The delivery of radio frequency (RF) energy to target regions within solid tissue is known for a variety of purposes of particular interest to the present invention. In one particular application, RF energy may be delivered to diseased tissue regions (e.g., tumors) for the purpose of ablating predictable volumes of tissue with minimal patient trauma. Of particular relevance to the invention, it may be necessary to treat, especially ablate, target tissue with RF energy in a particular region near or adjacent to an anatomical vessel, such as a blood vessel or bronchial tube.
As an example of a treatment process, RF energy may be delivered to a target tissue region via one or more electrodes coupled to an RF generator. The transmission of the RF energy results in ion agitation of the cells in the surrounding tissue, leading to the generation of frictional heat. This causes the temperature of the cells to increase, resulting in irreversible cell damage, referred to as coagulation necrosis. A lesion is then created in the target tissue region undergoing the ablation. This technique of applying RF energy to treat diseased tissue is most often performed percutaneously, although it may also be performed during open surgery.
To more effectively treat diseased tissue with RF energy, an electrically conductive fluid, such as a saline solution, may be delivered to the target tissue receiving the RF energy. Typically, the electrically conductive fluid is delivered to the diseased target tissue percutaneously via a syringe or other similar delivery device. The introduction of electrically conductive fluid to the target tissue has been shown to increase the tissue's conductivity, thereby creating a larger legion size when RF energy induces cell necrosis. In addition, the presence of electrically conductive fluid has also been shown to reduce the local temperature of the tissue region, thereby minimizing tissue vaporization and charring during the treatment procedure.
One issue that arises when RF energy is used to treat tissue in the region of or adjacent to a vessel is that heat generated by the RF energy may be conducted away from the target vessel region by mobile fluids in the vessel itself or in surrounding vessels, creating a heat-sink effect. Because of this heat loss, the tissue targeted for treatment in the vessel region may not reach the desired temperature for effective necrosis.
The heat-sink effect may be offset during an open surgical procedure by a clamping the respective vessel, for example, with fingers or forceps, to reduce or eliminate fluid flow, such as blood flow, adjacent to or through the treatment site. This technique is called a “Pringle maneuver.” However, a Pringle maneuver may not be possible during a percutaneous ablation procedure due to the difficulties of accessing the vessel.
Therefore, there is a need in the art for a treatment system that delivers electrically conductive fluid to a target vessel region while counteracting the heat sink effect by preventing, or at least minimizing, heat loss due to surrounding fluid movement when RF energy is delivered to the target vessel region.