Feeding structure for dual slot microwave ablation probe
A dual slot microwave probe for tissue ablation provides axially spaced slots producing an improved heating pattern with reduced axial extent. Degradation in this heating pattern caused by the addition of ceramic support elements and/or fluid cooling is realized through a feeding structure delivering separate sources of microwave energy to the different slots of the probe aligned with the slots of the probe.
1. A probe for microwave ablation comprising:
a generally elongate shaft extending along a shaft axis and sized for percutaneous insertion into a patient along the axis, the shaft further providing:
(a) a conductive antenna shell providing a first antenna opening free from conductive material to provide for a radial passage of microwave energy therethrough at a distal end of the shaft and a second antenna opening free from conductive material to provide for a radial passage of microwave energy therethrough, the second antenna opening axially displaced from the first antenna opening toward a proximal end of the shaft; and
(b) a feeding structure positioned within and spaced from the antenna shell, the feeding structure providing a center conductor connectable to a source of microwave power and a conductive feeding shell surrounding the center conductor and spaced therefrom, the feeding shell having a feeding opening providing a gap free from conductive material between axially displaced sections of the conductive feeding shell for radial passage of microwave energy therethrough.
2. The probe of claim 1 wherein the feeding opening is substantially aligned in a radial direction with the second antenna opening.
3. The probe of claim 1 wherein the second antenna and feeding openings are of different axially extent.
4. The probe of claim 3 wherein the first and second antenna openings are axially flanked by conductive material.
5. The probe of claim 4 further including a conductive tip on the distal end of the shaft spaced from the antenna shell and the feeding shell.
6. The probe of claim 5 wherein a distal end of the center conductor is spaced from the conductive tip.
7. The probe of claim 6 wherein the conductive tip is a sharpened point extending axially.
8. The probe of claim 1 wherein the antenna shell is spaced coaxially from the feeding shell to provide a space between portions thereof and further including a blocking wall extending radially from an outer surface of the feeding shell to an inner surface of the antenna shell, the blocking wall being on a proximal side of the second antenna and feeding openings, the blocking wall defining a compartment sealed at a distal end and open at the proximal end of the shaft for receiving and circulating a cooling fluid.
9. The probe of claim 8 further including a coolant tube fitting within the sealed compartment for conducting cooling fluid from the proximal end of the shaft to a point proximate to the blocking wall.
10. The probe of claim 7 further including a cooling fluid of water within the sealed compartment.
11. The probe of claim 1 wherein a portion of the feeding structure extending distal to the feeding opening has a length providing 180 degrees of phase shift for reflection of the microwave field.
12. The probe of claim 1 further including a dielectric material extending radially between portions of the antenna shell and the feeding shell distal to the second antenna and feeding openings.
13. The probe of claim 12 wherein the dielectric material is a ceramic.
14. The probe of claim 12 wherein a portion of the dielectric material extends within the antenna shell proximal to the second antenna opening to provide a blocking impedance to microwave conduction along the antenna shell proximal to the second opening in the antenna shell.
15. The probe of claim 12 further including a conductive tip supported by the dielectric material axially removed from the antenna shell, the feeding shell, and the center conductor.
16. A method of tissue ablation employing a probe for microwave ablation having:
a generally elongate shaft extending along a shaft axis and sized for percutaneous insertion into a patient along the axis, the shaft further providing:
a conductive antenna shell providing a first antenna opening free from conductive material to provide for the radial passage of microwave energy therethrough at a distal end of the shaft and a second antenna opening free from conductive material to provide for the radial passage of microwave energy therethrough, the second antenna opening axially displaced from the first antenna opening toward the proximal end of the shaft;
a feeding structure positioned within and spaced from the antenna shell, the feeding structure providing a center conductor connectable to a source of microwave power and a conductive feeding shell surrounding the center conductor and spaced therefrom, the feeding shell having a feeding opening providing a gap free from conductive material between axially displaced sections of the conductive feeding shell for radial passage of microwave energy therethrough the method comprising the steps of:
(a) inserting a distal end of the shaft into tissue to locate the first and second antenna openings in a region to be ablated;
(b) applying microwave energy between the feeding shell and the center conductor to ablate tissue by microwave energy.
17. The method of claim 16 wherein step (a) inserts the shaft into tissue percutaneously.
18. The method of claim 16 wherein the antenna shell is spaced coaxially from the feeding shell to provide a space between portions thereof and further including a blocking wall extending radially from an outer surface of the feeding shell to an inner surface of the antenna shell, the blocking wall being on a proximal side of the second antenna and feeding openings, the blocking wall defining a compartment sealed at a distal end and open at the proximal end of the shaft for receiving and circulating a cooling fluid; and including the step of circulating a fluid through the compartment.
19. The method of claim 18 wherein the fluid is chilled water.