title: Sample-specific diamagnetic and paramagnetic passive shimming.
abstract: When homogenizing the static magnetic field over extended in vivo volumes, significant residual inhomogeneity can remain after spherical harmonic shim optimization. This is due to the low spatial orders of shims available on in vivo MR systems and the presence of higher-order inhomogeneity in the vicinity of anatomic air cavities. Mediation of this problem through the development of higher-order spherical harmonic shims is severely impeded by bore space limitations. Sample-specific passive shims are not limited to low-order spatial compensation and offer an alternative means to increased homogenization. Here, we present a novel construction protocol for sample-specific passive shims comprised of both diamagnetic (bismuth) and paramagnetic (zirconium) materials. A prototype shim is constructed and shown to significantly homogenize the mouse brain at 9.4 T. Further homogenization capabilities are simulated through alteration of the shim construction.
authors.affiliation: Magnetic Resonance Research Center, Yale University, New Haven, CT, USA. kevin.koch@yale.edu
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Koch
authors.forename: Peter B
authors.initials: PB
authors.lastname: Brown
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Rothman
authors.forename: Robin A
authors.initials: RA
authors.lastname: de Graaf
mesh_terms: D000818:Animals; D001729:Bismuth; D001931:Brain Mapping / Q000295:instrumentation*; D002138:Calibration; D004867:Equipment Design; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D051379:Mice; D008810:Mice, Inbred C57BL; D015040:Zirconium
chemical_list: D015040:Zirconium; D001729:Bismuth