Conradi Mark S, Yablonskiy Dmitriy A, Woods Jason C, Gierada David S, Bartel Seth-Emil T, Haywood Susan E, Menard Christopher
Department of Physics, Washington University, Saint Louis, MO 63130, USA.
Acad Radiol. 2008 Jun;15(6):675-82. doi: 10.1016/j.acra.2007.09.019.
The hyperpolarized (3)He long-range diffusion coefficient (LRDC) in lungs is sensitive to changes in lung structure due to emphysema, reflecting the increase in collateral paths resulting from tissue destruction. However, no clear understanding of LRDC in healthy lungs has emerged. Here we compare LRDC measured in healthy lungs with computer simulations of diffusion along the airway tree with no collateral connections.
Computer simulations of diffusion of spatially modulated spin magnetization were performed in computer-generated, symmetric-branching models of lungs and compared with existing LRDC measurements in canine and human lungs.
The simulations predict LRDC values of order 0.001 cm(2)/sec, approximately 20 times smaller than the measured LRDC. We consider and rule out possible mechanisms for LRDC not included in the simulations: incomplete breath hold, cardiac motion, and passage of dissolved (3)He through airway walls. However, a very low density of small (micron) holes in the airways is shown to account for the observed LRDC.
It is proposed that LRDC in healthy lungs is determined by small collateral pathways.
肺内超极化（3）氦气的长程扩散系数（LRDC）对肺气肿导致的肺结构变化敏感，反映了组织破坏引起的侧支通路增加。然而，目前对健康肺脏中LRDC尚无清晰认识。在此，我们将健康肺脏中测量的LRDC与无侧支连接的气道树扩散计算机模拟结果进行比较。
在计算机生成的对称分支肺模型中进行空间调制自旋磁化扩散的计算机模拟，并与犬类和人类肺脏中现有的LRDC测量结果进行比较。
模拟预测的LRDC值约为0.001 cm²/秒，比测量的LRDC小约20倍。我们考虑并排除了模拟中未包含的LRDC可能机制：屏气不完全、心脏运动以及溶解的（3）氦气通过气道壁。然而，气道中极低密度的微小（微米级）孔洞被证明可解释观察到的LRDC。
有人提出健康肺脏中的LRDC由小的侧支通路决定。
