Studies Of Xenon-129 Hyperpolarizer For The Human Lung Magnetic Resonance Imaging

As the main organ in the respiratory system, lung has two most important functions, i.e., gas-gas and gas-blood exchange, which is vital for the human lives and health. Probably due to the environment pollution and the other harmful factors, pulmonary disease is becoming a serious issue which jeopards lives and health and the quality of life. It has been reported that the mortality of lung cancer is higher than others. The morbidity of the other pulmonary disease, such as COPD (chronic obstructive pulmonary disease) is also very high, showing an ascending trend. The conventional imaging modality, such as chest X-ray, CT (Computer Tomography), PET (Positron Emission Tomography), have been used for the diagnosis of pulmonary disease. However, these techniques are radioactive or low signal-noise ratio (SNR), and they could not provide the comprehensive function information of the lung, which greatly hampers the diagnosis of the pulmonary disease at the early stage. With the development of laser technology, the technique of spin-exchange optical pumping (SEOP) is able to produce hyperpolarized noble gases at a large volume. Magnetic resonance imaging (MRI) with hyperpolarized noble gases makes gas imaging fesible, thus providing a non-radioactive and non-invasive way for the diagnosis of pulmonary disease at high sensitivity. As it is well known, the most regions of the lung are airspace, resulting in a void signal if using the conventional proton MRI at thermal polarization. However, hyperpolarized noble gases MRI enable to visulize both ventilation structure and gas exchange function of the lung.The work presented in this thesis is regarding research and development of xenon-129 hyperpolarizer for the human lung MRI.First, the fundamental physics is introduced, including the principle of optical pumping of the alkali metal atoms, spin exchange collisions and related important parameters. Due to the laser heating effect in the spin-exchange optical pumping, a new cascade optical cell and regional thermal control are proposed and implemented. Through the study of the relaxation mechanism of the solid hyperpolarized xenon-129, a new spiral collection cold finger and magnet is designed and manufactured in order to maximumly preserve and recover the spin polarization of hyperpolarized xenon-129 in process of the accumulation and sublimation. Finally, the key parameters in such continuous flow mode xenon-129 hyperpolarizer have been optimized using a low field (20 G) NMR spectrometer. It includes the optimization of the cell temperature, gas misture’s pressure and flow rate, laser wavelength and so on. After the optimization, the polarization of hyperpolarized xenon-129 was achived a more than 50,000-fold enhancement in comparison to the thermal equilibrium one. Human lung and multi-slice MRI with such hyperpolarized gas xenon-129 have also been succefully obtained.