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目的 探讨采用能谱CT和传统多层螺旋CT行肝脏增强扫描门静脉期中的辐射剂量和图像质量的差异,评估能谱CT单能量成像在肝脏三期增强扫描中的应用价值.方法 收集临床明确有肝结节性病变的60例患者,按照数字表法随机分为能谱CT组和常规CT组行肝脏三期增强扫描,每组30例.能谱CT组平扫、动脉期和肝实质期采用螺旋扫描,门静脉期使用能谱扫描模式,双电压快速切换；常规CT组行常规辐射剂量下传统肝脏三期扫描.对于常规CT图像,在肝门水平测量肝实质的图像噪声,并用肝实质作为对照测量门静脉主干的对比噪声比(CNR)值.对于能谱门静脉增强扫描,首先从扫描数据中重组出40 ～ 140 keV能量段的101组单能量图像,得出门静脉主干CNR随能量变化曲线,从中得出能谱CT成像中实现门静脉主干的最高CNR值的最佳能量点.选择能谱CT成像中70 keV能量点测量能谱图像的噪声.对2组患者门静脉期成像的CT剂量指数、图像噪声和门静脉主干的CNR行独立样本t检验.结果 能谱CT组患者的CT剂量指数均为15.64 mGy;常规CT组患者CT剂量指数为(22.44±5.09) mGy,能谱CT组比常规CT组剂量降低30％,差异有统计学意义(t=29.56,P＜0.01).能谱CT组和常规CT组图像噪声分别为22.81±2.85和23.80±3.31,差异无统计学意义(t=0.76,P＞0.05).能谱CT组门静脉主干在最佳能量点的CNR为7.17±2.09,是常规CT组2.76±1.34的2倍以上,门静脉主干及分支显影更加清晰,差异有统计学意义(t =7.21,P＜0.01).结论 和常规多层螺旋CT肝脏成像相比,能谱CT成像提供多组单能量图像,在明显降低辐射剂量的前提下保持相似的图像噪声,并能显著提高门静脉和肝实质的对比噪声比,很好地显示门静脉及其分支.

Objective To evaluate the clinical value of spectral CT mode in imaging liver by comparing the radiation dose and image quality between spectral CT and conventional multi-slice spiral CT (MSCT).Methods Thirty patients (group A) underwent three-phasic enhanced CT scans spectral CT mode in the portal phase (PP) and conventional helical mode in other phases (Discovery CT 750 HD,GE Healthcare).Another 30 patients in group B underwent conventional three-phasic enhanced CT on a 64-slice MSCT (VCT,GE Healthcare) with 120 kVp and automatic tube current modulation (ATCM) and noise index of 15.The images in PP from the two imaging modes were retrospectively compared.The contrast-noiseratio (CNR) for the veins was calculated using liver parenchyma as background.For the spectral CT mode,101 sets of monochromatic images were reconstructed from 40 to 140 keV,and the optimal energy level for obtaining the highest CNR was determined using the Gemstone Spectral Imaging (GSI)-viewer software.Image noise (at 70 keV),CNR (at the optimal keV level) for the vein and radiation dose to the patient were obtained for spectral images and statistically compared with those in group B with the conventional MSCT using t test.Results The CTDIw value in PP for spectral CT was 15.64 mGy,30％lower than the (22.44 ± 5.09) mGy for the conventional MSCT (t =29.56,P ＜ 0.01).Image noises on the liver parenchyma were 22.81 ±2.85 and 23.80 ±3.31 for the conventional MDCT and spectral CT images at 70 keV,respectively,with no significant difference (t =0.76,P ＞ 0.05).On the other hand,CNR for the vein at the optimal energy level in spectral CT was 7.17 ± 2.09,which was significantly higher than the 2.76 ± 1.34 for the conventional MSCT (t =7.21,P ＜ 0.01).Conclusion Compared with conventional standard-dose liver MSCT,spectral CT imaging provides improved CNR for vessels,comparable image noise for liver parenchyma with 30％ dose reduction.