ADJUSTABLE TUNING OF A DIELECTRICALLY LOADED LOOP ANTENNA
A microwave antenna assembly is disclosed. The antenna assembly includes an elongated member defining a longitudinal axis and having proximal and distal ends. The antenna assembly also includes an outer conductor and an inner conductor each disposed within the elongated member and extending along the longitudinal axis. A portion of the inner conductor is deployable relative to the outer conductor such that the antenna assembly may transition from a first configuration to a second configuration. The antenna assembly also includes an expandable sheath at least partially disposed about a distal portion of the inner conductor and defining at one or more lumens configured to couple to a supply of dielectric material used to regulate the expansion of the expandable sheath.
This application is a continuation application of U.S. patent application Ser. No. 14/281,344 filed on May 19, 2014, which is a continuation application of U.S. patent application Ser. No. 12/826,897 filed on Jun. 30, 2010, now U.S. Pat. No. 8,740,893, the entire contents of each of which are incorporated herein by reference.
BACKGROUND1. Technical Field
The present disclosure relates generally to microwave antennas. More particularly, the present disclosure is directed to flexible loop antenna having a variable dielectric loading.
2. Background of Related Art
Treatment of certain diseases requires destruction of malignant tissue growths (e.g., tumors). It is known that tumor cells denature at elevated temperatures that are slightly lower than temperatures injurious to surrounding healthy cells. Therefore, known treatment methods, such as hyperthermia therapy, heat tumor cells to temperatures above 41° C., while maintaining adjacent healthy cells at lower temperatures to avoid irreversible cell damage. Such methods involve applying electromagnetic radiation to heat tissue and include ablation and coagulation of tissue. In particular, microwave energy is used to coagulate and/or ablate tissue to denature or kill the cancerous cells.
Microwave energy is applied via microwave ablation antennas that penetrate tissue to reach tumors. There are several types of microwave antennas, such as monopole and dipole, in which microwave energy radiates perpendicularly from the axis of the conductor. A monopole antenna includes a single, elongated microwave conductor whereas a dipole antenna includes two conductors. In a dipole antenna, the conductors may be in a coaxial configuration including an inner conductor and an outer conductor separated by a dielectric portion. More specifically, dipole microwave antennas may have a long, thin inner conductor that extends along a longitudinal axis of the antenna and is surrounded by an outer conductor. In certain variations, a portion or portions of the outer conductor may be selectively removed to provide more effective outward radiation of energy. This type of microwave antenna construction is typically referred to as a “leaky waveguide” or “leaky coaxial” antenna.
SUMMARYAccording to one embodiment of the present disclosure, a microwave antenna assembly is disclosed. The antenna assembly includes an elongated member defining a longitudinal axis and having proximal and distal ends. The antenna assembly also includes an outer conductor and an inner conductor each disposed within the elongated member and extending along the longitudinal axis. A portion of the inner conductor is deployable relative to the outer conductor such that the antenna assembly may transition from a first configuration to a second configuration. The antenna assembly also includes an expandable sheath at least partially disposed about a distal portion of the inner conductor and defining at least one lumen configured to couple to a supply of dielectric material used to selectively expand the sheath.
According to another embodiment of the present disclosure, a microwave ablation system is disclosed. The system includes an antenna assembly having an elongated member defining a longitudinal axis and having proximal and distal ends. The antenna assembly also includes an outer conductor and an inner conductor each disposed within the elongated member and extending along the longitudinal axis. A portion of the inner conductor is deployable relative to the outer conductor such that the antenna assembly may transition from a first configuration to a second configuration. The antenna assembly also includes an expandable sheath at least partially disposed about a distal portion of the inner conductor and defining at least one lumen configured to receive a dielectric material. The system includes a fill source coupled to the lumen and configured to regulate the amount of the dielectric material within the lumen to control the expansion of the expandable sheath.
A method for performing microwave ablation is also contemplated by the present disclosure. The method includes the initial step of inserting an antenna assembly into a tissue volume. The antenna assembly includes an outer conductor, an inner conductor and an expandable sheath at least partially disposed about a distal portion of the inner conductor and defining at least one lumen. The method also includes the steps of deploying at least a portion of the inner conductor from the outer conductor such that the antenna assembly may transition from a first configuration to a second configuration and regulating an amount of a dielectric material supplied to the at least one lumen to control expansion of the expandable sheath. The method further includes the steps of energizing the antenna assembly to ablate the tissue volume and withdrawing the dielectric material from the at least one lumen to deflate the expandable sheath.
The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which:
Particular embodiments of the present disclosure are described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. In the drawings and in the description that follows, the term “proximal,” as is traditional, will refer to the end of the apparatus that is closest to the clinician, while the term “distal” will refer to the end that is furthest from the clinician.
Referring to
The system 10 also includes a fill source 40, e.g., an electric motor pump, a peristaltic pump or the like, as a mechanism for circulating a dielectric material “M,” such as gas (e.g., nitrogen, air, etc.) or liquid (e.g., saline, water, etc.) through the antenna assembly 100, as described below. Antenna assembly 100 may further include a pusher or deployment assembly 50 that includes a deployment knob 52 operatively engaged with or coupled to the antenna assembly 100, as described in further detail below.
Referring now to
Feedline 30 may range in length from about 1 foot (0.3048 m) to about 15 feet (4.572 m), or greater depending on a particular application. In one embodiment, the feedline 30 may be formed from a coaxial, semi-rigid or flexible cable having a wire with a 0.047″ outer diameter rated for 50 Ohms. As depicted in
Referring now to
In non-deployed configuration, the elongated member 114 conceals a distal portion 102a (
At least a portion of the inner conductor 102, i.e. distal portion 102a, is deployable relative to distal portion 104a of the outer conductor, such that the antenna assembly 100 may transition from a first, non-deployed configuration (
Movement from the first configuration to the second configuration may be facilitated through the use of any suitable mechanism, such as, for example, a deployment assembly 50 (
In one embodiment, as seen in
With continued reference to
The proximal end 130 of sheath 116 may be located at any suitable location along the length of distal portion 102a of the inner conductor, dependent upon the desired volume of lumen 128. Although depicted as substantially incisive, the present disclosure contemplates that distal-most tip 134 may be substantially arcuate, duckbilled, or any other such configuration suitable for facilitating the entry of the microwave tissue treatment device into the tissue of a patient.
Sheath 116 may be formed of any suitable biocompatible, impermeable material capable of retaining gas and/or fluid therein, including and not limited to PTFE and tetrafluorethylene-perfluorpropylene (FEP). The present disclosure contemplates that sheath 116 may be either substantially rigid, or substantially non-rigid in character.
Referring back to
In one embodiment, the inner conductor may be formed from a 0.022″ Nitinol wire and the sheath 116 may be formed from PTFE sleeve having an inner diameter of about 0.022″ and an outer diameter of about 0.050.″ The sheath 116 may be inflated using the fill source 40 to adjust the dielectric properties along the length of the inner conductor 102. The sheath 116 may be in a deflated state during the deployment of inner conductor 102 within the tissue. Once inner conductor 102 has been desirably positioned, sheath 106 may be filled with the desired dielectric material “M,” until the sheath 116 has inflated sufficiently about the inner conductor 102. The size of inflated sheath 116 may be varied according to the desired radiative effects, the length of deployed inner conductor 102, as well as the type of tissue.
In one embodiment, the lumen 128 may be filled with any dielectric material “M” having a relatively low dielectric permittivity as compared to the material forming the sheath 116. In another embodiment, the lumen 128 may be filled with air, since air has a dielectric constant of 1. A lower dielectric permittivity within the lumen 128 allows for microwave energy to travel through the gap “G” easier than through the sheath 116. Therefore, positioning of the inner conductor 102 in contact with the sheath 116 (e.g., off-center) and curving the antenna assembly 100 such that the gap “G” is facing toward the center of the curved antenna assembly 100 directs the microwave energy toward the center of the looped antenna assembly 100. In particular, this configuration of the gap “G” directs the microwave energy into the looped antenna assembly 100 more efficiently along the inside thereof as opposed to the outside. In other words, this configuration maximizes matching toward the center of the curved inner conductor 102, allowing for better microwave transmission, thereby maximizing ablation within the inner conductor 102. Conversely, this configuration minimizes effects outside the curved inner conductor 102, since the dielectric material “M” of the sheath 116 limits microwave transmission and provides for poor impedance matching between the tissue and the antenna assembly 100.
The cross-sectional shape of the inner conductors 302 and 402 provide for an enhanced dielectric gap “G.” In particular, the shape of the inner conductors 302 and 402 in combination with the enhanced dielectric gaps “G” provide for directed deposition of microwave energy toward the center of the curved antenna assemblies 300 and 400. In other words, these configurations direct the microwave energy more efficiently along the inside thereof as opposed to the outside.
The sheath 516 at least partially surrounds the distal portion 502a of the inner conductor 502 and defines a lumen 528 thereabout. The sheath 516 may be fixedly, releasably, or slidably connected to distal portion 502a in any suitable manner including, but not being limited to, welding or adhering, as would be appreciated by one skilled in the art. The sheath 516 may be formed of any suitable biocompatible, impermeable material capable of retaining gas and/or fluid therein, including, but not limited to, PTFE and tetrafluorethylene-perfluorpropylene (FEP).
The sheath 516 is formed from a flexible expandable material, such that during inflation, the sheath 516 expands to accommodate the increased volume of the dielectric material “M.” The lumen 528 is in fluid communication with the fill source 40 such that one or more dielectric materials (e.g., fluids or gases) may be circulated therethrough, which are used to inflate the sheath 516.
Suitable dielectric fluids include, but are not limited to, water, saline, liquid chlorodifluoromethane, or any suitable perfluorocarbon fluid, such as Fluorinert®, distributed commercially by Minnesota Mining and Manufacturing Company (3M™), St. Paul, Minn., USA. Suitable dielectric gases include air, nitrogen, nitrous oxide, carbon dioxide and the like. In yet another variation, a combination of liquids and/or gases may be utilized. The selection of dielectric mixtures may be used to provide for better matching microwave energy to different tissue types and sizes.
In addition to the varying dielectric properties of the dielectric compounds, the flexible nature of the sheath 516 also provides for dynamic impedance matching by varying the amount of dielectric material “M” filling the lumen 528. The varying amount of the dielectric material “M” affects the bulk impedance of the antenna assembly 500 based on: (1) the amount of the dielectric material “M” present and (2) the dimension of the sheath 516, which is also based on the amount of the dielectric material “M” present therein.
Based on the dielectric constant of the material, the amount of the dielectric material “M” may be used to increase or decrease the dielectric permittivity of the antenna assembly 500. More specifically, if a dielectric material “M” having a dielectric constant of 2 or more is used then increasing the amount of the material within the lumen 528 reduces the effectiveness of microwave transmission. If a dielectric material “M” having a dielectric constant of 1 or less is used then increasing the amount of such material within the lumen 528 increases the effectiveness of microwave transmission.
The dielectric material “M” may also be used to vary dielectric permittivity of the sheath 516. As shown in
The core 529 provides structural integrity to the antenna assembly 500 by securing the inner conductor 512 at the center of the sheath 516. In addition, the dielectric material of the core 529 provides additional dielectric matching capabilities to the antenna assembly 500. The porous and/or fibrous structure of the core 529 allows the thickness of the sheath 516 to be varied as discussed above with respect to
Under higher pressure, as illustrated in
The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Various modifications and variations can be made without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.
Claims
1-19. (canceled)
20. A microwave antenna assembly comprising:
- a feedline including an inner conductor, an outer conductor, and an insulator disposed between the inner and outer conductors, the inner conductor configured to at least partially encircle target tissue; and
- an expandable sheath defining a lumen configured to receive a dielectric material to expand the expandable sheath, at least a portion of the inner conductor disposed off-center within the lumen, the inner conductor in contact with a first portion of the expandable sheath and defining a dielectric gap between the inner conductor and a second portion of the expandable sheath, the dielectric gap configured to face the target tissue when the inner conductor at least partially encircles target tissue.
21. The microwave antenna assembly according to claim 20, wherein the expandable sheath is disposed about a distal portion of the inner conductor.
22. The microwave antenna assembly according to claim 20, wherein a distal end of the expandable sheath is disposed proximal to a distal end of the inner conductor.
23. The microwave antenna assembly according to claim 20, wherein the expandable sheath is formed of a material selected from the group consisting of polytetrafluoroethylene and tetrafluorethylene-perfluorpropylene.
24. A microwave ablation system, comprising:
- a microwave antenna assembly including: a feedline including an inner conductor, an outer conductor, and an insulator disposed between the inner and outer conductors; an elongated member disposed about the feedline, the inner conductor configured to deploy from a distal end portion of the elongated member to at least partially encircle target tissue; and an expandable sheath defining a lumen, the inner conductor disposed off-center within the lumen to define a dielectric gap between the inner conductor and the expandable sheath, the dielectric gap configured to face the target tissue when the inner conductor is deployed from the distal end portion of the elongated member; and
- a fill source coupled to the lumen and configured to deliver dielectric material to the lumen.
25. The microwave ablation system according to claim 24, wherein the fill source includes a pump configured to circulate the dielectric material through the lumen.
26. The microwave ablation system according to claim 24, where at least a portion of the inner conductor is in contact with the expandable sheath.
27. The microwave ablation system according to claim 24, wherein the expandable sheath is disposed about a distal portion of the inner conductor.
28. The microwave ablation system according to claim 24, wherein a distal end of the expandable sheath is disposed proximal to a distal end of the inner conductor.
29. The microwave ablation system according to claim 24, wherein the expandable sheath is formed of a material selected from the group consisting of polytetrafluoroethylene and tetrafluorethylene-perfluorpropylene.
30. A method for performing microwave ablation, the method comprising:
- inserting a microwave antenna assembly into tissue, the microwave antenna assembly including an expandable sheath defining a lumen and an inner conductor disposed off-center within the lumen;
- at least partially encircling target tissue with the inner conductor;
- delivering a dielectric material to the lumen to expand the expandable sheath; and
- energizing the microwave antenna assembly to ablate the at least partially encircled target tissue.
31. A method according to claim 30, further comprising withdrawing the dielectric material from the lumen to contract the expandable sheath.
32. The method according to claim 30, wherein delivering the dielectric material to the lumen creates a dielectric gap between the inner conductor and the expandable sheath.
Type: Application
Filed: Jan 23, 2017
Publication Date: May 18, 2017
Inventors: BRIAN SHIU (SUNNYVALE, CA), KENLYN S. BONN (LAKEWOOD, CO), MANI N. PRAKASH (BOULDER, CO), TAO NGUYEN (REDWOOD CITY, CA)
Application Number: 15/412,188