Patent Publication Number: US-2023149080-A1

Title: Flexible instruments with patterned antenna assemblies having variable recoverable flexibility

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application claims priority to the following pending applications: 
     U.S. Provisional Pat. Application No. 63/008,615, filed Apr. 10, 2020; and 
     U.S. Provisional Pat. Application No. 63/028,928, filed May 22, 2020. 
     All of the foregoing applications are incorporated herein by reference in their entireties. Further, components and features of embodiments disclosed in the applications incorporated by reference may be combined with various components and features disclosed and claimed in the present application. 
    
    
     TECHNICAL FIELD 
     The present disclosure is directed to minimally invasive ablation devices and systems and associated methods of use. 
     BACKGROUND 
     Minimally invasive medical techniques are intended to reduce the amount of tissue that is damaged during medical procedures, thereby reducing patient recovery time, discomfort, and harmful side effects. Such minimally invasive techniques may be performed through natural orifices in a patient anatomy or through one or more surgical incisions. Through these natural orifices or incisions, an operator may insert minimally invasive medical tools to reach a target tissue location. Minimally invasive medical tools include instruments such as therapeutic, diagnostic, biopsy, and surgical instruments. Minimally invasive medical tools may also include ablation instruments. Ablation instruments transmit energy, e.g., in the form of electromagnetic waves to a targeted area of tissue, such as a tumor or other growth, within the patient anatomy to destroy the targeted tissue. Some minimally invasive medical tools and ablation instruments may be teleoperated or otherwise computer-assisted or delivered by a teleoperated, robotic, or otherwise computer-assisted system. Various features may improve the effectiveness of minimally invasive ablation instruments. 
     SUMMARY 
     Embodiments of the present technology are best summarized by the claims that follow the description. 
     In some embodiments, a flexible instrument comprises an elongate device including an inner conductor, an outer conductor surrounding the inner conductor, and a dielectric layer insulating the inner conductor from the outer conductor. The flexible instrument also includes a recess formed in the outer conductor. An insert is positioned within the recess and about the inner conductor. 
     In some embodiments, an energy delivery system comprises a flexible instrument. The flexible instrument includes a transmission member, an antenna at a distal end of the transmission member, a sheath surrounding the antenna and the transmission member, and at least one fluid conduit at least partially disposed within the sheath. The at least one fluid conduit defines a fluid inlet channel configured to transport fluid proximal to a distal end of the antenna. Additionally, the at least one fluid conduit is configured to provide variable recoverable flexibility along at least a section of the flexible instrument. The at least one fluid conduit is further composed of a material that prevents interference of energy delivery by the antenna. 
     In these and other embodiments, an energy delivery system comprises a flexible instrument and a fluid conduit. The flexible instrument includes a transmission member, an antenna at a distal end of the transmission member, and a sheath surrounding the transmission member and the antenna. The fluid conduit is at least partially disposed within the sheath. The sheath defines a fluid channel surrounding at least a distal end portion of the antenna. The energy delivery system further comprises a translation actuator to alter the state of the fluid conduit from a first state to a second state. The first state includes an extended position overlapping the antenna with the fluid conduit. The second state includes a retracted position not overlapping the antenna with the fluid conduit. 
     In these and other embodiments, a method of operating an energy delivery system comprises (i) providing resilient flexibility and (ii) delivering energy. The energy delivery system includes a flexible instrument having a transmission member, an antenna at a distal end of the transmission member, a sheath surrounding the flexible instrument, and a sliding element at least partially disposed within the sheath. Providing resilient flexibility includes providing resilient flexibility using the sliding element while the sliding element is positioned to overlap with at least a section of the antenna during navigation of the flexible antenna to a target within a subject. Delivering energy to the target includes delivering energy to the target via the antenna while the sliding element is positioned proximal to the antenna. 
     In these and still other embodiments, a method of operating an energy delivery system comprises (i) providing resilient flexibility and (ii) delivering fluid. The energy delivery system includes a flexible instrument having a transmission member, an antenna at a distal end portion of the transmission member, a sheath surrounding the flexible instrument, and a fluid conduit at least partially disposed within the sheath. Providing resilient flexibility includes providing resilient flexibility, using the fluid conduit, to at least a section of the flexible instrument during navigation of the flexible instrument through patient anatomy to a target within a patient. Delivering fluid includes delivering fluid proximate the antenna at least while delivering energy to the target via the antenna. The fluid is delivered via the fluid conduit while a distal end portion of the fluid conduit is extended to a distal end portion of the antenna. 
     In these and other embodiments, an energy delivery system comprises a flexible instrument having an elongate device with an inner conductor, an outer conductor surrounding the inner conductor, and a dielectric layer insulating the inner conductor from the outer conductor. The flexible instrument further includes a recess formed in the outer conductor and an insert disposed within the recess and about the inner conductor. The energy delivery system also comprises a sheath surrounding the flexible instrument and at least one fluid conduit at least partially disposed within the sheath and extending along the flexible instrument. The at least one fluid conduit defines a fluid inlet channel configured to transport fluid to a distal end region of the flexible instrument, and further provides variable recoverable flexibility along at least a portion of the flexible instrument. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory in nature and are intended to provide an understanding of the present disclosure without limiting the scope of the present disclosure. In that regard, additional aspects, features, and advantages of the present disclosure will be apparent to one skilled in the art from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on illustrating clearly the principles of the present disclosure. The drawings should not be taken to limit the disclosure to the specific embodiments depicted, but are for explanation and understanding only. 
         FIG.  1    is a side cross-sectional view of a flexible instrument for tissue ablation configured in accordance with an embodiment of the present technology. 
         FIG.  2    is a side cross-sectional view of a flexible instrument for tissue ablation configured in accordance with another embodiment of the present technology. 
         FIG.  3    is a side cross-sectional view of an energy delivery system for tissue ablation configured in accordance with an embodiment of the present technology. 
         FIG.  4    is a side cross-sectional view of an energy delivery system for tissue ablation configured in accordance with another embodiment of the present technology. 
         FIG.  5    is a side cross-sectional view of an energy delivery system for tissue ablation configured in accordance with a further embodiment of the present technology. 
         FIGS.  6 A and  6 B  are side views of patterned fluid conduits configured in accordance with various embodiments of the present technology. 
         FIG.  7    is a flow diagram illustrating a method for manufacturing an energy delivery system in accordance with an embodiment of the present technology. 
         FIG.  8    is a flow diagram illustrating a method of operating an energy delivery system in accordance with an embodiment of the present technology. 
         FIG.  9 A  is a perspective view of an energy delivery system for tissue ablation configured in accordance with various embodiments of the present technology. 
         FIG.  9 B  is a cross-sectional end view of a flexible instrument of the energy delivery system of  FIG.  9 A  configured in accordance with various embodiments of the present technology. 
         FIG.  10    is a cross-sectional side view of an energy delivery system for tissue ablation configured in accordance with various embodiments of the present technology. 
         FIG.  11    is a cross-sectional side view of an energy delivery system for tissue ablation configured in accordance with various embodiments of the present technology. 
         FIG.  12    is a cross-sectional side view of an energy delivery system for tissue ablation configured in accordance with various embodiments of the present technology. 
         FIG.  13    is a cross-sectional side view of an energy delivery system for tissue ablation configured in accordance with various embodiments of the present technology. 
         FIG.  14 A  is a cross-sectional side view of an energy delivery system for tissue ablation in a first state configured in accordance with various embodiments of the present technology. 
         FIG.  14 B  is a cross-sectional side view of the energy delivery system of  FIG.  14 A  in a second state configured in accordance with various embodiments of the present technology. 
         FIG.  15    is a flow diagram illustrating a method of operating an energy delivery system in accordance with various embodiments of the present technology. 
         FIG.  16    is a flow diagram illustrating a method for manufacturing an energy delivery system in accordance with various embodiments of the present technology. 
         FIG.  17    is a simplified diagram of a teleoperated medical system configured in accordance with various embodiments of the present technology. 
         FIG.  18 A  is a simplified diagram of a medical instrument system configured in accordance with various embodiments of the present technology. 
         FIG.  18 B  is a simplified diagram of a medical instrument system configured in accordance with various embodiments of the present technology. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed to energy delivery systems including minimally invasive ablation devices and systems (and associated methods). The energy delivery systems are used for tissue ablation, causing an increase in temperature of an anatomic target area by transmitting electromagnetic waves from the energy delivery system to the anatomic target area or ablation site. In some embodiments, an energy delivery system includes a flexible instrument having a transmission member and an antenna assembly extending from a distal end portion of the transmission member. The transmission member and antenna assembly can be formed from an elongate device (such as a coaxial cable) having an inner conductor, an outer conductor, and an insulating layer electrically separating the inner and outer conductors. The antenna assembly can be patterned with one or more recesses formed in the outer conductor to modify the field pattern of electromagnetic energy used to affect tissue. 
     To prevent excessive heating that may cause unwanted damage to patient tissue, energy delivery systems configured in accordance with the present technology may be cooled by a coolant (e.g., a fluid or gas). Thus, in some embodiments, an energy delivery system includes a fluid cooling system and a flexible instrument. The flexible instrument includes (i) a transmission member, (ii) an antenna extending from a distal end of the transmission member, and (iii) one or more fluid conduits. The transmission member, the antenna, and the one or more fluid conduits are disposed within a sheath. A fluid channel is formed between the sheath and at least a portion of the antenna. 
     To facilitate delivery of the flexible instrument to a target site within patient anatomy, the flexible instrument must be sufficiently flexible to undergo substantial deformation while navigating patient anatomy, yet axially rigid and stiff enough to puncture tissue without buckling or kinking. Additionally, the distal section of the flexible instrument must be resilient enough to return (e.g., recover, spring back, etc.) to an initial (e.g., undeformed) state or shape after being deformed (e.g., to reduce navigational error and/or align the flexible instrument with a desired axis before performing a puncture operation). Flexible coaxial cables having a multifilament outer conductor layer (e.g., a braided or wrapped layer) are generally more deformable compared to semi-rigid coaxial cables having a solid outer conductor layer, and may therefore be more suitable for navigation through tortuous patient anatomy (e.g., the airways of the lungs). However, it may be more difficult to form recesses in a flexible coaxial cable because the multifilament outer conductor layer tends to unravel or fray when cut. Additionally, the exposed inner conductor and insulating layer may be mechanically weak, which may increase the likelihood of mechanical failure when the flexible instrument is bent, make it more difficult to insert the flexible instrument into tissue, reduce recoverability, etc. Moreover, conventional coaxial cables may include a thick layer of material over the outer conductor, which may reduce the deformability of the flexible instrument, prevent the flexible instrument from being introduced into narrow passages, and/or interfere with coolant flow around the flexible instrument. 
     Accordingly, to overcome these and other challenges, the flexible instruments described herein may be reinforced at or near the location of the recess in the outer conductor. In some embodiments, for example, an insert made of a non-conductive material (e.g., plastic, adhesive, filler, etc.) is positioned within the recess to protect and provide mechanical support to the corresponding portions of the insulator layer and inner conductor. This non-conductive material is preferably something with low RF loss and can withstand the temperatures needed for ablation (such as polytetrafluoroethylene (PTFE), polyetheretherketone (PEEK), etc.). Additionally, an intermediate layer (e.g., a jacket layer or coax jacket layer) can be positioned over at least a portion of the outer conductor to reduce or prevent unraveling at the recess. The intermediate layer can be made of a material (e.g., fluoropolymers including ethylene tetrafluoroethylene (ETFE) or PEEK, plastic, polyethylene terephthalate (PET) coating, heat-shrink, etc.) that also provides mechanical support, axial rigidity, and/or recoverability to the flexible instrument. The intermediate layer may be composed a non-conductive material or a partially conductive material (depending upon positioning relative to the antenna assembly). The intermediate layer can be thin enough to avoid interference with coolant flow and permit the flexible instrument to be navigated within narrow and/or tortuous anatomic passageways. 
     As noted previously, in some embodiments, the energy delivery systems described herein include one or more fluid conduits for delivering coolant to the flexible instrument. The fluid conduit(s) may extend to at least a distal end portion of the antenna assembly to provide recoverable flexibility and support along a maximized length of the flexible instrument, as well as an added benefit of delivering coolant to the distal end portion of the antenna assembly for increased and/or more uniform cooling of the antenna assembly. However, many shape memory and other resiliently flexible materials (including nitinol) are conductive at the microwave frequency range (e.g., 300 megahertz (MHz) to 300 gigahertz (GHz) of the antenna assembly, meaning that any region of the fluid conduit that runs alongside the antenna assembly and is formed of a conductive material would interfere with the antenna assembly during energy delivery. Accordingly, the region of the fluid conduit that runs alongside the antenna assembly can be formed of a plastic, polymer, or other non-conductive material that does not interfere with the antenna assembly during energy delivery; and/or the conductive, shape-memory region of the fluid conduit can be variably positioned such that the conductive material is not positioned alongside the antenna assembly during energy delivery. 
     Resiliently flexible materials, such as nitinol or other shape memory materials, are often expensive relative to other materials. Moreover, a proximal section of the flexible instrument typically does not undergo the extent of deformation experienced by the distal section of the flexible instrument. As such, recoverable flexibility can be less of a concern along the proximal section than the distal section of the flexible instrument. Thus, in some embodiments, the fluid conduits can include a region that can be formed of a less expensive material (e.g., stainless steel, PEEK, or other metals and plastics) and that can run along at least a portion of the proximal section of the flexible instrument. 
     Specific details of several embodiments of the present technology are described herein with reference to  FIGS.  1 - 18 B . Although many of the embodiments are described below in the context of navigating and performing medical procedures within lungs of a patient, other applications and other embodiments in addition to those described herein are within the scope of the present technology. For example, unless otherwise specified or made clear from context, the devices, systems, and methods of the present technology can be used for navigating and performing medical procedures on, in, or adjacent other patient anatomy, such as the bladder, urinary tract, GI system, and/or heart of a patient. 
     It should be noted that other embodiments in addition to those disclosed herein are within the scope of the present technology. Further, embodiments of the present technology can have different configurations, components, and/or procedures than those shown or described herein. Moreover, a person of ordinary skill in the art will understand that embodiments of the present technology can have configurations, components, and/or procedures in addition to those shown or described herein and that these and other embodiments can be without several of the configurations, components, and/or procedures shown or described herein without deviating from the present technology. 
     This disclosure describes various instruments and portions of instruments in terms of their state in three-dimensional space. As used herein, the term “position” refers to the location of an object or a portion of an object in a three-dimensional space (e.g., three degrees of translational freedom along Cartesian x-, y-, and z-coordinates). As used herein, the term “orientation” refers to the rotational placement of an object or a portion of an object (three degrees of rotational freedom—e.g., roll, pitch, and yaw). As used herein, the term “pose” refers to the position of an object or a portion of an obj ect in at least one degree of translational freedom and to the orientation of that object or portion of the object in at least one degree of rotational freedom (up to six total degrees of freedom). As used herein, the term “shape” refers to a set of poses, positions, or orientations measured along an object. 
     As used herein, the term “operator” shall be understood to include any type of personnel who may be performing or assisting a procedure and, thus, is inclusive of a physician, a surgeon, a doctor, a nurse, a medical technician, other personnel or user of the technology disclosed herein, and any combination thereof. As used herein, the term “patient” should be considered to include human and/or non-human (e.g., animal) patients upon which a medical procedure is being performed. 
       FIGS.  1 - 5    illustrate various embodiments of flexible instruments and energy delivery systems. In some embodiments, the energy delivery systems are used for tissue ablation, such as by causing an increase in temperature of an anatomic target area by transmitting electromagnetic waves from an antenna assembly to the anatomic target area or ablation site. As described in greater detail below, the antenna assembly can be sufficiently flexible to allow for navigation through tortuous passages in the target area, while also having sufficient mechanical strength and structural integrity to withstand deformation (e.g., bending) and/or insertion into tissue without mechanical failure (e.g., buckling, kinking). To prevent excessive heating that may cause unwanted damage to patient tissue, the energy delivery system can be cooled by a coolant (e.g., a fluid, liquid, or gas) as disclosed in the following embodiments. In some embodiments, the energy delivery systems may be suitable for use in, for example, surgical, diagnostic, therapeutic, ablative, and/or biopsy procedures. In some embodiments, the energy delivery systems may be used as a medical instrument in procedures performed with a teleoperated medical system, as described in further detail below. While some embodiments are provided herein with respect to such procedures, any reference to medical or surgical instruments and medical or surgical methods is non-limiting. In some embodiments, the energy delivery systems may be used for non-teleoperational or non-robotic procedures involving traditional manually operated medical instruments. The systems, instruments, and methods described herein may be used for animals, human cadavers, animal cadavers, portions of human or animal anatomy, non-surgical diagnosis, as well as for industrial systems and general robotic, general teleoperational, or robotic medical systems. 
       FIG.  1    is a side cross-sectional view of a flexible instrument  100  for tissue ablation configured in accordance with an embodiment of the present technology. As shown in  FIG.  1   , the flexible instrument  100  includes a transmission member  102  and an antenna assembly  104 . The transmission member  102  can be an elongate structure having a proximal end (not shown) and a distal portion  106 . The antenna assembly  104  is located at the distal portion  106  of the transmission member  102 , and extends distally from the transmission member  102  between a proximal portion  108  and a distal tip  110  of the antenna assembly  104 . 
     The transmission member  102  is configured to conduct energy from a proximal energy source (not shown) to the antenna assembly  104 . As described in greater detail below, the antenna assembly  104  is used to radiate energy (e. g., microwave energy) for use in the tissue ablation process. In some embodiments, the antenna assembly  104  is used to create electromagnetic radiation within a wavelength range of one meter to one millimeter, and within a frequency range of approximately 300 MHz to 300 GHz (e.g., a microwave). A microwave, which is a type of radio wave, is made up of a magnetic field at a right angle to an electric field, and both the magnetic field and the electric field oscillate at a specific frequency and travel together along a direction that is perpendicular to both the magnetic field and the electric field. In some embodiments, the wavelength and the frequency of the microwaves being radiated by the antenna assembly  104  may be modified to cause a desired type of ablation at the ablation target site. As described in greater detail below, the antenna assembly  104  can include an antenna body  112 , and optionally a cap structure  114 , having features configured to generate a desired energy radiation pattern for ablation. 
     In some embodiments, the transmission member  102  and the antenna body  112  are formed from an elongate device such as a coaxial cable (e.g., a flexible coaxial cable). The transmission member  102  and antenna body  112  can be integrally formed from a single elongate device, e.g. coaxial cable, such that a proximal section of the elongate device forms the transmission member  102  and a distal section of the elongate device forms the antenna body  112 . The elongate device can have an inner conductor  116 , an outer conductor  118  at least partially surrounding the inner conductor  116 , and at least one insulating layer  120  between the inner conductor  116  and the outer conductor  118 . The insulating layer  120  can at least partially surround the inner conductor  116  to insulate and electrically separate the inner conductor  116  from the outer conductor  118 . The inner conductor  116  and outer conductor  118  can each be composed of a conductive material (e.g., nitinol, copper, etc.). In some embodiments, the inner conductor  116  and outer conductor  118  are composed of the same conductive material, while in other embodiments the inner conductor  116  and outer conductor  118  can be composed of different conductive materials. The insulating layer  120  can be composed of a non-conductive material (e.g., a dielectric material such as a polymer). In some embodiments, the material of the insulating layer  120  may be chosen to provide a high axial stiffness along the axis A to allow greater rigidity to puncture tissue. Rigid materials such as PEEK or polyetherimide (such as those manufactured by SABIC of Riyadh, Saudi Arabia and sold under the trademark ULTEM) may be used, for example, to increase stiffness in the flexible instrument  100  and prevent buckling or kinking during a puncture operation. 
     The structures of the inner conductor  116 , outer conductor  118 , and/or insulating layer  120  can be configured to impart flexibility to the transmission member  102  and antenna body  112 . For example, as shown in  FIG.  1   , the inner conductor  116  can be an elongated flexible structure (e.g., one or more wires, filaments, fibers, etc.) extending along the length of the transmission member  102  and antenna body  112 . The insulating layer  120  can be a layer of solid material, or can include one or more filaments of non-conductive material that are braided, woven, or wrapped around the inner conductor  116 . The outer conductor  118  can include one or more layers of material around the insulating layer  120 . By varying construction of layers, flexibility of the elongate device and thus the flexible instrument  100  can be altered. For example, constructing the outer conductor  118  or insulating layer  120  of a solid tube or layers of concentric solid tubes, could provide for a stiffer flexible instrument  100  than use of a material wound in a ribbon layer or plurality of ribbon layers. A more flexible construction could be provided by constructing braided layers of filaments wound in different directions. Accordingly, in some embodiments, the outer conductor  118  includes at least one multi-filament layer having a plurality of filaments (e.g., ribbons, tapes, wires, fibers, etc.) that are braided or woven around the insulating layer  120 . The filaments can be made of a conductive material (e.g., nitinol, copper, etc.). Alternatively or in combination, the outer conductor  118  can include at least one layer in which a single filament of conductive material is wrapped around the insulating layer  120  (e.g., a wrapped metal ribbon). Optionally, the outer conductor  118  can include at least one layer of a solid material (e.g., a foil layer, sheet, coating, a tube, etc.). 
     In some embodiments, the outer conductor  118  is composed entirely of a single material and/or structure. For example, the outer conductor  118  can include one or more filaments that are braided or wrapped along the entire length of the flexible instrument  100 . As another example, the outer conductor  118  can include a thin solid tube that extends along the entire length of the flexible instrument  100 . In other embodiments, however, different portions of the outer conductor  118  can be composed of different materials and/or structures. For example, the outer conductor  118  can include a combination of braided and wrapped materials, such as a first layer or region composed of a braided material, and a second layer or region composed of a wrapped material. As another example, the outer conductor  118  can include an outer braided multi-filament layer and an inner foil layer. In some examples, the foil layer could made of a material provided for shielding (e.g. copper). In other embodiments requiring higher stiffness, the inner layer can be made of a nitinol tube or ribbon providing for less conductivity than copper but higher stiffness and recoverability. In a further example, the outer conductor  118  can include a braided multi-filament layer, a foil layer, and a layer made of a resiliently flexible material (e.g., nitinol) to impart recoverability to the flexible instrument  100 . In some embodiments, the material properties of the outer conductor  118  may vary down a length of the outer conductor  118 . For example, a distal section may require higher stiffness to allow for puncturing of tissue by the flexible instrument  100 . Accordingly, at a distal section the inner layer may be made of a nitinol tube and/or the outer layer may be made of a ribbon layer, while at a proximal section, the inner layer may be made of a foil layer and/or the outer layer may be braided. 
     The flexible instrument  100  can also include at least one jacket layer or coax jacket layer  122  (also referred to herein as an “intermediate layer”) positioned over at least a portion of the outer conductor  118 . In the illustrated embodiment, the jacket layer  122  extends along and surrounds the entire length of the outer conductor  118 . Similarly, the jacket layer  122  can be formed over the entire length of the antenna body  112  and the transmission member  102 . In other embodiments, however, the jacket layer  122  can be formed over only a portion of the outer conductor  118 . For example, the jacket layer  122  can be located only at the distal section of the outer conductor  118 , such as the region corresponding to the antenna body  112 , and, optionally, a portion of the transmission member  102  (e.g., the distal portion  106 ). As another example, the jacket layer  122  can be localized to discrete regions of the outer conductor  118  at or near the locations where recesses are to be formed, as discussed further below. 
     The jacket layer  122  can improve the structural integrity of and/or provide mechanical support to at least a portion of the flexible instrument  100  (e.g., to the antenna body  112 ). Additionally, in embodiments where the outer conductor  118  is made of braided, woven, or wrapped filaments, the jacket layer  122  can hold the filaments together to reduce fraying or unraveling when the outer conductor  118  is cut to form a recess, as described in greater detail below. The jacket layer  122  can also be resiliently flexible to improve the recoverability of the flexible instrument  100  after deformation. Optionally, the jacket layer  122  can also increase the stiffness of the flexible instrument  100  along axis A, e.g., to facilitate puncturing of tissue. The jacket layer  122  can be sufficiently thin so the overall diameter of the flexible instrument  100  remains small enough to navigate narrow and/or tortuous passageways, while also avoiding interference with coolant flow around the flexible instrument  100  (described in greater detail below). For example, the thickness of the jacket layer  122  can be less than or equal to 30 microns, 25 microns, 20 microns, 15 microns, 10 microns, or 5 microns. In some embodiments, the thickness can be within a range from 25.4 microns to 6.35 microns. In some embodiments, the jacket layer  122  is composed of a non-conductive material, such as a polymer, a plastic, a PET coating, a heat-shrink material, or a combination thereof. In other embodiments, however, the jacket layer  122  may be composed of a partially conductive material (depending upon the positioning of the layer relative to the antenna body  112 ). The jacket layer  122  can be applied as a single layer of material, or can be applied in multiple layers by braiding multi-filament layers, wrapping ribbon layers, or heat shrinking. 
     In additional embodiments, one or more aspects of the inner conductor  116 , outer conductor  118 , insulating layer  120 , and/or jacket layer  122  may be modified to help further prevent kinking while the flexible instrument  100  is bending through narrow and/or tortuous passageways. Such modifications can include, for example, varying layer thickness, material selection, and/or braiding to obtain an optimal stiffness for the flexible instrument  100  while simultaneously allowing for sufficient flexibility for navigation. 
     In some embodiments, the antenna body  112  is patterned with one or more recesses, such as a first recess  124   a  and a second recess  124   b  (collectively, “recesses  124 ”). The recesses  124  can be any structure configured to allow energy to radiate from the inner conductor  116 , such as apertures, slots, grooves, channels, trenches, spirals, cuts, etc. As shown in  FIG.  1   , the recesses  124  are formed in and extend through the entire thickness of the jacket layer  122  and the outer conductor  118 , with the insulating layer  120  and inner conductor  116  remaining intact. Alternatively, the recesses  124  can also be formed in and extend at least partially through the insulating layer  120 , with the inner conductor  116  remaining intact. In embodiments where the recesses  124  extend through the entire thickness of the insulating layer  120 , the exposed surfaces of the inner conductor  116  and/or outer conductor  118  at the recesses  124  can be sealed or otherwise insulated from each other (e.g., using a non-conductive material) to prevent electrical shorting between the inner conductor  116  and outer conductor  118  at those locations. The recesses  124  can be formed by cutting or otherwise removing portions of the jacket layer  122 , outer conductor  118 , and (in some instances) the insulating layer  120 , as described in greater detail below. 
     The configuration of the recesses  124  (e.g., depth, number, position, size, shape, etc.) can form a recess pattern which can be selected to produce a desired pattern of energy radiation from the antenna body  112  and the proper frequency responses needed for the particular medium that the antenna body  112  is radiating in. The depth of the recess, the recess length, the spacing between the recesses  124 , the number of recesses  124 , the shape of the recesses  124 , the positioning of the recesses  124  along antenna body  112 , and/or the relative positioning of the recesses  124  to one another, can define the recess pattern. In the illustrated embodiment, for example, the first recess  124   a  is located at a distal tip portion  126  of the antenna body  112 , and the second recess  124   b  is positioned proximal to the first recess  124   a . The first recess  124   a  and second recess  124   b  can be separated from each other by a separation distance within a range from 3 mm to 10 mm, such as 6.5 mm. As shown in  FIG.  1   , the recesses  124  each extend partially or entirely around the circumference of the antenna body  112  to form a pair of arcuate or circular slots having rectangular cross-sectional shapes. The length of each recess  124  (e.g., as measured along the longitudinal direction parallel to axis A) can be greater than 0 mm and less than or equal to 10 mm (e.g., 1 mm). Optionally, the recesses  124  can have different dimensions, e.g., the first recess  124   a  can be longer than the second recess  124   b , or vice-versa. In other embodiments, however, some or all of the recesses  124  can have the same dimensions, e.g., the first recess  124   a  can have the same length as the second recess  124   b . The configuration of the recesses  124  shown in  FIG.  1    can produce an energy radiation pattern having a spherical or generally spherical electric field profile, which may be beneficial for efficient tissue ablation. The configuration of the recesses  124  also affects the frequency response in a particular medium, which affects how efficiently the antenna body  112  radiates into the medium. 
     In other embodiments, for example, the antenna body  112  can include a different number of recesses  124  (e.g., one, three, four, or more). The locations of the recesses  124  can also be changed, e.g., the first recess  124   a  or the second recess  124   b  can be omitted, the antenna body can include one or more additional recesses between the first recess  124   a  and the second recess  124   b , and so on. Additionally, one or more of the recesses  124  can have a different overall shape (e.g., linear, curved, curvilinear, annular, helical, serpentine, zig-zag, etc.) and/or cross-sectional shape (e.g., square, trapezoidal, triangular, circular, oval, etc.). Although  FIG.  1    illustrates each recess  124  as extending circumferentially around the antenna body  112 , in other embodiments one or more of the recesses  124  can be arranged differently, e.g., extending longitudinally along the length of the antenna body  112 , extending helically around the antenna body  112 , or any other suitable geometry. 
     In some embodiments, in addition to recesses  124 , the outer conductor  118  may include patterning, e.g., a cut pattern within just the outer conductor  118  to alter flexibility. As compared to recesses  124 , such patterning may not extend through the jacket layer  122  and would not alter delivery of energy. The patterning can include a number of different shapes/arrangements (e.g., discrete slits, spiral/helical slits or cuts, rectangular openings, H-shaped patterns, etc.). The patterning may extend along only a selected portion or portions of the outer conductor  118  along the length of the flexible instrument  100 . Further, in some embodiments, the patterning can vary along the length of the outer conductor  118 . 
     The antenna assembly  104  further includes one or more inserts coupled to the antenna body  112 , such as a first insert  128   a  and a second insert  128   b  (collectively, “inserts 128”). Each insert  128  is positioned within a respective recess  124  to cover and protect the portions of the inner conductor  116  and/or insulating layer  120  at or near the recess  124 . As previously described, when portions of the jacket layer  122 , outer conductor  188 , and/or insulating layer  120  are removed to form the recesses  124 , the remaining portions of the insulating layer  120  and/or inner conductor  116  may lack sufficient mechanical strength and/or axial rigidity to withstand bending or other deformations that may occur during operation of the flexible instrument  100 . Accordingly, the inserts  128  can reinforce the antenna body  112  at or near the recesses  124  to reduce the likelihood of mechanical failure (e.g., buckling, kinking) at those locations. The presence of the inserts  128  can also increase the stiffness of the antenna body  112  to facilitate puncturing of tissue. 
     The inserts  128  can be composed of a low RF or microwave loss non-conductive material to reduce interference with energy radiation from the inner conductor  116 . The non-conductive material can be, for example, a plastic material (e.g., PTFE, PEEK, fluorinated ethylene propylene (FEP), polyurethane), a heat-shrink material, or a combination thereof. In some embodiments, the inserts  128  are provided as pre-formed solid components that are positioned within the recesses  124  and secured in place (e.g., using adhesives, fasteners, an additional layer of material over the inserts  128 , etc.). For example, the inserts  128  can be tubes that are positioned within the recesses  124 . The tubes can be slit or otherwise expandable to allow the tubes to slipped over the antenna body  112  and into the recesses  124 . In other embodiments the inserts  128  can be composed of a filler (e.g., beads, fibers, glue, resin, foam, etc.) that are placed into the recesses  124 , then solidified (e.g., by bonding, curing, adhering, etc.) to form the inserts  128 . For example, the filler can be plastic beads (e.g., beads composed of regular PTFE, PTFE foam, FEP, PEEK, etc.). As another example, the filler can be a glue or other flow-able material (e.g., polyurethane) that fills the recesses  124  and is subsequently hardened and/or cured in place to form the inserts  128 . In some embodiments, the filler material is a low RF or microwave loss material that can also withstand the temperatures needed when the antenna body  112  is operating at or near maximum power. 
     In the illustrated embodiment, each insert  128  fills the entirety of the corresponding recess  124 , with the geometry (e.g., size, shape) of each insert  128  being generally similar or identical to the geometry of the corresponding recess  124 . For example, the inserts  128  can each be arcuate or annular structures (e.g., tubes, rings, bands, etc.) shaped to fit into the recesses  124 . As shown in  FIG.  1   , the first insert  128   a  has a rectangular cross-sectional shape corresponding to the rectangular cross-sectional shape of the first recess  124   a , and the second insert  128   b  has a rectangular cross-sectional shape corresponding to the rectangular cross-sectional shape of the second recess  124   b . Likewise, the length and height of each insert  128  can match the length and height of the respective recess  124 . In other embodiments, however, the inserts  128  may not fill the entire recess  124 . For example, the inserts  128  can fill only the portions of the recess  124  closest to the inner conductor  116 , while leaving the other portions of the recess  124  empty. In such embodiments, the geometry of the inserts  128  can be different from the geometry of the corresponding recesses  124  (e.g., the inserts  128  can have a smaller length and/or height compared to the recesses  124 ). 
     In some embodiments, the antenna assembly  104  further includes a cap structure  114  coupled to the distal tip portion  126  of the antenna body  112 , e.g., at a location distal to the first recess  124   a  and first insert  128   a . The cap structure  114  can be coupled to the inner conductor  116  (e.g., by soldering), formed on the inner conductor  116 , or integrally formed with the inner conductor  116 . The cap structure  114  can be made of a conductive material, such as a metal (e.g., nitinol, copper, etc.). For example, the cap structure  114  may be formed from a conductive metal tube (e.g., nitinol, copper, etc.) surrounding a portion of the inner conductor  116  extending distally beyond the outer conductor  118  and distal tip portion  126  of the antenna body  112 . The cap structure  114  can be electrically coupled with solder to the inner conductor  114 . The geometry of the cap structure  114  (e.g., shape, length, diameter, etc.) can be configured to affect the energy radiation pattern of the antenna assembly  104 . For example, in the illustrated embodiment, the cap structure  114  has a generally cylindrical shape with a length within a range from 1 mm to 3 mm (e.g., 2 mm), and a diameter identical or similar to the combined diameter of the inner conductor  116 , outer conductor  118 , and insulating layer  120 . In other embodiments, however, the cap structure  114  can have a different shape, such as a conical, pointed, domed, hemispherical, or rounded shape. For example, the cap structure  114  can have a conical or pointed shape, e.g., to allow the flexible instrument  100  to puncture tissue. In still other embodiments, the cap structure  114  may be optional and may be omitted from the antenna assembly  104 . In such embodiments, a portion of the inner conductor  116  can extend distally beyond the outer conductor  118  and the distal tip portion  126  of the antenna body  112 . 
     Optionally, at least a portion of the cap structure  114  (e.g., the distal end of the cap structure  114 ) can be sealed with a plug (not shown). The plug can be made of a non-conductive material, such as glue or another adhesive, a conformal coating (e.g., a parylene coating or vapor-deposited coating), or a reflowable material. In some embodiments, for example, the plug is formed by adding glue to the distal end of the cap structure  114 . As another example, the plug can be formed by molding a reflowable material with a glass mold. The plug can be configured to seal the cap structure  114  and/or other portions of the antenna assembly  104  from ingress of fluid. 
     The recess pattern and the length, diameter, and/or shape of the cap structure  114  (if the antenna assembly  104  includes the cap structure  114 ), all affect the frequency behavior and the resulting radiation into the medium. The configuration of the recesses  124  and inserts  128  can also be varied as desired to produce different energy radiation patterns. 
     The flexible instrument  100  can include one or more additional layers of material over the antenna assembly  104 . As shown in  FIG.  1   , for example, the flexible instrument  100  includes a barrier layer  130  positioned over at least a portion of the antenna assembly  104  (e.g., the outer conductor  118 , jacket layer  122 , inserts  128 , and/or cap structure  114 ). In embodiments where the cap structure  114  is sealed with a plug, the barrier layer  130  can extend partially or entirely over the cap structure  114  and plug. In some embodiments, the barrier layer  130  is localized only to the portions of the antenna assembly  104  at or near the locations of the recesses  124  and inserts  128 . In other embodiments, however, the barrier layer  130  can extend over the entire length of the antenna assembly  104 . Optionally, the barrier layer  130  can also extend partially or completely over the transmission member  102 . 
     The barrier layer  130  can create a barrier or seal to prevent inward migration of fluid (e.g., coolant, body fluid, etc.). For example, the barrier layer  130  can prevent fluid from moving beyond the inserts  128  and toward the inner conductor  116  and/or insulating layer  120 . The barrier layer  130  can also seal the distal tip  110  of the antenna assembly  104  to prevent entry of fluid. In some embodiments, the barrier layer  130  also secures the inserts  128  within the recesses  124 , in addition or as an alternative to adhesives. Optionally, the barrier layer  130  can provide mechanical stability and axial rigidity to the flexible instrument  100 . In some embodiments, the barrier layer  130  can include multiple layers, e.g., an inner barrier layer (not shown) which can help secure the inserts  128  and the cap structure  114  and/or an outer barrier layer (not shown) which can provide the seal to prevent fluid ingress. In some embodiments, multiple layers may be used to achieve desired bending and stiffness, by using various materials and varying the number of layers. 
     The barrier layer  130  may be formed of a flexible and fluid impermeable material. In some embodiments, the barrier layer  130  is composed of a non-conductive material, such as a polymer (e.g., fluropolymer), a plastic, a PET coating, a heat-shrink material, or other conformal coating (e.g., a parylene coating or vapor-deposited coating), or a combination thereof. The barrier layer  130  may be thin and form fit around the components of the flexible instrument  100 , or may maintain a flexible tubular form. Optionally, the region of the barrier layer  130  at the distal tip  110  of the antenna assembly  104  can be formed from or sealed with an adhesive. In such embodiments the adhesive may be composed of the same material as the rest of the barrier layer  130 , or may be composed of a different material. 
     Although  FIG.  1    illustrates a particular configuration for the flexible instrument  100 , it will be appreciated that this configuration can be varied in many different ways. For example, other elongate device configurations with different configurations, shapes, etc. of the inner conductor  116 , outer conductor  118 , and insulating layer  120  can be used. As another example, the flexible instrument  100  can include additional layers of material (e.g., insulating layers, jacket layers, barrier layers, etc.) not shown in  FIG.  1   . Additionally, although  FIG.  1    depicts the transmission member  102  and antenna assembly  104  as being integrally formed with each other, in other embodiments the transmission member  102  and antenna assembly  104  can be discrete components that are subsequently coupled to each other. For example, the transmission member  102  can be formed from a first elongate device section and the antenna assembly  104  can be formed from a second, different elongate device section that is distinct from the first elongate device section. The second elongate device section can be fixedly coupled to the distal end of the first elongate device section to form the flexible instrument  100 . In such embodiments, the first and second elongate device sections can each have a respective inner conductor, outer conductor, and insulating layer with features that are identical or generally similar to the features of the inner conductor  116 , outer conductor  118 , and insulating layer  120 . 
       FIG.  2    is a side cross-sectional view of a flexible instrument  200  for tissue ablation configured in accordance with another embodiment of the present technology. The flexible instrument  200  is generally similar to the flexible instrument  100  of  FIG.  1    such that like reference numerals are used to identify like elements illustrated in  FIGS.  1  and  2    (e.g., transmission member  102  versus transmission member  202 ). Accordingly, the discussion of the flexible instrument  200  will be limited to those features that differ from the flexible instrument  100  of  FIG.  1   . 
     The flexible instrument  200  includes an antenna assembly  204  having an antenna body  212  with a first recess  224   a  and a second recess  224   b . In contrast to the flexible instrument  100  of  FIG.  1   , the first recess  224   a  is not located at the distal tip portion  226  of the antenna body  212 . Instead, the first recess  224   a  is proximal to and spaced apart from the distal tip portion  226 , such that the outer conductor  218  and jacket layer  222  at the distal tip portion  226  remain intact. The distance between the first recess  224   a  and the distal tip portion  226  can be greater than 0 mm and less than or equal to 10 mm. 
     Additionally, rather than a cap structure, the antenna assembly  202  includes a conductive material  250  coupled to the distal tip portion  226  of the antenna body  212 . In one embodiment, the conductive material  250  can be electrically coupled to the inner conductor  218  only or the outer conductor  216  only. In another embodiment, however, the conductive material  250  can electrically couple (e.g., electrically short) the inner conductor  216  with the outer conductor  218  of the antenna body  212 . The conductive material  250  may comprise solder or other suitable conductive materials. The conductive material  250  may also comprise copper (e.g., a copper tube). The geometry (e.g., shape, length, diameter, etc.) of the conductive material  250  can be configured to affect the energy radiation pattern of the antenna assembly  104 . Optionally, at least a portion of the conductive material  250  (e.g., the distal end of the conductive material  250 ) can be sealed with a plug (not shown). The plug can be made of a non-conductive material, such as glue or another adhesive, a conformal coating (e.g., a parylene coating or vapor-deposited coating), or a reflowable material. In some embodiments, for example, the plug is formed by adding glue to the distal end of the conductive material  250 , or by molding a reflowable material with a glass mold. The plug can be configured to seal the conductive material  250  and/or other portions of the antenna assembly  204  from ingress of fluid. 
       FIG.  3    is a side cross-sectional view of an energy delivery system  300  for tissue ablation configured in accordance with an embodiment of the present technology. In the illustrated embodiment, the energy delivery system  300  includes the flexible instrument  100  of  FIG.  1   , a sheath  302 , at least one fluid conduit  304 , and a fluid cooling system  306 . In other embodiments, however, the flexible instrument  100  can be replaced with any of the other embodiments of flexible instruments described herein (e.g., flexible instrument  200  of  FIG.  2   ). 
     The sheath  302  is an elongated hollow structure having a central lumen or channel  308  extending between a distal end portion  310  and a proximal end portion (not shown). The flexible instrument  100  is disposed within the central lumen  308 . In some embodiments, the sheath  302  may be formed from a thermoplastic material or from other flexible and fluid impermeable materials. In some embodiments, the sheath  302  is closed, sealed, or otherwise restricts fluid from passing into or out of the sheath  302 . For example, the sheath  302  can be coupled to and/or sealed by a tip section  312  at the distal end portion  310  of the sheath  302 . The tip section  312  may allow the sheath  302  to more easily puncture anatomic tissue. In some embodiments, the tip section  312  may be formed in any shape, including any number of faces forming the tip, at any angle, and/or with any ratio of sizes (e.g., width vs. length) that will optimize tissue penetration. In the illustrated embodiment, for example, the tip section  312  is a conical structure with a triangular cross-sectional shape. In other embodiments, the tip section  312  can have a different shape, such as a domed, hemispherical, or rounded shape. The tip section  312  can be formed using glass molds or other suitable techniques. The tip section  312  may be composed of fluoropolymers, e.g., ethylene tetrafluoroethylene (ETFE), PEEK, other high temperature plastic materials, and/or other suitable materials. In still further embodiments, the tip section  312  may have other configurations/features. For example, one or more portions of the tip section  312  may be radiopaque. In such embodiments, the tip section  312  may comprise a material or materials to make the tip section radiopaque and/or the tip section may include an insert made of a highly radiopaque material. 
     Various tips for optimizing tissue penetration are described in U.S. Pat. App. Serial No. 16/670,846 filed Oct. 31, 2019, disclosing “Tissue Penetrating Device Tips” and PCT App No. PCT/US19/24564 filed Mar. 28, 2019, disclosing “Systems and Methods Related to Flexible Antennas,” which are both incorporated by reference herein in their entireties. Alternatively or in combination, the sheath  302  may have openings, slits, or otherwise be unsealed at or along any portion of the sheath  302  (e.g., at the distal end portion  310  of the sheath  302 ) to allow fluid to pass into the sheath  302  or out from the sheath  302 . Optionally, the tip section  312  can be omitted, and the distal end portion  310  can have a flat end face, or can be left open. 
     The fluid cooling system  306  can be configured to cool the flexible instrument  100  by introducing a coolant (e.g., a fluid  314  or another liquid or gaseous cooling agent) into the central lumen  308  (e.g., also referred to herein as a chamber or channel) of the sheath  302 . The fluid  314  may be, for example, water or a saline solution. The fluid cooling system  306  can be coupled to the central lumen  308  and/or the sheath  302  to deliver the fluid  314  into the central lumen  308 . The fluid cooling system  306  may include a fluid reservoir  316  (shown schematically) and other components such as pumps, valves, refrigeration systems, suction systems, and/or sensors (not shown). In the illustrated embodiment, for example, the fluid cooling system  306  includes or is coupled to at least one fluid conduit  304  that extends through at least a portion of the central lumen  308  within the sheath  302 . The fluid conduit  304  can extend along at least a portion of the flexible instrument  100 , such as along the transmission member  102  and/or the antenna assembly  104 . The fluid  314  may be directed within the central lumen  308  through the fluid conduit  304 . Accordingly, a channel may be formed between the flexible instrument  100  and the interior of the sheath  302 . In some embodiments, the fluid conduit  304  may extend to at least a distal end portion of the antenna assembly  104  to provide recoverable flexibility and support along a maximized length of the flexible instrument  100  and an added benefit of delivering coolant to the distal end portion of the antenna assembly  104  for increased and/or more uniform cooling of the antenna. Further details regarding such embodiments are described below with reference to  FIGS.  9 A- 16   . 
     The flexible instrument  100  can have an outer diameter that is sufficiently small to reduce or avoid interference with flow of the fluid  314  through the channel. For example, the outer diameter of the flexible instrument  100  can be less than or equal to 2 mm, 1.75 mm, 1.5 mm, 1.25 mm, 1 mm, or 0.75 mm. In some embodiments, the maximum clearance between the outer surface of the flexible instrument  100  and the inner surface of the sheath  302  can be at least 0.1 mm, 0.25 mm, 0.5 mm, 0.75 m, 1 mm, or 1.25 mm. 
     The fluid cooling system  306  may be an open loop system, a partially open loop system, a closed loop system, or any other suitable type of cooling system. The fluid conduit  304  may be used, for example, to provide inflow of the fluid  314  to the central lumen  308 . The fluid  314  can circulate about the antenna assembly  104  and/or the transmission member  102  within the central lumen  308 , and can return in a proximal direction within the central lumen  308  to be purged in a reservoir (not shown) or purged to the environment. In other embodiments, the fluid  314  can exit the sheath  302  via openings or slits in the sheath  302 , or return to the fluid cooling system  306  via the central lumen  308  and/or another fluid conduit (not shown). Alternatively, the fluid conduit  304  can be used to provide return flow of the fluid  314  from the central lumen  308  by discontinuing inlet fluid from the fluid reservoir  316 , reversing flow, and providing suction to the fluid conduit  304  using the fluid cooling system  306 . In other embodiments, a separate fluid conduit (not shown) can be provided that does not provide inflow of fluid  314  and is only used for return flow. In some embodiments, the return flow can be purged in a combination of tlow through the central lumen  308  in a proximal direction, flow through fluid conduits, and/or through openings in sheath  302 . 
     During operation of the energy delivery system  300 , the sheath  302  containing the flexible instrument  100  is inserted into the patient’s anatomy and navigated to a target site. To facilitate delivery of the sheath  302  and flexible instrument  100  to the target site, the sheath  302  and/or flexible instrument  100  must be sufficiently flexible to navigate tortuous anatomical passageways. In addition, the distal section of the sheath  302  and/or flexible instrument  100  typically undergoes substantial deformation during delivery to the target site. Thus, the sheath  302  and/or flexible instrument  100  must be able to recover to an initial (e.g., undeformed) shape or state after deformation to reduce trajectory error once near a target site, where puncturing of tissue is required to accurately deliver the antenna assembly  104  to the target site. Accordingly, in some embodiments, the sheath  302  itself is composed of one or more materials that provide mechanical properties for recoverability (e.g., spring back) and stiffness. For example, the sheath  302  can be formed of a resiliently flexible material (e.g., nitinol or another suitable shape memory material). The sheath  302  may be composed a non-conductive material and/or a conductive material (e.g., depending upon positioning relative to the antenna assembly). Alternatively or in combination, the flexible instrument  100  may include resiliently flexible materials, as previously described. Additionally, in some embodiments, the fluid conduit  304  is also composed partially or entirely of a resilient flexible material to provide recoverability. However, many shape memory and other resiliently flexible materials (including nitinol) are conductive at the microwave frequency range (e.g., 300 MHz to 300 GHz), meaning that any region of the fluid conduit  304  that runs alongside the antenna assembly  104  within the sheath  302  and is formed of a conductive material would interfere with the antenna assembly  104  during energy delivery. 
     Accordingly, the fluid conduit  304  can include a first region  318  formed of a resiliently flexible material (e.g., a shape memory material such as nitinol) and a second region  320  formed of a non-conductive material (e.g., PEEK, PTFE, PET, or another suitable plastic or polymer material). The first region  318  extends along the transmission member  102  and the second region  320  extends along the antenna assembly  104 . As illustrated in  FIG.  3   , the first region  318  terminates at a point along the length of the flexible instrument  100  proximate to the proximal portion  108  of the antenna assembly  104  such that the first region  318  does not interfere with the antenna assembly  104  during energy delivery. The second region  320  can terminate at or near the di stal tip  110  of the antenna assembly  104 , or can extend to the distal end portion  310  of the sheath  302  (e.g., to provide stiffness and axial rigidity along the entire length of the flexible instrument  100  and/or sheath  302 ). Because the second region  320  of the fluid conduit  304  is formed of a material that is non-conductive at the frequency range of the antenna assembly  104 , the second region  320  does not interfere with the antenna assembly  104  during energy delivery. 
     In this manner, the fluid conduit  304  illustrated in  FIG.  3    provides the flexibility to navigate the sheath  302  and flexible instrument  100  throughout patient anatomy as well as the rigidity to accurately deliver the antenna assembly  104  to a target site during a puncture operation. In particular, the first region  318  of the fluid conduit  304  provides recoverable flexibility to the sheath  302  while the second region  320  of the fluid conduit  304  provides added stiffness to the portion of the sheath  302  corresponding to the antenna assembly  104  without interfering with the antenna assembly  104  during energy delivery. In addition, the first and second regions  318  and  320  of the fluid conduit  304  provide axial rigidity along the axis A to facilitate delivery of the antenna assembly  104  to a target site during a puncture operation while reducing the likelihood of buckling or kinking along the sheath  302  and/or flexible instrument  100 . 
     It will be appreciated that, in some instances, a transition section between the first and second regions  318  and  320  may be a point of weakness along the length of the flexible instrument  100 , and in some instances can cause kinking. To help address this issue, the second region  320  of the fluid conduit  304  can be joined to the first region  318  using any of a variety of methods to help provide a consistent and reliable connection. For example, in some embodiments to form the fluid conduit  304 , a tube forming the second region  320  (e.g., a tube composed of PEEK or plastic material) can be inserted into a tube forming the first region  318  (e.g., a tube composed of nitinol), and then the mating ends of the two tubes can be tapered. In another embodiment, the proximal end portion of the second region  320  can be spliced to extend over or within the distal end portion of the first region  318 . As another example, the second region  320  can be butt-jointed and welded or glued with the first region  318 . As still another example, the first region  318  can be slot cut to reduce its stiffness (e.g., as described in greater detail below with respect to  FIG.  5   ) and then overlapped with the second region  320  to create a gradual transition between the first and second regions  318  and  320 . In some embodiments, a FEP layer may surround the fluid conduit  304  to aid in joining the first region  318  and the second region  320 . In some embodiments, a transition section between the first region  318  (e.g., composed of nitinol) and the second region  320  (e.g., composed of plastic or polymer material) may be composed of a mixture of the two different materials. In other embodiments, however, the transition section may have a different composition. 
     Although  FIG.  3    illustrates a single fluid conduit  304 , in other embodiments the energy delivery system  300  can include multiple fluid conduits  304  (e.g., two, three, or more). In such embodiments, each fluid conduit  304  can be separate from one another such that each can flex independently of one another when the sheath  302  is navigated to a target. In some embodiments, separate fluid conduits  304  provide greater recoverable flexibility and/or axial rigidity than fluid conduits  304  that are attached to one another. In other embodiments of the present technology, however, the fluid conduits  304  can be joined to one another and/or can be formed as a single structure. Each fluid conduit  304  can be fixed within the sheath  302 , or can be slidable or otherwise movable within the sheath  302  (e.g., distally and/or proximally along a direction parallel with the axis A). In still further embodiments including multiple fluid conduits  304 , the conduits  304  can be staggered longitudinally (i.e., the longitudinal positioning of the distal ends of the tubes can be different along the length of the device.) Additionally, in embodiments including multiple conduits  304 , the portions of the individual conduits  304  that composed of different materials (i.e., the first regions and the second regions) can differ between the different conduits  304 . For example, the longitudinal lengths of the first regions  318  (e.g., composed of nitinol) relative to the lengths of the second regions  320  (e.g., composed of plastic material(s)) can vary between the individual conduits. Moreover, in some embodiments, the slot cut patterns for the individual conduits  304  can also vary. 
       FIG.  4    is a cross-sectional view of an energy delivery system  400  configured in accordance with another embodiment of the present technology. The energy delivery system  400  is generally similar to the energy delivery system  300  of  FIG.  3    except that the fluid conduit  404  of the energy delivery system  400  illustrated in  FIG.  4    includes a third region  422  proximal to the first region  418 . Accordingly, like reference numerals are used to identify like elements illustrated in  FIGS.  3  and  4   , and the discussion of the energy delivery system  400  will be limited to those features that differ from the energy delivery system  300  of  FIG.  3   . Further, it will be appreciated that the components of the energy delivery system  400  may have many of the same features and advantages as the energy delivery system  300  described above. 
     As illustrated in  FIG.  4   , the sheath  402  includes a proximal section  424  and a distal section  426 . The distal section  426  extends distally from the proximal section  424  at a point along the length of the transmission member  102  to at least the distal tip  110  of the antenna assembly  104  (e.g., to the distal end  410  of the sheath  402 ). The third region  422  of the fluid conduit  404  can extend along at least a portion of the proximal section  424  of the sheath  402 , while the first region  418  of the fluid conduit  404  can extend along at least a portion of the distal section  426  of the sheath  402  to provide recoverable flexibility along this portion of the sheath  402 . The second region  420  of the fluid conduit  404  can extend along the antenna assembly  104 , terminating at or near the distal tip  110  of the antenna assembly  104 . 
     Resiliently flexible materials, such as nitinol or other shape memory materials, are often expensive relative to other materials. Moreover, the proximal section  424  of the sheath  402  typically does not undergo the extent of deformation experienced by the distal section  426  of the sheath  402 . As such, recoverable flexibility can be less of a concern along the proximal section  424  of the sheath  402  than the distal section  426 . Therefore, to reduce costs, the third region  422  of the fluid conduit  404  can be formed of a material that is less expensive than the resiliently flexible material (e.g., nitinol) used to form the first region  418  of the fluid conduit  404 . For example, the third region  422  of the fluid conduit  404  can be formed of a plastic, a polymer, or other suitable material (e.g., stainless steel) which can provide support and axial rigidity to the proximal section  424  of the sheath  402  but does not provide the recoverable flexibility offered by a more expensive material such as nitinol. In some embodiments, the material used to form the third region  422  of the fluid conduit  404  can be selected based on a desired flexibility (e.g., stiffness) and/or axial rigidity of the proximal section  424  of the sheath  402 . The second region  420  can be formed of a non-conductive material as previously described. In alternative embodiments where cooling and rigidity needs do not require the fluid conduit  404  to extend to the distal tip  110  of antenna assembly  104 , the second region  420  can be omitted. 
     The third region  422  of the fluid conduit  404  can be joined to the first region  418  using any of a variety of methods. For example, the distal end portion of the third region  422  can be spliced to extend over or within the proximal end of the first region  418 . Alternatively, the distal end portion of the third region  422  can be shrunk and at least partially overlapped by the proximal end of the first region  418 . As another example, the third region  422  can be butt-jointed with or glued or welded to the first region  418 . As still another example, the first region  418  can be slot cut to reduce its stiffness (e.g., as described in greater detail below with respect to  FIG.  5   ) and then be overlapped with the third region  422  to create a gradual transition between the regions  422  and  418 . In some embodiments, a FEP layer may surround the fluid conduit  404  to aid in joining the third region  422  and the first region  418 . 
       FIG.  5    is a cross-sectional view of an energy delivery system  500  configured in accordance with a further embodiment of the present technology. The energy delivery system  500  is generally similar to the energy delivery systems  300 / 400  of  FIGS.  3  and  4    except that the fluid conduit  504  illustrated in  FIG.  5    is patterned with a plurality of slots  528  (e.g., cutouts, slits, etc.). Accordingly, like reference numerals are used to identify like elements illustrated in  FIGS.  3 - 5   , and the discussion of the energy delivery system  500  will be limited to those features that differ from the energy delivery systems  300 / 400  of  FIGS.  3  and  4   . Further, the components of the energy delivery system  500  may have many of the same features and advantages as the energy delivery systems  300  and  400  described above. 
     As shown in  FIG.  5   , the fluid conduit  504  includes a first region  518  and a second region  520 . In the illustrated embodiment, both the first region  518  and the second region  520  of the fluid conduit  504  include a gradient of slots  528  along their lengths to vary the stiffness of the corresponding regions  518  and  520  of the fluid conduit  504 . For example, the fluid conduit  504  can include slots  528  at various locations along the first region  518  and/or the second region  520  to vary the stiffness of the fluid conduit  504  such that the transition between the first region  518  and the second region  520  is gradual (e.g., to maintain structural integrity of the fluid conduit  504  across the transition portion). As another example, the first region  518  and/or the second region  520  of the fluid conduit  504  can include a greater number of slots  528  at locations where a greater amount of flexibility is desired and/or a lesser number of slots  528  at locations where a greater amount of stiffness is desired. As shown in  FIG.  5   , for example, both the first region  518  and the second region  520  include spiral slots or slits  528  along their lengths. The second region  520  includes a greater number of spiral slots  528  toward the distal tip  110  of the antenna  104  to increase the flexibility of the fluid conduit  504  along this portion of the fluid conduit  504 . The number of spiral slots  528  decreases proximally over the length of the second region  520  and over the transition from the second region  520  to the first region  518  such that the fluid conduit  504  maintains a greater amount of stiffness and/or recoverable flexibility along this portion of the fluid conduit  504  and/or such that the transition between the first region  518  and the second region  520  is gradual. 
     Although the fluid conduit  504  is illustrated as having spiral slots  528 , fluid conduits configured in accordance with other embodiments of the present technology can include slots of other shapes and/or patterns. For example,  FIG.  6 A  is a side view of a patterned fluid conduit  604   a  having a plurality of slots  628   a  in the shape of discrete slits. As another example,  FIG.  6 B  is a side view of a patterned fluid conduit  604   b  having a plurality of slots  628   b  in the shape of rectangular cutouts. Both the slots  628   a  ( FIG.  6 A ) and the slots  628   b  ( FIG.  6 B ) are cut into the fluid conduits  604   a  and  604   b , respectively, in an “H” pattern. Other patterns (e.g., spiral, zig zag, straight, etc.) are of course possible and within the scope of the present technology. 
     Referring again to  FIG.  5   , in some embodiments, the patterning of the slots  528  can be configured to reinforce point of weakness along the flexible instrument  100  and/or sheath  502 . For example, the portions of the flexible instrument  100  containing the recesses  124  and inserts  128  can be relatively weak compared to the remaining portions of the flexible instrument  100 . Accordingly, the fluid conduit  504  can include fewer or no slots  528  near those portions of the flexible instrument  100 . Additionally, patterned slots can be utilized to create a more gradual transition between components made from different materials to reduce or eliminate weaknesses associated with these points. 
     In some embodiments, one or more of the slots  528  in can serve as points of exit for the fluid  514  to exit the fluid conduit  504  and enter the central lumen  508  (or vice versa.). For example, fluid  514  can be delivered to the central lumen  508  during delivery of the sheath  502  and flexible instrument  100  to a target site within a patient. In these embodiments, the fluid  514  can exit one or more of the slots  528  and fill the central lumen  508 , thereby increasing stiffness of the sheath  502  and/or flexible instrument  100  during navigation of patient anatomy and to reduce the likelihood that the sheath  502  and/or flexible instrument  100  will buckle or kink during a puncture operation. Additionally, or alternatively, heat-shrink (not shown) can be laminated on the outside of all or a portion of the first region  518  and/or all or a portion of the second region  520  to prevent the fluid  514  from entering or exiting one or more of the slots  528  in the fluid conduit  504 . 
     Although the energy delivery systems  300 – 500  described with respect to  FIG.  3   -6B are fluid-cooled systems, in other embodiments the energy delivery systems described herein can be cooled using other techniques, or can be non-cooled systems. For example, a non-cooled energy delivery system can include a flexible instrument (e.g., flexible instrument  100  of  FIG.  1    or flexible instrument  200  of  FIG.  2   ) inserted into a sheath (e.g., sheath  302  of  FIG.  3   , sheath  402  of  FIG.  4   , or sheath  502  of  FIG.  5   ) without any fluid conduits or other cooling components. Optionally, a non-cooled energy delivery system can include a flexible instrument (e.g., flexible instrument  100  of  FIG.  1    or flexible instrument  200  of  FIG.  2   ) by itself without any sheath. 
       FIG.  7    is a flow diagram illustrating a method  700  for manufacturing an energy delivery system in accordance with an embodiment of the present technology. The method  700  is illustrated as a set of steps, operations, or processes  710 – 780 , and is described with additional reference to  FIG.  1   . Beginning at step  710 , the method  700  includes applying a jacket layer (e.g., jacket layer  122 ) over at least a portion of an elongate device for transmission of energy (e.g., a coaxial cable). The elongate device can include an inner conductor (e.g., inner conductor  116 ), an insulating layer (e.g., insulating layer  120 ), and an outer conductor (e.g., outer conductor  118 ) surrounding the inner conductor. As previously described, the jacket layer can be formed from various materials such as plastic, PET coating, or heat-shrink. The jacket layer can be applied as a single layer of material, or can be applied in multiple layers by braiding multi-filament layers, wrapping ribbon layers, or heat shrinking. Additionally, as discussed above, the jacket layer can be sufficiently thin (e.g., less than or equal to 25 microns) so that the overall diameter of the elongate device remains small enough to navigate narrow and/or tortuous passageways, while also avoiding interference with coolant flow around the device. In embodiments where the elongate device is a coaxial cable including a thick material layer (e.g., greater than 25 microns) over the outer conductor, step  710  can include removing the thick material layer before applying the thin jacket layer. 
     In some embodiments, the jacket layer is formed over the entire length of the outer conductor. In other embodiments, however, the jacket layer can be formed over only a portion of the outer conductor. For example, the jacket layer can be located only at the distal region of the outer conductor. As another example, the jacket layer can be localized to discrete regions of the outer conductor at or near the locations where recesses are to be formed. 
     At step  720 , the method  700  includes forming one or more recesses (e.g., recess  124   a ,  124   b ) in the elongate device (e.g., coaxial cable) to form an antenna body (e.g., antenna body  112 ). The recess(es) can be formed, for example, by cutting or otherwise removing a portion of outer conductor covered by the jacket layer, and the corresponding portion of a jacket layer over the portion of the outer conductor. The jacket layer can prevent layers of braided, wrapped, or foiled material from fraying or unraveling during cutting. In some embodiments, various layers of the outer conductor can be additionally peeled away to expose the insulating layer. Optionally, a corresponding portion of an insulating layer near the portion of the outer conductor can be removed. The recess(es) can be formed using cutting tools (e.g., a blade), lasers, or any other suitable technique. Optionally, step  720  can include forming multiple recesses in the antenna body (e.g., two, three, four, or more recesses). The number, position, and geometry of the recess(es) can be configured to produce a desired energy radiation pattern, as previously described. 
     At step  730 , an insert (e.g., insert  128 ) is positioned within each recess. In some embodiments, the insert is a pre-formed component (e.g., a slit tube) that is shaped to fit within the recess. For example, a tube can be slipped over the antenna body and placed into the recess. In such embodiments, the insert can be secured within the recess by adhesives and/or by positioning a layer of material (e.g., barrier layer  130 ) over the insert. In other embodiments, the insert can be formed from filler materials (e.g., plastic beads, glue, flowable material) that are introduced into the recess and subsequently fixed in place (e.g., by curing, hardening, gluing, bonding, etc.). In embodiments where the antenna body include multiple recesses, an insert can be positioned within each recess. 
     At optional step  740 , a conductive material (e.g., cap structure  114  or conductive material  250  ( FIG.  2   )) can be coupled or formed on a distal tip portion (e.g., distal tip portion  126 ) of the antenna body by soldering or other suitable techniques. The conductive material can be coupled to or formed on the inner conductor of the antenna body at the distal tip portion. For example, when cutting a recess at a distal tip portion of the elongate device (e.g. the recess  124   a  at distal tip portion  126 ), a portion of the inner conductor can be exposed to extend distally past the distal tip portion. The conductive material formed of a tube can placed around and soldered to the exposed inner conductor or formed and welded around to the inner conductor. Optionally, the conductive material can also be coupled to or formed on the outer conductor of the antenna body at the distal tip portion to electrically couple (e.g., electrically short) the inner conductor with the outer conductor. The conductive material can have a geometry configured to affect the energy radiation pattern produced by the antenna body, as previously described. 
     At step  750 , a barrier layer (e.g., barrier layer  130 ) can be positioned over an antenna assembly (e.g., antenna assembly  104 ) that encompasses the antenna body, the insert, and the conductive material. The barrier layer can secure the insert within the recess and secure the conductive material to the inner conductor and the antenna body. The barrier layer can additionally be positioned over at least the insert and recess to prevent fluid migration into the antenna body. In some embodiments, the barrier layer also extends over the distal tip of the antenna assembly to prevent inward migration of fluid via the distal tip. Optionally, the barrier layer can extend over the entire length of the antenna assembly. The barrier layer can also extend over other portions of the energy delivery system, such as over a portion of a transmission member (e.g., transmission member  102 ) or over the entire length of the transmission member. The barrier layer can be applied as heat shrink tubing, heated and melted over the antenna assembly/transmission member or applied as a coating (e.g., parylene coating or vapor-deposited coating). In some embodiments the barrier layer may be applied in multiple layers including a first layer to secure the inserts and the conductive material to the antenna assembly, and a second layer applied over the first layer to ensure sealing to prevent fluid migration into the antenna body. Optionally, after the barrier layer has been applied, a portion of the conductive material (e.g., a distal end of the conductive material) is sealed with or otherwise coupled to a plug. The plug can be made of a non-conductive material, such as glue or another adhesive, a conformal coating (e.g., a parylene coating or vapor-deposited coating), or a reflowable material. The plug can be placed inside the barrier layer such that the barrier layer extends partially or entirely over the conductive material and the plug. 
     At optional step  760 , a flexible instrument (e.g., flexible instrument  100  or  200  ( FIG.  2   )) can be inserted into a sheath (e.g., sheath  302 ,  402 , or  504  of  FIGS.  3 ,  4 , or  5   , respectively). The flexible instrument can include the antenna assembly, the transmission member, and the barrier layer. At optional step  770 , one or more fluid conduits (e.g., fluid conduit  304 ,  404 ,  504 ,  604   a ,  604   b ) can be inserted into the sheath. In some embodiments, steps  760  and  770  can be performed simultaneously. At step  780 , proximal end components, such as components of a fluid cooling system (e.g., fluid cooling system  306 ,  406 , or  506 ) or other component such as handles, connectors, etc. can be coupled to a proximal end portion of the flexible instrument. 
     Although the steps of the method  700  are discussed and illustrated in a particular order, the method  700  illustrated in  FIG.  7    is not so limited. In other embodiments, for example, the method  700  can be performed in a different order (e.g., step  740  can be performed before step  720  and/or step  730 ). In these and other embodiments, any of the steps of the method  700  can be performed before, during, and/or after any of the other steps of the method  700 . Moreover, a person of ordinary skill in the relevant art will recognize that the illustrated method  700  can be altered and still remain within these and other embodiments of the present technology. For example, one or more steps of the method  700  illustrated in  FIG.  7    can be omitted (e.g., steps  740 ,  760 , and/or  770 ) and/or repeated in some embodiments. For example, step  770  can be omitted in embodiments where the energy delivery system is a non-cooled system. Optionally, steps  760  and  770  can be omitted in embodiments where the flexible instrument is intended to be used without a sheath. 
       FIG.  8    is a flow diagram illustrating a method  800  of operating an energy delivery system in accordance with an embodiment of the present technology. The method  800  is illustrated as a set of steps, operations, or processes  810 – 850 . In some embodiments, one or more of the steps  810 – 850  may be implemented, at least in part, in the form of executable code stored on non-transitory, tangible, machine-readable media. All or a subset of the steps  810 – 850  of the method  800  can be executed at least in part by various components or devices of an energy delivery system, such as any of the embodiments described above with respect to  FIGS.  1 - 6 B . For example, all or a subset of the steps  810 – 850  can be executed at least in part by components or devices of (i) a flexible instrument, (ii) an antenna assembly, (iii) a transmission member, (iv) one or more fluid conduits, and/or (v) a fluid cooling system. Additionally, or alternatively, all or a subset of the steps  810 – 850  of the method  800  can be executed at least in part by an operator (e.g., a physician, a user, etc.) of the energy delivery system, and/or by a robotically controlled surgical system via user inputs from the operator through a user input device or automatically through using closed loop control and/or pre-programmed instructions through a processor of the robotically controlled surgical system. Furthermore, any one or more of the steps  810 – 850  of the method  800  can be executed in accordance with the discussion above. 
     The method  800  begins at step  810  with delivering an energy delivery system (e.g. energy delivery system  300 ,  400 , or  500  of  FIGS.  3 ,  4 , or  5   , respectively) at or near a target site within a patient’s anatomy. The target site can be within an airway of the lungs of the patient. In some embodiments, the target site is a tumor within the airway or another anatomical region. As described above, delivering the energy delivery system can involve navigating the complex, tortuous patient anatomy until the distal portion of the energy delivery system is at a desired location, and then orienting the energy delivery system toward the target site or tumor. In some embodiments, delivery of the energy delivery system may be performed manually, the energy delivery system may be robotically controlled by user control through an input device, or the energy delivery system may be robotically controlled automatically using a pre-programmed set of instructions from a robotic system such as robotic medical systems described in detail below. In some embodiments the energy delivery system is delivered within a separate manual device or with the robotic medical system. 
     At step  820 , once the distal portion of the energy delivery system is positioned and oriented appropriately within the airway, the method  800  can optionally include delivering a coolant (e.g., fluid  314 ,  414 , or  514  of  FIGS.  3 ,  4 , or  5   , respectively) to cool at least a portion of the flexible instrument (e.g., to the distal portion and/or to an antenna assembly). The coolant can be used to cool the antenna assembly (e.g., antenna assembly  104 ) of the flexible instrument. The coolant can also be circulated to dissipate heat from tissue at the target site and/or from the transmission member (e.g., transmission member  102 ) of the flexible instrument. In some embodiments, the flexible instrument is positioned within a central lumen (e.g. central lumen  308 ,  408 , or  508  of  FIGS.  3 ,  4 , or  5   , respectively) of a sheath, and a fluid cooling system (e.g., fluid cooling system  306 ,  406 , or  506 ) and/or one or more fluid conduits (e.g., fluid conduit  304 ,  404 ,  504 ,  604   a ,  604   b ) could be used to deliver the coolant near a distal tip (e.g. distal tip  110  of  FIGS.  3 ,  4 , or  5   ) of the flexible instrument. The coolant can be circulated around the distal tip, and return through the central lumen to exit the sheath. In some embodiments, the coolant can be delivered via one or more slots patterned into a fluid conduit and/or be purged from the sheath via one or more slots patterned within the sheath. In some embodiments, step  820  may be performed simultaneously with step  810 . In alternative embodiments, step  820  may be performed before step  810 , e.g. immediately before energy delivery, immediately upon positioning of the energy delivery system towards the target, or during a setup stage before the energy delivery system is inserted into patient anatomy. Additionally, step  820  may be omitted in embodiments where the energy delivery system is a non-cooled system. 
     At step  830 , the method  800  optionally includes inserting the energy delivery system into tissue. For example, step  830  can include puncturing an airway wall with atip section (e.g., tip section  312 ,  412 , or  512 . of  FIGS.  3 ,  4 , or  5   , respectively) of a sheath containing the flexible instrument, and positioning the portion of the sheath containing the antenna assembly at the target site (e.g., within the target tumor or lesion). Alternatively, the flexible instrument can be used to puncture the airway wall without using any sheath. As explained above, the distal end portion of the flexible instrument and/or sheath can have sufficient axial rigidity to puncture tissue without buckling or kinking. The rigidity of the flexible instrument can be increased, for example, by reinforcing the antenna assembly with inserts (e.g., inserts  128 ) and/or one or more material layers (e.g., jacket layer  122 , barrier layer  130 ), as previously described. In an alternative embodiment, a separate puncturing device, such as a needle, can be used to make an initial puncture of the airway wall. The needle can be removed and the energy delivery system can be inserted into an opening created by the needle in the airway wall. In some embodiments, the positioning of the energy delivery system may be performed manually, the energy delivery system may be robotically controlled by user control through an input device, or the energy delivery system may be robotically controlled automatically using a pre-programmed set of instructions from a robotic system. In some embodiments the energy delivery system is delivered within a separate delivery device such as a manual flexible device or a flexible device controlled by a robotic medical system. The delivery device of the robotic medical system can be positioned in a stationary pose directed towards the target site, and the energy delivery system can be inserted through delivery device to be inserted within the tissue. In some embodiments, step  830  may be performed before or simultaneously with step  820 . 
     At step  840 , the method  800  continues with delivering energy through the transmission member to the antenna assembly (e.g., using a generator electrically coupled to the transmission member) to ablate tissue at the target site (e.g., the tumor). Once ablation is complete (e.g., once tumor/lesion and tissue margins have been adequately ablated as confirmed by sensor feedback such as impedance, temperature, imaging, and/or the like or once a predetermined period of time has elapsed), the method  800  continues to step  850 . At step  850 , once ablation is complete, ablation energy delivery can be terminated, coolant delivery can be terminated, and/or the energy delivery system may be retracted and removed from patient anatomy. In some embodiments, the energy delivery system may be retracted manually, the energy delivery system may be robotically retracted by user control through an input device, or the energy delivery system may be robotically retracted automatically. 
     Although the steps of the method  800  are discussed and illustrated in a particular order, the method  800  illustrated in  FIG.  8    is not so limited. In other embodiments, the method  800  can be performed in a different order. In these and other embodiments, any of the steps of the method  800  can be performed before, during, and/or after any of the other steps of the method  800 . Moreover, a person of ordinary skill in the relevant art will recognize that the illustrated method  800  can be altered and still remain within these and other embodiments of the present technology. For example, one or more steps of the method  800  illustrated in  FIG.  5    can be omitted and/or repeated in some embodiments. 
       FIGS.  9 A- 14 B  illustrate additional energy delivery systems configured in accordance with embodiments of the present technology, and can include a number of features, materials, and/or components similar to or identical to the energy delivery systems described above.  FIG.  9 A , for example, is a perspective view of an energy delivery system  900  for tissue ablation configured in accordance with various embodiments of the present technology. As shown in  FIG.  9 A , the energy delivery system  900  generally includes a flexible instrument  902  and a fluid cooling system  932 . The flexible instrument  902  includes an antenna  904  and an elongate transmission member  906  positioned within a sheath  924 . The antenna  904  extends distally from the elongate transmission member  906  between a proximal end portion  908  and a distal end portion  910 . The elongate transmission member  906  includes an outer conductor  912  at least partially surrounding an inner conductor  916 , and an insulator  914  (e.g., a dielectric layer) substantially surrounding the inner conductor  916  to insulate the outer conductor  912  from the inner conductor  916 . In the illustrated embodiment, a portion  918  of the insulator  914  and the inner conductor  916  extend distally beyond the outer conductor  912  and form part of the antenna  904 . Additionally, the elongate transmission member  906  is illustrated as a coaxial cable, but jacket layers and other details may not be illustrated for simplicity. For example, in some embodiments, the transmission member  906  can further include a protective or insulative layer (not shown) surrounding the outer conductor  912  (e.g., to provide structural integrity to the outer conductor  912 ). Other coaxial cable configurations with different configurations, shapes, etc. of inner conductor, outer conductor, and dielectric layers could also be used. In alternative embodiments, any type of elongate transmission member  906  may be used for the flexible instrument  902 . 
     In accordance with embodiments of the present technology, the antenna  904  can be one of various types of antennas known in the art. For example, the antenna  904  can be a helical dipole antenna as shown and described in greater detail in U.S. Pat. App. Serial No. 16/670,847 filed Oct. 31, 2019 disclosing “Coiled Dipole Antenna”, or U.S. Pat. App. Serial No. 16/670,947 filed Oct. 31, 2019 disclosing “Coiled Antenna with Fluid Cooling,” which are both incorporated by reference herein in their entirety. In other embodiments, the antenna  904  can be a patterned tube antenna as shown and described in greater detail in PCT Patent App. No. PCT/US19/24564 filed Mar. 28, 2019 disclosing “Systems and Methods Related to Flexible Antennas” which is incorporated by reference herein in its entirety. In other embodiments, the antenna  904  can be a double helical, slot, dual slot, monopole, solid tube or another type of antenna. In the illustrated embodiment, the antenna  904  extends along a longitudinal axis A and includes the portion  918  of the inner conductor  916  that extends distally beyond the outer conductor  912 . The antenna  904  can be used to radiate microwave energy for use in the tissue ablation process. More specifically, the antenna  904  is used to create electromagnetic radiation within a wavelength range of one meter to one millimeter, and within a frequency range of approximately 300 Megahertz (MHz) to 300 Gigahertz (GHz) (e.g., a microwave). In some embodiments, the wavelength and the frequency of the microwaves being radiated by the antenna  904  may be modified to cause a desired type of ablation at the ablation target site. 
     In some embodiments, the material of the insulator  914  may be chosen to provide a high axial stiffness along the axis A to allow greater rigidity to puncture tissue. Rigid materials such as PEEK or polyetherimide (such as those manufactured by SABIC of Riyadh, Saudi Arabia and sold under the trademark ULTEM) may be used, for example, to increase stiffness in the antenna and prevent buckling or kinking during a puncture operation. 
       FIG.  9 B  is a cross-sectional end view of the energy delivery system  900  taken along line 9B-9B of  FIG.  9    A. Referring to  FIGS.  9 A and  9 B  together, the energy delivery system  900  in some embodiments can include a barrier layer  926  that extends along the flexible instrument  902 , creating a barrier or seal to prevent inward migration of fluid. The barrier layer  926  may be formed of a thermoplastic such as polyethylene terephthalate (PET) or other flexible and fluid insulating and impermeable materials. The barrier layer  926  may be thin and form fit around the components of the flexible instrument  902  or may maintain a flexible tubular form. In some embodiments, the barrier layer  926  may provide added rigidity to support the antenna  904 . 
     In the illustrated embodiment, the antenna  904  and the transmission member  906  are disposed within the sheath  924 . In some embodiments, the sheath  924  is closed, sealed, or otherwise restricts fluid from passing into or out of the sheath  924 . For example, the sheath  924  may optionally be coupled to and/or sealed by a tip section  966  ( FIG.  9 A ) at a distal end  927  ( FIG.  9 A ) of the sheath  924 . The sheath  924  and tip section  966  can be identical or generally similar to the sheath  302  and tip section  166 , respectively, of  FIG.  3   . 
     A chamber or channel  928  is formed between the sheath  924  and the barrier layer  926  and receives a coolant (e.g., a fluid  930  ( FIG.  9 A ) or other cooling agent, such as gas) to cool the flexible instrument  902 . The fluid  930  may be, for example, water or a saline solution. The fluid  930  may be provided to the channel  928  from a fluid cooling system  932  ( FIG.  9 A ) coupled to the channel  928 . The fluid cooling system  932  may be identical or generally similar to the fluid cooling system  306  of  FIG.  3   . In the illustrated embodiment, the fluid cooling system  932  also includes or is coupled to fluid conduits  936  and  937  ( FIG.  9 B ) that extend through at least a portion of the channel  928  and run alongside at least the transmission member  906  ( FIG.  9 A ) within the sheath  924 . The coolant may be directed within the channel  928  through the fluid conduit  936  and/or through the fluid conduit  937 . Each of the fluid conduits  936 ,  937 , for example, may be identical or generally similar to the fluid conduit  304  of  FIG.  3   . 
     The fluid conduit  936  and/or the fluid conduit  937  may be used, for example, to provide inflow of the fluid  930  to the channel  928 . The fluid  930  can circulate about the antenna  904  and/or the transmission member  906  within the channel  928 , and can return in a proximal direction within the channel  928  to be purged in a reservoir (not shown) or purged to the environment. In another embodiment, the fluid  930  can exit the sheath  924  via openings or slits in the sheath  924  or return to a fluid cooling system  932  via the channel  928  and/or another fluid conduit (not shown). Alternatively, the fluid conduit  936  and/or  937  can be used to provide return flow of the fluid  930  from the channel  928  by discontinuing inlet fluid from the fluid reservoir  934 , reversing flow and providing suction to the fluid conduit  936  and/or  937  using the fluid cooling system. In another embodiment, a separate fluid conduit (not shown) can be provided that does not provide inflow of fluid  930  and is only used for return flow. In some embodiments, the return flow can be purged in a combination of flow through the channel  928  in a proximal direction, flow through fluid conduits, and through openings in sheath  924 . 
     In the illustrated embodiment, the fluid conduits  936  and  937  are separate from one another such that each can flex independently of one another when the flexible instrument is navigated to a target. In some embodiments, separate fluid conduits provide greater recoverable flexibility and/or axial rigidity than fluid conduits that are attached to one another. In other embodiments of the present technology, however, the fluid conduits  936  and  937  can be joined to one another and/or can be formed as a single structure. 
     Although the energy delivery system  900  is illustrated in  FIGS.  9 A and  9 B  with two circular fluid conduits  936  and  937  that run alongside the off-centered transmission member  906  ( FIG.  9 A ), energy delivery systems configured in accordance with other embodiments of the present technology can include a different number, shape, and/or position of fluid conduits. For example, an energy delivery system of the present technology can include one, or three or more fluid conduits in some embodiments. In some embodiments, a single fluid conduit may result in an unbalanced device or size requirements, and high frictional losses (high pressure drops due to added wall thickness of additional fluid conduits) may limit the number of fluid conduits to three or less. The transmission member  906  may be centered within the channel  928  and the fluid conduits may be distributed evenly or un-evenly around the transmission member  906 . Additionally, or alternatively, all or a subset of the fluid conduits can have a non-circular (e.g., a “D”-shaped, a rectangular, etc.) cross-sectional shape. In some embodiments with a single fluid conduit, the fluid conduit can be irregularly shaped to balance the symmetry of the design. In these and still other embodiments, at least one fluid conduit can be positioned concentric with the transmission member  906  (e.g., surrounding the inner conductor  916 , the insulator  914 , the outer conductor  912 , and/or the transmission member  906 ) within the sheath  924  and terminate at or near the proximal end  908  of the antenna  904 . A minimum wall thickness of the fluid conduits  936  and/or  937  may be necessary to prevent kinking of the channel  928 . The wall thickness may, however, limit the overall cross-sectional area of other components within the device in order to maintain a desired total outer diameter. 
     As described previously, the flexible instrument  902  (and associated fluid conduits  936  and  937 ) must be sufficiently flexible to navigate tortuous anatomical passageways and facilitate delivery of the flexible instrument  902  to a target site within patient anatomy. The flexible instrument  902  and fluid conduits  936  and  937  may be identical or generally similar to the flexible instrument  302  and fluid conduit(s)  304  described above with reference to  FIG.  3    and have many or all of the same features and advantages. For example, the fluid conduits  936  and/or  937  can be formed of a resiliently flexible material (e.g., nitinol or another suitable shape memory material). If constructed from nitinol, the fluid conduit can be laser cut or ground to adjust stiffness over the length of the fluid conduits  936  and/or  937 . In some embodiments, a fluorinated ethylene propylene (FEP) layer may surround the fluid conduit  936  and/or the fluid conduit  937 . In still further embodiments, the fluid conduits  936  and/or  937  may be constructed entirely from a polymer material (and not include nitinol). 
       FIGS.  10 - 13 ,  14 A, and  14 B  are cross-sectional side views of energy delivery systems  1000 ,  1100 ,  1200 ,  1300 , and  1400 , respectively, for tissue ablation configured in accordance with various embodiments of the present technology. The energy delivery systems  1000 – 1300  and  1400  of  FIGS.  10 - 13 ,  14 A, and  14 B  are similar to the energy delivery system  900  of  FIG.  9    with exception to differences disclosed herein. Thus, like reference numerals are used to identify like elements illustrated in  FIGS.  9 - 14 B . Furthermore,  FIGS.  10 - 14 B  are each discussed in detail below with reference to a single fluid conduit. A person of ordinary skill in the art will readily appreciate, however, that any of the energy delivery systems  1000 – 1300  and  1400  described below can include multiple fluid conduits and that all or a subset of the fluid conduits of each system  1000 – 1300  and  1400  can share one or more of the features of the fluid conduits described herein. 
     Referring to  FIG.  10   , the energy delivery system  1000  includes a flexible instrument  1002  having antenna  904 , elongate transmission member  906 , and a fluid conduit  1036  disposed within sheath  924 . Barrier layer  926  extends along the flexible instrument  1002 , creating a barrier or seal to prevent inward migration of fluid. As mentioned previously, the barrier layer  926  may be thin and form fit (e.g. heat shrink) around components (e.g., the antenna  904 , the transmission member  906 , etc.) of the flexible instrument  1002  or may maintain a flexible tubular form. 
     As discussed above, channel  928  is formed between the sheath  924  and the barrier layer  926  and receives fluid flow of fluid  930  (e.g., a coolant such as saline, water, or another cooling agent, such as gas) to cool the flexible instrument  1002 . In the illustrated embodiment, the antenna  904  terminates before the distal end  927  of the sheath  924  such that the channel  928  surrounds the distal end portion  910  of the antenna  904 . In other embodiments, the antenna  904  can extend to the distal end  927  of the sheath  924  such that the channel  928  does not surround the distal end portion  910  of the antenna  904  within the sheath  924 . 
     The fluid conduit  1036  can be identical or generally identical to the fluid conduit  304  described above with reference to  FIG.  3   , and can be fabricated using the same or similar techniques and/or materials. In the illustrated embodiment, for example, the fluid conduit  1036  includes a first region  1031  and a second region  1032 . The fluid conduit  1036  extends through at least a portion of the channel  928  and runs alongside the transmission member  906  within the sheath  924 , terminating near the distal end portion  910  of the antenna  904 . Extending the fluid conduit  1036  to at least the distal end portion  910  of the antenna  904  can provide an added benefit of delivering coolant to the distal end portion  910  of the antenna for increased and/or more uniform cooling of the antenna  904 . Additionally, terminating the fluid conduit  1036  near a proximal end portion  908  of antenna  904  (as illustrated in  FIG.  9 A ) leaves the portion of the flexible instrument  1002  from the proximal end portion  908  of the antenna  904  to the distal end portion  927  of the sheath  924  unsupported by the fluid conduit  1036 , reducing axial stiffness of the flexible instrument  1002  along the axis A. In addition, a point of weakness can be created along the flexible instrument  1002  at or near the proximal end portion  908  of the antenna  904  where the first region  1031  of the fluid conduit  1036  terminates. Such a point of weakness can reduce the bend radius of the flexible instrument  1002  during delivery of the antenna  904  through patient anatomy and can increase the likelihood of the flexible instrument  1002  buckling or kinking along the unsupported portion during a puncture operation (especially if the antenna  904  is off-centered within the sheath  924 ). 
     As previously described, forming the fluid conduit  1036  of a shape memory-material can provide (i) the flexibility (e.g., the deformability) required to facilitate delivery of the flexible instrument  1002  through tortuous patient anatomy and (ii) the resiliency (e.g., recoverability, spring back, etc.) required to return the fluid conduit  1036  (and therefore the flexible instrument  1002 .) to its initial (e.g., undeformed) state or shape after deformation to reduce trajectory error and facilitate accurate delivery of the antenna  904  to the target site during a puncture operation. However, many shape memory and other resiliently flexible materials (including nitinol) are conductive at the frequency range (e.g., 300 MHz to 300 GHz) of the microwave antenna  904 , meaning that any region of the fluid conduit  1036  that runs alongside the antenna  904  within the sheath  924  and is formed of a conductive material would interfere with the antenna  904  during energy delivery. 
     Accordingly, the first region  1031  of the fluid conduit  1036  can be formed of a shape memory material, such as nitinol, and extend along the elongate transmission member  906 , whereas the second region  1032  of the fluid conduit  1036  can be formed of a non-conductive material, such as a plastic or polymer, and extend along the antenna  904 . As illustrated in  FIG.  10   , the first region  1031  terminates at a point along the length of the flexible instrument  1002  proximal the proximal end portion  908  of the antenna  904  such that the first region  1031  does not interfere with the antenna  904  during energy delivery The second region  1032  can terminate at or near the distal end portion  910  of the antenna  904  or can extend to the distal end portion  927  of the sheath  924  (e.g., to provide stiffness and axial rigidity along the entire length of the flexible instrument  1002 ). Because the second region  1032  of the fluid conduit  1036  is formed of a material that is non-conductive at the frequency range of the antenna  904 , the second region  1032  does not interfere with the antenna  904  during energy delivery. 
       FIG.  11    is a cross-sectional view of an energy delivery system  1100  having a flexible instrument  1102  configured in accordance with another embodiment of the present technology. The energy delivery system  1100  and the flexible instrument  1102  are similar to the energy delivery system  1000  and the flexible instrument  1002 , respectively, of  FIG.  10    except that the fluid conduit  1136  of the flexible instrument  1102  illustrated in  FIG.  11    includes a third region  1133  proximal the first region  1031 . 
     As illustrated in  FIG.  11   , the flexible instrument  1102  includes a proximal section  1141  and a distal section  1142 . The distal section  1142  extends distally from the proximal section  1141  at a point along the length of the transmission member  906  to at least the distal end portion  910  of the antenna  904  (e.g., to the distal end  927  of the sheath  924 ). The third region  1133  of the fluid conduit  1136  can extend along at least a portion of the proximal section  1141  of the flexible instrument  1102 , while the first region  1031  of the fluid conduit  1136  can extend along at least a portion of the distal section  1142  of the flexible instrument  1102  to provide recoverable flexibility along this portion of the flexible instrument  1102 . The second region  1032  of the fluid conduit 1  136  can extend along the antenna  904 , terminating at distal end portion  910  of antenna  904 . In some embodiments, the various regions/sections of the fluid conduit  1136  may be fabricated using materials and techniques similar to or identical to those described above with reference to  FIG.  4   . 
       FIG.  12    is a cross-sectional view of an energy delivery system  1200  having a flexible instrument  1202  configured in accordance with another embodiment of the present technology. The energy delivery system  1200  and the flexible instrument  1202  are similar to the energy delivery systems  900 / 1000 / 1100 / 1200  and the flexible instruments  902 / 1002 / 1102 , respectively, of  FIGS.  9 / 10 / 11    except that the flexible instrument  1202  illustrated in  FIG.  12    comprises a fluid conduit  1236  that is patterned with slots  1282  (e.g., cutouts, slits, etc.). In particular, both the first region  1031  and the second region  1032  of the fluid conduit  1236  include a gradient of slots  1282  along their lengths to vary the stiffness of the corresponding regions  1031  and  1032  of the fluid conduit  1236 . 
     In some embodiments, the slots/openings of fluid conduit  1236  can be generally similar to or identical to the slots described above with reference to  FIGS.  5 - 6 B . Further, as described above with reference to  FIG.  5   , one or more of the slots in some embodiments can serve as points of exit for a coolant (e.g., a fluid or gas) to exit the fluid conduit  1236  and enter the channel (or vice versa). In further embodiments, patterned slots as described above can be included at any point of weakness along the flexible instrument. For example, the change in diameters between the outer conductor  912  and the inner conductor  916  could result in a point of weakness. In this case, a set of patterned slots can be utilized to create a more gradual transition between these components. Other points of weakness can occur at transitions between different materials. Accordingly, in an embodiment where the materials of the outer conductor  912 , the inner conductor  916 , the dielectric material  914 , and/or the fluid conduits  1236  are not uniform, any transition between different materials could be considered a point of weakness and patterned slots can be utilized to make the transition gradual, thereby reducing or eliminating the point of weakness. 
       FIG.  13    is a cross-sectional view of an energy delivery system  1300  having a flexible instrument  1302  configured in accordance with still another embodiment of the present technology. The energy delivery system  1300  and the flexible instrument  1302  are similar to the energy delivery system  1000  and the flexible instrument  1002 , respectively, of  FIG.  10    except that the flexible instrument  1302  illustrated in  FIG.  13    comprises a fluid conduit  1336  formed of a continuous material along its entire length. In some embodiments, for example, the fluid conduit  1336  is formed of a material that is non-conductive at the frequency range of the antenna  904  such that the fluid conduit  1336  does not interfere with the antenna  904  during energy delivery. For example, the fluid conduit  1336  can be formed of a plastic, polymer, or other non-conductive material. In the illustrated embodiment, the fluid conduit  1336  runs along substantially the entire length of the flexible instrument  1302  from a proximal end portion of the flexible instrument  1302  to at least the distal end portion  910  of the antenna  904 . 
     To provide recoverable flexibility and/or axial stiffness to the flexible instrument  1302  during delivery of the flexible instrument  1302  to a target site through patient anatomy and/or during a puncture operation, a stylet  1372  can be inserted into a lumen of the fluid conduit  1336  (e.g., via a port or valve  1374  of the fluid conduit  1336 ) and extended to at least the distal end portion  910  of the antenna  904 . In some embodiments, the stylet  1372  can be formed of a resiliently flexible material, such as nitinol or another shape memory material. 
     In some embodiments, the stylet  1372  and fluid conduit  1336  are sized to allow for space within the lumen of the fluid conduit so that a coolant (e.g., a cooling fluid or gas) can be delivered to or removed from the channel  928  via the fluid conduit  1336  and/or another fluid conduit (not shown) of the flexible instrument  1302  while the stylet  1372  is inserted into the fluid conduit  1336 . In other embodiments, the stylet  1372  can be removed from the fluid conduit  1336  before transporting the coolant to or from the channel  928  via the fluid conduit  1336 . For example, the stylet  1372  can be removed from the fluid conduit  1336  (e.g., via the port  1374 ) once the flexible instrument  1302  is positioned at a target site, and a coolant (not shown in  FIG.  13   ) can subsequently be delivered to or removed from the channel  928  via the fluid conduit  1336  to cool the antenna  904 , particularly during delivery of ablative energy. 
     In some embodiments, a proximal end portion of the stylet  1372  can be directly or indirectly connected to a slidable mechanism (not shown). The slidable mechanism can be configured to distally and/or proximally slide the stylet  1372  within the fluid conduit  1336 . For example, the slidable mechanism can be robotically controlled to (e.g., automatically and/or in response to an operator command) extend the stylet  1372  into the fluid conduit  1336  before and/or during navigation of the flexible instrument  1302  and/or before and/or during a puncture operation using one or more actuators such as motors and/or motor driven leadscrews, a hydraulic system, a motor driven cable system, a robotic arm, and/or the like (not shown). Additionally, or alternatively, the slidable mechanism can be robotically controlled to (e.g., automatically and/or in response to an operator command) retract the stylet  1372  from the fluid conduit  1336  after the flexible instrument  1302  is positioned at a target site, before transporting coolant via the fluid conduit  1336 , and/or before delivery energy via the antenna  904 . 
       FIGS.  14 A and  14 B  are cross-sectional views of an energy delivery system  1400  having a flexible instrument  1402  configured in accordance with a further embodiment of the present technology. The energy delivery system  1400  and the flexible instrument  1402  are similar to the energy delivery system  1100  and the flexible instrument  1102 , respectively, of  FIG.  11    except that the flexible instrument  1402  illustrated in  FIG.  14    comprises a fluid conduit  1436  distally and proximally slidable within the sheath  924  in a direction parallel with axis A. In some embodiments, the fluid conduit  1436  may be formed of a single material similar to fluid conduit  1336  of  FIG.  13   . In alternative embodiments, the fluid conduit  1436  can be formed of more than one material similar to the fluid conduit  1136  of  FIG.  11   . For example, the fluid conduit  1436  can include a first region (e.g. similar to the first region  1031  of  FIG.  11   ) formed of a resiliently flexible material, a second region (e.g., similar to the second region  1032  of  FIG.  11   ) formed of a non-conductive material, and/or a third region (e.g., similar to the third region  1133  of  FIG.  11   ) formed of a less expensive material (e.g., to reduce costs). In other embodiments and as shown in  FIGS.  14 A and  14 B , the fluid conduit  1436  can be formed of a continuous material along its entire length, such as a resiliently flexible material (e.g. nitinol or another suitable shape memory material). 
       FIG.  14 A  illustrates the fluid conduit  1436  in a fully extended state. In particular, the fluid conduit  1436  can be slid distally within the sheath  924  in a direction parallel with the axis A until the distal end portion  1019  of the fluid conduit  1436  is positioned at or near the distal end portion  927  of the sheath  924 . Alternatively, the fluid conduit  1436  can be slide distally within the sheath  924  until the distal end portion  1019  of the fluid conduit  1436  is positioned just short of the distal end portion  927  of the sheath  924  (e.g., at the distal end portion  910  of the antenna  904 ) to allow a coolant to enter/exit the fluid conduit  1436  from/into the channel  928 . 
     In some embodiments, the fluid conduit  1436  can be positioned in the fully extended state while navigating the flexible instrument  1402  through patient anatomy (e.g., to provide recoverable flexibility) and/or while performing a puncture operation (e.g., to provide stiffness along the axis A and reduce the likelihood of the flexible instrument  1402  buckling or kinking at a point along its length). In one embodiment, a coolant (e.g., the fluid  930  shown in  FIG.  14 B  or a gas) can be continually delivered to the channel  928  while the fluid conduit  1436  is in the fully extended state to provide additional stiffness to the flexible instrument  1402 . In other embodiments, a coolant can be intermittently delivered to the channel  928  while the fluid conduit  1436  is in the fully extended state. For example, in one embodiment, coolant is not delivered to the channel  928  while navigating the flexible instrument  1402  through patient anatomy to maintain maximum flexibility of the flexible instrument  1402 , but coolant is delivered to the channel  928  before and/or during a puncture operation to provide additional stiffness to the flexible instrument  1402 . In still other embodiments, coolant is not provided to the channel  928  while the fluid conduit  1436  is in the fully extended state. 
       FIG.  14 B  illustrates the fluid conduit  1436  in a retracted state. In particular, the fluid conduit  1436  can be slid proximally within the sheath  924  in a direction parallel with the axis A at least until the distal end portion  1019  of the fluid conduit  1436  is positioned proximal the proximal end portion  908  of the antenna  904  (e.g., at or near the distal end portion  1007  of the transmission member  906 ). In this manner, the fluid conduit  1436  can be retracted within the sheath  924  to a position where the fluid conduit  1436  will not interference with the antenna  904  during energy delivery. In some embodiments, the fluid conduit  1436  can be positioned in the fully retracted state after the flexible instrument  1402  is positioned at a target site and/or before delivering energy via the antenna  904 . A coolant can then be delivered to or removed from the channel  928  via the fluid conduit  1436  to cool the antenna  904  during energy delivery. 
     Referring to  FIGS.  14 A and  14 B  together, the energy delivery system  1400  can further include a translation actuator in the form of a slidable mechanism  1496  and/or a heat source  1498 . In some embodiments, the slidable mechanism  1496  can be directly or indirectly connected to a proximal end portion  1415  of the fluid conduit  1436  and configured to slide the fluid conduit  1436  distally and/or proximally within the jacket in a direction parallel with the axis A and between the fully extended and fully retracted states. For example, the proximal end portion  1415  of the fluid conduit  1436  can be translated in a direction parallel with the axis A using one or more actuators such as motors and/or motor driven leadscrews, a hydraulic system, a motor driven cable system, a robotic arm, and/or the like (not shown). In some embodiments the proximal end portion can be mounted on a linear slide (not shown) of the slidable mechanism  1496 . In other embodiments, the proximal end portion is mounted to a robotic arm and translated in a parallel direction by actuating the robotic arm. In some embodiments, the slidable mechanism  1496  can be robotically controlled to (e.g., automatically and/or in response to an operator command) slide the fluid conduit  1436  distally within the sheath  924  before and/or during navigation of the flexible instrument  1402  through patient anatomy and/or before and/or during a puncture operation. Additionally, or alternatively, the slidable mechanism  1496  can be robotically controlled to (e.g., automatically and/or in response to an operator command) slide the fluid conduit  1436  proximally within the sheath  924  after delivery of the flexible instrument  1402  to a target site, before transporting a coolant via the fluid conduit  1336 , and/or before delivering energy via the antenna  904 . In some embodiments, the fluid cooling system  932  and proximal end portion  1415  are both mounted on the slidable mechanism  1436 . In an alternative embodiment, only the proximal end portion  1415  is mounted on the slidable mechanism and a compliant coupling (not shown) couples the fluid conduit  1436  to the fluid cooling system  932  which is stationary relative to the proximal end portion  1415 . 
     In these and other embodiments, the fluid conduit  1436  can be formed of a material (e.g., nitinol, shape memory polymer, a shape memory metal or alloy) that changes in shape (e.g., transforms between a first configuration and a second different configuration) in response to a stimulus (e.g., thermal energy, heat, mechanical loading). In one embodiment, for example, the fluid conduit  1436  can be anchored at a proximal end portion and heat can be applied to the fluid conduit  1436  to transform (e.g., contract, retract) the fluid conduit  1436  proximally within the sheath  924 . In one example, thermal energy generated by the antenna  904  during energy delivery can activate a portion of the fluid conduit  1436  to transform (retract) proximally within the sheath  924  to an extent where the fluid conduit  1436  no longer overlaps with the antenna  904 . The energy delivery can be altered such that a first frequency range is applied to retract the fluid conduit  1436 . Subsequently, once the fluid conduit  1436  is retracted to a position where the fluid conduit  1436  does not overlap with antenna  904 , a second frequency range is applied for tissue ablation. As another example, the heat source  1498  can (e.g., electrically) apply heat to the proximal end portion  1415  and/or to one or more other portions along the length of the fluid conduit  1436  (e.g., after the flexible instrument  1402  is positioned at a target site and/or before delivering energy via the antenna  904  and before delivering energy via the antenna  904 ) to retract the fluid conduit  1436  proximally within the sheath  924  to an extent where the fluid conduit  1436  does not overlap with the antenna  904 . 
       FIG.  15    is a flow diagram illustrating a method  1500  for manufacturing an energy delivery system in accordance with various embodiments of the present technology. The method  1500  is illustrated as a set of steps, operations, or processes  1502 – 1512 . At step  1502 , the method  1500  begins with connecting a tip section (e.g., tip section  966 ) to or forming a tip section from a jacket (e.g., sheath  924 ). At step  1504 , an antenna (e.g., antenna  904 ) can be formed at and/or be connected to a distal end of a transmission member (e.g., transmission member  906 ). At step  1506 , a barrier layer (e.g., barrier layer  926 ) can be extended over the antenna and the transmission member. At step  1508 , the antenna, the transmission member, and the barrier layer can be inserted into a central lumen of the jacket. At step  1510 , one or more fluid conduit(s) (e.g., fluid conduit  936 ,  937 ,  1036 ,  1136 ,  1236 ,  1336 , and/or  1436 ) can be inserted into the central lumen of the jacket to form a flexible instrument (e.g., flexible instrument  902 ,  1002 ,  1102 ,  1202 ,  1302 , and/or  1402 ). In some embodiments, steps  1508  and  1510  can be performed simultaneously. At step  1512 , proximal end components (e.g., components of a fluid cooling system (e.g., fluid cooling system  932 ), components of a slidable mechanism (e.g., slidable mechanism  1496 ), components of a heat source (e.g., heat source  1498 ), handles, connectors, etc.) can be coupled to a proximal end portion of the flexible instrument. 
     Although the steps of the method  1500  are discussed and illustrated in a particular order, the method  1500  illustrated in  FIG.  15    is not so limited. In other embodiments, the method  1500  can be performed in a different order. In these and other embodiments, any of the steps of the method  1500  can be performed before, during, and/or after any of the other steps of the method  1500 . Moreover, a person of ordinary skill in the relevant art will recognize that the illustrated method  1500  can be altered and still remain within these and other embodiments of the present technology. For example, one or more steps of the method  1500  illustrated in  FIG.  15    can be omitted and/or repeated in some embodiments. 
       FIG.  16    is a flow diagram illustrating a method  1600  of operating an energy delivery system in accordance with various embodiments of the present technology. The method  1600  is illustrated as a set of steps, operations, or processes  1601 – 1612 . In some embodiments, one or more of the steps  1601 – 1612  may be implemented, at least in part, in the form of executable code stored on non-transitory, tangible, machine-readable media. All or a subset of the steps  1601 – 1612  of the method  1600  can be executed at least in part by various components or devices of an energy delivery system, such as any of the energy delivery systems described above with respect to  FIGS.  9 - 15   . For example, all or a subset of the steps  1601 – 1612  can be executed at least in part by components or devices of (i) a fluid cooling system, (ii) a flexible instrument, (iii) a transmission member, (iv) an antenna, (v) one or more fluid conduits, (vi) a stylet, (vii) a translation actuator, (viii) a slidable mechanism, and/or (ix) a heat source. Additionally, or alternatively, all or a subset of the steps  1601 – 1612  of the method  1600  can be executed at least in part by an operator (e.g., a physician, a user, etc.) of the energy delivery system, and/or by a robotically controlled surgical system via user inputs from the operator through a user input device or automatically through using closed loop control and/or pre-programmed instructions through a processor of the robotically controlled surgical system. Furthermore, any one or more of the steps  1601 – 1612  of the method  1600  can be executed in accordance with the discussion above. 
     The method  1600  begins at step  1601  with positioning a sliding element in a fully extended position within a flexible instrument. As discussed previously, at least a distal section of the flexible instrument can undergo substantial deformation during navigation of the patient anatomy. As such, the flexible instrument must be flexible enough to navigate patient anatomy, yet resilient enough to return to an initial (e.g., undeformed) state or shape after deformation. Accordingly, positioning the sliding element in a fully extended position within the flexible instrument provides recoverable flexibility to the flexible instrument. For example, the sliding element may include a fluid conduit slidably disposed within a jacket of the flexible instrument. Providing recoverable flexibility to the flexible instrument can include sliding the fluid conduit within the jacket (e.g., using a motorized, controllable slidable mechanism connected to a proximal end portion of the fluid conduit) until a resiliently flexible region of the fluid conduit aligns with the portion of the distal section of the flexible instrument. In yet another embodiment, the sliding element may comprise a stylet. For example, providing recoverable flexibility to the flexible instrument can include inserting and/or sliding a stylet formed of a resiliently flexible material into a lumen of a fluid conduit (e.g., using a motorized, controllable slidable mechanism connected to a proximal end portion of the stylet). In this example, the fluid conduit may be fixedly positioned along the distal section of the flexible instrument while the stylet slidably extends within the fluid conduit. 
     The method  1600  continues at step  1602  with delivering a distal portion of the flexible instrument at or near a target site within an airway of the patient. As described above, delivering the flexible instrument comprises navigating the complex, tortuous patient anatomy until the distal portion of the flexible instrument is at a desired location, and then orienting the flexible instrument toward the target site or tumor. In some embodiments, delivery of the flexible instrument may be performed manually, the flexible instrument may be robotically controlled by user control through an input device, or the flexible instrument may be robotically controlled automatically using a pre-programmed set of instructions from a robotic system. 
     At step  1603 , once the distal portion of the flexible instrument is positioned and oriented appropriately within the airway, the method  1600  can optionally include delivering a coolant (e.g., a cooling fluid or other cooling agent, such as a gas) or increasing an amount of coolant being delivered to increase rigidity of the flexible instrument. For example, the coolant can be delivered to and/or removed from the channel using a fluid cooling system and/or one or more fluid conduits of the flexible instrument. In some embodiments, delivering the coolant can include delivering the coolant to or removing the coolant from the channel via one or more slots patterned into a fluid conduit. 
     Coolant delivery may be automatically triggered and controlled by the fluid cooling system based on a detected position of the flexible instrument or may be triggered and controlled based on a user input. For example, the coolant may be automatically delivered when the flexible instrument is detected to have reached the target site or when the flexible instrument has been detected to be oriented towards the target tumor. In another example, the coolant can be delivered through the channel before and/or while positioning the flexible instrument at the target site. In this example, the coolant can be delivered to provide added stiffness to the flexible instrument and/or to prevent the flexible instrument from buckling or kinking during delivery. Accordingly, a volume of coolant may be varied based on the detected position of the flexible instrument through a path to the target. For example, the volume of coolant delivered through the channel can be decreased when the flexible instrument is navigating around tight bends, and/or the volume of coolant delivered through the channel can be increased when the flexible instrument is entering a small diameter structure or when penetrating tissue (as will be described below during step  1604 ). Additionally, as described in detail below, coolant may also be circulated through the channel to cool the antenna of the flexible instrument. Coolant may also be circulated to dissipate heat from tissue at the target site and/or from the transmission member coupled to the antenna. 
     At step  1604 , the method  1600  includes puncturing an airway wall with a distal end portion of the flexible instrument and positioning an antenna of the flexible instrument at the target site (e.g., within the target tumor or lesion). As explained above, the distal end portion of the flexible instrument must be rigid enough (axially) to puncture tissue without buckling or kinking and can in some examples, be altered to be more rigid using an increase in coolant delivery. In some embodiments, the positioning of the flexible instrument may be performed manually, the flexible instrument may be robotically controlled by user control through an input device, or the flexible instrument may be robotically controlled automatically using a pre-programmed set of instructions from a robotic system. 
     Once the antenna is positioned within the tumor (or other target tissue), the method  1600  continues at step  1605  with proximal retraction of the sliding element. In some embodiments, for example, the sliding element is the fluid conduit which can be retracted at least until a distal end of the fluid conduit is positioned proximal the proximal end of the antenna such that the fluid conduit does not interfere with the antenna during energy delivery but the fluid conduit remains within the flexible instrument for coolant delivery. In another embodiment, the sliding element is the stylet which can be retracted until the stylet is removed from or at least retracted within the fluid conduit allowing for coolant to be transported via the fluid conduit to a distal portion of the flexible instrument. In some embodiments, the fluid conduit and/or the stylet can be connected to a slidable mechanism (e.g., a controllable mechanism at proximal end portions of the fluid conduit and/or the stylet). In these embodiments, the fluid conduit and/or the stylet can be proximally slid within the jacket using the slidable mechanism. In these and other embodiments, where the fluid conduit is constructed of a shape memory material, the fluid conduit can be proximally retracted within the jacket by applying energy (e.g., thermal energy) to a proximal end portion and/or one or more other portions of the fluid conduit along the length of the fluid conduit (e.g., using a heat source). In some embodiments, retraction of the sliding element may be performed manually, the sliding element may be robotically retracted by user control through an input device, or the sliding element may be robotically retracted automatically based on detection of the antenna within the target tumor. 
     At step  1606 , the method  1600  continues with delivering energy through the transmission member to the antenna (e.g., using a generator electrically coupled to the transmission member) to ablate tissue at the target site (e.g., the tumor), and at step  1607  the method  1600  includes delivering coolant (or continuing/increasing coolant delivery). While in the illustrated embodiment, energy delivery is performed prior to coolant delivery, in various embodiments coolant delivery may be performed prior to energy delivery, or energy delivery and coolant delivery may be performed simultaneously. In various embodiments, rate of energy delivery, delivery flow rate of the coolant, and evacuation flow rate of the coolant can be controlled by operator selection or altered in a closed-loop fashion automatically under control of a computer processor based on sensor feedback (e.g. measured impedance, temperature, imaging information, and/or the like for detection of tissue ablation efficacy). In some embodiments, where the fluid conduit is constructed from shape memory materials, heat generated by the antenna and applied to a portion of the fluid conduit can cause the fluid conduit to contract (e.g., retract, shrink, etc.) proximally within a jacket of the flexible instrument at least until a conductive region of the fluid conduit is positioned proximal the proximal end of the antenna within the jacket. In this embodiment, coolant delivery may be varied to maintain a temperature of the fluid conduit and thus maintain a contraction length of the fluid conduit to a desirable position. Additionally, as mentioned previously and as will be described in more detail below, coolant may be circulated to dissipate heat from tissue at the target site and/or from the transmission member coupled to the antenna. 
     In some embodiments, the method  1600  may optionally include steps (e.g., steps 1608-1611) for measuring temperature and altering coolant delivery (as necessary) in a closed-loop fashion to maintain a temperature of the antenna preventing overheating and damage to the antenna. At step  1608 , for example, the method  1600  may include measuring temperature at or adjacent the antenna and/or the target site. At decision block  1609 , if the measured temperature is above a first threshold temperature or range of temperatures (e.g., 110° C. to 130° C., or about 120° C.), the method  1600  includes increasing coolant delivery (step  1610 ) and then returning to step  1608  for another temperature measurement. If the measured temperature is not above the first threshold temperature, the method includes maintaining coolant delivery (step  1611 ) and returning to step  1608 . The method continues within a loop returning to step  1608  for another temperature measurement until energy delivery for ablation is complete. As provided above, this closed-loop process is an optional portion of the method  1600  that may not be included in some embodiments of the present technology. 
     Once ablation is complete (e.g., once tumor/lesion and tissue margins have been adequately ablated as confirmed by sensor feedback such as impedance, temperature, imaging, and/or the like or once a pre-determined period of time has elapsed), the method  1600  continues to step  1612 . At step  1612 , ablation energy delivery can be terminated, coolant delivery can be terminated, and/or the flexible instrument may be retracted and removed from patient anatomy. In some embodiments where an additional ablation is to be performed at an additional target site, the sliding elements may be repositioned to a fully extended position prior to repositioning of the flexible instrument at a next target site. If no additional targets are to be ablated, however, it may be unnecessary to reposition the sliding elements within the flexible instrument during retraction of the flexible instrument from patient anatomy. In some embodiments, the flexible instrument may be retracted manually, the flexible instrument may be robotically retracted by user control through an input device, or the flexible instrument may be robotically retracted automatically. 
     Although the steps of the method  1600  are discussed and illustrated in a particular order, the method  1600  illustrated in  FIG.  16    is not so limited. In other embodiments, the method  1600  can be performed in a different order. In these and other embodiments, any of the steps of the method  1600  can be performed before, during, and/or after any of the other steps of the method  1600 . For example, step  1607  can be performed before, during, and/or after any of the other steps of the method  1600 . Moreover, a person of ordinary skill in the relevant art will recognize that the illustrated method  1600  can be altered and still remain within these and other embodiments of the present technology. For example, one or more steps of the method  1600  illustrated in  FIG.  16    can be omitted and/or repeated in some embodiments. As a specific example, a flexible instrument in some embodiments can include a fluid conduit (e.g., the fluid conduit  1036  of  FIG.  10    or the fluid conduit  1136  of  FIG.  11   ) fixedly positioned within a jacket such that a resiliently flexible region of the fluid conduit is permanently positioned along a portion of the distal section of the antenna instrument. In these embodiments, steps  1601  and  1605  may be omitted. In other embodiments, steps  1603 ,  1607 ,  1608 ,  1609 ,  1610 , and/or  1611  can be omitted. 
     While various embodiments, any of the described energy delivery systems may be used as a medical instrument delivered manually, in other embodiments, any of the energy delivery systems may be used as a medical instrument delivered by, coupled to, and/or controlled by a robotic teleoperated and/or non-teleoperated medical system.  FIG.  17   , for example, is a simplified diagram of a teleoperated medical system  1700  (“medical system  1700 ”) configured in accordance with various embodiments of the present technology. In some embodiments, the medical system  1700  may be suitable for use in, for example, surgical, diagnostic, therapeutic, or biopsy procedures. While some embodiments are provided herein with respect to such procedures, any reference to medical or surgical instruments and medical or surgical methods is non-limiting. The systems, instruments, and methods described herein may be used for animals, human cadavers, animal cadavers, portions of human or animal anatomy, non-surgical diagnosis, as well as for industrial systems and general robotic or teleoperational systems. 
     As shown in  FIG.  17   , the medical system  1700  generally includes a manipulator assembly  1702  for operating a medical instrument  1704  in performing various procedures on a patient P positioned on a table T. In some embodiments, the medical instrument  1704  may include, deliver, couple to, and/or control any of the flexible instruments described herein. The manipulator assembly  1702  may be teleoperated, non-teleoperated, or a hybrid teleoperated and non-teleoperated assembly with select degrees of freedom of motion that may be motorized and/or teleoperated and select degrees of freedom of motion that may be non-motorized and/or non-teleoperated. 
     The medical system  1700  further includes a master assembly  1706  having one or more control devices for controlling the manipulator assembly  1702 . The manipulator assembly  1702  supports the medical instrument  1704  and may optionally include a plurality of actuators or motors that drive inputs on the medical instrument  1704  in response to commands from a control system  1712 . The actuators may optionally include drive systems that when coupled to the medical instrument  1704  may advance the medical instrument  1704  into a naturally or surgically created anatomic orifice. Other drive systems may move the distal end of the medical instrument  1704  in multiple degrees of freedom, which may include three degrees of linear motion (e.g., linear motion along the X, Y, and Z Cartesian axes) and in three degrees of rotational motion (e.g., rotation about the X, Y, and Z Cartesian axes). Additionally, the actuators can be used to actuate an articulable end effector of the medical instrument  1704  for grasping tissue in the jaws of a biopsy device and/or the like. Actuator position sensors such as resolvers, encoders, potentiometers, and other mechanisms may provide sensor data to the medical system  1700  describing the rotation and orientation of the motor shafts. This position sensor data may be used to determine motion of the objects manipulated by the actuators. 
     The medical system  1700  also includes a display system  1710  for displaying an image or representation of the surgical site and the medical instrument  1704  generated by subsystems of a sensor system  1708  and/or any auxiliary information related to a procedure including information related to ablation (e.g. temperature, impedance, energy delivery power levels, frequency, current, energy delivery duration, indicators of tissue ablation, etc.). The display system  1710  and the master assembly  1706  may be oriented so an operator O can control the medical instrument  1704  and the master assembly  1706  with the perception of telepresence. 
     In some embodiments, the medical instrument  1704  may include components of an imaging system, which may include an imaging scope assembly or imaging instrument that records a concurrent or real-time image of a surgical site and provides the image to the operator O through one or more displays of the medical system  1700 , such as one or more displays of the display system  1710 . The concurrent image may be, for example, a two or three-dimensional image captured by an imaging instrument positioned within the surgical site. In some embodiments, the imaging system includes endoscopic imaging instrument components that may be integrally or removably coupled to the medical instrument  1704 . In some embodiments, however, a separate endoscope, attached to a separate manipulator assembly may be used with the medical instrument  1704  to image the surgical site. In some embodiments, the imaging system includes a channel (not shown) that may provide for a delivery of instruments, devices, catheters, and/or the flexible instruments described herein. The imaging system may be implemented as hardware, firmware, software, or a combination thereof which interact with or are otherwise executed by one or more computer processors, which may include the processors of the control system  1712 . 
     The medical system  1700  may also include the control system  1712 . The control system  1712  includes at least one memory and at least one computer processor (not shown) for effecting control the between medical instrument  1704 , the master assembly  1706 , the sensor system  1708 , and the display system  1710 . The control system  1712  also includes programmed instructions (e.g., a non-transitory machine-readable medium storing the instructions) to implement some or all of the methods described in accordance with aspects disclosed herein, including instructions for providing information to the display system  1710 . 
     The control system  1712  may optionally further include a virtual visualization system to provide navigation assistance to the operator O when controlling the medical instrument  1704  during an image-guided surgical procedure. Virtual navigation using the virtual visualization system may be based upon reference to an acquired preoperative or intraoperative dataset of anatomic passageways. The virtual visualization system processes images of the surgical site imaged using imaging technology such as computerized tomography (CT), magnetic resonance imaging (MRI), fluoroscopy, thermography, ultrasound, optical coherence tomography (OCT), thermal imaging, impedance imaging, laser imaging, nanotube X-ray imaging, and/or the like. 
       FIG.  18 A  is a simplified diagram of a medical instrument system  1800  configured in accordance with various embodiments of the present technology. The medical instrument system  1800  includes an elongate flexible device  1802 , such as a flexible catheter, coupled to a drive unit  1804 . The elongate flexible device  1802  includes a flexible body  1816  having a proximal end  1817  and a distal end or tip portion  1818 . The medical instrument system  1800  further includes a tracking system  1830  for determining the position, orientation, speed, velocity, pose, and/or shape of the distal end  1818  and/or of one or more segments  1824  along the flexible body  1816  using one or more sensors and/or imaging devices as described in further detail below. 
     The tracking system  1830  may optionally track the distal end  1818  and/or one or more of the segments  1824  using a shape sensor  1822 . The shape sensor  1822  may optionally include an optical fiber aligned with the flexible body  1816  (e.g., provided within an interior channel (not shown) or mounted externally). The optical fiber of the shape sensor  1822  forms a fiber optic bend sensor for determining the shape of the flexible body  1816 . In one alternative, optical fibers including Fiber Bragg Gratings (FBGs) are used to provide strain measurements in structures in one or more dimensions. Various systems and methods for monitoring the shape and relative position of an optical fiber in three dimensions are described in U.S. Pat. No. 7,781,724 (filed Sep. 26, 2006, disclosing “Fiber optic position and shape sensing device and method relating thereto”; U.S. Pat. No. 7,772,541, filed Mar. 12, 2008, titled “ Fiber Optic Position and/or Shape Sensing Based on Rayleigh Scatter”; and U.S. Pat. No. 6,389,187, filed Apr. 21, 2000, disclosing “Optical Fiber Bend Sensor,” which are all incorporated by reference herein in their entireties. In some embodiments, the tracking system  1830  may optionally and/or additionally track the distal end  1818  using a position sensor system  1820 . The position sensor system  1820  may be a component of an EM sensor system with the position sensor system  1820  including one or more conductive coils that may be subjected to an externally generated electromagnetic field. In some embodiments, the position sensor system  1820  may be configured and positioned to measure six degrees of freedom (e.g., three position coordinates X, Y, and Z and three orientation angles indicating pitch, yaw, and roll of a base point) or five degrees of freedom (e.g., three position coordinates X, Y, and Z and two orientation angles indicating pitch and yaw of a base point). Further description of a position sensor system is provided in U.S. Pat. No. 6,380,732, filed Aug. 9, 1999, disclosing “Six-Degree of Freedom Tracking System Having a Passive Transponder on the Object Being Tracked,” which is incorporated by reference herein in its entirety. In some embodiments, an optical fiber sensor may be used to measure temperature or force. In some embodiments, a temperature sensor, a force sensor, an impedance sensor, or other types of sensors may be included within the flexible body. In various embodiments, one or more position sensors (e.g. fiber shape sensors, EM sensors, and/or the like) may be integrated within the medical instrument  1826  and used to track the position, orientation, speed, velocity, pose, and/or shape of a distal end or portion of medical instrument  1826  using the tracking system  1830 . 
     The flexible body  1816  includes a channel  1821  sized and shaped to receive a medical instrument  1826 .  FIG.  18 B , for example, is a simplified diagram of the flexible body  1816  with the medical instrument  1826  extended according to some embodiments. In some embodiments, the medical instrument  1826  may be used for procedures such as imaging, visualization, surgery, biopsy, ablation, illumination, irrigation, and/or suction. The medical instrument  1826  can be deployed through the channel  1821  of the flexible body  1816  and used at a target location within the anatomy. The medical instrument  1826  may include, for example, image capture probes, biopsy instruments, laser ablation fibers, and/or other surgical, diagnostic, or therapeutic tools, including any of the flexible instruments (e.g., flexible instruments  100  or  200 ) or energy delivery systems (e.g., energy delivery systems  300 ,  400 , or  500 ) described above. The medical instrument  1826  may be used with an imaging instrument (e.g., an image capture probe) within the flexible body  1816 . The imaging instrument may include a cable coupled to the camera for transmitting the captured image data. In some embodiments, the imaging instrument may be a fiber- optic bundle, such as a fiberscope, that couples to an image processing system  1831 . The imaging instrument may be single or multi-spectral, for example capturing image data in one or more of the visible, infrared, and/or ultraviolet spectrums. The medical instrument  1826  may be advanced from the opening of channel  1821  to perform the procedure and then be retracted back into the channel  1821  when the procedure is complete. The medical instrument  1826  may be removed from the proximal end  1817  of the flexible body  1816  or from another optional instrument port (not shown) along the flexible body  1816 . 
     The flexible body  1816  may also house cables, linkages, or other steering controls (not shown) that extend between the drive unit  1804  and the distal end  1818  to controllably bend the distal end  1818  as shown, for example, by broken dashed line depictions  1819  of the distal end  1818 . In some embodiments, at least four cables are used to provide independent “up-down” steering to control a pitch of the distal end  1818  and “left-right” steering to control a yaw of the distal end  1818 . Steerable elongate flexible devices are described in detail in U.S. Pat. No. 9,452,276, filed Oct. 14, 2011, disclosing “Catheter with Removable Vision Probe,” and which is incorporated by reference herein in its entirety. In various embodiments, medical instrument  1826  (e.g., flexible instruments  100  or  200 , or energy delivery systems  300 ,  400 , or  500 ) may be coupled to drive unit  1804  or a separate second drive unit (not shown) and be controllably or robotically bendable using steering controls. 
     The information from the tracking system  1830  may be sent to a navigation system  1832  where it is combined with information from the image processing system  1831  and/or the preoperatively obtained models to provide the operator with real-time position information. In some embodiments, the real-time position information may be displayed on the display system  1710  of  FIG.  17    for use in the control of the medical instrument system  1800 . In some embodiments, the control system  1712  of  FIG.  17    may utilize the position information as feedback for positioning the medical instrument system  1800 . Various systems for using fiber optic sensors to register and display a surgical instrument with surgical images are provided in U.S. Pat. No. 8,900,131, filed May 13, 2011, disclosing “Medical System Providing Dynamic Registration of a Model of an Anatomic Structure for Image-Guided Surgery,” which is incorporated by reference herein in its entirety. 
     In some embodiments, the medical instrument system  1800  may be teleoperated within the medical system  1700  of  FIG.  17   . In some embodiments, the manipulator assembly  1702  of  FIG.  17    may be replaced by direct operator control. In some embodiments, the direct operator control may include various handles and operator interfaces for hand-held operation of the instrument. 
     EXAMPLES 
     Several aspects of the present technology are set forth in the following examples:
     1. A flexible instrument, comprising: 
   an elongate device including an inner conductor, an outer conductor surrounding the inner conductor, and a dielectric layer insulating the inner conductor from the outer conductor,   a recess formed in the outer conductor; and   an insert positioned within the recess and about the inner conductor.   
   

     2. The flexible instrument of example 1 wherein the elongate device includes a proximal section and a distal section, and wherein the recess is positioned at the distal section of the elongate device to form an antenna body. 
     3. The flexible instrument of example 2, further comprising a barrier layer extending over at least a portion of the antenna body and positioned over the insert. 
     4. The flexible instrument of example 3 wherein the barrier layer includes a plurality of non-conductive layers. 
     5. The flexible instrument of example 3 or example 4 wherein the barrier layer is configured to secure the insert within the recess. 
     6. The flexible instrument of example 3 or example 4 wherein one of the plurality of non-conductive layers is configured to seal the antenna body from fluid. 
     7. The flexible instrument example 3 or example 4 wherein the barrier layer is composed of a fluoropolymer, a plastic material, a heat-shrink material, or a conformal coating. 
     8. The flexible instrument of any one of examples 1-7, further comprising a jacket layer positioned over at least a portion of the outer conductor. 
     9. The flexible instrument of example 8, wherein the recess is further formed in the jacket layer. 
     10. The flexible instrument of example 8 or example 9 wherein the jacket layer is non-conductive. 
     11. The flexible instrument of any one of examples 8-10 wherein the jacket layer is composed of a plastic material, a PET coating, or a heat-shrink material. 
     12. The flexible instrument of any one of examples 1-11, further comprising a conductive material electrically coupling the inner conductor to the outer conductor near a distal tip of the flexible instrument. 
     13. The flexible instrument of any one of examples 1-11, further comprising a conductive material near a distal tip of the flexible instrument and electrically coupled to the inner conductor. 
     14. The flexible instrument of example 13, further comprising a barrier layer extending over the conductive material, the insert, and over at least a portion of the elongate device. 
     15. The flexible instrument of example 13, further comprising: 
     a non-conductive plug formed at a distal end of the conductive material; and   a barrier layer positioned over extending over the conductive material, the non-conductive plug, the insert, and over at least a portion of the elongate device.   

     16. The flexible instrument of any one of examples 1-15 wherein the insert is a slit tube. 
     17. The flexible instrument of any one of examples 1-16 wherein the insert is secured within the recess using an adhesive. 
     18. The flexible instrument of any one of examples 1-17 wherein the insert is non-conductive. 
     19. The flexible instrument of any one of examples 1-18 wherein the insert fills the recess entirely. 
     20. The flexible instrument of any one of examples 1-19 wherein the recess has a rectangular, square, trapezoidal, triangular, circular, or oval cross-sectional shape. 
     21. The flexible instrument of any one of examples 1-19 wherein the recess has a linear, curved, curvilinear, annular, helical, serpentine, or zig-zag shape along a length of the outer conductor. 
     22. The flexible instrument of any one of examples 1-21 wherein the recess is further formed in the dielectric layer. 
     23. The flexible instrument of any one of examples 1-22 wherein the outer conductor includes a multi-filament layer. 
     23. The flexible instrument of any one of examples 1-23 wherein the outer conductor includes at least one of a braided layer, a foil layer, or a nitinol layer. 
     24. The flexible instrument of any one of examples 1-23 wherein the recess forms a portion of a recess pattern, and wherein the recess pattern includes a first recess and a second recess each formed along a distal section of the outer conductor. 
     25. The flexible instrument of example 24 wherein the recess pattern is defined by a spacing of the first recess and the second recess, a position of the first recess and the second recess, a shape of the first recess and the second recess, or a size of the first recess and the second recess. 
     27. The flexible instrument of example 24 wherein: 
     the insert is a first insert positioned within the first recess; and   the flexible instrument further includes a second insert positioned within the second recess and about the inner conductor.   

     28. The flexible instrument of any one of examples 1-27 wherein the elongate device includes a proximal section and a distal section, and wherein the proximal section of the elongate device and the distal section of the elongate device are distinct and fixedly coupled cable sections. 
     29. An energy delivery system, comprising: 
     the flexible instrument of example 2,   wherein the flexible instrument further comprises— 
   a transmission member, wherein the antenna body is at a distal end portion of the transmission member;   a sheath surrounding the antenna body and the transmission member; and   at least one fluid conduit at least partially disposed within the sheath, wherein-   the at least one fluid conduit defines a fluid inlet channel configured to transport fluid proximal to a distal end of the antenna body, and   the at least one fluid conduit is configured to provide variable recoverable flexibility along at least a section of the flexible instrument.   
   

     30. The system of example 29 wherein the at least one fluid conduit is composed of a material that prevents interference with energy delivery of the antenna body. 
     31. The system of example 29 or example 30 wherein the at least one fluid conduit includes a first region formed of a resiliently flexible material and a second region formed of a non-conductive material. 
     32. The system of example 31 wherein the resiliently flexible material is a shape memory material and the non-conductive material is a plastic or a polymer. 
     33. The system of example 31 or example 32 wherein the first region extends alongside at least a portion of the transmission member within the sheath and terminates at or proximal to the distal end portion of the transmission member. 
     34. The system of any one of examples 31-33 wherein the at least one fluid conduit further comprises a transition region, wherein the transition region couples the first region to the second region via overlapping or tapering. 
     35. The system of any one of examples 29-34, further comprising a stylet configured for slidable insertion within the at least one fluid conduit. 
     36. The system of any one of examples 29-35 wherein the at least one fluid conduit is composed of a non-conductive material and the stylet is formed of a resiliently flexible material. 
     37. The system of any one of examples 29-36, further comprising a slidable mechanism at a proximal end of the flexible instrument, wherein the slidable mechanism is mechanically coupled to a proximal end portion of the at least one fluid conduit. 
     38. The system of example 37 wherein the slidable mechanism includes at least one of a linear slide, a cable drive assembly, a robotic arm, or a motor driven leadscrew. 
     39. The system of any one of examples 29-38 wherein the at least one fluid conduit includes one or more slots or cutouts patterned into the fluid conduit, and wherein at least one slot or cutout of the one or more slots or cutouts is shaped and sized such that fluid exits the at least one fluid conduit into a channel of the flexible instrument about the antenna body. 
     40. The system of any one of examples 29-38 wherein the at least one fluid conduit includes one or more slots or cutouts patterned into the fluid conduit, and wherein the one or more slots or cutouts is laminated with heat shrink such that the fluid is prevented from exiting the fluid conduit via the slot or cutout. 
     41. The system of any one of examples 29-40 wherein the at least one fluid conduit includes a first fluid conduit and a second fluid conduit at least partially disposed within the sheath, and wherein a distal end of the first fluid conduit is positioned at a different location along a length of the sheath than a distal end of the second fluid conduit. 
     42. A method of operating an energy delivery system, the energy delivery system including a flexible instrument having a transmission member, an antenna at a distal end portion of the transmission member, a sheath surrounding the flexible instrument, and a fluid conduit at least partially disposed within the sheath, the method comprising: 
     providing resilient flexibility, using the fluid conduit, to at least a section of the flexible instrument during navigation of the flexible instrument to a target within a patient;   delivering energy to the target via the antenna; and   delivering fluid proximate the antenna at least while delivering energy to the target,   wherein the fluid is delivered via the fluid conduit while a distal end of the fluid conduit is extended to a distal end portion of the antenna.   

     43. The method of example 42 wherein providing resilient flexibility includes using a shape memory material extended to at least the distal end portion of the antenna during the navigation. 
     44. The method of example 43, further comprising retracting the distal end of the shape memory material to at least the distal end of the transmission member before delivering energy to the target tissue via the antenna. 
     45. The method of example 43 or example 44 wherein the shape memory material forms a stylet slideably positioned within the fluid conduit, and wherein the fluid conduit is formed of a non-conductive material. 
     46. The method of any one of examples 43-45 wherein the shape memory material forms the fluid conduit, and wherein the fluid conduit is configured to be slideable within the jacket. 
     47. An energy delivery system, the system comprising: 
     a flexible instrument comprising an elongate device having an inner conductor, an outer conductor surrounding the inner conductor, and a dielectric layer insulating the inner conductor from the outer conductor, the flexible instrument further including: 
   a recess formed in the outer conductor; and   an insert disposed within the recess and about the inner conductor;   
   a sheath surrounding the flexible instrument; and   at least one fluid conduit at least partially disposed within the sheath and extending along the flexible instrument,   wherein the at least one fluid conduit defines a fluid inlet channel configured to transport fluid to a distal end region of the flexible instrument, and further wherein the at least one fluid conduit provides variable recoverable flexibility along at least a portion of the flexible instrument.   

     48. The energy delivery system of example 47 wherein the elongate device includes a proximal section and a distal section, and wherein the recess is positioned at the distal section of the elongate device to form an antenna body. 
     49. The energy delivery system of example 47 or example 48 wherein the insert fills the recess entirely. 
     50. The energy delivery system of any one of examples 47-49 wherein the recess has a rectangular, square, trapezoidal, triangular, circular, or oval cross-sectional shape. 
     51. The energy delivery system of any one of examples 47-49 wherein the recess has a linear, curved, curvilinear, annular, helical, serpentine, or zig-zag shape along a length of the outer conductor. 
     52. The energy delivery system of any one of examples 47-51 wherein the insert is a slit tube. 
     53. The energy delivery system of any one of examples 47-52 wherein the insert is secured within the recess using an adhesive. 
     54. The energy delivery system of any one of examples 47-53 wherein the insert is composed of glue, PTFE, FEP, PEEK, or polyurethane. 
     55. The energy delivery system of any one of examples 47-54, further comprising a stylet configured for slidable insertion within the at least one fluid conduit. 
     56. The energy delivery system of any one of examples 47-55 wherein the at least one fluid conduit includes a first fluid conduit and a second fluid conduit at least partially disposed within the sheath, and wherein the first fluid conduit runs alongside and is separate from the second fluid conduit. 
     CONCLUSION 
     The systems and methods described herein can be provided in the form of tangible and non-transitory machine-readable medium or media (such as a hard disk drive, hardware memory, optical medium, semiconductor medium, magnetic medium, etc.) having instructions recorded thereon for execution by a processor or computer. The set of instructions can include various commands that instruct the computer or processor to perform specific operations such as the methods and processes of the various embodiments described here. The set of instructions can be in the form of a software program or application. Programmed instructions may be implemented as a number of separate programs or subroutines, or they may be integrated into a number of other aspects of the systems described herein. The computer storage media can include volatile and non-volatile media, and removable and non-removable media, for storage of information such as computer-readable instructions, data structures, program modules or other data. The computer storage media can include, but are not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid-state memory technology, CD-ROM, DVD, or other optical storage, magnetic disk storage, or any other hardware medium which can be used to store desired information and that can be accessed by components of the system. Components of the system can communicate with each other via wired or wireless communication. In one embodiment, the control system supports wireless communication protocols such as Bluetooth, IrDA, HomeRF, IEEE 802.11, DECT, and Wireless Telemetry. The components can be separate from each other, or various combinations of components can be integrated together into a monitor or processor or contained within a workstation with standard computer hardware (for example, processors, circuitry, logic circuits, memory, and the like). The system can include processing devices such as microprocessors, microcontrollers, integrated circuits, control units, storage media, and other hardware. 
     Medical tools that may be delivered through the elongate flexible devices or catheters disclosed herein may include, for example, image capture probes, biopsy instruments, laser ablation fibers, and/or other surgical, diagnostic, or therapeutic tools. Medical tools may include integrally formed and/or separately attached end effectors having a single working member such as a scalpel, a blunt blade, an optical fiber, an electrode, and/or the like. Other end effectors may include, for example, forceps, graspers, scissors, clip appliers, and/or the like. Other end effectors may further include electrically activated end effectors such as electrosurgical electrodes, transducers, sensors, and/or the like. Medical tools may include image capture probes that include a stereoscopic or monoscopic camera for capturing images (including video images). Medical tools may additionally house cables, linkages, or other actuation controls (not shown) that extend between their proximal and distal ends to controllably bend the distal ends of the tools. Steerable instruments are described in detail in U.S. Pat. No. 7,316,681, filed Oct. 4, 2005, disclosing “Articulated Surgical Instrument for Performing Minimally Invasive Surgery with Enhanced Dexterity and Sensitivity” and U.S. Pat. No. 9,259,274, filed Sept. 30, 2008, disclosing “Passive Preload and Capstan Drive for Surgical Instruments,” which are incorporated by reference herein in their entireties. 
     The systems described herein may be suited for navigation and treatment of anatomic tissues, via natural or surgically created connected passageways, in any of a variety of anatomic systems, including the lung, colon, stomach, intestines, kidneys and kidney calices, bladder, liver, gall bladder, pancreas, spleen, meter, ovaries, uterus, brain, the circulatory system including the heart, vasculature, and/or the like. 
     Note that the processes and displays presented may not inherently be related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the operations described. The required structure for a variety of these systems will appear as elements in the claims. In addition, the embodiments of the invention are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein. 
     While certain exemplary embodiments of the invention have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that the embodiments of the invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. The above detailed descriptions of embodiments of the technology are not intended to be exhaustive or to limit the technology to the precise form disclosed above. Although specific embodiments of, and examples for, the technology are described above for illustrative purposes, various equivalent modifications are possible within the scope of the technology, as those skilled in the relevant art will recognize. For example, while steps are presented in a given order, alternative embodiments can perform steps in a different order. Furthermore, the various embodiments described herein can also be combined to provide further embodiments. 
     From the foregoing, it will be appreciated that specific embodiments of the technology have been described herein for purposes of illustration, but well-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the technology. To the extent any materials incorporated herein by reference conflict with the present disclosure, the present disclosure controls. Where the context permits, singular or plural terms can also include the plural or singular term, respectively. Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. As used herein, the phrase “and/or” as in “A and/or B” refers to A alone, B alone, and both A and B. Where the context permits, singular or plural terms can also include the plural or singular term, respectively. Additionally, the terms “comprising,” “including,” “having” and “with” are used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional types of other features are not precluded. 
     Furthermore, as used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result. 
     From the foregoing, it will also be appreciated that various modifications can be made without deviating from the technology. For example, various components of the technology can be further divided into subcomponents, or various components and functions of the technology can be combined and/or integrated. Furthermore, although advantages associated with certain embodiments of the technology have been described in the context of those embodiments, other embodiments can also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.