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WO 2015/138050 Al 17 September 2015 (17.09.2015) P O P C T

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WO 2015/138050 Al 17 September 2015 (17.09.2015) P O P C T (12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (19) World Intellectual Property Organization International Bureau (10) International Publication Number (43) International Publication Date WO 2015/138050 Al 17 September 2015 (17.09.2015) P O P C T (51) International Patent Classification: (81) Designated States (unless otherwise indicated, for every A61B 18/18 (2006.01) G01R 29/10 (2006.01) kind of national protection available): AE, AG, AL, AM, AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY, (21) International Application Number: BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM, PCT/US2015/012615 DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, (22) International Filing Date: HN, HR, HU, ID, IL, IN, IR, IS, JP, KE, KG, KN, KP, KR, 23 January 20 15 (23.01 .2015) KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM, (25) Filing Language: English PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW, SA, SC, (26) Publication Language: English SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW. (30) Priority Data: 14/202,786 10 March 2014 (10.03.2014) US (84) Designated States (unless otherwise indicated, for every kind of regional protection available): ARIPO (BW, GH, (71) Applicant: WISCONSIN ALUMNI RESEARCH GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ, FOUNDATION [US/US]; 614 Walnut Street, Madison, TZ, UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU, Wisconsin 53726 (US). TJ, TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, (72) Inventors: BEHDAD, Nader; 6442 Urich Terrace, Madis LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, on, Wisconsin 53719 (US). HAGNESS, Susan C ; 124 SM, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, Vista Rd., Madison, Wisconsin 53726 (US). LUYEN, GW, KM, ML, MR, NE, SN, TD, TG). Hung Thanh; 401 Eagle Heights, Apt. F, Madison, Wis consin 53705 (US). Published: (74) Agents: BELL, Callie M. et al; Bell & Manning, LLC, — with international search report (Art. 21(3)) 2801 W. Beltline Hwy., Ste. 210, Madison, Wisconsin 5371 3 (US). (54) Title: MICROWAVE ABLATION ANTENNA SYSTEM 100\ Coaxial cable 02 Impedance matching structure 104 Antenna 106 o 00 Fig. 1 (57) Abstract: An antenna system is provided. The antenna system includes a coaxial cable, an antenna, and an impedance matching structure. The coaxial cable includes a center conductor extending a length of the coaxial cable, a dielectric material surrounding the o center conductor along the length of the coaxial cable, and a conductive shield surrounding the dielectric material along the length of the coaxial cable. The antenna includes a conductor having an electrical length of half a wavelength at a selected operating fre - quency. The impedance matching structure includes a second center conductor mounted between an end of the center conductor of the coaxial cable and a feed end of the antenna. The impedance matching structure is configured to match an impedance of the coaxi al cable to an impedance of the antenna. MICROWAVE ABLATION ANTENNA SYSTEM CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application claims priority to U.S. Patent Application No. 14/202,786 that was filed March 10, 2014, the entire contents of which is hereby incorporated by reference. BACKGROUND [0002] Microwave ablation (MWA) is a form of thermal ablation used in interventional radiology to treat cancer. MWA uses electromagnetic waves in the microwave energy spectrum (300 megahertz to 300 gigahertz) to produce tissue- heating effects. MWA is generally used for minimally invasive treatment and/or palliation of solid tumors in patients. MWA offers several advantages over other ablation technologies such as radiofrequency (RF) and cryoablation including higher temperatures than RF, larger ablation zone volumes, shorter ablation times, and better ablation performance near arteries, which act as heat sinks. [0003] Typically, interstitial antennas used for MWA are implemented using coaxial cables. When a balanced antenna is fed by an unbalanced transmission line unwanted electric currents are excited on the outer conductors of the feeding coaxial cables. If not properly suppressed, these currents can result in undesired heating and potentially ablation of healthy tissue along the insertion path of the antenna. Balanced to unbalanced transformers (Baluns) are generally implemented to solve this problem. A balun uses a hollow circular conductor to encompass the feeding coaxial cable and, depending on the design, may or may not be electrically connected to it. SUMMARY [0004] An antenna system is provided. The antenna system includes, but is not limited to, a coaxial cable, an antenna, and an impedance matching structure. The coaxial cable includes, but is not limited to, a center conductor extending a length of the coaxial cable, a dielectric material surrounding the center conductor along the length of the coaxial cable, and a conductive shield surrounding the dielectric material along the length of the coaxial cable. The antenna includes, but is not limited to, a conductor having an electrical length of half a wavelength at a selected operating frequency. The impedance matching structure includes, but is not limited to, a second center conductor mounted between an end of the center conductor of the coaxial cable and a feed end of the antenna. The impedance matching structure is configured to match an impedance of the coaxial cable to an impedance of the antenna. [0005] A transmitter is provided that includes the antenna system, a signal generator, and a connector. The signal generator is configured to generate a signal at the selected operating frequency. The connector is configured to connect a second end of the coaxial cable opposite the end of the center conductor to the signal generator to receive the generated signal. [0006] Other principal features of the disclosed subject matter will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS [0007] Illustrative embodiments of the disclosed subject matter will hereafter be described referring to the accompanying drawings, wherein like numerals denote like elements. [0008] Fig. 1 depicts a block diagram of a microwave ablation (MWA) antenna system in accordance with an illustrative embodiment. [0009] Fig. 2 depicts a side cross sectional view of an MWA antenna system of Fig. 1 in accordance with an illustrative embodiment. [0010] Fig. 3a depicts the view of the MWA antenna system of Fig. 2 and an equivalent circuit model of the MWA antenna system of Fig. 2 in accordance with an illustrative embodiment. [001 1] Fig. 3b depicts a view of a second MWA antenna system and an equivalent circuit model of the second MWA antenna system in accordance with an illustrative embodiment. [0012] Fig. 3c depicts a view of a third MWA antenna system and an equivalent circuit model of the third MWA antenna system in accordance with an illustrative embodiment. [0013] Fig. 3d depicts a view of a fourth MWA antenna system and an equivalent circuit model of the fourth MWA antenna system in accordance with an illustrative embodiment. [0014] Fig. 4 shows a comparison between a simulated and a measured input impedance, Sn, of the MWA antenna system of Fig. 2 in accordance with an illustrative embodiment. [0015] Fig. 5 shows a simulated specific absorption rate (SAR) pattern of the MWA antenna system of Fig. 2 in liver tissue in accordance with an illustrative embodiment. [0016] Fig. 6 depicts a side cross sectional view of a second MWA antenna system of Fig. 1 in accordance with an illustrative embodiment. [0017] Fig. 7 shows a simulated input impedance, S , of the MWA antenna system of Fig. 6 in liver tissue in accordance with an illustrative embodiment. [0018] Fig. 8 shows a simulated SAR pattern of the MWA antenna system of Fig. 6 in the liver tissue in accordance with an illustrative embodiment. [0019] Fig. 9 depicts a block diagram of a transmitter incorporating the MWA antenna system of Fig. 1 in accordance with an illustrative embodiment. [0020] Fig. 10 depicts a side cross sectional view of a third MWA antenna system in accordance with an illustrative embodiment. [0021] Fig. 11 depicts a side cross sectional view of a fourth MWA antenna system in accordance with an illustrative embodiment. [0022] Fig. 12 depicts a front cross-sectional view of a two-wire transmission line of the third and/or fourth MWA antenna system of Figs. 10 and 11 in accordance with an illustrative embodiment. [0023] Fig. 13 depicts a front cross-sectional view of a second two-wire transmission line of the third and/or fourth MWA antenna system of Figs. 10 and 11 in accordance with an illustrative embodiment. [0024] Fig. 14 shows a simulated input impedance, S , of the MWA antenna system of Fig. 10 in the liver tissue in accordance with an illustrative embodiment. [0025] Fig. 15 shows a simulated SAR pattern of the MWA antenna system of Fig. 10 in the liver tissue in accordance with an illustrative embodiment. DETAILED DESCRIPTION [0026] With reference to Fig. 1, a block diagram of an antenna system 100 is shown in accordance with an illustrative embodiment. Antenna system 100 may include a coaxial cable 102, an impedance matching structure 104, and an antenna 106. Impedance matching structure 104 is configured to match an impedance of coaxial cable 102 to an impedance of antenna 106. Antenna system 100 may be used to perform microwave ablation (MWA), for example, of tissue.
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