Structural design of novel three-layer figure-of-8 coil for transcranial magnetic stimulation
Hui XIONG(),Zhao JING,Jin-zhen LIU
1. School of Electrical Engineering and Automation, TIANGONG University, Tianjin 300387, China 2. Tianjin Key Laboratory of Advanced Technology of Electrical Engineering and Energy, TIANGONG University, Tianjin 300387, China
A new three-layer figure-of-8 coil with the special structure and current direction was designed and optimized based on the superposition and cancellation of magnetic field. COMSOL simulation software was used to analyze the effects of the three-layer figure-of-8 coil with the changing of size and the rotation angle along the tangent line on the stimulation performance, and the coil structure was optimized. The stimulation intensity of the optimized three-layer figure-of-8 coil was increased by 33.92% and the focality was improved by 25.43% compared with figure-of-8 coil. Results show that the three-layer figure-of-8 coil has better stimulation intensity and focality at a certain target position. Then the adverse effects of non-target areas were greatly reduced, and the safety of TMS treatment was guaranteed. The performance advantages of the optimized three-layer-8-shaped coil were verified by stimulating the realistic head model.
Hui XIONG,Zhao JING,Jin-zhen LIU. Structural design of novel three-layer figure-of-8 coil for transcranial magnetic stimulation. Journal of ZheJiang University (Engineering Science), 2021, 55(4): 793-800.
Fig.1Two layers ball-shaped head model with stimulation coils
Fig.2Three-layer figure-of-8 coil with different stimulating current directions and radii as well as three types of structures rotating along tangent
线圈类型
参数
Ⅰ类
Routi=15.5 mm，routi = 27.5 mm
Ⅱ类
Routi=17.5 mm，routi = 25.5 mm
Ⅲ类
Routi=19.5 mm，routi = 23.5 mm
Ⅳ类
Routi =21.5 mm，routi = 21.5 mm
Ⅴ类
Routi =23.5 mm，routi =19.5 mm
Ⅵ类
Routi =25.5 mm，routi =17.5 mm
Ⅶ类
Routi =27.5 mm，routi =15.5 mm
Tab.1Seven types of coils with various outer radii
线圈
Emax /（V·m?1）
d1/2 /mm
S1/2 /cm2
8字形线圈
167.74
18.38
14.820
双层-8字形线圈
189.33
16.34
12.845
三层-8字形线圈
172.98
14.12
9.925
Tab.2Stimulation calculation results of three different coils
Fig.3Relation between maximum electric field strength，rotation angel θ and radius
Fig.4Relation between stimulation depth，rotation angel θ and radius
Fig.5Relation between focusing area，rotation angel θ and radius
Fig.6Electric field strength distribution induced by optimal three-layer figure-of-8 coil at cerebral cortex
线圈
Emax /（V·m?1）
d1/2 /mm
S1/2 /cm2
8字形线圈
167.741
18.380
14.822
三层-8字形线圈
172.980
14.123
9.925
优化后的Ⅱ类三层-8字形线圈 (Routi=17.5 mm，routi=25.5 mm，θ=3°)
224.643
15.004
11.052
Tab.3Stimulation calculation results of figure-of-8 and three-layer figure-of-8 coil before and after optimization
Fig.7Structure of realistic head model
Fig.8Induced electric field strength distribution map of three coils based on realistic head model
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