Dependence on b-value of the direction-averaged diffusion-weighted imaging signal in brain.
Dependence on b-value of the direction-averaged diffusion-weighted imaging signal in brain.
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DOI：
10.1016/j.mri.2016.10.026
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发表时间：
2017-02
影响因子：
2.5
通讯作者：
Helpern JA
中科院分区：
文献类型：
--
作者：
McKinnon ET;Jensen JH;Glenn GR;Helpern JA
研究了脑中方向平均弥散加权成像（DWI）信号与b值的关系，以帮助阐明弥散加权与脑微结构之间的关系。高角分辨率扩散成像（HARDI）数据采集自两名志愿者，具有128个扩散编码方向和6个b值壳，范围为1000至6000 s/mm 2，增量为1000 s/mm 2。通过对所有扩散编码方向求平均值，计算每个壳的方向平均信号，并将信号绘制为选定感兴趣区域的b值的函数。作为补充分析，我们还将类似的方法应用于从人类连接体项目（HCP）获得的回顾性DWI数据，其中包括高达10，000 s/mm 2的b值。对于所有感兴趣的区域，一个简单的幂律关系准确地描述了所观察到的依赖的方向平均信号作为扩散加权的函数。在白色物质中，特征指数为0.56 ± 0.05，而在灰质中为0.88 ± 0.11。使用HCP数据获得了相似的结果。对于1000和6000 s/mm 2之间的b值，方向平均DWI信号作为b值的幂变化，达到良好的近似值。表征这种幂律行为的指数对于白色和灰质是明显不同的，指示了鲜明对比的微结构环境。这些结果可能会通知用于解释DWI信号的微观结构模型的建设。
The dependence of the direction-averaged diffusion-weighted imaging (DWI) signal in brain was studied as a function of b-value in order to help elucidate the relationship between diffusion weighting and brain microstructure. High angular resolution diffusion imaging (HARDI) data were acquired from two human volunteers with 128 diffusion-encoding directions and six b-value shells ranging from 1000 to 6000 s/mm2 in increments of 1000 s/mm2. The direction-averaged signal was calculated for each shell by averaging over all diffusion-encoding directions, and the signal was plotted as a function of b-value for selected regions of interest. As a supplementary analysis, we also applied similar methods to retrospective DWI data obtained from the human connectome project (HCP), which includes b-values up to 10,000 s/mm2. For all regions of interest, a simple power law relationship accurately described the observed dependence of the direction-averaged signal as a function of the diffusion weighting. In white matter, the characteristic exponent was 0.56 ± 0.05, while in gray matter it was 0.88 ± 0.11. Similar results were obtained with the HCP data. The direction-averaged DWI signal varies, to a good approximation, as a power of the b-value, for b-values between 1000 and 6000 s/mm2. The exponents characterizing this power law behavior were markedly different for white and gray matter, indicative of sharply contrasting microstructural environments. These results may inform the construction of microstructural models used to interpret the DWI signal.