Laboratory of Biomedical Imaging and Signal Processing, Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
Magn Reson Imaging. 2012 Sep;30(7):993-1001. doi: 10.1016/j.mri.2012.02.012. Epub 2012 Apr 9.
Quantitative diffusion tensor imaging (DTI) offers a valuable tool to probe the microstructural changes in neural tissues in vivo, where absolute quantitation accuracy and reproducibility are essential. It has been long recognized that measurement of apparent diffusion coefficient (ADC) using DTI could be influenced by the presence of water molecules in cerebrovasculature. However, little is known about to what extent such blood signal affects DTI quantitation. In this study, we quantitatively examined the effect of cerebral hemodynamic change on DTI indices by using a standard multislice echo planar imaging (EPI) spin echo (SE) DTI acquisition protocol and a rat model of hypercapnia. In response to 5% CO(2) challenge, mean, radial and axial diffusivities measured with diffusion factor (b-value) of b=1.0 ms/μm(2) were found to increase in whole brain (1.52%±0.22%, 1.66%±0.16% and 1.35%±0.37%, respectively), gray matter (1.56%±0.23%, 1.63%±0.14% and 1.47%±0.45%, respectively) and white matter regions (1.45%±0.28%, 1.88%±0.33% and 1.10%±0.26%, respectively). Fractional anisotropy (FA) was found to decrease by 1.67%±0.38%, 1.91%±0.59% and 1.46%±0.30% in whole brain, gray matter and white matter regions, respectively. In addition, these diffusivity increases and FA decreases became more pronounced at a lower b-value (b=0.3 ms/μm(2)). The results indicated that in vivo DTI quantitation in brain can be contaminated by vascular factors on the order of few percentages. Consequently, alterations in cerebrovasculature and hemodynamics can affect the DTI quantitation and its efficacy in characterizing the neural tissue microstructures in normal and diseased states. Caution should be taken in designing and interpreting quantitative DTI studies as all DTI indices can be potentially confounded by physiologic conditions and by cerebrovascular and hemodynamic characteristics.
定量扩散张量成像（DTI）提供了一种有价值的工具，可以探测活体神经组织的微观结构变化，其中绝对定量准确性和可重复性至关重要。人们早就认识到，使用 DTI 测量表观扩散系数（ADC）可能会受到脑血管内水分子的影响。然而，对于这种血液信号对 DTI 定量的影响程度知之甚少。在这项研究中，我们使用标准的多层回波平面成像（EPI）自旋回波（SE）DTI 采集方案和高碳酸血症大鼠模型，定量研究了脑血流动力学变化对 DTI 指标的影响。在 5%CO2 刺激下，用扩散因子（b 值）b=1.0 ms/μm2 测量的全脑、灰质和白质的平均、径向和轴向扩散系数分别增加了 1.52%±0.22%、1.66%±0.16%和 1.35%±0.37%；1.56%±0.23%、1.63%±0.14%和 1.47%±0.45%；1.45%±0.28%、1.88%±0.33%和 1.10%±0.26%。各向异性分数（FA）在全脑、灰质和白质区域分别降低了 1.67%±0.38%、1.91%±0.59%和 1.46%±0.30%。此外，在较低的 b 值（b=0.3 ms/μm2）下，这些扩散系数的增加和 FA 的降低变得更加明显。结果表明，活体脑 DTI 定量可能会受到几%的血管因素的污染。因此，脑血管和血流动力学的变化会影响 DTI 定量及其在正常和疾病状态下描述神经组织微观结构的效果。在设计和解释定量 DTI 研究时应谨慎，因为所有 DTI 指数都可能受到生理条件以及脑血管和血流动力学特征的潜在影响。
