Department of Biomedical Engineering, Duke University, Durham, North Carolina;
J Appl Physiol (1985). 2013 Sep;115(6):850-60. doi: 10.1152/japplphysiol.00092.2013. Epub 2013 Jul 11.
Although some central aspects of pulmonary function (ventilation and perfusion) are known to be heterogeneous, the distribution of diffusive gas exchange remains poorly characterized. A solution is offered by hyperpolarized 129Xe magnetic resonance (MR) imaging, because this gas can be separately detected in the lung's air spaces and dissolved in its tissues. Early dissolved-phase 129Xe images exhibited intensity gradients that favored the dependent lung. To quantitatively corroborate this finding, we developed an interleaved, three-dimensional radial sequence to image the gaseous and dissolved 129Xe distributions in the same breath. These images were normalized and divided to calculate "129Xe gas-transfer" maps. We hypothesized that, for healthy volunteers, 129Xe gas-transfer maps would retain the previously observed posture-dependent gradients. This was tested in nine subjects: when the subjects were supine, 129Xe gas transfer exhibited a posterior-anterior gradient of -2.00 ± 0.74%/cm; when the subjects were prone, the gradient reversed to 1.94 ± 1.14%/cm (P < 0.001). The 129Xe gas-transfer maps also exhibited significant heterogeneity, as measured by the coefficient of variation, that correlated with subject total lung capacity (r = 0.77, P = 0.015). Gas-transfer intensity varied nonmonotonically with slice position and increased in slices proximal to the main pulmonary arteries. Despite substantial heterogeneity, the mean gas transfer for all subjects was 1.00 ± 0.01 while supine and 1.01 ± 0.01 while prone (P = 0.25), indicating good "matching" between gas- and dissolved-phase distributions. This study demonstrates that single-breath gas- and dissolved-phase 129Xe MR imaging yields 129Xe gas-transfer maps that are sensitive to altered gas exchange caused by differences in lung inflation and posture.
虽然人们已经了解了一些肺部功能（通气和灌注）的中心方面存在异质性，但弥散性气体交换的分布仍未得到很好的描述。高极化 129Xe 磁共振（MR）成像提供了一种解决方案，因为这种气体可以分别在肺部的气腔和组织中被检测到。早期的溶解相 129Xe 图像显示出有利于依赖肺部的强度梯度。为了定量证实这一发现，我们开发了一种交错的三维径向序列，用于在同一呼吸中对气态和溶解 129Xe 分布进行成像。这些图像被归一化并分割以计算“129Xe 气体转移”图。我们假设，对于健康志愿者，129Xe 气体转移图将保留先前观察到的与姿势相关的梯度。这在九名受试者中进行了测试：当受试者仰卧时，129Xe 气体转移显示出 -2.00 ± 0.74%/cm 的后前梯度；当受试者俯卧时，梯度反转至 1.94 ± 1.14%/cm（P < 0.001）。129Xe 气体转移图也表现出显著的异质性，用变异系数来衡量，与受试者的总肺活量相关（r = 0.77，P = 0.015）。气体转移强度与切片位置的变化非线性相关，并在靠近主肺动脉的切片中增加。尽管存在很大的异质性，但所有受试者的平均气体转移为 1.00 ± 0.01，仰卧时为 1.01 ± 0.01，俯卧时为 1.01 ± 0.01（P = 0.25），表明气体和溶解相分布之间存在良好的“匹配”。这项研究表明，单次呼吸 129Xe 气-溶相磁共振成像可产生 129Xe 气体转移图，这些图对因肺膨胀和姿势差异引起的气体交换改变敏感。
