Myelin Imaging Using 3D Dual-echo Ultra-short Echo Time MRI with Rosette k-Space Pattern

Purpose This study aimed to develop a new 3D dual-echo rosette k-space trajectory, specifically for applications of ultra-short echo time (UTE) magnetic resonance imaging (MRI). 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 rosette UTE scans with varied echo times (TEs). Dual-exponential model fitting was performed to separate uT2 signals, with the output of uT2 fraction, uT2 value and long T2 value. Results The reconstructed images’ signal contrast between white 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 about 0.12 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.