Methods and systems for assessing pulmonary gas exchange and/or alveolar-capillary barrier status include obtaining at least one MRI image and/or image data of 129Xe dissolved in the red blood cells (RBC) in the gas exchange regions of the lungs of a patient. The image is sufficiently sensitive to allow a clinician or image recognition program to assess at least one of pulmonary gas exchange, barrier thickness or barrier function based on the 129Xe MRI RBC image.