 Xenon , particularly hyperpolarized 129Xe , is a useful contrast agent for magnetic resonance imaging ( MRI ) . In the gas phase , it can be used to image empty space such as cavities in a porous sample or alveoli in lungs . Hyperpolarization renders 129Xe much more detectable via magnetic resonance imaging and has been used for studies of the lungs and other tissues . It can be used , for example , to trace the flow of gases within the lungs . Because xenon is soluble in water and also in hydrophobic solvents , it can be used to image various soft living tissues . 
