Eccentric figure-eight coils for transcranial magnetic stimulation.
Previously we proposed an eccentric figure-eight coil that can cause threshold stimulation in the brain at lower driving currents. In this study, we performed numerical simulations and magnetic stimulations to healthy subjects for evaluating the advantages of the eccentric coil. The simulations were performed using a simplified spherical brain model and a realistic human brain model. We found that the eccentric coil required a driving current intensity of approximately 18% less than that required by the concentric coil to cause comparable eddy current densities within the brain. The eddy current localization of the eccentric coil was slightly higher than that of the concentric coil. A prototype eccentric coil was designed and fabricated. Instead of winding a wire around a bobbin, we cut eccentric-spiral slits on the insulator cases, and a wire was woven through the slits. The coils were used to deliver magnetic stimulation to healthy subjects; among our results, we found that the current slew rate corresponding to motor threshold values for the concentric and eccentric coils were 86 and 78 A/µs, respectively. The results indicate that the eccentric coil consistently requires a lower driving current to reach the motor threshold than the concentric coil. Future development of compact magnetic stimulators will enable the treatment of some intractable neurological diseases at home.
Department of Electrical Engineering and Information Systems, Graduate School of Engineering, University of Tokyo, Tokyo, Japan; Department of Neuromodulation and Neurosurgery, Graduate School of Medicine, Osaka University, Suita, Japan.
Masaki
M
Sekino
Hiroyuki
H
Ohsaki
Yoshihiro
Y
Takiyama
Keita
K
Yamamoto
Taiga
T
Matsuzaki
Yoshihiro
Y
Yasumuro
Atsushi
A
Nishikawa
Tomoyuki
T
Maruo
Koichi
K
Hosomi
Youichi
Y
Saitoh
D001921:Brain / Q000502:physiology; D003198:Computer Simulation; D004576:Electromyography; D004867:Equipment Design; D019054:Evoked Potentials, Motor; D006801:Humans; D008959:Models, Neurological; D050781:Transcranial Magnetic Stimulation / Q000295:instrumentation* / Q000379:methods
brain; coil; eddy current; medical application; transcranial magnetic stimulation