Diffusion Imaging At Low Field Strength MRI

Diffusion MRI can be used to study the random motion and transportation of water molecule protons in vivo, which has a high clinical value. Diffusion weighted imaging(DWI) is able to detect ultra-acute and acute cerebral infarction, and can detect acute ischemic changes within minutes of onset. DWI can distinguish acute cerebral from chronic cerebral infarction. DWI can also diagnose brain tumor and white matter pathology. Diffusion anisotropy can reveal the fabric of brain.Diffusion tensor image (DWI) can specialize the small structure in brain; it can identify the small change in white matter. DTI also promises to further our understanding of abnormalities in variety of diseases such as stroke, tumors, multiple sclerosis, and schizophrenia. The most advanced application is that of fiber tracking in the brain. Combined with conventional MRI and FMRI, fiber tracking will be a new method for preoperative plan and postoperative evaluation.Due to the development of technology in recent years, the performance of permanent MRI is improving constantly; the price and the running cost are low. So it is more and more popular in the market. At the same time, with the open structure of magnet, permanent MRI lets the patients free of claustrophobia. And the interventional therapy will be possible; Using of life-support system and monitoring equipment will be easier.However, the quality of diffusion image is still not ideal whether at the low field strengths MRI,. There are number of problems to be concerned: the image distortion, which is caused by eddy current, residual magnetization and susceptibility, the ghost artifacts due to physiological motion of the patients, as well as the poor SNR. All these problems will lead to diagnosis and quantitative analysis difficult.Based on the above reasons, we study the diffusion imaging method at permanent MRI system in this thesis. The main contents include:1. Diffusion weighted imaging using line scan method. The ADC values were obtained from the brain of healthy volunteers using this method.2. Diffusion tensor imaging using line scan method. The diffusion tensor data were obtained from the brain of healthy volunteers.3. Correction of motion artifacts in diffusion weighted image using navigator echoes.