Measurement and Pre-Emphasis of Shim Responses Using Frequency Sweeps

Signe Johanna Vannesjo¹, Benjamin Dietrich¹, Christoph Barmet¹, Bertram J. Wilm¹, David O. Brunner¹, Klaas P. Pruessmann¹

Dynamic use of higher-order shims to improve static B0, puts increasing demands on characterization of shim field dynamics and requires pre-emphasis implementations to counteract eddy current effects. Measurements of the shim impulse response function (SIRF), using a dynamic field camera, and rectangular test functions, have previously been shown to provide detailed information on shim responses. Here, frequency-sweeped test pulses are implemented for wide bandwidth coverage and increased sensitivity of the SIRF measurements. It is shown that SIRFs thus measured could form a basis for digital pre-emphasis, enabling a flat frequency response and fast shim settling after a switching event.