Abstract:
Apparatus and methods for treating body tissue by heat energy. The apparatus includes: a coil for transmitting an alternating electrical current therethrough to generate an alternating electromagnetic field that is capable of exciting material positioned in the body, the material being operative to inductively generate the heat energy in response to the electromagnetic field; means for measuring an amplitude of the current; and means for mapping the amplitude into a temperature of the magnetic material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11/801,453, entitled “Systems and Methods for Treating Body Tissue” by Tom et al., filed on May 9, 2007, and incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure generally relates to medical methods and apparatus, more particularly, to treating various types of body tissue by RF inductive heating. 
         [0003]    Human and/or animal can suffer from various types of tissue-related illnesses, such as breast cancer and tumors. One of the approaches to treat the illness is thermotherapy. Thermotherapy, such as hyperthermia treatment, in which miniscule particles including ferromagnetic material are injected into the target tissue and then the malignant cells are destroyed by subsequent overheating by external alternating magnetic fields, enables a targeted overheating of only the region of the target tissue. The particles may be coated with a molecular layer of enzyme that has an affinity to the malignant cells. 
         [0004]    In the hyperthermia treatment, diseased tissue may be treated by elevating the temperature of its individual cells to a lethal level. For instance, temperatures in a range about 40° C. to about 45° C. can cause irreversible damage to diseased cells, while healthy cells may survive exposure to temperature up to around 46.5° C. As such, a precise control of the temperature is needed for safe and effective hyperthermia treatments. 
         [0005]    A known technique to measure the temperature of the target tissue during treatment may be inserting a temperature probe into the tissue in advance and reading the signal from the probe during treatment, as disclosed in U.S. Patent Application Publication No. 2005/0159780 A1. This technique has difficulties in treating certain types of tissue. For instance, brain tumor may require drilling a hole in the skull to push the probe into the tissue. For another instance, the invasive breast cancer cells break free of where they originate, invading the surrounding tissues that support the ducts and lobules of the breast. In this case, a temperature probe may be used to monitor the temperature of a limited area at the best. Depending on the size and distribution of the diseased lobules, a treatment may require multiple insertions of a probe into different locations of the breast, which may be time consuming and unpleasant to the patient. 
         [0006]    Another difficulty in hyperthermia treatments may be locating the injected particles such that the external magnetic field is effectively coupled to the particles during operation. A known technique to locate the injected particles may be the real-time fluoroscopy using X-ray that can damage healthy cells if overexposed inadvertently. Even if the location of injected particles is known, existing systems may be able to position the external magnetic fields relative to the particles. As such, there is a strong need for systems and methods to precisely position the external magnetic field relative to the injected particles and monitor the temperature of the particles during treatment. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    In one embodiment, an apparatus for treating tissue of a body by heat energy includes: a coil for transmitting an alternating electrical current therethrough to generate an alternating electromagnetic field that is capable of exciting material positioned in the body, the material being operative to inductively generate the heat energy in response to the electromagnetic field; means for measuring a quantity associated with the current; and means for mapping the amplitude into a temperature of the magnetic material. 
         [0008]    In another embodiment, a method for treating tissue of a body by heat energy includes steps of: disposing material into the body, the material being operative to inductively generate the heat energy in response to an electromagnetic field external to the body; transmitting an alternating current through a coil to generate the electromagnetic field thereby causing the material to generate the heat energy; measuring a quantity associated with the current; mapping the measured quantity into a temperature of the material; and displaying the temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG.1  shows a schematic diagram of a system for treating target tissue in accordance with one embodiment of the present invention; 
           [0010]      FIG. 2  shows a schematic perspective view of a paddle in  FIG. 1 ; 
           [0011]      FIG. 3  shows a schematic side view of the paddle in  FIG. 2 ; 
           [0012]      FIG. 4  shows a schematic front view of a coil unit included in the paddle in  FIG. 2 ; 
           [0013]      FIG. 5  shows a schematic cross sectional diagram of the coil unit in  FIG. 4 , taken along the line V-V; 
           [0014]      FIG. 6  shows a schematic perspective view of a paddle in accordance with another embodiment of the present invention; and 
           [0015]      FIG. 7  shows a schematic side view of the paddle in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention because the scope of the invention is best defined by the appended claims. 
         [0017]    Referring now to  FIG. 1 ,  FIG.1  shows a schematic diagram of a system  100  for treating target tissue in accordance with one embodiment of the present invention. For the purpose of illustration, a breast cancer is shown as exemplary target tissue  111 . However, it should be apparent to those of ordinary skill that the system  100  can be used to treat other suitable diseased and/or malignant tissue as well as blood vessels, such as varicose veins to be destroyed. As depicted, system includes a controller  102 , a paddle  110 , and an umbilical cord  104  for connecting the paddle  110  to the controller  102 . In an exemplary embodiment, the umbilical cord  104  may be connected to the controller  102  via a detachable connector  106  that permits various types of the paddle to be detachably connected to the controller  102 . 
         [0018]    As will be detailed, the electromagnetic field generated by the paddle  110  may excite particles delivered into the patient&#39;s body. In some applications, the electromagnetic flux generated by the paddle  110  may not penetrate deep into the patient&#39;s body to reach the target tissue. In another exemplary embodiment, multiple paddles may be coupled to the controller  102  via multiple umbilical cords  104 . For instance, two paddles arranged in opposite with respect to the patient&#39;s body may be activated simultaneously, forming a Helmholtz configuration to cause the electromagnetic flux generated by the coil to penetrate deep into the body. In yet another exemplary embodiment, the controller  102  may be used to operate a coil dimensioned to surround a portion of the patient&#39;s body so that the electromagnetic flux generated by the coil may penetrate deep into the body. 
         [0019]    The controller  102  includes indicators  105 ,  107 , a display panel  108 , on/off switch  109 , or the like. The indicators  105  may be LED light indicators and indicate the operational status, such as power on, fault conditions, activation of magnetic filed, or the like. The indicators  107 , preferably LED light indicators, may indicate operational status, such as cooling fluid in/out, power to the paddle, or the like. The display  108  may display various quantities, such as the temperature of the particles during treatment, time lapsed in each treatment cycle, or the like. It is noted that the number and size of indicators, switch, and display panel on the controller  102  may be varied without deviating from the scope and spirit of the present teachings. 
         [0020]    The controller  102  includes a microprocessor based subsystem that converts main (AC) power to a high frequency alternating current source. The alternating current, which is preferably in the radio frequency (RF) range, is applied to the paddle  110 , more specifically, electrical coil, to generate alternating electromagnetic field. As will be detained in conjunction with  FIGS. 4-5 , the coil may be made from a conducting tube through which cooling fluid passes. The controller  102  may include a pump for circulating the cooling fluid through the coil and a heat exchanger for dissipating the heat energy from the cooling fluid. Some of the indicators  107  may be used to indicate the flow through the coil. The controller  102  may include an automatic feedback control subsystem to monitor the cooling fluid temperature and regulate the flow rate to regulate the fluid temperature. 
         [0021]    The controller  102  may include a user programmable timer that allows a user to set time interval for treatment such that the system  100  will de-energize the coil after a predetermined amount of elapsed time. The controller  102  may also include a control button that allows a user to set the time interval manually. 
         [0022]    The controller  102  may also control the amount of energy (in the form of heat) delivered to the target tissue  111 . In one exemplary embodiment, the controller  102  may measure the amount of time the target tissue  111  is at the target temperature. By use of a closed loop control subsystem included in the controller  102 , the heat loss due to conduction via blood vessels during treatment can be taken into account in determining the amount of time. The liver, for example, is highly vascular and would present a large thermal heat sink. Operating in a purely timed mode may result in under treatment of such target tissue. 
         [0023]      FIGS. 2 and 3  show schematic perspective and side views of the paddle  110  in  FIG. 1 . As illustrated, the paddle  110  includes a handle  112  and a coil unit  120  secured to the handle  112 . The handle  112  may include a control switch  116  to activate a coil in the coil unit  120  and two indicators  114   a ,  114   b , which are preferably LED light indicators and operative to indicate the operational status of the system  100 , such as the controller power and activation of coil in the paddle  110 . The handle  112  is preferably, but not limited to, formed of hollow plastic defining a cavity or empty space  121  and configured to provide enhanced grip and ergonomic comfort for the user. One end of the umbilical cord  104  is connected to the handle  112  such that several electrical wires (not shown in  FIG. 2 ) in the umbilical cord  104  can extend into the cavity  121 . The electrical wires are connected to the indicators  114   a ,  114   b  and controller  102 . In one exemplary embodiment, to activate the coil in the coil unit  120 , the user may operate the switch  116  coupled to the controller  102  via a pair of electrical wires extending through the cavity  121  to the controller  102 . In another exemplary embodiment, a foot operated switch (not shown in  FIG. 2 ) may be coupled to the controller  102  so that the user can remotely operate the coil unit  120  by operating the switch. In yet another exemplary embodiment, other types of switches, such as pneumatic or optical switch, may be used to operate the coil unit  120 . 
         [0024]    A pair of tubes for providing cooling fluid to the coil unit  120  also extend from the controller  102  through the umbilical cord  104  and cavity  121 . It is noted that the handle  112  may include other indicators and display panels. For instance, the temperature of the particles measured by the system  100  can be displayed on one display panel. For another instance, the time elapsed in each treatment cycle can be displayed on another display panel. For yet another instance, an LED indicator for flow in the coil unit  120  may be mounted on the handle  112 . 
         [0025]    The coil unit  120  generates alternating electromagnetic field that excites particles delivered into the target tissue  111 . Systems and methods for delivering the particles into various target tissues are disclose in U.S. patent application Ser. No.______ , entitled “Systems and Methods for Delivering Particles Into Patient Body,” filed on Jun. 27, 2007, which is herein incorporated by reference in its entirety. 
         [0026]      FIG. 4  shows a schematic front view of the coil unit  120  seen along the direction  124  ( FIG. 3 ).  FIG. 5  shows a schematic cross sectional diagram of the coil unit  120 , taken along the line V-V ( FIG. 4 ). As depicted, the coil unit  120  has a generally cylindrical shape and includes: an outer housing  130  formed of electrically insulating material; a flux concentrator  132  secured to the inner surface of the housing and having a generally cylindrical shape with a U-shaped channel formed in the front surface portion thereof; and inductor coil  136  disposed in the channel and secured to the flux concentrator by electrically insulating adhesive or glue  134  so that the coil  136  is electrically insulated from the flux concentrator  132 . 
         [0027]    The outer housing  130  is securely connected to the handle  112 . In one exemplary embodiment, the housing  130  and handle  112  are formed in one integral body. The flux concentrator  132  may be formed of material with a high permeability, wherein the material may include semi-conducting or non-conducting material, such as ferrite. The material may also include conducting material, such as nickel alloy. The flux concentrator  132  may block the electromagnetic flux propagating rearward, perhaps toward the user, and redirect the blocked magnetic flux toward the front surface  122  of the coil unit  120 . 
         [0028]    The ideal flux concentrator would not heat up if it were 100% efficient. However, the flux concentrator  132  may get warm as it is somewhat lossy, i.e., a portion of the flux is converted into heat energy by the concentrator. To minimize heat build up in the flux concentrator  132 , a thermally conductive (but not electrically conductive) glue  134 , such as heat epoxy, can be use to transport the heat from the concentrator  132  to the liquid cooled coil  136 . 
         [0029]    The coil  136  is formed of a metal tube, such as copper, and coupled to a power source  150  that may be included in the controller  102  via a pair of electrical wires  142   a ,  142   b . The power source  150 , which is preferably an RF power source, may be activated by the switch  116  on the handle  112  and/or a switch on the controller  102 . Two end portions  144  of the coil  136  extend through the flux concentrator  132  to couplers  146 . Each coupler  146  couples one end of the coil to a flexible tube  145  connected to the controller  102  for cooling fluid communication. The flexible tube  145 , positioned in the umbilical cord  104 , may be formed of, but not limited to, polymer and operative to carry cooling fluid from the controller  102  to the coil  136 . 
         [0030]    Typically, the alternating current applied to the coil  136  propagates along the surface of the coil, more specifically, within a skin depth from the surface. Thus, to increase the intensity of electromagnetic flux emitted by the coil unit  102 , the surface area or turn density (number of turn/coil diameter) of the coil  136  needs to be increased. The coil  136  has a generally flattened tubular shape that permits a larger number of coil turns for a given channel in the flux concentrator  132 , increasing the surface area of the coil  136  thereby to enhance the flux intensity. In one exemplary embodiment, the coil  136  may be formed of copper tube and the surface of the coil  136  may be plated with a highly conductive material, such as silver, to enhance flux intensity. As the coil  136  may be operated at high frequencies, most of the electrical current may flow along the surface of the copper coil, i.e., the current may flow through the highly conductive material. 
         [0031]    The coil unit  120  may include a capacitor  138  forming an LC tank circuit with the coil  136 . In one exemplary embodiment, the capacitor  138  may be located in the handle  112  in close proximity to the coil  136 . A matching network  140 , which may be located in either coil unit  120  or controller  102 , can be coupled to the electrical wires  142   a ,  142   b  to match the output impedance of the controller  102  to that of the coil  136 . 
         [0032]    The paddle  110  is designed to activate particles that are within a preset distance, for instance 0 to 2 centimeters, from the front surface  122  of the paddle  110 . Generally speaking, the particles are better coupled with the external electromagnetic field when located inside the projection area of the front surface  122  of the flux concentrator  132 . Each paddle  110  may be assigned a unique ID associated with information of operational characteristics, such as the preset distance, duty cycle, and resonant frequency, as well as effective projection area. The information may also include the expected target mass, i.e., the expected amount of particle mass to be heated by the paddle  110 . 
         [0033]    The particles delivered to the target tissue  111  may be formed of material that can generate heat energy in response to the electromagnetic field generated by the coil  120 . The material includes, but is not limited to, metal, plastic, polymer, ceramic, or alloys thereof. Typically, the permeability of material for the particles decreases as its temperature increases up to Curie temperature at which the material becomes paramagnetic. During operation, the coil  136  can be electromagnetically coupled with the particles, causing the resonant frequency of the LC tank circuit (coil  136  and capacitor  138 ) to shift from the unloaded frequency. Hereinafter, the term unloaded (or, equivalently, reference) refers to a state where the coil is located remotely from the particles. As the temperature of the particles changes, this shift may also change and, as a consequence, the amplitude of the current or voltage in the coil  136  may also change. Hereinafter, the term amplitude refers to peak-to-peak or RMS value of the alternating current or voltage. In one exemplary embodiment, the controller  102  may include a closed-loop control subsystem for tuning the operational frequency of the power source  150  to the resonant frequency of the LC tank circuit thereby to optimize the operational efficiency of the coil  136 . 
         [0034]    As the amplitude of the current in the coil  136  changes, the intensity of the electromagnetic field may also change. In one exemplary embodiment, the closed-loop control subsystem may continuously monitor the amplitude of the current and/or voltage in the coil  136  and vary one or more operating parameters, such as the voltage, frequency, and duty cycle of the power source  150 , etc., to maintain optimum operation of the coil  136 . In another embodiment, the change in amplitude of the current or voltage in the coil  136  can be monitored and mapped into the change in the particle temperature, i.e., the measured amplitude or voltage of the current can be mapped into the particle temperature. For given dose of particle delivered to the target tissue, the relationship between the current or voltage in the coil  136  and the particle temperature can be obtained. Then, based on the relationship, the measured amplitude or voltage of the current in the coil  136  can be used to read the temperature of the particles. The particle temperature may be displayed on a display window mounted on the controller  102  and/or handle  112 . 
         [0035]    In one exemplary embodiment, the current in the coil  136  can be measured by a current sensing transformer in line with the circuit feeding current into the coil  136 . In another exemplary embodiment, the current in the coil  136  can be measured by a coil or loop disposed in close proximity to the coil  136  that can pick up the alternating magnetic field generated by the coil  136 . The controller  102  may include a suitable circuit and a microprocessor that may map the measured current into the particle temperature. 
         [0036]    Each paddle  110  (or coil) may have a unique ID that allows the controller  102  to set the optimum frequency and duty cycle for operation of the coil  136 . To aid the user in positioning the paddle relative to the patient body so as to place the particles within the optimum working range of the alternating electromagnetic field generated by the paddle  110 , the controller  102  may be switched to a “guidance” mode. In the guidance mode, the controller  102  may activate the paddle  110  at the unloaded resonant frequency associated with the unique ID. Then, as the user moves the paddle  110  around the patient body, the controller  102  may send an audio and/or visual signal indicating the shift or deviation of the amplitude of the current or voltage in the coil  136  from a reference value, such as the amplitude at unloaded state. Typically, the greater the deviation is, the closer the paddle is located to the particles. In one embodiment, the controller  102  (or the handle  112 ) may increase the beeping sound frequency as the shift increases, aiding the user in finding the optimum location of the paddle  110  relative to the particles. In another embodiment, the controller  102  (or the handle  112 ) may increase the light intensity of an LED as the shift increases. 
         [0037]    It is noted that the measured deviation in the guidance mode can be used as a safety feature. If the paddle  110  is inadvertently placed on a large ferromagnetic mass, such as an examination table, the controller  102  may sense the larger than expected mass and will not activate the system  100 . 
         [0038]      FIGS. 6 and 7  show schematic perspective and side views of a paddle in accordance with another embodiment of the present invention. As depicted, the paddle  200  includes a handle  204  and a coil unit  202  secured to the handle. The handle includes a control switch  208  to activate a coil in the coil unit  202  and two indicators  206   a ,  206 , which are preferably LED light indicators. The handle  204  is connected to an umbilical cord  212  and have similar structure as the handle  112  in  FIGS. 2-5 . As the paddle may have similar structural and operational mechanisms as the paddle  110  ( FIG. 2-3 ), detailed description of the paddle  200  is not repeated for brevity. 
         [0039]    It is noted that the system  100  can be used with other types of heat generating masses in place of the particles. For instance, various types of catheters disclosed in the parent U.S. application, Ser. No. 11/801,453, entitled “Systems and Methods for Treating Body Tissue,” and filed on May 9, 2007, can be inserted in the patient body for the similar hyperthermia treatment. Detailed description of how to operate the system  100  in conjunction with the catheters is not repeated for brevity since the interaction of the paddle  110  with the heat generating portions of the catheters disclosed in the parent application may be similar to the interaction between the paddle and particles. 
         [0040]    It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.