Phase matched RF pulse design for imaging a reduced field of excitation with a fast TSE acquisition

Abstract

A method is described to design parallel transmit (PTX) excitation pulses that are compatible with turbo spin echo (TSE) sequences, based on information available from conventional per-channel B1+ mapping. The excitation phase of PTX pulses that generate a reduced field of excitation (rFOX) is matched to the phase the quadrature mode of a PTX coil. This enables TSE imaging of a PTX-enabled rFOX excitation combined with standard nonselective refocusing pulses transmitted in the quadrature mode. In-vivo imaging experiments were performed at 7T using a dual channel parallel transmit head coil. In combination with simulations, the CPMG-required excitation phase was confirmed in TSE sequences with refocusing pulses of variable flip angle. Further experiments showed that the same rFOX was generated in TSE and gradient echo sequences, enabling high-resolution imaging with parallel imaging acceleration of the rFOX.