Apparatus and method for ablating tissue
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 cardiac tissue, comprising the steps of:
providing an ablating device having an ultrasonic transducer, the device emitting focused ultrasound which is focused in at least one dimension;
positioning the ablating device in contact with cardiac tissue; and
activating the ultrasonic transducer to direct the focused ultrasound into the cardiac tissue.
2 . The method of claim 1 , wherein:
the activating step is carried out to electrically isolate one part of the heart from another part of the heart.
3 . The method of claim 1 , wherein:
the providing and activating steps are carried out with the focused ultrasound being focused along a focal axis and diverging when viewed perpendicular to the focal axis.
4 . The method of claim 1 , further comprising the step of:
moving a focus of the focused ultrasound relative to the cardiac tissue.
5 . The method of claim 4 , wherein:
the moving step is carried out to move the focus closer to a near surface of the cardiac tissue.
6 . The method of claim 1 , wherein:
the providing step is carried out so that at least 90% of the focused ultrasound passes within a focus area defined by a focal length of about 2 to 20 mm and an angle of about 10 to 170 degrees when viewed along a focal axis.
7 . The method of claim 1 , wherein:
the providing step is carried out with the focused energy being emitted by a concave surface.
8 . The method of claim 1 , wherein:
the providing step is carried out with the concave surface being attached to a piezoelectric transducer.
9 . The method of claim 7 , wherein:
the providing step is carried out with the concave surface having a focal length of 2-20 mm.
10 . The method of claim 9 , wherein:
the providing step is carried out with the focused energy having a focal length of 2 to 12 mm.
11 . The method of claim 1 , wherein:
the activating step is carried out by activating the ultrasonic transducer for a first period of time at a first frequency and a second period of time at a second frequency which is different than the first frequency and occurs after the first period of time.
12 . The method of claim 11 , wherein:
the activating step is carried out with the first frequency being lower than the second frequency.
13 . The method of claim 12 , wherein:
the activating step is carried out with the first period of time being shorter than the second period of time.
14 . The method of claim 13 , wherein:
the activating step is carried out with the first period of time being less than 1 second.
15 . The method of claim 11 , wherein:
the activating step is carried out with the ultrasonic transducer being activated at the first frequency for a number of discrete time periods.
16 . The method of claim 15 , wherein:
the activating step is carried out with the ultrasonic transducer being inactive for 3-8 seconds between each of the number of discrete time periods.
17 . The method of claim 1 , further comprising the step of:
approximating a temperature of the tissue.
18 . The method of claim 1 , further comprising the step of:
assessing the adequacy of contact between the device and the tissue.
19 . The method of claim 1 , further comprising the step of:
determining a tissue layer thickness using the ultrasound transducer.
20 . The method of claim 19 , wherein:
the determining step is carried out with the tissue layer being a tissue layer between a near surface and a far surface.
21 . The method of claim 19 , wherein:
the determining step is carried out with the tissue layer being a fat layer which lies over a muscle layer.
22 . The method of claim 1 , further comprising the step of:
measuring a blood flow velocity with the ultrasonic transducer.
23 . The method of claim 1 , further comprising the step of:
moving the a focus of the focused ultrasound relative to the tissue.
24 . The method of claim 23 , wherein:
the moving step is carried out with the ultrasonic transducer being tilted.
25 . The method of claim 1 , wherein:
the providing step is carried out with the ablating device having a number of ultrasonic transducers.
26 - 62 . (canceled)
63 . A method of ablating cardiac tissue, comprising the steps of:
providing an ablating device having an ultrasonic transducer;
positioning the ablating device in contact with a tissue structure to be ablated; and
activating the ultrasonic transducer for a first period of time at a first power to produce ultrasonic energy which is directed at the tissue structure, the activating step also being carried out with the ultrasonic transducer being activated for a second period of time at a second power which is different than the first power.
64 . The method of claim 63 , wherein:
the activating step is carried out with the ultrasonic transducer being activated at different frequencies during the first and second periods of time.
65 . The method of claim 63 , wherein:
the activating step is carried out with the first period of time being smaller than the second period of time.
66 . The method of claim 65 , wherein:
the activating step is carried out with the first power being higher than the second power.
67 . A device for ablating tissue, comprising:
a body having a longitudinal axis and a contact surface configured to be positioned adjacent tissue to be ablated;
a first transducer coupled to the body;
a second transducer coupled to the body and spaced apart from the first transducer by a space; and
wherein at least one of the first and second transducers directs ultrasound energy to tissue lying beneath the space between the first and second transducers.
68 . The device of claim 67 , wherein:
both the first and second transducers direct ultrasound energy to tissue lying beneath the space between the first and second transducers.
69 . The device of claim 67 , wherein:
a flexible membrane extends over the at least one of the first and second transducers, the flexible membrane conforming to the surface of the tissue and being filled with a substance which transmits the ultrasound energy from the transducer to the tissue.
70 . The device of claim 67 , wherein:
the first and second transducers have the same shape, the first and second transducers each directing ultrasound energy to tissue beneath the first and second transducers, respectively, and the first and second transducers also directing ultrasound energy to tissue lying beneath the space between the first and second transducers.
71 . A device for ablating cardiac tissue, comprising:
a body having a longitudinal axis and a contact surface configured to be positioned adjacent tissue to be ablated;
a first transducer coupled to the body;
a second transducer coupled to the body and spaced apart from the first transducer by a space, wherein the first and second transducers each emit ultrasound energy to the tissue to be ablated; and
means for changing the direction of the ultrasound energy from the first transducer toward tissue beneath the gap between the first and second transducers.
72 . The device of claim 71 , further comprising;
an inflatable membrane positioned beneath the first transducer to form the contact surface below the first transducer, the transducer moving upon inflation of the balloon.
73 - 114 . (canceled)