RF ablation probes with tine valves

[0001] This application is a continuation of U.S. application Ser. No. 11/323,941 filed on Dec. 29, 2005, now issued as U.S. Pat. No. 7,896,874, the disclosure of which is hereby incorporated by reference.

[0002] The field of the invention relates generally to the structure and use of radio frequency (RF) electrosurgical probes for the treatment of tissue.

[0003] In oncology, cancer treatment is often performed using radio frequency (RF) ablation techniques. Conventional ablation techniques use an array of RF needles or tines (“tine array”), which may be configured to deploy in a pre-determined shape or pattern for transferring RF energy into surrounding tissue. For example, in an undeployed state, tines are inserted into a target area while housed within the lumen of a cannula. An undeployed tine array enclosed within a cannula may be placed by inserting the cannula through bone and tissue into a target area. Once inserted, the electrode tine array may be deployed by forcing the electrode tines out of a cannula and into the surrounding target tissue. After deployment, RF energy may be transmitted from the electrode tine array to ablate the target tissue, causing heating and eventual necrosis of cancerous or malignant tissue. RF ablation occurs when a high frequency alternating current flows from one electrode to another, completing a current path, causing ionic agitation. Ionic agitation occurs around an active electrode as a result of frictional heating in the tissue surrounding the electrode tines (e.g., electrodes, RF needle probes, and the like) on an array, leading to cell death and necrosis. After ablating the target tissue, the electrode tine array is then retracted into the cannula

[0004] A need continues for lower profile (smaller gauge) RF probes with larger electrode arrays. In designing for these characteristics, every diminutive amount of space inside the cannula of the RF probe must be utilized. As a result, an electrode array assembly must hold extremely tight clearances and tolerances in concert with the inner diameter of the cannula. Some problems associated with conventional ablation techniques are associated with the deployment of tine arrays. In particular, biological material (e.g., tissue, coagulated blood, and the like) can enter the lumen of a cannula during deployment or retraction. If blood and tissue enters the cannula, mechanical interference (i.e., blockage, jamming, and the like) may result when the electrode tine array is retracted or deployed again. When retracting the electrode tine array, necrosed tissue and blood resulting from the ablation may adhere to the RF needle probes, causing a mechanical interference.

[0005] There, thus, remains a need to minimize the entry of biological material into an RF ablation cannula during deployment and/or retraction of electrode tines.

[0006] In accordance with a first aspect of the present inventions, a tissue ablation probe is provided. The tissue ablation probe comprises an elongated shaft, at least one electrode tine carried by the elongated shaft, at least one tine exit from which the electrode tine(s) can be deployed from the elongated shaft and retracted within the elongated shaft, and a sheath covering the electrode tine exit(s). The sheath may, e.g., line an exterior surface of the elongated shaft or an interior surface of the elongated shaft. The sheath has at least one pre-formed tine valve (e.g., a slit) positioned over the electrode tine exit(s) and configured to open when the electrode tine is deployed and to close when the electrode tine(s) is retracted. In one embodiment, the tine valve(s) is configured to open in response to pressure exerted during deployment of the electrode tine(s). In another embodiment, the tine valve(s) is configured to hinder the entry of biological material within the elongated shaft. In one embodiment, the sheath is pliable, such that the tine valve(s) can more easily hinder the entry of the biological material.

[0007] In accordance with a second aspect of the present inventions, another tissue ablation probe is provided. The tissue ablation probe comprises an elongated shaft, at least one electrode tine carried by the elongated shaft, at least one tine exit from which the electrode tine(s) can be deployed from the elongated shaft and retracted within the elongated shaft, and a sheath covering the electrode tine exit(s). The sheath may, e.g., line an exterior surface of the elongated shaft or an interior surface of the elongated shaft. The sheath has at least one tine valve positioned over the electrode tine exit(s) and configured to seal over the electrode tine when deployed to hinder the entry of biological material within the elongated shaft. The tine valve(s) may be preformed in the sheath, or alternatively, can be configured to be created upon puncturing of the sheath via deployment of the of electrode tine(s).

[0008] The sheath is pliable, such that the tine valve(s) can more easily seal over the electrode tine(s) when deployed and close when the electrode tine(s) are retracted. In one embodiment, the tine valve(s) is configured to close in response to the retraction of the at least one electrode tine into the elongated shaft.

[0009] In accordance with a third aspect of the present inventions, still another tissue ablation probe is provided. The tissue ablation probe comprises an elongated shaft, at least one electrode tine carried by the elongated shaft, at least one tine exit from which the electrode tine(s) can be deployed from the elongated shaft and retracted within the elongated shaft, and a sheath covering the electrode tine exit(s). The sheath may, e.g., line an exterior surface of the elongated shaft or an interior surface of the elongated shaft. The sheath is configured to seal over the electrode tine when the electrode tine traverses the sheath to hinder the entry of biological material within the elongated shaft. The sheath is pliable, such that sheath can more easily seal over the electrode tine(s) when deployed. In an optional embodiment, the sheath remains sealed in response to the retraction of the electrode tine(s) into the elongated shaft. In performing the sealing function, the sheath may have at least one pre-formed tine valve that seals over the at least one electrode tine when the electrode tine(s) traverses the sheath, or alternatively, may be configured to puncture when the electrode tine(s) traverses the sheath to seal over the electrode tine(s).

[0018] The following described embodiments utilize tine valves that are used to prevent mechanical interferences that may interfere with the deployment or retraction of a tine array. Tine valves secure tine exits, acting as a barrier to prevent or otherwise minimize, filter, reduce, material from entering a cannula during deployment and retraction of a tine array. A covering material (i.e., sheath) may be used to cover the electrode tine exits, enabling the tine valves to open or close when a tine array is deployed or retracted. The tine valves may be preformed within the sheath or can be made when the tine array punctures the sheath. The sheath seals over the electrode tine exits as the electrode tine array is fully retracted into a cannula and opens fully when deploying the electrode tine array. During either retraction or deployment, the sheath also forms a seal and contact with the individual tines of the electrode tine array. The sheath may remove (or minimize, reduce) any material adhering to the electrode tines as the electrode tine array is retracted or prevent (or minimize, reduce) material from entering the cannula. The tine valves prevent (or minimize, reduce) any mechanical interference resulting from material (e.g., necrosed tissue or blood) adhering to individual tines when a tine array is retracted or deployed. Several examples are provided below, but are not limited to only the described implementations.

[0019] Referring to FIGS. 1-4, an exemplary ablation probe 100 constructed in accordance with one embodiment of the present inventions is described. The ablation probe 100 comprises an elongated cannula 102 and an array of electrode tines 104 (shown in FIGS. 2 and 4) configured to be selectively deployed out of, and retracted within, the cannula 102 via tine exits 106 formed in the side of the cannula 102. In the illustrated embodiment, the elongated cannula 102 is rigid, so that it can be percutaneously introduced through tissue. As shown in FIG. 2, the electrode tines 104, when in a retracted state, reside within an interior 108 of the cannula 102. In the example shown, there are four tines 104 lying within the interior 108 of the cannula 102 and positioned for deployment or retraction through four tine exits 106.

[0020] The ablation probe 100 further comprises a sheath 110 with tine valves 112 that provide for the deployment and retraction of the electrode tines 104. The sheath 110 may be a pliable, malleable covering (e.g., Fluorinated Ethylene Propylene (FEP), polyester, rubber, plastic, polyvinyl chloride (PVC), or other similar material) that forms an outer coat or layer over cannula 102. In other examples, sheath 110 may be implemented using a stiff or resistant material. The sheath 110 may be formed onto the surface of the cannula 102 using any suitable technique, such as coating, spraying, electrolysis, etc. In the illustrated embodiments, the tine valves 112 take the form of longitudinal cuts or “slits”, which can open, as illustrated in FIG. 3. Alternatively, the tine valves 112 can also be criss-cross shape, horizontal, or shaped to the electrode tine geometry and using the cross section of the electrode tine to act as a plug when retracted. In other examples, tine valves 112 may be implemented as transverse or angled slits in sheath 110. In the illustrated embodiment, the tine valves 112 are preformed within the sheath 110. That is to say, the tine valves 112 exist prior to the initial deployment of the electrode tines 104 from the cannula 102. Alternatively, the tine valves 112 may be created within the sheath 110 as the deployment of the electrode tines 104 punctures the sheath 110.

[0021] When force is applied, the individual tines 104 are pushed through tine valves 112, which open (or created if not preformed in the sheath 110) in response to the applied pressure of the electrode tines 104 exiting cannula 102, as illustrated in FIG. 4. As the electrode tines 104 are deployed, the pliable, malleable material used for sheath 110 provides a seal around individual tines 104, preventing, or otherwise minimizing or reducing, any biological material from entering cannula 102 through the covered tine exits 106 and into the inside of the cannula 102. As a tine array is retracted, the sides of tine valves 112 contact and provide a seal over tine exits 106. In some examples, sheath 110 may form a hermetic, airtight, non-airtight, full, or partial seal around the electrode tines 104 as they are deployed or retracted. Thus, it can be appreciated that the tine valves 112 prevent mechanical interference with the electrode tine array during either deployment or retraction and reduces the possibility that a tine array may require surgical removal if the electrode tine array is stuck in a deployed or “open” state.

[0022] In the embodiment illustrated in FIGS. 1-4, the sheath 110 externally covers the cannula 102 and tine exits 106. Alternatively, as illustrated in FIG. 5, the sheath 110 may be located inside of the cannula 102, e.g., as an inner coat or layer within the cannula 102. In this case, the tine valves 112 may, in some examples, protrude or extend through tine exits 106 and cannula 102 as the electrode tines 104 are deployed. Alternatively, a tine valve 112 may not extrude from cannula 116 and, instead, may be forced to one side of a tine exit 106.

[0023] In the embodiments illustrated in FIGS. 1-5, the sheath 110 extends the entire length of the cannula 102. Alternatively, as illustrated in FIG. 6, the sheath 110 may be configured to cover and overlap the electrode tine exits 106, but not the entire length of cannula 102. In the embodiments illustrated in FIGS. 1-6, the tine valves 112 are aligned around the longitudinal axis of the cannula 102. Alternatively, the tine valves 112 may be positioned at offset intervals relative to a transverse axis 114, as illustrated in FIG. 7. In this case, the electrode tines 104 may be deployed though tine valves 112 at varying intervals, accommodating tine arrays of varying sizes and positions lying within cannula 102. In other examples, several sets of tine valves 112 may be used to accommodate more than one tine array (e.g., a distal and proximal tine arrays).

[0024] Although particular embodiments of the present invention have been shown and described, it should be understood that the above discussion is not intended to limit the present invention to these embodiments. It will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. Thus, the present invention is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the present invention as defined by the claims.