Research On Algorithm Of Ghost Artifacts Removing In EPI

With the development of medical level and computer technology, magnetic resonance imaging technique is becoming one indispensable part of disease diagnosis. Unfortunately, MR imaging time is too long to satisfy the need for some special patients, such as bad or incoordinate patients. So, people insist on developing the fast imaging technique for magnetic resonance. Now echo planar imaging (EPI) is one of the fastest imaging ways, which can finish a whole image in 30 ms. The EPI method uses reverse direction frequency read-out gradient to get the odd and even MR signals in turns. Because of the ununiformity of static magnetic field, eddy current causing by the high speed switch of gradient magnetic field, chemical shift etc, phase differences are caused between odd and even echoes, which in turn generate Ghost artifact in phase code direction.The Ghost artifact is one of the popular artifacts in EPI. The false information carried by the artifact which makes the clinician hard to make decision. So, the research on removing the Ghost artifact is one of the hot topics in EPI study. In this paper, through deeply understanding the generation theory of the Ghost artifact, we focus our interest on two popular removing methods base on the image. One is respective reconstruction of odd and even which proposed by the Buonocore inl996 , the other is the iterative method which proposed by the Lee in 2002. From experiments we found that the Buonocore's method only uses two step reconstruction and one step calibration. But one of the drawbacks is that need the high signal to noise ratio (SNR) and accurate parameters, which caused this method to fail to apply to in vivo data. Lee's method needs to reconstruct and calibrate times after time. Moreover, it has to choose different region of interest (ROI) for different images. But this method doesn't require high SNR, it gets a better result than Buoncore's method when removing the Ghost artifact in vivo. In this paper, a novel algorithm, namely "a method to remove the Ghost artifact base on the K-space conjugate symmetry", is...