Transcranial Magnetic Stimulation: Focused Coils and Brain Phantoms

R.L. Hadimani, H. Magsood, I. Carmona, D. Jiles, A. Pandurangi
Virginia Commonwealth University,
United States

Keywords: focused brain stimulation, non-invasive brain stimulation, realistic brain phantom, TMS coils

Summary:

Transcranial Magnetic Stimulation (TMS) is a promising and non-invasive technique for diagnostics and treatments of various neurological diseases [1]–[3]. However, the lack of realistic and anatomical brain phantoms made the examination of induced electric fields on the brain tissues to be not well established and measured. We have developed a 3-D anatomically realistic brain phantom that can mimics the electrical conduction and mechanical stiffness of the brain. We used MRI images, software for brain tissue segmentation, 3-D printer, and polymer with conductive fillers. The phantom will be used for the purpose of evaluation of the neuromodulation such as transcranial magnetic stimulation (TMS). It enables the professional in the field of the brain modulation and treatment to test and perform actual brain stimulations on the phantom that are accurate and match the clinical setting of the of TMS treatment. There are currently no brain phantoms that can experimentally verify TMS parameters. To produce the phantom for the work at hand, we 3-D printed shells for each tissue layer of the brain. Brain tissues are divided mainly into cerebrospinal fluid (CSF), white matter (WM), grey matter (GM), ventricles, and cerebellum. These layers are made into shells and after 3D printing them, they are filled with a conductive material (silicon with graphite, multi walled carbon nanotubes (MWCNT) and silver nanoparticles) that is capable of mimicking the electrical conductive properties of different brain tissues. The electrical conductivity of different brain tissue that we are matching in this phantom is as follows, ventricles & CSF=1.77 Sm-1, GM=0.23 Sm-1, WM=0.24 Sm-1, and cerebellum=0.65 Sm-1. A rational design of polymers with varied loading of fillers, based on functional performance and processability, is planned to advance the state of the art in the field. The phantom will be examined under different TMS parameters and compared with FEM modelling of induced electric field and magnetic fields in different tissues of the brain. Microelectrodes will be placed at different locations/depths on the phantom to measure the current I and resistance Ω. Since the phantom exhibits same electrical properties of the brain, close readings to actual TMS procedures is expected to be achieved. References: [1] M. Kobayashi and A. Pascual-Leone, “Transcranial magnetic stimulation in neurology,” Lancet, vol. 2, no. 3, pp. 145–156, 2003. [2] S. H. Lisanby, B. Luber, T. Perera, and H. a. Sackeim, “Transcranial magnetic stimulation: applications in basic neuroscience and neuropsychopharmacology.,” Int. J. Neuropsychopharmacol., vol. 3, no. 3, pp. 259–273, 2000. [3] E. M. Wassermann and S. H. Lisanby, “Therapeutic application of repetitive transcranial magnetic stimulation: a review,” Clin. Neurophysiol., vol. 112, pp. 1367–1377, 2001.