大螺距联合自适应迭代重建技术对胸部能谱成像影响的体模研究

The effect of high-pitch combined adaptive iterative reconstruction on chest energy spectrum imaging:a phantom study

目的:通过胸部模型研究,探讨在能谱CT智能匹配技术下大螺距能谱扫描结合自适应迭代重建(ASIR-V)后重建技术对图像质量与辐射剂量的影响。方法:使用GE Revolution CT对仿真胸部体模进行能谱扫描,开启GSI assit,试验组采用大螺距1.531,采用ASIR-V后重建技术(0%~100%,间隔10%)重建5 mm层厚的70 keV能谱单能量图像,获得A组图像;对照组采用常规螺距0.992,采用滤波反投影法(FBP,即0%ASIR-V)重建5 mm层厚的70 keV能谱单能量图像,得到B组图像。肺窗图像采用骨算法、纵隔窗图像采用标准算法重建。对两组图像进行客观评价(肺窗肺组织、纵隔窗心脏噪声)及主观评分(5分制,1分最低、5分最高)。记录并比较两组的有效辐射剂量(ED)。结果:A、B两组图像中肺窗肺组织噪声两两比较差异均无统计学意义(P值均>0.05)。A组纵隔窗心脏噪声分别为(7.33±0.31)、(6.72±0.28)、(6.10±0.24)、(5.63±0.19)、(4.98±0.19)、(4.53±0.20)、(3.73±0.10)、(3.08±0.04)、(2.85±0.08)、(2.35±0.08)、(2.03±0.12)HU,B组纵隔窗心脏噪声为(6.75±0.26)HU。A组纵隔窗心脏噪声随ASIR-V升高而降低,两两比较差异均有统计学意义(P值均<0.05)。B组纵隔窗心脏噪声低于A组0%ASIR-V,高于A组20%~100%ASIR-V,差异均有统计学意义(P值均<0.05);B组纵隔窗心脏噪声与A组10%ASIR-V差异无统计学意义(P>0.05)。A组10%~60%ASIR-V和B组肺窗、纵隔窗图像的主观评分最高(5分),综合主客观评价,60%为大螺距能谱单能量成像的最佳ASIR-V权重。大螺距A组ED值为5.31 mSv,较常规螺距B组ED值(6.84 mSv)降低22.37%。结论:能谱CT智能匹配技术下,大螺距能谱成像较常规螺距能谱成像的辐射剂量降低;结合10%~60%ASIR-V后重建技术,可降低大螺距能谱单能量图像的噪声,提高综合成像质量,60%为最佳ASIR-V权重。

Objective:To explore the effect of high-pitch spectral CT scanning combined with adaptive iterative reconstruction-V(ASIR-V)using the intelligent matching technology on the image quality and radiation dose based on a chest phantom.Methods:A chest phantom was scanned on a revolution energy spectrum CT scanner using automatic spectral imaging mode selection.In the study group(group A),1.531 helical pitch was used and monochromatic 70KeV images were reconstructed using different levels of pro-ASIR-V(from 0%to 100%,step by 10%)with a slice thickness of 5mm.In the control group(group B),0.992 helical pitch was used and monochromatic 70KeV images were reconstructed using FBP(0%ASIR-V)with a slice thickness of 5mm.Images of lung window and mediastinal window were separately reconstructed by bone algorithm and standard algorithm.The image noise of lung tissue on lung window,heart on mediastinal window were objectively evaluated and the image quality was subjectively scored(5-point system,1 point is the lowest,5 points is the highest).Effective radiation doses in two groups were recorded.Results:No significant difference in image noise of lung tissue on lung window was found between group A and group B(P>0.05).The image noise of heart on mediastinal window were(7.33±0.31)HU,(6.72±0.28)HU,(6.10±0.24)HU,(5.63±0.19)HU,(4.98±0.19)HU,(4.53±0.20)HU,(3.73±0.10)HU,(3.08±0.04)HU,(2.85±0.08)HU,(2.35±0.08)HU and(2.03±0.12)HU in group A,respectively.The image noise of heart on mediastinal window was(6.75±0.26)HU in group B.The image noise of heart on mediastinal window decreased with the increase of ASIR-V in group A,and the difference between the two groups was statistically significant(P<0.05).The image noise of heart on mediastinal window of group B was significantly lower than that of group A(0%ASIR-V)and significantly higher than that of group A(from 20%to 100%ASIR-V)(all P<0.05).There was no significant difference in image noise of heart on mediastinal window between group B and group A(10%ASIR-V)(P>0.05).The mean subjective scores of images in group B and group A(from 10%to 60%ASIR-V)were all 5 points.The optimal image quality was obtained with 60%pro-ASIR-V.The effective dose(ED)value of the high-pitch in group A is 5.31mSv,which was 22.37%lower than that of the routine-pitch in group B.Conclusion:The radiation dose of high-pitch is lower than that of routine-pitch spectral CT monochromatic imaging based on intelligent matching technology.The use of pro-ASIR-V(from 10%to 60%)results in improving image quality of high-pitch spectral CT monochromatic image by reducing image noises,and 60%Pro-ASIR-V could obtain optimal image quality.