Valente, V.; (2011) Novel methods and circuits for field shaping in deep brain stimulation. Doctoral thesis , UCL (University College London).

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Abstract

Deep Brain Stimulation (DBS) is a clinical tool used to treat various neurological disorders, including tremor, Parkinson’s disease (PD) and dystonia. Today’s routine use of this therapy is a result of the pioneering work of Benabid and colleagues, who assessed the benefits of applying high-frequency stimulation to the ventral intermediate nucleus and reported substantial long-term improvements in PD patients. Clinical applications of DBS, however, have preceded research and left a number of challenges to optimise this therapeutic technique in terms of quality, therapy costs and understanding of its underlying mechanisms. DBS is based on monopolar or bipolar stimulation techniques, which are characterised by a limited control over the effects of stimulation and, in particular, over the shape and direction of the electric field propagating around the electrode. This thesis proposes two approaches to achieve dynamic electric field control during deep brain stimulation. The first method is based on the use of current-steering multipolar electrode drive, adopted to split the stimulation current between 2 or more contacts, in order to shift the stimulation field to a desired location. The work included the design, development and testing of an integrated circuit current-steering tripolar current source, developed in AMS 0.35μm technology. The second method is based on the use of phased arrays (PAs) in order to create an electromagnetic beam, which can be steered to a desired location. Computational models have shown the ability to steer and focus the electromagnetic fields in brain tissue by varying the phase and frequency of stimulation. Modelling simulations have shown that the use of multipolar electrode configurations is essential to achieve dynamic control over the shape and area of tissue stimulated. Configurations with larger number of cathodes allow for several stimulation patterns, making this stimulation approach beneficial in a clinical environment. Tests on the performance of the integrated tripolar current source have shown its capability to generate stimulation currents up to 1.86mA, to linearly steer the stimulation current to one of the anodes and to generate biphasic square and exponential current pulses, with time constant up to 28ms. In vitro experiments, carried out to map the electric potential generated by a dynamic tripolar current source, validated the model results, by showing the ability to shape the potential distribution around the electrode during stimulation. Finally, models of the behaviour of PA fields in brain tissue have shown that PAs could be introduced to DBS to allow for more accurate field steering and shaping in DBS. This thesis presents methods and implementations to achieve dynamic field shaping in DBS, which can greatly ameliorate the efficacy of clinical DBS.

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