Biological Magnetic-Resonance-Imaging Using Laser Polarized Xe-129

AS currently implemented, magnetic resonance imaging (MRI) relies on the protons of water molecules in tissue to provide the NMR signal. Protons are, however, notoriously difficult to image in some biological environments of interest, notably the lungs(1) and lipid bilayer membranes such as those in the brain(2). Here we show that Xe-129 gas can be used for high-resolution MRI when the nuclear-spin polarization of the atoms is increased by laser optical pumping and spin exchange(3-6). This process produces hyperpolarized Xe-129, in which the magnetization is enhanced by a factor of about 10(5). By introducing hyperpolarized Xe-129 into mouse lungs we have obtained images of the lung gas space with a speed and a resolution better than those available from proton MRI(1,7) or emission tomography(8,9). As xenon (a safe general anaesthetic) is rapidly-and safely transferred from the lungs to blood and thence to other tissues(8,9), where it is concentrated in lipid(10-15) and protein(13,15-18) components, images of the circulatory system, the brain and other vital organs can also be obtained. Because the magnetic behaviour of Xe-129 is very sensitive to its environment, and is different from that of (H2O)-H-1, MRI using hyperpolarized Xe-129 should involve distinct and sensitive mechanisms for tissue contrast.