Nuclear Spin Imaging With Hyperpolarized Nuclei Created By Brute Force Method

We have been developing a polarized HD target for particle physics at the SPring-8 under the leadership of the RCNP, Osaka University for the past 5 years. Nuclear polarizaton is created by means of the brute force method which uses a high magnetic field (similar to 17 T) and a low temperature (similar to 10 mK). As one of the promising applications of the brute force method to life sciences we started a new project, "NSI" (Nuclear Spin Imaging), where hyperpolarized nuclei are used for the MRI (Magnetic Resonance Imaging). The candidate nuclei with spin 1/2 (h) over bar are He-3, C-13, N-15, F-19, Si-29, and P-31, which are important elements for the composition of the biomolecules. Since the NMR signals from these isotopes are enhanced by orders of magnitudes, the spacial resolution in the imaging would be much more improved compared to the practical MRI used so far. Another advantage of hyperpolarized MRI is that the MRI is basically free from the radiation, while the problems of radiation exposure caused by the X-ray CT or PET (Positron Emission Tomography) cannot be neglected. In fact, the risk of cancer for Japanese due to the radiation exposure through these diagnoses is exceptionally high among the advanced countries. As the first step of the NSI project, we are developing a system to produce hyperpolarized He-3 gas for the diagnosis of serious lung diseases, for example, COPD (Chronic Obstructive Pulmonary Disease). The system employs the same He-3/He-4 dilution refrigerator and superconducting solenoidal coil as those used for the polarized HD target with some modification allowing the He-3 Pomeranchuk cooling and the following rapid melting of the polarized solid He-3 to avoid the depolarization. In this report, the present and future steps of our project will be outlined with some latest experimental results.