length as measured between arm distal boundary 605 and arm proximal boundary 513. Fig. 9 Shows Figure 6 The distal boundary 605 has a sinusoidal pattern between the distal boundary portions 607 and 608. The radiating portion 621 has a different length at each of the different portions of the distal boundary 605. The sinusoidal shape of the distal boundary 605 creates different resonant frequencies for the antenna 601.

[0060] Figure 7A coaxial antenna 701 having a probe distal end 531 and a cap 511 including a cap base 515 and a cap tip 517 are shown. A proximal boundary 516 of the cap 511 maintains a constant consistent distance from the probe distal end 531. An arm 704 of the antenna 701 includes a distal boundary 705 that is continuously variable in its length and distance from the distal end 531. The distal boundary 705 has a first length 753 from the probe distal end 531, which is defined between the probe distal end 531 and a first portion 707 of the distal boundary 705. The distal boundary 705 has a second length 755 from the probe distal end 531, which is defined between the probe distal end 531 and a second portion 708 of the distal boundary 705. Figure 7 In the example of FIG. 7 , the distal boundary 705 of the arm 704 also has a variable length relative to the proximal boundary 513 of the arm. Fig.10 Shows Figure 7 The distal boundary 705 forms a sawtooth pattern between the distal boundary portions 707 and 708. The radiating portion 721 has a different length at each of the different portions of the distal boundary 705.

[0061] Variable cap length and radiating section length

[0062] Figures 11 to 13 An alternative example of an antenna having a portion having a different size than an adjacent portion is shown. For illustration purposes, Figures 11 to 13 Only the coaxial cable antenna and cap are shown at the distal end of the proximal boundary 1113 of the arm where the cannula ends, similar to Figures 5 to 7 The part shown. Figures 11 to 13 In the example of , the arm length and the cap tip length remain constant, while the radiating portion length and the cap base length are both variable. Since the cap base length is variable, the cap length is also variable.

[0063] exist Fig.11, a coaxial antenna 1101 includes an outer conductor 1103 having a distal boundary 1105. The outer conductor 1103 has a distal boundary 1105 having a constant length 1151 between the distal boundary 1105 and the probe distal end 1131. In addition, the arm length of the antenna 1101 between the proximal boundary 1113 of the arm and the distal boundary 1105 of the arm remains constant. The cap base 1115 has a proximal boundary 1116 that provides a variable cap base length. A radiating portion 1121 is defined between the distal boundary 1105 of the outer conductor 1103 and the proximal boundary 1116 of the cap base 1115. The variable cap base length allows the radiating portion 1121 to have a variable length. The cap base length includes a first length 1153, which is defined between the probe distal end 1131 and a first portion 1181 of the cap base proximal boundary. The cap base length includes a second length 1155 defined between the probe distal end 1131 and a second portion 1182 of the cap base proximal boundary. The cap base length includes a third length 1157 defined between the probe distal end 1131 and a third portion 1183 of the cap base proximal boundary. The difference between the proximal boundary portions 1181, 1182, and 1183 of the respective lengths forms a proximal boundary 1116 of the cap base 1115 having a stepped shape. The radiating portion 1121 has a different length at each of the different portions 1181, 1182, and 1183 of the proximal boundary. Each of the portions 1181, 1182, and 1183 forms a different resonant frequency of the antenna 1101.

[0064] Fig.12 The antenna 1201 is shown with a cap base 1215 having a sinusoidal proximal boundary 1216. The sinusoidal proximal boundary 1216 includes a first cap length 1253 between a first portion 1281 of the proximal boundary and the probe distal end 1131, and a second length 1255 between the probe distal end 1131 and a second portion 1282 of the proximal boundary. Between the first portion 1281 and the second portion 1282, the proximal boundary 1216 is continuously variable, thereby providing a continuously variable cap length. The variable cap base length enables the radiating portion 1221 to have a variable length.

[0065] Fig.13 An antenna 1301 including an outer conductor 1303 and a cap base 1315 having a sawtooth proximal boundary 1316 is shown. The sawtooth proximal boundary 1316 forms a first cap length 1353 between the probe distal end 1131 and a first portion 1381 of the proximal boundary, and a second cap length 1355 between the probe distal end 1131 and a second portion 1382 of the proximal boundary. The variable cap base length enables the radiating portion 1321 to have a variable length. The rectangular shape of the proximal boundary 1316 forms a continuously variable cap length, thereby forming a variety of different resonant frequencies of the antenna 1301.

[0066] Variable arm length, cap length and radiating section length

[0067] Figures 14 to 16 is a schematic diagram of a variable length antenna according to some examples. For illustrative purposes, Figures 14 to 16 Only the coaxial cable antenna and cap are shown. For illustration purposes, Figures 14 to 16 Only the coaxial cable antenna and cap are shown at the distal end of the proximal boundary 1113 of the arm where the cannula ends, similar to Figures 5 to 7 and Figures 11 to 13 The part shown. Figures 14 to 16 In the example of , the arm length, the radiating portion length, and the cap length each include a portion having a different length compared to the distal end of the probe and compared to the adjacent portion. Figures 14 to 16 In an example of the present invention, the cap includes a cap base and a cap tip. The cap tip has a constant length, and the cap base has a variable length.

[0068] exist Fig.14 , a coaxial antenna 1401 includes an outer conductor 1403 defining an arm 1404. The outer conductor 1403 has a distal boundary 1405 having different segments 1406, 1407, and 1408 each located at a different length from a probe distal end 1431. A cap 1411 includes a cap base 1415 and a cap tip 1417. Additionally, the cap base 1415 has a proximal boundary 1416 consisting of different segments 1481, 1482, 1483 each having a different length from the probe distal end 1431. A radiating portion 1421 has a variable length defined between the distal boundary 1405 of the outer conductor 1403 and the proximal boundary 1416 of the cap base 1415. The distal boundary 1405 of the outer conductor 1403 and the proximal boundary 1416 of the cap base 1415 form the variable length of the radiating portion 1421. The minimum length of the radiating portion 1421 is located between the distal boundary portion 1407 of the arm 1404 and the proximal boundary portion 1482 of the cap base 1415. The maximum length of the radiating portion 1421 is located between the distal boundary portion 1408 of the arm 1404 and the proximal boundary portion 1483 of the cap base 1415. The variable distal boundary 1405 forms a variable arm length, wherein the distance of the outer conductor distal boundary from the probe distal end 1431 varies. The variable proximal boundary 1416 forms a variable cap length, wherein the distance of the cap base proximal boundary 1416 from the probe distal end 1431 varies. These variable lengths of the arm 1404, the radiating portion 1421, and the cap 1411 form a series of different resonant frequencies of the antenna 1401.

[0069] Fig.23 is a partially cut-away perspective view of antenna 2301 for a microwave ablation probe. Antenna 2301 is similar to antenna 1401 in that both the arm length and the cap length vary in stepped segments. Fig.14 Compared to antenna 1401, antenna 2301 has different sizes and proportions of the stepped segments. Fig.23 The perspective view provides additional insight into the structure of the antenna having variable sizes of arms and cap base. Fig.23 The cannula is not shown.

[0070] Antenna 2301 has a variable arm length and a variable cap length, and therefore a variable radiating portion length. Antenna 2301 is a coaxial electrical antenna having a center conductor 2302 and an outer conductor 2303. Dielectric material 2306 separates center conductor 2302 from outer conductor 2303. Outer conductor 2303 forms arm 2304. Outer conductor 2303 has a distal boundary 2305 that varies in distance from a probe distal end 2331. Antenna 2301 further includes a cap base 2315 having a proximal boundary 2316 that has a variable distance from the probe distal end 2331. Variable proximal boundary 2316 provides a variable length to cap 2311, which includes a cap tip 2317 and cap base 2315. Radiating portion 2321 is defined between distal boundary 2305 and proximal boundary 2316.

[0071] exist Fig.15 , a coaxial antenna 1501 includes an outer conductor 1403 defining an arm 1504. The arm 1504 has a sinusoidal distal boundary 1505. The coaxial antenna 1501 further includes a cap base 1515 having a sinusoidal proximal boundary 1516. The antenna 1501 also includes a cap tip 1517. The distal boundary 1505 of the arm 1504 includes a first distal boundary portion 1507 and a second distal boundary portion 1508. The proximal boundary 1516 of the cap base 1515 includes a first proximal boundary portion 1581 and a second proximal boundary portion 1582. The distal boundary 1505 and the proximal boundary 1516 form a variable length of a radiating portion 1521. The radiating portion 1521 has a minimum length between the first proximal portion 1581 of the cap base 1515 and the first distal portion 1507 of the arm 1504. Radiating portion 1521 has a maximum length between second proximal portion 1582 of cap base 1515 and second distal portion 1508 of arm 1504. Variable distal boundary 1505 forms a variable arm length, wherein the distance of the outer conductor distal boundary from the probe distal end 1431 varies. Variable proximal boundary 1516 forms a variable cap length, wherein the distance of the cap proximal boundary from the probe distal end 1431 varies. These variable lengths of arm 1504, radiating portion 1521, and cap form a series of different resonant frequencies for antenna 1501.

[0072] exist Fig.16, the coaxial antenna 1601 includes an outer conductor 1403 defining an arm 1604. The arm 1604 has a sawtooth distal boundary 1605. The coaxial antenna 1601 further includes a cap 1611 having a cap base 1615 and a cap tip 1617. The cap base 1615 has a sawtooth proximal boundary 1616. The distal boundary 1605 of the arm 1604 includes a first distal boundary portion 1607 and a second distal boundary portion 1608. The proximal boundary 1616 of the cap base 1615 includes a first proximal boundary portion 1681 and a second proximal boundary portion 1682. The distal boundary 1605 and the proximal boundary 1616 form a variable length of a radiating portion 1621. The radiating portion 1621 has a minimum length between the first proximal portion 1681 of the cap base 1615 and the first distal portion 1607 of the arm 1604. Radiating portion 1621 has a maximum length between second proximal portion 1682 of cap base 1615 and second distal portion 1608 of arm 1604. Variable distal boundary 1605 forms a variable arm length, wherein the outer conductor distal boundary varies in distance from probe distal end 1431. Variable proximal boundary 1616 forms a variable cap length, wherein the cap proximal boundary varies in distance from probe distal end 1431. These variable lengths of arm 1604, radiating portion 1621, and cap 1611 form a range of different resonant frequencies for antenna 1601.

[0073] Alternative Antenna Types

[0074] Figures 17 to 21 Cross-sectional views are shown of different coaxial microwave antenna types that may be used to form variable length antennas in accordance with the techniques disclosed herein. Figures 17 to 21 A distal portion of a coaxial cable forming part of each antenna is shown, the coaxial cable including a center conductor, an outer conductor, and an insulating layer between the inner and outer conductors.

[0075] exist Fig.17 , microwave antenna 1701 is a slot antenna having a center conductor 1702 and an outer conductor 1703. In some examples, a distal boundary 1705 of the outer conductor 1703 can be configured to have a variable distance from the distal end of the microwave ablation probe. In some examples, a proximal boundary 1716 of the cap base 1715 can be configured to have a variable distance from the distal end of the microwave ablation probe. In some examples, both the distal boundary 1705 and the proximal boundary 1716 can be configured to have a variable distance from the distal end of the microwave ablation probe. These variable lengths allow the section of the radiating portion 1721 located between the distal boundary 1705 and the proximal boundary 1716 to have a variable width, thereby providing the antenna 1701 with a range of different resonant frequencies.

[0076] exist Fig.18In FIG. 1 , the microwave antenna 1801 has a central conductor 1802 and an outer conductor 1803. Fig.18 In the example of , microwave antenna 1801 is a monopole antenna. Distal boundary 1805 of outer conductor 1803 can be configured to have a variable distance from the end of the microwave ablation probe, thereby providing antenna 1801 with a variable arm length and providing antenna 1801 with a range of different resonant frequencies.

[0077] exist Fig.19 , microwave antenna 1901 is a dipole antenna having a center conductor 1902 and an outer conductor 1903. Antenna 1901 is further provided with a cap 1915. The proximal boundary 1916 of the cap base, the distal boundary 1905 of the outer conductor 1903, or both can be provided with variable lengths from the distal end of the microwave ablation probe. These variable lengths allow the section of the radiating portion 1921 located between the distal boundary 1905 and the proximal boundary 1916 to have a variable width, thereby providing a range of different resonant frequencies to the antenna 1901.

[0078] exist Fig. 20 , the microwave antenna 2001 is a three-axis antenna having a center conductor 2002 and an outer conductor 2003. The three-axis antenna 2001 further has an outer sleeve including a shielding portion 2071. The distal boundary 2005 of the outer conductor 2003 can be provided with a variable length from the distal end of the probe. Alternatively or in addition, the distal boundary 2075 of the outer shielding portion 2071 can be provided with a variable length from the distal end of the probe. The distal boundary 2005 of the outer conductor 2003 determines the length of the radiating portion 2021. The variable distal boundary provides the antenna 2001 with a series of different resonant frequencies.

[0079] exist Fig.21 , the microwave antenna 2101 is an antenna with a choke having a coaxial cable, which has a center conductor 2102, an outer conductor 2103, and a choke 2131. The microwave antenna 2101 further includes a cap base 2115. The cap base 2115 may be provided with a proximal boundary 2116 having a variable distance from the distal end of the probe. The radiating portion 2121 of the antenna 2101 has a variable length determined between the choke 2131 and the proximal boundary 2116 of the cap base 2115. The variable proximal boundary 2116 provides the microwave antenna 2101 with a series of different resonant frequencies.

[0080] Variable choke length and choke contacts

[0081] Fig. 22 22 is a side cross-sectional view showing an alternative example of a microwave ablation probe having a range of resonant frequencies. The probe 2211 has a coaxial antenna 2201 including an arm 2204 and a cap 2214. The cap 2214 includes a cap base 2215 and a cap tip 2217. Fig. 22In the example of the present invention, the cap base 2215 has a constant proximal boundary 2216, and the arm 2204 has a variable distal boundary 2205. The radiating portion 2221 has a variable length that varies based on the distal boundary 2205 of the arm 2204. The probe 2211 further includes a shielding portion 2212, which may include a cannula 2213. The cannula 2213 is shown from a side view and extends from the proximal portion of the probe to the distal boundary 2241 of the cannula 2213. The distal boundary 2241 of the cannula 2213 can have a variable distance from the probe distal end 2231. The ablation probe 2211 further includes a choke contact 2265, wherein the cannula 2213 is electrically connected to the outer conductor below. The choke length 2266 is defined between the choke contact 2265 and the distal boundary 2241 of the cannula 2213. In some examples, the choke length 2266 remains constant, wherein the contour of the choke contact 2265 follows the contour of the distal boundary 2241, such as Fig. 22 In an alternative example, the choke contact 2265 has a constant consistent distance from the probe distal end 2231. In other alternative examples, the cap 2214 can have a varying border.

[0082] Cooling Antenna Example

[0083] Fig.24 24 is a cross-sectional view of an irrigated and cooled microwave ablation probe according to some examples. The probe 2411 includes a shielding portion 2414, which includes a cannula 2413. The probe 2411 also includes a coaxial cable 2451 and a liner 2461. The probe body 2412 has a proximal portion 2402 and a distal portion 2403. The coaxial cable 2451 has an inner conductor 2432, an outer conductor 2431, and an insulator 2433 that electrically isolates the inner conductor 2432 from the outer conductor 2431. The antenna 2452 includes a radiating portion 2453 that is aligned with the radiation window 2419 of the probe body 2412.

[0084] A cooled fluid is provided along a flushing path 2471. The flushing path 2471 includes an inlet path 2491 that receives the cooling fluid from an external portion of the probe 2411, and an outlet path 2492 that directs the fluid away from the probe body 2412 and into a cooling fluid reservoir outside the probe. In some examples, the fluid can be collected in a separate waste reservoir. The cooling fluid cools the coaxial cable 2451 and the probe body 2412. The outer conductor 2431 has a distal boundary 2405 that can have a variable distance from the probe distal end 2462. The cap base 2415 has a proximal boundary 2416 that can have a variable distance from the probe distal end 2462. The radiating portion 2453 has a length defined between the distal boundary 2405 of the outer conductor 2431 and the proximal boundary 2416 of the cap base 2415. The radiating portion 2453 can have a variable length. The variable parameters of antenna 2452 allow probe 2411 to have a range of different resonant frequencies.

[0085] The liner 2461 can be made of an electrically insulating material, such as a polymer having a sufficiently high melting temperature to withstand the heat generated in the system. Some example materials include fluoropolymers or polyamides. The polyamide tubing can have a wall thickness of about 0.001 inches (0.025 mm), less than 0.001 inches (0.025 mm), at least about 0.001 inches (0.025 mm), or at least about 0.001 inches (0.025 mm) and at most about 0.002 inches (0.051 mm). The polymer tubing can have a wall thickness of about 0.003 inches (0.076 mm), at least about 0.003 inches (0.076 mm), or at least about 0.003 inches (0.076 mm) and at most about 0.004 inches (0.102 mm).

[0086] In some examples, the inner diameter of liner 2461 is less than about 0.005 inches (0.13 mm) larger than the outer diameter of coaxial cable 2451. In some examples, the inner diameter of cannula 2413 is at least 0.001 inches (0.025 mm) larger than the outer diameter of liner 2461 and less than 0.005 inches (0.13 mm) larger than the outer diameter of liner 2461.

[0087] In some examples, the flow rate of cooling fluid through flushing path 2471 can be between about 10 ml per minute and 90 ml per minute. In some examples, the flow rate can be between about 30 ml per minute and 50 ml per minute.

[0088] Microwave ablation method

[0089] A microwave ablation method for a microwave ablation probe is provided, the microwave ablation probe having an antenna having a variable length parameter. The ablation probe includes a probe body having a shielding portion, a radiation window, and a cap having a cap tip. In some examples, a choke is provided. The probe further includes a coaxial cable antenna having an outer conductor, a center conductor, and a dielectric disposed between the center conductor and the outer conductor. The antenna has a radiating portion, the radiating portion including a center conductor surrounded by a dielectric, wherein there is no outer conductor. The probe has a choke length and an arm length, a radiating portion length, a cap base length, a cap tip length, and a cap length, the cap length being defined as the cap base length plus the cap tip length. At least one of the arm length, the radiating portion length, and the cap length is variable around the circumference of the antenna. Around the circumference of the antenna, different parameter lengths provide the ablation probe with the ability to have a wide-band resonant frequency.

[0090] The method includes inserting a microwave ablation probe into patient tissue. The method further includes ablating the patient tissue by delivering microwave energy to the distal end of a microwave antenna via a coaxial cable. The microwave energy is emitted from a radiating portion of the antenna into the patient tissue. The patient tissue has a first temperature prior to ablation. At least a first portion of the variable length antenna has a resonant frequency at a desired operating frequency for the ablation process, for example, 945 MHz or 2.45 GHz. As the ablation process proceeds, the temperature of the patient tissue and the antenna increases, causing the resonant frequency to change. A second portion of the variable length antenna has a resonant frequency at a desired operating frequency for the ablation process. At an increased temperature, the first portion of the variable length antenna has a resonant frequency that is different from the desired operating frequency for the process.

[0091] Material

[0092] The cannula described herein can be made of a metal material. In some examples, the cannula is a metal tube, such as a brass tube or a stainless steel hypodermic tube (hypotube). In an alternative example, the cannula can be a polymer tube constructed of a material such as PEBA (polyether block amide), polyimide, polyether ether ketone (PEEK) or polytetrafluoroethylene (PTFE). If the cannula is constructed of a polymer, a separate metal structure can be provided to act as a choke inside the cannula, the choke including a choke contact point with an outer conductor and a choke length tube or foil attached to the choke contact point. In one example, the cannula has an inner diameter of about 0.033 inches (0.84mm), an outer diameter of about 0.039 inches (0.99mm) and a wall thickness of about 0.006 inches (0.15mm). In some examples, the cannula has an outer diameter of 0.13 inches (3.4mm) or less. In some examples, the outer diameter of the cannula is at least about 18 gauge (1.02 mm), at least about 17 gauge (1.15 mm), or at least about 16 gauge (1.29 mm). In some examples, the outer diameter of the cannula 113 is at most about 12 gauge (2.01 mm), at most about 13 gauge (1.83 mm), or at most about 14 gauge (1.63 mm). It will be appreciated that other sizes are possible for the cannula 113. In some examples, the cannula provides structural integrity to the probe body.

[0093] In some examples, the radiation window is an extended tubular member forming the surface of the probe. In some examples, the radiation window can be constructed of fluoropolymers, polyurethanes, polyether block amides (PEBA), polypropylene, polyethylene, polyamides (nylons), polyimides, polyetherimides (PEI), polysulfones, and polyetheretherketones (PEEK). In some examples, the radiation window can include aluminum oxide. In some examples, the radiation window is a dielectric layer between a metal cannula and an outer conductor, and the material of the radiation window extends between the inner diameter of the cannula and the outer diameter of the coaxial cable at the proximal end of the radiation window portion.

[0094] The coaxial cable forming the antenna may be a coaxial cable having an outer diameter of at least about 0.5 mm, at least about 0.7 mm, at most about 2 mm, at most about 5 mm, in the range of about 0.5 mm to about 5 mm, or in the range of about 0.7 mm to about 2 mm. The cable may be a coaxial cable having an outer diameter of about 0.864 mm, which is commercially available from Micro-Coax (Carlisle Interconnect Technologies, Inc.) of Scottsdale, Arizona, as part number UT-034.

[0095] The cap can be constructed of a metal such as brass or stainless steel. In some examples, the cap can be constructed of a ceramic material. In some examples, the cap has a sharp trocar tip that has sufficient structural integrity to pierce tissue, thereby allowing the ablation probe to be inserted into the tissue to be ablated. If the cap is made of a metal material, the length of the metal can be varied to provide a variable length for the antenna.

[0096] It should be noted that, as used in this specification and the appended claims, the singular includes the plural, unless the context clearly indicates otherwise. It should also be noted that the term "or" is generally used in a sense that includes "and / or" unless the context clearly indicates otherwise. It should also be noted that, as used in this specification and the appended claims, the phrase "configured" describes a system, device or other structure that is constructed or configured to perform a specific task or adopt a specific configuration. The phrase "configured" can be used interchangeably with other similar phrases such as "arranged and configured", "constructed and arranged", "constructed", "manufactured and arranged", etc.

[0097] All publications and patent applications cited in this specification are herein incorporated by reference in their entirety.

[0098] The disclosed technology has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications can be made while remaining within the spirit and scope of the present invention.

Claims

1. A microwave ablation probe (112; 411; 2211; 2411), comprising: A probe body (412; 2412) comprising a shielding portion (115; 417; 2212; 2414) and a radiation window (119; 419; 2419) at least partially transparent to microwave energy; The coaxial cable (151; 2451) in the probe body (412; 2412) comprises: Center conductor (121; 2432), a dielectric material (141; 2433) surrounding a center conductor of the cable, and an outer conductor (131; 2431), the outer conductor (131; 2431) having an outer conductor distal boundary, wherein the center conductor (121; 2432) comprises a radiating portion extending beyond a distal boundary (133; 505; 1105; 1405; 1505; 1605; 1705; 1905; 2005; 2405) of the outer conductor (131; 2431), wherein the radiating portion is configured to emit microwave energy, wherein the radiating portion is aligned with the radiation window (119; 419; 2419); and a cap (161; 511; 1411; 1611; 1915; 2214), the cap (161; 511; 1411; 1611; 1915; 2214) being located at a distal end of the probe, the cap (161; 511; 1411; 1611; 1915; 2214) comprising a cap proximal boundary (164; 516; 1116; 1216; 1316; 1416; 1516; 1616; 1716; 2116; 2416); Wherein, the length of the radiating portion varies around the circumference of the coaxial cable, and the radiating portion further comprises: a first portion having a first length, the first portion configured to transmit microwave energy at a first resonant frequency; and A second portion has a second length, the second portion configured to transmit microwave energy at a second resonant frequency different from the first resonant frequency.

2. The probe according to claim 1, wherein The outer conductor distal boundary has a variable distance from the probe distal end.

3. The probe according to claim 1, wherein The cap includes a metallic material, and a proximal boundary of the cap has a varying distance from a distal end of the probe.

4. The probe according to claim 1, wherein The outer conductor distal boundary and the cap proximal boundary are located at varying distances from the probe distal end.

5. The probe according to claim 1, wherein The outer conductor distal end boundary is at a uniform distance from the probe distal end.

6. The probe according to claim 1, wherein The cap proximal edge is located at a uniform distance from the distal end of the probe.

7. The probe according to any one of claims 1 to 6, wherein The shielding portion of the probe body includes a metal cannula.

8. The probe of claim 7, further comprising a choke, the choke comprising: a choke contact between the metal insert and the outer conductor; as well as A choke length extends between the choke contact and a distal end of the metal cannula.

9. The probe according to claim 8, wherein The choke contact or the distal end of the cannula is located at a varying distance from the distal end of the probe.

10. The probe according to any one of claims 1 to 6, wherein The cap further includes a cap tip configured to pierce tissue at the cap distal end.

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