Experimental Study On Reducing Base Metal Post Core Crown Artifacts In MR Imaging

Objectives To investigate size of MR artifacts generated by base metal post core crown in different sequences and the influence of MR-relevant parameters. We hoped to provide references of dental materials for clinicians and get high quality MR images of patients with unremoval metal material.Material and Methods Lower left six clinical standard models were made as experimental group using two clinical common Ni-Cr alloy and Co-Cr alloy. The same size and shape model using acrylic resin was made as control group. Water models were scanned by 1.5T MR using head coil. The experimental group and the control group underwent axial T1 WI, T2 WI, FLAIR, T2*WI, DWI sequence scanning. MR-relevant parameters of every sequence were adjusted, then models of Ni-Cr alloy and Co-Cr alloy were scanned. To observe the level of artifacts in the largest area of each sequence and measure its area by three times. The datas were analyzed by software of SAS V 8, taking P<0.05 as the difference had statistical significanceResults The artifacts areas generated by Ni-Cr alloy、Co-Cr alloy and Acrylic resin were statistically significant difference among different sequences(P<0.0001). No statistically significant difference existed between T1 WI and FLAIR. There was indicated significant difference betwen above two and T2WI、T2*WI 、DWI. Ni-Cr alloy artifacts than Co-Cr alloy artifacts were significantly affected by changing parameters. By reducing the echo time can reduce the artifacts in T2*WI(P<0.05);minimizing field of view can reduce Co-Cr alloy artifact in FLAIR and DWI(P<0.05)increasing the bandwidth can reduce the artifacts in T1WI(P<0.05); increasing matrix can reduce the artifacts in T1 WI and Ni-Cr alloy artifact in FLAIR(P<0.05);increasing slice thickness can increase the artifacts in T2*WI(P<0.05); increasing echo chain length can reduce Ni-Cr alloy artifacts in T2 WI and Co-Cr alloy artifacts in FLAIR(P<0.05); increasing FA can reduce Ni-Cr alloy artifacts in FLAIR(P<0.05); increasing the number of excitations can reducing Co-Cr alloy artifact in DWI(P<0.05).Conclusions 1 The artifact generated by Ni-Cr alloy was larger than Co-Cr alloy. 2 The artifact size of different scanning sequence was different. The DWI artifact was maximum, T2*WI, then T2 WI, T1 WI and FLAIR sequences of the smallest shadow, andthere was no difference between T1 WI and T2 WI. 3 The artifacts can be reduced by reducing the echo time, increasing bandwidth, thin-layer scanning, increasing matrix,narrowing vision, increasing echo chain length, choosing the special imaging sequence.