目的:评估正畸导线在MRI上产生的磁化率伪影以及导线特性和MRI图像序列对伪影大小的影响。
方法:拱形正畸丝[四种不锈钢(SS),一种钴铬(CC)合金,13钛(Ti)合金]嵌入聚酯模型中,并使用带有八通道相控阵线圈的1.5T超导磁体扫描仪进行扫描。根据美国材料与试验协会(ASTM)F2119-07标准,用T1加权自旋回波(SE)和梯度回波(GRE)序列扫描所有导线。体模还扫描了其他八个序列。使用ASTMF2119-07定义和OsiriX软件测量伪影。根据金属成分分析了人工制品的体积,导线长度,电线数量,导线厚度,和成像顺序作为因素。
结果:使用SE/GRE,所有SS线产生的黑色/白色伪影体积均显着大于CC和Ti线产生的伪影体积(P<0.01)。有了GRE,SS线的黑色人工制品量最高。有了SE,黑色文物体积很小,而白色人工制品是明显的。SS线的伪影的颅尾范围明显更长(P<0.01)。虽然与导线长度有直接关系,记录了导线数量和导线厚度以及人工制品体积,这些因素不影响颅尾方向的伪影扩展。
结论:由于磁场均匀性的局部改变,铁磁/顺磁性正畸丝产生伪影。SS型导线产生的伪影最大,其次是CC和Ti。
OBJECTIVE: To evaluate magnetic susceptibility
artefacts produced by orthodontic wires on MRI and the influence of wire properties and MRI image sequences on the magnitude of the artefact.
METHODS: Arch form orthodontic wires [four stainless steels (SS), one cobalt chromium (CC) alloy, 13 titanium (Ti) alloys] were embedded in a polyester phantom, and scanned using a 1.5-T superconducting magnet scanner with an eight-channel phased-array coil. All wires were scanned with T1-weighted spin echo (SE) and gradient echo (GRE) sequences according to the American Society for Testing and Materials (ASTM) F2119-07 standard. The phantom was also scanned other eight sequences.
Artefacts were measured using the ASTM F2119-07 definition and OsiriX software. Artefact volume was analyzed according to metal composition, wire length, number of wires, wire thickness, and imaging sequence as factors.
RESULTS: With SE/GRE, black/white artefacts volumes from all SS wires were significantly larger than those produced by CC and Ti wires (P < 0.01). With the GRE, the black
artefacts volume was highest with the SS wires. With the SE, the black
artefacts volume was small, whereas white
artefacts were noticeable. The cranio-caudal extent of the artefacts was significantly longer with SS wires (P < 0.01). Although a direct relationship of wire length, number of wires and wire thickness with artefact volume was noted, these factors did not influence artefact extension in the cranio-caudal direction.
CONCLUSIONS: Ferromagnetic/paramagnetic orthodontic wires create artefacts due to local alteration of magnetic field homogeneity. The SS-type wires produced the largest
artefacts followed by CC and Ti.