Method and Apparatus for Tissue Ablation

Abstract

Ablation catheters and systems include multiple inline chambers for containing and heating an ablative agent. The heating chamber includes one or more channels to increase the contact surface area of the ablative agent with the walls of the heating chamber to provide more efficient heating. Induction heating is used to heat a chamber and vaporize a fluid within by wrapping a coil about a ferromagnetic chamber and providing an alternating current to the coil. A magnetic field is created in the area surrounding the chamber which induces electric current flow in the chamber, heating the chamber and vaporizing the fluid inside. Positioning elements help maintain the device in the proper position with respect to the target tissue and also prevent the passage of ablative agent to normal tissues.

We claim: 
     
         1 . A steam-based ablation system comprising:
 a disposable fluid circuit comprising:
 a water reservoir containing water; 
 a water heating chamber having a length, wherein the water heating chamber comprises a non-ferromagnetic material having a lumen extending therethrough and a ferromagnetic material positioned within said lumen and wherein the ferromagnetic material is separated from the non-ferromagnetic material, across the length of the water heating chamber, by a space; 
 a catheter comprising a proximal end and a distal end, wherein the distal end comprises one or more ports; and 
 a contiguous fluid channel connecting said water reservoir, said water heating chamber, and the proximal end of said catheter; 
   an induction chamber adapted to receive said water heating chamber, wherein said induction chamber comprises a plurality of coils for receiving an electrical current and for generating a magnetic field;   an induction circuit for delivering said electrical current to said induction chamber; and   a pump or motor for applying a force to said water in the water reservoir in order to move the water from the water reservoir and into the water heating chamber.   
     
     
         2 . The steam-based ablation system of  claim 1 , wherein the induction circuit generates a sinusoidal wave form and comprises a switching circuit having a resonant tank circuit. 
     
     
         3 . The steam-based ablation system of  claim 1 , wherein the non-ferromagnetic material is electrically insulating. 
     
     
         4 . The steam-based ablation system of  claim 3 , wherein, during operation, a lumen surface of the non-ferromagnetic material is configured to be heated to a temperature greater than 100 degrees Celsius. 
     
     
         5 . The steam-based ablation system of  claim 4 , wherein, during operation, an external surface of the non-ferromagnetic material is configured to be heated to a temperature no greater than 100 degrees Celsius. 
     
     
         6 . The steam-based ablation system of  claim 1 , wherein the induction chamber comprises a substantially cylindrical volume around which said plurality of coils are positioned and a lumen positioned within said cylindrical volume adapted to receive said water heating chamber. 
     
     
         7 . The steam-based ablation system of  claim 1 , wherein said water is at least one of ionized water, non-ionized water, sterile water, or a solution of metal salt and water. 
     
     
         8 . The steam-based ablation system of  claim 1 , wherein the electrical current has a frequency of between 100 Hz and 100 kHz. 
     
     
         9 . The steam-based ablation system of  claim 1 , wherein, during operation, the water heating chamber and induction chamber are magnetically coupled and wherein a conversion of magnetic energy into heat within the water heating chamber has an efficiency of greater than 60%. 
     
     
         10 . The steam-based ablation system of  claim 1 , wherein the non-ferromagnetic material is a cylinder and the ferromagnetic material is a metal rod. 
     
     
         11 . The steam-based ablation system of  claim 1 , wherein the ferromagnetic material comprises any one of, or alloys of, iron, nickel, stainless steel, manganese, silicon, carbon, copper, electrically conducting material, electrically insulating material or a Curie material having a Curie temperature between 60° C. and 500° C. 
     
     
         12 . The steam-based ablation system of  claim 1 , wherein the disposable fluid circuit does not comprise any input ports or openings for receiving fluid from an external source into said disposable fluid circuit. 
     
     
         13 . The steam-based ablation system of  claim 1 , wherein the disposable fluid circuit does not comprise any other ports or openings, other than the one or more ports in the catheter, for receiving or expelling fluid external to said disposable fluid circuit. 
     
     
         14 . The steam-based ablation system of  claim 1 , wherein the fluid channel comprises flexible tubing and wherein the water reservoir is a pliable plastic bag or a syringe. 
     
     
         15 . The steam-based ablation system of  claim 1 , wherein, prior to use, a portion of the fluid channel positioned between the water reservoir and the water heating chamber is blocked by a barrier, thereby blocking water from passively flowing from the water reservoir to the water heating chamber. 
     
     
         16 . The steam-based ablation system of  claim 15 , wherein, during use, said barrier is adapted to be breached by an increase in water pressure to permit water to flow from the water reservoir to the water heating chamber. 
     
     
         17 . The steam-based ablation system of  claim 1 , further comprising a check valve or a fracture diaphragm positioned in the contiguous fluid channel between the water reservoir and the water heating chamber to prevent water from entering said water heating chamber until force is applied to said water. 
     
     
         18 . The steam-based ablation system of  claim 1 , wherein a temperature of an external surface of said water heating chamber does not increase by more than 500 percent of its pre-operation external surface temperature during five minutes or less of continuous operation. 
     
     
         19 . The steam-based ablation system of  claim 1 , wherein, during operation, a temperature of an external surface of said water heating chamber does not exceed 120 degrees Celsius. 
     
     
         20 . The steam-based ablation system of  claim 1 , wherein, during operation, a temperature profile of the water heating chamber is measured to identify a maximum temperature and a location of said maximum temperature in said heating chamber.