Deep Brain Stimulator
The Deep Brain Stimulation (DBS) therapy involves implantation of small electrodes in deep brain structures, connected to a pulse generator, which is so bulky that it should to be implanted in the upper chest wall and wired subcutaneously to the electrode contacts emerging from the top of the head. According to several studies the subcutaneous extension wires and their connectors are a source of morbidity for patients and the primary cause of mechanical failure in DBS implants.
The main objective of this research is to develop a significantly smaller, more efficient, integrated microstimulator that can be practically attached to the head at the point of electrode entry to the brain. Existing DBS circuits can only control the pulse width, frequency, and either voltage or current amplitude. Voltage-controlled stimulation (VCS) provides greater power-efficiency but it can only be used when the electrodenand tissue impedances are well known. Current-controlled stimulation (CCS) is safer and provides more control over the stimulus parameters, but it consumes more power. Today’s DBS implants, which have inherited the heart pacemaker technology, are VCS-based and manufacturers have to indicate the safety limits by providing tables in terms of the electrode/tissue impedance, pulse width, and pulse amplitude.
DBS Prototype Board: This wirelessly controlled DBS prototype can generate three types of stimulus pulses based on VCS, CCS, and SCS stimulation strategies. This system can accurately measure the amount of charge injected into the tissue.
We have designed novel switched-capacitor based stimulation (SCS) circuitry that directly controls the amount of injected charge into the neural tissue. This is accomplished by generating charge-controlled, exponentially decaying bursts of stimulus pulses. The SCS circuit combines the power efficiency of the VCS circuits with the safety and stimulation parameter controllability of the CCS circuits. This innovative technique is expected to substantially simplify the pulse generator architecture and reduce its size and power requirements.
As part of this research we use Finite Element Analysis (FEA) to explore the impact of microstimulating arrays on biological tissue and distribution of current as a function of electrodes geometry, configuration, and stimulus waveforms. Techniques to determine the electric field, potential, current densities, and heat distributions are used to determine the feasibility and efficacy of an electrode design. Using these 3-Dimensional models, alternative layouts and electrode designs can be evaluated prior to prototyping. Further, these models can be applied to several different types of electrodes including cortical, cochlear, and retinal in addition to deep-brain stimulating electrodes.
- J. Simpson and M. Ghovanloo, “An experimental study of voltage, current, and charge controlled stimulation front-end circuitry,” Proc. IEEE Intl. Symp. on Circuits and Systems, pp. 325-328, May 2007.
- M. Ghovanloo, “Switched-capacitor based implantable low-power wireless microstimulating systems,” IEEE Intl. Symp. on Circuits and Systems, pp. 2197-2200, May 2006.
- R.M. Field and M. Ghovanloo, “Finite element analysis of planar micromachined silicon electrodes for cortical stimulation,” IEEE-EMBS Special Topic Conf. on Microtechnologies in Med. and Biol., pp. 297-300, May 2006.