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目的探究使用0.04m Sv极低剂量CT联用自适应性迭代重建的(adaptive statistical iterative reconstruction,ASIR)算法成像技术,实现3岁以内婴幼儿胸部及气道疾病的诊断筛查。方法选取三岁以下的临床怀疑气道畸形,气道狭窄,血管环等大气道病变行增强CT检查的患儿共22例。平扫运用80k V,4m As极低剂量扫描作为实验组。实质期使用常规辐射剂量100k V,噪声指数为12的自动管电流调节技术扫描图像作为对照组。将实验组原始图像分别重建为层厚5mm的滤波反投影(FBP)、40%权重的ASIR、100%权重的ASIR共六组图像,对照组重建为层厚5mm的40%权重的ASIR图像。比较同一患者平扫与静脉期放射剂量及主观、客观图像质量,主观图像质量评价由两位医师应用1~4分制评价(4分最好,3分合格)图像总体噪声、大气道显示情况及肺内病变显示情况。客观噪声测量左心室最大层面内的左心室内、背部均匀的肌肉、脂肪、降主动脉及肺野,并计算优化信噪比(signal noise ratio,SNR)。使用秩和检验评价主观图像质量评分结果的差异,配对方差分析评价客观图像质量及放射剂量的差异。结果实验组有效剂量为(0.04±0.01)m Sv,对照组辐射有效剂量(0.55±0.13)m Sv。层厚5mm的FBP、40%ASIR、100%ASIR及对照组主观图像评分分别为1.71±0.68,2.01±0.76,2.59±0.99,3.59±0.50;大气道的主观评分分别为2.32±0.56,2.89±0.39,3.82±0.39,3.89±0.32。左心室噪声值分别为38.72±7.36,31.55±7.15,21.00±5.15,7.83±1.20。运用100%权重的ASIR,图像噪声降低明显,主观评分上升明显。实验组与对照组之间的客观评分、主观评分依然差异明显(P<0.05),图像不能满足胸部病变的诊断要求,但完全能显示肺部病变的位置、范围、边缘,以及纵隔的形态异常情况,达到定位定量的诊断要求。而对于大气道的显示主观评分均可满足诊断要求,100%ASIR试验组与对照组差异不明显(P>0.05),达到了常规CT的诊断水平。放射剂量方面和常规胸部正侧位胸片剂量相仿。结论婴幼儿胸部CT使用极低剂量(0.04m Sv)扫描方案,有效降低了辐射剂量,可做为气道疾病的低剂量筛查方案。
Objective To investigate the diagnostic and screening of thorax and airway diseases in infants under 3 years of age using 0.04 m Sv very low dose CT combined with adaptive statistical iterative reconstruction (ASIR) imaging technique. Methods A total of 22 children with suspected airway deformity, airway stenosis, vascular loop and other airway diseases under the age of three were enrolled in this study. Plain scan with 80k V, 4mAs very low dose scanning as the experimental group. The actual period of use of conventional radiation dose of 100k V, noise index of 12 automatic tube current regulation technology scan images as a control group. The original images of the experimental group were respectively reconstructed into six groups of images: filtered back projection (FBP), 40% weighted ASIR and 100% weighted ASIR. The control group was reconstructed into 40% weight ASIR images with 5mm layer thickness . Comparison of the same patient plain scan and venous radiation dose and subjective and objective image quality, subjective image quality evaluation by two physicians applied 1 to 4 points of evaluation (4 points best, 3 points pass) the overall image noise, airway display And lung lesions showed. Objective noise was measured in the left ventricle at the level of the left ventricle, the back of the uniform muscle, fat, descending aorta and lung field, and calculate the optimal signal-to-noise ratio (SNR). The rank sum test was used to evaluate the differences of the subjective image quality scores. Paired variance analysis was used to evaluate the differences of objective image quality and radiation dose. Results The effective dose of the experimental group was (0.04 ± 0.01) m Sv and that of the control group was (0.55 ± 0.13) m Sv. Subjective image scores of FBP, 40% ASIR, 100% ASIR and control group with a thickness of 5mm were 1.71 ± 0.68, 2.10 ± 0.76, 2.59 ± 0.99 and 3.59 ± 0.50 respectively. The subjective scores of the airways were 2.32 ± 0.56 and 2.89 ± 0.39, 3.82 ± 0.39, 3.89 ± 0.32. Left ventricular noise values were 38.72 ± 7.36,31.55 ± 7.15,21.00 ± 5.15,7.83 ± 1.20. With 100% weighted ASIR, the image noise was significantly reduced and the subjective score increased significantly. The objective score and subjective score were still significantly different between the experimental group and the control group (P <0.05). The image could not meet the diagnostic requirements of chest lesions, but could completely display the location, extent, margins, and abnormality of the mediastinum The situation, to locate the quantitative diagnosis requirements. However, the subjective assessment of the airway can meet the diagnostic requirements. The difference between the 100% ASIR test group and the control group was not significant (P> 0.05), which reached the diagnostic level of conventional CT. Radiation dose and the chest is lateral chest x-ray dose is similar. Conclusion Infant chest CT scan with extremely low dose (0.04m Sv) can effectively reduce the radiation dose and can be used as a low dose screening program for airway diseases.