快递稳态进动采集序列磁敏感伪影和伪影抑制方法的研究

Magnetic susceptibility artifact in FIESTA and its reduction

目的 :研究快速稳态进动采集(fast imaging employing steady-state acquisition,FIESTA)序列磁敏感伪影的成因以及抑制方法。方法:采用不同匀场技术、带宽和部分回波技术的FIESTA序列对患者进行腹部冠状位扫描。以膈肌以下肝脏部位为感兴趣区,比较不同扫描策略时,感兴趣区磁敏感伪影的差异。结果:匀场技术可以改善伪影,半扫描野(field of view,FOV)匀场效果优于全FOV匀场效果(Z=-6.211,P=0.000);随着带宽的增加,感兴趣区的磁敏感伪影逐渐减少(F=5.044,P=0.011);部分回波技术扫描所得图像较全回波技术扫描所得图像伪影减少,差异有统计学意义(t=5.111,P=0.000)。结论 :FIESTA序列腹部冠状位扫描时膈肌附近易产生磁敏感伪影;伪影是由于肺部组织与腹腔实质器官磁敏感性差异较大引起的;施加局部匀场、增加带宽和采用部分回波技术可以减少磁敏感伪影。

Objective To investigate the mechanism of magnetic susceptibility artifact of fast imaging employing steady-state acquisition（FIESTA） and the methods to reduce it. Methods The patients underwent FIESTA abdominal coronal MR scanning with different shimming techniques, bandwidths and partial echo technique. The liver under the diaphragm was selected as the region of interest（ ROI） and the susceptibility artifacts of ROI of different scanning strategies were compared. Results The shimming technique could reduce the magnetic susceptibility artifacts, and shimming of half field of view（FOV） was better than that of full FOV（Z=-6.211,P=0.000）. The susceptibility artifact of ROI decreased with the bandwidth increased（F=5.044, P=0.011）. The susceptibility artifact of the image by partial echo technique was significantly less than that by whole echo technique（t=5.111, P=0.000）. Conclusion Magnetic susceptibility artifact may occur near the diaphragm in FIESTA abdominal coronal MR imaging, which is caused by the magnetic susceptibility difference between the lung and abdominal organs. Shimming technique, increased bandwidth and partial echo technique can reduce magnetic susceptibility artifact.