Towards the Development of Phased Array Systems for Deep Brain Stimulation Virgilio Valente and Andreas Demosthenous Department of Electronic Engineering University College of London London, WC1E 7JE, United Kingdom Email: v.valente@ee.ucl.ac.uk Richard Bayford Department of Natural Sciences Middlesex University Middlesex, EN3 4SF, United Kingdom Abstract—Deep brain stimulation (DBS) is a clinical technique adopted for the treatment of various neurological disorders. One major limitation of today’s DBS systems is the inability to focus the electric field in the desired direction and provide a more efficient stimulation. This study adopted 2D and 3D FEM tools to explore the the application of phased array (PA) techniques to control the direction of the stimulation pattern delivered during DBS. Results illustrate that a PA DBS system can be used to steer the stimulation pattern from broadside to endfire, by driving the electrode contacts with high frequency sinusoids with phase delays varying from 0 ◦ to 90 ◦ . This study can provide a framework for future investigation in the development of more efficient DBS systems based on PA technology. I. I NTRODUCTION Deep brain stimulation (DBS) is a clinical tool used to treat various neurological disorders, including chronic pain, incontinence and movement disorders. Today’s routine use of such therapy comes from promising results obtained by the pilot study of Benabid and colleagues [1], who assessed the benefits of applying high-frequency stimulation to the ventral intermediate nucleus. Substantial long-term improve- ments were reported on several cases of patients affected by Parkinson’s disease, essential tremor and other movement disorders. The therapeutic effectiveness of DBS has lead to its adoption as standard treatment for movement disorders. Clinical applications, however, have preceded research and left researchers with a number of challenges to optimize this therapeutic technique in terms of quality, minimization of costs and understanding of its underlying mechanisms [2]. One of the major challenges reported in several studies consists of determining the electric field and volume of tissue activated (VTA) by stimulation, which is strictly related to the clinical benefit of DBS and its potential side effects [3]. Due to the inability of measuring the VTA during therapeutic stimula- tions, researches have attempted to quantitatively characterize the VTA by the adoption of two- and three-dimensional repre- sentations of the DBS electrodes and the anatomical structure of the stimulation target including the neural response to DBS [3]–[8]. These studies have highlighted the limited control over the effects of stimulation and, in particular, over the shape and direction of the electric field propagating around the electrode. These issues suggest the need for a system which allows control of the direction, shape and intensity of the electric field To achieve this, we propose the use of stimulation based on phased arrays (PAs). So far application of PAs to stimulation of human tissue has not been extensively investigated. Abbas and colleagues [9] have presented a preliminary study of using PA stimulation to control cardiac activation wavefronts and their work shows promising results for the application of PAs to control deep brain stimulation. This study represents a first investigation on the applicability of PA systems to DBS. Computational models were adopted to simulate the behavior of the electric field generated by an electrode, driven as a PA. These models aim at exploring the ability of current DBS systems to drive phased array stimulation (PAS) and investigate the major problems related to this. II. METHODS This study aims at evaluating the use of PA for DBS. In order to do so we have analyzed the main properties of PAs and developed 2D and 3D finite element models (FEM) of PA DBS electrodes, with the aid of a FEM commercial package (Comsol, Sweden) to simulate the steering of the electric field around the stimulating electrode. The models adopted the structure of a commercially available DBS electrode (3389 Model, Medtronic, USA) used for clinical DBS. A. Phased Arrays (PAs) PAs consist of multiple antenna elements which use variable phase or time-delay control at each element to scan the radiation beam to a desired angle. A particular geometrical arrangement of the array elements results in the radiation from each element adding up in a particular direction. The radiated electric field, E(R 0 , ϑ, φ), at a point Q(R 0 , ϑ, φ) of an antenna array consisting of N elements is the sum of the contributions of the electric fields radiated from each element: E(R 0 , ϑ, φ)= f e (ϑ, φ)  e -jkR0 R 0  N  i=1 [A i e jikdcosϑ ] (1) where f e (θ,φ) is the pattern generated by a single ele- ment, e -jkR0 /R 0 represents the spherical propagation factor, e jikdcosθ indicates the phase of the propagation factor of each element, described but the wavenumber k =2π/λ, where 978-1-4244-2879-3/08/$25.00 ©2008 IEEE 261