MRI gradient-echo phase contrast of the brain at ultra-short TE with off-resonance saturation.
MRI gradient-echo phase contrast of the brain at ultra-short TE with off-resonance saturation.
复制标题
具有偏共振饱和度的超短 TE 下大脑的 MRI 梯度回波相位对比。
DOI：
10.1016/j.neuroimage.2018.03.066
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发表时间：
2018
期刊：
影响因子：
5.7
通讯作者：
Liu,Chunlei
中科院分区：
文献类型：
--
作者：
Wei,Hongjiang;Cao,Peng;Bischof,Antje;Henry,RolandG;Larson,PederEZ;Liu,Chunlei
梯度回波序列测量的Larmor频移或图像相位提供了一种新的MRI对比度来源。这种对比被用来研究大脑的结构和功能。到目前为止，大脑的相位图像已经在很大程度上在长回波时间获得，因为最大相位信噪比（SNR）在TE = T2*（3T时为40 ms）处实现。然而，大脑的结构是分隔的，并且具有广泛的信号弛豫时间。在这样的长TE处，短T2分量被大大衰减并且对相位对比的贡献最小。本研究的目的是确定质子梯度回波图像的大脑是否表现出相位对比在超短TE（UTE）。我们的数据表明，在7 T无非共振饱和下采集的UTE图像不包含灰色和白色物质之间的显着相位对比。然而，通过使用非共振RF饱和脉冲，即使在106 μs的标称TE下，脑部的UTE图像也可以获得强相位对比，该非共振RF饱和脉冲通过磁化转移提供超短T2分量的直接饱和和较长T2分量的间接饱和。此外，与在长TE处获取的长T2信号相比，在具有非共振饱和的情况下在UTE处获取的灰色和白色物质之间的相位对比被反转。这一发现为操纵大脑的图像相位对比开辟了一条潜在的新途径。通过访问短和超短T2种类，MRI相位图像可以进一步改善脑中组织微结构的表征。
Larmor-frequency shift or image phase measured by gradient-echo sequences has provided a new source of MRI contrast. This contrast is being used to study both the structure and function of the brain. So far, phase images of the brain have been largely obtained at long echo times as maximum phase signal-to-noise ratio (SNR) is achieved at TE = T2* (∼40 ms at 3T). The structures of the brain, however, are compartmentalized and complex with a wide range of signal relaxation times. At such long TE, the short-T2 components are largely attenuated and contribute minimally to phase contrast. The purpose of this study was to determine whether proton gradient-echo images of the brain exhibit phase contrast at ultra-short TE (UTE). Our data showed that UTE images acquired at 7 T without off-resonance saturation do not contain significant phase contrast between gray and white matter. However, UTE images of the brain can attain strong phase contrast even at a nominal TE of 106 μs by using off-resonance RF saturation pulses, which provide direct saturation of ultra-short-T2 components and indirect saturation of longer-T2 components via magnetization transfer. In addition, phase contrast between gray and white matter acquired at UTE with off-resonance saturation is reversed compared to that of the long-T2 signals acquired at long TEs. This finding opens up a potential new way to manipulate image phase contrast of the brain. By accessing short and ultra-short-T2 species, MRI phase images may further improve the characterization of tissue microstructure in the brain.