Design, construction, and deployment of a multi-locus transcranial magnetic stimulation system for clinical use

Abstract

Background: Transcranial magnetic stimulation (TMS) is an established method for noninvasive brain stimulation, used for investigating and treating brain disorders. Recently, multi-locus TMS (mTMS) has expanded the capabilities of TMS by employing an array of overlapping stimulation coils, enabling delivery of stimulation pulses at different cortical locations without physical coil movement. We aimed to design, construct, and deploy an mTMS device and a five-coil array for clinical environment, emphasizing safety of the system.

Methods: Our mTMS device is controlled by a field-programmable gate array (FPGA). The power electronics comprises five stimulation channels, each consisting of a high-voltage capacitor connected to a pulse circuit, controlling a single coil in the array. The device contains custom-designed circuit boards, with functions such as monitoring the system state, reporting errors, and delivering pulses. Our design utilizes redundancy in both hardware and firmware to ensure robust operation and safety. We performed an automated motor mapping test to verify the electronic targeting capabilities of the device.

Results: We constructed the mTMS device and deployed it to the Hertie Institute for Clinical Brain Research (Tübingen, Germany). Compared to our earlier prototype, the new design improves patient and operator safety. The motor mapping test confirmed that our device can accurately target stimulation pulses in the cortex.

Significance: mTMS or other similar technologies are currently not available for hospital use. The present device and its installation are major steps toward establishing multicoil TMS as an accessible clinical tool for investigation and treatment of the brain.

Keywords: Functional imaging; Motor mapping; Patient safety; Transcranial magnetic stimulation; mTMS.

Fig. 1

Spatial and orientation response graphs for both subjects. Normalized MEP amplitudes as a function of 2-dimensional electronic shifting of the stimulation target before (A) and after (B) moving the coil array. The black and white crosses mark the weighted centroid before and after the movement, respectively. The black arrow indicates the zero angle of the peak electric field. The black line forming a right angle serves as an anatomical reference. A Gaussian spatial filter was applied to the data to remove noise and highlight the areas of maximal response. (C) The orientation-dependent MEP response at the centroid (white cross) after moving the coil array in 30-degree increments

Fig. 2

The components of the system: A mTMS cabinet, B coil array and trackers, C robotic arm, D stereo camera for navigation, E patient chair, F configurable foot pedal, G PC with control software, H data acquisition system, I size scale of 1 m

Fig. 3

A schematic of the mTMS power electronics cabinet. B an individual channel consisting of the electronics required to drive the TMS pulse and the stimulation coil. C Photographs of the device. Left: with front door removed. Middle: after transportation. Right: final installation with coil array connected

Fig. 4

The internal modules of the mTMS device and their connectivity. The modules that contain a microcontroller are marked with a microcontroller symbol. A control unit, B optical conversion, C DC power distribution (blue board), charger interface and safety monitor (green board), high-voltage charger (gray box), D safety bus, E channels, consisting of the pulse capacitors (gray cylinders), discharge controllers (red boards), and H-bridges (dark gray), F door switches, emergency button, and coil connectivity indicator, G sensor interface, H coil-specific memories and sensors. The inset shows local and global heartbeat signals

Fig. 5

The basic operation loop for controlling the mTMS device. A simple experiment consists of charging each channel to the desired voltage and scheduling a simultaneous pulse at a specific time. This sequence is repeated for the duration of the experiment. Control of triggers is omitted for simplicity

Fig. 6

The five-coil array, its parts, winding patterns, and the measured electric field distributions: A coil cable holder, B coil winding plates, C a temperature sensor, D coil winding patterns and their normalized electric field patterns on a spherical surface under the array’s center, E the complete coil array

Fig. 7

Experimental workflow. An experiment is performed by a script executing a loop on the control PC. The dark gray boxes represent flexible code blocks, allowing the user to implement their own algorithms and methods. During the experiment, the mTMS device waits for instructions from the PC while maintaining clock synchronization with the EMG/EEG device