NUCLEAR-MAGNETIC-RESONANCE IMAGING WITH HYPERPOLARIZED HE-3

Background Magnetic resonance imaging (MRI) relies on magnetisation of hydrogen nuclei (protons) of water molecules in tissue as source of t he signal. This technique has been valuable for studying tissues that contain significant amounts of water, but biological settings with low proton content, notably the lungs, are difficult to image. We report use of spin-polarised helium-3 for lung MRI. Methods A volunteer inhal ed hyperpolarised He-3 to fill the lungs, which were imaged with a con ventional MRI detector assembly. The nuclear spin polarisation of heli um, and other noble gases, can be greatly enhanced by laser optical pu mping and is about 10(5) times larger than the polarisation of water p rotons, This enormous gain in polarisation easily overcomes the loss i n signal due to the lower density of the gas. Findings The in-vivo exp eriment was done in a whole-body MRI scanner. The He-3 image showed cl ear demarcation of the lung against diaphragm, heart, chest wall, and blood vessels (which gave no signal). The signal intensity within the air spaces was greatest in lung regions that are preferentially ventil ated in the supine position; less well ventilated areas, such as the a pices, showed a weaker signal. Interpretation MRI with hyperpolarised He-3 gas could be an alternative to established nuclear medicine metho ds, The ability to image air spaces offers the possibility of investig ating physiological and pathophysiological processes in pulmonary vent ilation and differences in its regional distribution.