口腔金属材料磁共振成像伪影的初步探讨

Artifacts from dental metal alloys in magnetic resonance imaging

目的探讨1．5T、3．0T场强下口腔内常用3种金属材料在磁共振检查时是否产生伪影和伪影的严重程度，并比较不同成像序列对伪影的影响。方法将3种口腔内常用金属材料组成的烤瓷冠及对照组树脂冠制备成琼脂模型，分别使用1．5T、3．0T的磁共振扫描仪进行扫描，测量伪影直径。统计采用4×4×2三因素析因设计，分析不同材料、不同成像序列以及不同磁场强度对MRI成像伪影大小的影响。结果析因设计方差分析发现，不同材料、成像序列以及磁场强度对成像伪影大小的影响差异均有统计学意义（材料：F=124．796，df=3，P=0．000；成像序列：F=3．020，df=3，P=0．036；磁场强度：F=9．367，df=1，P=0．003）。金属材料中，金合金产生的伪影最小；与其他成像序列相比，FSE序列的伪影直径最小；磁场强度为1．5T的伪影直径〈3．0T。而各因素间的交互作用对伪影的影响差异无统计学意义（P〉0．05）。结论合理选择金属材料和扫描序列可以减轻伪影；量化指标显示3．0T场强下伪影增幅只在10％左右，因此，为了临床需要选择高场机器是可行的。

Objective To evaluate the artifact sizes at 3.0 T compared to at 1.5 T caused by three kinds of metallic dental materials, and to evaluate the influences of different magnetic resonance imaging （MRI） sequences on the artifact. Methods Samples of metal-ceramic crown of three kinds of dental materials （ Ni-Cr alloy, Co-Cr alloy, and gold alloy） agarose gel. Acrylic resin crown was used as control. were placed in a cylindrical plastic vessel filled with Images were performed by means of 1.5 T and 3.0T MRI apparatus with 4 different sequences commonly used in brain MRI sequences. Artifact diameter was calculated and compared quantitatively. A 4 × 4 × 2 factorial design was applied to determine the effects on the MRI artifact of different metal materials, different sequences, and different magnetic field strengths. Results ANOVA of factorial design showed that the influences of material, magnetic field strength, and sequence were all significantly different（ materials ： F = 124. 796, df= 3, P = 0.000 ; magnetic field strength ： F = 9.367, df = 1, P = 0. 003 ; sequence ： F = 3. 020, df = 3, P = 0. 036 ）. Among the 3 kinds of alloys, the gold alloy produced the least artifact. Among the 4 imaging sequences, fast spin echo （FSE） produced the least artifact. The artifact sizes increased at 3.0 T compared to at 1.5T. Interactions among the 3 factors did not influence the artifacts significantly （ P 〉 0.05 ）. Conclusion Selection of specific metal material and imaging sequence can minimize the metal artifacts in MRI. The increment of artifacts at 3.0 T is only by 10% compared to that at 1.5 T. But 3.0 T MRI system has great advantages, so it is eligible on patients with metal restoration.