Abstract:
An ablation apparatus includes a handpiece, an electrode extending from a handpiece distal end, a probe, a thermal sensor and an energy source. The electrode includes a distal end and a lumen, a cooling medium inlet conduit and a cooling medium exit conduit. Both conduits extend through the electrode lumen to an electrode distal end. A sidewall port, isolated from a cooling medium flowing in the inlet and outlet conduits, is formed in the electrode. The probe is at least partially positionable in the electrode lumen and configured to be advanced and retracted in and out of the sidewall aperture. The thermal sensor is supported by the probe. The electrode is coupled to an energy source.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is continuation of U.S. Ser. No. 08/964,034, filed Nov. 4, 1997, now U.S. Pat. No. 6,059,780 which is a continuation-in-part of U.S. patent application Ser. No. 08/616,928, filed Mar. 15, 1996, now U.S. Pat. No. 5,810,804 which is a continuation-in-part of Ser. No. 08/515,379, filed Aug. 15, 1995, now U.S. Pat. No. 5,683,384 all of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to an ablation apparatus with an internally cooled electrode, and more particularly to an electrode with a closed looped cooling device positioned in an electrode lumen, and an electrode sidewall port isolated from a cooling medium flowing through the closed looped cooling device. 
     2. Description of the Related Art 
     Current open procedures for treatment of tumors are extremely disruptive and cause a great deal of damage to healthy tissue. During the surgical procedure, the physician must exercise care in not cutting the tumor in a manner that creates seeding of the tumor, resulting in metastasis. In recent years, development of products has been directed with an emphasis on minimizing the traumatic nature of traditional surgical procedures. 
     There has been a relatively significant amount of activity in the area of hyperthermia as a tool for treatment of tumors. It is known that elevating the temperature of tumors is helpful in the treatment and management of cancerous tissues. The mechanisms of selective cancer cell eradication by hyperthermia are not completely understood. However, four cellular effects of hyperthermia on cancerous tissue have been proposed, (i) changes in cell or nuclear membrane permeability or fluidity, (ii) cytoplasmic lysomal disintegration, causing release of digestive enzymes, (iii) protein thermal damage affecting cell respiration and the synthesis of DNA or RNA and (iv) potential excitation of immunologic systems. Treatment methods for applying heat to tumors include the use of direct contact radio-frequency (RF) applicators, microwave radiation, inductively coupled RF fields, ultrasound, and a variety of simple thermal conduction techniques. 
     Among the problems associated with all of these procedures is the requirement that highly localized heat be produced at depths of several centimeters beneath the surface of the skin. 
     Attempts to use interstitial local hyperthermia have not proven to be very successful. Results have often produced nonuniform temperatures throughout the tumor. It is believed that tumor mass reduction by hyperthermia is related to thermal dose. Thermal dose is the minimum effective temperature applied throughout the tumor mass for a defined period of time. Because blood flow is the major mechanism of heat loss for tumors being heated, and blood flow varies throughout the tumor, more even heating of tumor tissue is needed to ensure effective treatment. 
     The same is true for ablation of the tumor itself through the use of RF energy. Different methods have been utilized for the RF ablation of masses such as tumors. Instead of heating the tumor it is ablated through the application of energy. This process has been difficult to achieve due to a variety of factors including, (i) positioning of the RF ablation electrodes to effectively ablate all of the mass, (ii) introduction of the RF ablation electrodes to the tumor site and (iii) controlled delivery and monitoring of RF energy to achieve successful ablation without damage to non-tumor tissue. 
     RF ablation electrodes tend to impede out when used at higher power levels. The tissue adjacent to the electrode surface tends to char. There have been numerous cooled electrodes. Examples of cooled electrodes are found in U.S. Pat. Nos. 4,290,435; 4,140,130; 4,881,543; 5,334,193; 5,342,357; 5,348,554; 5,423,811; 5,423,807; 5,437,662; and 5,462,521. 
     There is a need for an ablation apparatus with a closed loop cooling device positioned in an electrode lumen. There is a further need for an ablation apparatus with a closed loop cooling device positioned in an electrode lumen, and an electrode sidewall port isolated from the closed loop cooling device and suitable for the introduction of probes and/or infusion solutions into a selected tissue site. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the invention to provide an ablation apparatus and method with an ablation electrode that does not impede out. 
     Another object of the invention is to provide an ablation apparatus and method with a cooled ablation electrode. 
     Yet another object of the invention is to provide an ablation apparatus and method with a closed loop cooled ablation electrode. 
     A further object of the invention is to provide an ablation apparatus and method with a closed loop cooled ablation electrode and an electrode sidewall port that is isolated from a cooling medium flowing through the ablation electrode. 
     Still another object of the invention is to provide an ablation apparatus and method with a closed loop cooled ablation electrode, an electrode sidewall port isolated from a cooling medium flowing through the ablation electrode and a probe with a sensor that is advanced in and out of the sideport. 
     Another object of the invention is to provide an ablation apparatus and method with a closed loop cooled ablation electrode, an electrode sidewall port isolated from a cooling medium flowing through the ablation electrode and an infusion medium introduced into a selected tissue site through the sidewall port. 
     These and other objectives are achieved in an ablation apparatus that has a handpiece, an electrode extending from a handpiece distal end, a probe, a thermal sensor and an energy source. The electrode includes a distal end, a lumen, a cooling medium inlet conduit and a cooling medium exit conduit. Both conduits extend through the electrode lumen to an electrode distal end. A sidewall port, isolated from a cooling medium flowing in the inlet and outlet conduits, is formed in the electrode. The probe is at least partially positionable in the electrode lumen and configured to be advanced and retracted in and out of the sidewall port. The thermal sensor is supported by the probe. The electrode is coupled to an energy source. 
     The present invention is also a method for creating an ablation volume in a selected tissue mass. An ablation device is provided that has a handpiece, an electrode, a probe and a thermal sensor supported by the probe. The electrode includes a distal end, a lumen, a cooling medium inlet conduit coupled to a cooling medium outlet conduit which both extend through the electrode lumen to the electrode&#39;s distal end. A sidewall port is formed in a sidewall of the electrode and is isolated from a cooling medium flowing through the electrode. The electrode is inserted into the selected tissue mass. At least a portion of the probe is positioned in the electrode after the electrode has been inserted into the selected tissue mass. A distal end of the probe is advanced from the aperture into the selected tissue. At least a portion of an electrode ablation surface is cooled. Electromagnetic energy is delivered from the electrode to the selected tissue mass. Temperature is measured at a site in the selected tissue mass, and an ablation volume is created. 
     As electromagnetic energy, including but not limited to RF, is delivered to the selected tissue site, the tissue interface adjacent to the electrode can begin to char and conductivity through the tissue decreases. With a cooling medium the tissue interface remains at a temperature suitable for the delivery of electromagnetic energy to the periphery of the desired ablation site. While a cooling medium is flowing through the electrode, one or more probes, with associated sensors, are deployed into the desired ablation site. The ablation is monitored and controlled. Sensors can be positioned not only at the distal ends of the probes but also at intermediate positions. This permits monitoring of the ablation process between the electrode and the periphery of the targeted ablation volume. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a cross-sectional view of the ablation apparatus of the present invention illustrating an electrode with a lumen, a cooling medium inlet conduit, a cooling medium outlet conduit and two probes extending from sidewall ports formed in the lumen. 
     FIG. 2 is a cross-sectional view of the closed loop distal end of the two cooling medium conduits of FIG.  1 . 
     FIG. 3 is a cross-sectional view of another embodiment of the closed loop distal end of the two cooling medium conduits. 
     FIG. 4 is a cross-sectional of FIG. 1 taken along the lines  4 — 4 . 
     FIG. 5 illustrates the creation of a 4 cm spherical ablation volume, with one sensor positioned at the periphery of the ablation volume, and a second sensor positioned on the probe midpoint between the electrode and the distal end of the probe. 
     FIG. 6 is a perspective view of the ablation apparatus of the present invention illustrating two probes extending from a distal end of the electrode. 
     FIG. 7 is a perspective view of the distal end of the electrode of the present invention with probes extending from a distal end of an insulation sleeve. 
     FIG. 8 is a perspective view of the ablation apparatus of the present invention illustrating the deployment of four probes from the electrode. 
     FIG. 9 is a block diagram illustrating a feedback system useful ton control the temperature of energy delivering electrodes. 
     FIG. 10 illustrates a circuit useful to implement the feedback system of FIG.  9 . 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1, an ablation apparatus  10  includes a handpiece  11 , an electrode  12 , a cooling medium inlet conduit  16 , a cooling medium outlet conduit  16  and a cap  18 , with tapered distal end, that create a closed loop cooling system. Handpiece can be an insulated portion of electrode  12 . A variety of different cooling mediums can be used including but not limited to gas, cooled air, refrigerated air, compressed air, Freon, water, alcohol, saline and the like. A first sidewall port  20  is formed in a sidewall of electrode  12 . A second sidewall port  22  may also be included. First and second sidewall ports can be windows formed in electrode  12  which create a mechanical weak spot in electrode  12 . A first probe  24  is positionable in an electrode lumen before or following introduction of electrode  12  in a selected tissue mass. First probe  24  capable of being advanced and retracted in and out of first sidewall port  20 . An optional second probe  26  is also positioned in the electrode lumen and is capable of being advanced and retracted to a selected tissue ablation side through second sidewall port  22 . 
     Electrode  12  has an exterior ablation energy delivery surface which delivers electromagnetic energy to the selected tissue ablation mass, and may have a tapered or sharpened distal end. For the ablation of tumors, electrode  12  can have an exterior ablation energy delivery surface length of 0.25 inches or less, and an outer diameter for electrode  12  of about 0.072 inches or less. 
     Each probe  24  and  26  can be formed of a variety of materials, including but not limited to stainless steel, shaped memory metals and the like. The size of probes  24  and  26  vary depending on the medical application. For the treatment of tumors, probes  24  and  26  have a length extending from the sidewall ports into tissue of 3 cm or less. A first sensor  28  can be supported by probe  24  on an interior or exterior surface. First sensor  28  is preferably positioned at a distal end of probe  24 . A second sensor  30  may be positioned on probe  24  somewhere intermediate between an exterior surface of electrode  12  and the distal end of probe  24 . Preferably, second sensor  30  is located at a position where it can sense temperature at a midpoint in a selected tissue ablation volume. Second sensor  30  is useful to determine if probe  24  has encountered an obstruction, such as a blood vessel, to the ablation process. If first sensor  28  measures a higher temperature than second sensor  30 , then this can indicate that second sensor  30  is close to a circulatory vessel. When this occurs, ablation energy is carried away by the vessel. Similarly, second probe  26  can also include one or more sensors. A third sensor  32  can be positioned at an exterior surface of electrode  12 . 
     Sensors  28 ,  30  and  32  permit accurate measurement of temperature at a tissue site in order to determine, (i) the extent of ablation, (ii) the amount of ablation, (iii) whether or not further ablation is needed and (iv) the boundary or periphery of the ablated mass. Further, sensors  28 ,  30  and  32  prevent non-targeted tissue from being destroyed or ablated. 
     Sensors  28 ,  30  and  32  are of conventional design, including but not limited to thermistors, thermocouples, resistive wires, and the like. Suitable thermal sensors  24  include a T type thermocouple with copper constantene, J type, E type, K type, fiber optics, resistive wires, thermocouple IR detectors, and the like. Sensors  28 ,  30  and  32  need not be thermal sensors. 
     Sensors  28 ,  30  and  32  measure temperature and/or impedance to permit monitoring and a desired level of ablation to be achieved without destroying too much tissue. This reduces damage to tissue surrounding the targeted mass to be ablated. By monitoring the temperature at various points within the interior of the selected tissue mass, a determination of the selected tissue mass periphery can be made, as well as a determination of when ablation is complete. If at any time sensor  28 ,  30  or  32  determines that a desired ablation temperature is exceeded, then an appropriate feedback signal is received at energy source  34  which then regulates the amount of energy delivered to electrode  12 , as more fully explained hereafter. 
     Electrode  12  is coupled to an electromagnetic energy source  34  by wiring, soldering, connection to a common couplet, and the like. Electrode  12  can be independently coupled to electromagnetic energy source  34  from probes  24  and  26 . Electrode  12 , and probes  24  and  26  may be multiplexed so that when energy is delivered to electrode  12  it is not delivered to probes  24  and  26 . Electromagnetic energy power source can be an RF source, microwave source, shortwave source, and the like. 
     Electrode  12  is constructed to be rigid enough so that it can be introduced percutaneously or laparoscopically through tissue without an introducer. The actual length of electrode  12  depends on the location of the selected tissue mass to be ablated, its distance from the skin, its accessibility as well as whether or not the physician chooses a laparoscopic, percutaneous or other procedure. Suitable lengths include but are not limited to 17.5 cm, 25.0 cm. and 30.0 cm. Electrode  12 , can be introduced through a guide to the selected tissue ablation site. 
     An insulation sleeve  38  can be positioned in a surrounding relationship to an exterior surface of electrode  12 . Insulation sleeve  38  can be moveable along electrode&#39;s  12  exterior surface in order to provide a variable length ablation energy delivery surface. 
     In one embodiment, insulation sleeve  38  can comprise a polyimide material. A sensor may be positioned on top of polyimide insulation sleeve  38 . Polyamide insulation sleeve  18  is semi-rigid. The sensor can lay down substantially along the entire length of polyimide insulation sleeve  38 . Handpiece  11  can serve the function of a handpiece and include markings to show the length of insulation sleeve  38  and the length of electrode&#39;s  12  exposed ablation energy delivery surface. 
     Referring now to FIG. 2, cap  18  is illustrated as creating a closed loop cooling medium flow channel. Cap  18  is secured to the distal ends of conduits  14  and  16  by a variety of means, including but not limited to welding, soldering, application of an epoxy, and the like. Cap  18  can have a step which is secured to the distal end of electrode  12  by soldering, welding, press sit and the like. Instead of cap  18 , a “U” joint can be formed at the distal ends of conduits  16  and  18 , as shown in FIG.  3 . 
     Referring to FIG. 4, only a portion of electrode has an interface with cooling medium inlet conduit  14 . However, the diameters of cooling medium inlet conduit  14  and electrode  12  are dimensioned so that a tissue interface formed adjacent to the exterior surface of electrode  12  does not become sufficiently desiccated and charred to prevent the transfer of energy through the selected tissue ablation site to the periphery of the site. 
     The creation of a 4 cm diameter spherical ablation is illustrated in FIG. 5. A 4 cm ablation energy delivery surface of electrode  12  is exposed. First sidewall port  20  is positioned 2 cm from a distal end of electrode  12 . First probe  24  is advanced from electrode lumen with its distal end positioned at the periphery of the spherical ablation area. First sensor  28  is positioned at the distal end of first probe  24  and determines when the ablation has reached the periphery of the desired ablation area. Second sensor  30  is positioned midpoint on first probe  24  to monitor the transfer of electromagnetic energy through the desired ablation area, and determine if there are any obstructions to the ablation process at that position. Once the ablation is completed, first probe  24  is retracted back into the lumen of electrode  12 . 
     Electromagnetic energy delivered by electrode  12  causes the electrode/tissue interface at the electrode ablation delivery surface to heat, and return the heat to electrode  12 . As more heat is applied and returned, the charring effect electrode  12  increases. This can result in a loss of electromagnetic energy conductivity through the selected tissue site. The inclusion of cooling with electrode  12  does not affect the effective delivery of electromagnetic energy to the selected tissue ablation site. Cooling permits the entire selected tissue ablation site to be ablated while reducing or eliminating the heating of the electrode/tissue interface tissue. 
     In FIG. 6, probes  24  and  26  are each deployed out of the distal end of electrode  12  and introduced into the selected tissue mass. Probes  24  and  26  form a plane. 
     As shown in FIG. 7 insulation sleeve  38  can include one or more lumens for receiving secondary probes  24 ,  26  as well as additional probes which are deployed out of a distal end of insulation sleeve  38 . FIG. 8 illustrates four probes introduced out of different sidewall ports formed in the body of electrode  12 . Some or all of the probes provide an anchoring finction. 
     FIG. 9 illustrates a block diagram of a temperature/impedance feedback system that can be used to control cooling medium flow rate through electrode  12 . Electromagnetic energy is delivered to electrode  12  by energy source  34 , and applied to tissue. A monitor  42  ascertains tissue impedance, based on the energy delivered to tissue, and compares the measured impedance value to a set value. if the measured impedance exceeds the set value a disabling signal  44  is transmitted to energy source  34 , ceasing fuirther delivery of energy to electrode  12 . If measured impedance is within acceptable limits, energy continues to be applied to the tissue. During the application of energy to tissue sensor  46  measures the temperature of tissue and/or electrode  12 . A comparator  48  receives a signal representative of the measured temperature and compares this value to a pre-set signal representative of the desired temperature. Comparator  48  sends a signal to a flow regulator  50  representing a need for a higher cooling medium flow rate, if the tissue temperature is too high, or to maintain the flow rate if the temperature has not exceeded the desired temperature. 
     An output  52  from temperature comparator  48  can be input to energy source  34  to regulate the amount of power delivered by power source  32 . Output  54  from impedance monitor  106  can be input to flow regulator  50  to regulate fluid flow and thus control temperature of the tissue. 
     Referring now to FIG. 10, energy source  34  is coupled to electrode  12 , to apply a biologically safe voltage to the selected tissue site. In the embodiment illustrated in FIG. 10, ablation apparatus  10  is represented as a bipolar ablation device having an energy delivering electrode  12  and a ground electrode  56 . Both electrodes  12  and  56  are connected to a primary side of transformer windings  58  and  60 . The common primary winding  58 ,  60  is magnetically coupled with a transformer core to secondary windings  58 ′ and  60 ′. 
     The primary windings  58  of the first transformer t 1  couple the output voltage of ablation apparatus  10  to the secondary windings  58 ′. The primary windings  60  of the second transformer t 2  couple the output current of ablation apparatus  10  to the secondary windings  60 ′. 
     Measuring circuits determine the root mean square (RMS) values or magnitudes of the current and voltage. These values, represented as voltages, are inputted to a diving circuit D to geometrically calculate, by dividing the RMS voltage value by the RMS current value, the impedance of the tissue site at sensor  46 . 
     The output voltage of the divider circuit D is presented at the positive (+) input terminal of comparator A. A voltage source V o  supplies a voltage across the variable resistor R v , thus allowing one to manually adjust the voltage presented at the negative input of comparator A. This voltage represents a maximum impedance value beyond which power will not be applied to electrode  12 . Specifically, once the tissue is heated to a temperature corresponding to an impedance value greater than the maximum cut-off impedance, energy source  34  stops supplying energy to electrode  12 . Comparator A can be of any of a commercially available type that is able to control the amplitude or pulse width modulation of energy source  34 . 
     The flow rate of cooling medium can be controlled based on the tissue impedance, as represented by signal  62 , or based on tissue temperature, as represented by signal  64 . In one embodiment, the switch S is activated to allow the impedance signal  62  to enter the positive (+) input terminal of comparator A. This signal along with the reference voltage applied to the negative (−) input terminal actuates comparator A to produce an output signal. If the selected tissue ablation site is heated to a biologically damaging temperature, the tissue impedance will exceed a selected impedance value seen at the negative (−) input terminal, thereby generating disabling signal  44  to disable energy source  34 , ceasing the power supplied to electrode  12 . 
     The output signal of comparator A can be communicated to a pump  66 . If the temperature of the selected tissue ablation site is too high, despite the tissue impedance falling within acceptable limits, pump  66  adjusts the rate of cooling medium flow applied to electrode  12  to decrease the temperature of electrode  12 . The output signal of comparator A may either disable energy source&#39;s  34  energy output, depending on the tissue temperature as reflected by its impedance, or cool electrode  12  or perform both operations simultaneously. 
     The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. It is intended that the scope of the invention be defined by the following claims and their equivalents.