 Xenon , particularly <unk> 129Xe , is a useful contrast agent for magnetic resonance imaging ( <unk> ) . In the gas phase , it can be used to image empty space such as cavities in a porous sample or <unk> in lungs . <unk> 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 <unk> , it can be used to image various soft living tissues . 
