Eccentric figure‐eight coils for transcranial magnetic stimulation

Abstract

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 A/μs and 78 A/μs, respectively. The results indicate that the eccentric coil consistently requires a lower driving current to reach the motor threshold than does the concentric coil. Future development of compact magnetic stimulators will enable the treatment of some intractable neurological diseases at home.

Monophasic-Quadripulse Theta Burst Magnetic Stimulation for Motor Palsy Functional Evaluation After Intracerebral Hemorrhage

“…Therefore, a method that enables successful and stable MEP elicitation after TMS in awake patients would be beneficial. To the best of our knowledge, only a specialized coil design for TMS producing an efficient stimulus current in the brain has thus far been developed ( Sekino et al, 2015 ). Alternatively, techniques to amplify MEPs using repetitive multi-train transcranial electrical stimulation (mt-TES) during surgery under general anesthesia in neurologically normal individuals have been described ( Szelényi et al, 2007 ; Deletis and Sala, 2008 ; Tsutsui et al, 2015 ; Deletis and Fernández-Conejero, 2016 ), as have been the optimal repetition conditions of mt-TES in patients with impaired motor function during surgery ( Ushio et al, 2018 ).…”

Figure-Eight Coils for Magnetic Stimulation: From Focal Stimulation to Deep Stimulation

“…Because of the contributions of coil elements having obtuse angles, the coil provides electric field distributions with an enhanced focality. Eccentric figure-eight coils, shown in Figure 1F , can achieve an enhanced electric field intensity owing to their modified in-plane winding geometry ( Sekino et al, 2015 ). The winding centers of the left and right coils are shifted toward the middle, forming a dense coil conductor in the middle.…”

Review on biophysical modelling and simulation studies for transcranial magnetic stimulation

“…In summary, computational modelling studies were conducted to improve focality, depth, and power requirements, as listed in Table 2. In general, smaller coils have superior focality but lower depth (Thielscher and Kammer, 2004;Deng, Lisanby and Peterchev, 2013;Sekino et al, 2015), while larger coils favour deeper targets (Roth, Zangen and Hallett, 2002;Deng, Lisanby and Peterchev, 2014;Lu and Ueno, 2017;Samoudi et al, 2018). Nevertheless, all coils are subject to a trade-off between depth and focality (Deng, Lisanby and Peterchev, 2014;Guadagnin et al, 2016;Gomez, Goetz and Peterchev, 2018;Gomez-Tames et al, 2020).…”

“…Depth EF-decay EF vs penetration distance in the brain (Roth, Zangen and Hallett, 2002;Kim, Georghiou and Won, 2006;Salvador et al, 2009;Hernandez-Garcia et al, 2010;Lu andUeno, 2015a, 2015b;Sekino et al, 2015;Wei et al, 2017)…”