To investigate inter-subject variability with respect to cerebrospinal fluid thickness and brain-scalp distance, and to investigate intra-subject variability with different coil orientations. Simulations of the induced electric field (E-Field) using a figure-8 coil over the vertex were conducted on 50 unique head models and varying orientations on 25 models. Metrics exploring stimulation intensity, spread, and localization were used to describe inter-subject variability and effects of non-brain anatomy. Both brain-scalp distance and CSF thickness were correlated with weaker stimulation intensity and greater spread. Coil rotations show that for the dorsal portion of the stimulated brain, E-Field intensities are highest when the anterior-posterior axis of the coil is perpendicular to the longitudinal fissure, but highest for the medial portion of the stimulated brain when the coil is oriented parallel to the longitudinal fissure. Normal anatomical variation in healthy individuals leads to significant differences in the site of TMS, the intensity, and the spread. These variables are generally neglected but could explain significant variability in basic and clinical studies. This is the first work to show how brain-scalp distance and cerebrospinal fluid thickness influence focality, and to show the disassociation between dorsal and medial TMS.

Transcranial magnetic stimulation (TMS) is a non-invasive treatment for major depressive disorder. TMS coil design plays an important role in navigating the magnetic field to the required location in the brain. Development of deep brain TMS coils will help to stimulate sub-cortical structures, allowing for a significant expansion of the uses of TMS beyond superficial cortical targets. Stimulating deep brain regions may have beneficial effects on neurological disorders such as Parkinson's disease, Post-Traumatic Stress Disorder and mild traumatic brain injury. In this manuscript, design and testing of a multi-coil configuration, the Triple Halo Coil (THC) is proposed, which can stimulate deep brain structures such as the hippocampus and amygdala. A finite element tool is used to determine the induced electric field and magnetic field in these regions due to the THC alone and in combination with the Figure-of-8 coil. Analysis of the results are done with the help of an MRI-derived anatomically accurate heterogeneous head model of a 34-year-old man. Furthermore, the magnetic field of the THC is measured and compared with the simulated value.

Coil design for transcranial magnetic stimulation (TMS) is a critical factor that is constantly being investigated to provide more focused stimulation of the brain. The design of focal coils is important because TMS uses time-varying magnetic fields generated from electromagnetic coils to stimulate a specific region of interest of the brain non-invasively. TMS is a useful tool in both diagnostic and therapeutic purposes for identifying and treating psychiatric and neurological disorders. Currently, TMS is approved by the U.S. Food and Drug Administration for the treatment of chronic depression and is being researched for the treatment of stroke, obsessive compulsive disorder, post-traumatic stress disorder, and Parkinson's disease. In this paper, the authors are proposing to further improve the focality of the quadruple butterfly coil (QBC) by using a high-permeability ferromagnetic material acting as passive magnetic shield. Analyses of the resulting field profiles with 50 heterogeneous head models using a single and double magnetic shield has been conducted at two different positions in the brain: the vertex and the dorsolateral prefrontal cortex. Comparison of the results has been illustrated with the help of QBC and figure-8 coil by using parameters of interest such as maximum electric field intensities in both the brain and the entire head, the volume of the brain receiving strong stimulation intensities, and the surface area of the brain receiving strong stimulation intensities. There is a significant amount of improvement found in focality when the QBC is used with a magnetic shield. With a shield, the coil is still able to maintain a comparable maximum electric field intensity in the targeted region of the brain to that of the original QBC. Although both shielding solutions show significant improvement, no notable difference has been found in the results between single and double shields with the QBC.

Transcranial magnetic stimulation (TMS) is a non-invasive, safe, effective, and food and drug administration approved treatment for major depressive disorder. TMS relies on time-varying magnetic fields to induce an electric field in the brain, resulting in depolarization or hyperpolarization of the neurons. Recently, there has been extensive research to improve the magnetic coil design, effectiveness of TMS treatment, and improvement in the computer modeling of human brains, yet little development is reported on the TMS pulse generators and coil design for small animals. TMS pulse generators, or stimulators, are the circuits which provides pulse current to drive the inductive coils (TMS coils), used to generate time-varying magnetic fields. Commercial TMS stimulators are expensive and have limitations of using standard and non-customizable coils. These stimulators do not support small inductive loads, which require high-current capabilities. Furthermore, the commercial animal coil stimulates the entire body of a mouse, as they are designed for large animals. In this paper, the authors present the design of a small sized TMS stimulator and a focused coil for the application on small animals such as mice. The proposed TMS stimulator will have the potential of handling small inductive loads enabling stimulation of specific regions within the mouse brain.

Transcranial magnetic stimulation (TMS) is a non-invasive neuromodulation technique that is used for treating various neurological disorders such as major depressive disorder. TMS has been gaining popularity in the field of neurostimulation of the cerebellum, since the cerebellum is a complex structure connected with almost the entire central nervous system and TMS has promise for non-invasively probing cerebellar function. Recent studies have discovered that the cerebellum plays an important role not only in motor planning and behavior but also in the cognitive domain. However, few studies have explored how different coil designs and anatomical variations affect the effectiveness of cerebellar TMS. Therefore, in this paper, we investigated the effects of cerebellar TMS with different coil designs positioning on several locations. Finite-element modeling was conducted with Figure-8 coil and D-B80 coil. Each coil was positioned in the center, 1 and 3 cm to the left of center of the cerebellum, and all the locations were tangential to the scalp at a distance of 5 mm. Furthermore, 50 MRI derived head models were used in the computer modeling to examine how anatomical variations affect the distribution and intensity of electric field in cerebellar TMS.

Transcranial Magnetic Stimulation (TMS) is a non-invasive therapeutic and restorative mode of treating neurological disorders which has been approved by the United States Food and Drug Administration (FDA). It has proven to be an effective way of treating disorders as it is a less risky technology compared to conventional brain surgery. Various researchers have proposed coil designs for TMS aimed at achieving high focality and increased penetration depth of the induced electric field in the brain. In the present research, the authors compare the Figure of Eight (FOE) coil, Quadruple Butterfly Coil (QBC) and Triple Halo Coil (THC) on different head models to confirm the different effect of coil configuration on the induced electric field. Finite element simulations were conducted with Sim4life software to determine the maximum electric field intensity, E-Max (V/m) and the stimulated volume of the brain, V-Half (mm3). The coils were positioned at the dorsolateral prefrontal cortex (DLPFC) location of the head and results were compared of the gray matter and white matter with the entire anatomic structure of the brain to confirm the effect of coil configuration and the variability of the anatomical structure.