Fully balanced steady-state 3D-spin-echo (bSSSE) imaging at 3 Tesla

Abstract

In this work a 3D fully balanced steady-state spin-echo sequence (bSSSE) was designed and implemented on a 3-Tesla whole-body MR scanner. In contrast to previously introduced nonbalanced SSSE (nbSSSE) sequences, bSSSE features fully rewound imaging gradients. Additionally, all phase encodings and the readout prephasing are performed after the refocusing pulse. Its performance was compared with previously used gradient-echo (GE) and nbSSSE sequences. The signal response of each sequence was simulated by numerical solution of the Bloch equation. All sequences were then optimized based on these simulations for high-resolution (HR) imaging of tissues with short relaxation times and applied to in vivo HR-MRI of trabecular bone. bSSSE outperformed nbSSSE sequences in terms of SNR and SMR efficiency. Measurements of structural bone parameters revealed thinner trabeculae and a lower bone/bone-marrow fraction for the bSSSE sequence compared to the nbSSSE sequence. By applying a parallel imaging technique based on generalized autocalibrating partially parallel acquisition (GRAPPA) with a reduction factor of 2, we were able to maintain a clinically feasible scan time using bSSSE. Comparisons of structural bone parameters revealed a difference of less than 3% for all structural parameters between parallel and conventional imaging. © 2006 Wiley-Liss, Inc.