Apparatus and Method for Ablating Tissue

Abstract

A control system alters one or more characteristics of an ablating element to ablate tissue. In one aspect, the control system delivers energy nearer to the surface of the tissue by changing the frequency or power. In another aspect, the ablating element delivers focused ultrasound which is focused in at least one dimension. The ablating device may also have a number of ablating elements with different characteristics such as focal length.

1 . A method of ablating body tissue, the method comprising:
 providing a tissue ablation device including a plurality of ablating elements and at least one adjustment structure coupled to at least one of the plurality of ablating elements;   placing the tissue ablation device in a first position on a tissue surface;   activating the at least one of the plurality of ablating elements to emit ultrasonic energy focused in at least one dimension towards tissue to be ablated; and   adjusting at least one adjustment structure to move a focus of the ultrasonic energy emitted by the at least one of the plurality of ablating elements relative to the tissue to be ablated without relocating the device from the first position on the tissue surface.   
     
     
         2 . The method according to  claim 1 , wherein the step of adjusting the at least one adjustment structure to move a focus of the ultrasonic energy is carried out while the at least one of the plurality of ablating elements is activated. 
     
     
         3 . The method according to  claim 1 , wherein the step of adjusting the at least one adjustment structure to move a focus of the ultrasonic energy comprises filling an inflatable member positioned between the at least one of the plurality of ablating elements and the tissue surface with an ultrasonic transmission medium, whereby the at least one of the plurality of ablating elements is displaced relative to the tissue surface independent of at least one other of the plurality of ablating elements. 
     
     
         4 . The method according to  claim 1 , wherein the step of adjusting the at least one adjustment structure to move a focus of the ultrasonic energy comprises adjusting a movable foot to displace the at least one of the plurality of ablating elements relative to the tissue surface independent of at least one other of the plurality of ablating elements. 
     
     
         5 . The method according to  claim 1 , wherein the step of adjusting the at least one adjustment structure to move a focus of the ultrasonic energy comprises adjusting a mechanical pivot to displace the at least one of the plurality of ablating elements relative to the tissue surface independent of at least one other of the plurality of ablating elements. 
     
     
         6 . The method according to  claim 1 , wherein the step of adjusting the at least one adjustment structure to move a focus of the ultrasonic energy comprises adjusting variable acoustic lensing to move the focus of the ultrasonic energy. 
     
     
         7 . The method according to  claim 1 , wherein the step of adjusting the at least one adjustment structure to move a focus of the ultrasonic energy comprises adjusting the at least one adjustment structure such that the focus of the ultrasonic energy is located adjacent an endocardial surface. 
     
     
         8 . The method according to  claim 1 , wherein the step of adjusting the at least one adjustment structure to move a focus of the ultrasonic energy comprises adjusting the at least one adjustment structure such that the focus of the ultrasonic energy is proximate an endocardial surface. 
     
     
         9 . The method according to  claim 1 , wherein the step of activating the at least one of the plurality of ablating elements to emit ultrasonic energy focused in at least one dimension comprises pulse-activating the at least one of the plurality of ablating elements to emit ultrasonic energy. 
     
     
         10 . The method according to  claim 1 , further comprising:
 monitoring a temperature of the body tissue; and   adjusting one or more properties of the at least one of the plurality of ablating elements in response to the monitored temperature of the body tissue.   
     
     
         11 . The method according to  claim 10 , wherein the step of adjusting one or more properties of the at least one of the plurality of ablating elements in response to the monitored temperature of the body tissue comprises adjusting power delivered to the at least one of the plurality of ablating elements to maintain a preset temperature of the body tissue. 
     
     
         12 . The method according to  claim 1 , further comprising:
 monitoring an amount of blood cooling at an endocardial surface; and   adjusting one or more properties of the at least one of the plurality of ablating elements in response to the monitored amount of blood cooling at the endocardial surface.   
     
     
         13 . The method according to  claim 1 , wherein the tissue surface comprises an epicardial surface. 
     
     
         14 . An apparatus for applying ultrasound energy to body tissue, the apparatus comprising:
 a catheter;   an ultrasound transducer disposed on the catheter, the ultrasound transducer configured to emit ultrasonic energy; and   at least one expandable structure disposed around a circumference of the catheter, the expandable structure configured to contact an anatomical structure when expanded to position the ultrasound transducer relative to the body tissue.   
     
     
         15 . The apparatus of  claim 14 , wherein the catheter further comprises at least one lumen extending from a proximal end of the catheter to the at least one expandable structure, and wherein the at least one expandable structure is configured to be expanded by introducing a fluid through the at least one lumen. 
     
     
         16 . The apparatus of  claim 14 , wherein the transducer is mounted on a stylet. 
     
     
         17 . The apparatus of  claim 14 , wherein the at least one expandable structure is a balloon. 
     
     
         18 . The apparatus of  claim 14 , wherein the at least one expandable structure is positioned circumferentially opposite the ultrasound transducer. 
     
     
         19 . The apparatus of  claim 18 , wherein inflation of the at least one expandable structure decreases the distance between the ultrasound transducer and the tissue. 
     
     
         20 . An apparatus for applying ultrasound energy to body tissue, the apparatus comprising:
 a catheter;   an ultrasound transducer disposed on the catheter, the ultrasound transducer configured to emit ultrasonic energy;   an expandable balloon disposed around a circumference of the catheter, the expandable balloon configured to contact a tissue surface when expanded to position the ultrasound transducer relative to the body tissue;   a temperature sensor configured to measure a temperature of the body tissue; and   a means for adjusting one or more properties of the ultrasonic energy in response to the temperature.