Abstract:
The present invention discloses an electrode for radiofrequency tissue ablation which can coagulate and necrotize a tissue by radiofrequency electric energy. The electrode for radiofrequency tissue ablation precisely coagulates and necrotizes a target part of the tissue by sensing a temperature of the tissue. The electrode includes a horn-shaped closed end sharpened to its one end, a hollow tube type electrode extended long in the length direction from the other end of the closed end, an insulation member installed on the outer circumference of the hollow electrode except for the part connected to the closed end, at least one temperature sensor installed on the outer circumference of the hollow electrode to be positioned inside the insulation member, for sensing an ambient temperature, and a control unit connected to the hollow electrode and the temperature sensor, for deciding coagulation and necrosis of the tissue according to the temperature sensed by the temperature sensor, and controlling the output supplied to the hollow electrode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase application, pursuant to 35 U.S.C. §371, of International Patent Application No. PCT/KR2005/004585, having an international filing date of Dec. 27, 2005, designating the U.S., which claims priority to Korean Patent Application Number 10-2004-0113945, having an filing date of Dec. 28, 2004, the contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrode for radiofrequency tissue ablation which can coagulate and necrotize a tissue by radiofrequency electric energy, and more particularly, to an electrode for radiofrequency tissue ablation which can coagulate and necrotize a target part of a tissue by sensing a temperature of the tissue. 
     2. Description of Related Art 
     There has been suggested a method for coagulating or ablating a target tissue with radiofrequency energy by inserting a long hollow tube type electrode into the tissue. Here, a radiofrequency output is transmitted to the tissue to heat the tissue, so that the tissue and blood vessel can be coagulated by more or less complicated biochemical equipment. Such a process is carried out by coagulation of a cell (including tissue, blood vessel and blood) by heat distortion of protein in the cell over about 55° C. 
     However, the tissue and blood are excessively coagulated and carbonized near the electrode for radiofrequency tissue ablation. Such a carbonized tissue is operated as an insulator interrupting expansion of a tissue coagulation area. In order to solve the above problem, tissues can be coagulated and necrotized in a wide area by lowering a temperature of peripheral tissues by circulating a coolant saline solution in the electrode or externally ejecting the saline solution. In addition, the tissues can be coagulated and necrotized in a wide area by circulating a coolant saline solution and externally ejecting some of the saline solution at the same time. 
       FIG. 1  is a side-sectional view illustrating a conventional electrode for radiofrequency tissue ablation. 
     In detail, as illustrated in  FIG. 1 , the conventional electrode for radiofrequency tissue ablation includes a sharp closed end  10  inserted into a tissue, for generating radiofrequency energy, and a hollow electrode  20  connected to the closed end  10 . An insulation coating  24  is coated on the outer circumference of the hollow electrode  20  except for the part connected to the closed end  10 . A control unit (not shown) is installed to generate radiofrequency electric energy in the closed end  10  by supplying an output to the closed end  10  and the hollow electrode  20 . A hollow refrigerant tube  30  is installed in the hollow electrode  20  with a predetermined gap from the inner circumference of the hollow electrode  20 . Cooling water flowing into the refrigerant tube  30  is discharged between the refrigerant tube  30  and the hollow electrode  20  after cooling the closed end  10 . 
     If necessary, a hole  20   h  is formed on the part of the hollow electrode  20  adjacent to the closed end  10 , so that some of the cooling water can be directly injected into the tissue to prevent carbonization of the tissue and expand the electrode area to efficiently coagulate the tissue. 
     A temperature sensor  22  is installed on the outer circumference of the hollow electrode  20  adjacent to the closed end  10 , for sensing a temperature of the closed end  10 . According to the sensed temperature, the control unit controls the closed end  10  to generate radiofrequency electric energy for a predetermined time by adjusting the output. Here, the tissue is maintained over a predetermined temperature for a pre-determined time for complete coagulation and necrosis. 
     However, in the conventional electrode for radiofrequency tissue ablation, since the temperature sensor  22  is installed near the closed end  10  generating radiofrequency electric energy, the temperature sensor  20  can only sense the temperature of the closed end  10  and the temperature of the tissue adjacent to the closed end  10 . It is thus difficult to coagulate and necrotize only a target part by maintaining a pre-determined temperature in an accurate ablation part. 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     The present invention is achieved to solve the above problems. An object of the present invention is to provide an electrode for radiofrequency tissue ablation which can coagulate and necrotize only a target part of a tissue by sensing a temperature of the tissue in a part separated from a radiofrequency electric energy generation point by a predetermined gap, and controlling generation of radiofrequency electric energy according to the sensed temperature. 
     Technical Solution 
     In order to achieve the above-described object of the invention, there is provided an electrode for radiofrequency tissue ablation, including: a horn-shaped closed end sharpened to its one end; a hollow tube type electrode extended long in the length direction from the other end of the closed end; an insulation member installed on the outer circumference of the hollow electrode except for the part connected to the closed end; at least one temperature sensor installed on the outer circumference of the hollow electrode to be positioned inside the insulation member, for sensing an ambient temperature; and a control unit connected to the hollow electrode and the temperature sensor, for deciding coagulation and necrosis of the tissue according to the temperature sensed by the temperature sensor, and controlling the output supplied to the hollow electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become better understood with reference to the accompanying drawings which are given only by way of illustration and thus are not limitative of the present invention, wherein: 
         FIG. 1  is a side-sectional view illustrating a conventional electrode for radiofrequency tissue ablation; 
         FIG. 2  is a disassembly perspective view illustrating an electrode for radiofrequency tissue ablation in accordance with a first embodiment of the present invention; 
         FIG. 3  is a side-sectional view illustrating the electrode for radiofrequency tissue ablation in accordance with the first embodiment of the present invention; 
         FIG. 4  is a disassembly perspective view illustrating an electrode for radiofrequency tissue ablation in accordance with a second embodiment of the present invention; 
         FIG. 5  is a side-sectional view illustrating the electrode for radiofrequency tissue ablation in accordance with the second embodiment of the present invention; 
         FIG. 6  is a disassembly perspective view illustrating an electrode for radiofrequency tissue ablation in accordance with a third embodiment of the present invention; 
         FIG. 7  is a side-sectional view illustrating the electrode for radiofrequency tissue ablation in accordance with the third embodiment of the present invention; 
         FIG. 8  is a disassembly perspective view illustrating an electrode for radiofrequency tissue ablation in accordance with a fourth embodiment of the present invention; 
         FIG. 9  is a side-sectional view illustrating the electrode for radiofrequency tissue ablation in accordance with the fourth embodiment of the present invention; 
         FIG. 10  is a disassembly perspective view illustrating an electrode for radiofrequency tissue ablation in accordance with a fifth embodiment of the present invention; and 
         FIG. 11  is a side-sectional view illustrating the electrode for radiofrequency tissue ablation in accordance with the fifth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An electrode for radiofrequency tissue ablation in accordance with the preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
       FIGS. 2 and 3  are a disassembly perspective view and a side-sectional view illustrating an electrode for radiofrequency tissue ablation in accordance with a first embodiment of the present invention. 
     In accordance with the first embodiment of the present invention, referring to  FIGS. 2 and 3 , a hollow tube type electrode  60  formed long in the length direction and made of a material in which an output (radiofrequency electric energy) flows is connected to a closed end  50  having a sharp end. The hollow electrode  60  is more thickened than the general one. A mounting groove  64  is formed long in the length direction on the outer circumference of the hollow electrode  60  with a predetermined gap from the closed end  50 , so that a temperature sensor  62  can be mounted thereon. In a state where the temperature sensor  62  is mounted on the mounting groove  64 , an insulation member  66  is covered on the outer circumference of the hollow electrode  60  except for the part connected to the closed end  50 . 
     The electrode for radiofrequency tissue ablation includes a control unit (not shown) for supplying an output to the closed end  50  and the hollow electrode  60 . The control unit controls the output supplied to the closed end  50  and the hollow electrode  60  according to the temperature sensed by the temperature sensor  62 . 
     Preferably, the closed end  50  has a sharp end like a triangular pyramid or a circular cone to be easily inserted into the tissue, and is connected to the control unit by a radiofrequency generating wire (not shown) to generate radiofrequency as a whole. 
     The hollow electrode  60  transmits the output from the control unit to the closed end  50 . Since the part of the hollow electrode  60  connected to the closed end  50  is not covered with the insulation member  66 , when receiving the output from the control unit, the hollow electrode  60  generates radiofrequency electric energy. 
     As the closed end  50  and the hollow electrode  60  generate radiofrequency electric energy, the closed end  50  and the hollow electrode  60  may be excessively heated to carbonize the peripheral tissue. The carbonized tissue interrupts transmission of radiofrequency electric energy from the closed end  50  and the hollow electrode  60 . In order to solve the foregoing problem, a hollow refrigerant tube  70  is installed in the hollow electrode  60  for circulation of refrigerants. 
     In detail, the refrigerant tube  70  has a smaller diameter (about 0.8 mm) than the inside diameter of the hollow electrode  60 . The end of the refrigerant tube  70  is positioned with a predetermined gap from the closed end  50 . A temperature sensor line  80  is inserted into the refrigerant tube  70 , for sensing a temperature in the hollow electrode  60  and the closed end area  50 , so that the control unit can control output of the electrode or flow of the circulated refrigerants. A supply pipe (not shown) for supplying the refrigerants to the refrigerant tube  70  is connected to the refrigerant tube  70 . A discharge pipe (not shown) for discharging the refrigerants between the hollow electrode  60  and the refrigerant tube  70  is connected between the hollow electrode  60  and the refrigerant tube  70 . 
     Accordingly, the refrigerants pressurized by a high pressure (about 700 to 1060 Kpa) are sucked into the refrigerant tube  70  and rapidly transferred between the refrigerant tube  70  and the hollow electrode  60 , for cooling the closed end  50  and the part of the hollow electrode  60  contacting the tissue. 
     Especially, the hollow electrode  60  is divided into a non-insulation unit  60   a  which is not covered with the insulation member  66  and an insulation unit  60   b  covered with the insulation member  66 . Preferably, the outer circumference of the non-insulation unit  60   a  is grinded by about 0.3 mm in order to improve cooling efficiency of the non-insulation unit  60   a  and reduce the diameter of the electrode. The outer circumference of the non-insulation unit  60   a  and the outer circumference of the insulation unit  60   b  are smoothly connected to each other to be efficiently inserted into the patient&#39; body in the ablation. 
     Here, the length of the non-insulation unit  60   a  is longer than that of the closed end  50  by about five times. For example, the length of the closed end  50  can be 5 mm and the length of the non-insulation unit  60   a  can be 25 mm. 
     Some of the refrigerants discharged between the refrigerant tube  70  and the hollow electrode  60  can be directly discharged to the tissue, for preventing carbonization of the peripheral tissue. A hole  60   h  is formed on the non-insulation unit  60   a  adjacent to the closed end  50 , and a hollow tube  90  for discharging the refrigerants little by little by operating the flow resistance of the refrigerants to prevent excessive ejection of the pressurized refrigerants from the hole  60   h  covers the hole  60   h.    
     The size of the hollow tube  90  is decided to be inserted onto the non-insulation unit  60   a  of the hollow electrode  60 . The inside diameter of the hollow tube  90  is larger than the outside diameter of the non-insulation unit  60   a  of the hollow electrode  60  by a pre-determined tolerance. The outside diameter of the hollow tube  90  is identical to that of the insulation unit  60   b  of the hollow electrode  60 . A compressing unit  92  is formed in a zigzag shape on the outer circumference of the hollow tube  90 , for forming a path for transferring the refrigerants discharged from the hole  60   h  of the hollow electrode  60  with the flow resistance. A hole  90   h  is formed on one side of the hollow tube  90 , for directly discharging the decompressed refrigerants to the tissue. 
     The refrigerants sucked or discharged to/from the hollow electrode  60  and directly discharged to the tissue through the hole  60   h  are preferably a physiological saline solution which is not harmful to the tissue, for example, 0.9% saline solution, namely, an isotonic solution. 
     Since the end of the closed end  50  is smoothed, even through the hollow tube  90  is mounted on the non-insulation unit  60   a  of the hollow electrode  60 , the hollow tube  90  and the closed end  50  are smoothly connected to each other. In addition, the hollow tube  90  maintains the identical diameter to that of the insulation unit  60   b , so that the electrode can be efficiently inserted into the tissue. 
     Preferably, the temperature sensor  62  is a thermocouple. The mounting groove  64  is formed long in the length direction on the non-insulation unit  60   a  of the hollow electrode  60 , so that the temperature sensor  62  and the electric wire connected to the temperature sensor  62  can be stably mounted thereon. The mounting groove  64  is formed on the outer circumference of the insulation unit  60   b  of the hollow electrode  60  separated from the closed end  50  by a predetermined gap with the same depth as the thickness of the temperature sensor  62  and the electric wire. 
     Preferably, the mounting groove  64  is formed long in the length direction from the point separated from the end of the insulation unit  60   b  by at least 5 mm. Accordingly, although the temperature sensor  62  is mounted on the end of the mounting groove  64  for sensing the temperature, the temperature sensor  62  is less influenced by the non-insulation unit  60   a  maintaining a high temperature state by radiofrequency. 
     Preferably, the temperature sensor  62  is mounted on the position separated in the insulation unit  60   b  direction from the center C of the length of the closed end  50  and the non-insulation unit  60   a  by a coagulation and necrosis radius r d . More preferably, the temperature sensor  62  is installed to be movable in the mounting groove  64  in the length direction. 
     On the other hand, a pair of mounting grooves  64  are formed at an interval of 180 or a plurality of mounting grooves  64  are formed at predetermined intervals on the outer circumference of the insulation unit  60   b  of the hollow electrode  60 . The temperature sensors  62  (not shown) can be installed on the mounting grooves  64  (not shown), respectively. Each of the temperature sensors  62  can be separated in the insulation unit  60   b  direction from the center C of the length of the closed end  50  and the non-insulation unit  60   a  by different set values. Preferably, the set values are decided between a minimum radius r and a maximum radius R in consideration of a tolerance of an ablation part. 
     When the temperature sensor  62  and the electric wire are stably positioned on the mounting groove  64  of the hollow electrode  60 , the temperature sensor  62  and the electric wire maintain the same curved surface with the outer circumference of the hollow electrode  60 , thereby maintaining the diameter of the electrode as it is. Therefore, the electrode can be efficiently inserted into the tissue. 
     Since the coagulation and necrosis parts are different in size, it is advantageous to manufacture various electrodes in which the temperature sensors  62  are mounted on different positions of the hollow electrodes  60 . 
     The temperature sensor  62  can directly sense the temperature of the tissue. While the tissue is coagulated and necrotized by radiofrequency electric energy generated by the closed end  50  and the part of the hollow electrode  60 , the temperature sensor  62  senses the temperature of the tissue. When the temperature and time conditions are satisfactory in the tissue sensed by the temperature sensor  62 , the control unit decides that the target part of the tissue has been completely coagulated and necrotized, and stops supplying radiofrequency energy to the closed end  50  and the hollow electrode  60 . 
     Various temperature and time conditions for completely coagulating and necrotizing tissues have been known. In accordance with the present invention, the temperature condition is set as 55° C. and the time condition is set as 5 minutes. 
     The insulation member  66  is made of a resin or a polymer insulation tube and covered merely on the insulation unit  60   b . The insulation member  66  can be made of an insulation coating having a relatively small thickness. 
     The ablation for coagulating and necrotizing the tissue by the electrode will now be explained. The electrode is selected in consideration of the installation position of the temperature sensor  62  according to the size of the ablation part, or the installation position of the temperature sensor  62  is set by sliding. The electrode is inserted into the tissue so that the center C of the length of the closed end  50  and the non-insulation unit  60   a  can be positioned at the center of the ablation part. Since the hollow tube  90  is inserted onto the non-insulation unit  60   a  having a smaller diameter than the insulation unit  60   b , and the outer circumferences of the non-insulation unit  60   a  and the insulation unit  60   b  are smoothly connected to each other, the electrode wholly maintains a relatively uniform diameter. Furthermore, since the temperature sensor  62  is mounted to compose the same curved surface with the hollow electrode  60 , the electrode can be easily inserted into the tissue without being hooked. 
     Thereafter, the control unit supplies radiofrequency energy to the electrode. The output is transmitted to the hollow electrode  60  and the closed end  50 , thereby generating radiofrequency electric energy. The peripheral tissue is coagulated and necrotized from the elliptical shape to the spherical shape by radiofrequency electric energy. At the same time, the high pressure refrigerants are sucked through the refrigerant tube  70  and discharged between the refrigerant tube  70  and the hollow electrode  60 , thereby cooling the closed end  50  and the hollow electrode  60 . In addition, some of the refrigerants are discharged to the tissue through the hole  60   h  of the hollow electrode  60  and the hole  90   h  of the hollow tube  90 , thereby cooling the tissue. Accordingly, the peripheral tissue is not excessively heated and carbonized. Also, the refrigerants are operated as conductors for transmitting radiofrequency electric energy to the tissues in a wide area. As a result, a relatively large ablation part can be rapidly coagulated and necrotized. 
     Here, the control unit supplies the output so that the temperature sensed by the temperature sensor  62  can be maintained over about 55° C. for 5 minutes. If the above condition is satisfied, the control unit decides that the ablation part has been completely coagulated and necrotized, and stops supplying radiofrequency energy. 
     The electrode can be inserted into the accurate part of the tissue with the help of the laparoscope, transvaginal ultrasound and hysteroscope. For example, when the operator intends to insert the electrode into the target part of the liver cancer tissue, he/she preferably carries out the ablation with the help of the abdominal ultrasound. In the case that the operator inserts the electrode into a target part of an uterus myoma tissue, he/she can carry out the ablation with the help of the laparoscope, or by searching the accurate position of the uterus myoma tissue by the transvaginal ultrasound or hysteroscope, and inserting the electrode into the target part by an adapter adhered to the equipment or an operation space provided to the equipment. The electrodes discussed later are used in the same manner. 
       FIGS. 4 and 5  are a disassembly perspective view and a side-sectional view illustrating an electrode for radiofrequency tissue ablation in accordance with a second embodiment of the present invention. 
     The second embodiment of the present invention is almost identical to the first embodiment described above. As illustrated in  FIGS. 4 and 5 , the hollow electrode  60  includes two hollow tubes, namely, an inner tube  61   a  and an outer tube  61   b . The closed end  50  is coupled to the end of the inner tube  61   a , and the outer tube  61   b  is installed with a predetermined gap from the closed end  50 . The temperature sensor  62  and the electric wire are installed on a mounting hole  65  formed on the outer tube  61   b  to be connected to the control unit. The insulation member  66  is covered on the whole outer circumference of the outer tube  61   b.    
     Here, the inner tube  61   a  is a hollow tube having a smaller thickness than the general electrode. The closed end  50  is coupled to the end of the inner tube  61   a  by soldering or the like. 
     The refrigerant tube  70  and the temperature sensor line  80  are installed in the inner tube  61   a , so that high pressure refrigerants can be sucked or discharged for cooling. The hole  60   h  is formed on one side end of the inner tube  61   a  adjacent to the closed end  50 , and the hollow tube  90  is installed to transfer the high pressure refrigerants to the tissue through the frictional path little by little. Thus, cooling efficiency is improved, and radiofrequency electric energy is transmitted to a wider area. 
     The inside diameter of the outer tube  61   b  is identical to the outside diameter of the inner tube  61   a , so that the outer tube  61   b  can be inserted onto the inner tube  61   a . Preferably, one side end of the outer tube  61   b  is smoothed so that the outer circumferences of the inner tube  61   a  and the outer tube  61   b  can be smoothly connected to each other when the outer tube  61   b  is inserted onto the inner tube  61   a.    
     Since the hollow tube  90  having the same outside diameter as that of the outer tube  61   b  is inserted onto the inner tube  61   a , the outer circumferences of the inner tube  61   a  and the outer tube  61   b  need not to be specially smoothed. 
     In spite of radiofrequency electric energy, the inner tube  61   a  having a small thickness can be easily cooled by the refrigerants circulated therein and the refrigerants sprayed to the tissue, thereby preventing carbonization of the tissue and coagulating and necrotizing the tissue in a wide area by radiofrequency electric energy. Here, the outer tube  61   b  is inserted onto most of the inner tube  61   a , which reinforces intensity of the electrode in spite of small thickness of the inner tube  61   a  and large length of the whole electrode. 
     The slit type mounting hole  65  is formed from the position separated from one side end of the outer tube  61   b  by at least 5 mm to the other side end. Therefore, when the temperature sensor  62  is mounted on the mounting hole  65 , the temperature sensor  62  is less influenced by radiofrequency energy generated at the part of the inner tube  61   a  which is not covered with the insulation member  66 . 
     The length of the part of the inner tube  61   a  is larger than that of the closed end  50  by about five times. For example, when the length of the closed end  50  is 5 mm, the length of the part of the inner tube  61   a  which is not covered with the outer tube  61   b  is 25 mm. 
     Preferably, the temperature sensor  62  is mounted on the position separated in the outer tube  61   b  direction from the center C of the length of the closed end  50  and the inner tube  61   a  which is not covered with the insulation member  66  by the ablation radius r d . More preferably, the temperature sensor  62  is installed to be movable in the mounting hole  65  in the length direction. 
     A pair of mounting holes  65  are formed at an interval of 180 or a plurality of mounting holes  65  are formed at predetermined intervals on the outer tube  61   b . The temperature sensors  62  (not shown) can be installed on the mounting holes  65  (not shown), respectively. Each of the temperature sensors  62  can be separated in the outer tube  61   b  direction from the center C of the length of the closed end  50  and the inner tube  61   a  which is not covered with the insulation member  66  by different set values. Preferably, the set values are decided between the minimum radius r and the maximum radius R in consideration of the tolerance of the ablation part. 
     The closed end  50 , the temperature sensor  62 , the insulation member  66 , the refrigerant tube  70 , the temperature sensor line  80  and the hollow tube  90  of the second embodiment are identical to those of the first embodiment, and thus detailed explanations thereof are omitted. The operation of the whole electrode will now be explained. 
     The electrode is selected in consideration of the installation position of the temperature sensor  62  according to the size of the ablation part, or the installation position of the temperature sensor  62  is set by sliding. The electrode is inserted into the tissue so that the center C of the length of the closed end  50  and the inner tube  61   a  which is not covered with the insulation member  66  can be positioned at the center of the ablation part. Since the hollow tube  90  and the outer tube  61   b  having the same outside diameter are inserted onto the inner tube  61   a , the outer circumferences thereof are smoothly connected to each other. Thus, the electrode wholly maintains a relatively uniform diameter. Furthermore, since the temperature sensor  62  is mounted to compose the same curved surface with the hollow electrode  60 , the electrode can be easily inserted into the tissue without causing any damages to the tissue. 
     Thereafter, the control unit supplies radiofrequency energy to the electrode. The output is transmitted to the hollow electrode  60  and the closed end  50 , thereby generating radiofrequency electric energy in the closed end  50  and the part of the inner tube  61   a . The peripheral tissue is coagulated and necrotized from the elliptical shape to the spherical shape by radiofrequency electric energy. At the same time, the high pressure refrigerants are sucked through the refrigerant tube  70  and discharged between the refrigerant tube  70  and the hollow electrode  60 , thereby cooling the closed end  50  and the hollow electrode  60 . In addition, some of the refrigerants are discharged to the tissue through the hole  60   h  of the hollow electrode  60  and the hole  90   h  of the hollow tube  90 , thereby cooling the tissue. Accordingly, the peripheral tissue is not excessively heated and carbonized. Also, the refrigerants are operated as conductors for transmitting radiofrequency electric energy to the tissues in a wide area. As a result, a relatively large ablation part can be rapidly coagulated and necrotized. 
     Here, the control unit supplies the output so that the temperature sensed by the temperature sensor  62  can be maintained over about 55° C. for 5 minutes. If the above condition is satisfied, the control unit decides that the ablation part has been completely coagulated and necrotized, and stops supplying radiofrequency energy. 
       FIGS. 6 and 7  are a disassembly perspective view and a side-sectional view illustrating an electrode for radiofrequency tissue ablation in accordance with a third embodiment of the present invention. 
     The third embodiment of the present invention is almost identical to the second embodiment described above. As shown in  FIGS. 6 and 7 , the closed end  50  is coupled to the end of the inner tube  61   a , and the outer tube  61   b  on which the mounting hole  65  is formed is installed to cover the outer circumference of the inner tube  61   a  with a pre-determined gap from the closed end  50 . The temperature sensor  62  and the electric wire are installed on the mounting hole  65  formed on the outer tube  61   b  to be connected to the control unit. The insulation member  66  is covered on the whole outer circumference of the outer tube  61   b . The part of the inner tube  61   a  which is not covered with the insulation member  66  generates radiofrequency electric energy, thereby coagulating and necrotizing the peripheral tissue. The refrigerant tube  70  and the temperature sensor line  80  are installed, so that high pressure refrigerants can be sucked or discharged to cool the part of the inner tube  61   a  generating radiofrequency electric energy. 
     A special hollow tube is not inserted onto the inner tube  61   a . One side end of the outer tube  61   b  is preferably smoothed, so that the outer circumferences of the inner tube  61   a  and the outer tube  61   b  can be smoothly connected to each other when the outer tube  61   b  is mounted on the inner tube  61   a  to compose the hollow electrode  60 . 
     The closed end  50 , the temperature sensor  62 , the insulation member  66 , the refrigerant tube  70  and the temperature sensor line  80  of the third embodiment are identical to those of the second embodiment, and thus detailed explanations thereof are omitted. The operation of the whole electrode will now be explained. 
     The electrode is selected in consideration of the installation position of the temperature sensor  62  according to the size of the ablation part, or the installation position of the temperature sensor  62  is set by sliding. The electrode is inserted into the tissue so that the center C of the length of the closed end  50  and the inner tube  61   a  which is not covered with the insulation member  66  can be positioned at the center of the ablation part. Since the outer circumferences of the inner tube  61   a  and the outer tube  61   b  are smoothly connected to each other, the electrode wholly maintains a relatively uniform diameter. Furthermore, since the temperature sensor  62  is mounted to compose the same curved surface with the hollow electrode  60 , the electrode can be easily inserted into the tissue without being hooked. 
     Thereafter, the control unit supplies radiofrequency energy to the electrode. The output is transmitted to the hollow electrode  60  and the closed end  50 , thereby generating radiofrequency electric energy in the closed end  50  and the part of the inner tube  61   a . The peripheral tissue is coagulated and necrotized from the elliptical shape to the spherical shape by radiofrequency electric energy. At the same time, the high pressure refrigerants are sucked through the refrigerant tube  70  and discharged between the refrigerant tube  70  and the hollow electrode  60 , thereby cooling the closed end  50  and the hollow electrode  60 . Accordingly, the peripheral tissue is not excessively heated and carbonized, so that the tissues can be coagulated and necrotized in a wide area. 
     Here, the control unit supplies the output so that the temperature sensed by the temperature sensor  62  can be maintained over about 55° C. for 5 minutes. If the above condition is satisfied, the control unit decides that the ablation part has been completely coagulated and necrotized, and stops supplying radiofrequency energy. 
       FIGS. 8 and 9  are a disassembly perspective view and a side-sectional view illustrating an electrode for radiofrequency tissue ablation in accordance with a fourth embodiment of the present invention. 
     The fourth embodiment of the present invention is almost identical to the third embodiment described above. As depicted in  FIGS. 8 and 9 , the hollow electrode  60  includes the non-insulation unit  60   a  formed in a hollow tube shape at one side end connected to the closed end  50 , and the insulation unit  60   b  covered with the insulation member  66 . Even though the non-insulation unit  60   a  and the insulation unit  60   b  have the same outside diameter, the non-insulation unit  60   a  is grinded to have a larger inside diameter than the insulation unit  60   b . The mounting grooves  64  and  64  are formed long in the length direction on the outer circumference of the insulation unit  60   b . The temperature sensors  62  and  62  and the electric wires are installed on the mounting grooves  64  and  64  to be connected to the control unit. The insulation member  66  is covered on the whole outer circumference of the insulation unit  60   b . Only the non-insulation unit  60   a  generates radiofrequency electric energy, thereby coagulating and necrotizing the peripheral tissue. The refrigerant tube  70  and the temperature sensor line  80  are inserted into the hollow electrode  60 , so that high pressure refrigerants can be sucked or discharged to cool the non-insulation unit  60   a  generating radiofrequency electric energy. 
     Here, the hollow electrode  60  is a hollow tube thicker than the general hollow electrode. The inner circumference of one side end of the hollow electrode  60  connected to the closed end  50  is grinded to be thinned, for composing the non-insulation unit  60   a . The other part of the hollow electrode  60  composes the insulation unit  60   b . The mounting grooves  64  and  64  are formed long in the length direction on the outer circumference of the insulation unit  60   b  with a predetermined gap from the closed end  50 . Although the temperature sensors  62  and  62  are mounted on the mounting grooves  64  and  64 ′ the temperature sensors  62  and  62  compose the same curved surface with the outer circumference of the insulation unit  60   b.    
     As the non-insulation unit  60   a  is thinner than the insulation unit  60   b , cooling efficiency by the circulated refrigerants can be improved in spite of radiofrequency electric energy. Since the insulation unit  60   b  occupying the large part of the whole electrode is thicker than the non-insulation unit  60   a , when the electrode is inserted into the ablation part, intensity can be improved. 
     On the insulation unit  60   b , one of the mounting grooves  64  and  64  can be formed, the pair of mounting grooves  64  and  64  can be formed in the circumference direction at an interval of 180° or more than two mounting grooves  64  and  64 ′ can be formed in the circumference direction at predetermined intervals. The temperature sensors  62  and  62 ′ can be installed on the mounting grooves  64  and  64 ′ respectively. Each of the temperature sensors  62  and  62 ′ is installed in different positions within the ablation range considering a predetermined tolerance, for precisely sensing the temperature of the tissue and deciding coagulation and necrosis of the tissue. 
     Preferably, the mounting grooves  64  and  64 ′ are formed from the point separated from the end of the insulation unit  60   b  by at least 5 mm, so that the temperature sensors  62  and  62 ′ can be less influenced by heat generated by the non-insulation unit  60   a . The temperature sensors  62  and  62 ′ are mounted inside the mounting grooves  64  and  64 ′ The temperature sensors  62  and  62 ′ are installed on the position separated from the center C of the length of the closed end  50  and the non-insulation unit  60   a  by different set values r and R within the radius range considering a tolerance of an ablation part. When the temperature sensors  62  and  62 ′ are maintained over 55° C. for 5 minutes, the control unit decides that the ablation part has been completely coagulated and necrotized, and stops generating radiofrequency electric energy. 
     Various kinds of electrodes are manufactured according to the installation positions of the temperature sensors  62  and  62 ′ In addition, one electrode can be used for various sizes of ablation parts, by installing the temperature sensors  62  and  62 ′ to slide in the length direction. 
     The closed end  50 , the insulation member  66 , the refrigerant tube  70  and the temperature sensor line  80  of the fourth embodiment are identical to those of the third embodiment, and thus detailed explanations thereof are omitted. The operation of the whole electrode will now be explained. 
     The electrode is selected in consideration of the installation position of the temperature sensors  62  and  62 ′ according to the size of the ablation part, or the installation positions of the temperature sensors  62  and  62 ′ are set by sliding. The electrode is inserted into the tissue so that the center C of the length of the closed end  50  and the non-insulation unit  60   a  can be positioned at the center of the ablation part. Even through the insulation member  66  is covered on the insulation unit  60   b , since the outer circumferences of the non-insulation unit  60   a  and the insulation unit  60   b  maintain the same curved surface, the electrode can be easily inserted into the tissue without being hooked. 
     Thereafter, the control unit supplies radiofrequency energy to the electrode. The output is transmitted to the hollow electrode  60  and the closed end  50 , thereby generating radiofrequency electric energy in the closed end  50  and the non-insulation unit  60   a . The peripheral tissue is coagulated and necrotized from the elliptical shape to the spherical shape by radiofrequency electric energy. At the same time, the high pressure refrigerants are sucked through the refrigerant tube  70  and discharged between the refrigerant tube  70  and the hollow electrode  60 , thereby cooling the closed end  50  and the hollow electrode  60 . Accordingly, the peripheral tissue is not excessively heated and carbonized, so that the tissues can be coagulated and necrotized in a wide area. 
     Here, the control unit supplies the output so that the temperatures sensed by the temperature sensors  62  and  62 ′ can be maintained over about 55° C. for 5 minutes. If the above condition is satisfied, the control unit decides that the ablation part has been completely coagulated and necrotized, and stops supplying radiofrequency electric energy. 
       FIGS. 10 and 11  are a disassembly perspective view and a side-sectional view illustrating an electrode for radiofrequency tissue ablation in accordance with a fifth embodiment of the present invention. 
     In accordance with the fifth embodiment of the present invention, referring to  FIGS. 10 and 11 , the hollow electrode  60  is thicker than the general hollow electrode. The closed end  50  is connected to one end of the hollow electrode  60 . The mounting groove  64  is formed long in the length direction with a predetermined gap from the closed end  50 . The temperature sensor  62  and the electric wire are installed on the mounting groove  64  to be connected to the control unit. The insulation member  66  is inserted onto the outer circumference of the closed end  50  to cover the mounting groove  64 . Therefore, the part of the hollow electrode  60  adjacent to the closed end  50  generates radiofrequency electric energy, thereby coagulating and necrotizing the peripheral tissue. A saline solution is injected into the hollow electrode  60  and the plurality of holes  60   h  are formed on the part of the hollow electrode  60  adjacent to the closed end  50 , so that the saline solution can be discharged to the tissue contacting the closed end  50  and the part of the hollow electrode  60  generating radiofrequency electric energy. Thus, radiofrequency electric energy can be transmitted to the wide area. 
     Here, the hollow electrode  60  includes the non-insulation unit  60   a  which is not covered with the insulation member  66  and the insulation unit  60   b  covered with the insulation member  66 . The non-insulation unit  60   a  and the insulation unit  60   b  are hollow tubes having the uniform inside and outside diameters. The plurality of holes  60   h  are formed on the non-insulation unit  60   a  in the circumference direction and the length direction at predetermined intervals. 
     Preferably, a low pressure saline solution is injected into the hollow electrode  60  to be directly discharged to the tissue through the holes  60   h  of the hollow electrode  60 . The saline solution is a physiological saline solution which is not harmful to the tissue, for example, 0.9% saline solution, namely, an isotonic solution. 
     The closed end  50 , the temperature sensor  62  and the insulation member  66  of the fifth embodiment are identical to those of the other embodiments, and thus detailed explanations thereof are omitted. The operation of the whole electrode will now be explained. 
     The electrode is selected in consideration of the installation position of the temperature sensor  62  according to the size of the ablation part, or the installation position of the temperature sensor  62  is set by sliding. The electrode is inserted into the tissue so that the center C of the length of the closed end  50  and the non-insulation unit  60   a  can be positioned at the center of the ablation part. Since the outer circumferences of the non-insulation unit  60   a  and the insulation unit  60   b  are smoothly connected to each other, the electrode can be easily inserted into the tissue without being hooked. 
     Thereafter, the control unit supplies radiofrequency energy to the electrode. The output is transmitted to the hollow electrode  60  and the closed end  50 , so that the closed end  50  and the non-insulation unit  60   a  can generate radiofrequency electric energy in the closed end  50  and the non-insulation unit  60   a . The peripheral tissue is coagulated and necrotized from the elliptical shape to the spherical shape by radiofrequency electric energy. At the same time, the low pressure refrigerants are sucked through the hollow electrode  60  and directly discharged to the tissue through the holes  60   h  formed on the non-insulation unit  60   a  adjacent to the closed end  50 . Accordingly, the peripheral tissue is not carbonized, and the refrigerants are operated as conductors for transmitting radiofrequency electric energy to the whole tissues to which the refrigerants are sucked. As a result, a relatively large ablation part can be rapidly coagulated and necrotized. 
     Here, the control unit supplies the output so that the temperature sensed by the temperature sensor  62  can be maintained over about 55° C. for 5 minutes. If the above condition is satisfied, the control unit decides that the ablation part has been completely coagulated and necrotized, and stops supplying radiofrequency energy. 
     As discussed earlier, in accordance with the present invention, the high pressure refrigerants are sucked or discharged to/from the electrode and some of the refrigerants are discharged to the tissue for cooling, the high pressure refrigerants are sucked or discharged to/from the electrode for cooling, or the low pressure refrigerants are sucked to the electrode and wholly discharged to the tissue for cooling. Although the preferred embodiments of the present invention have been described, it is understood that the present invention should not be limited to these preferred embodiments but various changes and modifications can be made by one skilled in the art within the spirit and scope of the present invention as hereinafter claimed. 
     INDUSTRIAL APPLICABILITY 
     In the electrode for radiofrequency tissue ablation, at least one temperature sensor is mounted inside the insulation member on the outer circumference of the hollow electrode separated from the closed end generating radiofrequency electric energy by a predetermined gap. Generation of radiofrequency electric energy is controlled by adjusting the output supplied to the closed end and the hollow electrode according to the temperature sensed by the temperature sensor. Whether the target part of the tissue is completely coagulated and necrotized can be decided according to the temperature sensed by the temperature sensor. As a result, the specific part of the tissue can be precisely coagulated and necrotized by selectively using the electrodes whose temperature sensors are installed in different positions, which results in precise ablation.