Department of Radiology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
J Appl Physiol (1985). 2012 Aug 15;113(4):666-76. doi: 10.1152/japplphysiol.01628.2011. Epub 2012 Jun 7.
Magnetic resonance elastography (MRE) is a MR imaging method capable of spatially resolving the intrinsic mechanical properties of normal lung parenchyma. We tested the hypothesis that the mechanical properties of edematous lung exhibit local properties similar to those of a fluid-filled lung at transpulmonary pressures (P(tp)) up to 25 cm H(2)O. Pulmonary edema was induced in anesthetized female adult Sprague-Dawley rats by mechanical ventilation to a pressure of 40 cm H(2)O for ≈ 30 min. Prior to imaging the wet weight of each ex vivo lung set was measured. MRE, high-resolution T(1)-weighted spin echo and T(2)* gradient echo data were acquired at each P(tp) for both normal and injured ex vivo lungs. At P(tp)s of 6 cm H(2)O and greater, the shear stiffness of normal lungs was greater than injured lungs (P ≤ 0.0003). For P(tp)s up to 12 cm H(2)O, shear stiffness was equal to 1.00, 1.07, 1.16, and 1.26 kPa for the injured and 1.31, 1.89, 2.41, and 2.93 kPa for normal lungs at 3, 6, 9, and 12 cm H(2)O, respectively. For injured lungs MRE magnitude signal and shear stiffness within regions of differing degrees of alveolar flooding were calculated as a function of P(tp). Differences in shear stiffness were statistically significant between groups (P < 0.001) with regions of lower magnitude signal being stiffer than those of higher signal. These data demonstrate that when the alveolar space filling material is fluid, MRE-derived parenchymal shear stiffness of the lung decreases, and the lung becomes inherently softer compared with normal lung.
磁共振弹性成像（MRE）是一种能够空间分辨正常肺实质固有力学特性的磁共振成像方法。我们验证了如下假说：在跨肺压（P(tp)）高达 25 cm H(2)O 时，水肿肺的力学特性表现出类似于充满液体的肺的局部特性。通过对麻醉的成年雌性 Sprague-Dawley 大鼠进行机械通气至 40 cm H(2)O 的压力，在 ≈ 30 分钟内诱发肺水肿。在对每个离体肺进行成像之前，测量了其湿重。在每个 P(tp)下，对正常和受伤的离体肺分别进行 MRE、高分辨率 T(1)加权自旋回波和 T(2)*梯度回波数据采集。在 P(tp)为 6 cm H(2)O 及更高时，正常肺的剪切刚度大于受伤肺（P ≤ 0.0003）。对于 P(tp)高达 12 cm H(2)O，在 3、6、9 和 12 cm H(2)O 时，受伤肺的剪切刚度分别为 1.00、1.07、1.16 和 1.26 kPa，正常肺分别为 1.31、1.89、2.41 和 2.93 kPa。对于受伤肺，根据 P(tp)计算了不同程度肺泡积水区域的 MRE 幅度信号和剪切刚度。各组之间的剪切刚度差异具有统计学意义（P < 0.001），低幅度信号区域的刚度大于高信号区域。这些数据表明，当肺泡空间填充材料为液体时，肺的 MRE 衍生实质剪切刚度降低，与正常肺相比，肺变得更加柔软。
