Zhang Da-Ming, Wang Xuan, Xue Hua-Dan, Jin Zheng-Yu, Sun Hao, Chen Yu, He Yong-Lan
Chin Med Sci J. 2016 Jun 20;31(2):76-82. doi: 10.1016/s1001-9294(16)30029-3.
Objective To retrospectively determine the features of stones and calcifications in hepatobiliary system on virtual nonenhanced (VNE) dual-energy computed tomography (CT), and to evaluate the possibility of VNE images in diagnosis for those lesions.Methods A total of 128 gall stones and calcifications of the liver found in 110 patients were examined with triple phase abdominal CT scan from July 2007 to December 2011, in which true nonenhanced (TNE) phase and arterial phase were performed with single-energy CT (120 kVp) and portal venous phase was performed with dual-energy CT (100 kVp and 140 kVp). VNE images were generated from the portal venous phase dual-energy CT data sets by using commercially VNC software. The mean CT values for the stone, liver, bile and paraspinal muscle, mean lesion density and size in area dimension, contrast-to-noise ratio (CNR) of lesion to the liver or bile, and image noise were assessed and compared between VNE and TNE images. The effective dose and size-specific dose estimate (SSDE) were also calculated.Results The mean CT values of the lesions measured on VNE images declined significantly compared with those measured on TNE images (164.51±102.13 vs. 290.72±197.80 HU, P<0.001), so did the lesion-to-liver CNR (10.80±11.82 vs.18.81±17.06, P<0.001) and the lesion-to-bile CNR (17.24±14.41 vs. 21.32±17.31, P<0.001). There was no significant difference in size of lesions area between VNE and TNE images (0.69±0.88 vs. 0.72±0.85 cm, P=0.062). Compared to the 128 lesions found in TNE images, VNE images showed the same density in 30 (23.4%) lesions, lighter density in 88 (68.8%) lesions, while failed to show 10 (7.8%) lesions, and showed the same size in 61 (47.7%) lesions and smaller size in 57 (44.5%) lesions. The CT cutoff values of lesion and size were 229.21 HU and 0.15 cm, respectively. The total effective dose for triple phase scan protocol with TNE images was 19.51±7.03 mSv, and the SSDE was 39.84±11.10 mGy. The effective dose for dual phase scan protocol with VNE images instead of TNE images was 13.29±4.89 mSv, and the SSDE was 27.83±9.99 mGy. Compared with TNE images, the effective dose and SSDE of VNE images were down by 32.05%±3.69 % and 30.63%±2.34 %, respectively.Conclusions Although the CT values and CNR of the lesions decreased in VNE images, the lesions of which attenuation greater than 229.21 HU and size larger than 0.15 cm could be detected with good reliability and obvious dose reduction. There was good consistency in the size of stones and calcifications in hepatobiliary system between VNE images and TNE images, which ensured the possibility of the clinical application of VNE images.
目的 回顾性分析虚拟平扫（VNE）双能量计算机断层扫描（CT）对肝胆系统结石及钙化灶的显示特点，评估VNE图像对上述病变的诊断价值。方法 回顾性分析2007年7月至2011年12月期间110例患者的128处肝胆系统结石及钙化灶，均行腹部CT三期扫描，其中单能量CT（120 kVp）行真正平扫（TNE）期及动脉期扫描，双能量CT（100 kVp和140 kVp）行门静脉期扫描。利用商用VNC软件由门静脉期双能量CT数据生成VNE图像。比较VNE图像与TNE图像上结石、肝脏、胆汁及椎旁肌肉的平均CT值、病变平均密度及面积大小、病变与肝脏或胆汁的对比噪声比（CNR）及图像噪声。计算有效剂量及大小特异性剂量估计（SSDE）。结果 VNE图像上病变的平均CT值较TNE图像显著降低（164.51±102.13 vs. 290.72±197.80 HU，P<0.001），病变与肝脏的CNR（10.80±11.82 vs.18.81±17.06，P<0.001）及病变与胆汁的CNR（17.24±14.41 vs. 21.32±17.31，P<0.001）亦显著降低。VNE图像与TNE图像上病变面积大小差异无统计学意义（0.69±0.88 vs. 0.72±0.85 cm，P=0.062）。与TNE图像发现的128处病变相比，VNE图像上30处（23.4%）病变密度相同，88处（68.8%）病变密度减低，10处（7.8%）病变未显示；61处（47.7%）病变大小相同，57处（44.5%）病变变小。病变的CT阈值及大小阈值分别为229.21 HU和0.15 cm。TNE图像三期扫描方案的总有效剂量为19.51±7.03 mSv，SSDE为39.84±11.10 mGy。VNE图像替代TNE图像的双期扫描方案有效剂量为13.29±4.89 mSv，SSDE为27.83±9.99 mGy。与TNE图像相比，VNE图像的有效剂量及SSDE分别降低32.05%±3.69 %和30.63%±2.34 %。结论 尽管VNE图像上病变的CT值及CNR降低，但衰减大于229.21 HU且大小大于0.15 cm的病变可可靠检出，且明显降低了辐射剂量。VNE图像与TNE图像上肝胆系统结石及钙化灶大小具有良好的一致性，为VNE图像的临床应用提供了可能。
