Design and Validation of Miniaturized Repetitive Transcranial Magnetic Stimulation (rTMS) Head Coils.

Repetitive transcranial magnetic stimulation (rTMS) is a rapidly developing therapeutic modality for the safe and effective treatment of neuropsychiatric disorders. However, clinical rTMS driving systems and head coils are large, heavy, and expensive, so miniaturized, affordable rTMS devices may facilitate treatment access for patients at home, in underserved areas, in field and mobile hospitals, on ships and submarines, and in space. The central component of a portable rTMS system is a miniaturized, lightweight coil. Such a coil, when mated to lightweight driving circuits, must be able to induce B and E fields of sufficient intensity for medical use. This paper newly identifies and validates salient theoretical considerations specific to the dimensional scaling and miniaturization of coil geometries, particularly figure-8 coils, and delineates novel, key design criteria. In this context, the essential requirement of matching coil inductance with the characteristic resistance of the driver switches is highlighted. Computer simulations predicted E- and B-fields which were validated via benchtop experiments. Using a miniaturized coil with dimensions of 76 mm × 38 mm and weighing only 12.6 g, the peak E-field was 87 V/m at a distance of 1.5 cm. Practical considerations limited the maximum voltage and current to 350 V and 3.1 kA, respectively; nonetheless, this peak E-field value was well within the intensity range, 60-120 V/m, generally held to be therapeutically relevant. The presented parameters and results delineate coil and circuit guidelines for a future miniaturized, power-scalable rTMS system able to generate pulsed E-fields of sufficient amplitude for potential clinical use.

Intrinsically Linear Transistor for Millimeter-Wave Low Noise Amplifiers.

Transistors are the backbone of any electronic and telecommunication system but all known transistors are intrinsically nonlinear introducing signal distortion. Here, we demonstrate a novel transistor with the best linearity achieved to date, attained by sequential turn-on of multiple channels composed of a planar top-gate and several trigate Fin field-effect transistors (FETs), using AlGaN/GaN structures. A highly linearized transconductance plateau of >6 V resulted in a record linearity figure of merit OIP3/PDC of 15.9 dB at 5 GHz and a reduced third-order intermodulation power by 400× in reference to a conventional planar device. The proposed architecture also features an exceptional performance at 30 GHz with an OIP3/PDC of ≥8.2 dB and a minimum noise figure of 2.2 dB. The device demonstrated on a scalable Si substrate paves the way for GaN low noise amplifiers (LNAs) to be utilized in telecommunication systems, and is also translatable to other material systems.

A Compact Circuit for Boosting Electric Field Intensity in Repetitive Transcranial Magnetic Stimulation (rTMS).

The concept of a portable, wearable system for repetitive transcranial stimulation (rTMS) has attracted widespread attention, but significant power and field intensity requirements remain a key challenge. Here, a circuit topology is described that significantly increases induced electric field intensity over that attainable with similar current levels and coils in conventional rTMS systems. The resultant electric field is essentially monophasic, and has a controllable, shortened duration. The system is demonstrated in a compact circuit implementation for which an electric field of 94 V/m at a depth of 2 cm is measured (147 V/m at 1 cm depth) with a power supply voltage of 80 V, a maximum current of 500 A, and an effective pulse duration (half amplitude width) of 7 µsec. The peak electric field is on the same order as that of commercially available systems at full power and comparable depths. An electric field boost of 5x is demonstrated in comparison with our system operated conventionally, employing a 70 µsec rise time. It is shown that the power requirements for rTMS systems depend on the square of the product of electric field Ep and pulse duration tp, and that the proposed circuit technique enables continuous variation and optimization of the tradeoff between Ep and tp. It is shown that the electric field induced in a medium such as the human brain cortex at a specific depth is proportional to the voltage generated in a given loop of the generating coil, which allows insights into techniques for its optimization. This rTMS electric field enhancement strategy, termed 'boost rTMS (rbTMS)' is expected to increase the effectiveness of neural stimulation, and allow greater flexibility in the design of portable rTMS power systems.Clinical Relevance- This study aims to facilitate a compact, battery-powered rTMS prototype with enhanced electric field which will permit broader and more convenient rTMS treatment at home, in a small clinic, vessel, or field hospital, and potentially, on an ambulatory basis.

A Compact Battery-Powered rTMS Prototype.

This paper describes the design and testing of a compact, battery-powered repetitive Transcranial Magnetic Stimulation (rTMS) prototype. This device generates a 10 Hz magnetic pulse train with peak flux density of 100 mT at 2 cm distance. Circuit component design, including the inductor, switched LC resonator, and boost converter, are discussed in the context of weight and size reduction, and performance optimization. The experimental approach and rationale together with acquired results validating the rTMS prototype design are presented. To the best of our knowledge, this is the first comprehensive feasibility demonstration of an inexpensive, lightweight, and portable rTMS device able to generate therapeutic levels of current, pulse rise time, and number of pulses. The generated magnetic field was kept to 0.1 Tesla for safety and testing considerations, but nevertheless was very close to therapeutic intensity, with driving circuitry scalable to support much stronger fields.Clinical Relevance- This feasibility study of a compact, battery-powered rTMS prototype test platform aims to enable broader and more convenient rTMS treatment at home, in a small clinic, vessel, or field hospital, and potentially, on an ambulatory basis.

A reusable microfluidic plate with alternate-choice architecture for assessing growth preference in tissue culture.

We present the design of a chamber to evaluate in vitro how species and concentrations of soluble molecules control features of cell growth-potentially including cell proliferation, cell motility, process extension, and process termination. We have created a reusable cell culture plate that integrates a microfluidic media delivery network with standard cell culture environment. The microfluidic network delivers a stream of cell culture media with a step-like concentration gradient down a 50-100 microm wide microchannel called the presentation region. Migrating cells or growing cell processes freely choose between the two distinct chemical environments in the presentation region, but they are forced to exclusively choose either one environment or the other when they grow past a physical barrier acting as a decision point. Our fabrication technique requires little specialized equipment, and can be carried out in approximately 4 days per plate. We demonstrate the effectiveness of our plates as neurites from spiral ganglion explants preferentially grow in media containing neurotrophin-3 (NT-3) as opposed to media without NT-3. Our design could be used without modification to study dissociated cell responses to soluble growth cues, and for behavioral screening of small motile organisms.