多物质伪影降低技术对五种口腔修复材料能谱CT伪影消除作用初探

Preliminary study on the elimination of artifacts of five kinds of dental prosthetic materials by energy spectrum CT multi-material artifact reduction technology

目的探讨多物质伪影降低(multi-material artifact reduction,MMAR)技术对5种口腔修复材料能谱CT伪影的消除作用。方法分别用金合金、氧化锆、钴铬合金、镍铬合金及纯钛制作猪湿颅骨上颌第一前磨牙至第一磨牙的三单位固定桥,分别带入后进行能谱CT扫描。采用常规120 kVp扫描模式获得图像,计为常规组;采用能谱扫描模式重组80、90、100、110、120、130、140 keV的单能量水平图像,计为能谱组;采用能谱扫描模式,再应用MMAR技术重组图像,计为能谱MMAR组。各组均扫描10次,分别测量伪影最多层面图像中固定桥周围和邻近无伪影层面肌肉的CT值及噪声,并计算伪影指数;由2名放射专业主治医师对各组图像质量进行主观评分。采用Kruskal Wallis秩和检验比较常规组与最佳keV条件下能谱组和能谱MMAR组图像噪声、伪影指数及主观评分的差异。结果能谱组和能谱MMAR组图像噪声均随单能量水平的增高而逐渐降低。常规组图像伪影明显;140 keV条件下,能谱组图像伪影较常规组明显减少,能谱MMAR组各口腔修复材料的图像伪影最少。常规组、能谱组、能谱MMAR组纯钛伪影指数分别为71.0±8.0、21.4±2.7和14.7±2.7,均显著小于同组其他材料(P<0.05);能谱MMAR组金合金、氧化锆、钴铬合金、镍铬合金和纯钛的图像质量主观评分分别为(3.0±0.2)、(4.3±0.5)、(3.0±0.4)、(3.1±0.4)和(4.6±0.5)分,均显著小于常规组相同材料(P<0.05)。能谱组与能谱MMAR组相同修复材料的噪声差异无统计学意义(P均>0.05),均显著小于常规组(P<0.05)。结论纯钛产生的伪影最少,能谱扫描联合MMAR技术能有效减少金合金、氧化锆、钴铬合金、镍钛合金和纯钛的伪影,可作为去除口腔修复体伪影的有效方法。

Objective To investigate the effect of the multi-material artifact reduction(MMAR)algorithm of spectral CT in reducing the beam hardening artifacts in dental restoration material.Methods Three-unit fixed bridge restorations were fabricated on the first to third molars in pig jaw.Gold alloy,zirconia,cobalt chromium alloy,nickel chromium alloy and pure titanium were used as materials for these fixed bridges.After restoration delivery,the pig jaw was scaned using energy spectrum CT machines.Images in regular 120 kVp scan mode were used as conventional group,and reconstructed single-energy horizontal images of 80,90,100,110,120,130 and 140 keV in energy spectrum scanning mode were used as energy spectrum group,and reconstructed images applied MMAR technology in energy spectrum scanning mode were used as energy spectrum MMAR group.Each group was scanned 10 times to measure CT value and noise of muscles around dental prosthetic materials and adjacent non-artifact layers.Artifact index was calculated.Two radiologists scored the image quality of each group subjectively.Kruskal Wallis rank sum test was used to compare the difference of image noise,artifact index and subjective score among the control group and the best keV condition in the energy spectrum group and the energy spectrum MMAR group.Results The image noise of energy spectrum group and energy spectrum MMAR group decreased gradually with the increase of single energy level.The artifact index of pure titanium restorations in conventional group,energy spectrum group and energy spectrum MMAR group were 71.0±8.0,21.4±2.7 and 14.7±2.7 respectively,and these values were significantly lower than those of other materials in the same group(P<0.05).The subjective image quality scores in energy spectrum MMAR group were as follows:3.0±0.2 for gold alloy,4.3±0.5 for zirconia,3.0±0.4 for cobalt chromium alloy,3.1±0.4 for cobalt chromium alloy,and 4.6±0.5 for pure titanium.These scores were significantly smaller than those in the conventional group(P<0.05).There was no significant difference in noise between energy spectrum group and energy spectrum MMAR group(P>0.05),and the noise values in energy spectrum group and energy spectrum MMAR group were significantly lower than that in the conventional group(P<0.05).Conclusions Artifacts of pure titanium is minimal.Energy spectrum CT combined with MMAR technology can effectively reduce the artifacts of gold,zirconia,cobalt-chromium alloy,nickel-titanium alloy and pure titanium.This technique can be used as an effective method to remove artifacts of dental prosthesis.