Quantitative Assessment Of Human Pulmonary Tissues With Multinuclear (Hyperpolarized Xenon) Magnetic Resonance

Lung diseases,whose morbidity and mortality have been gradually increasing in recent years,have become a public health issue around the world.Pulmonary function tests(PFTs),chest X-ray,computed tomography(CT)and positron emission computed tomography(PET)are the most widely used diagnostic techniques for lung diseases in clinic.PFTs could obtain the global ventilation information of the lung without ionizing radiation,however,it cannot visualize the ventilation of the lung.Imaging methods such as CT and PET can visually assess the structure or metabolic function of the lungs.However,the repeated clinical applications of these methods in the short time are limited because of the ionizing radiation or radioactivity.Current clinical magnetic resonance imaging(MRI),whose images are based on mononuclear imaging,i.e.,hydrogen proton(1H)in the water,is non-ionizing radiation and non-radioactive,and also can provide the structure and function information of almost all the tissues and organs in human.Lung tissue is the "blind area" for conventional mononuclear(1H)MRI because of its special cavity structure,and its global 1H density is much lower than that in other tissues,which makes it difficult for conventional mononuclear(1H)MRI to image the lungs.Multinuclear MRI,which could image the tissues or organs of the human based on 13C、19F、23Na、31P、129Xe and other nuclei,could detect and quantify the structural changes,metabolic abnormalities or functional changes in tissues and organs such as brain,heart and muscle.Extremely low sensitivity is the biggest challenge of multinuclear MRI for clinical applications.Fortunately,the emerging hyperpolarized multinuclear MRI,which could enhance the sensitivity of MRI by 4 orders of magnitude,makes the clinical applications of multinuclear MRI possible.The technique of hyperpolarization that based on spin exchange optical pumping(SEOP)could enhance the MR signal sensitivity of noble gas(129Xe)by more than 50,000 times,and makes lung gas MRI possible,and opens the door for quantitatively visualizing lung tissue structure and function.In this paper,we developed new imaging method for measuring lung tissue structure and function based on multinuclear(hyperpolarized 129Xe)MR,and further applied the proposed method for quantitatively assessing physiological changes of human lungs caused by diseases.First,a method for optimizing radiotherapy planning in patients with lung cancer with multinuclear(hyperpolarized 129Xe)ventilation MRI has been developed.The ventilation function information of lung tissue obtained with hyperpolarized 129Xe MRI has been incorporated into the radiotherapy treatment planning to guide and optimize the radiotherapy planning for patients with lung cancer.The results show that the optimized radiotherapy planning can effectively reduce the radiation exposure in wellventilated areas of the lung tissue and reduce the potential radiation-induced lung injury while meeting the clinical treatment planning goals.Second,a method using variable-sampling-ratio compressed sensing patterns(VCS)for accelerating multinuclear(hyperpolarized 129Xe)diffusion-weighted imaging(DWI)was developed and used to quantitatively assess the microstructural changes of lung tissue caused by cigarette smoking.In the proposed method,different sampling ratios for different b-value DW images were utilized to accelerate the acquisition based on compressed sensing(CS)technique.The results show that VCS DWI can reduce the acquisition time,and meanwhile the retrospectively reconstructed images by VCS DWI are in good agreement with those using full sampled DWI.In addition,the method can also be used for evaluating the morphological changes of lung tissue caused by smoking.Third,the structure and functional changes of lung tissue caused by primary and secondary lung tumors were studied using multinuclear(hyperpolarized 129Xe)MRI and magnetic resonance spectroscopy(MRS).The structure and function changes of lung tissue including decreased ventilation function,enlarged pulmonary microstructure,and increase septal wall thickness were found in the patients with primary lung cancer.However,no significant differences were found in the lung tissue structure and function between patients with secondary lung cancer and healthy volunteers.These findings indicate hyperpolarized 129Xe MR might be used for differentiating the patients with primary and secondary lung cancer.Fourth,the structure and functional changes of lung tissue caused by COVID-19 were studied using multinuclear(hyperpolarized 129Xe)MRI and MRS.Preliminary results showed that there were no significant differences in structure and function of lung tissue between discharged patients with asymptomatic COVID-19 and healthy volunteers,indicating that the lung tissue structure and function of discharged patients with asymptomatic COVID-19 are in the normal levels.