Whole brain MP2RAGE-based mapping of the longitudinal relaxation time at 9.4T
Whole brain MP2RAGE-based mapping of the longitudinal relaxation time at 9.4T
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DOI：
10.1016/j.neuroimage.2016.09.047
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发表时间：
2017-01-01
期刊：
影响因子：
5.7
通讯作者：
Scheffler, K.
中科院分区：
文献类型：
--
作者：
Hagberg, G. E.;Bause, J.;Scheffler, K.
具有高准确度和精度的纵向弛豫时间（T-1）的映射对于神经科学和临床研究至关重要，因为它开辟了获得准确脑组织分割和获得髓鞘相关信息的可能性。理想的定量方法应该能够在有限的扫描时间内覆盖整个大脑，但允许使用亚毫米体素尺寸进行详细采样。超高磁场的使用非常适合于此目的，然而，不均匀的发射场潜在地阻碍了其使用。在目前的工作中，我们进行了全脑T-1映射的基础上的MP2 T序列在9.4 T，并探讨了潜在的陷阱，自动组织分类相比，3 T。通过单层T-1映射与反演恢复EPI测量，定量T-2映射使用多回波技术和模拟的布洛赫方程的绝热反演效率的数据精度和T-2依赖的变化进行了研究。我们发现，在9.4T的发射场的显着的空间变化（产生的翻转角之间的20%和180%的标称值）深刻地影响了图像分割和T-1映射的结果。这些影响可以通过校正翻转角和反转效率偏差来减轻。基于校正后的T-1标测图，生成了新的、“平坦化”的MP2造影图像，其不再受发射场变化的影响。与在9.4 T条件下采集的未校正MP2 T造影图像不同，这些平坦化图像产生的图像分割与3 T相当，因此无需在图像分割和组织分类之前进行偏置场校正。在高场的T-1估计方面，所提出的校正方法导致精度提高，重测变异性低于1%，25名受试者的变异系数低于3%。(C)2016 Elsevier Inc. All rights reserved.
Mapping of the longitudinal relaxation time (T-1) with high accuracy and precision is central for neuroscientific and clinical research, since it opens up the possibility to obtain accurate brain tissue segmentation and gain myelin-related information. An ideal, quantitative method should enable whole brain coverage within a limited scan time yet allow for detailed sampling with sub-millimeter voxel sizes. The use of ultra-high magnetic fields is well suited for this purpose, however the inhomogeneous transmit field potentially hampers its use. In the present work, we conducted whole brain T-1 mapping based on the MP2RAGE sequence at 9.4 T and explored potential pitfalls for automated tissue classification compared with 3 T. Data accuracy and T-2-dependent variation of the adiabatic inversion efficiency were investigated by single slice T-1 mapping with inversion recovery EPI measurements, quantitative T-2 mapping using multi-echo techniques and simulations of the Bloch equations. We found that the prominent spatial variation of the transmit field at 9.4T (yielding flip angles between 20% and 180% of nominal values) profoundly affected the result of image segmentation and T-1 mapping. These effects could be mitigated by correcting for both flip angle and inversion efficiency deviations. Based on the corrected T-1 maps, new, 'flattened', MP2RAGE contrast images were generated, that were no longer affected by variations of the transmit field. Unlike the uncorrected MP2RAGE contrast images acquired at 9.4 T, these flattened images yielded image segmentations comparable to 3 T, making bias-field correction prior to image segmentation and tissue classification unnecessary. In terms of the T-1 estimates at high field, the proposed correction methods resulted in an improved precision, with test-retest variability below 1% and a coefficient-of-variation across 25 subjects below 3%. (C) 2016 Elsevier Inc. All rights reserved.