回波平面成像中基于相位恢复的ghost伪影校正

EPI技术是基于方向相反的频率读出的梯度来交替采集MR信号的奇、偶回波，但是，由于成像物体的磁敏感性、化学位移及磁场曰。的不均匀性等因素的影响会导致奇、偶回波之间产生相位移动，因而会产生ghost伪影。为了消除成像中产生的ghost伪影，提出了基于相位恢复的ghost伪影消除方法，即用数学形态学的方法确定支撑域，支撑域外的ghost伪影被置为零，首先获得模板图像；然后以最小熵为收敛准则运行迭代算法，直到得到满意的图像。实验证明，运用该方法能够明显地降低ghost伪影，可见这种方法是可行的。

Removal of Ghost Artifacts Based on Phase Retrieval for EPI

Ghost artifacts occur in EPI reconstruction because odd and even lines of k-space are acquired with opposite polarity,and experimental imperfections such as gradient eddy current,B_0 field inhomogeneity,susceptibility,and chemical shift result in different phase offset between the even and odd echos.The method for removing ghost artifacts is based on the phase retrieval.First,a ROS(region of support) is specified using morphological method and ghost artifacts outside ROS are set to zero.Then a model image can be obtained.According to the criterion of entropy in the imaging field,the algorithm for several iterations is applied to obtain an acceptable image.It is shown that applying this method will reduce the ghost artifact evidently.The method has been tested using computer simulation and successfully removed most of ghost artifacts.The experimental results show the effectiveness of the method.