Researchers optimize design of transcranial magnetic stimulation coil with iron core

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Transcranial Magnetic Stimulation (TMS) has been widely used in clinical and scientific research in the fields of psychological cognitive sciences, neuropsychiatric diseases, etc. Researchers from the Suzhou Institute of Biomedical Engineering and Technology (SIBET) of the Chinese Academy of Sciences have recently proposed an improved TMS coil structure based on an iron core.

The design of the stimulation coil plays an important role in the formation of the intracranial electric field in TMS. The induced electric field generated by the magnetic stimulation coil in the brain must reach a certain threshold to achieve the stimulation goal.

Since the magnetic field away from the surface of the coil decays rapidly with distance, to ensure the electric field stimulation intensity in the target brain area, the coil must be energized with a large current, usually thousands of amps, which imposes a high demand. For alimentation.

Introducing ferromagnetic materials into the coil can help improve the value of the induced electric field of the coil and reduce the current demand. However, in the actual application, the weight of the coil brought by the iron core cannot be ignored. The influence of the position of the nucleus on the distribution of the electromagnetic field must also be discussed in more detail.

Based on the most commonly used 8-shaped coil and the slinky coil introduced with the iron core, the researchers analyzed the influence of the position and size of the iron core on the performance of the coil. structural.

In this study, by modifying the filling factor of the iron core in the coil and the position of the iron core in the coil, XU Yajie of SIBET and his collaborators obtained the comparison results of the maximum induced electric field, the depth of stimulation, focusing and energy consumption of the iron core of the iron core coil. This provides a reference for the method of adding an iron core to the coil in different cases.

A performance factor combining performance parameters including maximum induced electric field, stimulation depth, focus and heat loss was used to assess overall coil performance. This shows that the slinky iron core coil achieves the best overall performance when it has a fill factor of 0.4 and both legs of the iron core are close to the inner sides of the coil.

Researchers built three prototypes – the basic, optimized and full-size iron-core coil – and magnetic field sensing demonstrates the improved performance of the optimized iron-core coil.

According to the researchers, the proposed systematic optimization approach for the iron-core coil based on the Fo8 basic structure can be applied to improve the performance of the TMS coil, reduce power requirements and guide the design of other iron core TMS coils.

Related results were published in Journal of Neural Engineering in an article titled Optimal Transcranial Magnetic Stimulation Coil Design with Iron Core.


Fig. 1. Prototypes of slinky iron core coil coils. (a) without iron core, with fill factor iron core; (b), and natural size; (c) two legs of the iron core near the inner sides of the coil. (Image by SIBET)

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