Irrigation and cooling structure for microwave ablation tissue probe

Abstract

A microwave ablation probe is disclosed, comprising a probe body, the probe body comprising a shielding portion and a radiation window, the radiation window being at least partially transparent to microwave energy. The shielding portion comprises a cannula, a coaxial cable within the probe body, and an antenna, the antenna comprising a radiation portion for emitting microwave energy at a distal portion of the probe body, wherein the radiation portion is aligned with the radiation window. The probe body defines an irrigation path, the irrigation path being configured to transport a cooling fluid to and from the distal portion of the probe body. At least one wall defining the irrigation path comprises a heat exchange surface, the heat exchange surface having an average radius, wherein the surface area of ​​the heat exchange surface is greater than the surface area of ​​a smooth surface having a radius equal to the average radius.

Description

[0001] This application was filed as a PCT international patent application on December 18, 2019, in the name of Boston Scientific Scimed, Inc., a U.S. national corporation, as the applicant for all country designations and U.S. citizen Hong Cao and U.S. citizen Timothy A. Ostroot as inventors for all countries, and claims priority to U.S. Provisional Application No. 62 / 782,149 filed on December 19, 2018 and claims priority to U.S. Patent Application No. 16 / 717,113 filed on December 17, 2019, the contents of which are hereby incorporated by reference in their entirety. Background Art

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

[0003] One general aspect includes a microwave ablation probe, the microwave ablation probe comprising: a probe body, the probe body including a shielding portion and a radiation window, the radiation window being at least partially transparent to microwave energy, wherein the shielding portion includes a cannula. The microwave ablation probe also includes a coaxial cable within the probe body. The microwave ablation probe also includes an antenna, the antenna including a radiation portion for emitting microwave energy at a distal portion of the probe body, wherein the radiation portion is aligned with the radiation window. The probe body defines an irrigation path, the irrigation path being configured to transport a cooling fluid to and from the distal portion of the probe body, wherein at least one wall defining the irrigation path includes a heat exchange surface. The heat exchange surface has an average radius, wherein a surface area of ​​the heat exchange surface is greater than a surface area of ​​a smooth surface having a radius equal to the average radius.

[0004] Embodiments may include one or more of the following features. The heat exchange surface includes corrugations, undulations, fins, one or more ridges, axial corrugations, spiral corrugations, radial corrugations, spiral ridges, radial ridges, or axial ridges. The heat exchange surface is at different distances from the longitudinal axis of the probe. The heat exchange surface is located on at least a portion of the outer surface of the outer conductor of the cable. The heat exchange surface is located on at least a portion of the inner surface of the cannula. The heat exchange surface includes spiral ridges on at least a portion of the outer surface of the outer conductor of the cable. The heat exchange surface includes spiral ridges on at least a portion of the inner surface of the cannula. The heat exchange surface includes spiral ridges on at least a portion of the outer surface of the outer conductor of the cable, wherein the probe further includes an additional heat exchange surface, the additional heat exchange surface including spiral ridges on at least a portion of the inner surface of the cannula. The heat exchange surface includes axial corrugations on at least a portion of the inner surface of the cannula. The heat exchange surface includes axial corrugations on at least a portion of the outer surface of the outer conductor of the cable. The heat exchange surface comprises axial corrugations on at least a portion of the inner surface of the cannula, wherein the probe further comprises an additional heat exchange surface comprising axial corrugations on at least a portion of the outer surface of the outer conductor of the cable. The probe may further comprise a coolant source configured to deliver the cooling fluid to the flushing path and receive the cooling fluid. The probe may further comprise an inner liner concentric with the cannula and within the cannula, wherein a first segment of the flushing path is defined between an outer surface of the outer conductor and an inner surface of the inner liner, wherein a second segment of the flushing path is defined between an outer surface of the inner liner and an inner surface of the cannula. The first segment of the flushing path is an inlet path, and the second segment of the flushing path is an outlet path. The cannula comprises a cannula wall defining at least one cavity for a flow of cooling fluid.

[0005] One general aspect includes a microwave ablation system, the microwave ablation system including a microwave energy source, a cooling fluid source, and a microwave ablation probe, the probe including: a probe body, the probe body including a shielding portion and a radiation window, the radiation window being at least partially transparent to microwave energy, wherein the shielding portion includes a cannula. The microwave ablation system also includes a coaxial cable within the probe body, the coaxial cable connected to the microwave energy source, the cable including a center conductor, a dielectric material surrounding the center conductor, and an outer conductor, the outer conductor having an outer surface and a distal boundary, wherein the center conductor includes a radiating element 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 microwave ablation system also includes wherein the probe body defines an irrigation path, the irrigation path being configured to transport cooling fluid to and from a distal portion of the probe body, wherein the cooling fluid source is in fluid communication with the irrigation path. The microwave ablation system also includes wherein at least one wall defining the irrigation path includes a heat exchange surface. The microwave ablation system also includes wherein the heat exchange surface has an average radius, wherein a surface area of ​​the heat exchange surface is greater than a surface area of ​​a smooth surface having a radius equal to the average radius.

[0006] Embodiments may include one or more of the following features. The probe further includes a liner concentric with and within the cannula, wherein a first segment of the flushing path is defined between the outer surface of the outer conductor and the inner surface of the liner, wherein a second segment of the flushing path is defined between the outer surface of the liner and the inner surface of the cannula. The probe wherein the first segment of the flushing path is an inlet path and the second segment of the flushing path is an outlet path.

[0007] One general aspect includes a method of microwave ablation, the method comprising providing a microwave ablation probe, the probe comprising a probe body, the probe body comprising a shielding portion and a radiation window, the radiation window being at least partially transparent to microwave energy, wherein the shielding portion comprises a cannula. The microwave ablation probe also comprises a coaxial cable within the probe body. The microwave ablation probe also comprises an antenna electrically connected to the cable and within the probe body, the antenna having a radiation portion at a distal portion of the probe body for emitting microwave energy. The microwave ablation method also comprises wherein the radiation portion is aligned with the radiation window, wherein the probe body defines an irrigation path, the irrigation path being configured to convey a cooling fluid to and from the distal portion of the probe body, wherein at least one wall defining the irrigation path comprises a heat exchange surface, wherein the heat exchange surface has an average radius, and wherein the surface area of ​​the heat exchange surface is greater than the surface area of ​​a smooth surface having a radius equal to the average radius. The microwave ablation method also comprises delivering a cooling fluid to the irrigation path. The microwave ablation method also comprises delivering microwave energy to the antenna via the cable.

[0008] Implementations may include one or more of the following features. The method also includes receiving, at a cooling fluid source, cooling fluid returned from the flushing path. Implementations of the described technology may include hardware, methods or processes, or computer software on a computer accessible medium.

[0009] 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

[0010] Figure 1 is a schematic diagram of a microwave ablation system according to some examples.

[0011] Figure 2 is a cross-sectional view of a microwave ablation probe according to some examples.

[0012] Figure 3 is a cross-sectional view of a microwave ablation probe according to some examples.

[0013] Figure 4 is a cross-sectional view of an alternative example of a microwave ablation probe according to some examples.

[0014] Figure 5 is a cross-sectional view of an alternative example of a microwave ablation probe.

[0015] Figure 6 is a cross-sectional view of an alternative example of a microwave ablation probe according to some examples.

[0016] 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. In contrast, the purpose is to cover modifications, equivalents, and alternatives that fall within the spirit and scope of this article. DETAILED DESCRIPTION

[0017] Various examples of the technology described herein provide a microwave ablation probe and system with irrigation cooling. In one or more examples, the microwave ablation probe uses a coaxial cable antenna having a radiating portion to deliver microwave energy to the tissue. The microwave energy heats the tissue, thereby ablating the tissue. Energy is transmitted from an external microwave energy source through the proximal portion of the microwave ablation probe to the distal portion of the microwave ablation probe, where the energy is transmitted to the patient's tissue. Heating along the proximal portion of the microwave ablation probe can make the ablated lesion have an elongated tail or comet shape along the outside of the probe body. The design features of the disclosed technology can reduce the comet shape of the ablation lesion by including internal liquid cooling in the shaft of the microwave ablation probe. Irrigation can take away heat from both the antenna and the probe shaft to reduce the temperature rise of both the antenna and the patient's tissue. In some examples, a fin structure is provided within the ablation probe to improve the heat exchange between the cooling liquid and the internal components of the ablation probe. This can produce a more spherical lesion.

[0018] In some examples of the disclosed technology, an ablation probe includes a microwave dipole antenna that uses a coaxial cable to transmit microwave energy. A coolant enters the probe body through an inner lumen that contacts the coaxial antenna. The coolant exits the probe body through an outer lumen to carry heat away from an outer cannula that contacts the patient's tissue.

[0019] Without being bound by theory, the basic relationship for heat transfer by convection through physical contact of a coolant with a convection surface is given by Q = hA (T o -T c ), where Q is the amount of heat transferred per unit time, A is the surface area of ​​the convection surface in contact with the coolant, h is the heat transfer coefficient, and T o is the surface temperature of the convective surface, and Tc is the temperature of the coolant.

[0020] The heat transfer coefficient h depends on the flow rate and other factors. An increased flow rate can increase the amount of heat removed. However, a higher flow rate increases the pressure inside the microwave ablation probe, which also increases the mechanical stress on the small structures of the microwave ablation probe.

[0021] Various examples of the disclosed technology provide heat exchange surfaces having surface features that produce a surface area A that is greater than the surface area of ​​a smooth surface. Some examples of the disclosed technology include surface features that cause a cooling fluid to follow a nonlinear path through the body of an ablation probe. Each of these examples increases the surface area A in contact with the cooling fluid. Since A is proportional to Q, the amount of heat transferred from the ablation probe to the cooling fluid per unit time increases. Since Q is the amount of heat transferred per unit time, the more time the coolant remains grounded with the convective surface, the more heat can be removed from the system.

[0022] As will be discussed later with respect to the accompanying drawings, some examples of the disclosed technology provide an enhanced heat exchange surface on the inner surface of the probe cannula. Some examples provide an enhanced heat exchange surface on the outer surface of the coaxial cable antenna. Some examples provide an enhanced heat exchange surface on both the inner surface of the probe cannula and the outer surface of the coaxial cable antenna.

[0023] As used herein, the terms proximal and distal refer to the relationship between two different elements. The element designated as the proximal end is located closer to the external part of the system, that is, the part that does not enter the patient's body. The element designated as the distal end is located closer to the insertion end of the system.

[0024] Microwave Ablation System

[0025] Now referring to the accompanying drawings, Figure 1 1 is a schematic diagram of a microwave ablation system according to some examples. System 101 includes a microwave ablation control unit 103, which includes a microwave energy source 105 that delivers microwave energy to an ablation probe 111. Microwave ablation control unit 103 also includes: a controller 107, which can be a microprocessor that controls the microwave energy source; a user input device 102; and a display 104, allowing a physician or other medical professional to monitor and interact with the control unit 103.

[0026] An available microwave ablation generator is the Sairem GMS solid-state generator operating at a maximum of 200W and 2450MHz manufactured by Sairem of Naylor, France. Alternatively, the Emblation Microwave MSYS245 medical system operating at a maximum of 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.

[0027] Microwave Ablation Probe

[0028] The microwave ablation probe 111 includes a probe body 112 having a cannula 113 and a radiation window 119 at the insertion end 115 of the ablation probe 111. The radiation window 119 includes a section of an inner conductor 242 of a coaxial cable 251 extending away from the end of an outer conductor 242 of the coaxial cable 251. The elongated probe body 112 can be set to various lengths. The length of the probe body 112 is much greater than its diameter. For example, the length can 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 can be at least 5 cm or at least 10 cm. In some examples, the outer diameter of the probe body 112 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 probe body 112 is at most approximately 12 gauge (2.01 mm), at most approximately 13 gauge (1.83 mm), or at most approximately 14 gauge (1.63 mm).

[0029] The insertion end 115 is configured to be inserted into the patient tissue 123. In some examples, the insertion end 115 has a tissue piercing tip configured to percutaneously enter the patient tissue 123. The ablation probe 111 has a shielding portion 117 that prevents microwave energy from entering the patient tissue along the cannula 113 and a radiation window 119 that is transparent to the microwave energy, thereby allowing the microwave energy to be transmitted into the patient tissue 123 to form the lesion 121. The outer conductor 242 protects the patient's body from microwaves along the shielding portion 117 of the ablation probe 111. The radiation window 119 includes a material surrounding the center conductor 242 that is at least partially transparent to battery radiation emitted at a frequency of approximately 300 megahertz to 300 gigahertz in the microwave range of the electromagnetic spectrum. Examples of the radiation window 119 include fluoropolymers, polyurethanes, polyether block amides (PEBA), polypropylene, polyethylene, polyamides (nylons), polyimides, polyetherimides (PEI), polysulfones, and polyetheretherketones (PEEK). The length of the radiation window 119 is based on the specific antenna 252 used in the microwave ablation probe 111. In some examples, the length of the radiation window 119 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.

[0030] A cooling fluid reservoir 135 is connected to the ablation probe 111 to deliver cooling fluid into the system through a first conduit 137 and receive circulating fluid leaving the system through a second conduit 139. In some examples, the cooling fluid is a saline solution, such as a 0.9% saline solution. In an alternative example, the cooling fluid is deionized water. Other cooling fluids may also be used, and these equivalents fall within the scope of the disclosed technology.

[0031] Figure 2 is a cross-sectional view of a microwave ablation probe that may be used in some examples of the disclosed technology. Figure 3 yes Figure 2A first example of a cross section of a microwave ablation probe along line AA. Ablation probe 111 includes a probe body 112 having a longitudinal axis 205. In some examples, probe 111 includes a tissue piercing distal end 296. Cannula 113 includes a cavity 311. In some examples, cannula 113 is a metal tube, such as a stainless steel hypodermic tube (hypotube). In an alternative example, cannula 113 can be a polymer tube constructed of a material such as PEBA (polyether block amide), polyimide, polyether ether ketone (PEEK) or polytetrafluoroethylene (PTFE). In one example, cannula 113 has an inner diameter of about 0.033 inches (0.84 mm), an outer diameter of about 0.039 inches (0.99 mm), and a wall thickness of about 0.003 inches (0.075 mm). In some examples, the outer diameter of the cannula 113 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. The cannula 113 has an outer surface 209 and an inner surface 213. The cannula wall thickness 375 is defined between the outer surface 209 and the inner surface 213. The inner surface 213 forms a heat exchange surface 224 having a surface feature 313, which will be described in further detail below.

[0032] Adjacent to shielding portion 117 is radiation window 119 , which is at least partially transparent to microwave energy. In some examples, radiation window 119 is an extended tubular member forming a surface of probe body 112 .

[0033] Coaxial cable antenna

[0034] Inside the lumen 311 of the cannula 113 is a coaxial cable 251 that acts as a microwave ablation antenna 252. The coaxial cable 251 is connected to a microwave energy source 105. In some examples, the coaxial cable 251 is concentric with the cannula 113 and the probe body 112. The coaxial cable 251 includes an inner conductor 242, an outer conductor 244, and an insulator 243 that is concentric with the inner conductor 242 and the outer conductor 244. The insulator 243 electrically isolates the inner conductor 242 from the outer conductor 244. The insulator 243 can be a dielectric material, such as a dielectric polymer. The outer conductor 244 has an outer surface 214 that acts as a heat exchange surface 226 having a surface feature 312, which will be described in more detail below. The outer conductor 244 further has a distal boundary 247. The inner conductor 242 and the insulator 243 extend distally beyond the distal boundary 247 of the outer conductor 244. This portion of the coaxial cable 251 defines a radiating portion 253 at the distal portion 211 of the probe body 112. The radiating portion 253 extends distally beyond the distal boundary 247 of the outer conductor 244. The radiating portion 253 of the antenna 252 is configured to emit microwave energy transmitted from the microwave energy source 105 through the coaxial cable 251. The radiating portion 253 is aligned with the radiation window 119 so that when used for microwave ablation, the microwave energy is transmitted from the antenna 252 into the patient's tissue.

[0035] The coaxial cable 251 can have 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 a range of about 0.5 mm to about 5 mm, or in a range of about 0.7 mm to about 2 mm. The coaxial cable 251 can 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, under part number UT-034.

[0036] exist Figure 2 In the example of the probe 111, the microwave antenna 252 is a dipole antenna. The conductive member 255 covers the distal end of the coaxial cable 251 at the insertion end 115 of the probe 111. In an alternative example (not shown), the microwave antenna 252 can be a monopole antenna, a slot antenna, or a triaxial antenna. In some examples, the probe 111 further includes a choke (not shown).

[0037] Flushing path

[0038] exist Figure 2In some examples, the probe 111 further includes a liner 261. In some examples, the liner 261 is concentric with the cannula 113. The liner 261 has an inner surface 238 and an outer surface 295. The inner surface 238 defines a cavity 239. In some examples, the coaxial cable 251 is disposed inside the cavity 239 of the liner 261. In some examples, the coaxial cable 251 is concentric with the liner 261. In some examples, the liner 261 can be made of an insulating material such as a polymer tube or a fluoropolymer material. The liner 261 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 may have a wall thickness of about 0.001 inch (0.025 mm), less than 0.001 inch (0.025 mm), at least about 0.001 inch (0.025 mm), or at least about 0.001 (0.025 mm) inch and at most about 0.002 inch (0.051 mm), where the wall thickness is defined as the thickness between the inner surface 238 and the outer surface 295. The polymer tubing may have a wall thickness of about 0.003 inch (0.076 mm), at least about 0.003 inch (0.076 mm), or at least about 0.003 inch (0.076 mm) and at most about 0.004 inch (0.102 mm). In an alternative example, the liner 261 may be constructed of an insulating, conductive material such as stainless steel tubing or nitinol tubing with an insulating coating. The stainless steel or nitinol tubing may have a wall thickness of at least about 0.002 inches (0.051 mm), between about 0.002 inches (0.051 mm) and about 0.004 inches (0.102 mm), between about 0.003 inches (0.076 mm) and about 0.004 inches (0.102 mm), or at most about 0.004 inches (0.102 mm).

[0039] In some examples, the inner diameter of the liner 261 is at least 0.001 inches (0.025 mm) larger than the outer diameter of the coaxial cable 251. In some examples, the inner diameter of the liner 261 is less than about 0.005 inches (0.127 mm) larger than the outer diameter of the coaxial cable 251. In some examples, the inner diameter of the cannula 113 is at least 0.001 inches (0.025 mm) larger than the outer diameter of the liner 261 and less than 0.005 inches (0.127 mm) larger than the outer diameter of the liner 261.

[0040] The probe body 112 defines a flushing path 232 between the cannula 113 and the coaxial cable 251. The flushing path 232 is configured to direct cooling fluid to and from the distal portion 211 of the probe body 112. The flushing path 232 is defined by at least one wall or surface including heat exchange surfaces 224, 226. In some examples, the flushing path 232 is divided into a first section 291 and a second section 292 by a liner 261 located within the cannula 113. Figure 2 In the example of FIG. 1 , the first section 291 of the irrigation path 232 is defined between the outer surface 214 of the outer conductor 244 and the inner surface 238 of the liner 261 . The second section 292 is defined between the outer surface 295 of the liner 261 and the inner surface 213 of the cannula 113 .

[0041] In some examples, the first segment 291 of the irrigation path 232 is an inlet path, and the second segment 292 of the irrigation path 232 is an outlet path. In this case, the first segment 291 receives the cooled fluid from the cooling source 135 through the first conduit 137, and the second segment 292 delivers the circulating fluid from the distal portion 211 of the probe 111 that exits the probe body 112 through the conduit 139. The cooling fluid transmitted through the first segment 291 is exposed to the outer conductor 244 of the coaxial cable 251, and the cooling fluid transmitted through the second segment 292 is exposed to the inner surface 213 of the cannula 113.

[0042] exist Figure 2 In the example of FIG. 2 , when the first segment 291 is the inflow path, the cooling fluid entering the system is closer to the longitudinal axis 205 of the ablation probe 111 than the outflow path of the second segment 292. This allows the cooling fluid flowing into the probe body 112 to first encounter the antenna 252 and cool the antenna by contacting the heat exchange surface 226 on the outer surface 214 of the outer conductor 244, after which the cooling fluid travels around the distal end of the liner 261, now flowing toward the proximal end of the probe body 112, and exiting the second segment 292, thereby cooling the cannula 113 by contacting the heat exchange surface 224 on the inner surface 213 of the cannula 113. In an alternative example, the first segment 291 can be the outflow path and the second segment 292 can be the inflow path. In some examples, the heat exchange surfaces 224, 226 are coated with a wetting agent to increase the amount of heat conducted away from the surfaces 213, 214 by the cooling fluid.

[0043] In some examples, the flow rate of the cooling fluid through the flushing path 232 can be between about 10 milliliters (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. The coolant flow rate through the flushing path 232 affects the heat transfer coefficient h. In some examples, the flow rate is at most about 40 ml, 35 ml, 30 ml, 25 ml, 20 ml, 15 ml, or 10 ml per minute.

[0044] In some examples, the temperature of the cooling fluid when entering the system through the first conduit 137 is at the ambient temperature of the room. In some examples, the cooling fluid is below the ambient temperature of the room. In some examples, the temperature of the cooling fluid when leaving the system through the first conduit 137 is between about 0°C and 20°C. In some examples, the temperature increase of the cooling fluid between entering the system through the first conduit 137 and leaving the system through the second conduit 139 is between about 1°C and 10°C.

[0045] In some examples, the cooling source 135 is configured to cool the fluid received through the conduit 139 and recirculate the fluid through the system. In alternative examples, the coolant is no longer circulated through the system. In some examples, the positive pressure forces the fluid into the probe body 112 through the first conduit 137. In some examples, the negative pressure draws the fluid from the probe body 112 through the second conduit 139 and returns it to the cooling fluid reservoir 135. In some examples, both the positive pressure in the first conduit 137 and the negative pressure in the second conduit 139 are provided.

[0046] Heat exchange surface

[0047] The probe 111 may be provided with one or more heat exchange surfaces that increase the amount of heat that can be transferred from the system by increasing the surface area in contact with the cooling fluid. Figure 4 yes Figure 2 A second example of a cross-sectional view of a microwave ablation probe along line AA. Figure 4 In the example of , the probe 111 includes a cannula 113, an antenna 252, and a liner 261. The cannula 113 has an inner surface 213 and an outer surface 209. The inner surface 213 of the cannula 113 has a heat exchange surface 424, which includes a plurality of convection fins 434 around the circumference of the inner surface 213. The convection fins 434 are axial corrugations. The antenna 252 has an inner conductor 242, an insulator 243, and an outer conductor 244. The outer conductor 244 has an outer surface 214, which has a heat exchange surface 426 including a plurality of convection fins 436. The convection fins 434 and 436 provide increased area for the heat exchange surfaces 424 and 426, respectively, relative to a smooth cylindrical surface lacking these convection fins. In Figure 4 In the example of , the convection fins form peaks and valleys at different distances from the longitudinal axis 205 of the probe 111. In this example, the convection fins extend longitudinally along the inner surface 213 of the cannula 113 and the outer surface 214 of the outer conductor 244, parallel to the longitudinal axis 205. The surface features on the outer surface 214 of the outer conductor 244 and the inner surface 213 of the cannula 113 can be manufactured using many different techniques, including mechanical, grinding, laser, photolithography, chemical etching, machining, molding, extrusion, cold working or drawing techniques.

[0048] The heat exchange surface has surface features that can include corrugations, undulations, fins, one or more ridges, etc. In any of the examples described herein, the heat exchange surface can have a textured surface with peaks and valleys. The textured surface can increase the surface area along the flushing path, thereby allowing more cooling fluid to contact the surface at any time. In some examples, threads or knurling are used to form the texture. The knurled surface can include straight, angled, or intersecting grooves. Alternatively, the surface can be recessed or ribbed to increase the cooling surface area.

[0049] The heat exchange surface has a maximum radius, a minimum radius, and an average radius. For example, Figure 4 4. The heat exchange surface 424 in the embodiment of FIG. 4 is a heat exchange surface 424, the valley 441 has a distance r1, which is the maximum radius from the longitudinal axis 205, and the peak 442 has a different distance r2, which is the minimum radius from the longitudinal axis 205. The dashed line 451 represents the average distance r3 of the heat exchange surface 424 from the longitudinal axis 205, where the average distance r3 can be qualitatively conceptualized as being greater than the shortest distance r2 from the longitudinal axis 205 to the heat exchange surface 424, but less than the farthest distance r1 from the longitudinal axis 205 to the heat exchange surface 424. In practice, this means that the surface area of ​​the inner surface 213 of the cannula 113 is greater than the surface area of ​​a cylinder having a uniform radius r3. It should be noted that in FIG. Figure 4 In the example of , the surface area of ​​the heat exchange surface 424 is also greater than a cylinder having a uniform radius equal to r1 or r2. This increased surface area of ​​the heat exchange surface 424 provides increased heat transfer between the cannula 113 and the cooling fluid relative to a cannula having a smooth inner surface. The same effect is found for the heat exchange surface 426 having convection fins 436: the increased surface area of ​​the heat exchange surface 426 allows heat to be transferred away from the antenna 252 at a greater rate than an antenna having a smooth outer surface.

[0050] Both the cannula 113 and the coaxial cable 251 are generally tubular. In some examples, the surface features of the heat exchange surfaces 224, 226 are implemented as axial corrugations or ridges extending parallel to the axis of the probe 111; radial corrugations or ridges extending circumferentially along the surface of the cannula 113 or the coaxial cable 251; or helical corrugations or ridges extending helically around the surface of the cannula 113 or the coaxial cable 251.

[0051] In this article Figure 4 The description of heat exchange surfaces 424, 426 applies to Figure 3 The heat exchange surfaces 224, 226 of the convection fins are also included, and these convection fins are axially corrugated. Figure 4 Compared with the convection fins 434 and 436, Figure 3 The convection fins of the heat exchange surfaces 224, 226 have rounded peaks and rounded valleys.

[0052] Figure 3 and Figure 4 The probe is shown as having two heat exchange surfaces. In an alternative example, Figure 3 and Figure 4 The probe can be constructed to have only one heat exchange surface. For example, the inner surface of the cannula can be a smooth surface with a consistent radius, and the heat exchange surface can be provided only on the outer surface of the outer conductor. Conversely, the outer surface of the outer conductor can be a smooth surface with a consistent radius, and the heat exchange surface can be provided only on the inner surface of the cannula.

[0053] Cannula with lumen

[0054] Figure 5 is a cross-sectional view of an alternative example of a microwave ablation probe. Figure 5 In some examples, the probe 511 includes a cannula 513 having a cannula wall 515 that defines a plurality of lumens 521 extending through the cannula wall 515. The lumens 521 are configured to direct a cooling fluid to cool the probe 511. An inner surface 517 of the cannula 513 defines a lumen 575. Inside the lumen 575 is a coaxial cable 531 having an inner conductor 532, an outer conductor 534, and an insulator 536 separating the inner conductor 532 from the outer conductor 534. In some examples, the coaxial cable 531 is concentric with the cannula 513. The cannula 513 has a heat exchange surface 516 on an inner surface 517 of the cannula 513, and the coaxial cable 531 has a heat exchange surface 541 on an outer surface 542 of the outer conductor 534. The probe 511 is similar to Figures 1 to 4However, the probe 511 does not require a liner because one portion of the irrigation path is defined by the cavity 521 in the cannula wall 515. Another portion of the irrigation path is defined by the cavity 575 between the inner surface 517 of the cannula 513 and the heat exchange surface 541 of the coaxial cable 531.

[0055] In some examples, the wall 515 of the cannula 513 is approximately 0.007 inches (0.178 mm) thick and the cavity 521 spans a thickness of approximately 0.005 inches (0.127 mm) of the wall 515, resulting in a thickness of approximately 0.001 inches (0.025 mm) between the cavity 521 and the outer surface 519 of the cannula 513.

[0056] exist Figure 5 In the figure, the probe 511 is shown as having two heat exchange surfaces 516, 541. However, in an alternative example, the probe 511 can be configured to have only one heat exchange surface. For example, the inner surface 517 of the cannula 513 can be a smooth surface with a consistent radius, and the heat exchange surface 541 can be provided only on the outer surface 542 of the outer conductor 534. Conversely, the outer surface 542 of the outer conductor 534 can be a smooth surface with a consistent radius, and the heat exchange surface 516 can be provided only on the inner surface 517 of the cannula 513.

[0057] Spiral heat exchange surface

[0058] In an alternative example of the disclosed technology, the geometry of the tube causes the cooling fluid to follow a non-linear path through the body of the ablation probe. Figure 6 611 is a cross-sectional view of an alternative example of a microwave ablation probe according to some examples. Probe 611 includes cannula 613, coaxial cable 651, and liner 661. Figure 6 In the example of FIG. 6 , the cannula 613, the liner 661, and the coaxial cable 651 are concentric about the longitudinal axis 604 of the probe 611. The probe body 612 has a proximal portion 602 and a distal portion 603. The coaxial cable 651 has an inner conductor 632, an outer conductor 631, and an insulator 633 that electrically isolates the inner conductor 632 from the outer conductor 631. The antenna 652 includes a radiating portion 653 that is aligned with the radiation window 619 of the probe body 612.

[0059] The outer conductor 631 has a heat exchange surface 636 with a plurality of ridges 637 on an outer surface 635 of the outer conductor 631. The ridges 637 impart a non-uniform thickness to the outer conductor 631. Figure 6In some examples, ridge 637 is spirally wound around the outside of coaxial cable 651, similar to a threaded screw. Ridge 637 defines peaks and valleys at different distances from the longitudinal axis 604 of probe body 612. Ridge 637 of heat exchange surface 636 guides cooling fluid to flow spirally around outer surface 635 of outer conductor 631. In some examples, ridge 637 includes alternating peaks and valleys. In some examples, outer conductor 631 has a minimum wall thickness of about 0.001 inch (0.025mm). In some examples, the peak of ridge 637 increases the wall thickness of outer conductor 631 by about 0.001 inch (0.025mm). In some examples, the distance between adjacent ridges 637 is between about 0.001 inch (0.025mm) and 0.005 inch (0.127mm). In some examples, the peak of ridge 637 has a flat shape. In alternative configurations, the peak of ridge 637 can have other shapes, such as rounded corners, triangles, etc.

[0060] Similarly, the cannula 613 has an inner surface 621 that defines a heat exchange surface 622. The heat exchange surface 622 has surface features that include a plurality of undulations 624 on the inner surface 621 of the cannula 613. The undulations 624 define peaks and valleys at varying distances from the longitudinal axis 604 of the probe body 612, thereby creating an increased surface area.

[0061] The flushing path 671 is defined between the cannula 613 and the coaxial cable 651. The flushing path 671 can be divided into a first section 691 and a second section 692. The first section 691 can be defined between the heat exchange surface 636 of the outer conductor 631 and the liner 661, and the second section 692 can be defined between the heat exchange surface 622 of the cannula 613 and the liner 661. In some examples, the first section 691 is an inflow path for coolant to enter the probe body 612, and the second section 692 is an outflow path for coolant to leave the probe body 612.

[0062] The spiral configuration of the ridges 637 of the heat exchanging surface 636 directs coolant entering the first segment 691 into a spiral path around the outer circumference of the coaxial cable 651. The coolant following the spiral path in the probe body 612 spends more time in contact with the heat exchanging surface 636 than if the coolant flowed in a direction parallel to the longitudinal axis 604 of the probe 611. The more time the coolant can be in contact with the heat exchanging surface 636, the more heat the coolant can absorb and transfer away from the probe body 612.

[0063] In some examples, the ridges 624 create a fluid dynamic where there is a higher pressure drop across the flushing path 671 between the first segment 691 and the second segment 692. This causes an increased flow velocity of the coolant along the spiral path formed by the ridges 624.

[0064] exist Figure 6 In the figure, the probe 611 is shown as having two heat exchange surfaces 622, 636. However, in an alternative example, the probe 611 can be configured to have only one heat exchange surface. For example, the inner surface 621 of the cannula 613 can be a smooth surface with a consistent radius, and the heat exchange surface 636 can be provided only on the outer surface 635 of the outer conductor 631. Conversely, the outer surface 635 of the outer conductor 631 can be a smooth surface with a consistent radius, and the heat exchange surface 622 can be provided only on the inner surface 621 of the cannula 613.

[0065] Wetting agents for heat exchange surfaces

[0066] In any of the foregoing examples, any of the heat exchange surfaces may be coated with a wetting agent to improve contact between the heat exchange surface and the cooling fluid, thereby improving heat transfer. Additionally, in some cases, the polarity of the heat exchange surface may repel molecules of different polarity of the cooling fluid. The wetting agent may correct the polarity of the cooling fluid at the surface of the electrode to correct this effect. The wetting agent may also correct the surface effects produced by the textured surface elements on the heat exchange surface. For example, some wetting agents may prevent the formation of unwanted bubbles on the surface of the heat exchange surface. Some examples of wetting agents that may be appropriate are sodium stearate, sodium lauroyl sarcosinate (INCI), perfluorononanoic acid, perfluorooctanoic acid (PFOA or PFO), alkylbenzene sulfonates, lignin sulfonates, fatty alcohol ethoxylates, and alkylphenol ethoxylates. Alternatively, fluorinated surfactants, silicone surfactants, polypropylene oxides, and many other types of wetting agents may be used.

[0067] Cover structure

[0068] The cover can be constructed of a metal such as brass or stainless steel. In some examples, the cover can be constructed of a ceramic material. In some examples, the cover 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 cover is made of a metal material, the metal length can be varied to provide a variable length for the antenna. If the cover is made of a ceramic material, the cover length will not affect the resonant frequency of the antenna.

[0069] Microwave ablation method

[0070] During ablation therapy, the physician can adjust many parameters in the microwave ablation system to form the desired ablation lesions. These parameters can alternatively be automatically adjusted by a controller in a computer system. The amount of power provided to the microwave energy source can be adjusted. A higher amount of power to be delivered increases the intensity of the microwave radiation entering the tissue, or a lower amount of power to be delivered reduces the intensity of the microwave radiation entering the tissue. High-power ablation can effectively form large lesions. If the power is too high, negative effects such as tissue burning may occur. The system can also adjust the amount of time that microwave radiation is delivered to the tissue. A shorter time period is associated with a smaller risk of burning tissue, however, if the ablation therapy is terminated prematurely, the therapy may not successfully ablate all of the tissue desired to be ablated.

[0071] The microwave ablation system of the present disclosure can be used to perform a treatment method. The method can be used with a system including a probe having a probe body having a shielding portion and a radiation window that is at least partially transparent to microwave energy. The shielding portion includes a cannula. The probe further includes a coaxial cable within the probe body. An antenna in the probe is electrically connected to the cable. The antenna has a radiating portion for emitting microwave energy, and the radiating portion is aligned with the radiation window.

[0072] The probe body further defines a flushing path configured to carry a cooling fluid to and from a distal portion of the probe body. At least one wall defining the flushing path has a heat exchange surface. The heat exchange surface has an average radius, and a surface area of ​​the heat exchange surface is greater than a surface area of ​​a smooth surface having a radius equal to the average radius.

[0073] The method includes delivering a cooling fluid to the irrigation path, circulating the cooling fluid within the probe body, and delivering microwave energy to the antenna via the cable. The method may also include returning the cooling fluid to a cooling fluid source after the cooling fluid returns from the distal end of the probe body.

[0074] 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.

[0075] All publications and patent applications cited in this specification are herein incorporated by reference in their entirety.

[0076] 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 having a longitudinal axis, comprising: a probe body comprising a shielding portion and a radiation window, the radiation window being at least partially transparent to microwave energy, wherein the shielding portion comprises a cannula; A coaxial cable within the probe body; and an antenna including a radiating portion at a distal portion of the probe body for emitting microwave energy, wherein the radiating portion is aligned with the radiation window; wherein the probe body defines a flushing path between an inner surface of the cannula and an outer surface of the outer conductor of the coaxial cable, the flushing path being configured to carry a cooling fluid to and from the distal portion of the probe body, wherein at least a portion of the outer surface of the outer conductor and / or at least a portion of the inner surface of the cannula comprises a heat exchange surface; wherein the heat exchanging surface has an average radius, wherein the surface area of ​​the heat exchanging surface is greater than the surface area of ​​a smooth surface having a radius equal to the average radius, wherein the heat exchange surface is located on at least a portion of an inner surface of the probe body or on at least a portion of an outer surface of the coaxial cable outer conductor; Therein, the distance between the heat exchange surface and the longitudinal axis of the probe varies along its circumference, or the heat exchange surface comprises corrugations, undulations, fins or one or more ridges.

2. The probe according to claim 1, wherein The heat exchanging surface includes helical ridges on at least a portion of an outer surface of the outer conductor of the cable, helical ridges on at least a portion of an inner surface of the cannula, or both.

3. The probe according to claim 1, wherein The heat exchanging surface comprises axial corrugations on at least a portion of an inner surface of the cannula or comprises axial corrugations on at least a portion of an outer surface of an outer conductor of the cable.

4. The probe according to claim 1, wherein The heat exchange surface includes axial corrugations on at least a portion of an inner surface of the cannula, wherein the probe further includes an additional heat exchange surface including axial corrugations on at least a portion of an outer surface of an outer conductor of the cable.

5. The probe of any one of claims 1 to 2, further comprising a coolant source configured to deliver the cooling fluid to the irrigation path and to receive the cooling fluid.

6. The probe of any one of claims 1 to 2, further comprising a liner concentric with and within the cannula, wherein: A first segment of the irrigation path is defined between an outer surface of the outer conductor and an inner surface of the liner, wherein a second segment of the irrigation path is defined between an outer surface of the liner and an inner surface of the cannula.

7. The probe according to claim 6, wherein: The first segment of the flushing path is an inlet path, and the second segment of the flushing path is an outlet path.

8. The probe according to any one of claims 1 to 2, wherein: The flushing path circumferentially surrounds the coaxial cable.

9. The probe according to any one of claims 1 to 2, wherein: The heat exchanging surface forms a circumferentially continuous surface.

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