Abstract The purpose of this proposal to demonstrate the feasibility of building a practical shim sub-system based on a minimally interacting in-bore shim coil using a highly controllable power array for use in commercial MRI scanners for multi-band neuroimaging and spectroscopy applications at high fields. Over the past several years, the importance of improved B0 shimming for echo planar imaging (EPI) has been recognized by several groups. Technical developments have focused on ways of providing higher spatial frequency corrections and higher strength of local B0 corrections. Two methods of accomplishing those goals were applied: 1) multi-coil (MC) arrays frequently utilizing DC-coupled RF coils or 2) very-high order shim (VHOS) inserts based on spherical harmonic (SH) symmetries. Also, for the human brain, optimizing the B0 shim corrections on a slice-by-slice (SBS) basis was demonstrated to significantly improve homogeneity. Because of this, several groups have developed dynamic updating approaches, including strategies to mitigate artifacts due to eddy-current effects associated with dynamic shim updating (DSU). It has been demonstrated that the use of VHOS inserts based on 4th order SH can provide superior shim performance to sparse MC arrays for both static and dynamic shimming. It has also been demonstrated that theoretically and experimentally VHOS inserts can achieve MB=2 with equivalent homogeneity to SBS with significant gains over whole brain shimming maintained up to MB=4. Thus, a new VHOS insert technology capable of distinct corrections at up to 3 or 4 spatially disparate slice locations simultaneously with equivalent performance to SBS shimming enabled by DSU technology will greatly improve performance of MB EPI and other sensitive techniques. To achieve the goal of up to MB=4 we will leverage our recent work on second generation 7T scanners. The goal of this Phase I proposal is to demonstrate an optimized prototype of easily installable digitally controlled, real-time multiband shimming system for Siemens Terra 7T implementation with commercialization in Phase II.

Project Narrative Modern magnetic resonance imaging (MRI) techniques such as: functional magnetic resonance imaging (fMRI), white matter connectivity (tractography), susceptibility weighted imaging, CEST, and magnetic resonance spectroscopic imaging (MRSI) can benefit from accelerated data acquisition rates, parallel multi-band (MB) techniques and decreased distortion. Even the best shimming algorithms are subject to hardware limitations due to insufficient spatial frequency coverage, lack of strength and inability to perform dynamic shimming MB operations. In this work we are describing an agile, strong, true harmonic, very high order shim (VHOS) capable of generating a 4th order spherical harmonic shim (SH) that in combination with real-time, dynamic, techniques that can be used for acceleration of data acquisition rates through optimized MB shimming resulting in image quality improvements.