Patent Publication Number: US-10314648-B2

Title: Coaxial ablation probe and method and system for real-time monitoring of ablation therapy

Description:
1. PRIORITY CLAIM 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/915,962, filed Dec. 13, 2013, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     2. TECHNICAL FIELD 
     The presently disclosed subject matter relates to novel devices and methods for performing and real-time monitoring of ablation therapy, including, but not limited to electrochemical treatment (EChT). EChT is a percutaneous ablation technique utilizing direct current (DC) electricity to create toxic products to destroy abnormal tissue. The presently disclosed subject matter also relates to a coaxial ablation probe for EChT and/or other ablation techniques, including thermal ablation and irreversible electroporation. 
     3. BACKGROUND 
     Minimally invasive techniques for treating abnormal tissue have become widely accepted alternatives to surgery, especially with respect to liver tumors. Interventional radiologists can choose from a variety of percutaneous ablation devices that destroy abnormal tissue by delivering energy through needle-like probes placed through the skin. However, the current ablation technology is limited by an inability to monitor therapy in real-time, a high local recurrence rate, a need for multiple probes to treat larger tumors, and a risk of damage to adjacent structures. 
     4. SUMMARY 
     The presently disclosed subject matter relates to, in part, methods of employing magnetic resonance to perform real-time monitoring of ablation therapy, including, but not limited to EChT. In certain embodiments, the EChT-mediated ablation monitored by magnetic resonance is achieved using a coaxial ablation probe comprising an anode nested within an adjustable cathode cage. 
     The subject matter described relates to a coaxial ablation probe for percutaneous ablation. The probe includes an anode. The probe further includes a cathode cage surrounding the anode, the cathode cage includes a plurality of struts. The anode extends coaxially with respect to the struts that form the cathode cage. The cathode cage defines the treatment volume. 
    
    
     
       5. BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIGS. 1A and 1B  depict: (A) Axial T2 MRI of rabbit VX2 papilloma electrochemical treatment. The low signal intensity about the electrode represents gas formation. The sharply marginated T2 signal has nearly identical contours as the necrosis (B) seen on gross pathology. The same indentation is marked by the arrow; 
         FIG. 2A-2D  illustrates a coaxial ablation probe in various different states according to embodiments of the subject matter described herein; 
         FIGS. 2E-2I  illustrate different configurations for an outer sheath for a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIGS. 2J-2M  illustrate different views of an actuator and corresponding channels or slots for moving individual struts of a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIGS. 2N-2Q  illustrate different embodiments of a cathode cage for a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIGS. 2R-2V  illustrate different strut cross sections for a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIGS. 2AA-2GG  illustrate different anode configurations for a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIGS. 2HH-2JJ  illustrate different configurations of a cathode cage for a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIG. 3  is a schematic diagram illustrating a system for using a coaxial ablation probe to treat a patient&#39;s liver according to an embodiment of the subject matter described herein; 
         FIG. 4  is a flow chart illustrating an exemplary process for treating a patient using a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIGS. 5A-5D  illustrate the use of a coaxial ablation probe according to an embodiment of the subject matter described herein to treat a liver tumor; 
         FIG. 6A  illustrates various ablation targets in a human liver for a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIG. 6B  is an image of a liver showing an ablated region near the gall bladder  72  without damage to gall bladder; 
         FIG. 7  is a diagram illustrating lymph nodes as potential ablation targets for a coaxial ablation probe according to an embodiment of the subject matter described herein; 
         FIGS. 8A-8E  illustrate the use of a coaxial ablation probe according to an embodiment of the subject matter described herein to ablate a lymph node; 
         FIGS. 9A and 9B  illustrate, respectively, lymph nodes of the head and neck and the use of an ablation system as described herein to ablate tumors in lymph nodes of the head and neck; 
         FIG. 10  is an image of an ex vivo bovine liver illustrating the results of ablation at different times. Serial ablation of 3 cm diameter, 2 cm thick ex vivo bovine liver at 5, 10, and 15 minutes demonstrate complete ablation by 15 minutes (32 V, 1.2-1.8 A). Notice the central zone of coagulation about the anode and peripheral liquefaction about the cathodes. 
         FIG. 11A  illustrates real-time MRI monitoring of ablation treatment: In situ ablation progress was monitored using VIBE T1 sequences (TR/TE 5.0/2.2 ms, FA 15°, FOV 200 mm; Matrix 196×320; slice thickness 3 mm) along the short axis of the cathode cage. Sequences were performed before, during (3 minute intervals), and after ablation with the struts removed. In this example of a 3 cm ablation zone, T1 hypointense signal was seen to propagate circumferentially from the central anode towards the cathode with a leading edge of T1 hyperintense signal. Similar changes were seen at the cathode struts. Complete ablation was achieved when the signal changes coalesce. 
         FIG. 11B  illustrates gross pathology correlation: On the left, a post-ablation TSE-T2 (TR/TE 5400/96 ms) image demonstrated T2 hypointense signal representing the ablation zone. Central T2 hyperintense signal about the anode represented hemorrhagic necrosis and the T2 hyperintense signal about the cathodes represented liquefactive necrosis. These MRI findings correspond to the changes seen on gross pathology. 
         FIG. 11C  illustrates results from testing of a coaxial ablation: In situ testing of the coaxial ablation probe using VIBE T1 along the short axis demonstrated a 2 cm ablation zone (left image) after 15 minutes (32 V, 0.3-0.9 A). Subsequently the struts in the 10:00 to 2:00 positions were manually adjusted to increase the radius by 1 cm and direct ablation towards the hepatic parenchyma (right image); ablation was performed for 6 additional minutes (32 V, 0.3-0.6 A). 
     
    
    
     6. DETAILED DESCRIPTION 
     The presently disclosed subject matter relates to novel devices and methods for performing and real-time monitoring of EChT. EChT is a percutaneous ablation technique utilizing direct current (DC) electricity to create toxic products to destroy abnormal tissue. The presently disclosed subject matter also relates to a coaxial ablation probe for EChT and/or other ablation techniques, including thermal ablation and irreversible electroporation. 
     6.1 Definitions 
     Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below, 
     An “individual,” “patient” or “subject,” as used interchangeably herein, can be a human or non-human animal. Non-limiting examples of non-human animal subjects include non-human primates, dogs, cats, mice, rats, guinea pigs, rabbits, pigs, fowl, horses, cows, goats, sheep and cetaceans. 
     “Thermal ablation,” as used herein, relates to percutaneous thermal tumor ablation techniques (radiofrequency, microwave, cryoablation, laser interstitial and high-intensity focused ultrasound), which have become accepted as an alternative to surgery (11, 25-30). For example, the curative potential of percutaneous ablation has been recognized by the Barcelona Clinic Liver Cancer (BCLC) group, which asserts that radiofrequency ablation of very small hepatocellular carcinomas (HCCs) is equivalent to surgical resection in terms of overall survival. However, the BCLC group has also demonstrated the major limitation of current ablation techniques is the higher rate of local recurrence compared to surgical resection (31). The higher risk of local recurrence results from inability to completely ablate the target tumor. The major drawbacks of current ablation technology include lack of real-time monitoring with standard imaging modalities, wide zones of transition between treated and untreated tissue, risk of non-target tissue damage, and heat sink effects in perivascular regions (1-11). 
     “Irreversible electroporation” (IRE), as used herein, relates to techniques wherein up to 45 A and 3,000 V in the form of micropulses are administered through percutaneously placed electrodes resulting in irreversible damage to cell membranes As a non-thermal ablation technique, IRE offers several advantages over traditional thermal techniques such as the ability to ablate lesions near large blood vessels. However, IRE has multiple limitations that has impaired the widespread adoption of this technology (51, 52). Similar to thermal ablation modalities, IRE produces a central ablation zone with surrounding penumbra of tissue damage and it is difficult to accurately assess treatment response on follow-up imaging (52). IRE is theoretically compatible with MRI but the wide zone of transition as well as the brief treatment time impedes accurate real-time MRI monitoring (52). Lastly, and perhaps the most significant shortcoming of IRE, is the requirements for general anesthesia and complete muscle paralysis to safely perform this technique (44, 48, 51). 
     “EChT,” as used herein, relates to electrochemical treatment—an ablation technique that uses direct current (DC) to generate toxic species at the surface of electrodes and cause pH-mediated cell death. The main electrochemical reactions at the anode are the decomposition of water and oxidation of chloride ions resulting in free hydrogen ions, chlorine gas, and a strongly acidic environment resulting in coagulative necrosis (32):
 
2H 2 O O 2 +4H + +4 e   −  2Cl −   Cl 2 +2 e   − 
 
     At the cathode, the main reaction is the decomposition of water into hydroxyl ions, hydrogen gas, and a strongly alkaline environment resulting in liquefactive necrosis (32):
 
2H 2 O+2 e − H 2 +2OH—
 
     These species penetrate into the surrounding tissues predominately by diffusion and secondarily by electrically driven migration. Histologic examination of EChT demonstrates a sharply demarcated transition between necrotic and normal tissue with no damage to large vessels or extension of necrosis beyond an organ&#39;s capsule (13, 15-18). The most important treatment parameters that determine the rate and size of the EChT ablation zone are the electrode surface area, local ionic content and the total charge—a product of current and exposure time (12-24, 33-42). The total charge was found to have a linear relationship to the ablation rate and volume (15, 21, 22, 33, 36, 43). EChT has been performed on tens of thousands of patients to treat lung, GI, and soft tissue tumors with minimal local discomfort and without any reported serious side effects or deaths related to treatment (13-15, 17, 18, 37, 41). 
     The term “magnetic resonance” or “MR”, as used herein, is a diagnostic and imaging modality that is capable of providing a three-dimensional map, or image of tissues of interest. In magnetic resonance imaging (MRI), a target tissue is exposed to a strong, substantially constant static magnetic field. The static magnetic field causes the spin vectors of certain atomic nuclei within the tissue to randomly rotate or “precess” around an axis parallel to the direction of the static magnetic field. Radio frequency excitation energy is then applied to the tissue and this energy causes the nuclei to “precess” in phase and in an excited state. As the precessing atomic nuclei relax, weak radio frequency signals are emitted; such radio frequency signals are referred to herein as magnetic resonance signals. In this way, magnetic resonance offers the ability to produce three-dimensional tissue images without the ionizing radiation associated with other imaging modalities. Magnetic resonance also provides real-time images with excellent tissue contrast; thus, entire target tissues can be quickly and efficiently visualized and healthy, viable, tissue can be differentiated from abnormal tissue. 
     The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within 3 or more than 3 standard deviations, per the practice in the art. Alternatively, “about” can mean a range of up to +/−20%, preferably up to +/−10%, more preferably up to +/−5%, and more preferably still up to +/−1% of a given value. Alternatively, particularly with respect to biological systems or processes, the term can mean within an order of magnitude, preferably within 5-fold, and more preferably within 2-fold, of a value. 
     6.2 Coaxial Ablation Probe 
     In certain embodiments, the coaxial ablation probe employed in the context of the methods disclosed herein will be a nested electrode device. In certain embodiments, the device will be a coaxial probe. In certain embodiments, a coaxial ablation probe  10  will comprise a cathode cage (see  1  in  FIG. 2C ) surrounding an anode (see  2  in  FIG. 2C ). In certain embodiments the anode  2  will be provided with its own insulating sheath (see  3  in  FIG. 2C ). In certain embodiments, the anode sheath  3  will be fixed to the apex of the cathode cage to provide stability and the ability to use manual traction to expand the cage. In certain embodiments, the electrode pair is loaded into an outer insulating catheter or sheath (see  4  in  FIG. 2C ). In certain embodiments, the anode sheath  3  will have configurations similar to the outer catheter or sheath ( FIGS. 2E-2I ). In certain embodiments, the compact coaxial ablation probe design will be contained within a catheter having an inner diameter from about 0.3 mm to about 3.0 cm and will allow for percutaneous insertion under MR guidance. In certain embodiments, the catheter will have an outer diameter from about 0.4 mm to about 3.5 cm. In certain embodiments, the compact design and sharp tip of the un-deployed probe (see  FIG. 2A ) allows for easy percutaneous insertion. In certain embodiments, probe  10 , once inserted, can be opened to varying diameters. The dimensions and operational size range of probe  10  can be scaled according to a particular application. For example, if probe  10  is designed for ablating liver tumors, cathode cage  1  may have a diameter of about 2 cm upon insertion and may be expanded to a diameter of about 5 cm after expansion of struts  12  during treatment. If probe  10  is designed for ablating lymph node, cathode cage  1  may have a diameter of about 2 mm upon insertion and may be expandable to about 1 cm after expansion during treatment.  FIG. 2B  illustrates expansion of cathode cage  1  after unsheathing.  FIG. 2C  illustrates expansion of cathode cage  1  to a larger diameter than that in  FIG. 2B  after tissue ablation. 
     As illustrated in  FIG. 2A , probe  10  is in the un-deployed state where individual struts  12  are confined by outer sheath  4  to a generally cylindrical configuration. Individual struts  12  are resiliently biased against the inner wall of outer sheath  4 . When outer sheath  4  is moved axially away from probe tip  14 , struts  12  expand radially outwardly to form, in one embodiment, a generally spherical shape. In another embodiment, the shape defined by the volume surrounded by struts  12  may be any desired shape, such as a sphere, an ellipsoid, a non-curvilinear closed shape, or an open shape, as will be described in detail below. When energized by a power source, the volume surrounded by struts  12  defines a treatment region. 
     As illustrated in  FIG. 2D , if it is desirable to change the shape of the volume surrounded by struts  12  to change the treatment region, struts  12  can be individually moved to change the shape of the volume surrounded by struts  12 . In one embodiment, each strut  12  can be individually extended or retracted by pushing axially towards or away from the cathode tip  14  on each individual strut  12 . In another embodiment, as will be described in more detail below, outer sheath  4  may include actuators for individually moving each strut  12 . 
     In one embodiment, outer sheath  4  may include axial guides to prevent twisting of struts  12 .  FIGS. 2E-2G  illustrate one embodiment of outer sheath  4  that includes axially extending channels or guides to prevent twisting of struts  12 . Referring to  FIG. 2E , outer sheath  4 , when viewed from an axial direction, includes channels  16  formed in the inner diameter of outer sheath  4 . Channels  16  may extend axially the entire length of the outer sheath  4 . As illustrated in  FIG. 2G , struts  12  may rest in each channel  16 . 
     In  FIG. 2G , channels  16  are open on one side. In another embodiment, each channel  16  may be a cylindrical channel that is closed, as illustrated in  FIGS. 2H and 2I . In  FIG. 2H , each channel  16  comprises a cylindrical cavity extending axially through outer sheath  4 . Each strut  12  may reside in one of channels  16  to prevent or reduce twisting of struts  12 . 
     As stated above, probe  10  may allow struts  12  to be individually moved in an axial direction to change the shape of the volume defined by struts  12 .  FIG. 2J  illustrates that embodiment where outer sheath  4  includes actuators  18  that reside in grooves  20  formed in outer sheath  4 . Each actuator  18  may be attached to one of struts  12 . When an actuator  18  slides within a groove  20 , the respective strut  12  bends either radially outwards or inwards, depending on the direction of movement of the actuator  18 . Each actuator  18  may have a generally hyperbolic profile, if viewed from the side as illustrated in  FIG. 2K . The outward facing surface  22  of each actuator  18  may include ridges or grooves to facilitate gripping. As illustrated in the side view in  FIG. 2L , each actuator  18  may further include a strut holder  24  that extends into each groove  20  and holds its respective strut  12 . As illustrated in  FIG. 2M , strut holder  24  may include a central aperture  26  through which a strut  12  passes. As illustrated by the magnified view in  FIG. 2J , each groove  20  may include teeth  21  that allow locking of an actuator  18  in a position corresponding to a desired degree of radial expansion of its respective strut  12 . 
     Cathode cage  1  may have any one of a number of different shapes or configurations.  FIGS. 2M-2Q  illustrate different configurations of cathode cage  1  according to an embodiment of the subject matter described herein. As illustrated in  FIG. 2N , cathode cage  1  defines a closed volume that is generally ellipsoidal in shape. As illustrated in  FIG. 2O , cathode cage  1  defines an open volume that has a tulip-like shape. As illustrated in  FIG. 2P , cathode cage  1  includes cross-shaped support struts  28  extending laterally between struts  12  to provide structural support for cathode cage  1 . In  FIG. 2Q , linear support struts  30  extend between adjacent struts  12 . 
     According to another aspect of the subject matter described herein, struts  12  may include any of a plurality of different radial cross sections.  FIGS. 2R-2V  illustrate different radial cross sections and configurations for struts  12 . As illustrated in  FIG. 2R , an individual strut  12  comprises a hollow cylindrical tube with apertures  32  to allow fluid flow from within strut  12  to the volume surrounded by cathode cage  1 . In one example, a fluid may be pumped through apertures  32  to increase the rate of the chemical reaction occurring within the volume defined by cathode cage  1 . 
     Any suitable fluid may be pumped through apertures in cathode cage  1  or in anode  2  without departing from the scope of the subject matter described herein. Examples of fluids that may be pumped through apertures  32  in cathode cage  1  or in apertures in anode  2  (described below) include water, medication, chemotherapy, contrast agents, or ablation-assisting fluids, including electrolytes, such as a saline solution. In addition, apertures in cathode cage  1  and/or in anode  2  may be used to withdraw fluid and ablated tissue from the treatment region defined by cathode cage  1 . 
     In another embodiment, as illustrated in  FIG. 2S , a strut  12  may have a triangular profile where one vertex of the triangle extends radially outward. Such a profile may facilitate cutting into tissue by struts  12 . 
     In yet another example, as illustrated in  FIG. 2T , each strut  12  may have a circular profile either with or without apertures. 
       FIG. 2U  illustrates another example where each strut  12  has a blade-like radial profile. In such a profile, the sharpened point of the blade extends radially outward to facilitate cutting of tissue. 
     In yet another embodiment, as illustrated in  FIG. 2V , each strut  12  may have a rectangular profile. 
     As cathode cage  1  may include different configurations, anode  2  may also include different configurations.  FIGS. 2AA-2GG  illustrate different configurations of anode  2 . In  FIG. 2AA , anode  2  includes individual struts  33  that form a closed cage, similar to cathode cage  1  illustrated in  FIG. 2B . In such an embodiment, the volume defined by anode  2  may be smaller in diameter than that defined by cathode cage  1 . As illustrated in  FIG. 2BB , anode  2  includes individual struts  33  that define an open cage. In  FIG. 2CC , anode  2  comprises a wire with a generally cylindrical and solid radial cross section. In  FIG. 2DD , anode  2  comprises a hollow cylindrical tube with apertures  34  formed in the tube, with or without a closed tip, to facilitate pumping of a fluid, such as an electrolyte solution, through apertures  34 . In  FIG. 2EE , anode  2  includes a needle-like closed tip with apertures  34  to facilitate fluid flow from the interior of anode  2  into the treatment volume or from the treatment volume into the interior of anode  2 . In  FIG. 2FF , anode  2  forms a needle-like structure with or without apertures  34 . In  FIG. 2GG , anode  2  comprises a wire surrounded by an outer insulating tube, with or without a closed tip  36 . Apertures  38  may be formed in tube  36  to allow fluid flow from the interior of tube  36  into the treatment volume or from the treatment volume into the interior of tube  36 . It should also be noted that anode configurations in  FIGS. 2CC-2GG  may be used utilized in singularity or plurality. It should also be noted that anode  2  may have any of the cross sections illustrated in  FIGS. 2R-2V . It should also be noted that anode insulting sheaths  3  may have similar constructions as illustrated in  FIGS. 2E-2I  for different anode configurations and plurality. 
       FIGS. 2HH-2JJ  illustrate different embodiments of cathode cage  1 . In  FIG. 2HH , cathode cage  1  is formed by cutting axial grooves in a tube. In such an embodiment, struts  12  may not be adjustable. As illustrated in  FIG. 2HH , cathode cage  1  includes a lower portion  40  that is a generally cylindrical tube and an upper portion formed by struts  12 . In the illustrated example, cathode tip  14  comprises an uncut portion of the uncut tube that mechanically joins struts  12  together at the apex of cage  1 . In the example illustrated in  FIG. 2HH , probe tip  14  may allow anode  2  to pass through its inner diameter and puncture tissue. In an alternate embodiment, as illustrated in  FIG. 2A , cathode tip  14  may include a point or conical structure to facilitate puncturing of tissue. 
     In  FIG. 2II , cathode cage  1  includes struts  12  that are individually adjustable. As such, each strut  12  is axially separate from its adjacent times throughout the entire axial length of each strut  12 . 
       FIG. 2JJ  illustrates another embodiment of cage  1  where struts  12  form a tissue anchor  42  at the apex of cage  1 . Tissue anchor  42  is formed by bending the end of each strut  12  in an almost 180° bend to form a hook-like structure. In operation, tissue anchor  42  may anchor into tissue being treated to provide better stability of probe  10 . 
       FIG. 3  is a diagram illustrating an exemplary system for using probe  10  for ablating liver tumors according to an embodiment of the subject matter described herein. Referring to  FIG. 3 , probe  10  is designed to be used by inserting probe  10  into the patient  44  percutaneously and into the tissue being treated. A DC generator  46  creates a DC potential across anode  2  and cathode cage  1 . An infusion pump  48  may pump fluid from a fluid reservoir  50  into the tissue volume through apertures in struts  12  or in anode  2  as described above. DC generator  46  may be connected to anode  2  via anode wire  52 . DC generator  46  may be connected to each cathode strut via cathode strut wires  54 , A visualization system  56  may include surface MRI coils worn by the patient to receive the MRI signal generated in response to tissue excitation by MRI transmit coils. Because probe  10  is compact in size, probe  10  can be used to operate on a patient between the surface MRI coils and when the patient is within the bore defined by the MRI transmit coils. 
     During electrochemical treatment, the interventional radiologist may monitor the progress of the ablation via a display which displays in real time or in near real time a magnetic resonance image of the tissue volume being treated and the surrounding tissue. The display may be part of visualization system  56  and may be a monitor, a projector, or a head mounted display. Because surface coils are worn on the surface of the patient&#39;s body, high resolution images are available. 
       FIG. 4  is a flow chart illustrating an exemplary process for treating patients using probe  10  according to an embodiment of the subject matter described herein. Referring to  FIG. 4 , in step  100 , an ablation target is identified. The ablation target may be a liver tumor, a lymph node, or any other tissue for which ablation treatment is desired. In step  102 , probe  10  is inserted into the patient centered on the target identified in step  100 . Probe  10  may have any of the configurations described herein. Probe  10  may be inserted into the tissue to be treated, for example, into the patient&#39;s liver or other organ. 
     In step  104 , cathode cage  1  is unsheathed to a desired diameter. Unsheathing cathode cage  1  may include sliding sheath  4  axially away from apex  14  of probe  10  to allow struts  12  to expand to their pre-treatment diameter. In step  106 , a DC bias is applied to probe  10 . The DC bias is applied between anode  2  and cathode cage  1 . The DC bias causes an electrochemical reaction (described above) in the treatment volume, as defined by volume enclosed within the cathode cage struts  12 , which ablates tissue within the treatment volume with minimal effect on tissue outside of the treatment volume. In step  108 , a fluid is pumped into the treatment volume. The fluid may be any of the fluids described above, for example, to enhance the treatment or to allow better monitoring of treatment progress. In step  110 , the treatment progress and probe expansion are monitored. Monitoring the treatment progress and probe expansion may include viewing real time images of the treatment volume and the cathode cage as shown on the display coupled to the surface MRI coils. In step  112 , the probe and/or individual struts may be repositioned to change the treatment volume. Steps  110  and  112  may be repeated until the desired treatment has been achieved. For example, if the treatment is the ablation of a tumor, the probe may be repositioned until the entire tumor and desired margins around the tumor have been ablated. In step  114 , the loss of normal signal on the MRI monitoring sequence is identified. The normal signal may be the signal that indicates the tissue within the treatment volume. In step  116 , the probe is withdrawn and the tissue tract may be ablated with thermal energy or electrochemical ablation to reduce bleeding, if desired. Enlarging the cage or withdrawing the probe may include adjusting actuators  18  to return each strut  12  to the minimum of the adjustment range defined by each actuator  18 , sheathing cathode cage  1  to decrease the diameter of cathode cage  1  to its insertion diameter and then withdrawing probe  10  through the same tract used for insertion. 
     In certain embodiments cathode cage  1  will include a plurality of struts  12 . For example, but not by way of limitation, the number of struts  12  can range from 1 to about 100. In certain embodiments, the number of struts  12  will be from about 2 to about 25 struts. In certain embodiments the number of struts  12  will be from about 4 to about 16 struts  12 . In certain embodiments the number struts  12  will be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15. Struts  12  may have any of the configurations described above with respect to  FIGS. 2N-2V  In certain embodiments, cathode cage  1  will be comprised of wire having a diameter from about 0.1 mm to about 10 mm. Struts  12  may be formed of any suitable conductive material that has sufficient flexibility to allow expansion and contraction to achieve a desired treatment volume. Examples of suitable materials for struts  12  include metals, such as copper, gold, or platinum; metal alloys, such as nickel-titanium alloys; or conductive plastics. One example of a nickel-titanium alloy suitable for use to form struts  12  is nitinol. 
     Similar to struts  12 , anode  2  may also be formed of any suitable conductive material, such as any of the materials listed above for struts  12 . If anode  2  needs to have a flexible configuration, such as that illustrated in  FIGS. 2AA and 2BB , anode  2  may also be comprised of a flexible metallic material. If flexibility is not a requirement of anode  2 , more rigid materials can be used than those used for struts  12 . 
     Anode  2  may have any of the configurations described above with respect to  FIGS. 2AA-2GG . In addition, the number of anodes or number of anode members may vary. For example, but not by way of limitation, the number of anodes or anode members can range from 1 to about 100. In certain embodiments, the number of anodes or anode members will be from about 2 to about 25. In certain embodiments the number of anodes or anode members will be from about 4 to about 16. In certain embodiments the number anodes or anode members will be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15. In certain embodiments, the anode will be comprised of wire having a diameter from about 0.1 mm to about 10 mm. 
     In certain embodiments, cathode cage  1  will be freely mobile within the outer sheath and adjustable in diameter from about 0.05 to about 10 cm depending on the amount of unsheathing. Sheath  4  may confine cathode cage  1  to its minimum diameter before unsheathing. Sheath  4  may be cylindrical and uniform in diameter. Alternatively, sheath  4  may be tapered or conical in shape with the smaller diameter at the insertion end and a larger diameter at the opposite end for ergonomic purposes. Furthermore, as stated above, each strut  12  of cathode cage  1  may be able to move independently to allow for more versatile contouring. In certain embodiments, the arrangement of anode  2  and cathode cage  1  will permit enough space to inject any fluid into the treatment volume or withdraw material from the treatment volume, as described above. 
     EChT has traditionally been performed with two or more platinum electrodes (21, 41, 43). Because electrochemically soluble metals will dissolve with anodic current, platinum has traditionally been used for EChT electrodes (32). However, because the cathode is protected against electrochemical dissolution by the cathodic current, it is possible to use metals with mild solubility, such as nitinol, as the cathode for EChT (53). Thus, in certain embodiments, the cathode cage of the coaxial ablation probes described herein can be made of nitinol or any of the other materials described above. 
     Nitinol has seen increased utilization for medical devices since the 1980s because of its shape memory and MRI compatibility (54-57). Nitinol&#39;s shape memory results from transformation of the metal&#39;s atomic structure from a cubic crystal configuration at high temperatures (austenite) to a monoclinic crystal at low temperatures (martensite) (58, 59). These transitions are reproducible when the metal is heated to body temperature or if an electric current is passed through the wire (60). Overall, these properties allow for construction of a nitinol cathode cage that can be compacted around a platinum electrode for percutaneous delivery as a catheter. In certain embodiments, the catheter can have an inner diameter of about 2 mm to about 1 cm. 
     Once probe  10  is positioned and the cathode unsheathed, the heat from physiologic temperatures, electric current from the DC generator, and liquefactive necrosis created by cathode cage  1  will allow cage  1  to return to its shape-formed geometry. The shape-formed geometry may be any of the geometries described above for cathode cage  1 . The shape-formed geometry refers to the geometry formed by cathode cage  1  through self expansion after being unsheathed. In certain embodiments, such geometry is defined at manufacturing time when struts  12  are heated held in position to form the desired geometry, and then cooled so that the geometry will be maintained. This principal is similar to the design and function of nitinol self-expanding stents. In certain embodiments, manual traction applied to the probe can augment the re-expansion process. 
     In certain embodiments, the nested electrode devices (coaxial ablation probe) described herein can be controlled via a steering and deployment system. In certain embodiments, such steering and deployment system can be operably linked to the nested electrode device. For example, but not by way of limitation, a sleeve of similar or different diameter to the sheath (see ( 4 ) in  FIG. 2A ) can be used as housing for steering and deployment system. In certain embodiments, the steering and deployment system will allow for independent control of the struts of the cathode cage, for example, by way of independently controllable pistons. Exemplary steering and deployment systems can be found in U.S. Pat. Nos. 6,066,125, 8,548,567, U.S. Patent Application Publication No. 20110144576, and PCT Patent Publication WO 2012177586. 
     6.3 Real-Time Monitoring of EChT for Treatment of Abnormal Tissue 
     The presently disclosed subject matter provides for devices and methods for treating abnormal tissue using minimally invasive techniques and real-time monitoring of the administration of such treatments. One such minimally invasive technique, EChT, has traditionally been performed using two or more platinum electrodes, which can be cumbersome, slow, difficult to contour, and lack adequate methods for monitoring ablation progress. As described above, the techniques of the present application involve, in certain embodiments, the use of novel ablation devices comprising a coaxial ablation probe with a size- and shape-adjustable nitinol cathode cage encasing a platinum anode. The ability to shape form and adjust individual components of the nitinol cage allows for specific contouring to a target lesion&#39;s geometry. Nitinol&#39;s MR compatibility and the sharply demarcated EChT treatment margins allow for accurate real-time monitoring and adjustment of the ablation zone. Ablation sizes achieved using the devices and methods described herein will be dependent upon total charge delivered. In certain embodiments, the total charge will range from about 100 to about 1,000,000 Coulombs, depending on lesion size. A Coulomb is the unit for total charge and is defined as the charge transported by a constant current of one ampere in one second. In certain embodiments the total charge will range from about 100 to about 100,000 Coulombs/cm 3  at a direct current of about 0.1 to about 30 A. In certain embodiments, this charge will be delivered continuously rather than in pulses. 
     Advantages of the coaxial ablation probe and methods described herein over current thermal ablation techniques include, but are not limited to: the ability to achieve sharp demarcations between treated and untreated tissue; lowered risk of non-target injury to adjacent organs; little or no pain from the ablation; and immunity to heat sink effects from large vessels adjacent to the ablation target. Data disclosed herein, e.g.,  FIGS. 1A, 1B, 6B, 10, 11A, 11B, and 11C , demonstrate the sharply marginated EChT ablation zones correlates precisely to signal changes on magnetic resonance (MR) imaging. This offers a significant advantage over current ablation techniques as real-time monitoring of ablation can allow intra-procedural adjustments to ensure complete treatment of the target lesion. 
     Real-time monitoring of methods disclosed herein via magnetic resonance can be achieved using a variety of magnetic resonance imaging techniques. For example, but not by way of limitation, U.S. Pat. Nos. 5,647,361, 7,175,829, and 8,396,532 describe a variety of magnetic resonance imaging techniques that can find use with the compositions and methods disclosed herein. In certain embodiments, such real time monitoring allows for the characterization of the ablation operation during the course of the operation. This real-time information provides reliable indications of the characteristics (e.g. area, volume and/or depth) of the lesions created during ablation procedure, and thereby allows for intra-procedural adjustments. 
     In certain embodiments, the rate and size of ablation will be dependent upon the electrode surface area, total charge, and free ions in the treatment zone. Therefore, in certain embodiments, the rate of ablation can be enhanced and the ablation zone enlarged by making one or more of the following, non-limiting, adjustments: 1) expanding the nitinol cage diameter to increase surface area; 2) amplifying the current to increase total charge; and 3) injecting saline or other ionic fluid to augment free ions. 
     In certain embodiments, the methods disclosed herein will find use in the treatment of cancerous tumors, including, but not limited to hepatocellular carcinoma, hepatic metastases, other solid organ or soft tissue tumors, and metastatic lymph nodes. For example, but not by way of limitation, the curative potential of percutaneous ablation has been recognized by the Barcelona Clinic Liver Cancer (BCLC) group, which asserts that radiofrequency ablation of limited grade hepatocellular carcinomas (HCCs) up to 3 cm in size (and up to 3 nodules) is equivalent to surgical resection in terms of overall survival. However, the BCLC group conceded that the major limitation of current ablation techniques is the higher rate of local recurrence compared to surgical resection (31). This higher risk of local recurrence results from inability to completely ablate the target tumor in the treatment zone. Other major drawbacks of current ablation technology include wide zones of transition between treated and untreated tissue, risk of non-target tissue damage, heat sink effects in perivascular regions, and lack of real-time monitoring with standard imaging modalities (1-11). Implementation of the coaxial ablation probe and methods described herein, such as, but not limited to, the use of real-time magnetic resonance monitoring of electrochemical treatment administered via a coaxial ablation probe addresses the need identified in the art. 
     Although the coaxial ablation probes disclosed herein are primarily described in the context of the performance of EChT, these devices can also be used in the context of alternative ablation techniques. Such alternative ablation techniques include, but are not limited to: thermal ablation (where heat is transmitted to the treatment site via the metallic components of the coaxial ablation probe) and irreversible electroporation. 
     As stated above, probe  10  may be used to treat tumors in different parts of the human anatomy, including, but not limited to the liver, lymph nodes, or other solid organ tumors.  FIGS. 5A-5D  illustrate the use of probe  10  to treat a tumor in a human liver. In  FIG. 5A , probe  10  is shown in its insertion state with struts  12  of cathode cage  1  undeployed or sheathed. Probe  10  is inserted into tumor  60  in a human liver  62 . Probe  10  may be inserted an incision in the patient&#39;s skin  66 . 
     In  FIG. 5B , cathode cage  1  is unsheathed. At this stage, treatment begins applying a DC voltage across cathode cage  1  and anode  2 . Fluid may also be pumped into the treatment volume defined by cathode cage  1  through apertures in the cathode  1  or anode  2  as described above. 
       FIG. 5C  illustrates further expansion of cathode cage  1  as treatment progresses.  FIG. 5D  illustrates full expansion of cathode cage  1  and complete ablation of tumor  60 , indicated by the shaded region. 
       FIG. 6A  illustrates ablation of different regions in the human liver. In  FIG. 6A , A-D indicate possible ablation targets in the human liver  70 . Ablation target A is adjacent to the gall bladder  72 . Ablation target B is adjacent to a large blood vessel. Ablation target C is adjacent to the pancreas  74 . Ablation target D conforms to the hepatic capsule adjacent to the superior vena cava  76 . 
       FIG. 6B  is an image of a liver after ablation. In  FIG. 6B , liver  70  and gall bladder  72  are illustrated. The dark region in liver  70  adjacent to gall bladder  72  is the ablation region. The ablation region does not extend into gall bladder  72 , illustrating the ability of probe  10  to ablate tissue adjacent to vital structures without damage to that vital structure. 
     As stated above, probe  10  may be used to ablate tumors in the lymph node.  FIG. 7  illustrates the locations of different lymph nodes in the human body that can be affected by different locations of a primary tumor.  FIGS. 8A-8E  illustrate the use of probe  10  to treat a tumor within a lymph node. More particularly,  FIG. 8A  illustrates an exemplary lymph node  80 .  FIG. 8B  illustrates the insertion of probe  10  into lymph node  80 .  FIG. 8C  illustrates the expansion of cathode cage  1  after unsheathing of cathode cage  1  and application of a DC bias between anode  2  and cathode cage  1 . Fluid may also be pumped into the treatment volume defined by cathode cage  1  through apertures in the cathode  1  or anode  2  as described above.  FIG. 8D  illustrates further adjustment of the cathode cage  1  to contour the lymph node  80  capsule.  FIG. 8E  illustrates complete ablation of a lymph node indicated by the shaded area. 
     A coaxial ablation probe according to an embodiment of the subject matter described herein may also be used to ablate tumors in lymph nodes of the head and neck.  FIG. 9A  is a diagram illustrating lymph nodes of the head and neck that may be treated using a coaxial ablation probe according to the subject matter described herein.  FIG. 9B  is a system for treating lymph nodes of the head and neck using probe  10 . The components in  FIG. 9B  are the same as those illustrated in  FIG. 3  hence, a description thereof will not be repeated. However, probe  10  in  FIG. 9B  may be scaled in dimensions to treat lymph nodes, whereas the probe illustrated in  FIG. 3  is scaled for size to treat liver tumors. 
     Although the examples described above relate primarily to ablating liver and lymph nodes, the subject matter described herein is not limited to ablating only these types of tumors. Probe  10 , can be appropriately dimensioned or scaled to ablate any kind of soft tissue tumor in any region of the body where ablation is possible. 
     7. EXAMPLES 
     The following examples are merely illustrative of the presently disclosed subject matter and they should not be considered as limiting the scope of the presently disclosed subject matter in any way. 
     7.1 MRI Compatibility of EChT 
     Preliminary studies have demonstrated the safety and efficacy of the coaxial ablation probe as well as feasibility of MRI monitoring. These studies were performed with permission and in accordance with the practices of the University of Pennsylvania Institutional Review Board and Institutional Animal Care and Use Committee. 
     Safety and Proof of Concept: 
     Preliminary studies performed by the principal investigators utilized a B&amp;K Precision 1901 DC power supply (Yorba Linda, Calif.) as the DC generator, 18 G platinum wire as the anode, and 16 G nitinol wire struts loaded into a polyether ether ketone (PEEK) needle guide to simulate the cathode cage. 
     In a saline model, current scatter, heating effects, and local pH measurements were dependent upon system current and NaCl concentration. Current was found to be contained within the cathode cage with current scatter &lt;0.05 mA at 1 cm beyond the cathode cage for all saline concentrations and system settings of 2.0-5.0 A. Heat was produced at the anode with surface temperatures reaching 60° C. by 10 minutes (32 V, 2.8 A). No heat was produced at the cathode cage. Local pH changes were observed within 10 seconds with a pH of 13.8 at the cathodes and 3.2 at the anode (32 V, 2.8 A). Therefore, tissue ablation was predominantly pH mediated with no risk of current leakage. 
     Using a 2 cm thick ex vivo bovine liver model, ablation of 3, 4, 5, and 6 cm diameters were performed to determine the time to achieve complete ablation ( FIG. 10 ). Complete ablation was achieved by 15 minutes for the 3 cm cage diameter, 20 minutes for the 4 cm cage diameter, 35 minutes for the 5 cm cage diameter, and 40 minutes for the 6 cm cage (32 V, 0.6-1.8 A). These rates were comparable to similarly sized RF and microwave ablations (61). 
     MR Monitoring: 
     All in situ studies were performed with permission and in accordance with the practices of the Institutional Review Board and Institutional Animal Care and Use Committee. A total of 20 MR monitored ablation was performed on eight euthanized male Yorkshire swine (25-30 kg) in a Siemens Avanto 1.5 T clinical MRI scanner with spine and body matrix coils (Malvern, Pa.). A small incision was created to place the PEEK needle guide on the liver surface. Using the needle guide, ten 16 G nitinol wire struts were arranged to create regular 3, 4 and 5 cm diameter cathode cages into a single hepatic lobe; the platinum anode was placed in the isocenter. Wire positioning was confirmed using a volumetric interpolated breath-hold examination (VIBE) T1 sequence (TR/TE 5.0/2.2 ms, FA 15°, FOV 200 mm; Matrix 196×320; slice thickness 3 mm). Custom-made insulated 12 gauge copper wire with pure copper mini-alligator clips were connected to the DC generator and fed through the wave guide to clip onto the anode and cathodes. 
     Coronal oblique VIBE T1 sequences were performed along the short axis of the cathode cage to serve as the monitoring sequence. Ablations were performed at each diameter up to 60 minutes (32 V, 0.2-1), with VIBE T1 monitoring sequences performed at 3-minute intervals for the 3 cm ablation and 5-minute intervals for the 4 and 5 cm ablations. Ablation completion was defined as the time at which the anode and cathode signal changes coalesced. Upon ablation completion, the struts were removed and turbo spin echo (TSE) T2 (TR/TE 5400/96 ms) and VIBE T1 sequences were obtained along the short axis of the ablation axis. The liver was subsequently explanted and the gross pathology examined. 
     Within the first minute of ablation, tissue necrosis was seen to develop at the anode and propagate circumferentially towards the cathode as a zone of T1 hypointense signal with a leading edge of T1 hyperintensity ( FIG. 11A ). Similar signal changes were observed at each cathode strut with a central T1 hypointense signal and leading edge of T1 hyperintense signal. The TSE-T2 post-ablation sequences demonstrated increased signal about the cathode cage struts, which correlated with liquefied tissue at gross pathology ( FIG. 11B ). Complete ablation was achieved by 15 minutes at 3 cm cage diameter, 35 minutes at 4 cm cage diameter, and 50 minutes at 5 cm diameter. Specific absorption rate (SAR) remained less than 10 W/kg for all ablations. It is important to note that all ablations were performed adjacent to the gall bladder fossa and there was no detectable damage to the gall bladder wall ( FIGS. 11A and 11B ). 
     Size and Shape Adjustment: 
     In situ testing of the coaxial ablation probe was performed by percutaneously placing the device into the subcapsular left hepatic lobe in three Yorkshire swine (25-30 kg). The swine were loaded in a Siemens Avanto 1.5 T clinical MRI scanner with spine and body matrix coils. A 4 mm Invivo bone biopsy trochar (Gainesville, Fla.) was used to puncture the skin to the level of the hepatic capsule. Through the defect, the device was inserted into the liver, coaxial ablation probe position was confirmed using VIBE-T1. The device was subsequently unsheathed and ablation was performed (32 V, 0.3-0.9 A) for 15 minutes to allow for self-expansion. MR monitoring was with the T1-VIBE sequence at 3 minute intervals along the short axis of the probe. Subsequently manual traction was performed to adjust the size and shape of the coaxial ablation probe. The struts opposite the hepatic capsule were advanced to direct ablation away from the hepatic capsule and ablation was allowed to continue for 6 additional minutes ( FIG. 11C ). Post-adjustment MRI confirms the coaxial ablation probe&#39;s ability to be size and shape adjustable. 
     Although the presently disclosed subject matter and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the presently disclosed subject matter as defined by the appended claims. Moreover, the scope of the presently disclosed subject matter is not intended to be limited to the particular embodiments described in the specification. Accordingly, the appended claims are intended to include within their scope such modifications. 
     Patents, patent applications, publications, product descriptions, and protocols that may be cited throughout this application including in the following list of “References”, the disclosures of which are incorporated herein by reference in their entireties for all purposes. 
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