Dynamic Multi-Coil B0 Shimming for Diagnostic MRI of Frontal Brain

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PROJECT SUMMARY Fast gradient-echo MRI is the preferred method to visualize iron deposition in human brain tissue with susceptibility-weighted imaging (SWI), to map functional activity with echo-planar imaging (EPI) and to assess cranial nerve disorders with steady-state free precession (SSFP) MRI. However, its high susceptibility towards B0 magnetic field inhomogeneity poses serious challenges. Particularly strong and localized B0 deviations are observed above the sinus cavities in the prefrontal cortex (PFC), a brain area involved in many higher order cognitive functions, and the orbits comprising, among others, eyes and cranial nerves. Spatial image deformation and signal dropout induced by inhomogeneous B0 conditions can severely limit gradient-echo MRI quality and even render results useless, thereby fundamentally limiting its diagnostic potential. We have recently made major advances in the ability to obtain high levels of B0 homogeneity throughout the brain, including difficult-to-shim areas such as the PFC using a novel multi-coil hardware in combination with rapid B0 optimization methods and dynamic shimming. B0 shimming with this Dynamic Multi-Coil Technique (DYNAMITE) provides dramatically better B0 homogeneity than standard methods and in the future should close to completely eliminate B0 inhomogeneity as a problem. Our objective in this proposal is to combine DYNAMITE B0 shim with clinical RF technology to establish the first integrated multi-coil B0 and radio- frequency (MC/RF) setup dedicated to clinical diagnostics and workflow. Specific Aim 1: Electromagnetic field (EMF) simulations will be used to compare and optimize the potential of generating DYNAMITE B0 shim fields with a dedicated multi-coil B0 setup separate from the employed RF coil, by driving elements of an RF phased array with DC currents or a combination thereof in a hybrid approach, considering electromagnetic coupling and safety. Specific Aim 2: Computer-aided design (CAD) methods comprising electromagnetic, thermal and mechanical modeling will be used to realize the optimized MC/RF constellation for a clinical 3T MR scanner environment, providing diagnostic MRI capability in an efficient, reliable and safe fashion. Moreover, DYNAMITE B0 shimming tailored to routine clinical MRI protocols is expected to improve the overall image quality throughout the human brain compared to conventional spherical harmonic-based B0 shim technology. Specific Aim 3: DYNAMITE B0 shimming will be applied to diagnostic imaging of optic nerve diseases as part of routine protocols and workflow in a fully automated fashion transparent to the medical staff to test the hypothesis of enhanced diagnostic potential and a true clinical benefit due to MRI artifact mitigation. The approach is innovative because the best available B0 shimming and RF technologies are combined to provide unprecedented clinical MRI capabilities. The research is significant because it is expected to fundamentally leverage the diagnostic potential of gradient-echo MRI in the ventral PFC and orbits, setting the stage for widespread clinical use of state-of-the-art B0 shim technology and true translation from bench to bedside.