System and method for guiding a medical instrument with magnetic force control

1. A magnetic force control system for guiding a medical instrument within a body for a medical procedure, comprising:

a controlled magnet, coupled to the medical instrument, that is insertable into the body;

a controller magnet that exerts a magnetic force on the controlled magnet;

a magnetically permeable shield, placed between the controlled magnet and the controller magnet, that selectively modulates the magnetic force by rerouting magnetic field lines; and

a control system, having an actuator that varies the relative orientations of the shield and the controller magnet, a sensor system that measures at least one of the magnetic force and actuator position, and a controller that controls the modulation of the magnetic force.

2. The system of claim 1 , wherein the medical instrument has a navigating end, wherein the controlled magnet is located on the navigating end.

3. The system of claim 1 , wherein at least one of the controlled magnet and the controller magnet is a permanent magnet.

4. The system of claim 1 , wherein the actuator is coupled to the shield and moves at least a portion of the shield in translation.

5. The system of claim 4 , wherein the translation is in a plane generally perpendicular to an axis directly connecting the controller magnet and the controlled magnet.

6. The system of claim 4 , wherein the translation is along an axis directly connecting the controller magnet and the controlled magnet.

7. The system of claim 1 , wherein the actuator is coupled to the shield and moves at least a portion of the shield in rotation.

8. The system of claim 7 , wherein the rotation is in a plane generally perpendicular to an axis directly connecting the controller magnet and the controlled magnet.

9. The system of claim 7 , wherein the rotation is about a second axis generally perpendicular to a first axis directly connecting the controller magnet and the controlled magnet.

10. The system of claim 1 , wherein the shield defines a gap that modulates the magnetic force; wherein the actuator is coupled to the shield such that the actuator selectively opens and closes the gap.

11. The system of claim 1 , wherein the shield defines a continuous path for rerouted magnetic field lines that enables the rerouted magnetic field lines to form a complete circuit.

12. The system of claim 1 , wherein the shield is of generally non-uniform thickness.

13. The system of claim 1 , wherein the actuator is coupled to the controller magnet and moves the controller magnet relative to the shield.

14. The system of claim 1 , wherein the sensor system includes a sensor on the controller magnet.

15. The system of claim 1 , wherein the controller includes a successive-loop closure control algorithm.

16. A method for guiding a medical instrument within a body with magnetic force control, comprising the steps of:

providing a controlled magnet coupled to the medical instrument;

inserting the controlled magnet and the medical instrument into the body;

providing a controller magnet outside the body;

placing a magnetically permeable shield between the controlled magnet and the controller magnet;

applying a magnetic force to the controlled magnet with the controller magnet to influence the position of the controlled magnet; and

selectively modulating the magnetic force with the shield to vary at least one of amplitude and orientation of the magnetic force, thereby guiding the controlled magnet within the body.

17. The method of claim 16 , wherein the step of modulating the magnetic force includes opening and closing a gap defined by the shield.

18. The method of claim 16 , wherein the step of modulating the magnetic force further includes translating at least a portion of the shield.

19. The method of claim 16 , wherein the step of modulating the magnetic force further includes rotating at least a portion of the shield.

20. The method of claim 16 , wherein the step of modulating the magnetic force further includes moving the controller magnet relative to the shield.