Fig. 4.

Conventional ¹H-, hyperpolarized ³He- and ¹²⁹Xe-MRI of a single subject each with COPD and asthma. ¹H-MRI of the thoracic cavity (gray scale) was obtained in the coronal plane during inspiration breath hold, after inhalation of 1 liter of ultra-high purity N₂ gas from functional residual capacity (FRC). Within 3 min, the same subject inhaled a 1 liter mixture of hyperpolarized ³He gas mixed with N₂ gas from FRC for static ventilation imaging of ³He gas distribution (shown in red) acquired in a 15 s breath hold. Approximately 3 min later, the subject inhaled a 1 liter mixture of hyperpolarized ¹²⁹Xe gas mixed with ⁴He from FRC for static ventilation imaging of ¹²⁹Xe gas distribution (shown in purple) acquired in a 15 s breath hold. Note the qualitative differences in gas distribution abnormalities that are obvious between ¹²⁹Xe- and ³He-MRI for both subjects. It is also important to note that the exact etiology of such gas distribution abnormalities has not yet been established. Such differences between ³He- and ¹²⁹Xe-MRI gas distribution may be attributable to differences in the gas properties such as diffusion, viscosity, or perhaps tissue solubility.