Bipolar needle with adjustable electrode for geometrically controlled thermal ablation of biological tissue

1 . A method of ablating a tissue region using a therapy probe having a shaft with proximal and distal ends, and a plurality of therapy delivery electrodes at the distal end thereof, the method comprising:

inserting the therapy probe to place the distal end of the shaft at a desired location, the distal end of the shaft including a shaft electrode having an exposed portion proximal of the distal end of the shaft, a surface area of the exposed portion of the shaft electrode being adjustable;

advancing a needle electrode from the shaft to a desired position and manipulating a needle electrode sheath that adjustably exposes a portion of the needle electrode to thereby control a surface area of the exposed portion of the needle electrode;

delivering a first therapy while a surface area of the exposed portion of the needle electrode exceeds a surface area of the exposed portion of the shaft electrode, to thereby develop a first lesion adjacent the shaft electrode; and

delivering a second therapy while a surface area of the exposed portion of the shaft electrode exceeds the surface area of the exposed portion of the needle electrode, to thereby develop a second lesion adjacent the needle electrode.

2 . The method of claim 1 further comprising manipulating the exposed portion of the needle electrode between the steps of delivering the first therapy and delivering the second therapy.

3 . The method of claim 1 further comprising manipulating the exposed portion of the shaft electrode between the steps of delivering the first therapy and delivering the second therapy.

4 . The method of claim 1 wherein the therapy probe is configured such that the position of the exposed portion of the shaft electrode is adjustable relative to the distal end of the therapy probe, and the method further comprises adjusting the position of the exposed portion of the shaft electrode between the steps of delivering the first therapy and delivering the second therapy.

5 . The method of claim 1 wherein the first therapy takes the form of a thermal RF ablation therapy, and the second therapy takes the form of a thermal RF ablation therapy.

6 . The method of claim 1 wherein the therapy probe comprises:

an outer sheath of a non-conductive material;

the needle electrode sheath, also of a non-conductive material;

the shaft electrode disposed between the needle electrode sheath and the outer sheath;

the needle electrode disposed within the needle electrode sheath;

a first locking hub configured for selectively locking a relative position of the outer sheath to the shaft electrode;

a second locking hub configured for selectively locking a relative position of the shaft electrode to the needle electrode sheath; and

a third locking hub configured for selectively locking a relative position of the needle electrode sheath to the needle electrode.

7 . The method of claim 6 further comprising:

locking the first and third locking hubs before delivering the first therapy;

unlocking at least one of the first or third locking hubs after delivering the first therapy and manipulating the exposed surface area of at least one of the shaft electrode or the needle electrode;

relocking the at least one of the first or third locking hubs after manipulating the exposed surface area of the at least one of the shaft electrode or he needle electrode, before delivering the second therapy.

8 . A method of ablating a tissue region using an ablation probe having a shaft with proximal and distal ends, and a plurality of therapy delivery electrodes at the distal end thereof, the method comprising:

inserting the ablation probe to place the distal end of the shaft at a desired location, the distal end of the shaft including a shaft electrode having an exposed portion proximal of the distal end of the shaft, a surface area of the exposed portion of the shaft electrode being adjustable;

advancing a needle electrode from the shaft to a desired position and manipulating a needle electrode sheath that adjustably exposes a portion of the needle electrode to thereby control a surface area of the exposed portion of the needle electrode;

delivering a first therapy while a surface area of the exposed portion of the shaft electrode exceeds the surface area of the exposed portion of the needle electrode, to thereby develop a first lesion adjacent the needle electrode and, during delivery of the first therapy, withdrawing the needle electrode from the desired position and into the shaft while maintaining the exposed surface area of the needle electrode, to thereby extend the first lesion in a longitudinal direction relative to an axis of the needle electrode.

9 . The method of claim 8 wherein the therapy probe comprises:

an outer sheath of a non-conductive material;

the needle electrode sheath, also of a non-conductive material;

the shaft electrode disposed between the needle electrode sheath and the outer sheath;

the needle electrode disposed within the needle electrode sheath;

a first locking hub configured for selectively locking a relative position of the outer sheath to the shaft electrode;

a second locking hub configured for selectively locking a relative position of the shaft electrode to the needle electrode sheath; and

a third locking hub configured for selectively locking a relative position of the needle electrode sheath to the needle electrode.

10 . The method of claim 9 further comprising:

locking the first and third locking hubs before delivering the first therapy, to thereby fix the exposed surface areas of each of the shaft electrode and the needle electrode, while leaving the second locking hub unlocked to allow withdrawal of the needle electrode from the desired position and into the shaft.

11 . The method of claim 8 further comprising reducing a power level of the first therapy as the needle electrode is withdrawn from the desired position and into the shaft.

12 . The method of claim 8 further comprising sensing an impedance between the needle electrode and the shaft electrode, and sensing at least one temperature at a position adjacent the needle electrode, and responsive to the sensed impedance and at least one temperature, adjusting the power level of the first therapy as the needle electrode is withdrawn from the desired position and into the shaft.

13 . A system for ablation, comprising:

an ablation probe having a proximal end and a distal end, the ablation probe comprising:

an outer sheath of a non-conductive material;

an inner sheath of a non-conductive material;

a shaft electrode disposed between the inner and outer sheaths;

a needle electrode disposed within the inner sheath;

a first locking hub configured for selectively locking a relative position of the outer sheath to the shaft electrode;

a second locking hub configured for selectively locking a relative position of the shaft electrode to the inner sheath;

a third locking hub configured for selectively locking a relative position of the inner sheath to the needle electrode; and

means to indicate electrically a change in exposed surface area of at least one of the shaft and needle electrodes and/or means to indicate electrically a change in a distance between the shaft and needle electrodes; and

a signal generator adapted for electrical connection to each of the needle electrode and the shaft electrode, the signal generator configured to sense the distance between the electrodes and the surface area of the electrodes by linking to the locking hubs.

14 . The system for ablation of claim 13 wherein the needle electrode, inner sheath, shaft electrode, and outer sheath are each moveable relative to one another when none of the locking hubs are locked.

15 . The system for ablation of claim 13 wherein the third locking hub facilitates a step of defining an exposed surface area of the needle electrode, and the first locking hub facilitates a step of defining an exposed surface area of the shaft electrode, such that, in use, a user may lock the first and third locking hubs while moving the needle electrode, having a fixed surface area, relative to the shaft electrode, also having a fixed surface area.

16 . The system for ablation claim 15 wherein the signal generator is configured to sense an impedance between the needle electrode and the shaft electrode during therapy delivery to maintain a constant therapy current as the needle electrode and the shaft electrode are moved relative to one another.

17 . The system for ablation of claim 13 , further comprising a temperature sensor associated with at least one of the shaft electrode or the needle electrode.

18 . The system for ablation of claim 17 wherein the signal generator is configured to sense an impedance between the needle electrode and the shaft electrode during therapy delivery and to obtain a temperature signal from the temperature sensor, and to adjust a therapy voltage responsive to the temperature and impedance signals.

19 . The system for ablation of claim 18 wherein the signal generator is configured to operate as follows:

at initiation of a therapy output, sense temperature and impedance;

maintain or increase voltage until the sensed temperature reaches a temperature threshold;

measure impedance and voltage once the sensed temperature reaches the temperature threshold and store a target current;

after the temperature threshold is reached, monitor impedance to maintain the target current; and

if the sensed temperature rises above the temperature threshold, reduce the target current.

20 . The system for ablation of claim 13 , wherein the outer sheath includes a manifold, and the means to indicate electrically the change in exposed surface area includes at least one sensor for calculating the relative positions of the shaft and needle electrodes and their respective surface areas.