In vivo lung morphometry with hyperpolarized 3He diffusion MRI:: Theoretical background
In vivo lung morphometry with hyperpolarized 3He diffusion MRI:: Theoretical background
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DOI：
10.1016/j.jmr.2007.10.015
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发表时间：
2008-02-01
影响因子：
2.2
通讯作者：
Yablonskiy, D. A.
中科院分区：
文献类型：
--
作者：
Sukstanskii, A. L.;Yablonskiy, D. A.
基于MRI的肺内He-3气体扩散研究可提供肺微观结构的重要信息。肺腺泡气道可以用覆盖有肺泡套的圆柱体来描述[Haefeli-Bleuer，Weibel，Anat.Rec.220（1988）401]。对于相对较短的扩散时间（大约几ms），该几何形状允许根据两个扩散系数-相对于单个腺泡气道轴的纵向（D-L）和横向（D-T）-来描述肺中的3 He扩散衰减MR信号[Yablonskiy等人，PNAS 99（2002）3111]。本文通过计算机Monte Carlo模拟，建立了D-L和D-T与气道和肺泡几何参数之间的经验关系。还考虑了非高斯信号行为（D-L和D-T对b值的依赖性）的影响。所获得的结果在健康肺和轻度肺气肿肺的气道参数特征的生理学重要范围内是定量有效的。在晚期肺气肿的肺部，结果仅提供了“明显”的特征，但仍有可能用于评估肺气肿的进展。这为在体肺形态测量评价超极化He-3扩散MRI的腺泡气道几何参数奠定了基础，尽管气道太小而无法通过直接成像解决。这些结果还预测了He-3 ADC对实验可控扩散时间Delta的相当大的依赖性。如果Delta从3 ms减小到1 ms，正常人肺中的ADC可增加几乎50%。当比较用不同脉冲序列获得的实验数据时，应考虑这种影响。(c)2007年爱思唯尔公司All rights reserved.
MRI-based study of He-3 gas diffusion in lungs may provide important information on lung microstructure. Lung acinar airways can be described in terms of cylinders covered with alveolar sleeve [Haefeli-Bleuer, Weibel, Anat. Rec. 220 (1988) 401]. For relatively short diffusion times (on the order of a few ms) this geometry allows description of the 3 He diffusion attenuated MR signal in lungs in terms of two diffusion coefficients-longitudinal (D-L) and transverse (D-T) with respect to the individual acinar airway axis [Yablonskiy et al., PNAS 99 (2002) 3111]. In this paper, empirical relationships between D-L and D-T and the geometrical parameters of airways and alveoli are found by means of computer Monte Carlo simulations. The effects of non-Gaussian signal behavior (dependence of D-L and D-T on b-value) are also taken into account. The results obtained are quantitatively valid in the physiologically important range of airway parameters characteristic of healthy lungs and lungs with mild emphysema. In lungs with advanced emphysema, the results provide only "apparent" characteristics but still could potentially be used to evaluate emphysema progression. This creates a basis for in vivo lung morphometry-evaluation of the geometrical parameters of acinar airways from hyperpolarized He-3 diffusion MRI, despite the airways being too small to be resolved by direct imaging. These results also predict a rather substantial dependence of He-3 ADC on the experimentally-controllable diffusion time, Delta. If Delta is decreased from 3 ms to 1 ms, the ADC in normal human lungs may increase by almost 50%. This effect should be taken into account when comparing experimental data obtained with different pulse sequences. (c) 2007 Elsevier Inc. All rights reserved.