Quantitative magnetization transfer imaging of human brain at 7 T.
Quantitative magnetization transfer imaging of human brain at 7 T.
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DOI：
10.1016/j.neuroimage.2012.08.047
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发表时间：
2013-01-01
期刊：
影响因子：
5.7
通讯作者：
Smith, Seth A.
中科院分区：
文献类型：
--
作者：
Dortch, Richard D.;Moore, Jay;Li, Ke;Jankiewicz, Marcin;Gochberg, Daniel F.;Hirtle, Jane A.;Gore, John C.;Smith, Seth A.
定量磁化转移(QMT)成像产生了描述自由水质子和静止大分子质子之间相互作用的指数。这些指标包括大分子与游离池大小的比率(PSR)，它已被证明与白质中的髓鞘含量相关。由于全脑成像所需的扫描时间较长(≈为20-30分钟)，对人脑的QMT研究尚未得到广泛应用。在这里，我们调查了在7.0T时可用的提高的信噪比是否可以用来减少QMT扫描时间。更具体地说，我们开发了一种选择性反转恢复(SIR)QMT成像协议，该协议具有i)新颖的发射射频(B1+)和静电场(B0)不敏感的反转脉冲，ii)透射场-回波读出，以及iii)减少了tr。采用此方法(扫描时间≈40 S/切片，分辨率=2×2×3 mm~3)，在7.0T下获得健康志愿者的活体QMT数据。可靠性也在反复采集中进行了评估。这项研究的结果表明，即使在存在较大的B1+和B0不均匀的情况下，SIR QMT成像也可以在7.0T的射频功率限制下可靠地进行。与低场强QMT研究结果一致，在7.0T时，白质的PSR值(平均值±SD=17.6±1.3%)高于灰质(10.3±1.6%)。此外，白质的PSR值也存在区域性差异。总而言之，这些结果表明，在7.0T下进行QMT测量是可行的，并最终可能允许对活体中正常和患病人脑成分的变化进行高分辨率评估。
Quantitative magnetization transfer (qMT) imaging yields indices describing the interactions between free water protons and immobile macromolecular protons. These indices include the macromolecular to free pool size ratio (PSR), which has been shown to be correlated with myelin content in white matter. Because of the long scan times required for whole-brain imaging (≈20–30 min), qMT studies of the human brain have not found widespread application. Herein, we investigated whether the increased signal-to-noise ratio available at 7.0 T could be used to reduce qMT scan times. More specifically, we developed a selective inversion recovery (SIR) qMT imaging protocol with a i) novel transmit radiofrequency (B1+) and static field (B0) insensitive inversion pulse, ii) turbo field-echo readout, and iii) reduced TR. In vivo qMT data were obtained in the brains of healthy volunteers at 7.0 T using the resulting protocol (scan time≈40 s/slice, resolution=2×2×3 mm3). Reliability was also assessed in repeated acquisitions. The results of this study demonstrate that SIR qMT imaging can be reliably performed within the radiofrequency power restrictions present at 7.0 T, even in the presence of large B1+ and B0 inhomogeneities. Consistent with qMT studies at lower field strengths, the observed PSR values were higher in white matter (mean±SD=17.6±1.3%) relative to gray matter (10.3±1.6%) at 7.0 T. In addition, regional variations in PSR were observed in white matter. Together, these results suggest that qMT measurements are feasible at 7.0 T and may eventually allow for the high-resolution assessment of changes in composition throughout the normal and diseased human brain in vivo.
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