Fast Imaging Sequence Design And Research On Methods Of Eliminating Artifacts

MRI(Magnetic Resonance Imaging) is an advanced medical imaging methods in recently. It can obtain any part and any direction of the slice organization of medical images by using the magnetic resonance signals. In the process of magnetic resonance imaging, it requires the imaging sequence to control of spectrometer to generate the corresponding RF pulse, layer selection gradient, phase encoding gradient and the frequency encode gradient to produce an image. In order to pursue higher quality images, design better imaging sequence is a very important condition, so MRI sequence is the most direct carrier of magnetic resonance imaging technology.With the further development of MRI in the field of medical diagnostics, sequence from the mid-century spin echo imaging(spin echo, abbreviated SE) developed to the mid-1980 s gradient echo imaging, and then further development of the 1990 s echo planar imaging(echo planar imaging, referred to as EPI). MRI imaging sequences is the most basic and technical support platform of anatomical structures, functional imaging, molecular imaging. So, we are based on the current demand conditions of MRI sequences, use EPI sequence and true steady state free precession sequence(True-SSFP), and design a new sequence, a imaging time and image quality compared with the original sequence has improved sequence.The main contents are as follows:1. The basic principles of MRI. In this paper we introduce the basic principles of nuclear magnetic resonance imaging briefly, include phase encoding, frequency encoding gradient layer selection and K-space.2. Analyze EPI sequence and True-SSFP sequence. From the imaging principle, the use of parameters and characteristics, scope and other aspects of the sequence, clinical EPI sequence and True-SSFP sequence were analyzed. For EPI sequences, from single-shot echo planar sequence(single-shot EPI, SS-EPI) and multiple excitation echo planar sequence(multi-shot EPI, MS-EPI) explain the two cases. Also, I achieve a sequence diagram EPI sequence and True-SSFP sequence simulation, K-space simulation and image simulation by using ODIN simulation software.3. Design and implementation of single-shot EPI-SSFP sequence. Through in-depth analysis of the EPI-SSFP sequence for multi-shot EPI-SSFP sequence cardiac imaging speed can not meet the dynamic imaging characteristics, we proposed single-shot EPI-SSFP sequence. We solve the selection of a new sequence of incentives, the steady implementation of technical problems, and use the gradient bridge technology to solve the problem of sequence can not achieve the two-way compensation because of TR is too short. In this paper, we design and simulation of a sequence diagram of single-shot EPI-SSFP sequence, K-space filling process and image rendering.4. Analyze fast imaging sequences artifacts elimination method and sequence assessment. In this paper, we analyze fast imaging sequences artifacts elimination method, proposed ghost artifact removal method and achieve it. Finally, we evaluate the method elimination of artifacts, imaging time and image quality of the new sequence compared to the original series(EPI sequence and True-SSFP sequence) have a more significant improvement.