Abstract:
A radiation detector disposed on a microwave antenna assembly to receive unintended field exposure in an insufflated abdomen. The radiation detector includes a receiving antenna made up of at least two pieces of metal externally attached to the microwave antenna within the abdomen. The radiation detector is adapted to receive errant microwave energy that resonates in the abdomen. A rectifier is coupled between the two pieces of metal, where the pieces of metal are strips, rings, patches, or other geometric combinations. The rectifier is adapted to rectify at least a portion of the errant microwave energy. A filter is coupled to the rectifier and is adapted to convert the rectified microwave energy into a detection signal. An inflatable stop is located on a distal end of the microwave antenna and the inflatable stop is inflated when inserted within the abdomen. The inflated stop prevents inadvertent removal of the microwave antenna.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of a U.S. application Ser. No. 12/487,917 entitled “Microwave Ablation Antenna Radiation Detector” filed on Jun. 19, 2009, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to microwave antennas. More particularly, the present disclosure is directed to radiation detectors for microwave ablation antennas. 
     2. Background of Related Art 
     Treatment of certain diseases requires destruction of malignant tissue growths (e.g., tumors). It is known that tumor cells denature at elevated temperatures that are slightly lower than temperatures injurious to surrounding healthy cells. Therefore, known treatment methods, such as hyperthermia therapy, heat tumor cells to temperatures above 41° C., while maintaining adjacent healthy cells at lower temperatures to avoid irreversible cell damage. Such methods involve applying electromagnetic radiation to heat tissue and include ablation and coagulation of tissue. In particular, microwave energy is used to coagulate and/or ablate tissue to denature or kill the cancerous cells. 
     Microwave energy is applied via microwave ablation antennas that penetrate tissue to reach tumors. There are several types of microwave antennas, such as monopole and dipole, in which microwave energy radiates perpendicularly from the axis of the conductor. A monopole antenna includes a single, elongated microwave conductor whereas a dipole antenna includes two conductors. In a dipole antenna, the conductors may be in a coaxial configuration including an inner conductor and an outer conductor separated by a dielectric portion. More specifically, dipole microwave antennas may have a long, thin inner conductor that extends along a longitudinal axis of the antenna and is surrounded by an outer conductor. In certain variations, a portion or portions of the outer conductor may be selectively removed to provide more effective outward radiation of energy. This type of microwave antenna construction is typically referred to as a “leaky waveguide” or “leaky coaxial” antenna. 
     During microwave ablation, unintended field exposure to healthy tissue may occur due to incorrect device use. For example, damage to healthy tissue may occur if a surgeon inserts the probe to an insufficient depth while performing an ablation, the probe slipping out due to surgeon error or fatigue, or activation of the probe prior to placing the probe in tissue. Also, the repercussions of the unintended field exposure may increase during laparoscopic procedures due to high field intensities as a result of an insufflated abdomen acting as a resonant microwave cavity. Burns to the abdominal wall along device/probe insertion tracks have occurred due to these factors. 
     SUMMARY 
     A radiation detector disposed on a microwave antenna assembly to receive unintended field exposure in an insufflated abdomen. The radiation detector includes a receiving antenna made up of at least two pieces of metal externally attached to the microwave antenna on the distal end so as to be within the abdomen. The radiation detector is adapted to receive errant microwave energy that resonates in the abdomen. A rectifier is coupled between the two pieces of metal, where the pieces of metal are strips, rings, patches, or other geometric combinations. The rectifier is adapted to rectify at least a portion of the errant microwave energy. A filter is coupled to the rectifier and is adapted to convert the rectified microwave energy into a detection signal. An inflatable stop is located on a distal end of the microwave antenna and the stop is inflated when inserted within the abdomen. The inflated stop prevents inadvertent removal of the microwave antenna. 
     According to one aspect of the disclosure, a radiation detector disposed on a microwave antenna assembly is disclosed. The radiation detector includes a receiving antenna adapted to receive microwave energy. The receiving antenna is formed from two pieces of metal externally attached to a microwave antenna of the microwave antenna assembly. The radiation detector further includes at least one rectifier coupled between the pieces of metal adapted to rectify at least a portion of the microwave energy and a filter coupled to the at least one rectifier and adapted to convert the rectified microwave energy into a detection signal. 
     According to another aspect of the present disclosure, a microwave antenna assembly is disclosed. The microwave antenna assembly includes a hub adapted to couple the microwave antenna assembly to a microwave generator and a radiating section coupled to the hub through a feedline. The microwave antenna assembly further includes an inflatable stop surrounding the feedline. The inflatable stop is inflated when the feedline is placed within an abdomen of a patient to prevent the radiating section from inadvertently withdrawing from the abdomen. Additionally, the microwave antenna assembly includes a radiation detector disposed on the microwave antenna assembly near the radiating section. The radiation detector includes a receiving antenna adapted to receive microwave energy. The receiving antenna is formed from two pieces of metal externally attached to the feedline within the abdomen. The receiving antenna further includes at least one rectifier coupled between the pieces of metal adapted to rectify at least a portion of the microwave energy that resonates in the abdomen. Additionally, the receiving antenna includes a filter coupled to the at least one rectifier and adapted to convert the rectified microwave energy into a detection signal. 
     A method for detecting errant microwave energy is also contemplated by the present disclosure. The method includes the steps of receiving resonant microwave energy from an insulfated abdomen with a receiving antenna and rectifying at least a portion of the microwave energy through at least one rectifier coupled to the receiving antenna. Further the method includes the step of filtering the rectified microwave energy through a filter coupled to the at least one rectifier to convert the rectified microwave energy into a detection signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of a microwave ablation system according to an embodiment of the present disclosure; 
         FIGS. 2A-2C  are schematic diagrams of a microwave detector according to different embodiments of the present disclosure; 
         FIG. 3  is a schematic diagram of a linear antenna for use in detecting microwaves according to an embodiment of the present disclosure; and 
         FIG. 4  is a flow chart of a method according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Particular embodiments of the present disclosure as described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. 
     The present disclosure provides for a radiation detector disposed on a microwave antenna. Generally, the detector is disposed in a location such that any unintended and/or errant radiation of microwave energy within the abdomen is detected. The radiation detector converts the detected radiation into a detection signal, which is then transmitted to a control system (e.g., microwave generator) to either shut off the power supply and/or alert the user. 
       FIG. 1  shows a microwave ablation system  10  that includes a microwave antenna assembly  12  coupled to a microwave generator  14  via a flexible coaxial cable  16 . The generator  14  is configured to provide microwave energy at an operational frequency from about 500 MHz to about 10,000 MHz. In the illustrated embodiment, the antenna assembly  12  includes a radiating section  18  connected by feedline  20  (or shaft) to the cable  16 . More specifically, the feedline  20  is connected to a hub  22 , which is connected to the cable  16  through a cable connector  19 . The hub  22  may have a variety of suitable shapes, e.g., cylindrical, rectangular, etc. Further, the antenna assembly  12  includes a radiating section  18  with a tip  48  on the distal end of the feedline  20 . 
     The feedline  20  may be coaxial and include an inner conductor surrounded by an inner insulator, which is, in turn, surrounded by an outer conductor  17  (e.g., a cylindrical conducting sheath). The inner conductor and outer conductor  17  may be constructed of copper, gold, stainless steel or other conductive metals with similar conductivity values. The metals may be plated with other materials, e.g., other conductive materials, to improve their properties, e.g., to improve conductivity or decrease energy loss, etc. In one embodiment, the feedline  20  may be formed from a coaxial, semi-rigid or flexible cable having a wire with a 0.047″ outer diameter rated for 50 Ohms. 
     The antenna assembly  12  includes a radiation detector  50  disposed along the feedline  20  just on the inside of the abdominal wall  70 . Further, the radiation detector  50  may be located near an inflatable stop  30 . The radiation detector  50  is shown in detail in  FIGS. 2A-2C . The radiation detector  50  is connected through a filter (See  FIG. 2A ) to wire  71 . The wire  71  may be disposed anywhere along the antenna assembly  12  such that the wire  71  has minimal effect on the radiation efficiency of the antenna assembly  12 . The wire  71  may be connected to a light emitting diode (LED)  60 , a speaker  65 , and/or a controller (not shown) within the generator  14 . 
     The inflatable stop  30  is a balloon or other inflatable material that surrounds the feedline  20 . The stop  30  may be formed from materials having suitable mechanical properties (such as puncture resistance, pin hole resistance, tensile strength, conformability when inflated), chemical properties (such as forming a suitable bond to the feedline  20 ), and biocompatibility. In another embodiment, the walls of the inflatable stop  30  may be formed from a suitable polyvinyl chloride (PVC). Other suitable materials include polypropylene, polyethylene teraphthalate (PETP), low-density polyethylene (LDPE), silicone, neoprene, polyisoprene, or polyurethane (PU). 
     The inflatable stop  30  is located on the distal end of the feedline  20  so as to be inside the abdomen wall  70  or body cavity wall. The location of the inflatable stop  30  may be adjusted based on the size of the abdomen and/or the depth necessary to perform the surgery. 
     Prior to inserting the radiating section  18  and feedline  20  within the patient&#39;s abdomen or body cavity, the inflatable stop  30  is in a collapsed form. After inserting the radiating section  18  and feedline  20  within the patient&#39;s abdomen, the inflatable stop  30  is inflated using a conduit or catheter (not shown). The inflatable stop  30  may be filled with gaseous or fluid inflation media, e.g., air, water, saline etc., in a selective manner such that inflation media may be introduced and/or withdrawn from inflatable stop  30  as desired. Once inflated, the inflatable stop  30  prevents inadvertent removal of the radiating section  18 . Inadvertent removal may cause ablation to the wrong tissue. The inflatable stop  30  is then deflated upon completion of the procedure to allow removal of the radiating section  18  and feedline  20 . 
       FIG. 2A  shows a first embodiment of a radiation detector  50 . The radiation detector  50  includes two metal rings  52   a - 52   b  that wrap around the feed line  20 . The metal rings  52   a - 52   b  are connected together using a rectifying device  54  across gap  51 . The rectifying device  54  may be any type of suitable diodes such as Zener diode, Schottky diode, tunnel diode and the like. One metal ring  52   a  is connected LED  60  and ground circuit (R 2  and C 2  in parallel and G) through inductor L 1 . Alternatively, both metal rings  52   a - 52   b  may be connected to a ground circuit that includes a RF impendence/low DC impedance element L and a ground G. The DC ground connections are made in locations of low RF voltage. The inductor L 1  functions as a low pass filter and converts the signal from the rectifying device  54  into a DC signal which is sent across wire  71  to a LED  60 , speaker  65 , and/or a controller within the generator  14 . 
     The radiation detector  50  may be located anywhere along the feedline  20  and or radiating section  18  as long as the radiation detector  50  is within the patient&#39;s abdomen or body cavity. The radiation detector  50  is typically located along the feedline  20  so as to have gap  51  be in a location of high RF voltage. 
     The metal rings  52   a - 52   b  may be formed from a conformal sheet of conductive material such as copper, gold, stainless steel or other conductive metals with similar conductivity values. The width of each ring may be about 0.10 inches to about 2.5 inches with a thickness between about 0.001 inches to about 0.010 inches. The metal rings  52   a - 52   b  may be situated over a ground plane with a dielectric insulation providing separation. The dielectric insulation R 2  may be formed from a non-conductive conformal material such as polyesters, polyimides, polyamides, polyamide-imides, polyetherimides, polyacrylates, polyethylene terephthalate, polyethylene, polypropylene, polyvinylidene chloride, polysiloxanes, combinations thereof and the like. 
     The use of one rectifying device  54  in  FIG. 2A  allows for half wave rectifying.  FIG. 2B  shows an alternate embodiment of radiation detector  50  that includes two rectifying devices  54  and  56 . The rectifying devices  54  and  56  are soldered to metal pieces  52   a - 52   b  in reverse polarity. The rectifying devices  54  and  56  together allow for full wave rectifying. 
       FIG. 2C  shows another embodiment of radiation detector  55  that includes three rings  52   a - 52   c . The three rings are connected together with rectifying devices  54  and  57  in the same polarity. The use of three rings allows for a larger antenna aperture and increased bandwidth for detecting rectified microwave energy. Alternatively, the rings  52   a - 52   c  may be connected together with the rectifying devices  54  and  57  in reverse polarity. Additionally, two of the rectifying devices (e.g.  54  and  56 ) may be connected in reverse polarity in each gap  51  and  53 , similar to the arrangement shown in  FIG. 2B . 
       FIG. 3  discloses an alternative radiation detector  90  formed into a linear antenna from two strips of metal  92   a - 92   b . Depending on the operating frequency of the microwave ablation assembly  12 , the two strips  92   a - 92   b  may have a length and width that range between about 0.1 inches and about 2 inches with a thickness of about 0.005 inches. The strips of metal  92   a - 92   b  may be connected together with rectifying device  54 . Alternatively, the strips of metal  92   a - 92   b  may be connected together with two rectifying devices (e.g.  54  and  56 ) in reverse polarity to allow for full wave rectification, similar to the arrangement shown in  FIG. 2B . The rectifying device  54  is connected to a filter (inductor L 1 ) to convert the signal into a DC signal. The DC signal is sent over wire  71  to a LED  60 , speaker  65 , and/or a controller in the generator  14 . If the DC signal is above a set limit, then the user is notified visually through LED  50 , and/or audibly through speaker  65 . Alternatively, if the DC signal is above a set limit, then controller may automatically stop sending an electrical signal to the antenna assembly. This limit may vary between about 0.5 volts and about 3 volts based on the operating frequency of the microwave ablation assembly  12 . The linear antenna radiation detector  90  may also be used as a patch rectifier or a dipole rectifier. 
     The strips of metal  92   a - 92   b  may be attached to a grounding plane (not shown) with an insulating dielectric between. The strips of metal  92   a - 92   b  and grounding plane may be made of conductive material such as copper, gold, stainless steel or other conductive metals with similar conductivity values. The insulating dielectric may be a non-conductive conformal material such as polyesters, polyimides, polyamides, polyamide-imides, polyetherimides, polyacrylates, polyethylene terephthalate, polyethylene, polypropylene, polyvinylidene chloride, polysiloxanes, combinations thereof and the like. 
       FIG. 4  shows a process  400  for detecting errant microwave energy within an insufflated abdomen with reference to radiation detector  50 . It should be appreciated that the method may be practiced with other radiation detectors, such as the radiation detector  90 ,  55  and the like. The process  400  starts at step  405  with an initial step of attaching the radiating detector  50  on the microwave antenna assembly  12  at step  410  which includes wrapping the metal pieces  52   a - 52   b  around feedline  20 . The method may also include the step of connecting the radiation detector  50  to the generator  14  or another control system. Next, the microwave antenna  12  with radiation detector  50  is placed within a patient&#39;s abdomen or body cavity at step  420 . Alternatively, the detector  50  may be placed into the insufflated abdomen via a lap port (not shown) and slid over the radiating section  18  and around feedline  20  after insertion of radiating section  18  and feed line  20  through the abdominal wall to reduce gauge size of the device. Detector  50  interfaces with one or more electrode contacts (not shown) on feedline  20 . At step  430 , the microwave antenna  12  is secured in place within the abdomen. For example, the inflatable stop  30  may be inflated at step  430 . Other types of securement materials may also be contemplated. A controller (not shown) in generator  14  may prevent sending electrical energy to the microwave antenna  12  until the microwave antenna  12  is secured, e.g., until the inflatable stop  30  is inflated. Next, at step  440 , microwave energy is sent from the generator  14  to microwave antenna  12 . 
     During operation, any errant microwave radiation outside the desired emission area, such as outside the radiating section  18 , is picked up by the radiation antenna  50 , namely, the metal rings  52   a - 52   h  at step  450 . The detected microwave energy is then rectified by rectifier  54  at step  460  and the rectified signal is filtered by a filter into a detection signal (e.g., a DC voltage signal  71 ) at step  470 . The filter may include a simple inductor L 1 , or inductor resistor series elements (not shown). The detection signal is then transmitted to generator  14 , LED  60 , and/or speaker  65  at step  480 . The generator  14  and/or other control circuitry (not shown) compares the detection signal to a threshold value to determine whether the level of the microwave energy is unsafe. If the determination is made that the level of microwave energy is excessive, the generator  14  may either suspend the supply of microwave energy and/or notify the user of this occurrence at step  490  prior to process  400  ending at step  495 . The user may be notified using speaker  65  and/or LED  60 . 
     The described embodiments of the present disclosure are intended to be illustrative rather than restrictive, and are not intended to represent every embodiment of the present disclosure. Various modifications and variations can be made without departing from the spirit or scope of the disclosure as set forth in the following claims both literally and in equivalents recognized in law.