Several applications of 129Xe MRI imaging are under development, including diffusion-weighted and relaxation-weighted imaging (17-19). These techniques take advantage of the fact that the rate of loss of 129Xe polarization is significantly influenced by the local blood flow and concentration of molecular oxygen, as well as the restriction of 129Xe diffusion by small airway space dimensions. These data can be used to create maps of the lung reflecting regional ventilation/perfusion and micro-airway sizes. Other data that can be obtained with 129Xe MRI include the volumes of ventilated and unventilated lungs which can subsequently be analyzed to determine the homogeneity of gas distribution within the airspaces (17).