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Abstract:
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The electrical stimulation of the motor cortex generates neural impulses propagating along the motor pathways. When these impulses arrive to the target muscle, a muscle contraction results and the electrical activity of the muscle can be recorded. Intraoperative monitoring of these motor evoked potentials (MEPs) provides the virtually immediate and more accurate knowledge of spinal motor conduction. By proper practice of this monitoring principle, the risk of postoperative motor deficit is reduced. The purpose of this study was to design and construct a transcranial electrical stimulator capable of producing required electrical stimulation for monitoring MEPs during surgery. At first, it was assumed that MEPs could not be measured during surgical operations because of the diminishing effect of anesthetics on motor responses. To overcome this effect the stimulator must be able to produce fast pulse on motor resonses. To overcome this effect the stimulator must be able to produce fast pulse trains. It was essential that the stimulator meet relevant national safety standards. The specifications of the device were determined by thorough investigation of the theoretical and technical data available about the transcranial electrical stimulation method. The microcontoller- based operation of the stimulator system was found out to be an ideal solution. The construction and testing of the system was performed by using a self-made evaluation board. As being designed for production, the stimulator is compact and has additional features not yet been provided by other stimulators. The waveforms of the stimulus pulses are close to ideal. In addition, the built error detection system and utilization of the isolation transformers were found to increase the safety of operation. The programmable transcranial electrical stimulator can aid the utilization of the MEP minitoring in operating theatres in the future. /Kir10 |