Bio-Effects of Ultra-High MRI Gradient Slew Rates

DESCRIPTION (provided by applicant): The spatial resolution and acquisition times for magnetic resonance imaging and spectroscopy could be improved through the application of more powerful and rapid magnetic gradients, thereby potentially leading to improv ed cardiac imaging and delineation and detection of cancers. Unfortunately, gradient field strength is limited by concerns about potential neural and cardiac stimulation bio-effects and effectively by existing technology that currently does not provide fas ter slew rates. The overall goal of this project is to advance MRI technology by improving the performance of critical electronic subsystems that deliver magnetic gradient fields comprising what is known as the gradients (i.e., magnetic gradient amplifie rs, and associated gradient coils). These devices are used for the encoding of spatial coordinates during magnetic resonance imaging experiments. The gradients are also used for encoding numerous other parameters such as diffusion. One of the most visibl e characteristics of magnetic gradient subsystems is the magnetic field rise-time (also known as slew rate ). For example, Siemens recently boasted of a 400 Tesla per meter per second (400 T/m/s) slew rate, countering a Toshiba America claim of the faste st slew rate in the market with 100 T/m/s. The slew rate of the current generation of gradient field systems is limited by safety regulations concerned with potential neural stimulation bio-effects. Based on published theoretical studies on neural physiol ogy, we hypothesize that it is possible to increase slew rates without causing untoward bio-effects, by dramatically reducing rise- and fall-time durations. The proposed improvement in gradient-field transitions will be effected with novel pulsed- power te chnology that has not been previously applied to medical applications. Faster slew rates would afford faster imaging encoding times that could be useful in functional imaging and diffusion imaging as well as overall imaging speed time gains (i.e. faster mu lti-voxel magnetic resonance spectroscopy). Especially in the area of multi-parametric MRI studies, imaging times on patients can far exceed one hour. Faster slew rate gradients can reduce this time and or allow for more information gathering in the same t ime window. Phase I of the project will focus on construction of an electrical test-bed capable of producing ultra-fast magnetic field gradients, with phantom testing and proof-of-principle experiments using an invertebrate animal model. Follow-on phases w ill examine bio- effects in vertebrate animals and human volunteers. Commercialization strategies will include partnering with a coil manufacturer to customize gradient coils, and the incorporation of the technology in a novel PET/MRI device built in conju nction with a commercial strategic partner. Public Health Relevance The overall goal of this project is to advance MRI technology by improving the performance of critical subsystems that deliver magnetic gradient fields (i.e., magnetic gradient amplifiers, and associated gradient coils). One of the most visible characteristics of magnetic gradient subsystems is the magnetic field rise-time (also known as slew rate ). The slew rate of the current generation of gradient field systems is limited by safety reg ulations concerned with potential neural stimulation bio-effects. Based on published theoretical studies on neural physiology, we hypothesize that it is possible to increase slew rates without causing untoward bio-effects, by dramatically reducing rise- an d fall-time durations. The proposed improvement in gradient-field transitions will be effected with novel pulsed-power technology that has not been previously applied to medical applications. The project is expected to result in improvements for MRI safety , cardiac imaging, and cancer diagnosis.