This paper presents a study on the influence of strong magnetic field on NMOS transistors' electrical characteristics. Experiments have been carried out in a small animal 7T MRI scanner, and have shown that up to 7T the influence exists but remains manageable. It is demonstrated that it depends on the transistor size, on the orientation of the chip inside the field, and on the VGS voltage. A theoretical analysis in good agreement with experiments has been developed. Extrapolation to ultra-high field, i.e. above 10T, shows that at such a field magnitude the influence may be challenging, asking for specific design techniques to devise in order to make the circuit immune to the strong magnetic field.
Deep brain stimulation (DBS) is an established therapy for movement disorders such as essential tremor (ET). Positioning of the DBS lead in the patient's brain is crucial for effective treatment. Extensive evaluations of improvement and adverse effects of stimulation at different positions for various current amplitudes are performed intraoperatively. However, to choose the optimal position of the lead, the information has to be "mentally" visualized and analyzed. This paper introduces a new technique called "stimulation maps," which summarizes and visualizes the high amount of relevant data with the aim to assist in identifying the optimal DBS lead position. It combines three methods: outlines of the relevant anatomical structures, quantitative symptom evaluation, and patient-specific electric field simulations. Through this combination, each voxel in the stimulation region is assigned one value of symptom improvement, resulting in the division of stimulation region into areas with different improvement levels. This technique was applied retrospectively to five ET patients in the University Hospital in Clermont-Ferrand, France. Apart from identifying the optimal implant position, the resultant nine maps show that the highest improvement region is frequently in the posterior subthalamic area. The results demonstrate the utility of the stimulation maps in identifying the optimal implant position.
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