| Population health directly affects the economic development and social progress of a country. In recent years, chronic obstructive pulmonary disease (COPD), asthma and pneumoconiosis have been a rising threat on the population health. Lower respiratory tract infection, chronic obstructive pulmonary disease and lung cancer have ranked the top ten causes of death in Chinese population. Currently, about 1 in every 4 cancer deaths are causing by lung cancer in urban population. Early treatment of these lung diseases is urgent and necessary. Chest X-ray, computed tomography (CT) and positron emission tomography (PET) are the routine methods for evaluating the pulmonary structure and function. CT is by far the most ideal non-invasive radio logic imaging method for the diagnosis of the pulmonary diseases because it can achieve the best spatial resolution. PET and SPECT can obtain some information about pulmonary structure and function, but the spatial resolution of these two methods is much lower than that of CT. Unfortunately, all the methods mentioned above have the risk of cumulative radiation doses and cannot visualize the pulmonary gas exchange, which is the most important function of the lung. In pathology, the functional changes always happen prior to the structural lesions, and therefore it is significant to detect the gas exchange function for the early pulmonary diseases diagnosis. Lung is a challenge for the current clinical MRI, because it is mainly made of airspaces and the tissue densities is extremely low. Accordingly, it is impossible to visualize the lung airspace in the gas phase by using the conventional proton MRI.The method of spin-exchange optical pumping (SEOP) can enormously improve the MRI sensitivity (3He,13C,83Kr,129Xe) by enhancing their nuclear spin polarizations by four to five orders of magnitude over the thermal equilibrium, which makes the gas MRI feasible. Due to the high lipid solubility, large chemical shift sensitivity to the neighbor environment and absence of background signal in biological tissues, hyperpolarized 129Xe has an exclusive feature in assessing the pulmonary gas exchange.Firstly, the homebuilt system for hyperpolarized xenon gas MRI were presented and the lung gas MRI were successfully obtained in vivo by the system. The dynamics of hyperpolarized 129Xe were studied in vivo. Then, the effects of the fluctuation in the RBC xenon signal caused by the heartbeat on the physiological parameters were evaluated in healthy and smoke-exposed rats.Secondly, to get the pulmonary function when the polarization of xenon gas is not so strict and make it more accessible, we proposed an optimized CEST experiments, and the requirement of the signal intensity was very loose. The spatial distribution of the consumption time constant was analyzed in the healthy and COPD rats, and the consumption time constant was found obviously larger and heterogeneous in COPD rat pulmonary parenchyma.Finally, to maximize the utility of the limited high 129Xe nuclear spin polarization, the optimum ventilation strategies were investigated for hyperpolarized 129Xe brain MRI in order to obtain the maximal 129Xe signal from the lung. A more reliable and accurate parameter, the apparent relaxation time (To-c), was proposed and utilized to evaluate the dependence of hyperpolarized xenon signal in the brain on pulmonary oxygen concentration in animal experiments. The optimal pulmonary oxygen concentration obtained from the theoretical model was in agreement with the oxygen concentration of the air. Finally, the hyperpolarized 129Xe brain MRI was achieved in the rat. |
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