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 lungs and lipid bilayer membranes such as those in the brain. 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. This process produces hyperpolarized 129Xe, in which the magnetization is enhanced by a factor of about 10(5). 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 or emission tomography. As xenon (a safe general anaesthetic) is rapidly and safely transferred from the lungs to blood and thence to other tissues, where it is concentrated in lipid and protein components, images of the circulatory system, the brain and other vital organs can also be obtained. Because the magnetic behaviour of 129Xe is very sensitive to its environment, and is different from that of 1H2O, MRI using hyperpolarized 129Xe should involve distinct and sensitive mechanisms for tissue contrast.

Large Production System for Hyperpolarized 129Xe for Human Lung Imaging Studies

“…They can be introduced into the body non-invasively by breathing and imaged with no background. Two noble gases, 3 He and 129 Xe, have nuclear spin one-half and gyromagnetic ratios relative to that of the proton of 0.76 and 0.28, respectively. They present the advantage of having zero quadrupole moment and, as a consequence, long T 1 relaxation times after being polarized.…”

Functional lung imaging using hyperpolarized gas MRI

“…More recently, functional lung imaging has been performed using positron emission tomography (PET) (7,9 -11), and hyperpolarized gas MRI (HP MRI) (12)(13)(14)(15); techniques capable of providing three dimensional (3D) regional information and quantitative or semiquantitative measures of ventilation and perfusion. These new techniques are rapidly expanding the field of functional lung imaging for improved diagnosis and noninvasive monitoring of disease progression-in some cases with the necessary sensitivity to track an individual patient's response to therapy.…”

“…HP MRI has shown rapid development from the first images acquired in the early 1990s (12) to the present range of functional imaging techniques that exploit fast acquisition methods and unique contrast mechanisms. Specifically, the HP gases act as contrast agents that diffuse rapidly to fill the airspaces of the lungs and allow visualization and measurement of the ventilated airways and alveolar spaces.…”

Measurement of alveolar oxygen partial pressure in the rat lung using Carr‐Purcell‐Meiboom‐Gill spin–spin relaxation times of hyperpolarized 3He and 129Xe at 74 mT

“…Hyperpolarized 129 Xe gas was produced with a home-built, continuous flow polarizer, giving polarizations of 10-15% (29). The xenon polarizer employed natural abundance xenon gas (26.4% 129 Xe) in a gas mixture consisting of 1% Xe and 10% N 2 , balanced with 4 He. The polarizer operated at a total flow rate of $0.35 L min À1 .…”

“…The first MR images of HNG were produced in excised mouse lungs using 129 Xe (4). HNG MR imaging has been employed in a number of in vivo applications in both animals and humans (5-7), in particular, measurements of the apparent diffusion coefficient (ADC) of 3 He gas within the lung have been shown to reveal microanatomical changes associated with emphysema (8)(9)(10).…”