PARALLEL SPATIALLY SELECTIVE EXCITATION USING NONLINEAR NON-BIJECTIVE PATLOC ENCODING FIELDS: EXPERIMENTAL REALIZATION AND FIRST RESULTS

Introduction: The concept of PatLoc (Parallel Imaging Technique Using Local Gradients) [1] proposes the application of non-linear, non-bijective Spatially Encoding Magnetic Fields (SEMs) that can substitute or be added to conventional gradient fields with linear SEMs while the introduced encoding ambiguity is compensated for by parallel acquisition with sensitivity encoding. During the last years, several promising characteristics of PatLoc encoding have been reported on the acquisition side and there is strong evidence that these advantages can be exploited beneficially for Parallel Spatially Selective Excitation (PEX [2] / Transmit SENSE [3]) experiments, too: Locally increased spatial resolution [4] can improve the accuracy of excited target patterns [5]; encoding capabilities of PatLoc SEMs may outperform those of linear SEMS in specific regions [2] allowing higher excitation fidelity; finally faster switching times of symmetrically designed PatLoc gradient coils [6] may afford shorter pulse durations, which is one of the main limiting factors of Spatially Selective Excitation (SSE). In analogy to parallel acquisition, parallel transmission is mandatory in order to resolve encoding ambiguities during excitation. Based on previous work on parallel transmission and PatLoc hardware [6] as well as on design algorithms for parallel SSE pulses for PatLoc SEMs [5,7], this work demonstrates the first experimental realization of PEX with non-linear, non-bijective SEMs.