Magnetic stimulation of peripheral nerves: computation of the induced electric field in a cylinder-like structure

The uncertain site of excitation is the main factor that prevents magnetic stimulation of peripheral nerves from becoming a routine clinical tool. Long and straight fibres are thought to be excited by the first spatial derivative of the electric field component parallel to the fibre and by the electric field component perpendicular to the fibre. The authors have developed an analytical model to compute both of these field features inside pseudo-cylindrical structures. Here they analyse the computation of the electric fields induced with different stimulator arrangements: they examine the effects of changes in stimulator coil location, orientation, size, and geometry and of changes in the dimensions of the limbs and in the position of the nerve inside the limb.