Variable-flip-angle single-slab 3D GRASE imaging with phase-independent image reconstruction.

PURPOSE To develop a single-slab three-dimensional variable-flip-angle gradient- and spin-echo pulse sequence with phase-independent reconstruction that is highly energy- or encoding-efficient for high resolution isotropic imaging at high magnetic field. METHODS Amplitude modulation in the proposed pulse sequence was alleviated using a variable-flip-angle induced smooth signal evolution along the long echo train. To avoid phase modulation, instead of directly interleaving phase encoding signals with different off-resonance induced phase accumulation over multiple echoes, phase-independent image reconstruction was performed, wherein each echo image was separately reconstructed using convolution-interpolation with echo-interleaving self-calibration and then combined. Numerical and experimental studies were performed at 3.0 T for generation of clinical T2 -weighted contrast to investigate the effectiveness of the proposed method over existing methods. RESULTS Compared with conventional techniques, the proposed method produces smooth amplitude variation, no ghosting artifacts (no phase modulation), and competitive signal-to-noise ratio. An energy-efficient variable-flip-angle gradient- and spin-echo reduces specific absorption rate by 71% without significant loss of signal-to-noise ratio, while an encoding-efficient one decreases imaging time by 54% with a slight loss of signal-to-noise ratio. CONCLUSION We successfully demonstrated that the proposed variable-flip-angle gradient- and spin-echo can be a highly promising energy- or encoding-efficient alternative for high resolution isotropic imaging.