Patent Description:
One general aspect includes a microwave ablation probe including a probe body, a coaxial cable within the probe body, and a cap. The probe body includes a shielded portion and a radiation window that is at least partially transparent to microwave energy. The coaxial cable includes a center conductor, a dielectric material surrounding the center conductor of the cable, and an outer conductor having an outer conductor distal boundary. The center conductor includes a radiating portion that extends beyond a distal boundary of the outer conductor, where the radiating portion is configured for emission of microwave energy, where the radiating portion is aligned with the radiation window. The cap is located at a probe distal end and includes a cap proximal boundary, where the outer conductor distal boundary or the cap proximal boundary varies in its distance from the probe distal end.

Implementations may include one or more of the following features. The probe where the outer conductor distal boundary varies in distance from the probe distal end. The probe where the cap includes a metallic material and the cap proximal boundary varies in distance from the probe distal end. The probe where the outer conductor distal boundary and the cap proximal boundary varies in distance from the probe distal end. The probe where the outer conductor distal boundary or the cap proximal boundary includes a plurality of discrete sections, where adjacent discrete sections are at different distances from the probe distal end. The probe where the outer conductor distal boundary or the cap proximal boundary includes a wave shape. The probe where the outer conductor distal boundary or the cap proximal boundary includes a saw tooth shape. The probe where the outer conductor distal boundary is a uniform distance from the probe distal end. The probe where the cap proximal boundary is uniform in distance from the distal end of the probe. The probe further including a choke. The probe where the shielded portion of the probe body includes a metal cannula. The probe further including a dielectric layer in between the metal cannula and the outer conductor. The probe further including a choke including: a choke contact between the metal cannula and the outer conductor, and a choke length extending between the choke contact and a distal end of the metal cannula. The probe where the choke contact or the distal end of the cannula varies in its distance from the probe distal end. The probe where the radiation window includes a portion of the dielectric material of the cable surrounding the radiating portion of the center conductor. The probe where the cap further includes a cap tip configured to pierce tissue at a cap distal end. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

One general aspect includes a 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 located at a probe distal end, and a choke. The probe body includes a shielded 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 surrounding the center conductor of the cable, and an outer conductor having an outer conductor distal boundary. The center conductor includes a radiating portion that extends beyond a distal boundary of the outer conductor, where the radiating portion is configured for emission of microwave energy, where the radiating portion is aligned with the radiation window. The cap includes a cap tip configured to pierce tissue at a cap distal end, and a cap proximal boundary. The choke includes a choke contact between the metal cannula and the outer conductor, and a choke length extending between the choke contact and a distal end of the metal cannula. The outer conductor distal boundary or the cap proximal boundary varies in its distance from the probe distal end. The outer conductor distal boundary may vary in distance from the probe distal end. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

One general aspect includes a method of microwave ablation including providing a microwave ablation probe and delivering microwave energy to a radiating portion of the probe. The probe includes a probe body including a shielded 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 including a center conductor, a dielectric material surrounding the center conductor of the cable, and an outer conductor having an outer conductor distal boundary. The center conductor includes a radiating portion that extends beyond a distal boundary of the outer conductor, where the radiating portion is configured for emission of microwave energy, where the radiating portion is aligned with the radiation window. The probe includes a cap located at a probe distal end, the cap including a cap tip configured to pierce tissue at a cap distal end and a cap proximal boundary. The outer conductor distal boundary or the cap proximal boundary varies in its distance from the probe distal end. The probe may produce microwave energy at two or more resonant frequencies. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

This summary is an overview of some of the teachings of the present application and is not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details are found in the detailed description and appended claims. Other aspects will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which is not to be taken in a limiting sense. The scope herein is defined by the appended claims.

Some of the figures are schematic in nature and are not drawn to scale. Certain features are shown larger than their scale and certain features are omitted from some views for ease of illustration. While embodiments are susceptible to various modifications and alternative forms, specifics thereof have been shown by way of example and drawings, and will be described in detail. It should be understood, however, that the scope herein is not limited to the particular aspects described.

The present disclosure provides a wide band microwave tissue ablation probe with variable length antenna parameters. By use of the term "variable" herein, it is meant that different portions of the antenna structure have different dimensions compared to neighboring portions.

Microwave antennas have a resonant frequency. The resonant frequency of the antenna affects the efficiency of the system, because when the resonant frequency is correctly tuned to the surrounding tissue, a high ratio of energy is transmitted into the tissue versus the amount of energy that is reflected. When the resonant frequency is not tuned, more energy is reflected, leading to less of the energy being transmitted into patient tissue.

Different portions of the antenna with different dimensions allow the antenna to be capable of more than one resonant frequency, such as two, three, four or more resonant frequencies. The antenna has multiple portions, each having a different resonant frequency. The single antenna acts as though it were multiple antennas in parallel.

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

A number of factors affect the resonant frequency of the probe. One factor is the length of the various portions of the antenna. Changes in these lengths can significantly affect the resonant frequency. The choke length, the arm length, the radiating portion length, the cap base length, and the cap tip length can each affect the resonant frequency. Each of these lengths are described in more detail below. <FIG> is a cross-sectional view of a microwave ablation probe demonstrating the parameters that can be changed to affect the resonant frequency of the probe.

Turning to <FIG>, the probe <NUM> has a distal portion <NUM> and a proximal portion <NUM>. As used herein, the words proximal and distal express a relationship between two different elements. An element that is designated as being proximal is positioned closer to the external portion of the system, i.e., a portion that does not enter a patient's body. An element that is designated as being distal is positioned closer to the insertion end of the system. In some examples, the probe <NUM> includes a cannula <NUM> having a cannula distal boundary <NUM> adjacent to a radiation window <NUM>. The cannula <NUM> makes up part of a shielded portion <NUM> of the probe <NUM>. At the distal portion <NUM> of the probe <NUM> is a cap tip <NUM>. The radiation window <NUM> extends between the distal boundary <NUM> of the shielded portion <NUM> and the proximal boundary <NUM> of the cap tip <NUM>.

The microwave antenna <NUM> includes a coaxial cable <NUM> with a center conductor <NUM>, an outer conductor <NUM> coaxially surrounding the center conductor <NUM>, and a dielectric <NUM> surrounding the center conductor <NUM> and separating the center conductor <NUM> from the outer conductor <NUM>. Some examples of the technology also include a cap <NUM> at the distal portion <NUM> of the antenna <NUM>. In some examples, the cap <NUM> includes a cap base <NUM> and a cap tip <NUM> adjoining the cap base <NUM> and distal to the cap base <NUM>. In some examples, the cap tip <NUM> is a tissue-piercing trocar tip. The outer conductor <NUM> has a distal boundary <NUM> that abuts the radiating portion <NUM> of the antenna <NUM>. The cap <NUM> has a proximal boundary <NUM> of the cap base <NUM> that abuts the radiating portion <NUM> opposite the distal boundary <NUM> of the outer conductor <NUM>. The radiating portion <NUM> of the antenna <NUM> comprises an exposed portion of the dielectric <NUM> between the distal boundary <NUM> of the outer conductor <NUM> and the proximal boundary <NUM> of the cap base <NUM>. In some examples, the probe <NUM> includes a choke <NUM> that includes a length <NUM> of the cannula <NUM> defined between a choke contact <NUM> and the distal boundary <NUM> of the cannula <NUM>. The choke contact <NUM> electrically connects the cannula <NUM> to the outer conductor <NUM>. The choke contact <NUM> can be a soldered connection, for example. The choke <NUM> further includes a dielectric <NUM> between the cannula <NUM> and the outer conductor <NUM>. The dielectric <NUM> can be a polymer, or in alternative examples, the dielectric can be an air gap. The choke <NUM> is designed as a quarter wave reflector and acts as a barrier, preventing microwave energy from travelling back along the coaxial cable <NUM>.

The ablation probe <NUM> comprises the shielded portion <NUM> surrounding and coaxial with the antenna <NUM>. The radiation window <NUM> is aligned with the radiating portion <NUM> of the antenna <NUM>. During an ablation procedure, microwave energy propagates in the dielectric <NUM>, with the center conductor <NUM> and the outer conductor <NUM> as boundary constraints. At the distal end of the coaxial cable, the outer conductor <NUM> is removed so that the microwave energy can radiate into patient tissue to cause heating.

The arm length, the radiating portion length, and the cap length can each affect the resonant frequency of the antenna. As used herein, the word length refers to a distance measured along or parallel to a longitudinal axis of the ablation probe. Still referring to <FIG>, the arm <NUM> is a portion of the probe <NUM> in which the center conductor <NUM> is surrounded by the dielectric <NUM>, which is surrounded by the outer conductor <NUM>, and where the outer conductor <NUM> is surrounded by the radiation window <NUM>. The arm <NUM> has an arm length a defined between the distal boundary <NUM> of the cannula <NUM> and the distal boundary <NUM> of the outer conductor <NUM>. The choke <NUM> has a choke length <NUM> defined between the choke contact <NUM> and the distal boundary <NUM> of the cannula <NUM>. The radiating portion <NUM> has a radiating portion r length defined between the distal boundary <NUM> of the outer conductor <NUM> and the proximal boundary <NUM> of the cap <NUM>. The cap <NUM> has a cap length C defined between the proximal boundary <NUM> of the cap <NUM> and the probe distal end <NUM>. The proximal boundary <NUM> of the cap <NUM> is also the proximal boundary of the cap base <NUM>. The cap base <NUM> has a length Cb extending from its proximal boundary <NUM> to a proximal boundary of the cap tip <NUM>. The cap tip <NUM> has a length Ct extending from a distal end of the cap base <NUM> to the probe distal end <NUM>. The sum of Cb and Ct is the cap length C. The arm length and the cap length overlap with the inner conductor are parameters that can be varied to change the length of the radiating portion, and thereby change the resonant frequency of the antenna <NUM>.

Turning to <FIG>, a graph <NUM> shows how the resonant frequency of the antenna can change when the dimensions of particular structures of the antenna are changed. The graph <NUM> shows the antenna reflection coefficient, |S<NUM>| in decibels plotted against frequency in Gigahertz. A decrease in the reflection coefficient indicates that more energy at that particular frequency is transmitted into tissue. The graph <NUM> is FIG. <NUM>(a) from the article, <NPL>. The antenna reflection coefficient was determined experimentally within egg white. Reference numeral <NUM> shows the prominent resonant frequency of one example of a microwave antenna in a first configuration, where the downward spike at around <NUM> represents the prominent resonant frequency for that antenna configuration. The parameters of the first configuration have a choke length of <NUM> millimeters, an arm length of <NUM> millimeters, a radiating portion length of <NUM> millimeter, a cap base length of <NUM> millimeters, and a cap tip length of <NUM> millimeters, for an overall length of <NUM> millimeters. Reference numeral <NUM> shows a decrease in the resonant frequency of a different probe in which the radiating portion length of the antenna was increased by <NUM> millimeter versus the first configuration, while the other parameters remain constant. Reference numeral <NUM> shows an increase in resonant frequency of a third probe in which the length of the arm is decreased by <NUM> millimeter versus the first configuration, and reference numeral <NUM> shows a decrease in resonant frequency versus the original configuration for a fourth probe when the length of the arm is increased by <NUM> millimeter compared to the first configuration.

<FIG> shows a second graph <NUM> demonstrating the change in resonant frequency for a single configuration of a microwave antenna as the temperature of patient tissue surrounding the probe increases. The graph <NUM> also shows the antenna reflection coefficient, |S<NUM>| in decibels plotted against frequency in Gigahertz. The graph <NUM> is from <NPL>). Plot <NUM> shows a prominent resonance frequency for the antenna when the surrounding patient tissue is at temperature of <NUM> degrees Celsius. Plot <NUM> shows an increase in the prominent resonance frequency for the same antenna when the surrounding patient tissue is at a temperature of <NUM> degrees Celsius. In the example of <FIG> degrees Celsius, the resonant frequency of the antenna matches the liver tissue at about <NUM> with <NUM>% energy transmitted to tissue and <NUM>% reflected. However, at <NUM> degrees Celsius, the resonant frequency of the antenna shifts up to about <NUM> and only a small portion, about <NUM> percent of the energy, is transmitted into tissue.

As demonstrated in the graphs shown in <FIG> and <FIG>, the resonant frequency of a microwave ablation antenna is both temperature dependent and dependent on the dimensions of structures of the antenna. The resonant frequency is also dependent on the qualities of the patient tissue. When the parameters of the antenna are fixed, the antenna has a higher amplitude of radiation at the resonant frequency of the antenna. Since the dielectric properties of the tissue change when the tissue is heated to different temperature, a fixed antenna can only match the tissue resonant frequency at a given frequency and temperature. A fixed antenna loses efficiency as tissue heats up.

The change in tissue temperature due to heating during the ablation procedure causes the resonant frequency of the antenna to change, which creates a mismatch between the antenna resonant frequency and the desired working frequency (<NUM> or <NUM>). The technology herein describes an antenna design with variable antenna parameters. This variable parameter antenna has a wider range of resonance frequencies; although the amplitude of radiation of the disclosed variable parameter antenna is decreased versus a fixed parameter antenna, the resonant frequency of the variable parameter antenna coincides with the working frequency (<NUM> or <NUM>) over a wider range of temperatures so it can effectively radiate microwave energy into tissue. This is more suitable for different tissue ablation scenarios and results in better ablation performance.

The disclosed antenna with variable parameters acts as multiple antennas each with different resonant frequencies connected in parallel. The antenna with variable parameters has a part of the antenna with a resonant frequency at the working frequency (<NUM> or <NUM>) and transmits the energy with a sufficiently high energy amplitude to work with different tissue types and at different temperatures.

In the various implementations 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 from <NUM> to <NUM>. The antenna behaves as if there were multiple antennas with different resonant frequencies ranging from <NUM> to <NUM> connected in parallel. In this way, there is always a part of the antenna resonant at <NUM> even when the tissue properties change due to different tissue types and different tissue temperatures. As will be discussed below, the variable length parameters can be discrete or continuous.

<FIG> is a schematic view of a microwave ablation system according to some examples. The system <NUM> includes a microwave ablation control unit <NUM>, which includes a microwave energy source <NUM> that delivers microwave energy to an ablation probe <NUM>. The microwave ablation control unit <NUM> also includes a controller <NUM>, which can be a microprocessor that controls the microwave energy source, a user input <NUM>, and a display <NUM>, allowing a physician or other medical professional to monitor and interact with the control unit <NUM>.

An available microwave ablation generator is the Sairem GMS solid state generator, operating at 200W and <NUM>, manufactured by Sairem, of Neyron, France. Alternatively, the Emblation Microwave MSYS245 Medical System, operating at 100W and <NUM>, manufactured by Emblation Microwave, an Emblation Limited Company, of Scotland, UK can be used. These commercial systems and any combination can be used to implement the system described herein.

The microwave ablation probe includes a probe body <NUM> with a radiation window <NUM> at a distal portion <NUM> of the ablation probe <NUM>. The elongate probe body <NUM> can include a cannula <NUM> that is provided in a variety of lengths. The length of the probe body <NUM> is much larger than its diameter. For example, the length may be <NUM> times the diameter or more, <NUM> times the diameter or more, <NUM> times the diameter or more, or <NUM> times the diameter or more. The length may be at least <NUM> centimeters or at least <NUM> centimeters.

The probe <NUM> has a cap tip <NUM> at a distal portion <NUM> of the probe <NUM> that is configured to be inserted into patient tissue <NUM>. In some examples, the cap tip <NUM> has a tissue-piercing tip configured for percutaneous entry into patient tissue <NUM>. The ablation probe <NUM> has a shielded portion <NUM> that prevents microwave energy from entering patient tissue along the proximal portion <NUM> of the probe body <NUM>, and a radiation window <NUM> that is transparent to microwave energy, allowing microwave energy to be transmitted into the patient tissue <NUM> to create the lesion <NUM>. The radiation window <NUM> is at least partially transparent to electromagnetic radiation emitted in the microwave range of the electromagnetic spectrum with a frequency on the order of about <NUM> megahertz to <NUM> gigahertz. The length of the radiation window <NUM> is based on the particular antenna used in the microwave ablation probe <NUM>. In some examples, the length of the radiation window <NUM> is at least about <NUM> millimeters, at least about <NUM> millimeters, or at least about <NUM> millimeters. In some examples, the length is at most about <NUM> millimeters, or at most about <NUM> millimeters. In one example, the length is about <NUM> millimeters.

<FIG> are side views of variable length antennas according to some examples. <FIG> show unwrapped cylinder views of the variable length antennas in <FIG>. For purposes of illustration, a side view of a distal portion of the coaxial cable antenna and the cap that extends beyond a cannula is shown in <FIG>. The distal portion of the coaxial cable is shown from the distal end to the boundary <NUM> where the coaxial cable meets the cannula distal end or end of the choke length. The cannula and dielectric material that will surround the coaxial cable in the probe are omitted from <FIG> so that dimensions of the outer conductor, cap, and radiating portion can be described. The inner conductor of the coaxial cable is not visible in the side views of <FIG> as it is behind the dielectric material of the radiating window portion. In the example of <FIG>, the cap length, including the cap base length and the cap tip length remain constant. The arm length and the radiating portion length are variable in these examples, because of variance of the distal boundary of the outer conductor.

In <FIG>, the variance in antenna shape is a rectangular, stepped shape in which adjacent discrete sections of the outer conductor are at different distances from the probe distal end. In <FIG>, the variance in antenna shape is a sinusoidal wave shape. In <FIG>, the variance in antenna shape is a saw tooth shape. These shapes can be formed, for example, by laser cutting or die cutting of 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.

In <FIG>, a coaxial antenna <NUM> includes an outer conductor <NUM> having a distal boundary <NUM>. An arm <NUM> extends from the end <NUM> of the cannula to the distal boundary <NUM> of the outer conductor <NUM>. The proximal boundary of the arm <NUM> is the end <NUM> of the cannula. The arm proximal boundary is the axial location of the cannula distal end on the outer conductor <NUM>. A cap <NUM> includes a cap base <NUM> and a cap tip <NUM>. The cap base <NUM> has a proximal boundary <NUM>. The radiating portion <NUM> is defined between the distal boundary <NUM> of the outer conductor <NUM> and the proximal boundary <NUM> of the cap base <NUM>. As described herein, the cap <NUM> has a cap length <NUM> defined between the probe distal end <NUM> and the cap proximal boundary <NUM>. In the example of <FIG>, the cap proximal boundary <NUM> has a constant, uniform distance from the probe distal end <NUM>. The outer conductor distal boundary <NUM> comprises a plurality of discrete sections that are at different distances from the probe distal end <NUM>. <FIG> shows an unwrapped cylinder view of the example of <FIG>; as can be seen in <FIG>, a repeating stepped pattern of the distal boundary <NUM> is provided around the circumference of the coaxial antenna <NUM>. The distal boundary of the arm <NUM> is the distal boundary <NUM> of the outer conductor <NUM>. The distal boundary <NUM> of the outer conductor has a first distance <NUM> from the probe distal end <NUM>, defined between the probe distal end <NUM> and a first portion <NUM> of the outer conductor distal boundary <NUM>. The distal boundary <NUM> of the outer conductor has a second distance <NUM> from the probe distal end <NUM>, defined between the probe distal end <NUM> and a second portion <NUM> of the outer conductor distal boundary <NUM>. The outer conductor distal boundary <NUM> has a third distance <NUM> defined between the probe distal end <NUM> and a third portion <NUM> of the outer conductor distal boundary <NUM>. The variations between the distances <NUM>, <NUM>, and <NUM> create a distal boundary <NUM> that has a stepped shape. The arm <NUM> has a variable length, as measured between a distal boundary <NUM> of the arm <NUM> and the arm proximal boundary <NUM>. The radiating portion <NUM> has different lengths at each of the different portions <NUM>, <NUM>, and <NUM> of the distal boundary. Each of the portions <NUM>, <NUM>, and <NUM> create different resonant frequencies for the antenna <NUM>.

<FIG> shows the coaxial antenna <NUM> having a probe distal end <NUM>, and a cap <NUM> comprising a cap base <NUM> and a cap tip <NUM>. The proximal boundary <NUM> of the cap <NUM> remains at a constant, uniform distance from the probe distal end <NUM>. The arm <NUM> of the antenna <NUM> includes a distal boundary <NUM> that is continuously variable. The distal boundary <NUM> has a first length <NUM> from the probe distal end <NUM> defined between the probe distal end <NUM> and a first portion <NUM> of the distal boundary <NUM>. The distal boundary <NUM> has a second length <NUM> from the probe distal end <NUM> defined between the probe distal end <NUM> and a second portion <NUM> of the distal boundary <NUM>. In the example of <FIG>, the distal boundary <NUM> has a continuously variable length in relation to the probe distal end <NUM>, rather than discrete sections at different lengths. Stated differently, the example of <FIG> provides a continuously variable length of arm <NUM>. The arm <NUM> has a variable, as measured between the arm distal boundary <NUM> and the arm proximal boundary <NUM>. <FIG> shows an unwrapped cylindrical view of the example of <FIG>. The distal boundary <NUM> has a sinusoidal pattern between the distal boundary portions <NUM> and <NUM>. The radiating portion <NUM> has different lengths at each of the different portions of the distal boundary <NUM>. The sinusoidal shape of the distal boundary <NUM> creates different resonant frequencies for the antenna <NUM>.

<FIG> shows the coaxial antenna <NUM> having a probe distal end <NUM> and a cap <NUM> comprising a cap base <NUM> and a cap tip <NUM>. The proximal boundary <NUM> of the cap <NUM> remains at a constant, uniform distance from the probe distal end <NUM>. The arm <NUM> of the antenna <NUM> includes a distal boundary <NUM> that is continuously variable in its length and distance from distal end <NUM>. The distal boundary <NUM> has a first length <NUM> from the probe distal end <NUM>, defined between the probe distal end <NUM> and a first portion <NUM> of the distal boundary <NUM>. The distal boundary <NUM> has a second length <NUM> from the probe distal end <NUM>, defined between the probe distal end <NUM> and a second portion <NUM> of the distal boundary <NUM>. In the example of <FIG>, the distal boundary <NUM> of the arm <NUM> also has a variable length in relation to the arm proximal boundary <NUM>. <FIG> shows an unwrapped cylindrical view of the example of <FIG>. The distal boundary <NUM> creates a saw tooth pattern between the distal boundary portions <NUM> and <NUM>. The radiating portion <NUM> has different lengths at each of the different portions of the distal boundary <NUM>.

<FIG> show alternative examples of an antenna having portions with different dimensions from neighboring portions. For purposes of illustration, only the coaxial cable antenna and the cap are shown in <FIG>, distal to the proximal boundary <NUM> of the arm, where the cannula ends, similar to the portion illustrated in <FIG>. In the example of <FIG>, the arm length and cap tip length remain constant, while the radiating portion length and the cap base length are each variable. Because the cap base length is variable, the cap length is also variable.

In <FIG>, coaxial antenna <NUM> includes an outer conductor <NUM> having a distal boundary <NUM>. The outer conductor <NUM> has a distal boundary <NUM> that has a constant length <NUM> between the distal boundary <NUM> and the probe distal end <NUM>. Also, the arm length of the antenna <NUM>, between a proximal boundary <NUM> of the arm and the distal boundary <NUM> of the arm, remains constant. Cap base <NUM> has a proximal boundary <NUM> that provides a variable cap base length. The radiating portion <NUM> is defined between the distal boundary <NUM> of the outer conductor <NUM> and the proximal boundary <NUM> of the cap base <NUM>. The variable cap base length causes the radiating portion <NUM> to have a variable length. The cap base length includes a first length <NUM> defined between the probe distal end <NUM> and a first portion of the cap base proximal boundary <NUM>. The cap base length includes a second length <NUM> defined between the probe distal end <NUM> and a second portion of the cap base proximal boundary <NUM>. The cap base length includes a third length <NUM> defined between the probe distal end <NUM> and a third portion of the cap base proximal boundary <NUM>. The variations between the lengths of proximal boundary portions <NUM>, <NUM>, and <NUM> create a proximal boundary <NUM> of the cap base <NUM> that has a stepped shape. The radiating portion <NUM> has different lengths at each of the different portions <NUM>, <NUM>, and <NUM> of the proximal boundary. Each of the portions <NUM>, <NUM>, and <NUM> create different resonant frequencies for the antenna <NUM>.

<FIG> shows the antenna <NUM> with the cap base <NUM> having a sinusoidal proximal boundary <NUM>. The sinusoidal proximal boundary <NUM> comprises a first cap length <NUM> between a first portion <NUM> of the proximal boundary and the probe distal end <NUM>, and a second length <NUM> between the probe distal end <NUM> and a second portion <NUM> of the proximal boundary. In between the first portion <NUM> and the second portion <NUM>, the proximal boundary <NUM> is continuously variable, providing a continuously variable cap length. The variable cap base length causes the radiating portion <NUM> to have a variable length.

<FIG> shows the antenna <NUM> including an outer conductor <NUM> and with the cap base <NUM> having a saw tooth proximal boundary <NUM>. The saw tooth proximal boundary <NUM> creates a first cap length <NUM> between the probe distal end <NUM> and a first portion of the proximal boundary <NUM>, and a second cap length <NUM> between the probe distal end <NUM> and a second portion of the proximal boundary <NUM>. The variable cap base length causes the radiating portion <NUM> to have a variable length. The saw tooth shape of the proximal boundary <NUM> creates a continuously variable cap length, creating a variety of different resonant frequencies for the antenna <NUM>.

<FIG> are schematic views of variable length antennas according to some examples. For purposes of illustration, only the coaxial cable antenna and the cap are shown in <FIG>. For purposes of illustration, only the coaxial cable antenna and the cap are shown in <FIG>, distal to a proximal boundary <NUM> of the arm, where the cannula ends, similar to the portion illustrated in <FIG> and <FIG>. In the example of <FIG>, the arm length, the radiating portion length, and the cap length each include portions that vary in length compared to the distal end of the probe and compared to neighboring portions. In the example of <FIG>, 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.

In <FIG>, the coaxial antenna <NUM> includes an outer conductor <NUM> that defines an arm <NUM>. The outer conductor <NUM> has a distal boundary <NUM> that has different segments <NUM>, <NUM>, and <NUM> that each is located a different length from the probe distal end <NUM>. The A cap <NUM> includes a cape base <NUM> and a cap tip <NUM>. Additionally, the cap base <NUM> has a proximal boundary <NUM> that is made up of different segments <NUM>, <NUM>, <NUM> that each have different lengths from the probe distal end <NUM>. The radiating portion <NUM> has a variable length that is defined between the distal boundary <NUM> of the outer conductor <NUM> and the proximal boundary <NUM> of the cap base <NUM>. The distal boundary <NUM> of the outer conductor <NUM> and the proximal boundary <NUM> of the cap base <NUM> create a variable length for the radiating portion <NUM>. The minimum length of the radiating portion <NUM> is situated between the distal boundary portion <NUM> of the arm <NUM> and the proximal boundary portion <NUM> of the cap base <NUM>. The maximum length of the radiating portion <NUM> is situated between the distal boundary portion <NUM> of the arm <NUM> and the proximal boundary portion <NUM> of the cap base <NUM>. The variable distal boundary <NUM> creates a variable arm length, where the outer conductor distal boundary varies in distance from the probe distal end <NUM>. The variable proximal boundary <NUM> creates a variable cap length, where the cap base proximal boundary <NUM> varies in distance from the probe distal end <NUM>. These variable lengths of the arm <NUM>, the radiating portion <NUM>, and the cap <NUM> create a range of different resonant frequencies for the antenna <NUM>.

<FIG> is a partially cutaway perspective view of an antenna <NUM> for a microwave ablation probe. Antenna <NUM> is similar to antenna <NUM> because both the arm length and cap length vary in stepped segments. Antenna <NUM> has different dimensions and proportions of the stepped segments compared to antenna <NUM> of <FIG>. The perspective view of <FIG> provides additional insight into the structure of an antenna with variable dimensions for the arm and cap base. A cannula is not shown in <FIG>.

The antenna <NUM> has a variable arm length and a variable cap length, and as a result, a variable radiating portion length. The antenna <NUM> is a coaxial antenna having a center conductor <NUM> and an outer conductor <NUM>. A dielectric material <NUM> separates the center conductor <NUM> and the outer conductor <NUM>. The outer conductor <NUM> forms an arm <NUM>. The outer conductor <NUM> has a distal boundary <NUM> that varies in distance from the probe distal end <NUM>. The antenna <NUM> further includes a cap base <NUM> having a proximal boundary <NUM> that has a variable distance from the probe distal end <NUM>. The variable proximal boundary <NUM> provides the cap <NUM>, which includes a cap tip <NUM> and the cap base <NUM>, with a variable length. A radiating portion <NUM> is defined between the distal boundary <NUM> and the proximal boundary <NUM>.

In <FIG>, the coaxial antenna <NUM> includes the outer conductor <NUM> that defines an arm <NUM>. The arm <NUM> has a sinusoidal distal boundary <NUM>. The coaxial antenna <NUM> further includes a cap base <NUM> that has a sinusoidal proximal boundary <NUM>. The antenna <NUM> also includes a cap tip <NUM>. The distal boundary <NUM> of the arm <NUM> includes a first distal boundary portion <NUM> and a second distal boundary portion <NUM>. The proximal boundary <NUM> of the cap base <NUM> includes a first proximal boundary portion <NUM> and a second proximal boundary portion <NUM>. The distal boundary <NUM> and the proximal boundary <NUM> create a variable length for the radiating portion <NUM>. The radiating portion <NUM> has a minimum length between the first proximal portion <NUM> of the cap base <NUM>, and the first distal portion <NUM> of the arm <NUM>. The radiating portion <NUM> has a maximum length between the second proximal portion <NUM> of the cap base <NUM> and the second distal portion <NUM> of the arm <NUM>. The variable distal boundary <NUM> creates a variable arm length, where the outer conductor distal boundary varies in distance from the probe distal ends <NUM>. The variable proximal boundary <NUM> creates a variable cap length, where the cap proximal boundary varies in distance from the probe distal end <NUM>. These variable lengths of the arm <NUM>, the radiating portion <NUM>, and the cap create a range of different resonant frequencies for the antenna <NUM>.

In <FIG>, the coaxial antenna <NUM> includes the outer conductor <NUM> that defines an arm <NUM>. The arm <NUM> has a saw tooth distal boundary <NUM>. The coaxial antenna <NUM> further includes a cap <NUM> which has a cap base <NUM> and a cap tip <NUM>. The cap base <NUM> has a saw tooth proximal boundary <NUM>. The distal boundary <NUM> of the arm <NUM> includes a first distal boundary portion <NUM> and a second distal boundary portion <NUM>. The proximal boundary <NUM> of the cap base <NUM> includes a first proximal boundary portion <NUM> and a second proximal boundary portion <NUM>. The distal boundary <NUM> and the proximal boundary <NUM> create a variable length for the radiating portion <NUM>. The radiating portion <NUM> has a minimum length between the first proximal portion <NUM> of the cap base <NUM>, and the first distal portion <NUM> of the arm <NUM>. The radiating portion <NUM> has a maximum length between the second proximal portion <NUM> of the cap base <NUM> and the second distal portion <NUM> of the arm <NUM>. The variable distal boundary <NUM> creates a variable arm length, where the outer conductor distal boundary varies in distance from the probe distal ends <NUM>. The variable proximal boundary <NUM> creates a variable cap length, where the cap proximal boundary varies in distance from the probe distal end <NUM>. These variable lengths of the arm <NUM>, the radiating portion <NUM>, and the cap <NUM> create a range of different resonant frequencies for the antenna <NUM>.

<FIG> show cross-sectional drawings of different coaxial microwave antenna types that can be used to create variable length antennas according to the technology disclosed herein. <FIG> show a distal end portion of a coaxial cable that makes up part of each antenna, including a center conductor, an outer conductor, and an insulation layer in between the inner and outer conductor.

In <FIG>, the microwave antenna <NUM> is a slot antenna having a center conductor <NUM> and an outer conductor <NUM>. In some examples, a distal boundary <NUM> of the outer conductor <NUM> can be configured to have a variable distance from the distal end of a microwave ablation probe. In some examples, a proximal boundary <NUM> of a cap base <NUM> can be configured to have a variable distance from the distal end of a microwave ablation probe. In some examples, both the distal boundary <NUM> and the proximal boundary <NUM> can be configured to have a variable distance from the distal end of a microwave ablation probe. These variable lengths allow the length of a radiating portion <NUM> situated between the distal boundary <NUM> and of the proximal boundary <NUM> to have a variable width, providing the antenna <NUM> with a range of different resonant frequencies.

In <FIG>, the microwave antenna <NUM> has a center conductor <NUM> and an outer conductor <NUM>. In the example of <FIG>, the microwave antenna <NUM> is a monopole antenna. A distal boundary <NUM> of the outer conductor <NUM> can be configured to have a variable distance from the end of a microwave ablation probe, providing the antenna <NUM> with a variable arm length, and providing the antenna <NUM> with a range of different resonant frequencies.

In <FIG>, the microwave antenna <NUM> is a dipole antenna with the center conductor <NUM> and an outer conductor <NUM>. The antenna <NUM> is further provided with a cap <NUM>. A proximal boundary <NUM> of the cap base, a distal boundary <NUM> of the outer conductor <NUM>, or both can be provided with variable lengths from the distal end of microwave ablation probe. These variable lengths allow the length of a radiating portion <NUM> situated between the distal boundary <NUM> and the proximal boundary <NUM> to have a variable width, providing the antenna <NUM> with a range of different resonant frequencies.

In <FIG>, a microwave antenna <NUM> is a triaxial antenna with a center conductor <NUM> and an outer conductor <NUM>. The triaxial antenna <NUM> further has an outer sleeve comprising a shielded portion <NUM>. A distal boundary <NUM> of the outer conductor <NUM> can be provided with variable lengths from the probe distal end. Alternatively or in addition, a distal boundary <NUM> of the outer shielded portion <NUM> can be provided with variable lengths from the probe distal end. The distal boundary <NUM> of the outer conductor <NUM> determines the length of the radiating portion <NUM>. The variable distal boundaries provide the antenna <NUM> with a range of different resonant frequencies.

In <FIG>, a microwave antenna <NUM> is a choked antenna with a coaxial cable having a center conductor <NUM>, an outer conductor <NUM>, and a choke <NUM>. The microwave antenna <NUM> further includes a cap base <NUM>. The cap base <NUM> can be provided with a proximal boundary <NUM> that has a variable distance from a probe distal end. The radiating portion <NUM> of the antenna <NUM> has a variable length that is determined between the choke <NUM> and the proximal boundary <NUM> of the cap base <NUM>. The variable proximal boundary <NUM> provides the microwave antenna <NUM> with a range of different resonant frequencies.

<FIG> is a side, cutaway view showing an alternative example of a microwave ablation probe having a range of resonant frequencies. The probe <NUM> has a coaxial antenna <NUM> that includes an arm <NUM> and a cap <NUM>. A cap <NUM> includes a cap base <NUM> and a cap tip <NUM>. In the example of <FIG>, the cap base <NUM> has a constant proximal boundary <NUM>, and the arm <NUM> has a variable distal boundary <NUM>. The radiating portion <NUM> has a variable length that varies based on the distal boundary <NUM> of the arm <NUM>. The probe <NUM> further includes a shielded portion <NUM> that can include a cannula <NUM>. The cannula <NUM> is shown from a side view and extends from a proximal portion of the probe to the distal boundary <NUM> of cannula <NUM>. The distal boundary <NUM> of the cannula <NUM> can have a variable distance from the probe distal end <NUM>. The ablation probe <NUM> further includes a choke contact <NUM> where the cannula <NUM> is electrically connected to the underlying outer conductor. A choke length <NUM> is defined between the choke contact <NUM> and the distal boundary <NUM> of the cannula <NUM>. In some examples, the choke length <NUM> is held constant, where the outline of the choke contact <NUM> follows the outline of the distal boundary <NUM>, as shown in <FIG>. In alternative examples, the choke contact <NUM> can have a constant, uniform distance from the probe distal end <NUM>. In further alternative examples, the cap <NUM> can have a varying boundary.

<FIG> is a cross-sectional view of an irrigation-cooled microwave ablation probe according to some examples. The probe <NUM> includes a shielded portion <NUM> which includes a cannula <NUM>. The probe <NUM> also includes a coaxial cable <NUM> and a liner <NUM>. The probe body <NUM> has a proximal portion <NUM> and a distal portion <NUM>. The coaxial cable <NUM> has an inner conductor <NUM>, an outer conductor <NUM>, and an insulator <NUM> that electrically isolates the inner conductor <NUM> and the outer conductor <NUM>. An antenna <NUM> includes a radiating portion <NUM> that is aligned with the radiation window <NUM> of the probe body <NUM>.

A cooled fluid is provided along an irrigation path <NUM>. The irrigation path <NUM> includes an inlet path <NUM> that receives the cooling fluid from an external portion of the probe <NUM>, and an outlet path <NUM> that channels the fluid out of the probe body <NUM> and to a cooling fluid reservoir external to the probe. In some examples, the fluid can be collected in a separate waste fluid reservoir. The cooling fluid cools the coaxial cable <NUM> and the probe body <NUM>. The outer conductor <NUM> has a distal boundary <NUM> that can have a variable distance from the probe distal end <NUM>. A cap base <NUM> has a proximal boundary <NUM> that can have a variable distance from the probe distal end <NUM>. The radiating portion <NUM> has a length that is defined between the distal boundary <NUM> of the outer conductor <NUM> and the proximal boundary <NUM> of the cap base <NUM>. The radiating portion <NUM> can have a variable length. The variable parameters of the antenna <NUM> allows the probe <NUM> to have a range of different resonant frequencies.

The liner <NUM> can be made of an electrically insulating material such as a polymer with a sufficiently high melt temperature to withstand heat created in the system. Some example materials include fluoropolymers or polyamide. A polyamide tubing can have a wall thickness of about <NUM> inch (<NUM>), less than <NUM> inch (<NUM>), at least about <NUM> inch (<NUM>), or at least about <NUM> (<NUM>) inch and at most about <NUM> inch (<NUM>). A polymer tubing can have a wall thickness of about <NUM> inch (<NUM>), at least about <NUM> inch (<NUM>), or at least about <NUM> inch (<NUM>) and at most about <NUM> inch (<NUM>).

In some examples, the inner diameter of the liner <NUM> is less than about <NUM> (<NUM>) inches greater than the outer diameter of the coaxial cable <NUM>. In some examples, the inner diameter of the cannula <NUM> is at least <NUM> inches (<NUM>) greater than the outer diameter of the liner <NUM>, and less than <NUM> inches (<NUM>) greater than the outer diameter of the liner <NUM>.

In some examples, the flow rate of the cooling fluid through the irrigation path <NUM> can be between about <NUM> per minute and <NUM> per minute. In some examples, the flow rate can be between about <NUM> per minute and <NUM> per minute.

A microwave ablation method is provided for a microwave ablation probe having an antenna with variable length parameters. The ablation probe includes a probe body having a shielded 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 which includes the center conductor surrounded by the dielectric, where the outer conductor is not present. The probe has a choke length, and arm length, a radiating portion length, a cap base length, a cap tip length, and a cap length that is defined as the cap base length plus the cap tip link. At least one of the arm length, the radiating portion length, and the cap length are variable around a circumference of the antenna. Around the circumference of the antenna, the different parameter lengths provide the ablation probe with the ability to have a wide band of resonant frequencies.

The method includes inserting the microwave ablation probe into patient tissue. The method further includes ablating the patient tissue by delivering microwave energy through the coaxial cable to the distal end of the microwave antenna. The microwave energy is emitted from the radiating portion of the antenna into patient tissue. The patient tissue has a first temperature before ablation. At least a first portion of the variable length antenna has a resonant frequency in a desired working frequency for the ablation procedure, for example <NUM> or <NUM>. As the ablation procedure progresses, the patient tissue and the antenna increase in temperature, causing the resonant frequency to change. A second portion of the variable length antenna has a resonant frequency in the desired working frequency for the ablation procedure. At the increased temperature, the first portion of the variable length antenna has a resonant frequency different than the desired working frequency for the procedure.

The cannula of the probes described herein can be made out 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 alternative examples, the cannula can be a polymer tube constructed of materials such as PEBA (polyether block amide), polyimide, polyether ether ketone (PEEK), or polytetrafluoroethylene (PTFE). If the cannula is constructed from a polymer, a separate metallic structure may be provided to serve as a choke, including a choke contact point with the outer conductor and choke length tube or foil attached to the choke contact point, inside the cannula. In one example, the cannula has an inner diameter of about <NUM> inch (<NUM>), an outer diameter of about <NUM> inch (<NUM>), and a wall thickness of about <NUM> inch (<NUM>). In some examples, the cannula has an outer diameter of <NUM> inches (<NUM>) or less. In some examples, the outer diameter of the cannula is at least about <NUM> gauge (<NUM> millimeters), at least about <NUM> gauge (<NUM> millimeters), or at least about <NUM> gauge (<NUM> millimeters). In some examples, the outer diameter of the cannula <NUM> is at most about <NUM> gauge (<NUM> millimeters), at most about <NUM> gauge (<NUM> millimeters), or at most about <NUM> gauge (<NUM> millimeters). It will be appreciated that other dimensions are possible for the cannula <NUM>. In some examples, the cannula provides structural integrity to the probe body.

In some examples, the radiation window is a tubular member that forms an extension of the surface of the probe. In some examples, the radiation window can be constructed from fluoropolymers, urethanes, polyether block amides (PEBA), polypropylene, polyethylene, polyamide (nylon), polyimide, polyetherimide (PEI), polysulfone, and polyetheretherketone (PEEK). In some examples, the radiation window can include alumina. In some examples, the radiation window is a dielectric layer in between the metal cannula and the outer conductor, and the material of the radiation window extends proximal to the radiation window portion, between the inner diameter of the cannula and the outer diameter of the coaxial cable.

The coaxial cable forming the antenna can be a coaxial cable having an outer diameter of at least about <NUM> millimeters, at least about <NUM> millimeters, at most about <NUM> millimeters, at most about <NUM> millimeters, ranging from about <NUM> to about <NUM> millimeters, or ranging from about <NUM> to about <NUM> millimeters. The cable can be a coaxial cable having an outer diameter of about <NUM> millimeters, commercially available as part no. UT-<NUM> from Micro-Coax, a Carlisle Interconnect Technologies Company, of Scottsdale, AZ.

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

It should be noted that, as used in this specification and the appended claims, the singular forms include the plural unless the context clearly dictates otherwise. It should also be noted that the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

Claim 1:
A microwave ablation probe (<NUM>; <NUM>; <NUM>; <NUM>) comprising:
a probe body (<NUM>; <NUM>) comprising a shielded portion (<NUM>; <NUM>; <NUM>; <NUM>) and a radiation window (<NUM>; <NUM>; <NUM>) that is at least partially transparent to microwave energy, wherein the shielded portion of the probe body comprises a metal cannula;
a coaxial cable (<NUM>; <NUM>) within the probe body (<NUM>; <NUM>) comprising:
a center conductor (<NUM>; <NUM>),
a dielectric material (<NUM>; <NUM>) surrounding the center conductor of the cable, and
an outer conductor (<NUM>; <NUM>) having an outer conductor distal boundary,
wherein the center conductor (<NUM>; <NUM>) comprises a radiating portion that extends beyond a distal boundary (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) of the outer conductor (<NUM>; <NUM>), wherein the radiating portion is configured for emission of microwave energy, wherein the radiating portion is aligned with the radiation window (<NUM>; <NUM>; <NUM>);
a cap (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) located at a probe distal end, the cap comprising a cap proximal boundary (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>);
wherein the outer conductor distal boundary (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) or the cap proximal boundary (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>) varies in its distance from the probe distal end; and
a choke comprising:
a choke contact between the metal cannula and the outer conductor, and
a choke length extending between the choke contact and a distal end of the metal cannula, wherein the choke contact varies in its distance from the probe distal end.