Jacob Richard E, Laicher Gernot, Minard Kevin R
Pacific Northwest National Laboratory, MS P7-58, Richland, WA 99352, USA.
J Magn Reson. 2007 Oct;188(2):357-66. doi: 10.1016/j.jmr.2007.08.014. Epub 2007 Aug 24.
In (3)He magnetic resonance images of pulmonary air spaces, the confining architecture of the parenchymal tissue results in a non-Gaussian distribution of signal phase that non-exponentially attenuates image intensity as diffusion weighting is increased. Here, two approaches previously used for the analysis of non-Gaussian effects in the lung are compared and related using diffusion-weighted (3)He MR images of mechanically ventilated rats. One approach is model-based and was presented by Yablonskiy et al., while the other approach utilizes the second order decay contribution that is predicted from the cumulant expansion theorem. Total lung coverage is achieved using a hybrid 3D pulse sequence that combines conventional phase encoding with sparse radial sampling for efficient gas usage. This enables the acquisition of nine 3D images using a total of only approximately 1 L of hyperpolarized (3)He gas. Diffusion weighting ranges from 0 s/cm(2) to 40 s/cm(2). Results show that the non-Gaussian effects of (3)He gas diffusion in healthy rat lungs are directly attributed to the anisotropic geometry of lung microstructure as predicted by the Yablonskiy model, and that quantitative analysis over the entire lung can be reliably repeated in time-course studies of the same animal.
在肺内气腔的³He磁共振图像中，实质组织的限制结构导致信号相位呈非高斯分布，随着扩散加权增加，图像强度呈非指数衰减。在此，使用机械通气大鼠的扩散加权³He磁共振图像，对先前用于分析肺内非高斯效应的两种方法进行比较并建立关联。一种方法基于模型，由亚布隆斯基等人提出，而另一种方法利用从累积量展开定理预测的二阶衰减贡献。使用一种混合3D脉冲序列实现全肺覆盖，该序列将传统相位编码与稀疏径向采样相结合，以有效利用气体。这使得仅使用总共约1 L的超极化³He气体就能采集九幅3D图像。扩散加权范围为0 s/cm²至40 s/cm²。结果表明，健康大鼠肺内³He气体扩散的非高斯效应直接归因于亚布隆斯基模型所预测的肺微观结构的各向异性几何形状，并且在同一动物的时程研究中，可以可靠地重复对全肺的定量分析。
