Validation of TMS Animal Phantoms That Mimic Conductivity and Anatomy of the Brain*

Transcranial magnetic stimulation (TMS) has been found effective in the treatment of neurological and psychiatric conditions and is approved by the FDA to treat OCD, smoking cessation, and depression. Though this technology is by and large noninvasive, trials on live subjects are not always appropriate, which lead to the development of phantoms that mimic the electrical properties and anatomical features of the brain. These phantoms are individualized by computationally processing magnetic resonance images (MRI) and utilizing 3d printing technology to create molds for the brain regions. A well characterized composite of PDMS and carbon nanotubes (CNT) is used to fill the mold and mimic the conductivity of the native brain. Forming a network of CNT in the composite is crucial in reaching repeatable and uniform conductivities. One of several ways of achieving this is through high shear forces, which prevents haystacking of the CNT in the composite. 

These phantoms will allow for real time measurement of induced electric fields and voltages in the brain regions when stimulated by a time-varying magnetic field. Three dipole probes are placed neutrally orthogonal to create a triaxial dipole (TAD) probe that can measure the E field as a vector rather than just a point measurement. The phantom contains multiple TAD probes to help characterize the field.