WE-FG-206-01: Magnetization-Prepared Shells Trajectory with Automated Gradient Waveform Design.

PURPOSE: The 3D non-Cartesian shells trajectory uses helical spirals to sample concentric spherical shells in k-space. The ordering of the shells sampling can be flexibly arranged to adapt to magnetization-prepared (MP) type of acquisition. The sampling of the shells around the center of k-space can be tuned to when the peak contrast between the white matter and gray matter is reached. The prototype of the sequence (MP-SHELLS) was previously implemented with a manually prescribed empirical gradient waveform. Recently we have implemented an automated trajectory and view ordering design supporting flexibly selected imaging parameters. The purpose of this work is to evaluate the performance of the automated MPSHELLS and compare it with a clinically used Cartesian MP-RAGE sequence.

METHODS: The k-space is segmented into several groups of concentric shells with each shell sampled by a group of interleaves following pre-defined helical spiral trajectories. The number of interleaves for each shell was determined to satisfy the Nyquist criteria. For each interleave, the gradient waveform is automatically generated via a time-optimal waveform design strategy following the sampling requirement. To enable magnetization-preparation, the acquisition order for the readouts from different shells was automatically arranged according to the time-dependent, white-gray matter contrast. The pulse sequence was tested on a GE 3T scanner. Under an IRB-approved protocol, a healthy volunteer was scanned with the MP-Shells sequence and compared with a clinical MP-RAGE sequence.

RESULTS: The in vivo results showed that improved gray/white matter contrast was achieved with the MP-SHELLS acquisition as compared to MP-RAGE. The calculated CNR values for the MP-SHELLS and MP-RAGE image are 21.81 and 15.02, respectively. The acquisition time for the MP-SHELLS is 5:10 compares to MP-RAGE acquisition time 9:13.

CONCLUSION: We have demonstrated a fully automated MP-SHELLS design with superior gray/white matter contrast and shorter acquisition time than the conventional Cartesian MP-RAGE. Funding support: NIH R01EB010065.