磁共振血管MIP图像伪影形成机制、表现及解决办法探讨

The mechanism of formation and solution of artifacts on MIP image of MRA

目的了解最大密度投影重建(MIP)图像伪影的形成机制,熟悉磁共振血管成像中MIP伪影的各种表现,探讨其解决办法。材料与方法回顾性分析2003年12月～2004年6月磁共振血管检查患者共90例,其中头部3DTOF-MRA检查47例,颈部2DTOF-MRA检查20例,均同时进行了颈部3DCE-MRA检查;腹部3DCE-MRA检查25例。对各部位出现的MIP伪影进行分类、分析,探讨对不同表现形式的MIP伪影的解决办法。结果①头部TOF-MRA的整体MIP图像上细小血管分支未显示共40处(后交通动脉32处,前交通动脉8处),通过对原始图像的观察或局部薄层重建使上述两处血管均得到显示。②20例颈部TOF-MRA检查中夸大血管狭窄程度共14处,均出现在血管狭窄程度在50%以上的血管,占病变总数的93.3%(14蛐15),CE-MRA对TOF-MRA夸大狭窄均做出了准确的矫正。颈部20例TOF-MRA中,颈外动脉锯齿状伪影36处,出现的几率为90%(36蛐40)。CE-MRA对此种伪影均做出了矫正。④MIP图像上在特定投影方向上血管分支不显示,通过改变投影方向或去掉高信号的背景组织此种伪影均得到解决。结论磁共振血管检查MIP图像上出现伪影是常见现象,表现具有多样性;MIP图像伪影可造成错误的诊断。MIP图像的伪影可以通过不同的后处理方法或改变成像方法解决。在临床实际工作中不可单凭MIP图像做出最终诊断,需密切结合原始图像和不同处理方法的血管重建图像。

Objective: To improve the knowledge of the mechanism of how the artifacts in MIP reconstruction is formed and to be familiar with the appearances of different artifacts of MRA on MIP images, and also try to find out how to solve the problems. Methods: 3D TOF-MRA images was performed in 90 cases since December 2003. 3D TOF-MRA of the cerebral arteries was performed in 47 cases, 2D TOF-MRA and 3D CE-MRA of the carotid arteries and vertebral arteries were performed in 20 cases, abdominal 3D CE-MRA in 25 cases. Different kinds of artifacts were classified and analyzed in order to find out the solution. Results: ①Small vessels cannot be seen in 40 sites(32 were artery communicans posterior and 8 were artery communicans anterior). In the MIP image reconstructed by the source images near the interest vessels, all the artery communicans posterior and artery communicans anterior stand out clearly. ②The degree of narrowing was exaggerated in 14 sites(14/15, 93.3%) that is more than 50% in 20 cervical TOF-MRA. CE-MRA corrected the distortion of TOF-MRA. ③Thirty-six artifacts showed zigzag margin in all the external carotid arteries(90%), CE-MRA correct this artifact. ④The special branch of vessels cannot be seen in special direction of MIP. This problem can be solved by changing the direction of projection or removing the high signal tissue background. Conclusion: Different artifacts in MIP image of MRA are common in daily work. The artifacts of MIP image can cause false diagnosis. Different reconstruction or different examination method can solve the questions. The final diagnosis cannot be made by MIP alone. More attention should be paid to the source images and different reconstruction method.