Sebastian Littin^{1}, Stefan Kroboth^{1}, Huijun Yu^{1}, Feng Jia^{1}, Ying-Hua Chu^{1}, Yi-Cheng Hsu^{1}, and Maxim Zaitsev^{1}

The use of a matrix gradient coil enables to tailor spatial encoding magnetic Fields (SEMs) for slice specific frequency shifts. Applying such shifts in oscillatory manner allows for novel methods of signal separation in SMS imaging.

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Fig.1: Measured field maps of two individual slices. Each figure depicts one field for two different slices. With a limited number of matrix gradient coil elements a trade-off between achievable field strength and homogeneity can be made. These fields allow for an almost independent manipulation of each slice. Fields are in rad/s/A.

Fig.2: Exemplary gradient waveforms for two fields which are played out during data acquisition. A golden ratio between the two frequencies was chosen to reduce overlaps. The use of same frequencies with a phase shift of 90° is possible, as well.

Fig.3: SMS acquisition without any signal separation in a FOV of 220mm. Features of two slices overlap in one single image.

Fig.4: Application of wave gradients during read-out results in an aliased image. Due to an oscillation with a constant field, the traditional k-space formalism is not sufficient to describe the resulting artifact which is equivalent to a very fast oscillatory movement along frequency encoding direction.

Fig.5: The reconstruction uncovers the features of each slice. The use of
magnetic field
monitoring technology
is expected to remove artifacts which are believed to result from inaccuracies in timing and synchronization.