Ruiz-Cabello Jesús, Pérez-Sánchez José Manuel, Pérez de Alejo Rigoberto, Rodríguez Ignacio, González-Mangado Nicolás, Peces-Barba Germán, Cortijo Manuel
Grupo de Resonancia Magnética, Instituto de Estudios Biofuncionales, Universidad Complutense de Madrid, Paseo Juan XXIII 1, Madrid 28040, Spain.
Respir Physiol Neurobiol. 2005 Aug 25;148(1-2):43-56. doi: 10.1016/j.resp.2005.04.007.
Lung functional magnetic resonance imaging (MRI) has become a reality using different inert hyperpolarized gases, such as 3He and 129Xe, which have provided an extraordinary boost in lung imaging and has also attracted interest to other chemically inert gaseous contrast agents. In this context, we have recently demonstrated the first diffusion-weighted images using thermally polarized inhaled sulfur hexafluoride (SF6) in small animals. The aim of this study was to evaluate whether or not the diffusion coefficient of this fluorinated gas is sensitive to pulmonary structure, gas concentration and air pressure in the airways. Diffusion coefficients of SF6 (both pure and in air mixtures) measured in vitro at different pressures and 20 degrees C showed an excellent agreement with theoretical values. Measurements of diffusion coefficients were also performed in vivo and post-mortem on healthy rats, achieving satisfactory signal-to-noise ratios (SNRs), and SF6 gas was found to be in an almost completely restricted diffusion regime in the lung, i.e., the transport by molecular diffusion is delayed by collisions with barriers such as the alveolar septa. This observed low diffusivity means that this gas will be less sensitive to structural changes in the lungs than other magnetic resonance sensitive gas such as 3He, particularly at human scale. However, it is still possible that SF6 plays a role since it opens a new structural window. Thus, the interest of researchers in delimiting the important limiting technical factors that makes this process very challenging is obvious. Among them, T2 relaxation is very fast, so gradient systems with very fast switching rate and probably large radiofrequency (RF) power and high field systems will be needed for hexafluoride to be used in human studies.
利用不同的惰性超极化气体，如³He和¹²⁹Xe，肺部功能磁共振成像（MRI）已成为现实，这些气体极大地推动了肺部成像技术的发展，也引发了人们对其他化学惰性气体造影剂的兴趣。在此背景下，我们最近展示了在小动物中使用热极化吸入六氟化硫（SF6）获得的首批扩散加权图像。本研究的目的是评估这种氟化气体的扩散系数是否对肺部结构、气体浓度和气道内气压敏感。在不同压力和20摄氏度下体外测量的SF6（纯气体和空气混合物中的SF6）扩散系数与理论值高度吻合。还对健康大鼠进行了体内和死后扩散系数测量，获得了令人满意的信噪比（SNR），并且发现SF6气体在肺内几乎处于完全受限的扩散状态，即分子扩散传输因与肺泡隔等屏障碰撞而延迟。观察到的这种低扩散率意味着，与其他磁共振敏感气体如³He相比，这种气体对肺部结构变化的敏感度较低，尤其是在人体尺度上。然而，由于SF6打开了一个新的结构窗口，它仍有可能发挥作用。因此，研究人员明确界定使这一过程极具挑战性的重要限制技术因素的兴趣显而易见。其中，T2弛豫非常快，因此要将六氟化硫用于人体研究，可能需要具有非常快切换速率的梯度系统，或许还需要大功率射频（RF）和高场系统。
