Studies On The Method Of Hyperpolarized ¹²⁹Xe Diffusion-weighted MRI And Its Applications On Pulmonary Diseases

The lung is an important respiratory organ for humans.It is the main place for achieving the functions of gas-air exchange and gas-blood exchange,and plays an important role in maintaining the health of the human body.However,due to environmental pollution and personal bad habits such as smoking and other factors,make lung disease become the main factor affecting human health.The incidence of chronic obstructive pulmonary disease?COPD?is on the rise,rising from the fifth cause of death in 2002 to the third in2016.The incidence of lung cancer has also been on an upward trend.The number of deaths caused by lung cancer increased by 24.4%in 2016 compared with 2005,which is the fourth leading cause of death.The current tools for the diagnosis of lung disease are primarily pulmonary function test,but it can only measure overall lung function;other imaging modalities for diagnosing pulmonary diseases such as chest radiography,computed tomography?CT?,and positron emission Tomography?PET?,etc.,have limited clinical use due to their ionizing radiation or low signal-to-noise ratio.The proton magnetic resonance imaging?MRI?makes it difficult for the lungs to be imaged due to the predominantly hollow structure of the lungs and the low proton density.Hyperpolarized gas MRI is a new tool for lung disease by imaging hyperpolarized inert gases(³He or¹²⁹Xe)aspirated into the lungs.Currently,the use of hyperpolarized gas MRI imaging of the lungs can be visualized.At the same time,different research methods can be used to obtain information on the function of the lungs,the oxygen partial pressure in the lungs,the morphological structure of the alveoli,and the structural or functional information of blood and blood exchange.Due to the rare and expensive ³He,the future is almost impossible to apply to the clinic.The ¹²⁹Xe is abundant on the planet and low in price.Studies have shown that hyperpolarised ¹²⁹Xe can replace ³He to obtain structural and functional information about the lungs.Therefore,hyperpolarized ¹²⁹Xe MRI has a very wide range of clinical applications.The main work of this thesis is to study the methods and diseases using hyperpolarized ¹²⁹Xe diffusion-weighted MRI.The main work includes the following three aspects:First,compressed sensing?CS?technique was applied to hyperpolarized ¹²⁹Xe multi-b diffusion-weighted imaging?DWI?and the lung morphology was studied using this method.The results show that CS can reduce scan time and obtain the same lung morphological parameters as the full sampled acquisition.At the same time,the accelerated DWI method was applied to patients with COPD,the morphological parameters obtained and healthy volunteers were significantly different results.Second,hyperpolarized ¹²⁹Xe multi-b DWI method was used to detect smoking-induced lung injury.The results showed that the morphological parameters obtained by this method are strongly correlated with the parameters of pulmonary function DLco/VA.As the disease progresses,the trends of changes in lung morphological parameters were consistent with the results reported in the literature.In particular,the alveolar depth,h,was significantly different among healthy smoking volunteers?normal lung function and CT results?and asymptomatic smoking volunteers?normal pulmonary function and CT showed emphysema?,which was not possible with other parameters make a distinction.Thus,h is very sensitive to early emphysema.Third,hyperpolarized ¹²⁹Xe multi-b value DWI method was used for the visual detection of lung injury caused by radiotherapy.The results showed that the different performance of volunteers after different radiotherapy may be related to the MRI imaging time and radiation dose after radiotherapy.