LOW-COST WIRELESS TELEMETRY SYSTEM FOR DEEP BRAIN STIMULATION

Transcription

1 LOW-COST WIRELESS TELEMETRY SYSTEM FOR DEEP BRAIN STIMULATION MILNER VITHAYATHIL 1, PAULSON MEKKATTIL 2, BINOY VELLIYATH 3, JARIN T 4* 1 Research Scholar, Department of Electronics and Communication, NIT, Manipur, India. 2 Student, Department of Electrical and Electronics Engineering, Jyothi Engineering College, Thrissur, India. 3 Technology Lead, Atoll Solution, Bangalore, India. 4 Associate Professor, Department of Electrical and Electronics Engineering, Jyothi Engineering College, Thrissur, India. 1 vithayathilmilner@nitmanipur.ac.in, 2 paulsonmekkattil@gmail.com 3 binoy.j@atollsolutions.com, 4 jarint@jecc.ac.in Abstract: In this paper, a constant current stimulator is developed for Deep Brain Stimulation studies based on Brain- Computer Interface System. The system can deliver the precise amount of current pulse, and the feedback path ensures the system is reliable. The system has a size of 25mm* 35mm and weight of 8.5 grams including the battery which is a perfect suite in animal models. The main feature of this system is a low powered processor, long life of two months, low cost, precision and the compact size. In vitro results proved that the system is ready to use in animal models. Keywords: Deep Brain Stimulation, Current, Pulses, Intracranial Self Stimulation 1. INTRODUCTION Deep Brain Stimulation (DBS) is becoming a promising solution for treating Neuropsychological disorders. In many countries, this treatment is an approved and useful therapy for many patients. As the technology acquires a prominent space in our daily life, there is a new perspective to look into this treatment. Brain-Computer Interface is such a type of approach that makes to explore these fields. One of the applications of this technology is in the area of DBS. Studying the animal model using DBS is the most important factor since it is intended to apply in human models [1] DBS has a history of more than 50 years. So it took a long way to emerge as present [2]. An old way of DBS was using cable connections between the equipment and the subject. There were a lot of issues using cables connections about cable entanglement and breaking of the cables [3]. As a solution to all these, different types of wireless stimulators were introduced. There were many drawbacks related to size, precision, software and lifetime for these wireless stimulators. Though stimulators are available commercially, they are all expensive in nature and so customers are not interested to have this product [4]. In the view of all these factors, we are developing and modelling a new stimulator system that overcomes the limitation of size, weight, precision and lifetime. 2. METHOD The new wireless stimulator consists of a base station, system and backpack. Here the system can be either a computer or a mobile. This system will be serving as the main controller to the base station and the backpack. 697

2 2.1 Backpack The backpack contains a microprocessor, constant current circuit, battery and output leads. The microprocessor that we are using here is NRF51822 that provides low power and high precision with low voltage [5]. The microprocessor is inbuilt with Bluetooth, so the processor doesn't need to add an extra circuit to the system. It also contains a feedback path, for making the device precise in delivering the stimulation. A constant current circuit is developed using an instrumental amplifier, voltage follower and a resistor. The whole backpack system will be providing programmable current stimuli. Constant current circuit ensures the accuracy of the system. The entire size of the backpack is 25*35 millimetres and it weighs just 8.4 gram. The supply current source for the backpack ranges from volt. We are using CR2050 coin-sized battery in this system. This will be enough to run a stimulator for a period of 2-3 months. Figure 1. The transmitter and Receiver Design Figure 2. External Dimension 698

3 2.2 Base Station Base Station is powered by Bluebee Design. Base Station and system are connected via USB cable. Base Station acts as a transmitter and Backpack will be the receiver. Here the command received from the system is stored in Base Station. The transmitter will send the signal to the Receiver via Bluetooth for the further communication. 2.3 Software The control system on PC is written in C language. The program in Backpack unit is written in KEIL platform. Here the software can control Pulse Amplitude, Pulse Interval, No. of Pulses in a single trigger. The user can change the parameters without complication if needed. For the communication between the base station and backpack, we are using Hercules software installed in the system. The command for the communication is generated from this software. Figure. 3 Programming Unit 2.4 Waveform In this paper, the system is delivering a biphasic waveform from the base station. This controlled waveform can be further controlled by adding a digital resistor in series. Biphasic waves safeguard the tissues and cause less damage to electrodes [6]. 2.5 Cost Factor Here we are giving the complete cost estimation of the components of Stimulator unit. As we mentioned, stimulators commercially available now are highly expensive and they all lack appropriate technology to work efficiently. Table 1. Cost Estimation in US Dollar (US $) Quantity Reference Part Unit Price One board Cost 1 C5(capacitor) 120PF/16V C6,C9(capacitor) 0.1uF

4 2 C7,C8(capacitor) 12pF/16V C10,C11,C12,C13(capacitor) 1uF C14,C15(capacitor) 10uF D1(Surface Mount Device) SMLP36RGB1W J1,J4(connectors) CON J2,J3 (connectors) CON J5,J6 (connectors) CON L2(Inductor) 10uH L3(Inductor) 15nH L4(Inductor) EPL MLB Q1,Q2,Q3(MOSFET) 2N R3(Resistor) 0R/DNP R4,R5(Resistor) 100K R6(Resistor) 4K R7,R8,R9,R15,R16,R17(Resistor) 2.2K R10,R11,R12,R13,R14(Resistor) 10K R56(Resistor) 1M R57(Resistor) 178K SW1(switch) B3U-1000P U2(processor) MDBT42( NRF52 Module) U5(Switching Regulator) TPS61220DCKR Y1(crystal oscillator) ECS B PCB Assembly TOTAL RESULTS 3.1 In Vitro For checking the feasibility of the stimulator, we have immersed the electrode in 10% NaCl solution (Fluri et al. 2017). The output of the stimulator was connected to the electrode. To check the reading, we connected the probes to the oscilloscope and read the measurements to ensure that threshold value 250 ua current is been delivered by the stimulator within the frequency range of ( ) Hz. Output of the stimulator is as shown in the figure

5 Figure 4. Monopolar Output 4. DISCUSSION AND CONCLUSIONS The threshold values for the DBS system were successfully delivered from our device. A constant current stimulator for DBS treatment is proposed and successfully tested in this work. Using these all components, we can develop a smart efficient stimulator which can trigger highly accurate current pulses. This current stimulator can be further improved by introducing power harvest system. Once this system is developed, we can design the whole system using ASIC model. The waveform can also be enhanced using filter designs We have tested the device in different frequency by changing the period and in different pulse amplitudes. Since there are many research works going on in animal model using DBS, this device will be an effective solution for the problems of size limitation, weight, precision and lifetime in DBS experiments. REFERENCES [1] Acosta AI, Noor MS, Kiss ZHT and Murari K, A lightweight discrete biphasic current stimulator for rodent deep brain stimulation, Proceedings of the IEEE Biomedical Circuits and Systems Conference (BioCAS), Atlanta, USA (2015) October [2] Nowak K, Mix E, Gimsa J, Strauss U, Sriperumbudur KK, Benecke R and Gimsa U, Optimizing a rodent model of Parkinson's disease for exploring the effects and mechanisms of deep brain stimulation. Parkinsons Dis., (2011) doi: /2011/ [3] Fluri F, Mützel T, Schuhmann MK, Krstić M, Endres H, and Volkmann J, Development of a head-mounted wireless microstimulator for deep brain stimulation in rats. J Neurosci Methods, vol. 291, (2017), pp doi: /j.jneumeth [4] Haas R de, Struikmans R, van der Plasse G, van Kerkhof L, Brakkee JH, Kas MJH, and Westenberg HGM., Wireless implantable micro-stimulation device for high frequency bilateral deep brain stimulation in freely moving 701

6 mice. J Neurosci Methods., vol. 209, (2012) pp doi: /j.jneumeth [5] Nordic Semiconductor nrf (2014) [6] Merrill DR, Bikson M, and Jefferys JGR Electrical stimulation of excitable tissue: design of efficacious and safe protocols. J Neurosci Methods. Vol. 141, (2012), pp doi: /j.jneumeth