Microwave ablation antenna with bidirectional planar tissue heating
An ablation probe employs a triaxial construction with axial slots in an outer pair of tubular conductors separated by different dielectric materials to provide microwave power concentrated along a plane.
1 . A probe for microwave ablation comprising:
a first center conductor;
a second conductor spaced from and positioned around the first center conductor and including a first and second diametrically opposed slot extending parallel to the first center conductor;
a third conductor spaced from and positioned around the second conductor and including a third and fourth diametrically opposed slot extending parallel to the first center conductor, the third and fourth diametrically opposed slots radially aligned with the first and second diametrically opposed slots;
a first dielectric material providing a first relative permittivity in a volume between the first center conductor and the second conductor;
a second dielectric material providing a second relative permittivity different from the first relative permittivity in a volume between the second conductor and the third conductor; and
wherein the probe produces a microwave emission pattern concentrated along a plane of the slots.
2 . The probe of claim 1 wherein the first dielectric material has a relative permittivity of at least 15% less than the second dielectric.
3 . The probe of claim 1 wherein a circumferential extent of the slots in the second conductor and third conductor and values of the relative permittivity of the first dielectric material and second dielectric material provide for a planar emission of microwave energy in surrounding tissue bounded by a height of less than 50% of a bounding width in the plane of the slots at an isocontour of 10% of an electric field intensity maximum in the surrounding tissue.
4 . The probe of claim 1 wherein the first, second, third, and fourth slots are limited in length to less than 2 centimeters.
5 . The probe of claim 1 wherein the third conductor has an outside diameter of less than 8 mm.
6 . The probe of claim 1 further including an electrically insulating handle attached to a distal end of the probe in supporting a flexible electrical cable providing an electrical connector for receiving microwave power.
7 . The probe of claim 6 wherein a distal end of the probe includes a feature showing an orientation of the slots about a centerline of the probe.
8 . The probe of claim 1 further including a microwave power supply providing a microwave frequency voltage between the center conductor and second and third conductors of greater than 2 GHZ and at least 10 W.
9 . The probe of claim 1 wherein the first center conductor, second conductor, and third conductor are triaxially oriented conductors with circular cross-sections.
10 . The probe of claim 1 further including a biocompatible coating surrounding the third conductor.
11 . The probe of claim 1 including an end plate at a distal end of the probe connecting the first center conductor to the third conductor and including a first circumferential gap separating the end plate from a first distal portion of the second conductor and a second circumferential gap separating the first distal portion of the second conductor from a proximal portion of the second conductor.
12 . A method of ablation employing a microwave probe having a first center conductor; a second conductor spaced from and positioned around the first center conductor and including a first and second diametrically opposed slot extending parallel to the first center conductor; a third conductor spaced from and positioned around the second conductor and including a third and fourth diametrically opposed slot extending parallel to the first center conductor, the third and fourth diametrically opposed slots radially aligned with the first and second diametrically opposed slots; a first dielectric material providing a first relative permittivity in a volume between the first center conductor and second conductor; and a second dielectric material providing a second relative permittivity different from the first relative permittivity in a volume between the second conductor and the third conductor, the method comprising:
(a) inserting the probe into material to be ablated and aligning the slots with a desired ablation plane; and
(b) applying a gigahertz microwave frequency signal between the first center conductor and second and third conductors to ablate the material primarily along the desired ablation plane.
13 . The method of claim 12 , wherein the material is biological tissue.
14 . The method of claim 12 , wherein the material is a bone and the ablation plane is aligned with a bone growth plate.
15 . The method of claim 12 , wherein the gigahertz microwave frequency signal applies a voltage between the center conductor and second and third conductors of greater than 2 GHz and at least 10 W.