Myelin Imaging Using Dual-echo 3D 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 ultra-short echo time (UTE) magnetic resonance imaging (MRI) applications. The direct imaging of the myelin bilayer, which has ultra-short transverse relaxation time (uT 2 ), 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 k x -k y plane, with oscillated extensions in k z -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 uT 2 signals, with the output of uT 2 fraction, uT 2 value, and long T 2 value. Results The reconstructed images’ signal contrast between whiate matter (WM) and grey matter (GM) increased with longer TEs. The WM regions had higher uT 2 fraction values than GM (10.9%±1.9% vs. 5.7%±2.4%). The uT 2 value was approximately 0.15 milliseconds in WM. Conclusion The higher uT 2 fraction value in WM compared to GM demonstrated the ability of the proposed sequence to capture rapidly decaying signals.