CHAPTER 4: B₀ Shimming Technology

A homogeneous B₀ magnetic field is a critical requirement for the majority of MR studies, as inhomogeneities lead to signal loss and compromised data. The process by which the magnetic field is homogenized on a subject- or sample-specific basis is termed B₀ shimming. This chapter gives an overview of shimming-related concepts and technology. Following a description of the origins of magnetic field inhomogeneity, the theory and practical implementation of spherical harmonic (SH) based shimming are presented. Extensions to dynamic shimming for MRI applications are discussed in detail. Finally, a number of non-SH-based multi-coil shimming approaches are introduced. The focus of this chapter is on the practical aspects of subject-specific in vivo shimming, with an emphasis on human brain applications.