On 5 April 2019 Post Doctoral Researcher Jason Stockmann is giving a Global Excellence lecture entitled "Beyond B0 shimming: New Applications of Local B0 Field Control Using Multi-Coil Arrays".
B0 inhomogeneity arising from air-tissue interfaces remains an obstacle to MRI brain imaging, especially at ultra high field. Multi-coil B0 shim arrays provide an alternative or supplement to higher-order spherical harmonic shim insert coils for nulling high-spatial order B0 offsets in the brain. Multi-coil (MC) arrays are particularly well-suited to dynamically-switched shim updating due to their low inductance and minimal induced eddy currents in the bore, making them useful for slice-optimal distortion-correction in echo planar imaging (EPI). But recent work suggests that the utility of MC arrays goes well beyond conventional B0 shimming. In this abstract, we exploit the rapid switchability of MC arrays to perform local field control that improves data quality for two example applications in the brain: (1) improved lipid suppression in MR spectroscopy and (2) selective excitation for “zoomed” high-resolution single-shot EPI. In both cases, the B0 field offset generated by the MC array is switched to a new, optimized setting for each module of the pulse sequence (e.g., lipid suppression pulse, excitation pulse, spatial encoding, etc.) demonstrating the versatility of the MC approach. The work was previously shown in abstract form [Arango N, ISMRM2018 and Stockmann JP, ISMRM 2018].
We will also discuss practical issues involved in building MC shim arrays and driving them with stable currents inside the MRI scanner. We will show one example MC shim array design in which the same set of conductive loops is used both to receive RF signals and to carry B0shim currents. Using this 32-channel “AC/DC” coil design, we achieve an approximately 50% reduction in B0 inhomogeneity in slice-optimized shimming at both 3T and 7T, along with a proportional reduction in EPI geometric distortion, without introducing image artifacts.
Jason Stockmann is an Instructor and Researcher at The Athinoula A. Martinos Center for Biomedical Imaging at Massachusetts General Hospital which is one of the world’s premier research centers devoted to development and application of advanced biomedical imaging technologies.
The Global Excellence Lecture will be held in the MR Conference Room on 5 April 2019 at 9:00 o'clock.
