Abstract:
A tissue ablation system comprises a first electrode assembly adapted for insertion into a target tissue mass within a body, the first electrode assembly including a first electrode coupled to a source of RF energy in combination with an ultrasound imaging probe movably coupled to the first electrode assembly for insertion with the first electrode assembly to a desired location relative to the target tissue mass, the probe being movable relative to the first electrode assembly between an insertion configuration in which a distal end of the probe covers a distal end of the first electrode assembly and a deployed configuration in which the distal end of the first electrode assembly is uncovered. A method of ablating target tissue within a body comprises placing a distal dome of an ultrasound imaging probe in overlying alignment with a first cannula of an RF ablation device and inserting the probe and the RF ablation device through a lumen of an insertion device to a desired location adjacent to a target tissue mass in combination with moving the distal dome away from a distal end of the first cannula to expose a distal end thereof, inserting the distal end of the first cannula into the target tissue mass to position a first electrode of the RF ablation device at a first desired location within the target tissue mass, obtaining an image of the target tissue mass and the first electrode via the probe and applying RF energy to the target tissue mass via the first electrode.

Description:
BACKGROUND 
   Fibroids, tumors and other tissue masses are often treated by ablation. In many cases, local ablation of the diseased tissue is carried out by inserting a therapeutic device into the tissue and carrying out therapeutic activity designed to destroy the diseased cells. For example, electrical energy may be applied to the affected area by placing one or more electrodes into the affected tissue and discharging electric current therefrom to ablate the tissue. Alternatively, tissue may be ablated cryogenically, by applying heat or chemically by injecting fluids with appropriate properties to the target tissue. 
   However, as many tumors and fibroids are loosely held in place by ligaments and other structures, movement of the target tissue mass may make it difficult to insert a needle electrode or other energy delivery device thereinto. Grasping devices and anchors may be used to immobilize the target tissue mass while an electrode is inserted thereinto, but these procedures add more complexity to the operation and may require additional incisions. The surgeon may also require assistance from additional personnel to carry out such procedures. 
   RF ablation procedures also benefit from visualization methods used to correctly position the electrodes within the target tissue mass and to determine the effectiveness of treatment. A degree of visualization may be obtained by inserting the ablation device into the vicinity of the target tissue mass using an endoscopic instrument with a vision system. However, the field of view of these vision systems is small and may be insufficient to properly perform and assess the effectiveness of the treatment. Conventional vision systems may also have difficulty in facilitating the positioning of the electrodes within the tissue, as the tissue itself obscures viewing of the electrodes. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present invention is directed to a tissue ablation system comprising a first electrode assembly adapted for insertion into a target tissue mass within a body, the first electrode assembly including a first electrode coupled to a source of RF energy in combination with an ultrasound imaging probe movably coupled to the first electrode assembly for insertion with the first electrode assembly to a desired location relative to the target tissue mass, the probe being movable relative to the first electrode assembly between an insertion configuration in which a distal end of the probe covers a distal end of the first electrode assembly and a deployed configuration in which the distal end of the first electrode assembly is uncovered. 
   The present invention is further directed to a method of ablating target tissue within a body comprising placing a distal dome of an ultrasound imaging probe in overlying alignment with a first cannula of an RF ablation device and inserting the probe and the RF ablation device through a lumen of an insertion device to a desired location adjacent to a target tissue mass in combination with moving the distal dome away from a distal end of the first cannula to expose a distal end thereof, inserting the distal end of the first cannula into the target tissue mass to position a first electrode of the RF ablation device at a first desired location within the target tissue mass, obtaining an image of the target tissue mass and the first electrode via the probe and applying RF energy to the target tissue mass via the first electrode. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a perspective view showing an embodiment of the ablation device according to the present invention; 
       FIG. 2  is a front view showing the ablation device of  FIG. 1 ; 
       FIG. 3  is a perspective view of an ultrasound probe according to the present invention; 
       FIG. 4  is a perspective view of the ablation device of  FIG. 1 , with an insertion device; 
       FIG. 5  is a perspective view of another embodiment of the ablation device according to the present invention; 
       FIG. 6  is a front view showing the ablation device of  FIG. 5 ; and 
       FIG. 7  is a perspective view of another embodiment of the ablation device according to the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The present invention relates to devices for treating tissue such as fibroids, tumors and other tissue masses by applying electric energy through electrodes inserted into a target tissue mass. The present invention also relates to devices used to ablate tissue to reshape an organ. 
   In one embodiment, energy delivery elements of the apparatus according to the present invention are deployable from a single medical instrument. For example, such a single instrument may include two tined arrays or one tined array and one clamp which are placed on or within the target tissue mass to treat the target tissue. In other embodiments, the instrument may include devices for grasping and holding in place the target tissue mass, minimizing the minimum number of incisions and medical personnel required to perform the procedure. 
   Conventional systems for treating target tissue such as a tumor or fibroid with needle-based radio frequency (RF) devices include, for example, the LeVeen Needle Electrode™ from the Oncology Division of Boston Scientific Corp. and the Starburst™ product line available from RITA Medical Systems, Inc. When using these devices, the surgeon punctures the target tissue mass with the device&#39;s needle and then deploys one or more RF tines into the tissue mass. An electric voltage is then applied to the tines to necrose the target tissue so that it is ablated. Lower levels of energy may be applied to achieve other therapeutic goals on the target tissue. 
   As described above, these devices are most effectively used on their own only by highly skilled individuals as it is difficult to properly place such devices within target tissue masses which tend to move when contacted. Even with skilled practitioners, multiple attempts may be required before a needle is correctly positioned. Alternatively, grasping devices such as tumor screws may be used in conjunction with these devices to immobilize and apply traction to the target tissue mass during insertion of the needle. However, this requires more time (or additional personnel) and may require multiple entry points through the skin, further increasing the complexity, time required for and discomfort associated with the procedure. As would be understood by those skilled in the art, if the electrodes are not placed sufficiently close to a desired location within the target tissue mass, the targeted tissue may not be treated as desired as the range of RF ablation is limited. In addition, misplaced electrodes may damage non targeted tissue in proximity to the target tissue mass. Although ultrasonic monitoring devices may be used to correctly place the electrodes in the target tissue, the quality of the images depends on the size of the probe&#39;s distal dome and there has been a trade-off between image quality and the invasiveness of the procedure. In addition, the size of ultrasound probes which have been employed has been limited by the size of the working channels of the devices through which these probes have been inserted to the target tissue mass. 
     FIG. 1  shows an exemplary embodiment of a bipolar RF ablation system with an integrated ultrasound imaging probe, according to the invention. The system is designed and configured so that it can be inserted into the patient&#39;s body through a small access port or channel, similar to a trocar. In this manner, the system can be used to perform minimally invasive treatments, such as laparoscopically guided RF ablation of uterine fibroids. Other types of fibroids or abnormal tissues may also be treated with the exemplary system, particularly those formed in the lumens of hollow organs. It will be apparent to those of skill in the art that other procedures may also be carried out with the device according to the invention. For example, target tissues may be reshaped by ablation or resection, and other therapeutic goals may be achieved by delivering selected amounts of energy to the target tissue. 
   An RF ablation system  100  according to an exemplary embodiment of the invention comprises an RF portion having two cannulas  104 ,  106  and an integrated imaging portion having an imaging device shaft  108 . The system is configured to fit through a small port, through a trocar-like insertion device, or though the working channel of an endoscope to perform minimally invasive procedures. For example, an exemplary system may fit through openings less than 10 mm in diameter and may more preferably fit through openings less than 5 mm in diameter. RF ablation cannulas  104 ,  106  are shown in a side by side configuration, extending along parallel axes. The cannulas  104 ,  106  are extendable side by side, independently from one another, so that the distal end of each cannula may be positioned at a different desired site within a target tissue mass  102 . For example, a sharp distal end  114  of the RF cannula  104  may be inserted and positioned at one end of the target tissue mass  102  just inside a surface thereof while the sharp distal end  116  of the RF cannula  106  is inserted further into the target tissue mass  102  to a location at the opposite end of the target tissue mass  102 . Thus, an ablation region of desired dimensions may be created by properly positioning the two distal ends  114 ,  116  relative to one another. 
   After the RF cannulas  104 ,  106  have been inserted within the target tissue mass  102 , arrays of tines, or electrodes, may be deployed independently therefrom to better define the ablation region to be treated. For example, a first array of tines  110  may be deployed from an opening at the distal end  114  and a second array of tines  112  may be deployed from the second distal end  116 . As would be understood by those skilled in the art, the arrays  110 ,  112  are preferably shaped to define a size and shape of a region of the target tissue mass  102  to be ablated. Connections  118 ,  120  convey the RF energy from a generator  122  to each of the arrays  110 ,  112  with the polarity of the energy provided to the array  110  being opposite that provided to the array  112  to create a bipolar ablation device. Connections  118 ,  120  may be electric wires, or other types of electric connections used conventionally in RF ablation probes. 
   The configuration of the RF ablation system according to the invention may be used to treat target tissues of different dimensions, simply by varying the relative positions of arrays  110 ,  112  within the target tissue mass  102 . The system also allows for staged ablation of the target tissue mass  102 , thus enabling the operator to ablate a larger volume of tissue in one operation. For example, a first region of the target tissue mass  102  may be treated with the arrays  110 ,  112  relatively close to one another. The arrays  110 ,  112  may then be moved further apart, to treat a second, larger region of the target tissue mass  102 . The repositioning and treatment steps may be further repeated as needed to treat the entire target tissue mass  102 . 
   The ultrasound visualization portion of the exemplary device shown in  FIG. 1  includes an ultrasound probe comprising a shaft  108  which is placed side by side with the two RF cannulas  104 ,  106 . The RF cannulas  104 ,  106  can be moved longitudinally relative to the shaft  108 , but are attached thereto to form an integrated unit. The ultrasound probe also includes a dome  128  with a forward facing transducer  130  designed to be introduced into the body in the vicinity of the target tissue mass  102 . The shaft  108  has a smaller diameter than the dome  128 , to reduce the cross sectional area of the device. In addition, the dome  128  is mounted on the shaft  108  offset from an axis thereof. The assembly of the shaft  108  and the dome  128  can be rotated along the longitudinal axis, so that the dome  128  can be rotated toward and away from the RF cannulas  104 ,  106 . 
   According to the present invention, the dome  128  containing the ultrasound sensor transducer  130  is rotatable along the longitudinal axis of the shaft  108 . As depicted in greater detail in the front and perspective views shown in  FIGS. 2 and 3 , the dome  128  rotates about the centerline axis x of the shaft  108 . Since the dome  128  is offset relative to the shaft  108 , and since the shaft  108  is generally aligned with the distal portions of cannulas  104 ,  106 , it is possible to place the dome  128  in front of or beside the distal ends  114 ,  116  thereof. Specifically, when the shaft  108  is rotated as shown by the arrows A, the dome  128  swings along one of the paths shown by the arrows B and C.  FIG. 2  shows the dome  128  in an operative position, to the side of the cannulas  104 ,  106 . In the operative position, the dome  128  is moved away from and does not interfere with the openings at the distal ends  114 ,  116  so that deployment of the array of tines  110 ,  112  from the cannulas  104 ,  106  is unrestricted. At the same time, the operative position provides the dome  128  with an unobstructed view of an operative field forward of the transducer  130 . 
   When the shaft  108  is rotated approximately 180 degrees in either direction from the orientation shown in  FIG. 2 , the dome  128  is positioned in front of the openings  114 ,  116 , in an insertion/removal configuration. This configuration facilitates passage of the dome  128  to and from the target tissue mass by reducing the profile of the entire device. When the dome  128  is placed in front of the cannulas  104 ,  106 , the overall cross sectional area of the ablation system device  100  is reduced to a minimum. By properly selecting the geometry of the shaft  108  and of the dome  128 , the cross sectional area of the device  100  in the insertion configuration may be limited to the cross sectional area of the dome  128  with the width of the cannulas  104 ,  106  and of the shaft  108  shadowed behind the width of the distal dome  128 . 
   In the insertion configuration, the size of the dome  128 , and thus of the transducer  130 , is the limiting factor which determines whether the RF ablation device  100  can pass through a particular insertion lumen. In this configuration, the profile dimensions of the cannulas  104 ,  106  and of the shaft  108  are all contained within the profile dimension of the distal dome  128 . The profile dimension corresponds to the maximum width of the device as seen from the front as the RF device is introduced into a lumen of an endoscope, trocar, or other insertion device. According to the invention, the width of the dome  128  is at least as great as that of the rest of the device. The dome  128  can thus be selected to be as large as will fit through the insertion device. 
   In one exemplary embodiment, the dome  128  is dimensioned to contain an ultrasound transducer capable of operating approximately in the 5 to 8 MHz frequency range. This frequency range is desirable because it provides higher resolution images of biological structures surrounding the transducer. Although ultrasonic transducers utilizing lower frequencies may obtain higher quality images these transducers also require larger dimension domes. By providing a dome  128  which at least as large as the shaft  108 , and which is offset relative to the axis of the shaft  108 , the device according to embodiments of the present invention allow the dimensions of the transducer to be maximized. An imaging station  126  may be connected to the transducer  130  via an electric connection  124  which may include, for example, electric wires, a wireless connection, optical connections or other conventional means. 
   As described above, when in the insertion configuration, the large dome  128  is rotated in front of the cannulas  104 ,  106 , so that the entire RF ablation system  100  can fit through a small passage, such as a working channel of an endoscope or of a trocar-like tube  150 . Once the dome  128  has exited a distal end of the tube  150 , the dome  128  is rotated away from the cannulas  104 ,  106  to expose distal openings thereof so that the arrays of tines  110 ,  112  may be deployed therefrom.  FIG. 4  shows an exemplary embodiment of the RF ablation system  100  in the deployed configuration, with arrays of tines  110 ,  112  deployed and the dome  128  rotated away from cannulas  104 ,  106 . When the procedure has been completed, the arrays of tines  110 ,  112  are retracted and the dome  128  is rotated back into the insertion/removal configuration and the device is withdrawn proximally through the tube  150 . 
     FIGS. 5 and 6  show an RF ablation system  200  according to a second exemplary embodiment of the invention. A visualization portion of the RF ablation system  200  includes a shaft  108  and a dome  128  analogous to those described with reference to  FIG. 1 . As with the system  100  of  FIG. 1 , the dome  128  is offset relative to the shaft  108  and can be rotated away from and toward two cannulas  202 ,  204  between an insertion/removal configuration and a deployed configuration. The cannula  202  is a dual lumen cannula including first and second lumens  220 ,  222  through which arrays of tines  212  and  214  are deployed. As shown in  FIG. 6 , the lumens  220 ,  222  are preferably concentric with each allowing passage of one of the two arrays of tines  212 ,  214 . Alternatively, the lumens  220 ,  222  may be formed in a side-by-side or top-bottom arrangement. In the concentric arrangement, exit openings  208  are formed at one or more selected locations along the length of the cannula  202 , so that the array of tines  212  may be deployed through the wall separating the lumens  220 ,  222  at the selected locations relative to the location (e.g., opening  210  at the distal end of the cannula  202 ) from which the array of tines  214  is deployed. 
   The system  200  may further include a second cannula  204  through which a tissue anchoring device (e.g., a tissue screw  206 ) may be deployed. The cannula  204  may be fixed or movable relative to the cannula  202  and the shaft  208 , depending on the requirements of the system. For example, the cannula  204  may be inserted through the tube  150  until its distal end is in a desired position adjacent to the target tissue mass  102 . The tissue anchoring element  206  may then be deployed therefrom to retain the target tissue mass  102  in a desired position relative to the RF ablation system  200  (e.g., by grasping the target tissue mass  102 ) while the cannula  202  is inserted thereinto. The tubes forming the lumens  220 ,  222  may then be manipulated so that openings  208 ,  210  are placed in desired positions relative to the target tissue mass  102 . The correct positioning of the arrays may be ascertained using visualization provided by the ultrasound transducer  130 . The RF ablation procedure may then take place as described above with visualization of the tissue providing feedback which the operator may use to determine when a desired degree of treatment of the target tissue mass  102  has been achieved. 
   As described above, as the RF ablation system  200  is initially inserted into the patient through a tube  150 , the cannulas  202 ,  204  are maintained in the withdrawn position, behind the dome  128  which is maintained in the insertion/removal configuration—i.e., with the dome  128  rotated to cover the cannulas  202 ,  204 , minimizing the cross sectional profile of the device. Once the RF ablation system  200  has been located in a desired position adjacent to the target tissue mass  102 , the dome  128  is rotated away from the cannulas  202 ,  204  to the deployed configuration, the tissue anchoring device  206  is extended to grasp the target tissue mass  102  and the cannula  202  is extended into the target tissue mass  102 . Thereafter, the openings  208 ,  210  are located in desired positions within the target tissue mass  102  and the arrays of tines  212 ,  214  are deployed for tissue ablation. As described above, when the desired degree of treatment has been completed, the arrays of tines  212 ,  214  are retracted into the lumens  220 ,  222 , respectively, the tissue grasping device  206  is withdrawn into the cannula  204  and the cannulas  202  and  204  are withdrawn into the tube  150 . Then the dome  128  is rotated back into the insertion/removal configuration and the system  200  is withdrawn from the body via the tube  150 . 
     FIG. 7  shows another exemplary embodiment of an RF ablation system  300  according to the present invention. The ablation system  300  is substantially similar to the prior embodiments in construction and operation except for the construction of the electrodes  210 ,  212 . As opposed to the arrays of tines in the previous embodiments, the system  300  includes electrodes  210 ,  212  formed as conductive bands around the first and second cannulas  104 ,  106 , respectively. Those skilled in the art would understand that each of the electrodes  210 ,  212  may comprise one or more conductive bands which may be energized singularly or in any combinations desired. 
   The present invention has been described with reference to specific exemplary embodiments. Those skilled in the art will understand that changes may be made in details, particularly in matters of shape, size, material and arrangement of parts. For example, those skilled in the art will understand that above described bipolar RF ablation system could be replaced by a monopolar RF ablation system with only a single electrode inserted into the body. That is, those skilled in the art will understand that a monopolar RF ablation system could be formed including an ultrasound element movable between an insertion/removal configuration minimizing a profile of the system and a deployed condition in which a field of view of the ultrasound is unobstructed by a single electrode and does not interfere with deployment of this single electrode. Accordingly, various modifications and changes may be made to the embodiments. Additional or fewer components may be used, depending on the condition that is being treated using the described RF ablation system and devices. The specifications and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.