Ultrasonic tissue therapy device

Abstract

To provide devices and methods for the treatment of tissue through the application of energy. SOLUTION: Apparatus (220 / 20) and methods are described that include a transluminal ablation catheter (40) that includes at least one ultrasound transducer (50 / 52 / 150). The at least one ultrasound transducer is configured for insertion into a cardiac chamber (190) of a subject and configured to (a) ablate tissue by applying ultrasound energy to the tissue of the subject, and (b) image tissue by applying non-ablative ultrasound energy to the tissue of the subject. An expandable cage (30 / 301) is disposed about the at least one ultrasound transducer. The at least one ultrasound transducer is configured to rotate and translate axially back and forth within the expandable cage to generate a three-dimensional image of the tissue. Other applications are also described.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 63 / 153,477, entitled "ULTRASOUND TISSUE TREATMENT APPARATUS AND METHOD," filed February 25, 2021, to Megel, which is incorporated herein by reference.

[0002] Some applications of the present invention relate generally to devices and methods for the treatment of tissue through the application of energy, and more particularly to the ablation of cardiac tissue through the application of ultrasound energy to treat cardiac arrhythmias such as atrial fibrillation. [Background technology]

[0003] Atrial fibrillation is a common cardiac arrhythmia associated with the atria. During atrial fibrillation, the atria beat irregularly and lose coordination with the ventricles, which disrupts efficient heartbeats. Symptoms of atrial fibrillation often include palpitations, shortness of breath, and weakness. A major concern with atrial fibrillation is the potential for blood clots to form within the atria. These blood clots formed in the heart can circulate to other organs and cause serious medical conditions, such as stroke.

[0004] Atrial fibrillation is generally caused by abnormal electrical activity in the heart. During atrial fibrillation, electrical discharges can occur in parts of the atrium that normally do not, such as the ostia of the pulmonary veins.

[0005] Ablation procedures are commonly used to terminate faulty electrical pathways from multiple parts of the heart and restore the heart to a normal rhythm, especially in people who are prone to cardiac arrhythmias. For example, pulmonary vein isolation by ablation is a common medical procedure for treating atrial fibrillation. Summary of the Invention

[0006] According to some applications of the present invention, a device is provided for use with a lumen, such as a pulmonary vein, extending from a cardiac chamber, such as the left atrium of the heart. Typically, the device electrically isolates a pulmonary vein by applying ultrasonic energy to ablate tissue at the ostium of the pulmonary vein to treat cardiac arrhythmia. In some applications, the device includes a transluminal ablation catheter including at least one ultrasound transducer. The at least one ultrasound transducer is coupled to a distal portion of the catheter and configured for insertion into a subject's cardiac chamber and for applying ultrasonic energy to ablate tissue at the ostium of the pulmonary vein. The transluminal ablation catheter further includes a papillary-shaped expandable cage disposed around the ultrasound transducer. The papillary shape is typically formed by a central portion of the expandable cage having a diameter larger than a distal portion of the expandable cage, and the distal portion of the expandable cage has a shape and size for insertion into the ostium of the pulmonary vein and contacting the vein wall to temporarily secure the distal portion of the catheter within the pulmonary vein.

[0007] For some applications, the expandable cage includes a plurality of struts (e.g., flexible struts) that contact the pulmonary vein walls to anchor the distal portion of the transluminal ablation catheter within the pulmonary vein. In some cases, the struts are referred to herein as "flexible wires." These two terms are used interchangeably throughout this specification and claims. Typically, the struts are constructed to form an expandable cage with a plurality of relatively large gaps between them to allow blood flow and transmission of ultrasonic energy through the expandable cage. Furthermore, for some applications, at least some of the struts of the expandable cage are shaped to define one or more openings formed therein, further facilitating transmission of ultrasonic energy to tissue. For some applications, the openings are formed along the length of the struts. The openings formed in the struts typically increase the area over which ultrasonic energy is transmitted through the expandable cage, allowing more ultrasonic energy to reach the target tissue, resulting in increased tissue heating and more effective tissue ablation.

[0008] For some applications, in addition to the expandable cage, the device includes a fluid-filled expandable element, such as a balloon, disposed around the ultrasound transducer. Typically, the expandable element is inflated with a fluid, such as water and / or saline, through which ultrasonic energy is transmitted with negligible absorption. In such applications, the expandable cage is disposed around the expandable element to position the distal portion of a transluminal ablation catheter within the lumen, as described above.

[0009] Typically, a fluid-filled (e.g., water-filled) expandable element is placed around the ultrasonic transducer to partially replace the blood medium between the ultrasonic transducer and the tissue designated for ablation. Because ultrasonic energy is transmitted through water and is not generally absorbed by water, a greater amount of the transmitted ultrasonic energy reaches the tissue than would be the case if the energy were transmitted solely through blood.

[0010] In addition to or instead of applying ablative ultrasound energy, the ultrasound transducer is configured to image target tissue by applying non-ablative ultrasound energy. Typically, the expandable cage has a shape and size that allows the ultrasound transducer to rotate and translate axially back and forth within the expandable cage to generate a three-dimensional image of the tissue. Typically, the expandable cage is held stationary during rotation of the transluminal ablation catheter, which causes rotation of the ultrasound transducer. In some applications, the device includes a rotational force reduction mechanism for reducing rotational forces applied to the expandable cage during rotation of the transluminal ablation catheter.

[0011] Additionally or alternatively, according to some applications of the present invention, the ultrasound transducer comprises a curved piezoelectric ultrasound transducer shaped to define a convex surface extending outward from the longitudinal axis of the transducer. Typically, providing a curved piezoelectric ultrasound transducer enhances the thermal profile of the tissue (all other things being equal, compared to a non-curved piezoelectric ultrasound transducer), thereby heating a larger portion of the tissue more effectively and facilitating effective and rapid ablation of the tissue.

[0012] Thus, in accordance with some applications of the present invention, there is provided a device for use with tissue of a subject, the device comprising: 1. A transluminal ablation catheter, comprising: at least one ultrasound transducer configured for insertion into a cardiac chamber of the subject and configured to (a) ablate tissue by applying ultrasound energy to the tissue of the subject, and (b) image the tissue by applying non-ablative ultrasound energy to the tissue of the subject; an expandable cage configured to be disposed around at least one ultrasound transducer; and a transluminal ablation catheter including at least one ultrasound transducer configured to rotate and translate axially back and forth within the expandable cage to generate a three-dimensional image of the tissue.

[0013] In some applications, the at least one ultrasound transducer is configured to be inserted into the left atrium near the ostium of a pulmonary vein and configured to electrically isolate the pulmonary vein by ablating tissue at the ostium of the pulmonary vein.

[0014] In some applications, the tissue includes tissue at the mouth of a lumen extending from a cardiac chamber of the subject, and the ultrasound transducer is configured to generate a three-dimensional image of the tissue at the mouth of the lumen by applying non-ablative ultrasound energy to the tissue at the mouth of the lumen.

[0015] In some applications, the tissue includes tissue at the ostium of a lumen extending from a cardiac chamber of the subject, and the expandable cage includes a plurality of struts, at least a portion of which are configured to bend outward at at least two locations along the struts so that a portion of the struts contacts a wall of the lumen, thereby causing the cage to temporarily secure a distal portion of the transluminal ablation catheter within the lumen.

[0016] In some applications, the tissue includes tissue at the ostium of a lumen extending from a cardiac chamber of the subject, the expandable cage having a central portion and a distal portion, the expandable cage shaped such that the diameter of the central portion is larger than the diameter of the distal portion thereby defining a papillary structure, and the distal portion shaped and sized to be inserted into the ostium and contact the wall of the lumen to temporarily secure the distal portion within the lumen.

[0017] For some applications, the at least one ultrasonic transducer is configured to generate ultrasonic energy at a frequency between 8 and 20 MHz.

[0018] For some applications, the at least one ultrasonic transducer is shaped to define a convex surface facing outward from the longitudinal axis of the transducer, with a width between 0.5 and 3 mm and a radius of curvature between 0.75 and 5 mm.

[0019] In some applications, the tissue includes tissue at the mouth of a lumen extending from a heart chamber of the subject, and at least some of the plurality of struts include conductive struts configured to contact the lumen mouth tissue and drive a current into the lumen mouth tissue to ablate the lumen mouth tissue contacting the conductive struts.

[0020] For some applications, at least some of the conductive struts include an insulating portion and a conductive portion, the conductive portion configured to contact tissue at the ostium and ablate the tissue at the ostium.

[0021] For some applications, at least some of the plurality of struts are shaped to define apertures formed therein through which ultrasonic energy is transmitted from the ultrasonic transducer to the tissue.

[0022] In some applications, each of the struts in the plurality of struts has a width of 0.5 to 1 mm, and the strut opening has a width of 0.25 to 0.5 mm. In some applications, the strut thickness is 0.1 to 0.25 mm.

[0023] For some applications, the transluminal ablation catheter includes an elongate shaft including a proximal portion including a handle and a distal portion having at least one ultrasound transducer coupled thereto. For some applications, the elongate shaft is rotatably configured to rotate the ultrasound transducer, and the transluminal ablation catheter includes one or more sensors coupled to the distal portion of the elongate shaft and configured to detect a rotational position of the distal portion of the elongate shaft.

[0024] In some applications, the elongate shaft is rotatably configured to rotate the ultrasound transducer; The transluminal ablation catheter further includes a rotational force reduction mechanism configured to reduce the rotational force applied to the expandable cage by the elongate shaft upon rotation of the elongate shaft so as to keep the expandable cage stationary during rotation of the ultrasonic transducer.

[0025] In some applications, at least one ultrasound transducer configured to apply non-ablative ultrasound energy to tissue, such that at least a portion of the non-ablative ultrasound energy is reflected and received by the ultrasound transducer; The apparatus further includes a computer processor configured to assess parameters of the reflected energy to determine parameters of ultrasonic energy to be applied by the ultrasonic transducer to ablate tissue; The at least one ultrasound transducer is configured to apply ultrasound energy to tissue based on the determined parameters.

[0026] For some applications, the device further includes an expandable element configured to be disposed about the ultrasound transducer, hi some applications, the expandable element is configured to be expanded with at least one of water and saline.

[0027] For some applications, the at least one ultrasonic transducer comprises: a first ultrasound transducer configured to transmit ablative ultrasound energy toward the target tissue to thereby ablate the tissue; a second ultrasound transducer configured to image the tissue by transmitting one or more pulses of pulse-echo ultrasound energy toward the tissue of interest and receiving reflections of the transmitted pulse-echo ultrasound energy, the second ultrasound transducer configured to rotate and translate axially back and forth within the expandable cage to generate a three-dimensional image of the tissue.

[0028] For some applications, the transluminal ablation catheter comprises: a first support configured to support a first ultrasonic transducer and enable transmission of ablative ultrasonic energy toward tissue; a second attenuation support configured to support the second ultrasonic transducer and provide a higher level of attenuation than that provided by the first support, such that the second ultrasonic transducer can receive reflections of the transmitted pulse-echo ultrasonic energy while the first ultrasonic transducer transmits ablative ultrasonic energy toward the tissue; Includes.

[0029] In some applications, the first support includes an air barrier configured to permit vibration of the first ultrasonic transducer during transmission of ablative ultrasonic energy toward the tissue; The second damping support includes a mechanical support that includes at least one of a backing layer and a damping element.

[0030] Further, in accordance with some applications of the present invention, there is provided a device for use with a lumen of a subject extending from a chamber of the subject's heart, the device comprising: 1. A transluminal ablation catheter having a distal portion configured to be positioned within a lumen of a subject, comprising: at least one ultrasound transducer configured for insertion into a cardiac chamber of a subject and for ablating tissue at the ostium by applying ultrasound energy to the tissue at the ostium; an expandable cage including struts and configured to be disposed around an ultrasound transducer, the expandable cage having a central portion and a distal portion, the expandable cage being shaped to define a papillary structure when disposed in a radially unconstrained configuration, the central portion having a diameter greater than a diameter of the distal portion, the distal portion being shaped and sized to be inserted into the lumen orifice and contact the wall of the lumen to temporarily anchor the distal portion within the lumen; The present invention relates to a transluminal ablation catheter comprising:

[0031] In some applications, the expandable cage has a shape such that the struts define a convex curvature at the distal portion of the expandable cage, then pass through an inflection point and have a concave curvature in the central portion, thereby defining a papillary structure.

[0032] For some applications, the central portion of the expandable cage has a maximum diameter that is up to 5 times greater than the maximum diameter of the distal portion of the expandable cage.

[0033] For some applications, the central portion is configured to remain within the heart chamber when the distal portion is inserted into the ostium.

[0034] In some applications, the at least one ultrasound transducer is configured to be positioned in the left atrium near a pulmonary vein ostium and configured to electrically isolate the pulmonary vein by ablating tissue at the pulmonary vein ostium.

[0035] For some applications, the expandable cage is rotationally asymmetric.For some applications, the expandable cage is rotationally symmetric.

[0036] For some applications, the ultrasound transducer includes a side-pointing ultrasound transducer. For some applications, the ultrasound transducer includes a distal-pointing ultrasound transducer.

[0037] For some applications, the ultrasound transducer is further configured to image tissue of interest by applying non-ablative ultrasound energy to the tissue, and the ultrasound transducer is configured to rotate and translate axially back and forth within the expandable cage to generate a three-dimensional image of the tissue.

[0038] For some applications, at least some of the struts of the expandable cage are shaped to define openings formed therein through which ultrasonic energy is transmitted from the ultrasonic transducer to the tissue.

[0039] In some applications, each of the struts in the plurality of struts has a width of 0.5 to 1 mm, and the strut opening has a width of 0.25 to 0.5 mm. In some applications, the strut thickness is 0.1 to 0.25 mm.

[0040] Further, in accordance with some applications of the present invention, there is provided a device for use with a lumen of a subject extending from a chamber of the subject's heart, the device comprising: 1. A transluminal ablation catheter, comprising: at least one ultrasound transducer configured for insertion into a cardiac chamber of a subject and for ablating tissue at the ostium by applying ultrasound energy to the tissue at the ostium; an expandable cage configured to be disposed around an ultrasound transducer, the expandable cage including a plurality of struts, at least some of the struts shaped to define openings formed therein through which ultrasound energy is transmitted from the ultrasound transducer to tissue; The present invention relates to a transluminal ablation catheter comprising:

[0041] For some applications, each of the struts in the portion of the struts has a width of 0.5 to 1 mm, and the opening in each of the struts in the portion of the struts has a width of 0.25 to 0.5 mm. For some applications, at least some of the plurality of struts have a thickness of 0.1 to 0.25 mm.

[0042] Further, in accordance with some applications of the present invention, there is provided a device for use with a lumen of a subject extending from a chamber of the subject's heart, the device comprising: 1. A transluminal ablation catheter, comprising: at least one ultrasound transducer configured for insertion into a cardiac chamber of the subject and for imaging tissue of the subject; an expandable cage configured to be disposed around an ultrasound transducer and including a plurality of struts, at least some of the struts including conductive struts configured to contact tissue at the lumen ostium and to drive an electrical current into the tissue to ablate the tissue in contact with the conductive struts; The present invention relates to a transluminal ablation catheter comprising:

[0043] For some applications, at least some of the conductive struts include an insulating portion and a conductive portion, the conductive portion configured to contact tissue at the ostium and ablate the tissue at the ostium.

[0044] For some applications, the expandable cage is configured to drive radio frequency (RF) current into tissue. For some applications, the expandable cage is configured to drive alternating current (AC) into tissue. For some applications, the expandable cage is configured to drive direct current (DC) into tissue.

[0045] For some applications, the at least one ultrasound transducer is configured to rotate and translate axially back and forth within the expandable cage to generate a three-dimensional image of the tissue at the ostium of the lumen.

[0046] For some applications, the at least one ultrasonic transducer is configured to ablate tissue at the ostium by applying ultrasonic energy to the tissue at the ostium.

[0047] In some applications, the at least one ultrasound transducer is configured to be inserted into the left atrium near the ostium of a pulmonary vein and configured to electrically isolate the pulmonary vein by ablating tissue at the ostium of the pulmonary vein.

[0048] Further, in accordance with some applications of the present invention, there is provided a device for use with a heart chamber of a subject, the device comprising: 1. A transluminal ablation catheter, comprising: at least one ultrasound transducer configured for insertion into a cardiac chamber of the subject and for applying ultrasound energy to the tissue of the subject to thereby ablate the tissue; an expandable element configured to be disposed around the ultrasound transducer; an expandable cage disposed around the expandable element and configured to contact tissue of the subject to temporarily secure the transluminal ablation catheter within the cardiac chamber of the subject; The present invention relates to a transluminal ablation catheter comprising:

[0049] For some applications, the expandable element is configured to expand with water. hi some applications, the expandable element is configured to expand with saline.

[0050] For some applications, the at least one ultrasonic transducer is configured to generate ultrasonic energy at a frequency of 8-20 MHz, hi some applications, the at least one ultrasonic transducer is configured to generate ultrasonic energy at a frequency of 10-12 MHz, or hi some applications, the at least one ultrasonic transducer is configured to generate ultrasonic energy at a frequency of 11 MHz.

[0051] Furthermore, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A transluminal ablation catheter, comprising: an ultrasound transducer configured to transmit ultrasound energy toward the target tissue to thereby ablate the tissue; 1. A computer processor comprising: detecting an indication of blood carbonization in the vicinity of the ultrasound transducer; a computer processor configured to inhibit application of ultrasonic energy from the ultrasonic transducer in response to the detected indication of blood carbonization; The present invention relates to a transluminal ablation catheter comprising:

[0052] In some applications, the ultrasonic transducer is further configured to transmit one or more pulses of pulse-echo ultrasonic energy toward the tissue and receive reflections of the transmitted pulse-echo ultrasonic energy; The computer processor is configured to detect indications of blood carbonization in the vicinity of the ultrasound transducer by determining parameters of the reflected pulse-echo ultrasound energy.

[0053] For some applications, the ultrasound transducer is configured to transmit ultrasound energy at a power level of 3 to 50 W to ablate tissue, and the ultrasound transducer is configured to transmit pulse-echo ultrasound energy at a power level of less than 2 W.

[0054] In some applications, the ultrasonic transducer is a first ultrasonic transducer; The transluminal ablation catheter includes a second ultrasound transducer configured to transmit pulse-echo ultrasound energy into tissue and receive reflections of the transmitted pulse-echo ultrasound energy; The computer processor is configured to detect indications of blood carbonization in the vicinity of the ultrasound transducer by determining parameters of the reflected pulse-echo ultrasound energy.

[0055] For some applications, the first ultrasonic transducer is configured to transmit ultrasonic energy at a power level of 3 to 50 W to ablate tissue, and the second ultrasonic transducer is configured to transmit pulse-echo ultrasonic energy at a power level of less than 2 W.

[0056] Further, in accordance with some applications of the present invention, there is provided a device for use with a lumen of a subject extending from a chamber of the subject's heart, the device comprising: 1. A transluminal ablation catheter having a distal portion configured to be positioned within a lumen of a subject, comprising: at least one ultrasound transducer configured for insertion into a cardiac chamber of a subject and for ablating tissue at the ostium by applying ultrasound energy to the tissue at the ostium; an expandable cage configured to be disposed around an ultrasound transducer, the expandable cage including a plurality of struts, at least some of the struts configured to bend outward at at least two locations along the struts so that the portions of the struts contact a wall of the lumen, thereby temporarily securing the cage to a distal portion of the transluminal ablation catheter within the lumen; The present invention relates to a transluminal ablation catheter comprising:

[0057] In some applications, the at least one ultrasound transducer is configured to be inserted into the left atrium near the ostium of a pulmonary vein and configured to electrically isolate the pulmonary vein by ablating tissue at the ostium of the pulmonary vein.

[0058] For some applications, the expandable cage is rotationally asymmetric.For some applications, the expandable cage is rotationally symmetric.

[0059] In some applications, the expandable cage is configured to adjust the distance between the transducer and the tissue by applying pressure to push against the tissue when in a curved position and contacting the wall of the lumen.

[0060] In some applications, each strut that is curved outward in at least two locations has a shape such that the radius of curvature of the first curve is 10 to 20 mm and the radius of curvature of the second curve is 5 to 10 mm.

[0061] For some applications, at least some of the plurality of struts include conductive struts configured to contact tissue at the ostium of the lumen and to drive an electric current into the tissue at the ostium, thereby ablating the tissue at the ostium that is in contact with the conductive struts.

[0062] For some applications, at least some of the conductive struts include an insulating portion and a conductive portion, the conductive portion configured to contact tissue at the ostium and ablate the tissue at the ostium.

[0063] For some applications, the expandable cage is configured to drive radio frequency (RF) current into tissue. For some applications, the expandable cage is configured to drive alternating current (AC) into tissue. For some applications, the expandable cage is configured to drive direct current (DC) into tissue.

[0064] For some applications, at least some of the plurality of struts are shaped to define apertures formed therein through which ultrasonic energy is transmitted from the ultrasonic transducer to the tissue.

[0065] In some applications, each of the struts in the plurality of struts has a width of 0.5 to 1 mm, and the strut opening has a width of 0.25 to 0.5 mm. In some applications, the strut thickness is 0.1 to 0.25 mm.

[0066] For some applications, the transluminal ablation catheter includes an elongate shaft including a proximal portion including a handle and a distal portion having at least one ultrasound transducer coupled thereto, and for some applications, the device further includes one or more sensors coupled to the distal portion of the elongate shaft and configured to detect a rotational position of the distal portion of the elongate shaft.

[0067] For some applications, the ultrasound transducer includes a side-pointing ultrasound transducer. For some applications, the ultrasound transducer includes a distal-pointing ultrasound transducer.

[0068] For some applications, the distal tip of the transluminal ablation catheter includes an electrode configured to ablate tissue in the wall of the lumen.

[0069] For some applications, the ultrasound transducer is further configured to image tissue by applying non-ablative ultrasound energy to the target tissue, and the ultrasound transducer is configured to rotate and translate axially back and forth within the expandable cage to generate a three-dimensional image of the tissue.

[0070] For some applications, the tissue includes tissue at the ostium, and the ultrasound transducer is configured to image the tissue at the ostium by applying non-ablative ultrasound energy to the tissue at the ostium.

[0071] For some applications, the device further includes one or more acoustic reference markers disposed on the expandable cage.

[0072] Furthermore, in accordance with some applications of the present invention, there is provided an apparatus comprising: a transluminal ablation catheter, the transluminal ablation catheter comprising: The device includes a piezoelectric ultrasound transducer configured to be inserted into a cardiac chamber of a subject, the piezoelectric ultrasound transducer having a shape that defines a convex surface extending outward from a longitudinal axis of the transducer, the width being between 0.5 and 3 mm, and a radius of curvature being between 0.75 and 5 mm.

[0073] In some applications, the at least one ultrasound transducer is configured to be positioned in the left atrium near a pulmonary vein ostium and configured to electrically isolate the pulmonary vein by ablating tissue at the pulmonary vein ostium.

[0074] In some applications, the ultrasonic transducer has a width of 1 to 2 mm, a thickness of 0.1 to 0.3 mm, or a length of 2 to 20 mm.

[0075] Further, in accordance with some applications of the present invention, there is provided a device for use with a lumen of a subject extending from a chamber of the subject's heart, the device comprising: 1. A transluminal ablation catheter, comprising: an ultrasound transducer configured to ablate tissue by transmitting ultrasound energy to the target tissue; a sensor in operable communication with the transluminal ablation catheter and configured to detect changes in blood flow within the lumen; 1. A computer processor comprising: determining optimal tissue target sites for ablation based on the detected changes in blood flow; a computer processor configured to drive the ultrasound transducer to transmit ultrasound energy to an optimal tissue target; The present invention relates to a transluminal ablation catheter comprising:

[0076] For some applications, the sensor includes a Doppler ultrasound device. hi some applications, the sensor is configured to detect sound indications indicative of changes in blood flow within the lumen.

[0077] For some applications, the transluminal ablation catheter further includes an actuator configured to adjust the position of the ultrasound transducer in response to detected changes in blood flow so that the transmitted ultrasound energy is applied to an optimal tissue target site.

[0078] In some applications, Optimal tissue targets include the luminal ostium; the sensor is configured to detect a change in blood flow between the lumen and the heart chamber; The computer processor is configured to drive the ultrasound transducer to transmit ultrasound energy to the lumen ostium based on a detected change in blood flow between the lumen and the heart chamber.

[0079] In some applications, Optimal tissue targets include the pulmonary vein ostia; the ultrasound transducer is configured to be positioned within an atrium of the subject; the sensor is configured to detect a change in blood flow between the pulmonary vein and the atrium; The computer processor is configured to drive the ultrasound transducer to transmit ultrasound energy to the ostium of the pulmonary vein based on the detected change in blood flow between the pulmonary vein and the atrium.

[0080] Furthermore, in accordance with some applications of the present invention, there is provided a method, the method comprising: advancing a transluminal ablation catheter including at least one ultrasound transducer into an atrium of the subject; using a sensor to detect changes in blood flow near the at least one ultrasound transducer to determine the location of the pulmonary veins relative to the atrium; activating the ultrasound transducer to ablate tissue at the ostium of the pulmonary vein in response to determining the location; Includes.

[0081] For some applications, using the sensor includes using Doppler ultrasonography. For some applications, using the sensor includes detecting sound indications of changes in blood flow with the sensor. For some applications, the method further includes adjusting a position of the ultrasound transducer in response to determining the position.

[0082] In some applications, the method further comprises: generating three-dimensional image data of the atrium using an ultrasound transducer; determining the location of the pulmonary veins relative to the atrium using the image data in combination with the changes in blood flow detected by the sensor; Includes.

[0083] Furthermore, in accordance with some applications of the present invention, there is provided a method, the method comprising: advancing at least one ultrasound transducer into a cardiac chamber of the subject to ablate myocardial tissue of the subject; applying non-ablative ultrasonic energy to myocardial tissue such that at least a portion of the non-ablative ultrasonic energy is reflected and received by the ultrasound transducer; assessing parameters of the reflected energy to determine parameters of ultrasonic energy applied by the ultrasonic transducer to ablate the myocardial tissue; applying ultrasonic energy to the myocardial tissue based on the determined parameters; Includes.

[0084] For some applications, assessing the parameter of the reflected energy includes determining an energy level of the reflected energy. For some applications, assessing the parameter of the reflected energy to determine a parameter of ultrasonic energy applied by the ultrasonic transducer to ablate the myocardial tissue includes assessing the parameter of the reflected energy to determine a power level of ultrasonic energy applied by the ultrasonic transducer to ablate the myocardial tissue. For some applications, assessing the parameter of the reflected energy includes assessing the parameter of the reflected energy to determine whether the ultrasonic transducer is in a desired position and adjusting the position of the ultrasonic transducer accordingly.

[0085] Further, in accordance with some applications of the present invention, there is provided a device for use with a lumen of a subject extending from a chamber of the subject's heart, the device comprising: a transluminal ablation catheter, the transluminal ablation catheter comprising: an elongate shaft having a proximal portion and a distal portion; at least one ultrasound transducer coupled to a distal portion of the shaft and configured for insertion into a cardiac chamber of a subject and for ablating tissue by applying ultrasound energy to tissue at an ostium of the chamber; the elongate shaft is rotatably configured to rotate the ultrasound transducer; The transluminal ablation catheter further includes an expandable cage disposed in a distal portion of the shaft, the expandable cage configured to surround the ultrasound transducer in an expanded state of the cage when the ultrasound transducer is positioned within a cardiac chamber of the subject; a rotational force reduction mechanism configured to reduce a rotational force applied to the expandable cage by the elongate shaft upon rotation of the elongate shaft so as to keep the expandable cage stationary during rotation of the ultrasound transducer; Includes.

[0086] Furthermore, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A transluminal ablation catheter, comprising: a first ultrasound transducer configured to transmit ablative ultrasound energy toward the target tissue to thereby ablate the tissue; a second ultrasonic transducer configured to transmit one or more pulses of pulse-echo ultrasonic energy toward the tissue and receive reflections of the transmitted pulse-echo ultrasonic energy; a first support configured to support a first ultrasonic transducer and to enable transmission of ablative ultrasonic energy toward tissue; a second support configured to support the second ultrasonic transducer and provide a higher level of attenuation than that provided by the first support, such that the second transducer can receive reflections of the transmitted pulse-echo ultrasonic energy while the first ultrasonic transducer transmits ablative ultrasonic energy toward the tissue; The present invention relates to a transluminal ablation catheter comprising:

[0087] In some applications, the first support includes an air barrier configured to permit vibration of the first ultrasonic transducer during transmission of ablative ultrasonic energy toward the tissue; The second support includes a mechanical support including at least one of a backing layer and a damping element.

[0088] The present invention will be more fully understood from the following detailed description of the embodiments, taken in conjunction with the drawings. [Brief explanation of the drawings]

[0089] [Figure 1A] 1 is a schematic diagram of an apparatus for applying ultrasound energy to tissue within a subject, in accordance with some applications of the present invention. [Figure 1B]1 is a schematic diagram of an apparatus for applying ultrasound energy to tissue within a subject, in accordance with some applications of the present invention. [Figure 1C] 1 is a schematic diagram of an apparatus for applying ultrasound energy to tissue within a subject, in accordance with some applications of the present invention. [Figure 1D] 1 is a schematic diagram of an expandable cage of an apparatus for applying ultrasonic energy to tissue within a subject, according to some applications of the present invention. [Figure 1E] 1 is a schematic diagram of an apparatus for applying ultrasound energy to tissue positioned within a subject, in accordance with some applications of the present invention. [Figure 2A] 1 is a schematic diagram of an apparatus for applying ultrasound energy to tissue within a subject, in accordance with some applications of the present invention. [Figure 2B] 10 is a graph illustrating the effect of the distance of an ultrasound transducer from an ablation site on the absorption of ultrasound energy by various media through which the ultrasound energy is transmitted, in accordance with some applications of the present invention. [Figure 3A] 1 is a schematic diagram of an apparatus for applying ultrasound energy to tissue within a subject, in accordance with some applications of the present invention. [Figure 3B] 1 is a diagram of components of an apparatus for applying ultrasound energy to tissue within a subject, in accordance with some applications of the present invention. [Figure 3C] 1 is a diagram of components of an apparatus for applying ultrasound energy to tissue within a subject, in accordance with some applications of the present invention. [Figure 4A] 10 is a schematic diagram of a rotational force reduction mechanism for reducing rotational forces applied to an expandable cage during rotation of an ultrasound transducer, in accordance with some applications of the present invention. [Figure 4B] 10 is a schematic diagram of a rotational force reduction mechanism for reducing rotational forces applied to an expandable cage during rotation of an ultrasound transducer, in accordance with some applications of the present invention. [Figure 4C]10 is a schematic diagram of a rotational force reduction mechanism for reducing rotational forces applied to an expandable cage during rotation of an ultrasound transducer, in accordance with some applications of the present invention. [Figure 4D] 10 is a schematic diagram of a rotational force reduction mechanism for reducing rotational forces applied to an expandable cage during rotation of an ultrasound transducer, in accordance with some applications of the present invention. [Figure 4E] 10 is a schematic diagram of a rotational force reduction mechanism for reducing rotational forces applied to an expandable cage during rotation of an ultrasound transducer, in accordance with some applications of the present invention. [Figure 4F] 10 is a schematic diagram of a rotational force reduction mechanism for reducing rotational forces applied to an expandable cage during rotation of an ultrasound transducer, in accordance with some applications of the present invention. [Figure 5A] 1 is a schematic diagram of a curved piezoelectric ultrasonic transducer, in accordance with some applications of the present invention. [Figure 5B] 5B is an image of an ultrasonic energy transmission profile using the ultrasonic transducer of FIG. 5A, in accordance with some applications of the present invention. [Figure 5C] 5B is an image of an ultrasonic energy transmission profile using the ultrasonic transducer of FIG. 5A, in accordance with some applications of the present invention. [Figure 5D] 5B is a graph illustrating the effect of various transducer dimensions on the emission angle of the ultrasound transducer of FIG. 5A, in accordance with some applications of the present invention. [Figure 6] 4 is a flowchart illustrating method steps performed in accordance with some applications of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0090] Reference is now made to Figures 1A, 1B, and 1C, which are schematic illustrations of apparatus for applying ultrasonic energy to tissue within a subject, in accordance with some applications of the present invention.

[0091] Figure 1A shows an overview of a system 220 for ultrasound tissue treatment, including a control console 27, a handle 25, and a device 20 for applying ultrasound energy to tissue within a subject. Figures 1B-1C show embodiments of the device 20 having expandable cages of different shapes, which are described in more detail below.

[0092] 1A typically includes a device 20 having an ultrasound transducer 50 (and / or ultrasound transducers 52 / 150 described below) configured to apply ultrasound energy to target tissue. The device 20 is typically operable with a control console 27 including a computer processor 26 and a display 23.

[0093] For example, the computer processor 26 is configured to detect various parameters associated with the application of ultrasonic energy (e.g., parameters of the applied and / or reflected ultrasonic energy) and drive the ultrasonic transducer to transmit ultrasonic energy (e.g., by selecting optimal ultrasonic energy application parameters, etc.), as described in more detail below. In some applications, the computer processor 26 drives the ultrasonic transducer to rotate and / or translate back and forth, as described in more detail below. For example, the computer processor may control the movement of the ultrasonic transducer via an actuator (e.g., a motor) housed within the handle 25 (or elsewhere in the system 220). In some applications, the computer processor 26 is configured to control the device 20 in response to user input received via the handle 25 or another user input interface (e.g., keyboard 29).

[0094] The computer processor 26 is typically a hardware device that is programmed with computer program instructions to create a dedicated computer, e.g., when programmed to perform the techniques described herein, the computer processor 26 typically functions as a dedicated ultrasound energy application computer processor.

[0095] 1B, which is a schematic illustration of an apparatus 20 for applying ultrasound energy to tissue of a target anatomical structure within a subject, in accordance with some applications of the present invention. Apparatus 20 is typically configured for use with a lumen of the subject extending from a chamber of the subject's heart. In some applications, the chamber of the heart is an atrium, and the lumen extending from the atrium is a pulmonary vein.

[0096] Typically, device 20 applies ultrasonic energy to treat cardiac arrhythmias, such as atrial fibrillation. In accordance with some applications of the present invention, ultrasonic energy is applied to myocardial tissue, particularly to sites within the myocardial tissue involved in the initiation, maintenance, or propagation of cardiac arrhythmias, such as the ostia of pulmonary veins. To this end, as described above, device 20 is shaped and sized for use with pulmonary veins extending from the left atrium of the heart. Device 20 is configured to apply ultrasonic energy to ablate tissue at the ostia of the pulmonary veins, resulting in scarring of the tissue at the ablated sites. The scarring typically prevents abnormal electrical pulses generated at the ostia of the pulmonary veins from propagating into the heart chambers, thereby electrically isolating the pulmonary veins from the atria and reducing or preventing cardiac arrhythmias.

[0097] For some applications, device 20 comprises a transluminal ablation catheter 40 that includes an elongate shaft having a proximal portion including a handle 25 (shown, for example, in FIG. 1A ) and a distal portion coupled to at least one ultrasound transducer 50. In this context, as used herein and in the claims, "proximal" means closer to the user of the device, and "distal" means further from the user, i.e., deeper into the subject's body than the opening through which the device is initially inserted.

[0098] The transluminal ablation catheter 40 facilitates the advancement of an ultrasound transducer 50 into a target heart chamber (e.g., an atrium) in a minimally invasive procedure. The ultrasound transducer 50 is typically inserted into the atrium to apply ultrasound energy to tissue at a lumen ostium, such as the ostium of a pulmonary vein, thereby ablating the tissue. In addition to or instead of applying ablative ultrasound energy, the ultrasound transducer 50 is configured to image the target tissue by applying non-ablative ultrasound energy.

[0099] For some applications, the ultrasound transducer 50 includes a side-facing transducer. In other applications, the ultrasound transducer 50 includes a distally facing ultrasound transducer. For some applications, two or more ultrasound transducers 50 are coupled to the transluminal ablation catheter 40, at least one of which is a distally facing ultrasound transducer and at least one of which is a side-facing ultrasound transducer. Additionally, for some applications, to further assist in lesion formation in the tissue, the distal tip of the transluminal ablation catheter 40 includes an electrode configured to drive electrical current into the tissue designated for ablation treatment.

[0100] For some applications, device 20 further comprises a fixation element, such as an expandable cage, having a shape defining a three-dimensional structure configured to be disposed around ultrasound transducer 50 at the distal portion of transluminal ablation catheter 40. FIG. 1B illustrates expandable cage 30 having a shape according to some applications of the present invention, while FIGS. 1A and 1C illustrate expandable cage 301 having a shape according to other applications of the present invention.

[0101] 1B, the expandable cage 30 includes a plurality of struts 32 (e.g., flexible struts that may be made from a resilient metal such as nitinol, stainless steel, nickel titanium, or a combination thereof). As noted above, in some cases, the struts are referred to herein as "flexible wires." These two terms are used interchangeably throughout this specification and claims. The expandable cage 30 is configured to position a distal portion of a transluminal ablation catheter 40 within a lumen of a subject extending from a chamber of the subject's heart, for example, within the lumen of a pulmonary vein extending from an atrium of the heart.

[0102] The expandable cage 30 positions and temporarily secures the distal portion of the transluminal ablation catheter 40 within the lumen by contacting the lumen wall with the struts 32. Typically, the expandable cage 30 engages the wall of a lumen, such as a pulmonary vein, but does not obstruct blood flow through the lumen (as shown, the expandable cage 30 is shaped to allow blood to flow therethrough).

[0103] The expandable cage 30 is typically delivered in a collapsed state to a target anatomical site within a subject via a transluminal ablation catheter 40. The struts 32 typically comprise a shape memory alloy that automatically expands from a collapsed configuration to an expanded configuration upon deployment within a lumen, such as a pulmonary vein. When it is desired to withdraw the transluminal ablation catheter 40 from the subject, the struts 32 collapse from their expanded state to a pre-defined collapsed shape by applying a mechanical compressive or tensile force to the handle. The shape of the expandable cage and portions of the expandable cage described herein generally refers to the configured shape the expandable cage has when the expandable cage is in a radially unconstrained configuration (e.g., deployed at the target anatomical site).

[0104] In some applications, the expandable cage 30 is rotationally symmetric. In other applications, the expandable cage 30 is rotationally asymmetric.

[0105] For some applications, the expandable cage 30 is configured to position the transducer 50 and / or catheter 40 at the center of the lumen. In other applications, the expandable cage 30 is configured to position the transducer 50 and / or catheter 40 asymmetrically within the lumen, i.e., not at the center of the vascular lumen. For example, the expandable cage 30 can position the transducer 50 to aim at a portion of the lumen wall designated for ablation and / or imaging. For example, the expandable cage 30 can be configured to secure the transluminal ablation catheter 40 such that the ultrasound transducer 50 transmits ultrasound energy toward the lumen ostium when the lumen ostium is designated for ablation and / or imaging. For some applications, the expandable cage 30 is configured to maintain radial separation between the ultrasound transducer 50 and the lumen wall and to position the transducer 50 at a desired distance from the site designated for imaging or ablation. For example, the expandable cage 30 is configured to adjust the distance between the ultrasound transducer 50 and the tissue designated for ablation and / or imaging by applying pressure to push on the tissue when it contacts the lumen wall. In some applications, the expandable cage 30 is configured to maintain the ultrasound transducer 50 at a fixed distance from the tissue during imaging to detect lesion formation while reducing artifacts associated with tissue movement.

[0106] In some applications, the expandable cage 30 has a papillary configuration in which the distal portion 36 of the expandable cage 30 is narrower than the central portion 34 of the expandable cage 30. Having a narrow distal portion 36 typically facilitates insertion of the expandable cage 30 into relatively small or narrow anatomical structures of various diameters, such as vascular cavities such as pulmonary veins. For example, in some applications, only the narrow distal portion 36 of the cage 30 is inserted into a vein, while the remainder of the device 20 remains within the atrium. In some applications, the narrow distal portion 36 of the cage 30 thereby anchors the cage 30 relative to the pulmonary vein.

[0107] Typically, starting from the distal end of the expandable cage 30, the struts first define a convex curvature (with respect to the exterior of the expandable cage) and then, passing through an inflection point 21, have a concave curvature. A thin distal portion extends from the distal end of the expandable cage to the inflection point.

[0108] In some applications, the maximum diameter D1 at the central portion 34 of the expandable cage 30 is up to five times larger than the maximum diameter D2 of the narrow distal portion 36 of the expandable cage 30, thereby facilitating insertion of the narrow distal portion 36 into the pulmonary vein.

[0109] For some applications, the expandable cage 30 is constructed such that at least a portion of the struts 32 are curved outward (i.e., curved convexly toward the outside of the expandable cage) in at least two locations along a single strut, e.g., at curved locations 22 and 24. In some applications, the outwardly curved areas contact the lumen wall, thereby anchoring the transluminal ablation catheter 40 within the lumen. For some applications, the struts 32 that are curved outward in at least two locations (e.g., 22 and 24) are shaped such that the radius of curvature at the first curved location 22 is 10-20 mm and the radius of curvature at the second curved location 24 is 5-10 mm. Note that the radii of curvature at curved locations 22 and 24 are such that when these portions are forced against the lumen wall, tissue is generally not penetrated or damaged.

[0110] As described above, in some applications, the ultrasound transducer 50 is configured to generate images of tissue by applying non-ablative ultrasound energy to the tissue. In some applications, the ultrasound transducer 50 generates three-dimensional images (e.g., of a pulmonary vein ostium) by rotating in the direction indicated by arrow A1 about the longitudinal axis LA of the transluminal ablation catheter 40 and translating longitudinally back and forth along the longitudinal axis LA in the direction indicated by arrow A2. According to some applications of the present invention, the dimensions of the expandable cage 30 are such that, when the expandable cage 30 is disposed around the transducer, the transducer 50 can rotate within the cage in the directions indicated by arrows A1 and A2 and translate back and forth.

[0111] For some applications, expandable cage 30 is further configured to electrically stimulate and / or sense electrical signals from the anatomical structure in which device 20 is positioned. In some such applications, expandable cage 30 includes one or more electrodes 60 (shown in FIG. 3A ) configured to record electrical activity before, during, or after ablation to monitor the ablation procedure and lesion formation. For some applications, ablation treatment parameters (e.g., duration of energy application and / or level of energy applied to tissue) are adjusted based on monitoring by one or more electrodes 60.

[0112] Additionally or alternatively, at least a portion of the plurality of struts 32 forming the expandable cage 30 include conductive struts, such as flexible metallic wires, that are configured to contact tissue in the lumen wall (e.g., at the lumen ostium) and drive electrical current into the tissue to ablate the tissue in contact with the conductive struts / wires. Typically, in such applications, the ultrasound transducer 50 is used primarily to image the tissue.

[0113] In some such applications, at least some of the conductive struts include electrically conductive and electrically insulated portions. Typically, the insulated portions of the struts are coated with an insulating material, and the conductive portions are exposed. Typically, the portions of the struts 32 that contact tissue are electrically conductive and are adapted to drive current into the tissue to ablate it (e.g., curved portions 22 and 24 shown in FIG. 1B, typically biased against the lumen wall).

[0114] According to some applications of the present invention, the expandable cage 30 drives radio frequency (RF) current into the tissue via the conductive portions of the struts 32. Additionally or alternatively, the expandable cage 30 drives alternating and / or direct current (DC) into the tissue via the conductive portions of the struts 32.

[0115] Reference is now made to FIG. 1C, which is a schematic illustration of device 20, according to some applications of the present invention. As shown in FIG. 1C, in some applications, device 20 comprises an expandable cage 301, with struts 32 shaped to define the spherical shape of expandable cage 301. Generally, expandable cage 301 lacks the narrowing of distal portion 36 that gives expandable cage 30 (shown in FIG. 1B) its papillary shape. Expandable cage 301 is generally identical to expandable cage 30, except that narrow distal portion 36 extends from the distal end of the expandable cage to inflection point 21 (which is not present in expandable cage 301).

[0116] Referring again to Figure 1A, it should be noted that the shape of the expandable cage shown in Figure 1A is illustrated by way of example and not limitation. It should be noted that, mutatis mutandis, any other suitable shape of expandable cage may be used, including expandable cage 30 having the shape shown in Figure 1B, an oval-shaped expandable cage (not shown), or an expandable cage having any other shape. Furthermore, it should be noted that additional embodiments of the present invention described herein with reference to Figures 1D through 6 are applicable to any shape of expandable cage 30 or expandable cage 301.

[0117] Reference is now made to FIG. 1D , which is a schematic illustration of an expandable cage 30, in accordance with some applications of the present invention. As shown in FIG. 1B , the expandable cage 30 has a shape that defines a plurality of relatively large gaps 90 through which ultrasonic energy is transmitted from the ultrasound transducer 50 to tissue designated for ablation and / or imaging. Additionally, in some applications, at least some of the struts 32 of the expandable cage 30 are shaped to define one or more apertures 94 formed therein (the apertures 94 are shown in FIG. 1D ) to further facilitate transmission of ultrasonic energy to tissue. The apertures formed in the struts 32 typically increase the area over which ultrasonic energy is transmitted through the expandable cage 30, thereby allowing more ultrasonic energy to reach the target tissue, resulting in increased tissue heating and more effective tissue ablation.

[0118] The width of the struts 32 is typically narrow enough to allow for the formation of gaps 90 between the struts 32, while at the same time being wide enough to provide the necessary anchoring and stabilization of the distal portion of the transluminal ablation catheter 40 within the lumen. Thus, the provision of openings 94 in the struts 32 improves the transmission of ultrasonic energy through the expandable cage 30 to tissue while providing sufficient anchoring of the catheter 40 within the lumen. Typically, the width W1 of a single strut 32 is between 0.5 and 1 mm, e.g., 0.7 mm. The width W2 of a strut opening is between 0.25 and 0.5 mm, e.g., 0.35 mm. In some applications, the openings 94 extend along the entire length of the struts 32. Alternatively, in some applications, the openings 94 extend along only a portion of the length of the struts 32.

[0119] 1B-1D , typically, according to some applications of the present invention, the thickness of each or a portion of the plurality of struts 32 is less than the ultrasonic wavelength for the ultrasonic frequency generated by the ultrasonic transducer 50. When the thickness of the struts 32 is less than the ultrasonic wavelength (when propagating in blood) for the frequency used, interference with the propagation of the ultrasonic waves (e.g., obstruction by the struts) is reduced, so more energy reaches the tissue.

[0120] According to some applications of the present invention, to achieve effective heating and ablation of tissue, ultrasonic energy is applied at a frequency of 8-20 MHz, e.g., 10-12 MHz, e.g., 11 MHz. Generally, ultrasonic wavelength decreases as frequency increases, so when ultrasonic transducer 50 is operated at a frequency of, e.g., 8-20 MHz, e.g., 10-12 MHz, e.g., 11 MHz, struts 32 have a thickness of approximately 0.1-0.25 mm (e.g., 0.14-0.2 mm) to facilitate propagation of ultrasound through cage 30.

[0121] Reference is now made to FIG. 1E, which is a schematic illustration of device 20 positioned within a subject, in accordance with some applications of the present invention.

[0122] For some applications, the device 20 is advanced into the left atrium 190 and positioned adjacent to or within the ostia of a pulmonary vein. For some applications, the device 20 is advanced into the left atrium 190 using a transseptal approach (as shown in FIG. 1E). Alternatively, the device 20 may be advanced into the left atrium 190 using a transapical approach via the left ventricular apex and mitral valve (approach not shown). Alternatively, the device 20 may be advanced into the left atrium 190 via the aorta, left ventricle, and mitral valve (approach not shown).

[0123] Typically, the device 20 is advanced in a collapsed state into the left atrium 190 by the expandable cage 30. The struts 32 expand from the collapsed configuration to an expanded configuration within the left atrium of the heart, rendering the device 20 operational. The device 20 is positioned adjacent to the ostium of a pulmonary vein 160 and adjacent tissue of the atrial wall 170, such that a portion of the cage 30 (typically a portion of the central portion 34) is anchored to the wall 170. The distal portion 36 of the cage 30 is typically advanced into the pulmonary vein 160 to optimally position the ultrasound transducer 50 relative to the tissue designated for ablation (typically the ostium of the pulmonary vein). Additionally or alternatively, the distal portion 36 of the expandable cage 30 is advanced into the pulmonary vein 160 to apply pressure to the wall of the pulmonary vein, thereby anchoring and maintaining the device 20 in place during application of ultrasound energy.

[0124] It should be noted that although FIG. 1E shows the ultrasound transducer 50 positioned outside the pulmonary vein, the device 20 may be configured such that the ultrasound transducer is positioned further distally along the catheter 40 such that the ultrasound transducer advances into the pulmonary vein when the distal portion 36 of the cage 30 is advanced into the pulmonary vein.

[0125] Furthermore, it should be noted that the scope of the present invention includes the use of the devices and methods described herein in anatomical locations other than the left atrium and pulmonary veins.

[0126] Reference is now made to Figure 2A, which is a schematic illustration of an apparatus 20 for applying ultrasonic energy to tissue within a subject, in accordance with some applications of the present invention. Reference is also made to Figure 2B, which is a graph illustrating the absorption of ultrasonic energy by blood (shown by line 106) and myocardial tissue (shown by line 105) at increasing distances (in millimeters) from the ultrasonic transducer to a tissue site designated for ablation (e.g., a pulmonary vein) when ultrasonic energy is applied at a typically relatively high frequency (e.g., 8-20 MHz, e.g., 10-12 MHz, e.g., 11 MHz, e.g., 11.2 MHz).

[0127] As shown in FIG. 2A , for some applications, the device 20 includes, in addition to the expandable cage 30, a fluid-filled expandable element 100, such as a balloon, configured to be disposed around the ultrasound transducer 50. Typically, the expandable element 100 is inflated with a fluid, such as water (e.g., distilled water) and / or saline, and / or any liquid with an acoustic attenuation coefficient similar to that of saline. Ultrasound energy is transmitted through this fluid, with negligible absorption of the ultrasonic energy. In such applications, the expandable cage 30 is disposed around the expandable element 100 to position the distal portion of the transluminal ablation catheter 40 within the lumen, as described above.

[0128] Typically, when the expandable cage 30 is present but the inflatable element 100 is not (as shown in FIGS. 1B-1C), the primary medium through which ultrasonic energy emitted from the ultrasonic transducer 50 is transmitted to tissue is blood. This is because the expandable cage 30 has a shape that allows blood to flow through a vascular cavity (e.g., a pulmonary vein). As ultrasonic energy from the transducer 50 is transmitted to tissue through the blood, some of the energy is absorbed by the blood, thereby reducing the amount of ultrasonic energy that reaches the tissue. This is particularly true when using relatively high frequency ultrasound waves (e.g., 8-20 MHz, e.g., 10-12 MHz, e.g., 11 MHz) to effectively ablate tissue in accordance with some applications of the present invention, as compared to using lower frequencies, such as 6 MHz.

[0129] Typically, as shown in FIG. 2B, the greater the distance between the piezoelectric element (PZT) of the ultrasound transducer 50 and the tissue designated for ablation / imaging (e.g., pulmonary vein (PV)), the more ultrasound energy is absorbed by the blood in the vessel (and therefore, less energy reaches the tissue). For example, if the ultrasound transducer 50 is positioned approximately 10 mm from the tissue designated for ablation, only a portion (e.g., approximately 50%) of the transmitted ultrasound energy reaches the tissue. In such a case, the tissue may not be heated sufficiently to achieve ablation.

[0130] Typically, as shown in FIG. 2B, the absorption of ultrasonic energy by blood (line 106) increases as the distance traveled by the ultrasound increases, with a corresponding decrease in the absorption of ultrasonic energy by myocardial tissue (line 105).

[0131] As shown in Figure 2A, placement of a fluid-filled (e.g., water-filled) expandable element 100 around the ultrasonic transducer 50 partially displaces the blood medium between the ultrasonic transducer 50 and the tissue designated for ablation. As described above (and shown in Figure 2B), ultrasonic energy is transmitted through water but is not substantially absorbed by water, so a greater amount of the transmitted ultrasonic energy reaches the tissue than would be the case if the transmitted ultrasonic energy were transmitted solely through blood.

[0132] For example, the expandable element 100 may be inflated with water to occupy up to 50% (e.g., 30-40%) of the distance between the transducer 50 and the tissue designated for ablation, thereby reducing the amount of ultrasonic energy that might otherwise be absorbed by the blood in the lumen in the absence of the expandable element 100. Typically, the provision of the expandable element 100 allows the ultrasonic transducer 50 to operate at lower power levels and for shorter durations than would be possible if the transmitted ultrasonic energy were transmitted solely through blood.

[0133] Advantageously, because the expandable element 100 is used in addition to the expandable cage 30 (and therefore is not utilized to position the ablation catheter 40 within the lumen), the expandable element 100 may be inflated to any desired degree of expansion based, for example, on the anatomical location where the ultrasound transducer is inserted and / or the operating parameters of the ultrasound transducer 50. In some applications, the expandable element 100 is inflated with water to a diameter of 6-9 mm, for example, 8 mm.

[0134] Reference is now made to Figure 3A, which is a schematic illustration of an apparatus 20 for applying ultrasound energy to tissue within a subject, in accordance with certain applications of the present invention. Reference is also made to Figures 3B and 3C, which are illustrations of additional components of apparatus 20, in accordance with certain applications of the present invention.

[0135] According to some applications of the present invention, in addition to applying ultrasonic energy for ablation purposes, the ultrasonic transducer 50 is configured to perform acoustic sensing by transmitting one or more pulses of pulse-echo ultrasonic energy toward a designated tissue site and receiving reflections of the transmitted pulse-echo ultrasonic energy. Generally, parameters of the reflected pulse-echo ultrasonic energy can be indicative of the ultrasonic energy applied to the tissue and the effect of the ultrasonic energy on the tissue. As mentioned above, in some applications, the device 20 includes a control console 27 and a computer processor 26 (shown, for example, in FIG. 1A ), which are configured to determine parameters of the reflected pulse-echo ultrasonic energy to detect an effect or indication of the applied ultrasonic energy.

[0136] For some applications, in addition to the ultrasound transducer 50, a second ultrasound transducer 52 is coupled to the transluminal ablation catheter 40. In some such applications, the first ultrasound transducer 50 is configured to ablate tissue by transmitting ablative ultrasound energy toward the tissue in the lumen, and the second ultrasound transducer 52 is configured to transmit pulse-echo ultrasound waves to the tissue and receive reflections of the transmitted pulse-echo ultrasound waves. For example, the first ultrasound transducer 50 is configured to transmit ultrasound energy to ablate tissue at a power level greater than 3 W, e.g., between 3 W and 50 W, e.g., between 6 W and 35 W, and the second ultrasound transducer 52 is configured to transmit pulse-echo ultrasound energy at a power level of up to 2 W (e.g., less than 2 W).

[0137] Typically, the ultrasound transducer 50 is suspended above a first support that includes an air barrier (shown at 80 in FIG. 5A ) to allow for near-free vibration of the ultrasound transducer 50 with relatively low attenuation when applying ablation energy to tissue. This typically allows for effective transmission of the ablation energy to the tissue. In contrast, a pulse-echo ultrasound transducer 52 that detects return signals (reflections) of the transmitted pulse-echo ultrasound energy does not generally self-vibrate during detection of the reflected signals, as the transducer 52 does.

[0138] 3A, because transducers 50 and 52 are positioned adjacent to each other on ablation catheter 40 (and are typically assembled within a single housing), it is necessary to prevent mechanical vibrations of transducer 50 from reaching transducer 52, as vibrations of transducer 52 would likely reduce its effectiveness in detecting reflected signals, particularly signals reflected from very close to the transducer (e.g., from a distance of 1 mm).

[0139] Typically, the ultrasound transducer 50 is suspended above an air barrier, allowing the ultrasound transducer 50 to vibrate generally freely with relatively low attenuation when applying ablative energy to tissue, while the pulse-echo ultrasound transducer 52 is supported with relatively high attenuation by a damping support including a backing layer 120 (FIG. 3B) and / or a damping element 140, such as a damping ring (FIG. 3C). This allows sensing by the ultrasound transducer 52 and ablation energy transmission by the ultrasound transducer 50 while both transducers are positioned adjacent to one another. Typically, the backing layer 120 is surrounded by the damping element 140, which comprises a soft material and / or a high density (such as low-duty Pebax® or Pebax® and / or tungsten) intended to isolate the mechanical vibrations of the ultrasound transducer 50 from reaching the ultrasound transducer 52. 3C, the damping element 140 is shown as having a round shape by way of example and not limitation. The damping element 140 typically has a shape that corresponds to the shape of the ultrasound transducer 52 (e.g., may have a rectangular or square shape).

[0140] As described above, in some applications, the reflected ultrasound energy can indicate the ultrasound energy applied to the tissue and the effect of the ultrasound energy on the tissue and can serve as an input for modifying the operating parameters of the ultrasound transducer. For example, adjusting the ablation power, duty cycle, or any other parameter in response to the detected reflected ultrasound energy. In some applications, the reflected ultrasound energy is used to assess post-treatment results of the ablation therapy and / or to assess the progression of lesion formation during the ablation therapy.

[0141] For some applications, computer processor 26 is configured to detect indications of blood carbonization near ultrasound transducers 50 and / or 52 by determining parameters of the reflected pulse-echo ultrasound energy and, in response to the detected indication of blood carbonization, inhibit application of ultrasound energy from the ultrasound transducers. Because blood carbonization typically obstructs the transmission of ultrasound, and the distance between the transducer and the tissue is known, the indication of blood carbonization and its location can be derived from the parameters of the reflected ultrasound energy.

[0142] 1A-3A, which illustrate a device 20 according to some applications of the present invention. As described above, the transluminal ablation catheter 40 has an elongate shaft that includes a handle 25 at a proximal portion of the elongate shaft and at least one ultrasound transducer 50 at a distal portion of the elongate shaft.

[0143] Typically, ultrasound transducer 50 is rotatable in the direction indicated by arrow A1 in FIG. 1B relative to longitudinal axis LA of ablation catheter 40. Rotation of ultrasound transducer 50 (and / or transducer 52) generally facilitates various functions and operational features of device 20.

[0144] For example, the ultrasound transducer 50 (and / or transducer 52) rotates to generate images of the tissue. The images can be two-dimensional and / or three-dimensional. The generated images can be displayed on the display 23 shown in FIG. 1A. To generate the three-dimensional images, the ultrasound transducer 50 (and / or transducer 52) rotates (indicated by arrow A1 in FIG. 1A) and translates back and forth longitudinally along axis LA (indicated by arrow A2 in FIG. 1A). In some applications, the transducer 50 (and / or transducer 52) performs continuous imaging of the anatomical structure in which the transducer 50 (and / or transducer 52) is positioned (e.g., a heart chamber and the ostium of a lumen extending from the heart chamber). Typically, generating three-dimensional images of the anatomical structure allows for identification of an optimal location and optimal plane within the tissue at which to perform ablation. Typically, the transducer 50 (and / or transducer 52) also performs imaging near the anatomical structure designated for ablation. For example, imaging can be used to identify the location of the esophagus relative to device 20 to mitigate damage to the esophagus that may result from an ablation procedure performed on the heart.

[0145] Additionally or alternatively, the ultrasound transducer 50 can be rotated to aim the transducer 50 at the tissue site designated for ablation / imaging. Additionally or alternatively, the ultrasound transducer 50 can be rotated while continuously transmitting ablative ultrasound energy to create a continuous circular lesion surrounding the ostium of a blood vessel cavity (e.g., the ostium of a pulmonary vein).

[0146] Typically, rotation of the ultrasound transducer 50 (and / or transducer 52) is generated by rotation of the elongate shaft of the ablation catheter 40 to which the ultrasound transducer 50 (and / or transducer 52) is coupled. Rotation of the elongate shaft of the ablation catheter 40 is caused by rotation of an actuator (e.g., a knob or motor) at the proximal portion of the elongate shaft (e.g., the handle 25 shown in FIG. 1A). The rotational motion is transmitted from the proximal portion along the elongate shaft to the distal portion of the shaft to which the ultrasound transducer 50 (and / or transducer 52) is coupled, causing the ultrasound transducer 50 (and / or transducer 52) to rotate.

[0147] Generally, it is advantageous to determine the rotational and longitudinal positions of the ultrasound transducer 50 and / or transducer 52. For example, monitoring the rotational angle of the ultrasound transducer 50 (and / or transducer 52) typically facilitates the generation of smooth two-dimensional and three-dimensional images. Because rotational motion is generated at a proximal portion of the elongate shaft (e.g., a handle), measuring the rotational angle of the handle can assess the rotational angle of the ultrasound transducer 50 (and / or transducer 52). However, not all of the rotational motion generated at the proximal portion of the elongate shaft may be transmitted along the elongate shaft to the distal portion of the shaft. Furthermore, there may be a time lag between the rotational positions of the proximal portion of the elongate shaft and the distal portion of the elongate shaft. Thus, when it is desirable to precisely measure the rotational position of the ultrasonic transducer 50 (and / or of the transducer 52, e.g., to determine the rotational angle of the ultrasonic transducer 50 and / or the transducer 52), it may not be sufficient to measure the rotational angle of the proximal portion of the elongate shaft (e.g., the handle) where rotation begins.

[0148] According to some applications of the present invention, device 20 includes a mechanism configured to determine the rotational position of the distal portion of the elongate shaft separately from the rotational position of the proximal portion of the elongate shaft, thereby determining the rotational position of ultrasound transducer 50 (and / or transducer 52).

[0149] Accordingly, in some applications, device 20 includes a distal rotation detection sensor 28 (shown diagrammatically in FIG. 4A).

[0150] For example, a gyroscope is coupled to the ultrasonic transducer 50 (and / or transducer 52) and is typically configured to measure the angle of rotation of the distal portion of the elongate shaft, thereby determining the angle of rotation of the ultrasonic transducer 50 (and / or transducer 52).

[0151] Additionally or alternatively, the rotational position of the distal portion of the elongate shaft can be determined using image-guided techniques, such as utilizing fiducial markers (not shown) coupled to the expandable cage 30 that reflect ultrasonic energy emitted by the ultrasound transducer 50 (and / or transducer 52). As described below, the expandable cage 30 typically remains stationary during rotation of the distal portion of the elongate shaft and the ultrasound transducer 50 (and / or transducer 52). Thus, in some applications, the rotational position of the ultrasound transducer 50 (and / or transducer 52) relative to the stationary cage is identified by identifying the location of the fiducial markers in ultrasound images generated using the ultrasound transducer 50 (and / or transducer 52), thereby deriving the rotational position of the ultrasound transducer 50 (and / or transducer 52) relative to the expandable cage 30.

[0152] Additionally or alternatively, any other type of one or more sensors located on the distal portion of the shaft, on the expandable cage 30, and / or on the ultrasonic transducer 50 can be used to determine the rotational position of the distal portion of the elongate shaft. For example, a first magnetic coil can be coupled to the distal portion of the shaft and / or the ultrasonic transducer 50 (and / or the transducer 52) such that the rotational position of the first magnetic coil changes as the rotational position of the ultrasonic transducer 50 (and / or the transducer 52) changes. A second magnetic coil can be coupled to the cage such that the rotational position of the second magnetic coil remains constant as the ultrasonic transducer 50 (and / or the transducer 52) rotates. Additionally or alternatively, a second magnetic coil can be coupled to the distal portion of the shaft such that the rotational position of the second magnetic coil remains constant as the ultrasonic transducer 50 (and / or the transducer 52) rotates. By measuring the change in magnetic flux between the first and second coils, the rotational position of the ultrasound transducer 50 (and / or transducer 52) is derived.

[0153] As described above, both the expandable cage 30 and the ultrasound transducer 50 are disposed at the distal end of the elongate shaft of the transluminal ablation catheter 40. Although the expandable cage 30 is coupled to the shaft, the expandable cage 30 expands and remains stationary during rotation of the distal portion of the shaft and the ultrasound transducer 50. (Because there is limited space for the expandable cage 30 to rotate within the lumen, the expandable cage 30 is typically unable to rotate. Thus, attempts to rotate the expandable cage 30 would likely prevent rotation of the ultrasound transducer 50.) To maintain the expandable cage 30 stationary during rotation of the elongate shaft, in some applications, the device 20 includes a rotational force reduction mechanism for reducing the rotational force applied to the expandable cage 30 by the elongate shaft as the elongate shaft rotates, thereby keeping the expandable cage 30 stationary during rotation of the ultrasound transducer 50.

[0154] Reference is now made to Figures 4A through 4F, which are schematic illustrations of components of a rotational force reduction mechanism 200 configured to reduce the rotational force applied to the expandable cage 30 by the elongate shaft 42 of the transluminal ablation catheter 40 upon rotation of the elongate shaft 42. The components of the rotational force reduction mechanism 200 are typically disposed at a distal portion of the elongate shaft 42 and, similar to a swivel mechanism, allow rotation of the ultrasound transducer 50 while keeping the expandable cage 30 stationary. In some such applications, the elongate shaft 42 includes an inner elongate shaft 42I and an outer elongate shaft 42O. Typically, the proximal end of the expandable cage 30 is coupled to the outer elongate shaft 42O. More typically, the ultrasonic transducer 50 is disposed on the inner elongate shaft 42I, and rotation is transmitted to the ultrasonic transducer via rotation of the inner elongate shaft 42I within the outer elongate shaft 42O (i.e., the inner elongate shaft 42I rotates within the outer elongate shaft 42O, and the outer elongate shaft remains rotationally stationary).

[0155] For some applications, the rotational force reduction mechanism 200 includes a swivel bearing 44, a bearing stopper 46, and a distal tip cover 45 (FIGS. 4B, 4C, 4D, 4E, and 4F). Typically, the swivel bearing includes a narrow proximal portion 44A and a wider distal portion 44B having a larger diameter than the proximal portion. The swivel bearing 44 is typically coupled to a distal portion of the inner elongate shaft 42I (FIG. 4B) to rotate with the elongate shaft 42I. The bearing stopper 46 is positioned to surround the narrow proximal portion of the swivel bearing 44, such that the wider distal portion of the swivel bearing is positioned distal to the bearing stopper. The diameter of the distal widened portion of the swivel bearing is typically larger than the lumen defined by the bearing stopper, so that the distal widened portion of the swivel bearing prevents the swivel bearing from being pulled proximally against the bearing stopper. A distal tip cover 45 typically covers the distal widened portion 44B of the swivel bearing. The bearing stopper and distal tip cover are configured to allow continuous, smooth rotation of the swivel bearing (thereby allowing continuous, smooth rotation of the elongate shaft) while being held rotationally stationary.

[0156] Typically, the expandable cage 30 is prevented from rotating by (a) coupling the proximal end of the cage to the outer elongate shaft 42O and (b) contacting the cage itself with the target tissue, as described above. The distal portion of the cage (e.g., the cage distal ring 48) is typically coupled to a bearing stop 46, which applies a torsional force to the bearing stop that prevents rotation of the bearing stop. The bearing stop typically allows the swivel bearing 44 to rotate freely within the bearing stop, allowing the inner elongate shaft 42I to continue to rotate and isolating the rotational movement of the inner elongate shaft from the cage, preventing torsional forces from being applied to the cage 30.

[0157] The swivel bearing 44 typically allows for rotation of the elongate shaft 42 while allowing the expandable cage 30 to expand and collapse at the distal end of the elongate shaft 42. As mentioned above, the proximal end of the expandable cage 30 is typically coupled to the outer elongate shaft 42O. More typically, to radially expand the cage, the distal end of the inner elongate shaft 42I is pulled proximally toward the outer elongate shaft 42O, thereby pulling the distal end of the cage proximally toward the proximal end of the cage. The wide distal portion 44B typically transfers proximal movement of the distal end of the inner elongate shaft to the bearing stop, which in turn transfers proximal movement to the distal end of the cage, thereby pulling the distal end of the cage toward the proximal end of the cage, shortening it axially and expanding it radially. Typically, to radially contract the cage, the distal end of the inner elongate shaft 42I is pushed distally, away from the outer elongate shaft 42O, thereby pushing the distal end of the cage distally, away from the proximal end of the cage. The wide distal portion 44B typically transfers the distal motion of the distal end of the inner elongate shaft to the distal tip cover 45, which in turn transfers the distal motion to the bearing stop and the distal end of the cage, thereby pushing the distal end of the cage away from the proximal end of the cage, lengthening the cage axially and contracting it radially.

[0158] Thus, the rotational force reduction mechanism 200 is configured, on the one hand, to couple the axial movement of the inner elongate shaft 42I with the axial movement of the distal end of the cage 30, and, on the other hand, to decouple the rotational movement of the inner elongate shaft 42I from the rotational movement of the distal end of the cage 30.

[0159] FIG. 4F is a cross-sectional view of components of a rotational force reduction mechanism 200 assembled with the device 20 to prevent rotation of the expandable cage 30 during rotation of the ultrasonic transducer 50, as described above with reference to FIGS. 4A-4E.

[0160] Reference is now made to Figures 5A, 5B, and 5C, which are schematic illustrations of a curved piezoelectric ultrasonic transducer 150 and its ultrasonic energy transmission profile, according to certain applications of the present invention. Reference is also made to Figure 5D, which is a graph illustrating the effect of various radii of curvature and lengths of the piezoelectric ultrasonic transducer 150 on the radiation angle of the piezoelectric ultrasonic transducer 150, according to certain applications of the present invention.

[0161] As shown in Figure 5A, in some applications, the ultrasonic transducer 50 includes a curved piezoelectric ultrasonic transducer 150. Figure 5A shows a cross section of the curved piezoelectric ultrasonic transducer 150 disposed within a transducer housing encapsulation layer 154, suspended above an air barrier 80, near a cooling channel 156.

[0162] The piezoelectric ultrasonic transducer 150 is shaped to define a convex surface 152 facing outward from the longitudinal axis of the transducer, with the convex surface having a radius of curvature between 0.75 and 5 mm. Typically, the piezoelectric ultrasonic transducer 150 is configured to ablate tissue (e.g., at the ostium of a vein) by applying ultrasonic energy to the tissue (e.g., at the ostium of a vein) through the convex surface. Typically, the curvature of the transducer 150 increases the area affected by the ultrasonic energy (compared to using a flat transducer), allowing for faster and / or more efficient ablation procedures.

[0163] In some applications, the width of the ultrasonic transducer 150 is 0.5 to 3 mm (e.g., 1 to 2 mm) and the thickness is 0.1 to 0.3 mm. In some applications, the radius of curvature of the piezoelectric ultrasonic transducer 150 is 0.75 to 5 mm, for example, 1 to 3 mm, for example, 1.5 to 2 mm.

[0164] 5B and 5C show the thermal profile (FIG. 5B) and pressure profile (FIG. 5C) in a pulmonary vein when ablation is performed using a curved piezoelectric ultrasound transducer 150 in accordance with some applications of the present invention. Typically, providing a curved piezoelectric ultrasound transducer 150 can expand the tissue thermal profile so that a larger portion of the tissue is more effectively heated, facilitating effective and rapid tissue ablation. In some instances, using a curved piezoelectric ultrasound transducer 150, the tissue area heated is at least twice as large as when applying the same power parameters using a flat piezoelectric ultrasound transducer of the same width, length, and thickness. As shown in FIG. 5B, providing a piezoelectric ultrasound transducer 150 with a 2 mm radius of curvature and a 1.5 mm width resulted in a 28-degree radiation angle and a generally uniform tissue thermal profile, generally without side lobes (indicating a generally homogeneous lesion).

[0165] The graph in FIG. 5D shows the effect of the radius of curvature and surface width of the piezoelectric ultrasonic transducer 150 on the emission angle of the piezoelectric ultrasonic transducer 150, according to some applications of the present invention. In FIG. 5D, line 101 shows the effect of the radius of curvature on the emission angle using a piezoelectric ultrasonic transducer with a surface width of 1 mm. Line 102 shows the effect of the radius of curvature on the emission angle using a piezoelectric ultrasonic transducer with a surface width of 1.5 mm. Line 103 shows the effect of the radius of curvature on the emission angle using a piezoelectric ultrasonic transducer with a surface width of 2 mm. As shown, by providing an ultrasonic transducer 150 with a radius of curvature of 1.5-2 mm and a surface width of 1.5 mm, a emission angle of 28 degrees was obtained (shown by line 102).

[0166] Referring again to Figures 1A-5A and further to Figure 6, in some applications, a sensor in operative communication with (e.g., coupled to) the transluminal ablation catheter 40 is used to detect changes in blood flow between a lumen extending from a target heart chamber and the heart chamber (e.g., changes in blood flow between a pulmonary vein and an atrium) to indicate a connection point between the lumen and the heart chamber, thereby indicating the location of the lumen ostium. Typically, changes in blood flow can be detected when blood passes through a lumen ostium and enters a heart chamber (e.g., a pulmonary vein ostium and an atrium). Based on the detected changes in blood flow, the computer processor 26 is configured to determine an optimal tissue target site for ablation (e.g., a lumen ostium) and drive the ultrasound transducers 50 and / or 150 to deliver ultrasound energy to the optimal tissue target.

[0167] For some applications, the sensor includes a Doppler ultrasound device for sensing blood flow and detecting changes in blood flow patterns. Additionally or alternatively, transluminal ablation catheter 40 further includes an actuator configured to adjust the position of ultrasound transducers 50 and / or 150 in response to detected changes in blood flow so that the transmitted ultrasound energy is applied to an optimal tissue target site.

[0168] 6 is a flowchart illustrating method steps performed in response to detecting a change in blood flow, according to some applications of the present invention. In some applications, ultrasound transducer 50 and / or 150 is advanced into the atrium of the subject (step 310), changes in blood flow are detected near the ultrasound transducer to determine the location of the pulmonary vein relative to the atrium (step 320), and in response to the location determination, ultrasound transducer 50 and / or 150 is activated to ablate tissue at the pulmonary vein ostium (step 340). Optionally, the position of ultrasound transducer 50 and / or 150 is adjusted in response to the location determination (step 330) before activating the ultrasound transducer (step 340).

[0169] In some applications, position data derived from blood flow changes detected by Doppler ultrasound is used in combination with three-dimensional image data of the atria and pulmonary vein ostia to ascertain the location of the pulmonary vein ostia relative to the atria.

[0170] According to some applications of the present invention, any type of acoustic indication can be used to detect changes in blood flow patterns between the atria and the pulmonary veins and indicate the location of the pulmonary vein ostium, which is typically the desired ablation site. For example, any one of the ultrasound transducers 50, 52, and / or 150 described herein can be used to detect changes in blood flow patterns between the atria and the pulmonary veins.

[0171] Referring again to Figures 1A through 6, as described above, device 20 is configured to perform acoustic sensing in addition to tissue ablation and imaging of myocardial tissue.

[0172] For example, before transmitting ultrasonic energy for ablation purposes, device 20 is configured to assess, by acoustic sensing, whether ultrasonic transducer 50 is optimally positioned relative to the target tissue designated for ablation, and accordingly apply ablation energy to the tissue or adjust the position of ultrasonic transducer 50 and / or adjust the energy level applied to the tissue.

[0173] In some applications, the device 20 (particularly the ultrasound transducer 50 / 52 / 150 of the device 20) is configured to transmit low-intensity, non-ablative ultrasound energy to confirm proper positioning of the ultrasound transducer. In some applications, the device 20 assesses proper positioning of the ultrasound transducer 50 / 52 / 150 relative to the target tissue by assessing parameters of ultrasound echoes received by the transducer. For example, the device 20 assesses proper positioning of the ultrasound transducer 50 / 52 / 150 relative to the target tissue by measuring the amplitude (i.e., the energy level of the echo) of the ultrasound echoes received by the transducer. If the ultrasound transducer 50 / 52 / 150 is mispositioned relative to the tissue, the echo amplitude will be low (because the delivered energy is dispersed and improperly directed due to the angulation of the sound field relative to the tissue, creating a large contact area and therefore a low energy density), whereas if the ultrasound transducer 50 / 52 / 150 is properly positioned relative to the target tissue, the echo amplitude will be increased. Typically, in response to assessing that the ultrasound transducer 50 / 52 / 150 is in the desired position, the ultrasound transducer is activated to ablate the tissue. Alternatively, the energy level applied to the tissue is adjusted to compensate for non-optimal positioning of the ultrasound transducer 50 / 52 / 150. Alternatively, the position of the ultrasound transducer 50 / 52 / 150 is adjusted to more appropriately target the tissue.

[0174] Additionally or alternatively, when ablation energy is applied to form a lesion in tissue, ablation can be monitored by measuring the amplitude of return ultrasound echoes received by the transducer from the target tissue, where an increase in return ultrasound indicates a properly shaped lesion in the tissue, since the ultrasound energy does not transmit through the lesion.

[0175] Additionally or alternatively, measurements of the amplitude (or other parameters) of ultrasound echoes returning from various tissue depths are used to compare and assess changes (e.g., lesion formation) along the tissue depth. In some applications, a graphical representation of the returned ultrasound echoes is displayed. For example, a graphical representation (e.g., 0.1-0.3 mm resolution) can be presented in which each depth interval is assigned a color pixel indicating the extent of ablation that has occurred at each depth interval.

[0176] Continuing with reference to Figures 1A through 6, it should be noted that, according to some applications of the present invention, device 20 may be used to treat types of cardiac arrhythmias other than atrial fibrillation. For example, device 20 may be used to treat disorders such as ventricular tachycardia. In such applications, device 20 is advanced into a subject's cardiac chamber and ultrasonic energy is applied in accordance with applications of the present invention to ablate tissue in the chamber, thereby creating a lesion.

[0177] Furthermore, it should be noted that the application of ultrasonic energy to a myocardial site is not limited to vascular ostia, but may be applied to any region of the heart involved in inducing or maintaining cardiac arrhythmias.

[0178] Furthermore, while much of the description herein relates to cardiac tissue, and in particular to the left atrium and the pulmonary veins extending from the left atrium, it should be noted that the scope of the present invention includes the use of the devices and methods described herein with other lumens within the body ("lumen" generally refers to an internal open space, i.e., cavity, within an organ of a subject, which may, but is not necessarily, a tubular organ). For example, the devices and methods described herein may be used mutatis mutandis with the arteries, veins, intestines, heart, sacs, sinuses, stomach, lungs, pulmonary vasculature, airways, or genitourinary tract of a subject.

[0179] It should be noted that the devices and methods described herein may also be used, mutatis mutandis, to treat other tissues of interest for treatment, including renal denervation, targeted pulmonary denervation, pulmonary hypertension denervation, visceral nerve denervation, carotid body denervation, cancerous pulmonary nodule ablation, hypertrophic cardiomyopathy ablation, and / or hepatic artery denervation.

[0180] For some applications, the ultrasound energy application techniques described herein are performed in combination with other types of ablation, such as pulsed field ablation (PFA) and / or radiofrequency (RF) ablation. For some applications, other suitable energy sources (e.g., RF energy, laser energy, cryogenic energy, and / or electromagnetic energy, such as ultraviolet and / or infrared light) are used instead of or in addition to ultrasound ablation.

[0181] Those skilled in the art will recognize that the present invention is not limited to what has been particularly shown and described above. The scope of the present invention includes both combinations and subcombinations of the various features described above, as well as variations and modifications that would occur to one skilled in the art upon reading the foregoing description and that are not present in the prior art.

Claims

1. 1. An apparatus for use with tissue of a subject, comprising:

1. A transluminal ablation catheter comprising: at least one ultrasound transducer configured for insertion into a cardiac chamber of the subject; a computer processor configured to drive the at least one ultrasound transducer to (a) ablate tissue by applying ultrasound energy to the tissue of the target, and (b) image the tissue by applying non-ablative ultrasound energy to the tissue of the target; a fixation element configured to be disposed around the at least one ultrasonic transducer; and wherein the computer processor is configured to drive the at least one ultrasound transducer to rotate and translate axially back and forth within the fixation element to generate a three-dimensional image of the tissue.

2. 2. The apparatus of claim 1, wherein the at least one ultrasound transducer is configured for insertion into the left atrium near a pulmonary vein ostium and configured to electrically isolate the pulmonary vein by ablating tissue at the pulmonary vein ostium.

3. 2. The device of claim 1, wherein the tissue includes tissue at an ostium of a lumen extending from the heart chamber of the subject, and the ultrasound transducer is configured to generate a three-dimensional image of the tissue at the ostium of the lumen by applying non-ablative ultrasound energy to the tissue at the ostium of the lumen.

4. The apparatus of claim 1 , wherein the at least one ultrasonic transducer is configured to generate ultrasonic energy at a frequency between 8 and 20 MHz.

5. 10. The apparatus of claim 1, wherein the at least one ultrasonic transducer is shaped to define a convex surface facing outwardly from a longitudinal axis of the transducer and has a width of 0.5 to 3 mm and a radius of curvature of 0.75 to 5 mm.

6. 6. The device of claim 1, wherein the transluminal ablation catheter comprises an elongate shaft including a proximal portion including a handle and a distal portion having the at least one ultrasound transducer coupled thereto.

7. 7. The device of claim 6, wherein the elongate shaft is rotatably configured to rotate the ultrasound transducer, and the transluminal ablation catheter comprises one or more sensors coupled to the distal portion of the elongate shaft and configured to detect a rotational position of the distal portion of the elongate shaft.

8. the elongate shaft is rotatably configured to rotate the ultrasonic transducer; 7. The device of claim 6, wherein the transluminal ablation catheter further comprises a rotational force reduction mechanism configured to reduce a rotational force applied to the expandable cage by the elongate shaft as the elongate shaft rotates so as to keep the expandable cage stationary during rotation of the ultrasound transducer.

9. the at least one ultrasound transducer is configured to apply the non-ablative ultrasound energy to the tissue, such that at least a portion of the non-ablative ultrasound energy is reflected and received by the ultrasound transducer; the computer processor is configured to assess parameters of the reflected energy to determine parameters of the ultrasonic energy applied by the ultrasonic transducer to ablate the tissue; The apparatus of claim 1 , wherein the at least one ultrasonic transducer is configured to apply the ultrasonic energy to the tissue based on the determined parameters.

10. The at least one ultrasonic transducer comprises: a first ultrasonic transducer configured to transmit ablative ultrasonic energy toward the tissue of the subject, thereby ablating the tissue; a second ultrasonic transducer configured to image the tissue of the subject by transmitting one or more pulses of pulse-echo ultrasonic energy toward the tissue of the subject and receiving reflections of the transmitted pulse-echo ultrasonic energy, 6. The apparatus of claim 1, wherein a transducer is configured to rotate and translate axially back and forth within the fixation element to generate a three-dimensional image of the tissue.

11. The transluminal ablation catheter comprises: a first support configured to support the first ultrasonic transducer and enable transmission of the ablative ultrasonic energy towards the tissue; a second attenuation support configured to support the second ultrasonic transducer and provide a higher level of attenuation than that provided by the first support such that the second ultrasonic transducer can receive the reflection of the transmitted pulse-echo ultrasonic energy while the first ultrasonic transducer transmits the ablative ultrasonic energy toward the tissue; The apparatus of claim 10 , comprising:

12. the first support includes an air barrier configured to permit vibration of the first ultrasonic transducer during transmission of the ablative ultrasonic energy towards the tissue; The apparatus of claim 11 , wherein the second ultrasonic attenuation support comprises a mechanical support including at least one of a backing layer and an attenuation element.

13. The device described in claim 1, wherein the fixation element is an expandable cage.

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