Experimental Research On Artifacts Caused By Dental Metallic Materials And Artifact-Controlling Of MR Images

ObjectiveThe purpose of this study,was to investigate the effect of dental metallic materials positioning on MR imaging artifacts,and to approve that the MRI sequences and MR-relevant parameters can affect magnetic susceptibility artifacts caused by,dental metallic materials.The experimental results were hoped to give references for choices of dental materials and clinic MRI test.MethodsMetal crown samples of six kinds of dental materials(Ni-Cr alloy,Co-Cr alloy, titanium alloy,pure titanium,Ag-Pd alloy and Au-Pd alloy) were placed in a Cylindrical plastic phantom filled with 2%agarose gel.Acrylic resin crown was used as control.1.Images were performed by means of 1.5 T GE Twinspeed Infinity Exciteâ…¡MRI apparatus with 7 different sequences commonly used in brain MRI sequences(GRE T*₂WI,SE T₁WI,FSE T₁WI,FSE T₂WI,FLAIR T₁WI,FLAIR T₂WI and EPI-SE). And clinical referenced parameters,as the standard parameter,were choosen for each sequence.Artifact area was calculated and compared quantitatively.Covariance analysis applied to determine the effects on the MRI artifact of different metal materials and different sequences.2.Three kinds of materials(Co-Cr alloy,titanium alloy and Au-Pd alloy) were imaged with three MRI sequences(GRE T*₂WI,SE T₁WI and FSE T₂WI).Adjust MR-relevant parameters,including TE,FOV,BW and so on,to compare the artifacts with that generated before.Artifact area was mesured.Variance analysis and t-Test were applied to determine the effects on the MRI artifact of different patameters.Results1.Except for the EPI-SE sequence,the results indicated significant difference among different dental materials(F＝87.31,P＜0.000),of all materials,only Au-Pd alloys and Ag-Pd alloys showed no difference compared with arcrylic resin;and significant difference was observed among sequences evaluated(F＝36.73,P＜0.000),the sequence of GRE T*₂WI generated the largest artifact compared with other sequences.2.The results showed that the influence of some parameters was significantly different.(1) Influence of TE:on GRE T*₂WI sequence,artifacts caused by titanium alloy and Au-Pd alloy varied with variety of TE,the difference was significant.And significant difference of artifacts caused by the three kinds of alloy were also observed on SE T₁WI sequence.Long TE produced larger artifacts.(2) Influence of ETL:on FSE T₂WI sequence,artifacts caused by Au-Pd alloy varied with variety of ETL,the difference was significant.Increase in ETL led to a reduction of artifacts.(3) Artifacts size was not effected by the degree k-space coverage.Only when NEX increased,SNR of images was optimized.(4)With change of BW,significant difference of artifacts caused by the three kinds of alloy were observed on SE T₁WI and FSE T₂WI sequences.Narrow BW caused larger artifacts.(5) Influence of FOV: on GRE T*₂WI sequence,artifacts caused by titanium alloy and Au-Pd alloy varied with variety of Fov,the difference was significant.And significant difference of artifacts caused by the three alloys were also observed on FSE T₂WI sequence.An increase in FOV resulted in larger artifacts.(6) With increase of matrix,artifacts caused by Co-Cr alloy and titanium alloy became significantly smaller on GRE T*₂WI sequence.(7)With decrease of thick,artifact caused by Au-Pd alloy became significantly larger on FSE T₂WI sequence.(8) Artifact size was not significantly influenced by FA.Conclusion1.We concluded the selection of noble metallic material for fixed denture could minimize the size of artifacts.MR artifacts can be reduced by using optimal sequence in patients with metallic materials.2.The severity of artifacts caused by metal materials also depends on some imaging parameters.Adjustment of parameters can control the metal artifacts to a certain extent.