Magnetic stimulation devices and methods of therapy
Devices and systems are disclosed for the non-invasive treatment of medical conditions through delivery of energy to target tissue, comprising a source of electrical power, a magnetically permeable toroidal core, and a coil that is wound around the core. The coil and core are embedded in a continuous electrically conducting medium, which is adapted to have a shape that conforms to the contour of an arbitrarily oriented target body surface of a patient. The conducting medium is applied to that surface by any of several disclosed methods, and the source of power supplies a pulse of electric charge to the coil, such that the coil induces an electric current and/or an electric field within the patient, thereby stimulating tissue and/or one or more nerve fibers within the patient. The invention shapes an elongated electric field of effect that can be oriented parallel to a long nerve. In one embodiment, the device comprises two toroidal cores that lie adjacent to one another.
1. A method for selectively applying energy to a target region within a patient, the method comprising:
generating a time-varying magnetic field with an enclosed coil that is located essentially entirely outside of the patient;
shaping an electric field that is induced by said magnetic field by positioning an electrically conductive fluid around a portion of the enclosed coil; and
conducting an electric current that is induced by said magnetic field through an outer skin surface of the patient to the target region to modulate a nerve at the target region.
2. The method of claim 1 , wherein the target region is a nerve at least about 1 cm below the outer skin surface.
3. The method of claim 1 , wherein the target region is a nerve from about 2 cm to about 5 cm below the outer skin surface.
4. The method of claim 1 , further comprising substantially constraining the electric current from modulating one or more nerves in a second region between the outer skin surface and the target region.
5. The method of claim 1 , wherein the shaping further comprises generating a second time-varying magnetic field within a second enclosed coil positioned near or adjacent to the enclosed coil.
6. The method of claim 1 , wherein the shaping further comprises positioning an electrical insulator around a portion of the enclosed coil such that the component of the induced electric field normal to the surface of the insulator is zero.
7. The method of claim 1 , wherein the conducting is carried out by electrically coupling the induced electric field to the target region allowing current to flow through the outer skin surface of the patient.
8. The method of claim 1 , wherein the electric field comprises bursts of electrical impulses sufficient to modulate the nerve at the target region.
9. The method of claim 8 , wherein the bursts repeat from about 15 Hz to about 50 Hz.
10. The method of claim 8 , wherein each of the impulses has a duration from about 50 microseconds to about 1000 microseconds.
11. The method of claim 1 , further comprising:
positioning the enclosed coil adjacent to or near an outer skin surface of the patient's neck; and
inducing the electric field at or near a vagus nerve of the patient.
12. The method of claim 1 , wherein the enclosed coil is housed within a handheld device and substantially surrounded by the electrically conductive fluid within the handheld device.
13. The method of claim 1 , wherein the electrically conductive fluid comprises an electrically conductive gel.
14. The method of claim 1 , wherein the electrically conductive fluid comprises an electrically conductive liquid.