Patent Publication Number: US-2007112342-A1

Title: Tissue ablation apparatus and method

Description:
This application is a continuation of U.S. patent application Ser. No. 10/142,713 filed May 10, 2002, now allowed, which claims the benefit of U.S. Provisional Application No. 60/290,060 filed May 10, 2001, both of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD  
      This invention relates generally to a method for treating tissue, tissue masses, tissue tumors and lesions. More particularly, the invention relates to an apparatus and method for minimally invasive therapeutic treatment of tumors and tissue mass. Still more particularly, the invention relates to a method and apparatus utilizing fluid to enhance the delivery of energy to tumor and tissue masses to produce larger, faster ablation volumes with improved clinical outcomes.  
     BACKGROUND  
      Current methods for treating tumors using RF energy have several key shortcomings including incomplete ablation volumes, small ablation volumes, tissue desiccation and charring or protracted ablation times. The present invention provides a method and apparatus to solve these and other related problems.  
     SUMMARY  
      The invention includes, in one aspect, a tissue-ablation apparatus composed of an elongate delivery device having a lumen terminating at a distal end and a plurality of electrodes carried in the device for movement between retracted positions at which the electrodes are disposed within the device&#39;s lumen, and deployed positions at which the electrodes are deployed from the distal end at a plurality of arcuate, laterally extending, angularly spaced positions. Each deployed electrode defines an individual-electrode ablation volume which, in the early phases of ablation, is proximate to that electrode when an RF current is applied to that electrode, with such deployed in tissue, where contained application of RF current to the electrodes causes the individual-electrode ablation volumes to grow and merge with each other to form a combined-electrode ablation volume.  
      Also in the apparatus is a plurality of elongate sensor elements carried in the device for movement between retracted positions at which the sensor elements are disposed within the device&#39;s lumen, and deployed positions at which the sensor are deployed from the distal end at a plurality of angularly spaced positions within the volume corresponding to the combined-electrode ablation volume.  
      A control device or unit in the apparatus is operatively connected to the electrodes and to the sensor elements for (i) supplying an RF power to the electrodes, with such deployed in tissue, to produce tissue ablation that advances from the individual-electrode ablation volumes to fill the combined-electrode ablation volume, and (ii) determining the extent of ablation in the regions of the sensor elements. The supply of RF power to the electrodes can thus be regulated to control the level and extent of tissue ablation throughout the combined-electrode volume.  
      The electrodes and sensor elements may be operatively connected for movement as a unit from their retracted to their deployed positions. Alternatively, the electrodes may be movable from their retracted to their retracted and deployed positions independent of the movement of the sensor elements from their retracted and deployed positions.  
      The sensor elements are in their deployed positions may be disposed outside of the individual-electrode ablation volumes, preferably midway between pairs of adjacent electrodes in their deployed state.  
      In one embodiment, the sensor elements are conductive wires, and the control device is operable to determine the impedance of tissue in the regions of the wires, as a measure of extent of ablation in the region of the sensor elements.  
      In another embodiment, the sensor elements have thermal sensors, and the control device is operable to determine tissue temperature in the region of the thermal sensors, as a measure of the extent of ablation in the region of the sensor elements.  
      In still another embodiment, the sensor elements are optical fibers, and the control device is operable to determine optical properties in the region of the fibers, as a measure of the extent of ablation in the region of the sensor elements.  
      The electrodes may be hollow-needle electrodes, allowing liquid to be injected through said electrodes into tissue, with the electrodes deployed in tissue. An exemplary liquid is an electrolyte, such as a physiological salt solution. In a preferred embodiment, the electrodes are designed to allow controlled fluid flow through each electrode individually.  
      Each infusion electrode may have a plurality of infusion ports along its distal end regions, and may be covered by a sheath that is axially movable between deployment and infusion positions at which the infusion ports are covered and exposed, respectively.  
      The control unit may include a display function for displaying to a user the extent of ablation of in the regions of the sensor elements, and an adjustable function, such as an RF power function, or liquid-infusion function, by which the user can adjust or modulate the rate or extent of ablation by modulating power level or amount of liquid infused into the ablation volume. Preferably the power of infusion functions can be controlled at the level of the individual electrodes, allowing for control over the rate and extent of individual-electrode volumes during the ablation procedure.  
      Alternatively, or in addition, the control unit may automatically control the power level and/or rate of infusion of liquid to one or more electrodes, during an ablation procedure, to modulate the rate and/or extent of individual regions of the desired ablation volume, for example, to ensure a uniform rate and extent of ablation throughout the desired combined-electrode ablation volume.  
      In one general embodiment, the electrodes, when deployed, are positioned near the center of the faces of a platonic solid that defines a desired combined-electrode ablation volume. The number of faces of the platonic solid, and therefore the number of electrodes deployed will be determined, for example, by the size of the desired ablation volume. The sensor elements, when deployed, may be positioned near the vertices of the platonic solid. For example, for ablating a substantially spherical volume that circumscribes a pyramid, the apparatus may have four electrodes that are positioned near the center of the faces of the pyramid when deployed, and four sensors that are placed near the vertices of the pyramid when deployed.  
      In another aspect, the invention includes a method for ablating a selected volume of tissue in a patient. The method includes inserting into the tissue, a tissue-ablation apparatus having (a) an elongate delivery device with a lumen terminating at a distal end, and (b) a plurality of hollow-needle electrodes carried in the device for movement between retracted positions at which the electrodes are disposed within the device&#39;s lumen, and deployed positions at which the electrodes are deployed from the distal end at a plurality of arcuate, laterally extending, angularly spaced positions. The electrodes, in their deployed positions, define the selected tissue volume to be ablated. Liquid, such as an electrolyte is introduced into the tissue through the hollow-needle electrodes, by separately controlling the rate of liquid flow through each hollow-needle electrode. RF power is applied to the electrodes, to produce RF ablation of the tissue.  
      The liquid may be introduced at substantially equal flow rates through each electrode. An electrolyte having a desired electrolyte concentration may be selected. The liquid may be introduced prior to, during, or following the RF ablation step.  
      The method may further include monitoring the extent of ablation in the tissue volume during said applying step, and adjusting the rate at which liquid is introduced through individual hollow-needle electrodes in response to the monitoring, for example, to produce a uniform rate and extent of ablation throughout tissue volume being ablated.  
      These and other objects and features of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view illustrating the placement and deployment of an embodiment of a tissue infusion ablation apparatus for the treatment of tumors.  
       FIGS. 2   a  and  2   b  are perspective views illustrating the key components of a tissue infusion ablation including configurations of the infusion device having multiple syringes and multi-channel tubing.  
       FIG. 3  is a lateral view illustrating various components of the handpiece and associated coupled devices.  
       FIG. 4  is a lateral view illustrating an embodiment of the apparatus of  FIG. 1  or  2  having a deflectable introducer.  
       FIG. 5  is a lateral view illustrating an embodiment of the apparatus of  FIG. 1  or  2  having a deflectable portion at the distal end of the introducer.  
       FIG. 6  is a lateral view illustrating an embodiment having a hingedly attached deflectable portion of the introducer.  
       FIGS. 7   a  and  7   b  are lateral views illustrating use of an apparatus having a deflectable introducer useful in an embodiment of method the invention.  
       FIGS. 8   a - 8   j  are cross sectional views illustrating various cross sectional shapes of the introducer and lumen.  
       FIGS. 9   a - 9   h  are lateral views illustrating various configurations of the electrode including ring-like, ball, hemispherical, cylindrical, conical and needle-like.  
       FIG. 10  is lateral view illustrating an embodiment of a needle electrode configured to penetrate tissue.  
       FIG. 11  is lateral view illustrating a needle electrode having at least one radii of curvature.  
       FIG. 12  is a lateral view illustrating an embodiment of an electrode having a lumen and apertures for the delivery of fluid and the use of infused electrolytic fluid to create an enhanced electrode.  
       FIG. 13   a  is a lateral view illustrating an embodiment of an electrode or introducer having apertures with increasing diameters moving in a distal direction, and  FIG. 13   b  is a plot showing change in aperture size on progressing toward a needle end.  
       FIG. 14   a  is a lateral view illustrating an embodiment of an electrode or introducer having one or more apertures positioned on a force neutral axis.  
       FIG. 14   b  is a lateral view illustrating an embodiment of an electrode having apertures positioned on opposite lateral sides of the electrode.  
       FIG. 15   a  is a lateral view illustrating an embodiment of an RF electrode with apertures configured to provide a cooling fluid to the electrode and surrounding tissue.  
       FIG. 15   b  is an enlarged sectional view showing distribution of infused liquid from different shaped orifices.  
       FIG. 16  is a lateral view illustrating an embodiment of the electrode having laterally positioned apertures (e.g. side holes).  
       FIG. 17  is a lateral view illustrating an embodiment of the electrode having a non-stick coating to reduce plugging of fluid apertures by adherent and/or coagulated tissue.  
       FIGS. 18   a - 18   c  are lateral views illustrating use of an embodiment of the electrode having a protective sheath configured to reduce fluid aperture plugging.  
       FIG. 19  is a lateral view illustrating an embodiment of the electrode having a bevel angle configured to minimize plugging.  
       FIGS. 20   a  and  20   b  are lateral views illustrating an embodiment of the electrode or trocar having a porous or braided distal portion.  
       FIG. 21  is a lateral view illustrating an embodiment of a method of the invention in which fluid is infused through multiple electrodes to create infusion zones that coalesce to form a larger infusion volume.  
       FIGS. 22   a  and  22   b  are lateral perspective views illustrating the use of multiple infusing electrodes to generate an ablation volume.  
       FIG. 23  is a perspective view illustrating an embodiment of a tissue infusion ablation having one or more passive monitoring members and ablation electrodes/active members positionable at a tissue site.  
       FIG. 24  is a perspective view illustrating various embodiments of positioning of sensors on the passive member and coupling of sensors to monitoring resources.  
       FIG. 25  is a perspective view illustrating the position of passive members to define a sampling volume.  
       FIG. 26  is a perspective view illustrating the relative positioning of the active electrodes to define a tetrahedron shaped sampling volumes bounded by a spherical ablation volume.  
       FIG. 27  is a perspective view illustrating an embodiment of the apparatus having passive and active arrays configured such that the passive elements are equally spaced between the active elements/electrodes.  
       FIGS. 28   a - 28   c  are perspective views illustrating different embodiment of the trocar,  FIG. 28   a  illustrates a standard trocar having a sharpened leading edge;  FIG. 28   b  illustrates an embodiment of a trocar configured with a leading inner edge; and  FIG. 28   c  illustrates an embodiment of a trocar having a coated leading inner edge.  
       FIG. 29  is a frontal view illustrating an embodiment of the apparatus with a packing arrangement of active and passive member configured to prevent the passive members from contacting and being scythed or abraded by the sharpened edges of the trocar.  
       FIG. 30  is lateral view illustrating an embodiment of the trocar having an abrupt transition from the insulate to non-insulated trocar sections.  
       FIG. 31  is lateral view illustrating an embodiment of the trocar having a stepped distal end with a diameter configured to achieve a smooth transition form the insulated to non insulates trocar section.  
       FIG. 32  is a lateral view illustrating an embodiment of an energy delivery device with a radioactive section and its use in an embodiment of a method of the invention.  
       FIG. 33  is a lateral view illustrating use of photo-therapeutic agents in an embodiment of a method of the invention.  
       FIG. 34  is a block diagram illustrating the inclusion of a controller, energy source and other electronic components of the present invention.  
       FIG. 35  is a block diagram illustrating an analog amplifier, analog multiplexer and microprocessor used with the present invention.  
       FIG. 36  is a perspective view illustrating the use of platonic solids to optimize ablation volume in a method of the invention.  
       FIGS. 37   a - 37   e  are perspective views illustrating various platonic solids applicable to the embodiment of  FIG. 36 . 
    
    
     DETAILED DESCRIPTION  
      Embodiments of the present invention provide the benefit of a method and apparatus to treat tumors and lesions such as hepatic tumors by utilizing conductivity enhancing solutions to deliver ablative electromagnetic energy to produce faster, larger and more consistent ablation volumes than by conventional means. However one of the potential problems in infusing fluids through a hollow tube or hollow electrode is plugging of the electrode fluid lumen as the electrode is inserted into tissue, or a resulting of tissue coagulation from heating of the electrode during energy delivery or a combination of both. Further embodiments of the present invention provide a number of solutions to problem of tissue plugging of electrodes and infusion lumens occurring during insertion of the electrode into tissue or during the delivery of ablative energy.  
      An embodiment of a tissue infusion ablation apparatus  10  to treat tumors and lesions is shown in  FIG. 1 . The apparatus is configured to be positioned at a bone tissue site  5 ′ to treat or ablate a tumor or lesion  5 ″. Tissue site  5 ′ can be located in any location in various tissue including but not limited to liver, bone, breast, brain and lung. The apparatus can be configured to treat a number of lesions and ostepathologies including but not limited to metastatic lesions, osteolytic lesions, osteoblastic lesions, tumors, fractures, infected site, inflamed sites and the like. Once positioned at target tissue site  5 ′, apparatus  10  can be configured to treat and ablate tissue at that site as well as collect a tissue sample using a bone biopsy device described herein or known in the art.  
      Referring now to  FIG. 2 , an embodiment of a tissue infusion ablation apparatus  10  includes an elongated member or shaft  12  with a proximal end  14 , a distal end  16 , and an internal lumen extending therebetween or at least through a portion of the distal end region. Distal end  16  may be sufficiently sharp to penetrate tissue including bone, cartilage, muscle and fibrous and/or encapsulated tumor masses. In an embodiment, distal end  16  can be a needle that is integral or otherwise coupled to introducer  12  by joining means known in the art such as adhesive bonding, soldering, RF welding, crimping and the like. Shaft  12  may have one or more lumens  13  that may extend over all or a portion of its length. An energy delivery device, generally denoted as  18 , is coupled to distal end  16 ′. Energy delivery device  18  can be configured to be coupled to an energy or power source  20 . A sensor  22  may be coupled to shaft  12  including distal end  16 ′ and energy delivery device  18 .  
      For ease of discussion, shaft  12  will now be referred to as an introducer or delivery device  12 , but all other embodiments discussed herein are equally applicable. Referring now to  FIGS. 1-4 , in various embodiments, introducer  12  can also be coupled at its proximal end  14  to a handle or handpiece  24 . The shaft or introducer is also referred to herein as an elongate delivery device. All or portions of handpiece  24  can be detachable and can include ports  24 ′ and actuators  24 ″. Ports  24 ′ can be coupled to one or more lumens  13  and can include fluid and gas ports/connectors and electrical, optical connectors. In various embodiments, ports  24 ′ can be configured for aspiration (including the aspiration of tissue), and the delivery of cooling, conductivity enhancing, electrolytic, irrigation, polymer and other fluids (both liquid and gas) described herein. Ports  24 ′ can include but are not limited to luer fittings, valves (one-way, two-way), toughy-bourst connectors, swage fittings and other adaptors and medical fittings known in the art. Ports  24 ′ can also include lemo-connectors, computer connectors (serial, parallel, DIN, etc) micro connectors and other electrical varieties well known to those skilled in the art.  
      Further, ports  24 ′ can include opto-electronic connections which allow optical and electronic coupling of optical fibers and/or viewing scopes (such as an orthoscope) to illuminating sources, eye pieces, video monitors and the like. Actuators  24 ″ can include rocker switches, pivot bars, buttons, knobs, ratchets, cams, rack and pinion mechanisms, levers, slides and other mechanical actuators known in the art, all or portion of which can be indexed. These actuators can be configured to be mechanically, electro-mechanically, or optically coupled to pull wires, deflection mechanisms and the like allowing selective control and steering of introducer  12 . Hand piece  24  can be coupled to tissue aspiration/collection devices  26 , fluid delivery devices  28  (e.g. infusion pumps) fluid reservoirs (cooling, electrolytic, irrigation etc)  30  or power source  20  through the use of ports  24 ′. Tissue aspiration/collection devices  26  can include syringes, vacuum sources coupled to a filter or collection chamber/bag. Fluid delivery device  28  can include medical infusion pumps, Harvard pumps, peristaltic pumps, syringe pumps, syringes and the like.  
      Referring back to  FIG. 2 , in various embodiments fluid delivery device can be a syringe pump configured with multiple syringes  28   s , multiple-bore syringes  28   b  with each syringe coupled to a separate fluid lumen or channel  72  directly or via a valve such as an indexing valve  28   i . Related embodiments of infusion device  28  can include an indexing valve  28   i  as well as multi-lumen tubing or multichannel tubing  72   b  (which can be made from PEBAX, silicone or other resilient polymer) connected to one or more lumens  72  via lumen  13  or other channel within external to introducer  12 .  
      In various embodiments, at least portions of tissue infusion ablation apparatus  10  including introducer  12  and distal end  16  may be sufficiently radiopaque to be visible under fluoroscopy and the like and/or sufficiently echogenic to be visible using ultrasonography. In specific embodiments, introducer  12  can include radiopaque, magnopaque or echogenic markers  11 , at selected locations including along all or portions of introducer  12  including distal end  16 ′. Markers  11  can be disposed along introducer  12  to facilitate identification and location of tissue penetrating portion  16  including tissue collection portions, ports, sensors as well as other components and sections of tissue infusion ablation apparatus  10  described herein. In an embodiment, markers  11  can be ultrasound emitters known in the art. Also tissue infusion ablation apparatus  10  can include imaging capability including, but not limited to, fiber optics, viewing scopes such as a orthoscope, an expanded eyepiece, video imaging devices, ultrasound imaging devices and the like.  
      In various embodiments, apparatus  10  can be configured to be percutaneously introduced into tissue through a trocar, biopsy device, or orthoscope or other percutaneous or surgical access device known in the art. For any of these devices, apparatus  10  can be introduced with the aid of a guide wire  15  which introducer  12  is configured to track over. Guide wire  15  can be any of a variety of flexible and/or steerable guide wires or hypotubes known in the art. Introducer  12  can have sufficient length to position distal tip  16 ′ in any portion or lobe of the bone  5  using either a percutaneous or a bronchial/transoral approach. The length of introducer  12  can range from 5 to 180 cm with specific embodiments of 20, 40, 80, 100, 120 and 140 cm. A preferred range includes 25 to 60 cm. The length and other dimensional aspects of introducer  12  can also be configured for pediatric applications with a preferred range in these embodiments of 15 to 40 cm. The diameter of introducer  12  can range from 0.020 to 0.5 inches with specific embodiments of 0.05, 0.1 and 0.3 inches as well as 1, 3, 6, 8 and 10 french sizes as is known in the art. Again, the diameter can be configured for pediatric applications with pediatric sizes of 1, 3 and 6 french. In various embodiments, the diameter of distal end  16  can range from 0.010 to 0.1 inches, with specific embodiments of 0.020, 0.030 and 0.040 inches. The diameter of distal end  16 ′ can be configured to be positioned in various anatomical ducts, vasculature and bronchioles, such embodiment includes diameters of 0.40″ or smaller.  
      In various embodiments, introducer  12  can be a catheter, multi-lumen catheter, or a wire-reinforced or metal-braided polymer shaft, port device (such as those made by the Heartport® Corp., Redwood City, Calif.), subcutaneous port or other medical introducing device known to those skilled in the art. In a specific embodiment introducer  12  is a trocar or a safety trocar and the like. Introducer  12  can be constructed of a variety of metal grade metals known in the art including stainless steel such as 304 or 304V stainless steel as well shape memory metal such as Nitino. Introducer  12  can also be constructed from rigid polymers such as polycarbonate or ABS or resilient polymers including Pebax®, polyurethane, silicones HDPE, LDPE, polyesters and combinations thereof.  
      In various embodiments, introducer  12  can be rigid, semi-rigid, flexible, articulated and steerable and can contain fiber optics (including illumination and imaging fibers), fluid and gas paths, and sensor and electronic cabling. In an embodiment introducer  12  is sufficiently rigid (e.g. has sufficient column strength) to pierce tissue including bone tissue without significant deflection along it longitudinal axis so as to maintain a longitudinal or other position within a tissue site. In another embodiment, all or portions (e.g. the distal portion) of introducer  12  are sufficiently flexible to pierce tissue, and move in any desired direction through tissue to a desired tissue site  5 ′. In yet another embodiment, introducer  12  is sufficiently flexible to reverse its direction of travel and move in direction back upon itself.  
      Referring now to  FIGS. 3 and 4 , in other embodiments all or portions of introducer  12  can be configured to be deflectable and/or steerable using deflection mechanisms  25  which can include pull wires, ratchets, latch and lock mechanisms, piezoelectric materials and other deflection means known in the art. Deflection mechanism  25  can be coupled to or integral with a moveable or slidable actuator  25 ′ on handpiece  24 . Mechanism  25  and coupled actuator  25 ′ are configured to allow the physician to selectively control the amount of deflection  25 ″ of distal tip  16 ′ or other portion of introducer  12 . Actuator  25 ′ can be configured to both rotate and deflect distal tip  16  by a combination of rotation and longitudinal movement of the actuator. In a preferred embodiment deflection mechanism  25  comprises a pull wire coupled  15  to an actuator  24 ′ on handpiece  24  described herein.  
      The amount of deflection of introducer  12  is selectable and can be configured to allow the maneuvering of introducer  12  through very tortuous anatomy and negotiate both obtuse or oblique turns in around various and anatomical structures including vasculature, ducts and bone. In specific embodiments, the distal portions of introducer  12  can be configured to deflect 0-180° or more in up to three axes to allow the tip of introducer  12  to have retrograde positioning capability. The deflection can be continuous or indexed to pre-determined amounts selectable on handpiece  24  using an indexed actuator  25 ′.  
      Referring now to  FIGS. 5, 6  (lateral view of an embodiment having deflectable section  12   d  near the distal end of the introducer) and (lateral view showing a hingedly attached deflectable section), in a specific embodiment introducer  12  has a deflectable or articulated section  12   d  at or near its distal portion  16 . Deflectable portion  12   d  can be formed by use of corrugated or flexible materials (e.g. materials having a lower durometer than the adjoining less flexible section of the introducer) crimping, sectioning, molding, or other polymer metal working or catheter processing methods known in the art. Deflectable portion  12   d  can be deflected by a number of means including pull wires, ratchet mechanism, a can mechanism, a gear mechanism (including a rack and pinion or worm gear mechanism) coupled to a pull wire or a stiffening mandrel which is advanced and withdrawn through lumen  13  of the introducer. Deflectable portion  12   d  can also be hingedly or pivotally attached to introducer  12  using a hinge mechanism which comprises one or more hinged sections  12   h  actuated by a pull wire or stiffening mandrel  15 . Sections  12   h  can be mechanically coupled to introducer  12  and each other using one or more hinged or pivot joints  12   j  known in the art.  
      Referring to  FIGS. 7   a  and  7   b  (perspective views illustrating the use of the deflectable section  12   d ). In use, deflectable portion  12   d  allows the introducer to be introduced into tissue site  5 ′ in a first fixed position (preferably straight with respect to a longitudinal axis  12   al  of the introducer) and then deflected a selectable amount to a second position in order to facilitate deployment of one or more energy delivery devices  18  into tumor mass  5 ″ or tissue site  5 ′. Further, deflectable portion  12   d  allows the energy delivery devices to be deployed at a selectable angle (including ranges from acute to oblique) with respect to the longitudinal axis  12   al  of the introducer. These capabilities provides several benefits including (i) ensuring a more complete deployment of the energy delivery devices into the selected tumor mass; (ii) allowing faster deployment and withdrawal of the energy delivery devices reducing procedure time; (iii) allows the energy delivery device  18  to be positioned and deployed in an irregularly shaped tumor masses (e.g. oblong, oval); (iv) allows the apparatus and energy delivery devices to be positioned and deployed in curved or otherwise difficult to reach portions of the anatomy including the orthopedic anatomy; and (v) allows the apparatus and energy delivery devices to be deployed at tumor site near or adjacent a delicate or sensitive anatomical structure(e.g. the spinal cord, artery) with a reduced or otherwise inappreciable risk of injuring that structure). In alternative embodiments, deflectable portion  12   d  can also be used to direct the delivery of an infusion fluid (including a jet or stream of fluid) described herein to a selectable portion of the tissue site  5 ′ or tumor mass  5 ″.  
      In another embodiment introducer  12  can include side ports which allow electrodes  18  to be deployed at a selectable angle with respect to the longitudinal axis  12   al  of introducer  12 , including about 45 and 90°. The use of such side ports is described in U.S. Pat. No. 5,683,384, which is incorporated by reference herein.  
      Referring to  FIG. 8 , introducer  12  can have a substantially circular, semicircular, oval or crescent shaped cross section, as well as combinations thereof along its lengths. Similarly, lumens  13  can have a circular, semicircular, oval or crescent shaped cross section for all or a portion of the length  12 ″ of introducer  12 .  
      A variety of energy delivery devices and power sources can be utilized by embodiments of the invention. Specific energy delivery devices  18  and power sources  20  that can be employed in one or more embodiments include, but are not limited to, the following: (i) a microwave power source coupled to a microwave antenna providing microwave energy in the frequency range from about 915 MHz to about 2.45 GHz (ii) a radio-frequency (RF) power source coupled to an RF electrode, (iii) a coherent light source coupled to an optical fiber or light pipe, (iv) an incoherent light source coupled to an optical fiber, (v) a heated fluid coupled to a catheter with a closed or at least partially open lumen configured to receive the heated fluid, (vi) a cooled fluid coupled to a catheter with a closed or at least partially open lumen configured to receive the cooled fluid (viii) a cryogenic fluid, (ix) a resistive heating source coupled to a conductive wire, (x) an ultrasound power source coupled to an ultrasound emitter, wherein the ultrasound power source produces ultrasound energy in the range of about 300 KHZ to about 3 GHz, (xi) and combinations thereof.  
      For ease of discussion for the remainder of this application, the energy delivery device includes a plurality of RF electrodes  18  and the power source utilized is an RF power supply. For these and related embodiments RF power supply delivers 5 to 200 watts, preferably 5 to 100, and still more preferably 5 to 50 watts of electromagnetic energy is to the electrodes of energy delivery device  18  without impeding out. The electrodes  18  are electrically coupled to energy source  20 . The coupling can be direct from energy source  20  to each electrode  18  respectively, or indirect by using a collet, sleeve, connector, cable and the like which couples one or more electrodes to energy source  20 . Delivered energies can be in the range of 1 to 100,000 joules, more preferably in the range 100 to 50000 joules, still more preferably in the range of 100 to 5000 and still yet more preferably in the range 100 to 1000 joules. Lower amounts of energy can be delivered for the ablation of smaller structures such as nerves and small tumors with higher amounts of energy for larger tumors. Also delivered energies can be modified (by virtue of the signal modulation and frequency) to ablate or coagulate blood vessels vascularizing the tumor. This provides the benefit of providing a higher degree of assurance of destroying other otherwise occluding the blood supply of the tumor.  
      Turning now to a discussion of the fabrication and configuration of the RF electrodes, in various embodiments electrode  18  can be made of a variety of conductive materials, both metallic and non-metallic. Suitable materials for electrode  18  include, steel such as 304 stainless steel of hypodermic quality, platinum, gold, silver and alloys and combinations thereof. Also, electrode  18  can be made of conductive solid or hollow straight wires of various shapes such as round, flat, triangular, rectangular, hexagonal, elliptical and the like. In a specific embodiment all or portions of electrodes  18  can be made of a shaped memory metal, such as NiTi, commercially available from Raychem Corporation, Menlo Park, Calif.  
      Referring back to  FIGS. 1-2 , the plurality electrodes  18  are carried in the device for movement between retracted positions at which the electrodes are disposed within the device&#39;s lumen, and deployed positions at which the electrodes are deployed from the distal end, preferably at a plurality of arcuate, laterally extending, angularly spaced positions, as illustrated in  FIGS. 2 and 22 - 24  in particular. By arcuate is meant the electrodes fan out away from the device distal tip in a curved fashion with one or more radii of curvature. By laterally extending is meant that the electrodes in their deployed positions extend radially outwardly away from the device distal tip. By angularly spaced is meant that the electrodes, when viewed from the top as in  FIG. 23 , are spaced from one another with an angle typically between 20-120 degrees, depending on the number of electrodes in the electrode set. ‘As will be discussed below, each deployed electrode defines an individual-electrode ablation volume, such as a spherical volume, which is proximate to that electrode when an RF current is applied to that electrode, with such deployed in tissue. Also as discussed below, where continued application of RF current (which may be measured as power) to the electrodes causes the individual-electrode ablation volumes to grow and merge with each other to form a combined-electrode ablation volume.  
      The electrodes are typically ganged together at their proximal ends for movement as a unit between the retracted and deployed positions (which can include partially deployed positions). A handle or other actuator is carried on or otherwise functions with the device to allow the user to move the electrodes from their retracted positions to various deployed (partially or fully deployed) positions. Such electrode construction is known.  
      Electrodes, such as electrode  18 , can include one or more coupled sensors  22  to measure temperature and impedance (both of the electrode and surrounding tissue), voltage and current other physical properties of the electrode and adjacent tissue. Sensors  22  can be positioned on the exterior or interior surfaces of electrodes  18  at their distal ends or intermediate sections. A radiopaque marker  11  can be attached, soldered or coated on electrodes  18  for visualization purposes. Referring now to  FIGS. 9-11  in various embodiments electrodes  18  can have variety of shapes and geometries including but not limited to ring-like, ball, hemispherical, cylindrical, conical or needle-like as illustrated in  FIG. 9 . In an embodiment shown in  FIG. 10 , electrode  18  can be a needle with sufficient sharpness to penetrate tissue including bone, cartilage and fibrous tissue and encapsulated tumors. The distal end of electrode  18  can have a cut angle  68  that ranges from 1 to 60°, with preferred ranges of at least 25° or, at least 30° and specific embodiment of 25° and 30°. The surface electrode  18  can be smooth or textured and concave or convex. The conductive surface area  38 ′ of electrode  18  can range from 0.05 mm 2  to 100 cm 2 . Referring to  FIG. 11 , electrode  18  can also be configured to be flexible and or deflectable having one or more radii of curvature  70  which can exceed 180° of curvature. In use, electrode  18  can be configured and positioned to heat, necrose or ablate any selected target tissue volume  5 ′.  
      Electrode  18  can have selectable lengths  38  that are advanced from distal end  16  of introducer  12 . The lengths can be determined by the actual physical length of electrode(s)  18 , the length of an energy delivery surface  38 ′ of electrode  18  and the length,  38 ″ of electrode  18  that is covered by an insulator. Suitable lengths  38  include but are not limited to a range from 1-30 cm with specific embodiments of 0.5, 1, 3, 5, 10, 15 and 25.0 cm. The actual lengths of electrode  18  depends on the location of tissue site  5 ′ to be ablated, its distance from the site, its accessibility as well as whether or not the physician chooses a endoscopic, percutaneous, surgical or other procedure.  
      Referring now to  FIG. 12 , in various embodiments electrode  18  can include one or more lumens  72  (which can be contiguous with or the same as lumen  13 ) coupled to a plurality of fluid distribution ports  23  or apertures  23 . Fluid distribution ports  23  can be evenly formed around all or only a portion of electrode  18  and are configured to permit the introduction or infusion of a variety of fluids  27  to a selected tissue site as well to the electrode surface. This can be accomplished by having ports  23  fluidically coupled to lumens  13  (via lumens  72  or fluid channel) that are in turn fluidically coupled to fluid reservoir  30  and/or fluid delivery device  28 . Ports  23  can configured to delivery fluids at both low flow rates and Reynolds numbers (e.g. wicking) to high flow rates a (e.g., jetting) and levels there between as well as low and high viscosity fluids with a viscosity range including but not limited to 1 to 100 centipoise with specific embodiments of 1, 3, 5, 10 and 20 centipoise. This can be achieved by controlling diameter  23   d , number and location of ports  23  on one or more electrodes  23 .  
      Suitable fluids  27  that can infused or introduced via ports  23  include but are not limited to liquids, pastes, gels emulsions, conductivity enhancing fluids, electrolytic solutions, saline solutions, cooling fluids, cryogenic fluids, gases, chemotherapeutic agents, medicaments, gene therapy agents, photo-therapeutic agents, contrast agents, infusion media and combinations thereof. Examples of suitable conductive gels are carboxymethylcellulose gels made from aqueous electrolyte solutions such as physiological saline solutions, and the like.  
      In various embodiments the size and diameter of ports  23  can vary depending upon their position on the electrode as well as the size and shape of the electrode. Preferably at least a portion of apertures  23  are positioned and even more preferably concentrated near the distal ends  18   de  of electrodes  18 . In various embodiments 1 to 10 side apertures  23  are positioned near distal end  18   de , with specific embodiments of 2, 3 and five apertures. These and related configurations allow for the infusion of an conductivity enhancing solution  27  at a location where current density in around the electrode is greatest, allowing the electrode and tissue adjacent the electrode to carry increased current density without desiccation, charring and appreciable impedance rises causing impedance shut downs of power supply  20 . This in turn permits larger and faster ablation volumes to be performed without appreciable risk of impedance shut down. Apertures  23  are also configured to wet the surface  18   s  of electrode  18  (as is more fully described herein) to cool it, increase conductivity and prevent tissue adhesion and charring.  
      In an embodiment shown in  FIG. 13 , ports  23  can be configured to have an increasing diameter  23   d  moving in a distal direction so as to maintain the flow rate out of each port  23  approximately constant and/or prevent significant decreases due to pressure decreases. The relationship of increasing diameter to distance can linear, parabolic or logarithmic. In a preferred embodiment, the apertures  23  are configured to have increasing diameters going in a distal direction with respect to electrode  18   o  as to provide a substantially constant flow rate over the apertured portion  18   ap  of the electrode by decreasing the fluid resistance moving in the distal direction according to Poiseuille&#39;s law (F=DP p r 4/8 h l). This is achieved by increasing the aperture diameter  23   d  about 0.0625% (e.g. about 1:16 ratio) of the increase in lateral distance of placement of the aperture.  
      Referring now to  FIG. 14   a , in another related embodiment all or a portion of apertures  23  are substantially positioned on a neutral force axis  18   nfa  of one or more electrodes  18 . In these and related embodiments electrodes  18  can be configured to be bendable and/or deflectable. This can be achieved through the selection of the material properties for electrodes as well as its construction and the use off a deflection mechanism described herein. Suitable bendable embodiments of electrodes  18  include electrodes fabricated from spring steel, 304 stainless steel, shape memory metals, nickel titanium alloys (NITINOL), articulated metal, flexible wire, 0.018 flexible wire, high strength polymers, and the like. Positioning apertures  23  along force neutral axis  18   fna  provides the benefit of an electrode that can deflected or bent omni-directional, without appreciable loss of structural integrity and hence reduced probability of failure. Also the use of apertures  23  infusion holes in electrodes provides the benefit stop crack propagation.  
      In these and related embodiments apertures  23  can be fabricated using laser drilling or micro-machining or drilling techniques known in the art. The position of force neutral axis  18   nfa  can be determined from the geometric centerline of electrode  18 , calculated using mechanical engineering methods known in the art or identified real time using analytical optical techniques including but not limited to photo-elastic optical methods known in the art including but not limited to moire interferometry, digital speckle pattern interferometry (DSPI) and computer analysis of the fine grid technique. In one embodiment, apertures  23  can be drilled while the optical measurement of lines of stress or strain is being made to obtain a more accurate placement of the apertures along the force neutral line of the electrode. In these and related embodiments drilling of apertures  23  can be facilitated by the use of one or more fixtures known in the art.  
      In a related embodiment shown in  FIG. 14   b , apertures  23  can also be positioned on opposite lateral sides  18   ls  of electrodes  18  and offset a distance  23   ad  to preserve the structural integrity of electrode while reducing the likelihood of plugging on both side of the electrodes. In a specific embodiment one aperture can be positioned 4 mm (distance  23   ld   1 ) from electrode distal end  18   de  and second apertures can be positioned on the opposite side of the electrode at distance 6 mm (distance  23   ld   2 ) from distal end  18   de.    
      In an embodiment shown in  FIG. 15 , apertures  23  can be configured to provide cooling of one or more electrodes  18  and surrounding tissue to prevent tissue from the development of excessive impedance at electrode  18  from the deposition of charred tissue on the surface of electrode  18 . The cooling is accomplished by both the use of a cooled solution to cool the electrodes by convection, conduction and a combination thereof. The amount of cooling can be controlled by control of one or more of the following parameters (i) temperature of the cooling solution, (ii) flow rates of the cooling solution, and/or (iii) heat capacity (e.g. specific heat) of the cooling solution. Examples of cooling solutions include, water, saline solution and ethanol and combinations thereof. Other embodiments can utilize a cooling fluid or gas  27   g which serves to cool electrodes  18  by ebullient cooling or Joule Thomson Effect cooling as well as the mechanisms described above. Embodiments utilizing Joule-Thomson Effect cooling can have a nozzle-shaped aperture  27   n  to provide for expansion of a cooling fluid  27   g . Examples of cooling fluid  27   g  include, but are not limited to, freon, CO 2 , and liquid nitrogen.  
      Referring now to  FIGS. 12 and 15 , various embodiment apparatus can be configured to infuse or deliver a conductivity enhancing solution  27  or other solution into target tissue site  5 ′ including tissue mass  5 ″. The solution can be infused before during or after the delivery of energy to the tissue site by the energy delivery device. The infusion of a conductivity enhancing solution  27  into the target tissue  5 ′ creates an infused tissue area  5   i  that has an increased electrical conductivity (verses uninfused tissue) so as to act as an enhanced electrode  40 . During RF energy delivery the current densities in enhanced electrode  40  are greatly lowered allowing the delivery of greater amounts of RF power into electrode  40  and target tissue  5 ′ without impedance failures. In use, the infusion of the target tissue site with conductivity enhancing solution provides two important benefits: (i) faster ablation times; and (ii) the creation of larger lesions; both without impedance-related shut downs of the RF power supply. This is due to the fact that the conductivity enhancing solution reduces current densities and prevents desiccation of tissue adjacent the electrode that would otherwise result in increases in tissue impedance. An example of a conductivity enhancing solution includes saline solution, including hypotonic or hypertonic solution. Other examples include halide salt solutions, and colloidal-ferro solutions and colloidal silver solutions. The conductivity of enhanced electrode  40  can be increased by control of the rate and amount of infusion and the use of solutions with greater concentrations of electrolytes (e.g. saline) and hence greater conductivity.  
      In various embodiments the use of conductivity enhancing solution  27  allows the delivery of up to 2000 watts of power into the tissue site impedance shut down, with specific embodiments of 50, 100, 150, 250, 500, 1000 and 1500 watts achieved by varying the flow, amount and concentration of infusion solution  27 . The infusion of solution  27  can be continuous, pulsed or combinations thereof and can be controlled by a feedback control system described herein. In a specific embodiment a bolus of infusion solution  27  is delivered prior to energy delivery followed by a continuous delivery initiated before or during energy delivery with energy delivery device  18  or other means. In another embodiment feedback control is used to prevent impedance rises and failures by monitoring impedance at the electrode-tissue interface and increasing the flow rate of cooling and/or conductive fluid  27  in response to impedance increase using PID or other control algorithms known in the art. In related embodiment feedback control could also incorporate sensor input on the deployed length (e.g. deployment depth) of one or more electrodes and incorporate this into an algorithm to regulate fluid flow, energy delivery power level, duty cycle, duration and other ablation related parameters described herein.  
      In related embodiments, the conductivity of the tumor mass  5 ′ can be enhanced so as to preferentially increase the rate and total amount of energy delivery of energy to the tumor mass  5 ′ relative to healthy tissue. This can be achieved by infusing solution  27  directly into the tumor mass  5 ′ through the use of a needle electrode  18  placed within the tumor mass only. In related embodiments infusion solution  27  can be configured to remain or be preferentially absorbed or otherwise taken up by tumor mass  5 ″. This can be achieved by controlling by one or more of the osmolality, viscosity and concentration of solution  27 .  
      Embodiments of the invention utilizing infusion of a conductivity enhancing solution  27  provide several important benefits including more consistent and homogeneous ablation volumes as well as faster ablation times. This is achieved by infusing conductivity enhancing solution  27  into the desired ablation volume or target tissue site to both increase and homogenize tissue conductivities throughout the desired ablation volume. This in turn significantly reduces the incidence of tissue desiccation, charring as well as the size zones of higher impedance any of which can slow or prevent the delivery of ablative RF or thermal energy.  
      Referring now to  FIG. 16 , in various embodiments all or a portion of infusion ports  23  can be configured as side holes in the wall  18   w  of electrode  18  offset a minimum longitudinal distance  23   ld  from the distal tip  18   de  of electrode  18 . These and other embodiments solve the problem of tissue plugging or blocking of fluid delivery lumens  72  which may occur as the electrode is advanced into tissue by position aperture  23  proximally enough such that it is not obstructed by the tissue plug  23   tp . Distal end  18   de  can include an axial aperture  23   de  or in a preferred embodiment does not to eliminate any tissue coring effect of the electrode. In various embodiments distance  23   ld  can be in the range of 0.010 to 1 inches, more preferably 0.05 to 0.5 inches and still more preferably 0.1 to 0.25 inches. Specific embodiments can include 0.05, 0.1, 0.15 and 0.16 inches.  
      In an embodiment shown in  FIG. 17 , tissue plugging can be overcome through the use of a lubricous or non-stick coating  18   c  positioned over all or a portion of the surface  18   s  of electrode  18  including within lumens  72 . Coating  18   c  prevents tissue, including burnt or charred tissue and other biological material from coagulating, adhering or otherwise sticking onto electrode surface  18   s , apertures  23  or within lumens  72 . In specific embodiments coating  18   c  is configured to be thermally and/or electrically insulative to prevent any partially adhered tissue from cooking or coagulating onto the surface  18   s  of electrode  18  reducing the probability of permanent tissue plugging and making partially adherent tissue readily removable by flushing or increase flow rates or pressure of fluid  27 . Coating  18   c  can also be configured to have a sufficiently low surface tension such that tissue and other biological tissue do not stick to it. In various embodiments the surface tension can be below 50 dynes/cm, preferably in the range of 50 to 10 dynes/cm and more preferably in the range 40 to 18 dynes/cm, with specific embodiments of 25, 23, 19, 18.5, 18, 17 and 15 dynes/cm. Suitable coatings  18   c  can include but are not limited to including, polyamide, polyamide fluoro, PTFE, TEFLON, other fluoro-carbon polymers, silicones, paralene and other low surface tension non-stick coatings known in the art. Such coatings can range in thickness  18   ct  from 0.0001 to 0.1 inches with a preferred embodiment of 0.001 to 0.003 inches. Coatings  18   c  can be applied using co-extrusion dip coating, spray coating, co-extrusion, electro-deposition, plasma coating, lithographic and other coating methods known in the art.  
      Referring now to  FIGS. 18   a - 18   c , in various embodiments electrode  18  can include a fixed or movable sleeve or sheath  31   s  which covers a selectable portion of apertures  23  preventing them from being blocked or plugged by tissue during either electrode insertion and/or during or after the delivery of RF or other thermally ablative energy. For movable embodiments, sheath  31   s  can be configured to slide over the outer portion of the electrode or slide through the inner lumen  72  while still not appreciably obstructing fluid flow through the lumen. In an embodiment of a method of the invention sheath  31   s  can be positioned over all or portion of electrode  18  so as to cover and protect one or more apertures  23  during insertion of electrode into tissue and then subsequently pulled back to allow fluid infusion from uncovered aperture  23  before, during or after the delivery of ablative energy. In a related embodiment sheath  31  s can also be configured to be used to control the flow rate of infusion media  27 , as well as the total area of electrode  18  available for infusion by uncovering selected segments of apertured electrode  18  which are used for infusion.  
      Positioning of the slidable sheath  31   s  can be controlled by configuring the sheath to be directly coupled to an actuator  24 ″ on handpiece  24 . In alternative embodiments positioning of sheath  31   s  can be controlled by the use of a positioning wire, cam, rocker switch, ratchet mechanism, micropositioner, or servomechanism and the like which is mechanically or electrically coupled to the sheath an actuable by an actuator  24 ″ on handpiece  24 .  
      As discussed herein, sheath  31   s  can be pulled back (e.g. proximally) once electrodes  18  are positioned at the desired tissue site or in an alternative embodiment sheath  31   s  can have a sufficient inner diameter  31   sid  to provide enough of an annular channel or thickness  31   at  to allow fluid  27  to flow out in annular fashion from apertures  23  (either in a proximal or distal direction) to the desired tissue site. In an embodiment sheath  31   s  can have diameter 1-5 mm greater than of electrode  18  providing an annular channel with a thickness between 0.5 to 2.5 mm Sheath  31   s  can be actuated at handle  24  by the physician, and its position along electrode  18  is controlled. The sheath  31   s  can be made from a variety of polymers including, but not limited to resilient polymers, elastomers, polyesters, polyimides, polyurethanes, silicicones, PARALENE, flouropolymers, TEFLON and the like. Also in various embodiments, slidable sheath  31   s  can be configured to be electrically and/or thermally insulative or can be electrically and thermally conductive using conductive polymers known in the art. An example of a conductive polymer includes Durethane C manufactured by the Mearthane Products Corporation (Cranston, R.I.). Also, all or a portion of the sheath  31   s  can have radio-opaque, magno-opaque, or echogenic markers to facilitate viewing and placement of the sheath using X-ray, CAT scans, nmr ultrasound and the like.  
      Referring now to  FIG. 19 , in another embodiment of an electrode configured to reduce plugging of apertures comprises a needle configured to have a needle bevel angle  68  that minimizes tissue coring and hence plugging of lumen  72 . In various embodiments the needle angle  68  can be in the range of 5 to 30°, preferably 10 to 20° and still more preferably 12°.  
      Referring now to  FIGS. 20   a  and  20   b , in various embodiments introducer  12  or electrode  18  can include a porous distal section  12   pds  or  18   pds . Porous distal section  12   pds  or  18   pds  is configured to allow fluid to diffuse out of the pore and or interstitial spaces  12   pds ′ between braids  12   pds ″. In various embodiments section  12   pds  can comprise a braided section which has sufficient rigidity or column strength to penetrate tissue, but still porous enough to allow the passage of fluid. Braided section  12   pds  can be made from braid material known in the art including high strength material and can be wound or woven using methods known in the art including filament winding techniques and carbon fiber filament winding techniques. Suitable braid materials include metal braids such as stainless steel that can be hardened to increase stiffness or high strength polymer braids such as Nylon®, polyester and Kevlar® fibers, examples including Kevlar 29 and Kevlar 49 manufactured by the Dupont Corporation. Other suitable braid materials can include but are not limited to fiberglass, graphite or carbon fibers including Pitch and Pan based carbon fibers. Examples of fiberglass material include ASTROQUARTZ II, ASTROQUARTZ III and styles 106, 108, 7628 and 7637 manufactured by JPS Industries (Greenville, S.C.). The rigidity of braided or porous section  12   pds  or  18   pds  can be achieved through the use of a structural or stiffening member  12   sm  positionable within all or a portion of porous section  12   pds . In various embodiments, member  12   sm  can be a metal mandrel, such as stainless steel mandrel, a hardened steel mandrel or rigid polymer member made from polycarbonate or other thermoset polymer.  
      The packing or weave of braids or fibers  12   pds  or  18   pds  can be varied to control the fluid porosity of section  12   pds  that is amount of fluid that diffuses or wicks through the fibers. In various embodiments the porosity of section  12   pds  can be in the range of 1-2000 cc/min/cm 2 , preferably in the range of 10 to 1000 cc/min/cm 2 , with specific embodiments of 20, 50, 100, 250 and 500 cc/min/cm 2 .  
      In related embodiments all or portions of sections  12   pds  or  18   pds  can be fabricated from heat resistant materials and polymers such that the strength, stiffness or shape of section  12   pds  or  18   pds  is not appreciably degraded or altered during the delivery of RF or other thermal ablative energy. Such embodiments solve the problem of softening or deformation of a porous or fluid delivery section  12   pds  or other section of elongate member  12  that can occur during delivery of thermally ablative energy to a tissue site. Suitable heat resistant polymers and materials include polyetherimide available from the General Electric Company under the trademark ULTEM® and polyetheretherketone available from the General Electric Company under the trademark UNITREX®). In other embodiments all or portions of section  12   pds  can fabricated from electrically conductive or electrically dissipative polymers. Examples of electrically dissipative polymers include acetals such as UNITAL ESD available from the General Electric Company. In still other embodiments a braided porous section  12   pds  is configured to increase the surface area for conductive heat transfer from section  12   pds  and/or energy delivery device  18  to either fluid  27  or the surrounding tissue. These embodiments enhance the heat transfer from energy delivery device  18  and/or section  12   pds  reducing the likelihood of tissue desiccation and charring on or near the energy delivery device in turn reducing impedance of the energy delivery device and impedance caused shut downs (i.e. called impeding out) of power supply  20 .  
      In another embodiment porous section  12   pds  including electrode  18  can comprise a porous, microporous or liquid permeable material  12   pm  fluidically coupled to lumen  13  or  72  and configured to uniformly effuse or diffuse fluid through itself, onto its surface and into tissue. Suitable porous materials include polymer foam, polyester foam, OPCELL foam, ceramic, polyester, polyester membrane, Nylon membrane, glass fiber membranes DACRON, expanded PTFE membranes and porous ceramics known in the art. The pore sizes of porous material  12   pm  can be in range from 5 to 1000 microns, preferably 40 to 500 microns and more preferably 50 to 150 microns. In these and related embodiments porous section  12   pds  can be configured to wick, effuse, spray or jet fluid to wet, irrigate and cool the electrode by a combination of one or more of conductive, convective and evaporative cooling. Irrigating the electrodes provides the benefit of preventing and/or reducing an impedance rise at the electrode tissue interface. In embodiment the electrode can be coated with a hydrophilic coating or texture to facilitate wetting of the electrode surface. Examples of hydrophilic surfaces include metal, glass, and plasma treated polymers and metals, whereby the plasma treatment increases the surface tension of the substrate surface via chemical reaction and/or deposition with the surface. The plasma treatment can be a variety of plasma treatment known in the art such as argon plasma treatment.  
      In an embodiment of a method of the invention, tissue plugging can be prevented or reduced by infusing fluid through one or more electrode lumens  72  when the electrode is inserted into tissue and/or during the delivery of RF or other thermally ablative energy. In various embodiments the infusion rate can be in the range between 0.1 to 2 ml with specific embodiments of 0.2, 0.5, 1.0 and 1.5 ml/min. Tissue infusion flow via a fluid delivery device  28  such as an infusion or syringe pump can be initiated before or during insertion of apparatus  10  into tissue, or before or during deployment of needles  18  into tissue. Also in a related embodiment flow to one or more electrodes  18  can be monitored using sensors  22  to detect developing plugs and using feedback control (described herein) can be increased or otherwise modified to push out the plug or otherwise prevent plug formation. In specific embodiments feedback control can used to initiate a pressure or flow pulse or a series of pulses or related waveforms by the fluid delivery device (e.g. square waves, sinusoidal, step function, etc.) to push out a developing or existing plug. The pressure pulse can be in the range of 0.05 to 5 atm, preferably 0.1 to 2 atm and still more preferably 0.3 to 1 atm.  
      Turning now to a discussion of the use of infusion with RF energy delivery. While such a combination present advantages during ablative treatment there are also technical challenges as well. Two such challenges are (i) inconstant flow and (ii) inability to achieve a homogenous level of infusion, and or inability to infuse the entire volume of a target tissue volume particularly with only one infusion port or channel of infusion. Referring now to  FIGS. 1-2  and  12 - 15 , various embodiments of the invention solve these problems by providing an apparatus configured to infuse fluid through multiple electrodes  18  or other infusion channels so as to collectively define a larger, more predictable and homogenous or complete infusion volume than would be possible by infusing from a single electrode  18  or channel. Such embodiments solve the problem of inconstant flow or incomplete, uneven or otherwise non-homogenous ablation volumes that may result without infusion or with only a single infusion channel. Uneven ablations can occur with a single infusion channel due to uneven or incomplete infusion volumes and/or zones within the desired infusion volume receiving differing amounts of infusion fluid.  
      In various embodiments feedback control described herein can also be employed to improve the uniformity of infusion volumes as well as better control the infusion process. This can be achieved by utilizing feedback control to monitor and control flow rates through each electrode  18  or infusion channels  72  to compensate for flow variation in any one channel and ensure more uniform volume of infusion and subsequent ablation volumes. Embodiments of the invention configured to infuse through multiple electrodes provide the advantage of reducing collective back pressure that results from a single infusion channel from fluidic pressure at the target tissue site  5 ″ due to tissue resistance, obstruction or plugging of a single electrode. Consequently, by distributing infusion over multiple electrodes and multiple apertures at multiple site overall flow rates, infusion rates and infusion volumes can be increased and more uniform infusion can be achieved for a selected target tissue site than via use of a single point of infusion. In particular, by controlling infusion of liquid to the individual electrodes, liquid can be supplied through each electrode at a desired flow rate, independent of the resistance to flow of other individual electrodes, allowing, for example, equal flow rates to be applied to the electrodes.  
      Referring now to  FIG. 21 , in an embodiment of a method of the invention fluid is infused through one or more electrodes  18  or infusion channels such that the individual volumes or zones of local tissue infusion  5   ivl  surrounding each electrode grow or coalesce to form one large infusion volume  5   iv . This can be achieved by controlling the flow rate through the electrodes or infusion channels and monitoring the amount infused analytically or visually. The progression of the growth of the infusion volume  5   iv  can be monitored using imaging methods including but not limited to ultrasound, CT scan, MRI, and x-ray. In various embodiments of methods of the invention, the monitoring process can be facilitated by the use of X-ray or flouroscopic contrast agents, echogenic contrast agents, or MRI contrast agents known in the art which are added to infusion media  27 . The delivery of ablative energy can be initiated before during or after the completion of the infusion process. In one embodiment, the delivery of ablative energy such as RF energy is initiated only after the collective large infusion volume has formed or substantially about the same time. In another embodiment the delivery of RF energy is initiated before infusion, at it onset or as the local infusion volumes are growing.  
      In alternative embodiments the delivery of an infusing solution  27  can be enhanced by several means. In one embodiment, ultrasound energy can be delivered to the selected target tissue site  5 ″ during or post infusion to increase the diffusion and permeation of fluid  27  into tissue site  5 ″ including the interstitial space of tissue site  5 ′ via a combination of fluid sonication, agitation (fluid and tissue and/or brownian motion, this analogous to shaking up a bottle containing a dissolvable solid in a liquid to get the solid to dissolve. Further the energy can be configured to cause cell lysis, enabling fluid  27  to diffuse into cells. The ultrasound energy can be delivered by a piezoelectric transducer known in the art that is coupled to one or more electrodes or to a separate catheter/probe in turn coupled to an ultrasound energy source. In various embodiments ultrasound energy can be delivered in the frequency range from 0.5 to 30 MHz, more preferably from 1 to 10 MHz, with specific embodiments of 2, 3, 5 and 8 Mhz.  
      In another embodiment fluid delivery device  28  can be configured to produce pressure pulses in flow and/or pulsed flow to enhance diffusion. Still another embodiment employs the use of RF or DC voltage to create an electroporation effect known in the art. The DC voltage can be delivered by a separate probe coupled to a DC power source with a voltage known in the art to produce an electroporation affect. Such a voltage source can be in the range of 0.1 to 10 volts.  
      Referring now to  FIG. 22 , during the delivery of RF each RF electrode  18  is configured to generate an ablation volume  5   ave  proximate each electrode  18 . This volume, which may be spherical or columnar, depending on the length of active region(s) is also referred to herein as an individual-electrode ablation volume, and corresponds to the ablation volume produced by applying an RF current (RF power) to that electrode during the initial phase of RF ablation. When multiple electrode are used, and optionally, electrolyte solution is infused into tissue from the electrodes, application of RF energy to the multiple ablation volumes, e.g., spherical ablation volumes, will result in each ablation volume expanding and eventually merging and overlapping to form a single combined-electrode ablation volume  5   avc , also referred to herein as a meta volume.  
      Depending on the size and shape of the of the desired combined-electrode ablation volume  5   av , different number of electrodes  18  can be used to create the meta ablation volume  5   avce  whose shape a volume approximates that of the desired ablation volume. In various embodiments a range of 2-12, typically 3-10, electrodes are employed to create a corresponding number of individual-electrode ablation volumes. In a specific embodiments four electrodes used to create four ablation volumes  5   ave  which can have an approximately a tetrahedral orientation.  
      In a related embodiment platonic solids  5   ps  (described herein) can be used as a positioning geometric template for individual electrode ablation volumes  5   ave  to create the desired collective or meta ablation volume size  5   avc  using the fewest number of individual ablation volumes  5   ave . In a specific embodiment each individual electrode ablation volumes  5   ave  is positioned such that it is bisected by a single face or surface  5   pf  of the respective platonic solid, with one ablation volume  5   ave  positioned as such on all faces of the chosen platonic solid. Examples of suitable platonic solids include, but are not limited to a cube, tetrahedron and dodecahedron, as discussed below.  
      In accordance with one aspect of the invention, the progression of the ablation volumes  5   av  is monitored using one or more passive (non ablating) sensor elements. Referring now to  FIG. 23 , apparatus  10  includes one or more passive (non ablating) sensor elements or monitoring members  18   pm  advanceable from device  12  and positionable within a target tissue site  5 ′ concurrently or independently of the positioning of electrodes  18 . As will be appreciated, the sensor elements are carried on the delivery device for movement with respect therein between retracted positions, in which the sensor elements are carried within the lumen of the device, and deployed (including partially deployed) positions in which the sensor elements (or at least their distal ends) are deployed outside of and away from the distal end of the delivery device.  
      Typically, the sensor elements, when deployed, are arrayed in an arcuate, laterally extending, angularly spaced configuration, with the sensor elements being positioned within the volume corresponding to the combined-electrode ablation volume, and with the individual sensor elements being disposed between adjacent electrodes, as detailed below. Specifically, the sensor elements are typically arrayed outside of the individual-electrode ablation volume in the region of coalescence of ablation volumes of two adjacent electrodes. In this configuration, in the early phases of RF ablation, the sensor elements are located outside of the individual-electrode ablation volumes. As the individual volumes expand and begin to coalesce, the regions of ablation begin to overlap with the sensor elements positions. By placing the sensor elements outside of the initial ablation volumes, the spread of the ablation volume, and ultimately, the desired extent of ablation throughout the combined-electrode ablation volume can be monitored and controlled, as detailed herein.  
      As will be appreciated, the plural sensor elements may be ganged together for movement as a unit between retracted and deployed positions, as described above for the electrodes, or they may be individually movable to place the sensor elements at different extended positions in the combined-electrode ablation volume. When ganged together, the sensor elements and electrodes and be moved independently of one another or moved as a combined electrode/sensor unit between retracted and deployed positions.  
      The sensor elements are designed to sense tissue properties rather than deliver ablative energy and accordingly can include one or more sensors  22  or alternatively, all or portion of passive members can be sensing elements  22 . Preferably members  18   pm  are configured to be non conductive and/or to not delivery appreciable amounts of RF or other electromagnetic energy. In various embodiments this can be accomplished by coating all or portions of members  18   m  with an electrically insulative coating or layer  18   ic  that can also be thermally insulative as well. Suitable insulative coatings  18   ic  include, but are not limited to insulative polymers, PARALENE, polyimide, polyamide, TEFLON, NYLON, flouropolymers and other high dielectric materials and insulators known in the art. The coating can be applied using spray coating, dip-coating methods known in the art to produce a uniform coating thickness and consistency. The use of higher dielectric strength materials provides the benefit of thinner coatings which reduces the diameter of passive elements  18   mp  in turn providing the benefit of making members  18   mp  more flexible or maneuverable as well as allowing for the positioning and deployment of a greater number of members  18   mp  from introducer  12 . In various embodiments the thickness  18   ict  of coating  18   ic  can be in the range of 0.001 to 0.006 inches with specific embodiments of 0.002 and 0.003 inches.  
      Alternatively, all or portions of passive members  18   pm  can be fabricated from nonconductive materials such as resilient polymers tubing including not limited to polyethylene, PEBAX, polyimide and other polymers known in the catheter arts.  
      Passive members  18   pm  can be made of similar materials and/or have similar properties to electrodes  18 , e.g. tissue penetrating ends, bendability, resiliency, memory, spring memory, etc. which enable members  18   pm  to be deployed from introducer  12  and positioned at selectable locations within a target tissue site  5 ″, with the exceptions that members  18   pm  are configured either to not be conductive and or not deliver ablative amounts of RF or other electromagnetic energy. In an embodiment passive member can made from 304v steel or spring steel which has an insulative coating  18   ic  and also includes a lumen  72  for the passage of both fluids  27  and also electrical wires  15  for coupling to sensors  22 .  
      Referring now to  FIG. 24 , sensors  22  can be positioned in one or more locations along the length of one or more members  18   pm . Also in various embodiments, sensors  22  can be positioned on or flush with the surface of members  18   pm , in the interior of members  18   pm  including within lumens  72  or can be integral to members  18   pm  including the wall  18   pmw  of member  18   pm . Further sensor  22  can positioned using soldering or adhesive bonding methods known in the medical device arts. Sensors  22  can be electrically coupled directly to members  18   pm  (whereby an insulted conductive member  18   mp  provides an electrically coupling of the sensor to monitoring resources describe herein) or can be electrically coupled to one or more insulated wires  15  positioned within lumens  72  and electrically coupled to sensing resources. Suitable sensors  22  for use with members  18   pm  include but are not limited to temperature, chemical, optical and other sensors described herein.  
      In embodiment sensors  22  and/or passive members  18   pm  can be coupled to monitoring resources  20   mr  directly or via a multiplexing device allowing selective polling and signaling of one or more selected passive elements  18   pm  and or sensors  22 . In various embodiments, monitoring resources  20   mr  can comprise monitoring circuitry such as temperature or impedance monitoring circuitry or a monitoring unit  20   mu  comprising monitoring circuitry, a microprocessor/controller, a visual display known in the art and alarm circuitry. In an embodiment, the monitoring unit  20   mu  can be integral to or otherwise electronically or optically coupled to power source  20 .  
      Referring now to  FIG. 25 , in an embodiment the plurality  20   pmp  of passive members  18   pm  can be positioned to define a sampling volume  5   sv  either by circumscribing the volume and/or positioning within the interior of the sampling volume. Passive members can be manipulated to increase, decrease or change the shape of sample volume  5   sv  being monitored. In various embodiments sample volume  5   sv  can include all or a portion of ablation volume  5   av , can larger than the ablation volume so as to include all or portion of the ablation volume, define substantially the same volume as ablation volume  5   sv  or be smaller than ablation volume  5   av  to be completely or partially bounded by ablation volume  5   av . In a related embodiment volume  5   sv  can be configured or manipulated to be substantially separate or distinct from the ablation volume  5   av . Passive members can be manipulate to define sample volumes having a variety of geometric shapes including but not limited to substantially spherical, hemispherical, oval, pyramidal, tetrahdreral, rectangular, pentagonal, hexagonal, or another selectable platonic solid.  
      Referring to  FIG. 26 , in an embodiment the passive arrays are positioned to define a tetrahedron or pyramid  5   tv  which is approximately circumscribed by a sphere which can approximately correspond to the ablation volume  5   av . In this and other embodiments the ends  18   de  of the active array or electrodes  18  can be positioned approximately on the plane of  5   eqp  of the equator  5   eq  of the selected ablation volume. Preferably, the distal ends  18   pmd  of passive members  18   pm  are positioned above and below this plane. In related embodiments the central electrode  18   ce  can be positioned above plane  5   eqp  while in other embodiments one or more electrodes  18  can be positioned above or below plane  5   eqp . Further in other related embodiments, the ends  18   pmd  of the passive members  18   pm  can configured to define another geometric shape also circumscribed by a sphere including but not limited to a cube, rectangle, or oval.  
      Referring to  FIG. 23  in preferred embodiments the deployed length  38   p  of passive elements  18   pm  are longer than the active elements or electrodes  18  such that they can be positioned more distally than the electrodes and define a larger volume than the electrodes and that larger volume substantially contains the ablation volume  5   av . In various embodiments, the length  38   p  of the passive elements can be 0.1 to 5 cm longer than the deployed length  38  of the electrodes, preferably 0.5 to 2 cm longer and still more preferably 1 cm longer. In a specific embodiment the electrode or active array elements are approximately 2.5 cm in length and the passive array elements are approximately 3.5 cm in length. Use of passive arrays  18   pma , with one or more passive elements  18   pm  longer than electrodes  18  provides the novel benefit of being able to monitor in real time the development and progression of the ablation volume allowing for more complete, faster and controlled ablations and in turn, a more successful clinical outcome for the patient.  
      Referring now to  FIGS. 23 and 26 , in these and related embodiments the passive elements  18   pm  can be positioned in the spaces between the electrodes or active elements so as to sample tissue volumes or zones  5   vz  at the farthest point or otherwise equidistant from any two electrodes or active elements. Referring now to  FIG. 27 , in an embodiment this can be optimally achieved by configuring passive arrays  18   pma  and active arrays  18   a  with an equal number of equally spaced elements and positioning the passive elements  18   pm  approximately at a point which bisects the angle  18   ba  formed between any two active elements in a plane approximately perpendicular to the longitudinal axis  12   al  of introducer  12 . For example, for an embodiment having three electrodes and three passive elements the passive elements would be positioned at an angle  18   ba  of approximately 600 with respect to each of the three electrodes. Similarly for an embodiment having four passive elements and four electrodes angle  18   ba  would be approximately 450.  
      Use of passive arrays positioned in zones  5   vz  provides the benefit of a higher confidence of a complete and uniform ablation in that zones  5   vz  are typically the last to reach a temperature necessary to cause ablation and/or cell necrosis and as such are the most difficult or challenging areas to ablate using RF energy. Further, the use of passive elements  18   pm  eliminates any signal artifacts and/or hysteresis that might occur as result of positioning sensors  22  on the electrodes  18  or other active elements  18 . Accordingly, by using passive arrays to sample ablation volume  5   av , embodiments of the invention provide the benefit of a more representative and/or accurate sampling of tissue temperature (or other tissue property indicative of ablation) of the entire desired ablation volume and in turn a higher confidence (including a higher statistical confidence) of achieving a complete ablation. More specifically, such embodiments provide a higher statistical correlation of measured temperature to actual tissue temperature throughout a desired tissue volume and thus a higher confidence of achieving a desired treatment endpoint (as indicated by temperature or other measured tissue property).  
      In an embodiment of a method of the invention, passive arrays can be used to measure a temperature at the outermost portions of the ablation volume or other zones  5   vz  such that a clinical endpoint is established and energy is stopped or decreased once a selectable temperature is reached at or near those zones. Such embodiments provide the benefits of faster ablation times as well a decreased risk of damage to healthy surrounding tissue and structures including critical anatomical structures such as organs, nerves, blood vessels etc. In various embodiments the endpoint temperature can be in the range of 38 to 75° C., preferably 40 to 70° C. and still more preferably 50 to 70° C., with specific embodiments of 40, 41, 45, 50, 55, 60 and 65° C. In a related embodiment, temperature can continued to be monitored for a period of time after energy delivery is stopped and endpoint assessed by the time decay in tissue temperatures with a relatively constant post ablation tissue temperature or slower decay being indicative of endpoint.  
      In an embodiment the apparatus can include three or more power arrays or electrodes and three or more passive arrays. However other embodiment can comprise any number or combination of active electrodes and passive elements including, but not limited to (i) two or more electrodes and two or more passive elements; (ii) three or more electrodes and two or more passive elements; (iii) two or more electrodes and three or more passive elements; (iv) two or more electrodes and one or more passive elements; (v) one or more electrode and two or more passive elements; (vi) more electrodes than passive elements; (vii) more passive elements than electrodes; and (viii) and an equal number of passive elements and active elements. Further in various embodiments the exact number of the electrodes and passive elements as well as their defined volume (e.g. spherical, oval,) can be selectable by the physician depending upon factors such as the size and shape of the tumor, consistency and type of tumor (e.g. fibrous, degree of vascularity, necrotic, etc.), location of the tumor (e.g. liver vs. bone) and proximity of adjacent anatomical structures (e.g. blood vessels, organs etc.). This can be achieved though the use of a multiplexing device described herein, coupled to one or more electrodes and passive elements (so as to be able to switch them on or off) or advancing or withdrawing additional electrodes and passive elements through elongated member  12  and/or through electrodes or passive elements in place at the tissue site. Also the respective ablation or sample volume defined by the plurality of electrodes and passive elements can be adjusted by the physician by advancing or retracting one or more electrodes or passive elements or rotating one or more electrodes or passive elements or a combination of both techniques.  
      For ease of discussion introducer  12  will now be referred to as trocar  12 ; however all other embodiments discussed herein are equally applicable. Turning now to a discussion of trocar  12  and it use with passive arrays  18   pmp , one of the potential problems in using a sharpened trocar  12  with insulative passive arrays is the scraping or braiding of the insulation  18   ic  on passive elements  18   pm . Referring now to  FIGS. 28   a - 28   c , various embodiments of the invention provide solutions to this problem. As shown in  FIG. 28   a  a standard trocar  12  has a tissue penetrating distal end  16  with a sharpened leading edge  16   le . This sharpened leading edge can cause scraping or scything of the insulation layer of one or more passive member  18   pm  as the passive member pass over it during deployment to the tissue site  5 ″.  
      In various embodiments all or a portion of leading edge  16   le  can be smoothed so as reduce or eliminate its propensity to abrade or cut insulation layer  18   ic . In an embodiment shown in  FIG. 28   b , the leading edge  16   le  is only smoothed over all or a portion of its inner surface  16   lei  still leaving a sharpened outer surface  16   leo . This embodiment provides the benefit of allowing passive member  18   pm  to pass over and through leading edge  16   le  without being abraded or cut and still permits trocar tip  16  to be tissue penetrating (e.g. the cutting edge  16   leo  is substantially preserved). In one embodiment inner leading  16   lei  is radiused using machining casting, molding or EDM methods known in the art. In another embodiment it can be polished smooth using metal polishing methods known in the art or EDM methods known in the art. The edge  16   le  can also be deburred using deburring methods known in the art.  
      In various embodiments, the inner leading edge  16   lei  can have a radius of curvature in the range of 0.0001 to 0.2 inches with specific embodiments of 0.0005, 0.001, 0.005, 0.0.01, 0.05 and 0.1 inches. In another embodiment shown in FIG.  28   c , inner leading edge  16   lei  can be smoothed or otherwise made non-scything by virtue of an applied coating  16   c  which can be a lubricous polymer coating known in the art such as TEFLON and the like or a hard smooth coating such as polycarbonate, acrylic and the like. Coating  16   c  can be applied to all or a portion of leading edge  16   le  as well as distal tip area  16  but is preferably only substantially applied to inner leading edge  16   lei . In still another alternative embodiment, the problem of insulating scything can be solved using a hardened or high strength insulative coating known in the art such as polycarbonate, LUCITE, acrylic or high strength polyimide. In a related embodiment, all or a portion of trocar distal end  16  can fabricated from molded or machined plastic or elastomer that is configured to have sufficient rigidity, column strength and related material properties to penetrate and be advanced into tissue, but is also configured to have a radiused or smooth inner leading edge  16   lei  that is substantially non-scything. Plastic distal end  16   pl  can be attached to the body of introducer  12  using adhesive bonding, ultrasonic welding, butt joining, crimping or other tube joining method known in the medical device arts. Suitable materials for plastic distal end  16   pl  include polycarbonate, high-density polyethylene, acrylic and other rigid medical plastics known in the arts.  
      In other embodiments, insulative scything can be reduced or prevented via the geometric arrangement of the passive member and electrodes as they exit the trocar tip  16 . Referring now to  FIG. 29 , in an embodiment the passive members  18   pm and electrodes  18  can be packed or otherwise arranged such that the passive members  18   pm  do not pass over leading edge  16   le  as they exit trocar tip  16 . In this and related embodiments the passive members  18   pm  and electrodes  18  can be packed or bundled in a substantially circular arrangement  50  approximating the arrangement of a multiwire cable with passive members  18   pm  placed within the interior  50   i  of the arrangement surrounded by active members or electrodes  18  such that the passive members do not pass do not contact in the interior surface  16   is  of distal end  16  including leading edge  16   le.  In various embodiments the packing of electrodes around passive members  18   mpm  can be substantially hexagonal in order to maximize packing density. In another embodiment the packing arrangement can be octagonal. In one embodiment three passive members  18   pm  are surrounded by eight or more electrodes  18 . The maintenance of passive members  18   pm  within the interior  50   i  of packing  50  can facilitated by joining passive members  18   pm  and electrodes  18  at proximal locations that remain within introducer  12  using soldering, adhesive bonding or other wire bundling method known in the art.  
      Referring now to  FIGS. 30 and 31 , in various embodiments trocar  12  has electrically insulated and non-insulated sections  12   i  and  12   ni . Non-insulated section  12   ni  is conductive and tissue ablation can occur proximate to this section. However as shown in  FIG. 30 , the transition  12   t  from section  12   i  to  12   ni  can be abrupt due to the stepdown decrease in trocar outer diameter (going from  12   di  to  12   dni ) resulting from the end of the insulation layer  12   il.  Such an abrupt transition  12   t  can increase axial resistance or force necessary to insert and position trocar  12  into tissue position distal end  16  at the target tissue site. In an embodiment shown in  FIG. 31 , the transition  12   t  can be eliminated or substantially reduced by configuring a distal section  16   ds  of trocar  12  to have a larger diameter  16   d  than the remainder of trocar  12  such that distal section  16   ds  is substantially flush with the insulative layer  12   il  on the body of trocar  12  (e.g., distal end diameter  16   d  is substantially equivalent to diameter  12   di  of section  12   i ).  
      Distal section  16   ds  can be made of the same material as trocar  12  (e.g., stainless steel, 304 steel and the like) and fabricated using metal, machining, molding or forging methods known in the art. Section  16   ds  can be integral with trocar section  12   i  or alternatively can be joined to section  12   i  using soldering, brazing, crimping or other metal joining methods known in the art. Configuring distal section  16   ds  flush with trocar section  12   i  reduces the force necessary to insert the trocar into tissue and also smoothes out the insertion process giving the physician a better tactile feel for properly positioning the trocar at the target tissue site. Further these and related embodiments of a stepped trocar distal end provide the benefit of facilitating insertion and positioning of trocar  12  and distal section  16   ds  to the target tissue site, increasing the placement accuracy of distal section  16   ds,  reducing procedure time and increasing procedure efficacy. In an embodiment, distal section  16   ds  can have an outer diameter  16   dsod  of 0.087 to 0.089 inches while the outer diameter  12   iod  of the non-insulated trocar is 0.080 to 0.082 inches, and insulation layer  12   il  thickness of between 0.0025 to 0.0045 inches. The length  16   dsl  of distal section  16   ds  can be in the range of 6.5 to 8.5 mm.  
      Referring now to  FIG. 32 , in an embodiment, all or a portion of one or more of the energy delivery devices  18  can include a radioactive portion  18   r . Radioactive portion  18   r  is fabricated from a radioactive material having sufficient radioactive strength (e.g., curies) to necrose, ablate, ionize or otherwise kill tumorous tissue  5 ″ at tissue site  5 ′. In related embodiments, a radioactive absorbing sheath  18   s  can be configured to be slidably positioned over radioactive portion  18   r  so as to control the exposed length  18   r ′ of radioactive portion  18   r  and thus the dose of radioactivity delivered to the tumor mass  5 ″.  
      The radioactive material in section  18   r  can include gamma, alfa- or beta- emitting materials. Suitable gamma emitters include, but are not limited to Cobalt-60, Iodine-131, Iodine-123, Indium-111, Gallium-67 and Technetium-99 m. Suitable beta emitting particles include tritium. The amount of radioactive material in portion  18   r  can be configured to deliver 0.01 to 100 rads of radiation with specific embodiments of 0.1, 0.25, 0.5, 1, 10 and 50 rads. The amount of radiation delivered can measure using a radiation sensor  22  coupled to energy delivery device  18  or introducer  12 . Radioactive absorbing sheath  18   s  can include one or more radioactive absorbing materials known in the art that are impregnated or otherwise integral to a flexible metal or polymer layer. Such radioactive absorbing materials include but are not limited to lead, iron or graphite. In an embodiment, the radioactive absorbing material can be fabricated into a braided wire or sheath incorporated into the wall of sheath  18   s  using catheter production methods known in the art.  
      In use, radioactive section  18   r  provides the patient with the benefit of radiation therapy having a highly targeted delivery of radioactivity to the tumor mass while minimizing injury to surrounding tissue. The radiation can be delivered alone or as an adjunct to another ablative treatment describe herein (before during or after such treatment) to sensitize cancer cells to other forms of necrotic therapy or otherwise increase the probability of killing cancerous tissue. The dose of radiation can at such level for example below 1 rad that it has no affect on healthy or untreated tissue but when combined with another energetic therapy serves to surpass a lethal threshold for the selected tumorous tissue. Such therapy provides the benefit of an increased probability of killing all the cancer cells at the tumor site and thus an improved clinical outcome for the patient.  
      Other embodiments of the invention can employ photodynamic therapy described herein to treat tumors. Referring to  FIG. 33  (a perspective view illustrating an embodiment employing photo activated agents), in such embodiments apparatus  10  can be configured to deliver a phototherapeutic agent  27   pa  also known as a photodynamic agent  27   pa  to the target tissue site. Agent  27   a  can be configured to selectively be taken up and/or otherwise selectively bind to tumor mass  5 ″. Once the agent is delivered and taken up by the tumor  5 ″ an optical embodiment of the energy delivery device is used to delivery optical radiation to activate therapeutic agent  5 ″ and cause the necrosis or ablation of tumor mass  5 ″. However, prior to photo-activation agent  27   pa  remains in an inert or nontoxic state. Examples of optical energy delivery devices  18  include optical fibers, light pipes, wave-guides and the like. Examples of photo-therapeutic agents include chlorophyll-based compounds such as Bacteriochlorophyll-Serine and texaphyrin based compounds such as lutetium texaphyrin manufactured by Pharmacyclics, Inc. (Sunnyvale, Calif.). Examples of activating radiation include radiation in the infrared, near infrared and ultraviolet range of the spectrum. Such radiation can be delivered by the optical energy delivery devices described herein as well as other optical delivery devices known in the art. In an embodiment, agent  27   pa  can be delivered as a fluid through a bone access device or bone biopsy needle directly to the tumor site  5 ″ or through the Haversian canals.  
      In various embodiments, photo-dynamic therapy can be conducted prior, concurrently or after with thermal ablative therapy such as RF ablative therapy. In a related embodiment, photo-agent  27   pa  can also be configured to increase the hyperthermic affect of RF or other electromagnetic energy delivered to tumor mass  5 ″ or otherwise selectively sensitize tumor tissue to the necrotic affects of hyperthermic tumor treatment such as RF ablative treatment. In a specific embodiment photo-agent  27   pa  is configured to be repelled by bone tissue including calcium-based tissue or collagen-based tissue and thus increase the agents specificity for tumorous tissue. In another embodiment the photosentisizing agent  27   pa  can be configured to be activated by a wavelength of light that is reflected by bone tissue yet absorbed darker tumorous tissue. This and related embodiments provide the benefit of an agent  27   pa  that is highly specific to tumor tissue yet has little or no affect on healthy bone. Further, the use of agent  27   pa  allows the level of hypothermic treatment to be titrated to the size and type of tumor tissue. This can be accomplished by using a spectrum of agent&#39;s  27   pa  that increases or decreases the level of tumor sensitization as needed.  
      Other embodiments of the invention can combine thermal or other ablative therapy described herein with chemotherapy or other medicinal based therapy. Apparatus  10  can be used to deliver various chemotherapeutic or medicinal agents along or in combination before, during or post ablation. One such family of agent includes antisense-based compounds configured to inhibit the metabolism by the liver (by inhibition of liver enzymes) of various chemotherapeutic agents and thus extend their biological half-life (e.g. effectiveness) while minimizing side-affects. An example of such a compound includes NEUGENE®) antisense compound manufacture by AVI BioPharma Inc (Portland Oreg.). Such compounds can be delivered directly to the liver using apparatus  10  or other drug delivery device described herein or known in the art.  
      Referring now to  FIGS. 34 and 35 , a feedback control system  329  can be connected to energy source  320 , sensors  324  and energy delivery devices  314  and  316 . Feedback control system  329  receives temperature or impedance data from sensors  324  and the amount of electromagnetic energy received by energy delivery devices  314  and  316  is modified from an initial setting of ablation energy output, ablation time, temperature, and current density (the “Four Parameters”). Feedback control system  329  can automatically change any of the Four Parameters. Feedback control system  329  can detect impedance or temperature and change any of the Four Parameters. Feedback control system  329  can include a multiplexer to multiplex different antennas, a temperature detection circuit that provides a control signal representative of temperature or impedance detected at one or more sensors  324 . A microprocessor can be connected to the temperature control circuit.  
      The following discussion pertains particularly to the use of an RF energy source and lung treatment/ablation apparatus  10 . For purposes of this discussion, energy delivery devices  314  and  316  will now be referred to as RF electrodes/antennas  314  and  316  and energy source  320  will now be an RF energy source. However it will be appreciated that all other energy delivery devices and sources discussed herein are equally applicable and devices similar to those associated with lung treatment/ablation apparatus  10  can be utilized with laser optical fibers, microwave devices and the like. The temperature of the tissue, or of RF electrodes  314  and  316  is monitored, and the output power of energy source  320  adjusted accordingly. The physician can, if desired, override the closed or open loop system.  
      The user of apparatus  10  can input an impedance value that corresponds to a setting position located at apparatus  10 . Based on this value, along with measured impedance values, feedback control system  329  determines an optimal power and time needed in the delivery of RF energy. Temperature is also sensed for monitoring and feedback purposes. Temperature can be maintained to a certain level by having feedback control system  329  adjust the power output automatically to maintain that level.  
      In another embodiment, feedback control system  329  determines an optimal power and time for a baseline setting. Ablation volumes or lesions are formed at the baseline first. Larger lesions can be obtained by extending the time of ablation after a center core is formed at the baseline. The completion of lesion creation can be checked by advancing energy delivery device  316  from distal end  16 ′ of introducer  12  to a position corresponding to a desired lesion size and monitoring the temperature at the periphery of the lesion such that a temperature sufficient to produce a lesion is attained.  
      The dosed loop system  329  can also utilize a controller  338  to monitor the temperature, adjust the RF power, analyze the result, and then modulate the power. More specifically, controller  338  governs the power levels, cycles, and duration that the RF energy is distributed to electrodes  314  and  316  to achieve and maintain power levels appropriate to achieve the desired treatment objectives and clinical endpoints. Controller  338  can also in tandem govern the delivery of electrolytic, cooling fluid and, the removal of aspirated tissue. Controller  338  can also in tandem monitor for pressure leaks (via pressure flow sensors  324 ′) through introducer  312  tending to cause pneumothorax and actuate coupled control valves to block the fluid path causing the leak and/or initiate the delivery of sealant and/or energy at the target tissue site to seal the leak. Controller  338  can be integral to or otherwise coupled to power source  320 . The controller  338  can be also be coupled to an input/output (I/O) device such as a keyboard, touchpad, PDA, microphone (coupled to speech recognition software resident in controller  338  or other computer) and the like.  
      Referring now to  FIG. 34 , all or portions of feedback control system  329  are illustrated. Current delivered through RF electrodes  314  and  316  (also called primary and secondary RF electrodes/antennas  314  and  316 ) is measured by a current sensor  330 . Voltage is measured by voltage sensor  332 . Impedance and power are then calculated at power and impedance calculation device  334 . These values can then be displayed at a user interface and display  336 . Signals representative of power and impedance values are received by controller  338  which can be a microprocessor  339 .  
      A control signal is generated by controller  338  that is proportional to the difference between an actual measured value, and a desired value. The control signal is used by power circuits  340  to adjust the power output in an appropriate amount in order to maintain the desired power delivered at the respective primary and/or secondary antennas  314  and  316 . In a similar manner, temperatures detected at sensors  324  provide feedback for maintaining a selected power. The actual temperatures are measured at temperature measurement device  342 , and the temperatures are displayed at user interface and display  336 . A control signal is generated by controller  338  that is proportional to the difference between an actual measured temperature, and a desired temperature. The control signal is used by power circuits  340  to adjust the power output in an appropriate amount in order to maintain the desired temperature delivered at the respective sensor  324 . A multiplexer  346  can be included to measure current, voltage and temperature, at the numerous sensors  324  as well as deliver and distribute energy between primary electrodes  314  and secondary electrodes  316 .  
      Controller  338  can be a digital or analog controller, or a computer with embedded, resident or otherwise coupled software. In an embodiment controller  338  can be a Pentium®) family microprocessor manufacture by the Intel® Corporation (Santa Clara, Calif.). When controller  338  is a computer it can include a CPU coupled through a system bus. On this system can be a keyboard, a disk drive, or other non-volatile memory systems, a display, and other peripherals, as are known in the art. Also coupled to the bus are a program memory and a data memory. In various embodiments controller  338  can be coupled to imaging systems, including but not limited to ultrasound, CT scanners (including fast CT scanners such as those manufacture by the Imatron Corporation (South San Francisco, Calif.), X-ray, MRI, mammographic X-ray and the like. Further, direct visualization and tactile imaging can be utilized.  
      User interface and display  336  can include operator controls and a display. In an embodiment user interface  336  can be a PDA device known in the art such as a Palm® family computer manufactured by Palm® Computing (Santa Clara, Calif.). Interface  336  can be configured to allow the user to input control and processing variables, to enable the controller to generate appropriate command signals. Interface  336  can also receives real time processing feedback information from one or more sensors  324  for processing by controller  338 , to govern the delivery and distribution of energy, fluid etc.  
      The output of current sensor  330  and voltage sensor  332  is used by controller  338  to maintain a selected power level at primary and secondary antennas  314  and  316 . The amount of RF energy delivered controls the amount of power. A profile of power delivered can be incorporated in controller  338 , and a preset amount of energy to be delivered can also be profiled.  
      Circuitry, software and feedback to controller  338  results in process control, and the maintenance of the selected power, and are used to change, (i) the selected power, including RF, microwave, laser and the like, (ii) the duty cycle (on-off and wattage), (iii) bipolar or monopolar energy delivery and (iv) infusion medium delivery, including flow rate and pressure. These process variables are controlled and varied, while maintaining the desired delivery of power independent of changes in voltage or current, based on temperatures monitored at sensors  324 . A controller  338  can be incorporated into feedback control system  329  to switch power on and off, as well as modulate the power. Also, with the use of sensor  324  and feedback control system  329 , tissue adjacent to RF electrodes  314  and  316  can be maintained at a desired temperature for a selected period of time without causing a shut down of the power circuit to electrode  314  due to the development of excessive electrical impedance at electrode  314  or adjacent tissue.  
      Referring now to  FIG. 35 , current sensor  330  and voltage sensor  332  are connected to the input of an analog amplifier  344 . Analog amplifier  344  can be a conventional differential amplifier circuit for use with sensors  324 . The output of analog amplifier  344  is sequentially connected by an analog multiplexer  346  to the input of A/D converter  348 . The output of analog amplifier  344  is a voltage that represents the respective sensed temperatures. Digitized amplifier output voltages are supplied by A/D converter  348  to a microprocessor  350 . Microprocessor  350  may be Model No. 68HCII available from Motorola. However, it will be appreciated that any suitable microprocessor or general purpose digital or analog computer can be used to calculate impedance or temperature.  
      Microprocessor  350  sequentially receives and stores digital representations of impedance and temperature. Each digital value received by microprocessor  350  corresponds to different temperatures and impedances. Calculated power and impedance values can be indicated on user interface and display  336 . Alternatively, or in addition to the numerical indication of power or impedance, calculated impedance and power values can be compared by microprocessor  350  with power and impedance limits. When the values exceed predetermined power or impedance values, a warning can be given on user interface and display  336 , and additionally, the delivery of RF energy can be reduced, modified or interrupted. A control signal from microprocessor  350  can modify the power level supplied by energy source  320  to RF electrodes  314  and  316 . In a similar manner, temperatures detected at sensors  324  provide feedback for determining the extent and rate of (i) tissue hyperthermia, (ii) cell necrosis, and (iii) when a boundary of desired cell necrosis has reached the physical location of sensors  324 .  
      Platonic Solid Embodiments: An embodiment of a method of the invention provides a method to utilize platonic solid geometry to minimize the number of individual ablations required to produce a collective ablation volume larger than any single ablation volume. More specifically the embodiment provides a method to maximize the effect of overlapping ablations to treat tumors larger than the capabilities of current commercially available products. This and related embodiments are also applicable to the design of a multi-electrode device where each electrode will create a sub-lesion in order to create a meta-lesion that is the combination of the smaller lesions.  
      Specific embodiments provide method for using one or more of a series of optimal geometries used as a template for positioning overlapping ablations to create a meta-ablation volume. In order to find the most efficient geometry for the placement of the sub-lesions it is obvious that the more symmetric the pattern the larger the meta-lesion will be for a given number of sub-lesions at a given size.  
      Platonic solids are composed of regular convex polygons that have the same number of polygons meeting at each corner. In all Platonic solids the number of sides is equal to or less than the number of vertices. Because the goal is to reduce the number of sub-lesions required, the sub-lesions will be placed on each face of the platonic solid and not at the vertices.  
      Referring now to  FIG. 36  in an embodiment a platonic solid  5   ps  is used as a template or reference volume  5   rv  with which to place individual or sublesions  5   ave  in order to create a larger collective lesion or meta-lesion  5   avc . With the center of the sub-lesion  5   ave  on the center of the face of the platonic solid  5   ps  and the diameter of the sub-lesion circumscribing the vertices of the face of the platonic solid, a meta-lesion is formed that is defined by the diameter of the platonic solid, as measured between opposite corners. Referring to  FIGS. 37   a - 37   e  example platonic solids  5   ps  which can be used as the template or reference volume  5   rv  include, but are not limited to, Tetrahedron, Cube, Octahedron, Dodecahedron, and Icosahedron.  
      For platonic solids with 8 or fewer faces the sub-lesions overlap in the center of the meta-lesion. For platonic solids with 12 or more sides an additional sub-lesion in the center of the meta-lesion is required for a complete volumetric coverage. Using this concept and geometry it is possible to construct a table outlining the minimum number of ablations required to create a meta-lesion.  
                                              Number                                             Size   4   6   8   12*   20*                                                         1   1.06   1.23   1.23   1.65   1.9           3   3.18   3.69   3.69   4.95   5.7           5   5.3   6.15   6.15   8.25   9.5                         *One additional ablation required in the center to cause complete volumetric coverage             
 
      The apparatus and method of this invention are particularly useful for o benign and cancerous tumors using of RF energy and infused fluids. It will be readily apparent to a person skilled in the art that various embodiments and combinations of embodiments of the device and method can be used to sample or ablate/destroy body tissues, tissue locations that are accessible by percutaneous or endoscopic catheters, and is not limited to the bone in the liver, lung, bone, brain and breast. Such tissue locations and organs include, but are not limited to, the heart and cardiovascular system, upper respiratory tract and gastrointestinal system as well as the bone in the liver, lung, bone, brain and breast. Application of the apparatus and method in all of these organs and tissues are intended to be included within the scope of this invention.  
      Also this specification discloses various catheter-based systems and methods for treating the bone and adjoining tissue regions in the body. The systems and methods that embody features of the invention are also adaptable for use with systems and surgical techniques both in the bone and other areas of the body that are not necessarily catheter-based. Furthermore, this specification is not intended to be exhaustive or to limit the invention to the precise forms disclosed. It will be apparent that various modifications, applications, and different combinations of embodiments can be made without departing from the invention as claimed.