Improved acquisition efficiency in T2-weighted fetal MRI with optimized variable flip angles and prospective wave-encoding
Yamin Arefeen1, Borjan Gagoski2,3, Berkin Bilgic4,5, Ellen Grant2,3, and Elfar Adalsteinsson1,6,7
1Massachusetts Institute of Technology, Cambridge, MA, United States, 2Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children’s Hospital, Boston, MA, United States, 3Harvard Medical School, Boston, MA, United States, 4Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 5Department of Radiology, Harvard Medical School, Boston, MA, United States, 6Harvard-MIT Health Sciences and Technology, Cambridge, MA, United States, 7Institute for Medical Engineering and Science, Cambridge, MA, United States
Fetal MRI utilizes Half-Fourier-acquisition-single-shot-turbo-spin-echo (HASTE) for motion robust imaging. However, specific-absorption-rate (SAR) constraints from the refocusing pulse train lengthens scan time and increases vulnerability to motion-induced artifacts. Variable refocusing flip angle (VFA) acquisitions improve efficiency, but may suffer from poor contrast-to-noise-ratios (CNR). We propose an optimization technique for VFA that retains ~90% CNR with 2.5x SAR reduction. Furthermore, we demonstrate the first application of wave-encoding in fetal MRI at Rin-plane = 3-fold prospectively under-sampled acquisitions. Combining HASTE, VFA, and wave-encoding improves acquisition time with reduced repetition times and shorter echo-trains and could enable simultaneous-multislice acquisitions for further acceleration.
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