Abstract:
A device for tissue ablation comprises plural arrays of segmented needle electrodes, each of which contains a plurality of electrically conductive segments, a plurality of non-conductive joints, and a needle tip. Each of the electrically conductive segments is wired to a radio-frequency electrical power source and can be connected to and disconnected from the power source. After the needle electrodes of the device are penetrated into a target tissue to be ablated, the intended volume of ablation can be configured in three dimensions. Thus, the device allows physicians to effectively control ablation boundaries.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This patent application claims the priority from the provisional application 60/519,183 accorded with a filing date of Nov. 12, 2003. 

   FIELD OF INVENTION 
   This invention relates to medical devices and, in particular, to multi-needle-electrode array and the technology of employing bipolar radio-frequency energy for ablation of diseased tissues such as tumors, cancerous tissues, and abnormal tissues in living subjects. 
   BACKGROUND OF THE INVENTION 
   In treatment of tumors and cancerous tissues in human body, various methods are available, which include medication, radiation, dissection and ablation. Radio frequency (RF) ablation is commonly used to treat diseased tissues. RF ablation is a tissue treatment by which two or more electrodes are inserted into the vicinity of a diseased tissue and an alternating electrical current, typically at a frequency of a few hundred kHz, is applied to the tissue through the electrodes to ablate the tissue between the two electrodes. It is commonly believed that when the RF current passes through the tissue, electrical energy transforms into heat by what is known as Joule heating effect, and when the temperature of the tissue is high enough (it is generally believed that the temperature needs to be above 55° C.), the cells of the tissue between the two electrodes are destroyed. For most tissue ablation cases, it is desirable to ablate the tissues only within intended boundaries (e.g., desirable size and shape). Therefore, it is critical that the RF energy is directed only to the targeted tissue within the desirable boundaries to minimize damage to the healthy tissues surrounding the targeted tissue. 
   “Le Veen Needle Electrodes”, described by U.S. Pat. No. 5,868,740, is a device currently available on the market for the treatment of tumors and cancerous tissues. This device contains an array of deployable needles, which can be inserted into the tumor tissue, and a large grounding pad, which may be in contact with a large area of the skin of a patient. In an ablation operation, the needles are inserted into the diseased tissue and the ground pad is properly placed in contact with a large area of the skin of the patient. Then, an RF current is applied to all the needle electrodes at once. The current passes through the diseased tissue (and some normal tissues) at higher current density, the large area of skin at lower current density, and the grounding pad, going back to the RF power source. This technique is referred to as monopolar RF ablation technology. The drawback of the technique is that because the RF current goes through part of the healthy tissues, it sometimes causes unintended damages to them if the current is not carefully controlled. 
   In U.S. Pat. No. 5,693,078, Jawahar Desai discloses a device and technique for generating a large lesion to treat endocardiac tissue for ventricular tachycardia and other cardiac dysrhythmias. Desai used an array of electrodes, which was placed on the surface of the ablation zone and an RF power source that had a plurality of voltage outputs, each having an individual phase. Each individual electrode was connected to one of the individually phased outputs of the RF power source. When power was turned on, the electrode array together with the multi-phased RF power source produced plural current paths on the surface of the ablation zone and resulted in a uniform lesion with a size defined by the span of the electrode array. This method is good in the sense that it can generate a bigger lesion on the surface of a targeted area. However, it does not provide any means for controlling the depth of ablation; and the RF electrical current tends to concentrate in the vicinity of the needles. Therefore, this device cannot be used to achieve desirable three-dimensional large lesions consistently. 
   U.S. Pat. No. 6,514,252 disclosed a device for ablating tissue using two optional arrays of tissue penetration elements (needles) on a pair of actuable jaws using bipolar RF energy. This device extended the electrodes from the forceps to the tip of the needles. However, the application of this device is not really suitable for tumors or other type of tissues due to the fact that it is attached to a jaw mechanism. 
   For all the reasons mentioned above, there is a need for developing a device, which is capable of producing large and uniform three-dimensional lesions by using bipolar RF energy; and there is a need for developing a method capable of controlling the size and shape of three-dimensional lesions by using bipolar RF energy. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is the primary object of the present invention to improve the method for tissue ablation. 
   It is an object of the present invention to improve the tissue ablation method so that it can be used to ablate tissues with a desirable volume adjacent to a superficial position or at a desirable depth from the surface. 
   Another object of the present invention is to provide an improved tissue ablation method for achieving the desirable uniformity of lesions created by RF ablation. 
   It is yet another object of the present invention to improve the ability to configure the lesion created by RF ablation according to the shape and size of diseased tissue. 
   It is yet another object of the present invention to improve the method of treating tumors and cancerous tissue, and other diseased tissues with benign and malignant pathology such as abnormal endocardiac tissue and prostate gland. 
   These objects are accomplished by application of plural arrays of segmented needle electrodes, each of which contains a plurality of electrically conductive segments, a plurality of non-conductive joints, and a needle tip. Each of the electrically conductive segments is wired to a RF power source and can be connected to and disconnected from a power source. After the needle electrodes of the device are penetrated into the target tissue to be ablated, the intended volume of ablation can be configured in three dimensions. Thus, the device allows physicians to control ablation boundaries. 
   In one version of the present invention, each array of segmented needle electrodes contains a series of substantially co-linearly arranged segmented needle electrodes that are spaced at a small distance (a few mm to a few cm). In each array of the segmented needle electrodes, the needle electrodes are spaced close enough so that when all segments of needle electrodes in the same array are connected to the same RF energy source with same polarity, it forms virtually a plate electrode. The array of needle electrodes can be bundled together, partially bundled together, or be individually placed by a user (usually a physician) to allow the user to have control over how to place the needles in the tissue in ablation operations. 
   Each needle electrode is segmented. Each needle electrode has a plurality of individual segments, and each segment is electrically insulated from other segments and independently wired to a RF power source so that the user can choose to activate any of the segments of a particular needle. Therefore, the user can control the depth of the ablation. 
   The segmented needle electrodes can also be curved or shaped in a way to target certain tissue at certain anatomic structure to avoid, among other things, bones, major nerves and large blood vessels. 
   Two arrays of segmented needle electrodes are placed in parallel and adjacent to each other. Two arrays of segmented needle electrodes are then connected to the bipolar RF power source with opposite polarities. Larger lesions can be created by successive adjacent placement of arrays of segmented needle electrodes with alternative polarities. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates the configuration of a single segmented needle electrode; 
       FIG. 2  illustrates schematically the electrode configuration of a multi-array segmented needle electrodes connected to a bipolar RF energy source; 
       FIG. 3  illustrates schematically an array of segmented needle electrodes bundle. 
       FIG. 4  shows three examples of curved segmented needle electrodes; and 
       FIG. 5  illustrates an example of using curved segmented needle electrode for ablation of tubular structure. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2  illustrate schematically the configuration and the electrical connection of the improved ablation device. It generally contains a plurality of needle electrodes  100  through  119 , arranged in a matrix configuration. The needle electrodes  100  further contains a plurality of electrically conductive metal segments  100 A,  100 B,  100 C,  100 D, and  100 E, which are jointed by non-conductive tube joints  100 F,  100 G,  100 H, and  100 I. A pointing needle tip  100 J is assembled at the distal end of the needle electrode  100  to allow for easy penetration into tissues. While the needle tips and metal segments may be made of any of the well known metals such as stainless steel, copper alloys, they may be made of any type of electrically conductive materials. 
   The metal segments  100 A,  100 B,  100 C,  100 D, and  100 E are individually wired with a terminal wire bundle look containing five individual wires  100 L through  100 P, which are individually connected to branch wire bundle  120 A, power cable  121 A, and a power supply  122  such that each of the metal segments  100 A,  100 B,  100 C,  100 D, and  100 E can be connected to or disconnected from the power supply  122 , which is a bipolar RF power source. All metal segments of other electrodes in the first array are wired to the power supply  122  in a similar way. 
   The needle electrodes  100  through  104  form an array of electrodes. A second array of the needle electrodes  105  through  109  is formed like the first array. The metal segments of the needle electrode  105  in the second array is wired through a terminal wire bundle  105 K, branch wire bundle  120 B, and power cable  121 B to the power supply  122  through a switch  123 . All other segments are wired in the same way. All metal segments of the needle electrodes  105  through  109  in the second array are connected to the power supply  122  on the pole opposite to which the first array of the needle electrodes  100  through  104  are connected. The array of the needle electrodes  100  through  104  may be arranged in a straight or slightly curved line, which is substantially parallel to its neighbor array comprising the needle electrodes  110  through  114 . 
   The third and forth arrays of the needle electrodes  110  through  119  are formed in the same way except that the two arrays are connected to the power supply  122  in opposite polarity. The needle electrodes in the odd arrays are connected to one pole of the power supply  122  and the needle electrodes in the even arrays are connected to the other pole. 
   The switch  123  may be used to turn on or off the power supply  122 . The switch may be installed in any of the two power cables  121 A and  121 B (or be integrated into the RF power source) and may be controlled by the person who performs the ablation or by temperature or impedance readings feedback from the tissue to be ablated. 
   In a typical ablation operation ( FIG. 2 ), all the needle electrodes  100  through  119  are penetrated into a targeted tissue  124  such that desired ablation volume  125  (e.g. the tissue to be ablated) is surrounded by the needle electrodes  100  through  119 . In this illustration, the fifth metal segment  100 E at the distal end of the needle electrode  100  is not connected to the power supply  122  since that segment is outside the boundary of the ablation volume  125 . For the purpose of illustration, the needle electrode  119  is not connected to the power supply  122  since it is outside the boundary of the ablation volume  125 . 
   The second array is placed in parallel to the first array with a small distance apart, preferably a few millimeters to a couple of centimeters apart. The distance between two neighbor arrays of the needle electrodes is preferably to be small enough (a few millimeters to a couple of centimeters) to enable this array of the needle electrodes to be a virtual plate electrode. In other words, when electrical power is applied to all the needle electrodes, the electrical potential of the tissues at the middle point between two adjacent needle electrodes of the same array is substantially close to the electrical potential on the surface of those two needle electrodes. Preferably, the distance between the two arrays is close to and somewhat longer than the distance of the two adjacent needles electrodes in the same array to achieve the effect of virtual plate electrodes. 
     FIG. 3  illustrates schematically a needle electrode bundle  300  comprising four needle electrodes  301 ,  302 ,  303 , and  304  assembled together through a non-conductive fixture  305 . Each of the wire bundles  306 ,  307 ,  308 , and  309  is assigned to each of the needle electrodes  301 ,  302 ,  303 , and  304 , respectively; and each of the wire bundles contains a group of individual wires, each being connected to one segment of each of the needle electrodes  301 ,  302 ,  303 , and  304 . A bundled array of the needle electrodes might offer convenience of application, improve the accuracy of ablation, and reduce the time needed to place needles into targeted tissues for certain applications. The needle tip of any needle electrode can be of a shape other than a sharp tip. It can be a blunt tip. By way of example, the tips of the needle electrodes  301  and  302  can join together to form a U-shaped electrode, and the tips of the needle electrodes  303  and  304  can join together to form another U-shaped electrodes. However, they still belong to the same electrode array. This type of configuration may be useful in special cases where tubular tissue structure is to be ablated. 
     FIG. 4  shows three examples of curved needle electrodes  400 A,  400 B, and  400 C. The needle electrode  400 A is shaped substantially as a bent line. The needle electrode  400 B is curved substantially as a segment of a circle. The needle electrode  400 C is shaped substantially as “S” curve. Other shapes are also possible according to specific applications. Those shaped needle electrodes are useful for ablating tissues at certain anatomic locations to avoid bones, major nerves and large vessels. 
     FIG. 5  illustrates an example of the present invention using curved needle electrodes  500 ,  501 ,  502 , and  503  for ablation of a tubular structure (generally shown by  505  of  FIG. 5 ). In this case, the tubular structure is a prostate gland  504 . The first array of the curved needle electrodes  500  and  501  is placed in the inner tube of the prostate gland  504  in a circular pattern. The second array of the curved needle electrodes  502  and  503  is placed in the outer tube of the prostate gland  504  in a circular pattern. The prostate gland  504  is between the first and second array of the electrodes. The two arrays of the curved needle electrodes are connected to a power supply with opposite polarities (not shown in  FIG. 5 ) with only those segments of electrodes in contact with the prostate gland  504  to be activated. After a delivery of the desired amount of the RF energy, the prostate tissue is ablated. All other surrounding tissues, such as the bladder  506  and the penile  507 , would be preserved since most of the RF energy is provided to the tissue between the two arrays of the curved needle electrodes. 
   In those exemplary embodiments of the present invention, specific components, materials, arrangements, and processes are used to describe the invention. Obvious changes, modifications, and substitutions may be made by those skilled in the art to achieve the same purpose of the invention. The exemplary embodiments are, of course, merely examples and are not intended to limit the scope of the invention. It is intended that the present invention include all other embodiments that are within the scope of the appended claims and their equivalents.