Triple-echo steady-state T2 relaxometry of the human brain at high to ultra-high fields

Quantitative MRI techniques, such as T-2 relaxometry, have demonstrated the potential to detect changes in the tissue microstructure of the human brain with higher specificity to the underlying pathology than in conventional morphological imaging. At high to ultra-high field strengths, quantitative MR-based tissue characterization benefits from the higher signal-to-noise ratio traded for either improved resolution or reduced scan time, but is impaired by severe static (B-0) and transmit (B-1) field heterogeneities. The objective of this study was to derive a robust relaxometry technique for fast T-2 mapping of the human brain at high to ultra-high fields, which is highly insensitive to B-0 and B-1 field variations. The proposed method relies on a recently presented three-dimensional (3D) triple-echo steady-state (TESS) imaging approach that has proven to be suitable for fast intrinsically B-1-insensitive T-2 relaxometry of rigid targets. In this work, 3D TESS imaging is adapted for rapid high-to ultra-high-field two-dimensional (2D) acquisitions. The achieved short scan times of 2D TESS measurements reduce motion sensitivity and make TESS-based T-2 quantification feasible in the brain. After validation in vitro and in vivo at 3 T, T-2 maps of the human brain were obtained at 7 and 9.4 T. Excellent agreement between TESS-based T-2 measurements and reference single-echo spin-echo data was found in vitro and in vivo at 3 T, and T-2 relaxometry based on TESS imaging was proven to be feasible and reliable in the human brain at 7 and 9.4 T. Although prominent B-0 and B-1 field variations occur at ultra-high fields, the T-2 maps obtained show no B-0-or B-1-related degradations. In conclusion, as a result of the observed robustness, TESS T-2 may emerge as a valuable measure for the early diagnosis and progression monitoring of brain diseases in high-resolution 2D acquisitions at high to ultra-high fields. Copyright (C) 2014 John Wiley & Sons, Ltd.