b may be fed through the working channel of an endoscope or similar device to reach a target ablation site.

A cross sectional view of the distal region X of the ablation probe 100 is shown in FIG. 3. The ablation probe 100 generally comprises an applicator 102, a feeding or feed cable 104 and a tubular shaft 105 in which the feeding cable 104 is located. The terms “feeding cable” and “feed cable” are used interchangeably herein.

The applicator 102 is arranged to apply radiation to heat surrounding tissue. The applied radiation may be adapted to cause localised heating and destruction of malignant cells around or near to the applicator 102. The applicator 102 may be arranged to apply any suitable form of radiation to surrounding tissue such that the desired heating is caused. The applicator 102 may, for example, be arranged to emit microwave or RF radiation, or may emit any other suitable radiation to cause heating. The applicator 102 is arranged at or near a distal end of the ablation probe 100 so that it can be positioned in a desired position relative to the tissue to be treated. The applicator 102 may be formed from a ceramic material with suitable dielectric properties (for example, zirconia) according to the energy it is arranged to apply.

The feed or feeding cable 104 is arranged to supply electromagnetic energy to the applicator 102. Only part of the length of the feeding cable is shown in the Figures. The feeding cable 104 may be any elongate member suitable for supplying electromagnetic energy to the applicator (e.g. a conductor). The feeding cable 104 may run along at least part or all of the length of the ablation probe 100 to deliver a supply of energy to the applicator 102. In the described embodiment, a distal end of the feeding cable 104 is coupled to a proximal end of the applicator 102 and a proximal end of the feeding cable 104 (not shown in the Figures) is coupled to a generator (also not shown in the Figures) suitable for generating the desired signal to supply energy to the applicator 102. In the presently described embodiment, the feeding cable 104 comprises a coaxial cable. The coaxial cable comprises an inner conductor 104a insulator 104b, and outer conductor 104c. The feed cable 104 may comprise further components such as an outer sleeve as described later.

In the present embodiment, an applicator tip 102a is connected to the distal end of the applicator. The tip 104a forms a pointed distal tip of the ablation probe 100 that is suitable for piercing tissue in use. In other embodiments, the separate tip component may not be provided, or may be formed integrally with the applicator 102. In yet other embodiments, the ablation probe may have an atraumatic distal tip, rather than a pointed one. The tip 102a is coupled to the applicator 102 via a capsule 102b, which is arranged to house the applicator 102. The capsule 102b may be a tubular component surrounding the ceramic material of the applicator as shown in the Figures. The applicator 102, applicator tip 102a and capsule 102b form an applicator assembly.

Referring again to FIG. 3, the tubular shaft 105 comprises a tubular member 106 (such as a sheath or other such hollow elongate component (e.g. a hypotube, or braid/coil reinforced tubing)) arranged to house at least part of the length of the feeding cable 104. The tubular member 106 may be formed from a metal material which has sufficient rigidity to allow the ablation probe to be inserted into tissue. In other embodiments, the tubular member 106 may be formed from any other suitable material, and may be formed from a superelastic material, for example Nitinol.

Referring again to FIG. 1, the ablation probe 100 generally comprises two portions: a needle portion 100c and a catheter portion 100d. The needle portion 100c may be arranged at the distal end of the ablation probe 100 and is adapted to be inserted into tissue during use to reach the desired ablation location. The catheter portion 100d may be provided at the proximal end of the ablation probe 100 and is arranged to supply electromagnetic energy and a flow of coolant to and from the needle portion 100c. The catheter portion 100d may have an extended length and flexibility for endoscopic use. In other embodiments, a shorter, more rigid catheter portion 134 may be provided for percutaneous use.

In some embodiments, the needle portion 100c may form a small part of the overall length of the ablation probe. For example, the needle portion may be 5 mm to 2000 mm in length, and preferably may be around 70 mm in length. The length of the needle portion 100c may be chosen according to the anatomy to be accessed. For example, the needle portion may be approximately between 10 and 100 mm long for delivery of therapy to organs including the pancreas, or lung, or longer (for example 100-400 mm in length) for delivery of therapy percutaneously. A longer length of needle portion may be more suitable for accessing parts of the lung, for example. The catheter portion may be around 1000 mm to 2000 mm in length, and preferably around 1400 mm in length. The length of the catheter portion may be chosen according to the position of the ablation site which must be reached.

In other embodiments, the needle portion 100c of the ablation probe may form a greater proportion of the length of the ablation probe. In some embodiments, the entire length of the ablation probe may be formed by the needle portion 100c (i.e. such that a separately defined catheter portion is absent). For example, if the ablation probe is to be used percutaneously the catheter portion 100d may be shorter than for endoscopic use, or may not be required.

The ablation probe 100 further comprises a coolant circuit flow path forming a coolant supply circuit. The flow of coolant is shown by arrows in FIGS. 3 and 6. The coolant circuit comprises a first coolant path 108. In the described embodiment, the first coolant path 108 is a coolant delivery path via which coolant is able to flow in a direction towards the applicator 102. For example, the coolant delivery path 108 may deliver a flow of coolant towards the distal end of the ablation probe 100 from a coolant supply (not shown in the Figures) coupled to the coolant delivery path 108 at the proximal end of the ablation probe 100. The coolant may be pumped around the coolant circuit by a suitable pump such as a peristaltic pump. The flow of coolant may help control the temperature of the ablation probe 100 during use. This may allow energy to be delivered to the surrounding tissue for an extended period of time without the ablation probe 100 overheating and being damaged, or causing injury to healthy tissue. The coolant may be a fluid, and may be water, saline solution, a cryogenic gas or any other suitable coolant known in the art.

The coolant circuit flow path further comprises a second coolant path 110. In the described embodiment, the second coolant path 110 is a coolant return path via which coolant can return from the applicator 102. The coolant return path 110 may therefore return the supply of coolant from the distal end of the ablation probe 100 to the proximal end.

The first and second coolant flow paths are fluidly connected in the distal region of the ablation probe so as to form the coolant circuit. The first and second coolant flow paths may be connected by any suitable arrangement of channels or conduits, e.g. within the applicator assembly so that the applicator is cooled. For example, the coolant flow paths may be linked by channels or conduits formed within the ceramic material of the applicator 102 so that a continuous coolant circuit is formed.

In the presently described embodiment, both of the first and second coolant flow paths are located within the tubular member 106. The inner surface of the tubular member 106 is spaced apart from the outer surface of the feeding cable 104 as will be described in more detail later on. The first coolant flow path is defined by a coolant conduit 108a located within the tubular member. The coolant conduit 108a extends along the length of the feeding cable 104 to carry coolant to the distal region. The second coolant flow path is defined by an inner surface of the tubular member 106 and outer surface of the feed cable 104.

In other embodiments, the first coolant path 108 may act as a coolant return path. In this embodiment, the first coolant path 108 is arranged to carry a flow of coolant away from the applicator. In this embodiment, the second coolant path 110 may act as a coolant delivery path arranged to carry a flow of coolant towards the applicator. A combination of the first and second coolant paths may therefore form a coolant circuit arranged to deliver a flow of coolant towards and away from the applicator, where the coolant can flow in either direction along each of the first and second coolant paths.

The ablation probe 100 further comprises a choke 112 arranged to reduce power reflected from the applicator along the feed cable. In the present embodiment, the choke 112 is partly formed by an electrically conducting distal region of the tubular member 106 that surrounds the feeding cable 104. In order to provide an electrical connection between the feeding cable 104 and the tubular member 106 the choke comprises three bridging structures (or bridging members or struts) 114a, 114b, 114c. The bridging structures are arranged to extend across the space between the tubular member 106 and feeding cable 104 to provide an electrical connection between them. The bridging structures therefore form the base of the choke (i.e. the choke short). The bridging structures have spaces between them though which one or both of the first and second coolant flow paths may be located. This allows coolant to flow through the base of the choke, rather than around it, to improve cooling and help to make the ablation probe more compact. By forming the bridging structures from cut out regions of material they can be made in flexible components suitable for ensuring the ablation probe has an overall degree of flexibility for endoscopic (or similar) use.

In the presently described embodiment three (axially aligned) bridging structures are provided. Three bridging structures may be used to ensure concentricity between the feed cable 104 and the tubular member 106 (preventing undesired points of electrical contact effecting the operation of the choke). By using three bridging structures they may be sized to ensure concentricity, while still being suitable for manufacture. In other embodiments, other numbers of axially aligned bridging structures may be provided, so that more generally the ablation probe comprises at least one bridging structure. For example, it may also be possible to achieve concentricity with fewer bridging structures (e.g. one or two) that span a greater circumferential length around the feeding cable (e.g. angle α shown in FIG. 10). In other embodiments, more than three axially aligned bridging structures may also be provided, which may also provide a suitable concentric arrangement. In this paragraph axially aligned means at the same location along the length (longitudinal axis Y) of the ablation probe e.g. the same distance along the feed cable from the point of connection with the applicator. In some embodiments there may be further sets of non-axially aligned bridging structures as will be described later.

In the described embodiment, the portion of tubular member 106 surrounding the feeding cable 104 that extends distally from the bridging structures is formed from an electrically conductive material so that it forms part of the choke. In some embodiments, a larger region or all of the tubular member 106 may be formed from an electrically conductive material.

The three bridging structures 114a, 114b, 114c are located at the same distance from the proximal end of the applicator 102 along the longitudinal axis Y of the ablation probe (i.e. the point of electrical contact between the bridging structures 114a, 114b, 114c is the same distance from the applicator). They therefore form a first set of one or more axially aligned bridging structures. The distance between the point of electrical contact between the bridging structures 114a, 114b, 114c and tubular member 106 is proportional to approximately a multiple of an odd number of one quarter of the wavelength of the electromagnetic energy corresponding to the operating frequency of the ablation probe, or the wavelength of the electromagnetic energy in a medium surrounding the feeding cable 104 (e.g. the media within the choke). One or more further sets of bridging structures may be provided, each set being spaced apart along the length of the ablation probe by a similar multiple of an odd number of one quarter of the wavelength. This separation distance allows image currents in the choke to be provided which have the opposite phase to reflected current running back along the feeding cable.

As can been seen in the Figures, the feeding cable comprises a feed cable sleeve 116 that fits around the outer surface of the outer conductor. The feed cable sleeve 116 therefore forms an outer part or surface of the feed cable that is spaced apart from an inner surface of the tubular shaft (e.g. the tubular member in the present embodiment) in which it is housed. The bridging structures 114a, 114b, 114c are each formed from part of the sleeve 116. In the present embodiment, the sleeve 116 forms a close fit around the outer conductor of the feeding cable 104. In other embodiments, the sleeve may extend around an insulating layer around the outer conductor of the feeding cable. The sleeve is formed from an electrically conductive material, and is electrically connected to the outer conductor of the feed cable 104.

Each of the bridging structures 114a, 114b, 114c is formed from a respective deformed or angled region that is cut out from the wall of the sleeve 116. The deformed region extends out of alignment with the body of the sleeve 116 to extend across the gap between the feeding cable 102 and the tubular member 106. The bridging structures 114a, 114b, 114c therefore extend at least partly in the radial direction R relative to the longitudinal axis Y of the ablation probe. The bridging structures 114a, 114b, 114c are each formed from a strip of material cut-out from the body of the sleeve 116. The strips are bent or deformed so that they are out of alignment with the outer surface of the sleeve 116. The bridging structures are therefore splayed-out from the sleeve outer surface. In the present embodiment, the bridging structures 114a, 114b, 114c are therefore formed integrally with the body of the sleeve 116. By forming the bridging structures from a section of material defined by a cut-out or cut-outs in the body of the sleeve they may be more easily manufactured and assembled. In order to separate the strips or regions forming the bridging structures the sleeve may be laser cut. This provides accurate cutting. Other forms of cutting may however be used.

By forming the bridging structures 114a, 114b, 114c in this way they form a resiliently deformable structure. This allows them to be compressed (e.g. pushed back towards alignment with the outer surface of the sleeve 116) when inserted into the tubular member during assembly of the ablation probe. An interference fit is therefore provided between the bridging structures 114a, 114b, 114c and tubular member 106. This helps to ensure electrical contact is maintained between the bridging structures 114a, 114b, 114c and tubular member 106, without needing to manufacture components to a very narrow tolerance range.

In the presently described embodiment, the bridging structures 114a, 114b, 114c each form strips extending between a distal portion 116a and a proximal portion 116b of the sleeve 106. The bridging structures therefore comprise two oppositely angled sections 115a, 115b as can be seen in FIG. 11. The axially extending edges of the strips forming the bridging structures 114a, 114b, 114c are separated from the body of the sleeve member by three cuts-outs 118a, 118b, 118c (two of which are visible in the Figures).

In order to manufacture the bridging structure, the cut-outs forming the bridging structures are first formed in the sleeve to divide it into the distal and proximal sections 116a, 116b. Force is then applied at the distal and proximal ends of the sleeve in a direction along its axial length towards its centre. This compresses the length of the sleeve 116, and causes the strips forming the bridging structures to deform or splay out of alignment with the outer surface of the sleeve 116.

The bridging structures 114a, 114b, 114c each comprise a rounded portion at the point of contact with the tubular member 106.

As can be seen in the cross section of FIGS. 4 and 10, the bridging structures 114a, 114b, 114c are angularly spaced apart around the longitudinal axis Y. A space is therefore formed between each of the bridging structures 114a, 114b, 114c which can be used to allow coolant to flow. In the presently described embodiment, the bridging structures are evenly spaced (they have an equal angle between them) around the longitudinal axis Y and extend an equal distance radially from the outer surface of the sleeve 116. By providing three or more evenly spaced bridging structures of equal radial extent from the sleeve 116 the tubular member 106 is held in a concentric alignment with the feeding cable 104. This ensures that the feeding cable 104 remains spaced apart from the surrounding tubular member 106 so that there is no electrical connection between them other than that provided by the bridging structures 114a, 114b, 114c. This would otherwise lead to a loss of choke performance. In other embodiments, as mentioned above, a greater number of bridging structures (e.g. more than three) may be provided, or fewer than three bridging structures can be used. In both cases a concentric alignment may still be provided. In some embodiments, some or all of the bridging structures may not be evenly angularly spaced around the longitudinal axis Y.

The space between the bridging structures is used to provide space for the first and second coolant flow channels. The coolant conduit 108a forming the first coolant flow path 108 is arranged to extend between two of the bridging structures 114a, 114c as can be seen in FIG. 4. The remaining two spaces between the bridging structures provides space for the second coolant flow path 110, which in the present embodiment is defined by the inner surface of the tubular member 106 and the outer surface of the sleeve 116.

Referring to FIG. 10, the coolant flow paths defined between the bridging structures (i.e. the angle at which they are spaced apart) extend an angle ß of about 70° around the longitudinal axis. In other embodiments, the coolant flow paths may extend an angle in the range between 60° and 80° (again corresponding to the angular spacing between the bridging structures). By providing coolant flow paths sized within this range the base of the choke has the desired electromagnetic properties to reduce microwaves reflected from the applicator, while still allowing sufficient space to accommodate coolant flow paths of sufficient size without needing excessive coolant pressure. In the present embodiment in which there are three bridging structures, each of the bridging structures 114a, 114b, 114c extend an angle α of about 50° around the longitudinal axis Y. In other embodiments, the bridging structures may extend an angle in a range between about 40° and 60°, according to the desired space between them for coolant to flow.

The angular sizes (α) and spacing (β) in the previous paragraph may apply to other embodiments in which other numbers of bridging structures are provided. The number of bridging structures and their size can be adjusted to accommodate different angular spacing between them, or vice versa. More generally therefore, the angular spacing between bridging structures (B) may be in the range between 20° and 115°. Correspondingly, the angular size (a) of the bridging structures may be in the range between 5° and 100°. Examples of bridging structures with a small spacing and a relatively large spacing are shown in FIGS. 20 and 21. In the various embodiment described the bridging structures are equal in size and spacing as shown in the Figures to aid manufacture and concentric alignment. In other embodiments, they may have different sizes/spacing to each other.

The coolant conduit 108a has a flattened non-circular cross sectional profile (in a plane normal to the longitudinal axis Y). The coolant conduit 108a is shaped to conform to the shape of an inner surface of the tubular member 116 and an outer surface of the feed cable 104 between which it is located. The coolant conduit 108a therefore has curved walls such that it extends partly around the sleeve 106, and forms a close fit with the outer surface of the sleeve and the inner surface of the tubular member. By forming the coolant conduit