Biological magnetic resonance imaging using laser-polarized 129Xe

Abstract

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 lungs¹ and lipid bilayer membranes such as those in the brain². Here we show that ¹²⁹Xe 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 ¹²⁹Xe, in which the magnetization is enhanced by a factor of about 10⁵. By introducing hyperpolarized ¹²⁹Xe 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 trans-ferred 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 ¹²⁹Xe is very sensi-tive to its environment, and is different from that of ¹H₂O, MRI using hyperpolarized ¹²⁹Xe should involve distinct and sensitive mechanisms for tissue contrast.