Improved Intracranial Induced Electrical Field in Transcranial Magnetic Stimulation With Semiellipse Coil Pair

Abstract

A novel method for obtaining superior intracranial focusing field in transcranial magnetic stimulation is proposed in this paper. In order to improve stimulation intensity and focalization, a semiellipse coil pair (SEP) of special coil configuration is designed and introduced. Projected onto a plane parallel to stimulating target, the two adjacent coils are in semiellipse shapes. From the front view, the SEP is bent along a symmetrical axis at specific angles. Finite-element method is adopted to analyze the relations between the geometric structure characteristics of SEP and the three-dimensional spatial distributions of the induced electromagnetic field produced by SEP. The SEP coil is compared to a conventional figure of eight coil by the positive peak value of intracranial induced electrical field and the focusing area at a target plane located 20 mm below the scalp. Results indicate that under similar power loss, the design of SEP makes it possible to enhance the positive peak value of induced electrical field and decrease the focusing area simultaneously. A real human head modeled as homogeneous and isotropic is occupied in this paper to verify our method.