A diagnostic contrast composition includes a carrier fluid and a non-decaying gas-evolving fluid incorporated in the carrier fluid. The gas-evolving fluid has a vapor pressure sufficient to evolve the gas from a circulatory system within a lung of a patient. The gas-evolving fluid is a composition containing a sufficient quantity of atoms with an atomic number higher than 8 to provide an increased absorption sufficient to increase a Hounsfield Unit measurement in an image in a CT imaging system. The gas-evolving fluid is selected from the group consisting of xenon gas, krypton gas, sulfur hexafluoride, a perfluorocarbon, a brominated perfluorocarbon, and combinations thereof. The carrier fluid is selected from the group consisting of water, saline, saline comprising one or more blood proteins, and saline comprising dissolved lipids.