title: Multicoil shimming of the mouse brain.
abstract: MR imaging and spectroscopy allow the noninvasive measurement of brain function and physiology, but excellent magnetic field homogeneity is required for meaningful results. The homogenization of the magnetic field distribution in the mouse brain (i.e., shimming) is a difficult task due to complex susceptibility-induced field distortions combined with the small size of the object. To date, the achievement of satisfactory whole brain shimming in the mouse remains a major challenge. The magnetic fields generated by a set of 48 circular coils (diameter 13 mm) that were arranged in a cylinder-shaped pattern of 32 mm diameter and driven with individual dynamic current ranges of ±1 A are shown to be capable of substantially reducing the field distortions encountered in the mouse brain at 9.4 Tesla. Static multicoil shim fields allowed the reduction of the standard deviation of Larmor frequencies by 31% compared to second order spherical harmonics shimming and a 66% narrowing was achieved with the slice-specific application of the multicoil shimming with a dynamic approach. For gradient echo imaging, multicoil shimming minimized shim-related signal voids in the brain periphery and allowed overall signal gains of up to 51% compared to spherical harmonics shimming.
authors: Department of Diagnostic Radiology, Yale University School of Medicine, MR Research Center (MRRC), New Haven, Connecticut 06520, USA. christoph.juchem@yale.edu
authors: Christoph
authors: C
authors: Juchem
authors: Peter B
authors: PB
authors: Brown
authors: Terence W
authors: TW
authors: Nixon
authors: Scott
authors: S
authors: McIntyre
authors: Douglas L
authors: DL
authors: Rothman
authors: Robin A
authors: RA
authors: de Graaf
mesh_terms: D000818:Animals; D001931:Brain Mapping / Q000379:methods*; D007089:Image Enhancement / Q000295:instrumentation; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation; D016014:Linear Models; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D051379:Mice; D023421:Models, Animal