双能CT螺距和迭代重建权重对单能衰减和有效原子序数的影响:体模研究

Impact of pitch and iterative reconstruction weight on monochromatic attenuation and effective atomic number of dual-energy CT:A phantom study

目的采用双能CT不同螺距宝石能谱成像(GSI)模式观察能量、螺距和迭代重建(IR)算法对CT值和有效原子序数(Z_(eff))测值的影响。方法采用双能CT GSI模式扫描由聚四氟乙烯(Teflon)、空气(Air)、低密度聚乙烯(LDPE)及丙烯酸(Acrylic)构成的Catphan500标准体模,设定螺距为1.375、0.984及0.516,分别以混合权重为20%、60%和100%的IR重建图像;记录体模各种材料在3个能量水平下(60、73和80 keV)的CT值及Z_(eff),计算并比较其在不同单能量、螺距及IR权重下的平均相对误差(MRE-CT值和MRE-Z_(eff))。结果所有能量、螺距和IR权重下,MRE-CT值均为Air0.05)。所有螺距和IR权重下,MRE-Z_(eff)均为Acrylic0.05)。结论GSI扫描参数对不同材料的影响程度不同;CT值和Z_(eff)测量精度受螺距影响而与IR强度无明显相关;能量水平仅影响测量CT值精度。

Objective To investigate the impact of energy,pitch and iterative reconstruction(IR)algorithm on CT value and effective atomic number(Z_(eff))measurements of gemstone spectral imaging(GSI)mode with different pitches of dual-energy CT.Methods Dual-energy CT GSI mode was used to scan Catphan500 standard phantom composed of Teflon,Air,low density polyethylene(LDPE)and Acrylic,with the pitch of 1.375,0.984 and 0.516,respectively.Then images were reconstructed using IR with mixture weight of 20%,60%and 100%,respectively.CT value and Z_(eff)of each material were recorded at 60,73 and 80 keV energy level.The mean relative error(MRE-CT and MRE-Z_(eff))of the above 4 kinds of materials under different single energy,pitch and IR weights were calculated and compared.Results Under all energies,pitches and IR weights,MRE-CT values were Air0.05).Under all pitches and IR weights,MRE-Z_(eff)were Acryliceff of each material was significantly different under different pitches(all P<0.05).Under different IR weights,there was no significant difference of MRE-CT number nor MRE-Z_(eff)of each material(all P>0.05).Conclusion GSI scanning parameters had different impacts on different materials.The measuring accuracy of CT number and Z_(eff)were affected by the pitch but not significantly correlated with IR intensity,while the energy level only affected the measuring accuracy of CT number.