Microwave focusing with temporal interference for non-invasive deep brain stimulation

TL;DR

This study demonstrates a proof-of-principle of non-invasive microwave field focusing using iTR and TI in a realistic human head model, demonstrating that amplitude-modulated electromagnetic fields can be selectively and precisely shaped within predefined focal regions.

Abstract

Deep Brain Stimulation (DBS) is effective in treating neurological disorders but involves invasive surgery. Non-invasive DBS aims to overcome surgical risks by means of externally applied electromagnetic fields. In this work, we present a method for non-invasive microwave focusing of amplitude-modulated electric fields in the human brain using an external antenna array. The method combines iterative time-reversal (iTR) and genetic-algorithm-based temporal interference (TI) optimization to determine antenna positions, orientations, operating frequency, amplitudes, and phases of each element. Magnetic point dipoles are used as idealized radiative sources, providing a design-independent benchmark for optimization studies. Furthermore, this work incorporates realistic tissue properties from voxelized anatomical head models, accounting for variations in permittivity and conductivity. The iTR algorithm provides an initial antenna configuration that serves as a reliable starting point for the subsequent TI optimization, improving convergence and focusing precision. The results demonstrate that amplitude-modulated electromagnetic fields can be selectively and precisely shaped within predefined focal regions. Thereby, this study demonstrates a proof-of-principle of non-invasive microwave field focusing using iTR and TI in a realistic human head model.

Figures (14)

• Figure 1: Conceptual illustration of the clinically accepted invasive DBS treatment, with implanted electrodes that deliver electric fields to induce neural stimulation in a target region. The electrodes are connected to a pulse generator via leads.
• Figure 2: Conceptual illustration of the proposed non-invasive DBS treatment, where an external microwave antenna array delivers focused electric fields to induce neural stimulation in a target brain region.
• Figure 3: Conceptual illustration of the TR-based field focusing method. A point source $\bm{p}$ is placed inside the head generating a forward magnetic field $\bm{H}(\boldsymbol{\zeta})$, which is dependent on the optimization parameters in $\boldsymbol{\zeta}$.
• Figure 4: Flowchart showing the implemented iTR optimization.
• Figure 5: Conceptual illustration of TI-based non-invasive DBS. Two high frequency fields, $\bm{E}_{f_1}$ and $\bm{E}_{f_2}$, interfere to produce an amplitude-modulated field $\bm{E}_\mathrm{TI}= \bm{E}_{f_1} + \bm{E}_{f_2}$, resulting in a low-frequency envelope $E_\mathrm{AM}$.