Patent Publication Number: US-2021177512-A1

Title: Systems and methods for perivascular nerve denervation

Description:
STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR 
     Applicant designates the following article as a grace period publication in order to expedite examination of the application in accordance with 37 CFR 1.77(b)(6) and MPEP 608.01(a): “Laparoscopic Renal Denervation System for Treating Resistant Hypertension: Overcoming Limitations of Catheter-based Approaches” published in IEEE Transactions on Biomedical Engineering on Apr. 20, 2020 (early access). The disclosures of the article are incorporated herein by reference in their entirety for all purposes. 
     CROSS-REFERENCE TO RELATED APPLICATION 
     This Application is a continuation-in-part of U.S Pat. No. 16/239,718 filed on Jan. 4, 2019, which is a continuation-in-part of U.S Pat. No. 15/258,167 filed on Sep. 7, 2016, all which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to perivascular nerve  10  denervation in an autonomic nerve system, and more particularly to catheter apparatus for perivascular nerve denervation to reduce a nerve activity. 
     BACKGROUND 
     High blood pressure is often difficult to control. Resistant hypertension is defined as a blood pressure that remains above goal despite the concomitant use of full doses of three or more antihypertensive drugs from different classes. One approach to treat patients with resistant hypertension is renal denervation for blocking sympathetic nerve around the renal artery of the patients. 
     Recently, it has been reported that renal denervation for blocking sympathetic nerve around the renal artery using percutaneous catheter can be effective for lowering blood pressure in patients with resistant hypertension. Besides, this renal denervation strategy has gained attention for the usefulness in the treatment of patients with arrhythmia and cardiac failure. 
     However, in the existing approaches for performing renal denervation, it is difficult to destruct effectively renal nerves since most of the renal nerves are distributed far away from the intima of renal artery and the conventional percutaneous catheters are designed to destruct the renal nerves from inner side of the renal artery. Also, the conventional percutaneous catheters may severely damage the intima of the renal artery as well as the adventitia of the renal artery and, in some cases, may cause angiostenosis. 
     Therefore, there is a need for new catheters that can help the physicians effectively destruct the renal nerves for performing renal denervation without damaging the renal artery and nearby organs/tissues. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides a catheter apparatus for perivascular nerve denervation that effectively and completely destruct a circumferential tissue of vascular (e.g., artery), such as renal artery nerves, hepatic artery nerves, splenic artery nerves and pulmonary artery nerves. 
     In accordance with one aspect of the present disclosure, the catheter apparatus for perivascular nerve denervation includes: a shaft having a distal end; and a loop disposed near the distal end and configured to curl around a tissue and receive, via the shaft, energy to denervate at least a portion of the tissue, wherein the loop includes: a first film capable of bending to curl around the tissue and a plurality of electrodes disposed on the first film and made of a two-way shape-memory alloy. 
     In accordance with another aspect of the present disclosure, a method for perivascular nerve denervation using a catheter apparatus includes: positioning a loop near a tissue; causing the loop to curl at a first curvature at a temperature above a first transformation temperature as a plurality of electrodes is heated to a first transformation temperature by body temperature; delivering energy to the plurality of electrodes, thereby to cause the plurality of electrodes to convert the energy into heat energy; causing the loop to curl at a second curvature at a temperature above a second transformation temperature as the plurality of electrodes is heated to the second transformation temperature by the heat energy; and denervating at least the portion of a tissue using the heat energy. The catheter apparatus includes a shaft having a distal end and the loop disposed near the distal end and configured to curl around the tissue and receive, via the shaft, the energy to denervate at least a portion of the tissue. The loop includes a first film capable of bending to curl around the tissue and the plurality of electrodes disposed on the first film and made of a two-way shape-memory alloy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features and advantages of the present disclosure will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates anatomy of a human kidney. 
         FIG. 2A  is a schematic diagram of human renal nerves and renal artery. 
         FIG. 2B  is a cross sectional view of human renal artery and renal nerves. 
         FIG. 3  is a schematic block diagram of a catheter system for renal denervation according to embodiments of the present invention. 
         FIG. 4  is a side elevational view of a catheter according to embodiments of the present invention. 
         FIG. 5  illustrates an exemplary operation of a catheter according to embodiments of the present invention. 
         FIG. 6A  illustrates a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 6B  illustrates a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 6C  illustrates a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 6D  illustrates a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 7A  illustrates a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 7B  illustrates a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 7C  illustrates a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 7D  illustrates a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 8  is a schematic diagram of a catheter, illustrating renal denervation using the catheter according to embodiments of the present invention. 
         FIG. 9  is a flow chart illustrating exemplary steps that may be carried out to denervate renal nerves according to embodiments of the present invention. 
         FIG. 10  is a perspective view of a distal end portion of the catheter in  FIG. 4  according to embodiments of the present invention. 
         FIG. 11A  shows the loop in  FIG. 10  at a temperature below a critical temperature. 
         FIG. 11B  shows the loop in  FIG. 10  at a temperature above the critical temperature. 
         FIG. 12  shows a deformation of a substrate in response to a temperature change according to embodiments of the present invention. 
         FIG. 13  illustrate a loop of the catheter in  FIG. 4  according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the present disclosure are described with reference to the accompanying drawings in detail. The same reference numbers are used throughout the drawings to refer to the same or like parts. Detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present disclosure. 
     Components, or nodes, shown in diagrams are illustrative of exemplary embodiments of the invention and are meant to avoid obscuring the invention. It shall also be understood that throughout this discussion that components may be described as separate functional units, which may comprise sub-units, but those skilled in the art will recognize that various components, or portions thereof, may be divided into separate components or may be integrated together, including integrated within a single system or component. 
     Reference in the specification to “one embodiment,” “preferred embodiment,” “an embodiment,” or “embodiments” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention and may be in more than one embodiment. The appearances of the phrases “in one embodiment,” “in an embodiment,” or “in embodiments” in various places in the specification are not necessarily all referring to the same embodiment or embodiments. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. 
     In the present disclosure, the terms such as “include” and/or “have” may be construed to denote a certain characteristic, number, step, operation, constituent element, component or a combination thereof, but may not be construed to exclude the existence of or a possibility of addition of one or more other characteristics, numbers, steps, operations, constituent elements, components or combinations thereof. 
     Several embodiments of the present disclosure described herein relate generally to apparatus, systems and methods for therapeutically effecting neuromodulation (e.g., nerve disruption, nerve denervation, nerve stimulation) of target nerve to treat various medical conditions, disorders and diseases. In embodiments, neuromodulation of the target nerve may be used to treat or reduce the risk of occurrence of symptoms associated with a variety of metabolic diseases. For example, neuromodulation of the target nerve may treat or reduce the risk of occurrence of symptoms associated with hypertension or other hypertension-related diseases, diabetes or other diabetes-related disease. If human patient has a vascular diseases, such as hypertension, the methods described herein may advantageously treat hypertension without taking hypertension drugs and if human patient has diabetes mellitus, the methods described herein may advantageously treat diabetes without requiring daily insulin injection or constant monitoring of blood glucose levels. The treatment provided by the apparatus, systems and methods described herein may be permanent or at least semi-permanent, thereby reducing the need for continued or periodic treatment. 
     In embodiments, neuromodulation of the target nerve as described herein may be used for the treatment of insulin resistance, genetic metabolic syndromes, ventricular tachycardia, atrial fibrillation or flutter, arrhythmia, inflammatory diseases, hypertension, obesity, hyperglycemia, hyperlipidemia, eating disorders, and/or endocrine diseases. 
     The neuromodulation of the target nerve is not limited to the disease treatment described above and can be used to treat other suitable types of diseases that one skilled in the art appreciates or recognizes. 
       FIG. 1  illustrates a common human renal anatomy. As depicted, the kidneys K are supplied with oxygenated blood by renal arteries RA, which are connected to the heart by the abdominal aorta AA. Deoxygenated blood flows from the kidneys to the heart via renal veins RV and the inferior vena cava IVC. 
       FIG. 2A  illustrates a portion of human renal artery 
     RA and renal nerves RN.  FIG. 2B  illustrates a cross-sectional view taken along the radial plane A-A of  FIG. 2A . 
     As depicted, the renal artery RA has a lumen through which the blood B flows. The renal nerves RN are located in proximity to the adventitia of the renal artery ARA and run along the renal artery RA in a lengthwise direction L. More specifically, renal nerves RN are situated in a circumferential tissue  5  surrounding the outer wall of the renal artery RA and the circumferential tissue  5  may include other tissue, such as lymphatics and capillaries. 
     In the conventional approaches based on applying denervation energy to destroy the renal nerves RN, a catheter is inserted into the lumen and delivers heat energy to denervate the target renal nerves RN. During this process, the denervation energy may damage the adventitia ARA of renal artery RA before it reaches the renal nerves RN. Furthermore, a portion of the denervation energy may be absorbed by the adventitia of the renal artery ARA, reducing the efficiency in utilizing the energy. Accordingly, it may be more effective and safer to denervate from outside of the renal artery RA (i.e., apply energy from outside of RA) than to denervate from inside of the renal artery RA (i.e., apply energy from inside of RA). 
       FIG. 3  is a schematic block diagram of a catheter system  300  for renal denervation according to embodiments of the present invention. As depicted, the catheter system  300  includes: a catheter apparatus  100  having a distal portion  11  which may make a contact with a target tissue and/or be disposed in proximity to the target tissue for treatment; a control unit  200  for controlling one or more components of the system  300 ; an energy source generator (ESG)  205  for supplying energy to the target tissue through the distal portion  11  of the catheter apparatus  100 ; an imaging system  207  for processing visual images and displaying the images to the users; and wires/cables/buses  204  that connect the components of the system  300  to each other for communication. In the present disclosure, the target tissue is described as the renal artery nerves, but it should be apparent to those of ordinary skill in the art that the target tissue means various artery nerves, such as renal artery nerves, hepatic artery nerves, splenic artery nerves and pulmonary artery nerves 
     The control unit  200  may collectively refer to one or more components for controlling various components of the catheter system  300 . In embodiments, the control unit  200  may include a digital signal processor (DSP)  201 , such as CPU, and a memory  203 . The memory  203  may store various data and include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD-ROMs and holographic devices; magneto-optical media; and hardware devices that are specially configured to store or to store and execute program code, such as application specific integrated circuits (ASICs), programmable logic devices (PLDs), flash memory devices, and ROM and RAM devices. 
     In embodiments, a data logger  224  may be included in the memory  203  and store data (e.g., temperature of the target tissue) measured by the catheter  100  during the denervation procedure. It is note that the memory  203  may be located outside the control unit  200  and coupled to the control unit  200  via a wire/cable  204 . 
     It is noted that the control unit  200  may be a computer, a server, or any other suitable computing facility and include other components, such as printer, input device (such as keyboard and mouse), scanner, display device, and a network interface. 
     In embodiments, the distal portion  11  may include denervation element(s) and optionally an endoscope or some other type of imaging device, coupled to an imaging system  207 , to provide images of the target tissue using suitable imaging techniques. The imaging device may allow the operator/physician to visually identify the region being ablated/denervated, to monitor the progress of the ablation/denervation in real time, and to address safety concerns during operation. 
       FIG. 4  is a side elevational view of a catheter apparatus  100  according to embodiments of the present invention. As depicted, the catheter apparatus  100  comprises a shaft  10 , a loop  20 , a holder  30 , a slider  35 , a butt  50 , a handle  70  and a loop control  90 . 
     The shaft  10  has a proximal end  13  coupled to the holder  30  and a distal end  15  removably connected to the distal portion  11  of the catheter apparatus  100 . The shaft  10  has a shape of tube, forming a channel that extends from the proximal end  13  to the distal end  15 , and is dimensioned to allow a stylet and/or a wire(s) to pass therethrough. The distal portion  11  may form a passage through which the loop  20  travels, as explained in detail below. 
     In embodiments, the shaft  10  may be made of silicone, polyurethane (PU), Pebax, or a combination of PU and silicone, or some other biocompatible polymers and/ or metallic materials. The shaft  10  may be sufficiently large enough to house an imaging device, such as an endoscope, as well as components for ablation/denervation. In embodiments, the shaft  10  may include electrical wires/cables that run from the energy source generator  204  to the electrodes on the loop  20 . In embodiments, the shaft  10  may include wires/cables for providing electrical energy to the endoscope and transmitting visual images from the endoscope to the control unit  200 . In embodiments, the shaft  10  may be dimensioned to provide safe and easy treatment of the target tissue with minimal percutaneous access site on the patient, for example, on the abdominal region. 
     In embodiments, the loop  20  may be removably coupled to the distal end  15  of the shaft  10  and mechanically connected to the shaft  10 . 
     The holder  30  is connected to the proximal end  13  of the shaft  10 . More specifically, the holder  30  may have a structure for accepting the proximal end  13  of the shaft  10  therein and be electrically coupled to the proximal end  13 . In embodiments, a slider  35  may be rotatably coupled to the holder  30  and the operator may rotate the slider  35  to engage (or disengage) the shaft  10  to (or from) the holder  30 . 
     In embodiments, the holder  30  may include the butt  50  and a terminal  51  disposed on one side of the butt  50 . The terminal  51  may receive various types of energy from the energy source generator  205  via the wire/cable  204  and the energy is delivered from the terminal  51  to the loop  20  via suitable wires/cables running through the shaft  10 . In embodiments, the energy may be, but not limited to, at least one of a radio-frequency (RF) energy, electrical energy, laser energy, ultrasonic energy, high-intensity focused ultrasound (HIFU) energy, cryogenic energy, and thermal energy. Energy may be delivered to the loop  20 , simultaneously or sequentially, or selectively. For selective delivery, a clinician can select, via a user interface of the energy source generator  205 , such as an RF generator, a specific electrode to be utilized in the denervation process, where the electrode is disposed in the loop  20 . 
     The handle  70  may extend from the butt  50 . The handle may have a vacant space (hole) into which the operator may insert his finger(s) to have a firm grip of the holder  30 . 
     A push-button  61  may be disposed on another side of the butt  50  or one side of the handle  70 . The push-button  61  is operated by the operator to control the energy flow to the loop  20 . 
     The loop control  90  may be hinged on the butt  50  or the handle  70 . The loop control  90  may also have a vacant space (hole) in which the operator&#39;s thumb can be inserted. As described below, the operator may control the loop control  90  to coil/uncoil the loop  20 . 
       FIG. 5  illustrates an example of an operation of a catheter according to an embodiment of the present invention. As shown in the  FIG. 5 , the slider  35  may be rotated up to about 360 degrees about the longitudinal axis A of the shaft  10 . A rotational direction of the slider  35  may be bidirectional or unidirectional. As the slider  35  rotates, as indicated by the arrows  92 , the loop  20  may also rotate around the longitudinal axis A of the shaft  10 , as indicated by the arrows  90 . Thus, a rotation of the loop  20  about the longitudinal axis of the shaft  10  may be controlled by the rotation of the slider  35 . 
     In embodiments, when moved forward/backward (or upward/downward) by the operator&#39;s finger, as indicated by arrows  94 , the loop control  90  mechanically controls the loop  20 , where the loop control  90  may be designed to operate in various modes. In one mode, as the loop control  90  moves forward (or downward), the loop  20 , which is originally rolled, may be unrolled to a straight segment and extend along the longitudinal axis A of the shaft  10 . As the loop control  90  moves backward (or upward), the loop  20  is rolled to its original shape. In this mode, the operator may bring the loop  20  near the target tissue or renal artery RA and move the loop control  90  backward to curl the loop  20  around the target tissue or renal artery RA. 
     In another mode, the loop  20  may be retracted into the shaft  10 . As the loop control  90  is moved forward (or downward), the loop  20  may emerge from the distal portion  11  and become a straight segment or curl into a semi-circle. As the loop control  90  is moved backward (or upward), the loop  20  may curl around the target tissue or renal artery RA. 
       FIG. 6A  to  FIG. 6D  show a loop that curls as it emerges from the shaft  10  of the catheter apparatus according to embodiments of the present invention. As depicted, the loop  20  includes a body  21  and one or more electrodes  23  disposed on the body  21 . The loop  20  may remain inside the shaft  10  and distal portion  11  (retracted position) when the loop control  90  is in the neutral position. As the operator moves the loop control  90  forward (or downward), the loop emerges from the distal portion  11 , forming a curved segment. As depicted in  FIG. 6A to 6D , the loop  20  curls as the tip of the loop  20  proceeds from the position  60  toward the position  64 . 
     In embodiments, the body  21  may be made of a flexible material. In embodiments, the body  21  may be made of thermally non-conductive elastic material so that the energy delivered to the electrodes  23  is localized only to a portion(s) of the tissue that the electrodes  23  contact. As the localized energy is used to denervate the renal nerves RN (shown in  FIG. 3 ), the potential damage caused by the loop  20  to the tissue nearby the renal nerves RN may be significantly reduced during operation. 
     In embodiments, the loop  20  may be flexible and deformable to curl around a renal artery as discussed in conjunction with  FIG. 8 . The loop  20  may be designed for two different operational modes. In the first mode, the loop  20  may remain flat when the loop  20  is brought into proximity to the target tissue, such as the circumferential tissue  5  of the renal artery. Then, the operator may manipulate the loop control  90  to curl the loop  20  around the circumferential tissue  5  and perform denervation. Upon completing the denervation, the operator may release the loop control  90  to uncurl loop  20 . In the second mode, the loop  20  may remain curled when the distal portion  11  is brought into proximity to the target tissue. Then, the operator may manipulate the loop control  90  to uncurl the loop  20 , position the loop  20  around the target tissue, release the loop control  90  to curl the loop  20  around the renal artery and perform denervation. 
     In embodiments, the electrodes  23  may be disposed on the inner side of the body  21  so that the electrodes  23  may contact the circumferential tissue  5  when the loop  20  curls around the circumferential tissue  5 . In embodiments, the electrodes  23  may extend along the longitudinal direction of the body  21  and be arranged in parallel to each other. In one embodiment, the body  21  may be formed of dielectric material and the electrodes  23  may be formed on the inner surface of the body  21 . In embodiments, the body  21  may have a groove or a channel on the inner surface of the body  21  and the electrodes  23  may be formed by filling electrically conductive material in the groove or the channel. 
     In another embodiment, the body  21  may be formed of electrically conducting material and the entire surface of the body  21  may be covered with dielectric material except the location where the electrodes  23  are to be located. In embodiments, a dielectric body may be disposed between the two electrodes  23  to electrically isolate the electrodes  23  from each other. 
     In embodiments, the electrodes  23  may be formed of electrically-conductive elastic material so that they can deform along with the body  21  as the body  21  is curled/uncurled. In embodiments, the electrodes  23  may contact the circumferential tissue  5  surrounding the outer surface of the renal artery and generate heat energy when electrical energy, such as RF energy, is supplied, where the heat energy may be used to denervate the renal nerve RN. 
     In  FIG. 6A to 6D , only two electrodes  23  are shown. However, it should be apparent to those of ordinary skill in the art that any suitable number of electrodes may be used. For instance, if the electrical energy is supplied as unipolar energy, a single electrode may be used. In another example, if the electrical energy is supplied as bipolar energy, two or more electrodes may be used. 
       FIG. 7A to 7D  show a loop  400  according to embodiments of the present invention. As depicted, the loop  400  is similar to the loop  20 , with the difference that a sensor  425  is mounted to the body  421 . In embodiments, the sensor  425  and the electrodes  423  may be disposed on the inner side of the body  421 . 
     In embodiments, the sensor  425  may be mounted in the body  421  formed of dielectric material so that the sensor  425  may be electrically insulated from the electrode  423 . The electrodes  423  and sensor  425  may move along the body  421  when the loop  420  curls/uncurls around the target tissue. 
     When the electrode(s)  423  and the sensor  425  curl around the circumferential tissue  5  of the renal artery, in embodiments, the electrode(s)  423  and the sensor  425  contact the circumferential tissue  5 . For instance, the electrode(s)  423  may receive electrical energy such as RF energy and generate heat energy. The sensor  225  may measure the impedance of the electrodes  423  or the temperature of the circumferential tissue. The sensor  425  may be connected to the central controller  200  via a wire(s) that run through the catheter apparatus  100 , where electrical power for the sensor  425  may be also delivered via a wire(s). 
     Information of the measured impedance or temperature may be transmitted to the memory  203  of the catheter system  300 . In embodiments, the operator may diagnose the denervation process using the information. The power for delivering thermal energy may also be automatically controlled by the energy source generator  205  or the central controller  200  based on the information. It is noted that other types of sensor may be used to measure various quantities, where each quantity may indicate the status of the denervation process and provide guidance to the physician during operation. 
       FIG. 8  is a schematic diagram of a catheter, illustrating renal denervation using the catheter according to embodiments of the present invention 
     As shown in  FIG. 8 , the distal portion  11  of the catheter is advanced into proximity of the patient&#39;s renal artery RA. The operator may operate the loop control  90  so that the loop  20  (or  420 ) including a plurality of electrodes  23  (or  423 ) may curl around the circumferential tissue  5  of the renal artery to thereby directly or indirectly contact the circumferential tissue of the renal artery RA. The electrodes  23  (or  423 ) may be positioned on a circumferential treatment zone along a segment of the renal artery RA. The electrodes  23  (or  423 ) may include a first electrode to deliver thermal energy to a first treatment zone of the renal artery RA a second electrode to deliver thermal energy to a second treatment zone of the renal artery RA. 
     In embodiments, each of the electrodes may deliver thermal energy to a different treatment zone, respectively or deliver thermal energy to the same treatment zone. 
     In embodiments, the loop  20  (or  420 ) may be electrically coupled to energy source generator  205  for delivery of a desired electrical energy to the electrodes (or  423 ). In embodiments, the electrical energy may be thermal RF energy using Quantum Molecular Resonance (QMR). A frequency of the RF energy may be higher than or equal to 4 MHz and may destruct at least a portion of the circumferential tissue  5  of the renal artery RA. In embodiments, the temperature range of the electrodes  23  (or  423 ) during operation ranges from 60 degrees to 70 degrees. 
     In embodiments, the loop  20  (or  420 ) may supply electrical energy to the circumferential tissue  5  of the renal artery RA to cause renal denervation through the electrode  23  (or  423 ). The heat energy, which is generated by the electrodes  23  ( 423 ), may destruct a portion of the circumferential tissue of the renal artery, where the circumferential tissue may include at least one of a renal nerve RN, lymphatics and capillaries. This may be achieved via contact between the loop  20  (or  420 ) and the circumferential tissue  5  of the renal artery RA. In embodiments, during the denervation, an impedance of the electrode or a temperature of the circumferential tissue may be measured using the sensor  425 . 
       FIG. 9  is a flow chart  900  illustrating exemplary steps that may be carried out to denervate renal nerves according to embodiments of the present invention. The process starts at step  902 . At step  902 , the loop  20  (or  420 ) that is positioned near a target tissue, such as circumferential tissue  5  of the renal artery RA. In embodiments, the loop (or  420 ) may include one or more electrode  23  (or  423 ). Next, at step  904 , the loop  20  (or  420 ) may be curled around the target tissue. 
     At step  906 , energy may be delivered to the electrode  23 , where the electrode  23  may convert the energy into heat energy. Then, at step  908 , at least a portion of the target tissue may be denervated by the heat energy. 
       FIG. 10  is a perspective view of a distal end portion of the catheter in  FIG. 4  according to embodiments of the present invention.  FIG. 10  also includes a cross sectional view of the loop, taken along the line  53 - 53 , according to embodiments of the present invention. 
     As depicted, the loop  20  includes a body  21 , one or more electrodes  23  disposed on a surface of the body  21  and a substrate  25  embedded in the body  21  and separated from the electrodes  23  by a certain distance. 
     The body  21  may be made of insulating/elastic materials, such as silicon. The electrodes  23  may extend along the longitudinal direction of the body  21  and may be made of shape-memory alloy, such as Nitinol. The substrate  25  may also extend along the longitudinal direction of the body  21  like the electrodes  23  and may be made of the same material as the electrode. The substrate  25  may be electrically insulated from the electrodes  23 . In embodiments, the substrate  25  may be electrically coupled to the energy source generator  205  via a switch (not shown) and may receive electrical energy from the energy source generator  205 . 
     If the substrate  25  is not included in the body  21 , a portion of the heat energy generated by the electrode  23  may be transferred toward the backside surface  54  of the body  21 , as indicated by the arrows  56 . The substrate  25  may prevent the heat energy  56  from being transferred to a tissue on the backside surface  54  of the body  21  while most of the heat energy generated by the electrodes is transferred to the target tissue on the front side surface of the body  21 . As a result, the thermal efficiency of the loop  20  may be increased. 
     The substrate  25  may have a width W 1  wider than the width W 2  of each of the electrodes  23  to more efficiently prevent energy transfer to the tissue that is on the backside surface  54  of the body  21 . 
     In embodiments, the backside surface  54  of the body  21  may be coated with a thermally insulating material to block a transfer of the heat energy  56 . 
       FIG. 11A  and  FIG. 11B  show the loop in  FIG. 10  at two different temperatures according to embodiments of the present invention. 
     Referring to  FIG. 11A , the loop  20  curls around the circumferential tissue  5  (e.g., renal artery) as the tip of the loop  20  proceed from the position  60  toward the position  64  as depicted in  FIG. 6A to 6D . In other words, the operator may mechanically manipulate the loop control  90  to curl the loop  20  around the circumferential tissue  5  regardless of the temperature of the loop  20 . In some cases, the electrodes may firmly contact the circumferential tissue when the loop curls around the circumferential tissue by the operator&#39;s manipulation. In other cases, the electrodes of the curled loop may not firmly contact the circumferential tissue for various reasons, such as reduction in the mechanical elasticity of the loop due to the mechanical fatigue developed by repeated usage of the loop  20 , reduction in the mechanical force to tighten the loop and so on. 
     Referring to  FIG. 11B , the electrodes and/or the substrate may be made of shape-memory alloy whose shape changes at a critical temperature. In embodiments, as described in conjunction with  FIG. 12 , the electrodes  23  (or substrate  25 ) made of the shape-memory alloy may be curved at a first curvature at a low temperature (i.e., below the critical temperature) and return to its pre-deformed shape (i.e., curved at a second curvature) when heated above the critical temperature so that the loop  20  curls tightly around the circumferential tissue  5 . For example, the critical temperature may range between 35° C. and 45° C.; preferably, the critical temperature point may be the body temperature of the patient. 
     As discussed above, the energy delivered to the electrodes  23  or substrate  25  may include one or more of radio-frequency (RF) energy, electrical energy, laser energy, ultrasonic energy, high-intensity focused ultrasound (HIFU) energy, cryogenic energy, and thermal energy. The critical temperature of the shape-memory alloy that the electrodes  23  (or substrate  25 ) is made of may be reached in two ways. The first way may be that the critical temperature is reached by the energy delivered to the electrodes  23  and the second way may be that the critical temperature is reached by the energy delivered to the substrate  23 . More specifically, in the case of the first way, the energy is delivered to the electrodes  23 , causing the temperature of the electrodes to rise due to the heat energy generated by the electrodes  23 . Also, a portion of the heat energy is transferred to the substrate  25 , causing the temperature of the substrate  25  to rise to the critical temperature. As the temperature of the substrate  25  reaches the critical temperature, the substrate  25  may curl more tightly around the target tissue as the shape-memory alloy of the substrate  25  may return to the pre-deformed state. The loop  20  including the substrate  25  may curl more tightly around the target tissue so that the electrodes  23  included to the loop may firmly contact the circumferential tissue, as depicted in  FIG. 11B . In the case of the second way, the energy is directly delivered to the substrate  25  so that the temperature of the substrate  25  rises due to the heat energy generated by the substrate. As the temperature of the substrate  25  reaches the critical temperature, the substrate  25  may curl more tightly around the target tissue as the shape-memory alloy of the substrate  25  returns to the pre-deformed state. The loop  20  including the substrate  25  may curl tightly around the target tissue so that the electrodes  23  included to the loop  20  may firmly contact the circumferential tissue, as depicted in  FIG. 11B . 
     As described above, the electrodes  23  may firmly contact the circumferential tissue by either of the two ways, and as a consequence, the renal denervation may be performed more efficiently. 
       FIG. 12  shows a deformation of the substrate  25  in  FIG. 10  in response to a temperature change according to embodiments of the present invention. 
     As depicted in  FIG. 12 , at least a portion of the flat substrate is formed of shape-memory alloy and is deformed to different loops depending on its own temperature. In the first mode, when the temperature (T 1 ) of the substrate  25  is less than the critical temperature (Af) (i.e., no energy is delivered to the electrodes  23  or the substrate  25 ), a portion of the substrate  25  may be curled by manipulating the loop control  90 . At this time, the first circular loop of the substrate  25  may be formed by a mechanical bending force that may be applied by the operator&#39;s manipulation, where the first diameter (R 1 ) of the first circular loop is large enough to curl around the tissue. In embodiments, the first circular loop of the substrate  25  may be formed by delivering the energy to the electrodes  23  or the substrate  25  while the temperature of the substrate  25  is below the critical temperature. 
     In the second mode, as shown in  FIG. 12 , when the temperature (T 2 ) of the substrate  25  reaches the critical temperature (Af) by delivering the energy to the electrodes or the substrate  25 , a second circular loop of the substrate  25  may be formed, where the second diameter (R 2 ) of the second circular loop may be smaller than the first diameter (R 1 ). The shape-memory alloy of the substrate  25  may be pre-deformed such that the second diameter (R 2 ) is slightly larger than the circumferential tissue and the electrodes  23  firmly contact the circumferential tissue in the second mode. 
     In embodiments, the substrate may be made of two-way shape memory alloy but may be made of three-way (or higher order) shape-memory alloy, depending on the application. For instance, the substrate may be made of three-way shape-memory alloy and pre-deformed so that the substrate has return to three shapes at three different temperatures. 
       FIG. 13  illustrate a loop of the catheter in  FIG. 4  according to another embodiment of the present invention. The loop may be able to automatically wrap both the tissue and nerves for effective denervation regardless of the nerve distribution. The loop may be available in various sizes to cover main artery, accessory artery, and early-branching artery. 
     According to the present disclosure, it is possible to effectively ablate e.g., renal nerves while not being as invasive as sympathectomy to treat the resistant hypertension patients. Further, by a procedure using the catheter, the nerves could safely and completely denervated. 
     As depicted in  FIG. 13 , the loop may include a plurality of electrodes  1301 , a first film  1302 , a sensor  1303 , a second film  1304  and a third film  1305 . 
     The first film  1302  may be capable of bending to curl around the tissue. The first film  1302  may be disposed on the second film  1304 . The first film  1302  may be made of biocompatible polymers. For example, the first film  1302  may be a polyimide film. 
     The plurality of electrodes  1301  may be disposed on the first film  1302  and arranged in parallel to each other with a predetermined distance. The plurality of electrodes  1301  may contact the circumferential tissue when the loop curls around the circumferential tissue. 
     The plurality of electrodes  1301  may be formed of electrically-conductive elastic material so that they can deform along with the body as the body is curled/uncurled. By way of example, the plurality of electrodes  1301  may be made of a copper-coated-gold. 
     Since the plurality of electrodes  1301  are arranged in parallel to each other, the plurality of electrodes  1301  may form a bipolar configuration localizing electrical current path (e.g., thermal energy) between the plurality of electrodes  1301 , and the concentration results in heat generation at tissue. This configuration confines heat between surface of the plurality of electrodes  1301  and an outer wall of the tissue. 
     The plurality of electrodes  1301  may be configured to curl to directly or indirectly contact the tissue. The plurality of electrodes  1301  may contact the circumferential tissue surrounding the outer surface of the renal artery and generate heat energy when electrical energy, such as RF energy, is supplied, where the heat energy may be used to denervate the renal nerve RN. 
     In some cases, the plurality of electrodes  1301  may firmly contact the circumferential tissue when the loop curls around the circumferential tissue by the operator&#39;s manipulation. In other cases, the plurality of electrodes  1301  of the curled loop may not firmly contact the circumferential tissue for various reasons, such as reduction in the mechanical elasticity of the loop due to the mechanical fatigue developed by repeated usage of the loop, reduction in the mechanical force to tighten the loop and so on. 
     The plurality of electrodes  1301  made of the shape-memory alloy may be curved at a first curvature at a low temperature (i.e., below the critical temperature) and return to its pre-deformed shape (i.e., curved at a second curvature) when heated above the critical temperature so that the loop curls tightly around the circumferential tissue. For example, the critical temperature may range between 35° C. and 45° C.; preferably, the critical temperature point may be the body temperature of the patient. 
     The critical temperature of the shape-memory alloy that the plurality of electrodes  1301  may be made of may be reached in two ways. The critical temperature is reached by the energy delivered to the plurality of electrodes  1301 . More specifically, the energy is delivered to the plurality of electrodes  1301 , causing the temperature of the electrodes to rise due to the heat energy generated by the plurality of electrodes  1301 . Also, a portion of the heat energy is transferred to the entire loop, causing the temperature of the loop to rise to the critical temperature. As the temperature of the loop reaches the critical temperature, the loop may curl more tightly around the target tissue as the shape-memory alloy of the plurality of electrodes  1301  may return to the pre-deformed state. Thus, the loop may curl more tightly around the target tissue so that the plurality of electrodes  1301  included to the loop may firmly contact the circumferential tissue. 
     In the first mode, when the temperature (T 1 ) of the loop is less than the critical temperature (Af) (i.e., no energy is delivered to the plurality of electrodes  1301 ), a portion of the loop may be curled by manipulating the loop control. At this time, the first circular loop of the loop may be formed by a mechanical bending force that may be applied by the operator&#39;s manipulation, where the first diameter (R 1 ) of the first circular loop is large enough to curl around the tissue. In embodiments, the first circular loop of the loop may be formed by delivering the energy to the plurality of electrodes  1301  while the temperature of loop is below the critical temperature. 
     In the second mode, when the temperature (T 2 ) of the loop reaches the critical temperature (Af) by delivering the energy to the electrodes or the plurality of electrodes  1301 , a second circular loop of loop may be formed, where the second diameter (R 2 ) of the second circular loop may be smaller than the first diameter (R 1 ). The shape-memory alloy of the plurality of electrodes  1301  may be pre-deformed such that the second diameter (R 2 ) is slightly larger than the circumferential tissue and the plurality of electrodes  1301  firmly contact the circumferential tissue in the second mode. 
     In embodiments, the plurality of electrodes  1301  may be made of a two-way shape-memory alloy. For example, the plurality of electrodes  1301  may be made of Nitinol including at least one of nickel (Ni), titanium (Ti), chrome (Cr), copper (Cu), iron (Fe), lead (Nb), carbon (C), cobalt (Co), hydrogen (H 2 ), oxygen (O 2 ). 
     A shape memory alloy refers to an alloy having a property of recovering to its original shape before deformation when the deformed metal is heated to a specific temperature or higher. 
     When the temperature of the shape memory alloy is high, the shape memory alloy exists as a cubic austenite phase, but when the temperature of the shape memory alloy decreases, the shape memory alloy changes to a martensite phase in an orthorhombic structure, which is called a martensite transformation when cooled at a high temperature. 
     The martensitic transformation begins at the martensitic start temperature (Ms) and ends at the martensitic finish temperature (Mf). When an external force is applied to the martensite phase, the shape memory alloy is transformed without changing the relative position between atoms, unlike other metals. 
     On the contrary, when heated above the austenite transformation start temperature (As) in the martensite phase, the original shape is restored at the austenite transformation finish temperature (Af). 
     Meanwhile, the two-way shape memory alloy not only recovers to its original shape when heated, but also returns to the martensite phase when cooled. That is, the two-way shape memory alloy remembers both a shape at a high temperature and a shape at a low temperature. 
     In embodiments, the two-way shape-memory alloy that the plurality of electrodes  1301  may be made of may be curved at a first curvature at a temperature above a first transformation temperature (the austenite transformation start temperature) and curved at a second curvature at a temperature above a second transformation temperature (the austenite transformation finish temperature). Here, the first transformation temperature may be set between 35° C. and 45° C. and the second transformation temperature may be set between 50° C. and 60° C. 
     At this time, a diameter corresponding to the first curvature may be greater than a diameter of the tissue and a diameter corresponding to the second curvature may be substantially similar to the diameter of the tissue. That is, the first curvature may be greater than the second curvature. 
     Further, the two-way shape-memory alloy that the plurality of electrodes  1301  may be made of may be formed to be uncurled in a straight shape below a third transformation temperature (the martensitic start temperature). Here, the third transformation temperature may be between 20° C. and 25° C. That is, the loop  20  may maintain the straight shape inside a shaft. 
     According to the embodiments, when the loop  20  comes out of the shaft and is inserted near the renal artery, as the plurality of electrodes  1301  is heated to the first transformation temperature by body temperature, the loop  20  may be curl at the first curvature by the plurality of electrodes  1301 . At this time, the loop  20  may do not completely curl the tissue. 
     Thereafter, as will be described later, when the energy is delivered to the plurality of electrodes  1301 , the plurality of electrodes  1301  may be heated to the second transformation temperature, and thus, the loop  20  may be curl at the second curvature by the plurality of electrodes  1301 . That is, the second transformation temperature of the plurality of electrodes  1301  may be reached by the energy. At this time, the loop  20  may completely curl the tissue depending on the diameter of the tissue. That is, if the diameter of the tissue is wide, the tissue may be completely curled, but if the diameter of the tissue is narrow, the tissue may be not completely curled. 
     When the treatment of the tissue is completed, the energy is not delivered and thus the temperature of the plurality of electrodes  1301  are lowered to the first transformation temperature. Accordingly, the loop  20  may be transformed from the second curvature to the first curvature by the plurality of electrodes  1301 , and an operator can safely remove the loop  20  from the tissue. 
     When all the treatment are completed, the loop  20  is removed from the body so that the temperature of the plurality of electrodes  1301  are lowered to the third transformation temperature. Accordingly, the loop  20  may be uncurled in the straight shape by the plurality of electrodes  1301 . 
     Meanwhile, increasing an energy to reach beyond 2 mm would cause irreversible intima injury resulting in serious complications such as atherosclerosis, thrombosis, or stenosis. 
     To solve the problem, the plurality of electrodes  1301  may localize heat distribution between the plurality of electrodes  1301  and the outer wall of the tissue. Therefore, since thermal damage to tunica intima is prevented by concentrating the heat between the plurality of electrodes  1301  and the outer wall of the tissue, it is possible to achieve the nerve denervation without injuring the tissue and its adjacent organs. Further, it is possible to maximize nerve denervation by localizing the heat distribution within the nerves and thus neural density can be decreased enough. 
     For example, a temperature of the loop may remain 60° C. to form a thermal lesion boundary between tunica media and adventitia or the temperature of the loop may remain 65° C. to extend the lesion boundary to the tunica media. 
     The plurality of electrodes  1301  may be configured to supply bipolar energy. The energy supplied by the plurality of electrodes  1301  may be at least one selected from the group consisting of radio-frequency (RF) energy, electrical energy, laser energy, ultrasonic energy, high-intensity focused ultrasound (HIFU) energy, cryogenic energy, thermal energy 
     The plurality of electrodes  1301  may include a first electrode to deliver thermal energy to a first treatment zone of the tissue and a second electrode to deliver thermal energy to a second treatment zone of the tissue. Thermal energy delivered to the plurality of electrodes  1301  is localized between the first treatment zone and the second treatment zone. 
     The sensor  1303  may be disposed on the second film  1304 . The sensor  1303  may be disposed at a position corresponding to a position between the plurality of electrodes  1301 . The sensor  1303  may be electrically insulated from the plurality of electrodes  1301 . The sensor  1303  may sense at least one of an impedance of the plurality of electrodes  1301  and a temperature of the tissue. 
     The second film  1304  may be disposed on the third film  1305 . The second film  1304  may be made of biocompatible metals. By way of example, the second film  1304  may be a biocompatible heat-treated stainless steel plate that changes shape from straight to round when emerged from the distal portion, and it maintains its round shape without external load. The second film  1304  may be coated with a flexible printed circuit board. 
     The third film  1305  may also be made of biocompatible polymers. For example, the third film  1305  may be a polyimide film. 
     The apparatus and methods described herein can be used to treat not only hypertension, but also other suitable types of diseases, such as chronic renal diseases, cardiovascular disorders, cardiac arrhythmias, and clinical syndromes where the renal afferent activation is involved. Using the catheter in embodiments, as compared to percutaneous catheter and surgical instrumentation, the physician may treat the diseases in an easier and safer manner. 
     In the description, numerous details are set forth for purposes of explanation in order to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that not all of these specific details are required in order to practice the present invention. 
     Additionally, while specific embodiments have been illustrated and described in this specification, those of ordinary skill in the art appreciate that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments disclosed. This disclosure is intended to cover any and all adaptations or variations of the present invention, and it is to be understood that the terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with the established doctrines of claim interpretation, along with the full range of equivalents to which such claims are entitled.