肝脏门静脉期双能CT:单能量图像与融合图像的比较

Comparison of Monochromatic Images and Blended Images of Hepatic Dual-energy CT at Portal Venous Phase

目的:探比较双能CT(DECT)的单能量图像和融合图像在肝脏门静脉期增强的应用效果。方法:配置不同浓度碘对比剂溶液制成体模原型,在Siemens SOMATOM Definition Flash扫描仪上,采用上腹部推荐协议先后执行常规120k Vp扫描和100/Sn 140k Vp双能扫描。其中,后者所采集图像数据分别重建得到权重配比为0.5的线性融合图像(M_0.5)、最优非线性融合图像(OCM)和根据对比度噪声比(CNR)能谱曲线优选的单能量图像(Mono)。计算对比度、CNR和品质因数(FOM)以比较图像质量。回顾分析30例上腹部双能CT增强检查,比较门静脉期不同重建图像的肝实质和门静脉主干的增强幅度,并采用6分量表法对最大密度投影(MIP)和容积再现(VR)图像进行主观评价。结果:体模实验中,与120k Vp图像相比,M_0.5图像的对比度无显著差异(P=0.239)但CNR提高16.3%;DECT三种重建图像中,OCM和Mono图像的对比度、CNR分别比M_0.5图像提高33.3%、32.3%和16.6%、6.1%;DECT三种重建图像的FOM比120k Vp图像分别提高10.3%、94.2%和24.5%。临床病例的门静脉期OCM和Mono图像的肝实质和门静脉主干增强幅度比M_0.5图像分别提高20.4%、19.2%和16.2%、15.9%;MIP和VR图像的评分中,OCM组和Mono组无显著差别(P=0.317),均显著高于M_0.5组(P<0.001)。结论:在上腹部DECT增强检查中,为提高肝脏门静脉期图像增强效果应重建OCM图像。

Purpose： To compare the effect of contrast enhancement of monochromatic images and blended images obtained with dual-energy CT （DECT） at hepatic portal venous phase. Methods： A liver phantom prototype, which containing 9 tubes of various concentrations of contrast material bathing in a plastic bag filled with pure water, was scanned using a Siemens SOMATOM Definition Flash scanner under conventional （120kVp） and DECT （100/Sn 140） modes. Linear blended with mixture ratio 0.5 （M_0.5） images, vendor default optimal contrast mixed （OCM） images and virtual monochromatic （Mono） images with best contrast-to-noise ratio （CNR） were reconstructed using the DECT data. CNR and figure-of-metric （FOM） of images were used to compare the image quality. Thirty patients who underwent contrast-enhanced hepatic scan under DECT modes at portal venous phase were retrospectively analyzed for comparison of enhancement in the hepatic parenchyma and the main portal vein. And the quality of maximum intensityprojection （MIP） and volume rendering （VR） images was graded by 6-point Likert scales subjectively. Results： In the phantom experiments, the contrast of M_0.5 images was with no statistical significant difference with that of 120kVp images （P=0.239）, but the CNR of M_0.5 images was 16.3% higher than of 120kVp images. Contrast and CNR of OCM and Mono images were 33.3%, 32.3% and 16.6%, 6.1% higher than those of M_0.5 images. FOM of M_0.5, OCM and Mono images was 10.3%, 94.2% and 24.5% higher than that of 120kVp images. The quality scores of MIP and VR images of OCM group （5.00±0.83） were with no statistical significant difference with that of Mono images （4.93±0.74） （P=0.317）, but were significantly higher than that of M_0.5 group （4.20±0.99） （P〈0.001）. Conclusion： OCM images should be preferred to enhance the contrast of hepatic DECT at portal venous phase.