MRI OF HYPERPOLARIZED NOBLE GASES

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Recent advances in the imaging of hyperpolarized noble gases (3He, 129Xe) has opened up the possibilities for high resolution imaging of physiologically important airspaces, such as lungs and sinuses, which are otherwise virtually invisible to conventional proton MRI. A fundamental property of the hyperpolarized gases, one which makes them extremely promising for high resolution MRI, is their exceptionally large non-equilibrium nuclear polarization. This suggests that MRI of hyperpolarized gases can be useful in generating ventilation maps of the lungs, as well as assessing sinus ventilation. The overall goal of this project is to advance the novel MRI technique of hyperpolarized noble gas imaging to a clinically applicable stage, and to establish the feasibility of using it as a diagnostic tool in the pre- and post-operative evaluation of patients who undergo either a lung volume reduction surgery or a functional sinus surgery. Over the past 12 months we have built and assembled the components of the setup required for hyperpolarization, including a high-vacuum gas handling system and an optical unit based on a diode array laser. We have been able to produce a moderate degree of polarization in 3He (up to 6.5%). We have obtained a series of images of the lungs of both a normal volunteer and a patient with COPD. The images clearly showed the boundaries of different lung lobes, the trachea, the major bronchi, and some smaller airways. The images obtained from the healthy subject displayed homogeneous distribution of the inhaled gas, thus suggesting normal ventilation of the parenchyma. In contrast, the patient's lungs exhibited highly inhomogeneous pattern of distribution which was later correlated with images obtained using both arterial spin labeling and radionuclear methods of imaging. We have also demonstrated, for the first time, the feasibility of imaging hyperpolarized 3He in human paranasal sinu ses. All four types of paranasal sinuses were clearly depicted in the 3He images.