# US 7,611,508 B2 · Floating sleeve microwave antenna for tumor ablation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,611,508 B2 - Document ID: US7611508B2 - Status: Granted - Kind: B2 - Application number: 11/210,063 - Filed: 2005-08-23 - Published: 2007-03-01 - Granted: 2009-11-03 - Earliest claimed: 2005-08-23 - Assignees: Wisconsin Alumni Research Foundation - Inventors: Deshan Yang; John Michael Bertram; Mark Christopher Converse; John Goodwin Webster; David Mahvi - Web page: https://patentgrep.com/patent/US7611508B2 ## CPC - A61B 18/18: by applying electromagnetic radiation, e.g. microwaves - A61B 18/1815: {using microwaves} - H01Q 1/273: {Adaptation for carrying or wearing by persons or animals} - H01Q 9/20: Two collinear substantially straight active elements; Substantially straight single active elements (H01Q9/28 takes precedence) - H01Q 9/30: with feed to end of elongated active element, e.g. unipole (H01Q9/44 takes precedence) - A61B 5/4244: {liver} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) - H01Q: ANTENNAS, i.e. RADIO AERIALS (radiators or antennas for microwave heating H05B6/72) ## Abstract An antenna for microwave tumor ablation provides coaxial antenna conductors surrounded by an insulated sleeve of length and size promoting destructive interference of axial microwave energy passing inside and outside of the sleeve to limit the tail of SAR power toward the skin. ## Claims ### Claim 1 A microwave ablation antenna comprising: a substantially non-helical coaxial antenna having a center conductor and an outer conductor extending along an axis to allow positioning of a proximal end of the coaxial antenna within a patient at a site of a tumor and a distal end of the coaxial antenna outside of a patient to be connected to a microwave source having a microwave frequency; and a sleeve outside and electrically insulated from the outer conductor and the center conductor, the sleeve extending along the axis to provide a relative phase shift between microwave energy traveling axially outside the outer conductor and within the sleeve, and microwave energy traveling axially outside the sleeve, the relative phase shift equal substantially to an odd multiple of one half a wavelength of the microwave frequency; whereby microwave energy distal to the sleeve is suppressed by destructive cancellation of the microwave energy at an exit of the sleeve. ### Claim 2 (depends on 1) The microwave ablation antenna of claim 1 wherein the microwave frequency is at least 500 megahertz. ### Claim 3 (depends on 1) The microwave ablation antenna of claim 1 wherein the sleeve is metal and separated from the outer conductor with an insulator. ### Claim 4 (depends on 1) The microwave ablation antenna of claim 1 wherein the sleeve is a continuous coaxial tube. ### Claim 5 (depends on 1) The microwave ablation antenna of claim 1 further including an insulator outside of the sleeve. ### Claim 6 (depends on 1) The microwave ablation antenna of claim 1 wherein the sleeve is sized to be wholly within the patient during use. ### Claim 7 (depends on 1) The microwave ablation antenna of claim 1 wherein the sleeve provides a wavelength of microwave energy traveling axially outside the outer conductor and within the sleeve of at least five times the wavelength of the microwave energy traveling axially outside the sleeve. ### Claim 8 (depends on 7) The microwave ablation antenna of claim 7 wherein the sleeve is substantially one half the wavelength of the microwave energy traveling axially outside the sleeve. ### Claim 9 (depends on 1) The microwave ablation antenna of claim 1 wherein the sleeve includes an insulator having a dielectric of at least five times less than the dielectric of tissue of the patient. ### Claim 10 (depends on 1) The microwave ablation antenna of claim 1 wherein the sleeve is less than 100 mm in axial extent. ### Claim 11 (depends on 1) The microwave ablation antenna of claim 1 wherein the sleeve may slide axially with respect to the outer conductor. ### Claim 12 (depends on 1) The microwave ablation antenna of claim 1 further including a microwave source having a frequency in a range from 0.5 to 5 GHz. ### Claim 13 (depends on 1) The microwave ablation antenna of claim 1 further including at least one of a capacitive and inductive element reducing current flow on the outer conductor. ### Claim 14 (depends on 1) The microwave ablation antenna of claim 1 wherein the sleeve has an electrical length equal substantially to an odd multiple of the microwave energy traveling outside the sleeve and substantially unequal to an odd multiple of the microwave energy traveling within the sleeve. ### Claim 15 A method of treating a tumor comprising the steps of: (a) positioning a substantially non-helical coaxial antenna having a center conductor and an outer conductor extending along an axis with a proximal end of the coaxial antenna within a patient at a site of a tumor and a distal end of the coaxial antenna outside the patient; and (b) connecting the coaxial antenna to a microwave source having a microwave frequency; wherein the coaxial antenna includes a sleeve outside and electrically insulated from the outer conductor and the center conductor, the sleeve extending along the axis to provide a phase shift between microwave energy traveling axially outside the outer conductor and within the sleeve, and microwave energy traveling axially outside the sleeve of substantially an odd multiple of pi radians so as to cause destructive cancellation of the microwave energy at an axial exit of the sleeve between the energy traveling axially within the sleeve and energy traveling axially outside the sleeve. ### Claim 16 (depends on 15) The method of claim 15 wherein the sleeve has an electrical length equal substantially to an odd multiple of the microwave energy traveling outside the sleeve and substantially unequal to an odd multiple of the microwave energy traveling within the sleeve.