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Abstract #0217

A New Type of Gradient: The Detection Frequency Gradient. a New Capability: Retrospective Shimming

Jonathan C. Sharp1, Scott B. King2, Mike Smith2, Boguslaw Tomanek1

1Institute for Biodiagnostics (West), National Research Council of Canada, Calgary, Alberta, Canada; 2Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada

We introduce a new type of field gradient: the Detection Frequency Gradient (DFG), with detection frequency defined as ω EMF - ω PRECESSION. This gradient has some interesting properties, most notably the ability to adjust the shim retrospectively (post-acquisition). This represents genuine B0-shimming: signals from spins dephased by unwanted B0-gradients are brought back in to phase. This capability arises from a dynamically-defined B1 detector field, synthesized retrospectively by a time-dependent weighted combination of NMR signals from a receive coil array. Applications include post-acquisition shimming and eddy-current correction. The signal weightings are calculated from receiver coil field maps and a target B0-inhomogeneity.