Inert hyperpolarized gases are under development for imaging air spaces, including those in the lungs. Because they mostly contain air and water, lungs are difficult organs to image.
These ventilation agents (gases) have potential in lung imaging and are currently used in studies of the pulmonary ventilation:
Specific isotopes of inert gases can be hyperpolarized. Hyperpolarized is a state in which almost all of the atoms nuclei are spinning in the same direction. Once the nuclei in the isotope 3He have been hyperpolarized using a laser, they remain in this state for several days. The inert, hyperpolarized gas can then be used in a lung imaging study, where the high concentration of polarized nuclei provides a sharp contrast in MRI. The technique is already being developed with a view to commercialization by Magnetic Imaging Technologies in Durham, North Carolina. According to the company, existing MRI equipment can be used with a few minor modifications, along with a gas polarizer. The technique could provide early detection and monitoring of pulmonary disease.
Hyperpolarized 129Xe can also be used as a magnetic resonance tracer because of its MR-enhanced sensitivity combined with its high solubility. This isotope differs from 3He in that it can dissolve in the blood. Strong enhancement of the nuclear spin polarization of xenon in the gas phase can be achieved by optical pumping of rubidium and subsequent spin-exchange with the xenon nuclei. This technique can increase the magnetic resonance signal of xenon by five orders of magnitude, thus allowing NMR detection of xenon in very low concentration. MR spectroscopy and imaging of optically polarized xenon shows considerable potential for medical applications (see also back projection imaging).
Nycomed Amersham anticipated the market for inert gases in pulmonary imaging. The company obtained an exclusive license for the use of helium (He) and xenon (Xe) as MRI contrast agents. Currently, the US FDA has not yet approved the commercial distribution of inert gas imaging equipment, because the technique is still undergoing trials.