MRI Gradient Coils with Improved Stimulation Threshold

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DESCRIPTION (provided by applicant): With currently available high-power gradient amplifiers, magnetic resonance imaging (MRI) studies requiring strong, rapidly switched gradient fields are limited in speed, resolution, or accuracy due to the induction of PNS. They propose to develop, apply, and verify an accurate and efficient method for gradient coil design with consideration of peripheral nerve stimulation (PNS): SPECIFIC AIM 1: Develop fast and accurate 3 dimensional (3D) numerical method to calculate the electric fields induced in weakly conductive dielectric samples during the operation of pulsed magnetic coils. This will be accomplished by: 1. measurement of the electrical fields induced in simple liquid phantoms by magnetic coils to serve as a gold standard, 2. evaluation of existing and proposed numerical methods by comparison to gold standard experimental measurements. SPECIFIC AIM 2: Establish a calibration of calculated fields to PNS thresholds. This will be accomplished by: 1. measurement of stimulation thresholds and locations in human subjects exposed to existing high strength head gradient coils and, 2. calculation of electrical fields in a realistic multi-tissue human model in the head gradient coil and identification of electrical field values in locations of stimulation corresponding to the measured PNS thresholds. SPECIFIC AIM 3: Use calibrated numerical calculations to design a prototype head gradient coil with improved PNS threshold and verify performance in human subjects. This will be accomplished by: 1. calculation of PNS thresholds for variations of several candidate gradient coil designs and using optimization routine to identify optimal design, 2. construction of a prototype of the optimal coil, 3. verification of improved PNS thresholds of human volunteers in the prototype coil. Accomplishment of these aims will require significant engineering of the interaction between magnetic fields and the human body. In line with the program announcement, this proposal will produce instruments (gradient coils), techniques (coil design methods), and software (field calculation and coil design algorithms) toward more powerful and more precise technology for biomedical research. This work will lay the foundation for development of clinically useful head and body gradient coils that can outperform existing coils before inducing PNS.