Recently, there has been considerable interest in the development of MRI techniques for the evaluation of patient with functional pulmonary disorders. There are significant limitations, however, in all current imaging techniques for assessment of regional pulmonary function. Proton MRI of the lung parenchyma, for example, is intrinsically difficult due to significant magnetic field inhomogeneity which causes the transverse relaxation time to be extremely short. Recently, a novel form of NMR has been described in which the signal source is derived from optically polarized spin-1/2 noble gases such as 3He and 129Xe. This new technique introduces the possibility of a dramatic new contrast modality. Organs filled with air, such as the lungs, are optimal candidates for the application of this technique. We have assembled a system that produces helium cells with relaxation time of up to 35 hours. We have also implemented both software and hardware modifications for imaging 3He on a 1.5 T GE scanner. The implementation included the modification of a gradient echo pulse sequence to accommodate the use of a broad band receiver that operates at the Larmor frequency for 3He. We have also constructed a transmit/receive surface coil tuned to the helium frequency. We have implemented this method for nuclear polarization and imaging and have obtained images of pulmonary ventilation from both healthy subjects and a patient. These images surpass in quality those generated with radionuclear methods, while at the same time avoiding exposure to ionizing radiation. While we have produced up to 5% nuclear polarization the setup still suffers from a number of shortcomings. The laser power used in this setup is not sufficient and forces us to operate at a lower temperature which results in longer polarization times. We expect to obtain at least twice the polarization in the same amount of time ( ~ 10 hours) by using higher power laser. We plan to study ways to produce cells with long relaxation time that will be capable of few refills. We are also working on construction of a volume coil for lung imaging. Currently, we are using a surface coil for both transmit and receive. We plan to use this method for early detection of lung disease.
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