能谱CT单能量联合迭代重建对图像质量的影响

Influence of spectral CT monochromatic imaging in combination with iterative reconstruction algorithm on image quality

目的：探讨能谱CT单能量联合迭代重建对图像空间分辨率、密度分辨率、低对比可探测能力等图像质量指标的影响。方法：利用能谱CT对Catphan 500体模进行扫描,对扫描后的图像分别重建45~135 keV10级单能量图像,同时对每级单能量图像进行从10%到100%的不同迭代权重重建。选用Catphan 500体模的CTP528模块测量图像的空间分辨率;选用CTP515模块测量密度分辨率;以CTP515模块中对比度为1%、直径为9.0 mm的圆柱体为观察对象,分析图像的低对比可探测能力。采用多因素方差分析比较不同单能量及不同迭代重建水平对图像质量的影响。结果：迭代权重不变时,随着单能量数值的升高,对空间分辨率可分辨的线对数为：7、7、6、6、6、6、6、6、6、6 LP/cm;密度分辨率呈下降趋势,在55 keV、65 keV时最高;低对比可探测能力呈下降趋势,在55 keV、65 keV时最高。不同单能量对空间分辨率、密度分辨率、低对比可探测能力的影响差异均有统计学意义（P〈0.05）。当单能量ke V不变时,随着迭代权重比例的提高,对空间分辨率的影响差异无统计学意义（P〉0.05）;对密度分辨率和低对比可探测能力的影响差异均有统计学意义（P〈0.05）。结论：以5 mm的层厚做能谱CT扫描时,45 ke V至65 ke V较低的单能量图像联合20%权重迭代算法可以获得相对较高的图像质量。

Objective： To explore the effect of spectral CT monochromatic imaging in combination with adaptive statistical iterative reconstruction （ASiR） algorithm on the spatial resolution, density resolution and low-contrast detectability （LCD） of image in energy spectrum scanning. Methods： Catphan 500 phantoms were scanned using Gemstone Spectral CT. The images were reconstructed for 10 level of single energy from 45 keV to 135 keV, and meanwhile, the ASiR was applied to each keV from 10% to 100%. The CTP528 and CTP515 Catphan phantoms were used to measure the spatial resolution and density resolution, respectively. CTP515 cylinder phantoms with contrast ratio of 1% and diameter of 9.0 mm were chosen as research subjects to analyze low-contrast detectability （LCD） of images. The image quality was compared with multiple factors analysis of variance. Results： In a certain ASiR, as for spatial resolution, the distinguishable line pair per centimeter from 45 keV to 135 keV were 7, 7, 6, 6, 6, 6, 6, 6, 6 and 6 LP/cm, respectively. The density resolution and LCD decreased with the increasing of keV, and reached peaks at 55 and 65 keV. Different single energy was statistically significant （P〈0.05） on the spatial resolution, density resolution and LCD. When keV was fixed, ASiR was statistically significant （P〈0.05） on the density resolution and LCD, while there was no statistical difference on spatial resolution （P〉0.05）. Conclusion： Low single energy （45 keV to 65 keV） combined with 20% ASiR can achieve relatively high image quality in energy spectrum scanning with 5 mm slice thickness.