Prospective B0 correction

Body motion causes changes in the B0 magnetic field, even when that motion occurs outside of the imaged field of view. Changes in the field can be caused both inside and outside the object of interest. For example, the B0 field in the head changes after moving the head, but also changes due to breathing or motion of an arm. This chapter describes the origin of B0 field changes, and methods to both measure and compensate for the effects caused by dynamic B0 field changes. The chapter focuses on prospective techniques, where the goal is to keep the B0 field stable during scanning to prevent image artifacts. Sequences are discussed that are sensitive to frequency offsets in either signal readout or RF encoding, and where prospective correction can provide a solution to improve data quality.