扫描视野对双能CT成像CT值及物质分离的影响——模体研究

Effect of scan FOV on CT value and material decomposition measurement in dual energy CT:a phantom study

目的:探讨改变扫描视野是否会对双能CT能谱成像(GSI)时CT值的测定及物质分离的计算产生影响。方法:取清洗干净后消毒灭菌的试管17支,分别注入蒸馏水及不同浓度碘对比剂。17个试管的碘浓度分别为0、0.1、0.2、0.3、0.4、0.5、0.6、0.8、1.0、2.0、3.0、4.0、5.0、6.0、8.0、10.0和20.0mgI/ml。采用GE Discovery 750HD CT扫描机,宝石能谱成像(GSI)方式,扫描视野分别选取大(A组)和中等(B组)各扫描一次,共余扫描参数2组相同(转速0.8s/r,螺距0.984,探测器宽度40mm)。在混合能量、水基和碘基图像上分别测量每组试管的CT值、水及碘含量。ROI选取在试管长轴位的最大截面,大小约392mm2。采用Pearson相关分析和配对样本t检验进行统计学分析。结果:两组视野的图像,物质分离计算所得碘含量与真实值之间均具有明显相关性(A组r=0.9995,B组r=0.9996,P<0.001)。17个试管A组扫描测量平均CT值为(86.86±131.78)HU,平均水含量为(977.14±10.54)mg/ml,平均碘含量为(3.91±5.37)mg/ml;B组扫描测量平均CT值为(106.89±141.51)HU,平均水含量为(994.39±12.35)mg/ml,平均碘含量为(3.82±5.59)mg/ml。两组CT值及水含量的差异有极显著性意义(P<0.01),两组碘含量测量值的差异无统计学意义(P=0.19)。结论:双能CT能谱扫描能够反映不同浓度碘溶液中的碘含量并能进行定量分析,改变扫描视野可以影响混合能量图像中CT值的测定,但对物质分离计算中碘含量的测定没有显著影响。

Objective：To study whether change of scan field of view（FOV） has effect on measurement of CT value and material decomposition when using dual energy CT scan（Gemstone Spectral Imaging,GSI）.Methods：Seventeen tubes of water and iodine solution with different concentrations of iodine contrast were scanned with GSI mode.The iodine concentrations of these tubes were 0（water only）,0.1,0.2,0.3,0.4,0.5,0.6,0.8,1.0,2.0,3.0,4.0,5.0,6.0,8.0,10.0 and 20.0mgI/ml,respectively.All tubes were scanned twice with large and medium FOV,respectively（Group A：Large FOV;Group B：Medium FOV）.The CT value was measured on CT images with mixed energy.Aw4.4 workstation was used to calculate water and iodine decomposition in each tube.Results：The calculated iodine concentration was highly consistent with actual iodine concentration in the tubes（rA=0.9995,rB=0.9996,P=0.000）.Measured CT value and calculated water concentration were statistically different between the two FOV groups（P0.01）.There was no statistical difference on calculated iodine concentrations between the two FOV groups（P=0.19）.Conclusion：Dual energy CT images can reflect the content of iodine in different concentrations and can be used for quantitative analysis.Changing scan FOV will affect the measurement of CT value,but has no effect on calculation of iodine concentration.