Single Shot Spiral TSE with Annulated Segmentation

Abstract: Purpose: To develop, optimize and implement a single shot spiral TSE-sequence at 3 T and to demonstrate its feasibility to acquire artefact free images of the central nervous system with 1 mm spatial resolution in < 200 ms. Theory and Methods: Spiral TSE sequences with annulated spiral segmentation have been implemented with different acquisition modes. In fixed mode the duration of each spiral segment is fixed to fill the available acquisition time tacq. In tangential mode, the beginning of each spiral segment is reached via a straight tangential trajectory. Tangential mode allows faster transition and thus longer tacq for a given echo spacing ESP, but less data points can be acquired per acquisition interval. Alternating between spiral-in and spiral-out readout in alternating echoes leads to a somewhat different point spread function for off-resonant spins. Results: Images of the brain with 1 mm spatial resolution acquired with a variable density spiral with ~45 % undersampling can be acquired in a single shot. All acquisition modes produce comparable image quality. Only mild artifacts in regions of strong susceptibility effects can be observed for ESP of 10 ms and below. The use of variable flip angle schemes allows seamless acquisition of consecutive slices and/or dynamic scans without waiting time between consecutive acquisitions. Comparison with images acquired at 1.5 T shows reduced susceptibility artifacts within the brain and facial structures.. Conclusion: Single shot spiral TSE has been demonstrated to enable highly efficient acquisition of high-resolution images of the brain in < 200 ms per slice.