Diffusion of hyperpolarized 129Xe in the lung: a simplified model of 129Xe septal uptake and experimental results

We used hyperpolarized Xe-129 NMR to measure pulmonary alveolar surface area per unit gas volume S-A/V-gas, alveolar septal thickness h and capillary transit time tau, three critical determinants of the lung's primary role as a gas exchange organ. An analytical solution for a simplified diffusion model is described, together with a modification of the xenon transfer contrast imaging technique utilizing 90 degrees radio-frequency pulses applied to the dissolved phase, rather than traditional 180 degrees pulses. With this approach, three-dimensional (3D) maps of S-A/V-gas were obtained. We measured global S-A/V-gas, h and tau in four normal subjects, two subjects with mild interstitial lung disease (ILD) and two subjects with mild chronic obstructive pulmonary disease (COPD). In normals, S-A/V-gas decreased with increasing lung volume from similar to 320 to 80 cm(-1); both h similar to 13 mu m and tau similar to 1.5 s were relatively constant. For the two ILD subjects, h was, respectively, 36 and 97% larger than normal, quantifying an increased gas/blood tissue barrier; S-A/V-gas and tau were normal. The two COPD subjects had S-A/V-gas values similar to 25% that of normals, quantifying septal surface loss in emphysema; h and tau were normal. These are the first noninvasive, non-radiation-based, quantitative measurements of h and tau in patients with pulmonary disease.