Abstract
Purpose This study aimed to develop a new 3D dual-echo rosette k-space trajectory, specifically for ultra-short echo time (UTE) magnetic resonance imaging (MRI) applications. The direct imaging of the myelin bilayer, which has ultra-short transverse relaxation time (uT2), was acquired to test the performance of the proposed UTE sequence.
Theory and Methods The rosette trajectory was developed based on rotations of a ‘petal-like’ pattern in the kx-ky plane, with oscillated extensions in kz-direction for 3D coverage. Five healthy volunteers were recruited and underwent ten dual-echo 3D rosette UTE scans with various echo times (TEs). Dual-exponential complex model fitting was performed on the magnitude data to separate uT2 signals, with the output of uT2 fraction, uT2 value, and long T2 value.
Results The reconstructed images’ signal contrast between whiate matter (WM) and grey matter (GM) increased with longer TEs. The WM regions had higher uT2 fraction values than GM (10.9%±1.9% vs. 5.7%±2.4%). The uT2 value was approximately 0.15 milliseconds in WM.
Conclusion The higher uT2 fraction value in WM compared to GM demonstrated the ability of the proposed sequence to capture rapidly decaying signals.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
The content of the manuscript has been modified to address these, including 1) a comparison between the dual-echo 3D rosette and the conventional 3D golden angle radial UTE; 2)reconstruction results from regular regridding; 3) reconstructed images sampled by undersampling dual-echo 3D rosette patterns to demonstrate the prospective acceleration; 4) ultra-short T2 fraction and value maps from two representative individuals and 5) potential use of the second echo.