B0 Shimming: Coils and Methods
Jason Stockmann1
1Martinos Center for Biomedical Imaging, United States
1Martinos Center for Biomedical Imaging, United States
Synopsis
Keywords: Physics & Engineering: Hardware, Physics & Engineering: Physics
We describe how tissue susceptibility interfaces disturb the main B0 magnetic field inside the scanner bore, causing a wide variety of artifacts in MR acquisitions. We review field mapping approaches for measuring these ΔB0 field deviations, along with factors influencing field map accuracy and precision. Hardware for nulling the unwanted ΔB0 fields is then covered, including both passive shim inserts and active shim coils. We show how to simulate B0 shim performance for specific shim coils as well as for the "ultimate shim" using optimized coils. Last, we highlight open-source resources including shim optimization software and published coil wire patterns.
Acknowledgements
No acknowledgement found.References
No reference found.Figures
Example shim hardware. (a) Pyrolytic graphite intra-oral shims. (b) Subject-specific array of diamagnetic and paramagnetic material. (c) 18-channel higher-order spherical harmonic shim insert coil with RF coil nested inside. (d) Intra-oral multi-turn shim loops. (e) Six shim loops over the face targeting frontal lobes. (f) Generic “multi-coil” shim array of 48 loops on cylinder nested inside RF coil. (g) 16-ch array of shim loops placed outside transmit coil shield. (h) Integrated RF/B0 shim arrays in which RF receive loops are modified to add B0 shim current-carrying capability.