科研之友
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摘要
The spin lattice (T-1) and spin-spin (T-2) relaxation times, along with the proton density (PD) contain almost all of the information that H-1 MRI routinely uses in clinical diagnosis and research, but are seldom imaged directly. Here, three methods for directly imaging T-1, T-2, and PD with the least possible number of acquisitions - three, are presented. All methods utilize long 0 degrees self-refocusing adiabatic pre-pulses instead of spin-echoes to encode the T-2 information prior to a conventional gradient-echo MRI sequence. T-1 information is encoded by varying the flip-angle (FA) in the 'Dual-tau Dual-FA' and 'Four-FA' methods, or the sequence repetition period, TR, in the 'Dual-r Dual-TR' method. Inhomogeneity in the FA distribution and slice-selection profile are recognized as the main error sources for T-1 measurements. The former is remedied by integrating an extra FA-dependent acquisition into the 'Four-FA' method to provide selfcorrected T-1, T-2, PD, and FA in just four acquisitions - again, the minimum possible. Slice profile errors which manifest as differences between 2D and 3D T-1 measurements, can be addressed by Bloch equation analysis and experimental calibration. All three methods are validated in phantom studies, and the 'Dual-tau Dual-FA' and 'Four-FA' methods are validated in human brain studies using standard partial saturation and spin-echo methods for reference. The new methods offer a minimum-acquisition option for imaging single-component T-1, T-2, and PD. 'Four-FA' performs best overall in accuracy, with high efficiency per unit accuracy vs. existing methods when B-1-inhomogeneity is appropriately addressed.
- 出版日期2014-5
