目的 分析双源CT分别运用Sn100 kV能谱纯化技术(SPS)与120 kV未经SPS的2种扫描方案在胸部CT筛查中辐射剂量和图像质量之间的差异.方法 随机分配健康体检做胸部CT者192例运用双源CT Sn100 kV SPS作为研究组,200例运用120 kV未经SPS作为对照组.比较2种不同扫描方案的辐射剂量差异,肺窗和纵隔窗的客观与主观图像质量差异.结果 研究组的容积CT剂量指数(CTDIvol)、平均剂量长度乘积(DLP)、平均有效剂量(ED)分别为(0.61±0.10)mGy、(21.09±4.13) mGy·cm、(0.30±0.06) mSv;对照组分别为(2.50±1.18) mGy、(83.49±31.97) mGy·cm、(1.17士0.45)mSv,各项辐射剂量指标降低了75％左右.2组图像的肺窗信噪比(SNR)差异无统计学意义(P=0.42),对比噪声比(CNR)差异有统计学意义(P=0.04).2组图像的纵隔窗SNR(P =0.80),CNR(P =0.51)差异均无统计学意义.2名医师对2组图像的肺窗和纵隔窗主观评分中位数均为4分(3～5分).2名医师对2组肺窗图像质量评分的差异无统计学意义(P＞0.05),纵隔窗评分的差异有统计学意义(P＜0.05).结论 对于双源CT胸部筛查,运用Sn100 kV SPS与120 kV未经SPS相比,辐射剂量可降低75％左右,同时可以获得满足胸部筛查需求的图像质量.
目的:评价第3代能谱纯化技术对直肠肿瘤双能扫描图像质量及辐射剂量的影响.方法:选取70例直肠癌患者,均行双能扫描,按照锡滤过能谱纯化厚度的不同,将其分为2代组(36例)和3代组(34例),2代组采用第2代双源SOMATOM Definition Flash CT扫描,3代组采用第3代双源SOMATOM Definition Force CT能谱纯化技术进行扫描,分析比较两种扫描方法的CT剂量指数(CTDI)和剂量-长度乘积(DLP),计算线性融合(M=0.5)及单能谱+40 keV、60 keV图像肿块与血供信噪比(SNR)及对比噪声比(CNR).由两名诊断经验十年以上的放射科医师对图像质量和细小动脉用5分法进行评分.结果:3代组的CTDI为5.43(4.23～7.59 mGy),DLP为242.85(147.7～339.7 mGy·cm),明显低于2代组,且差异均有统计学意义(U=10,U=7;P<0.05);3代组融合图像肿块SNR、细小动脉CNR均高于2代组,且差异均有统计学意义(F=7.94,F=10.58;P<0.05);3代组内融合图像细小动脉SNR高于40 keV和60 keV,40 keV图像肿块与细小动脉的CNR高于融合与60 keV,且差异有统计学意义(FSNR=1.23,F=0.356;FCNR=0.53 F=0.45;P<0.05).结论:第3代能谱纯化技术能够提升直肠癌的图像质量、降低辐射剂量,联合mono-plus(40 keV)能够提高直肠细小动脉血管的显示.
For monitoring emission from utility boilers,the accuracy of differential optical absorption spectroscopy(DOAS) method is strongly affected by high concentration of dust and droplets in flue gas.Experiments were carried out in lab to simulate the real conditions in chimney.Absorption spectrums of SO2 were measured in different conditions,such as high concentration of dust and/or droplets,lower light intensity.Then,measured spectrums were analyzed with wavelet transform method.It was found that coefficients of wavelet transform in some wavelengths kept nearly constant in different conditions.Based on these experimental results,the new method of measuring concentration of SO2 was presented in this paper.Our aim is to establish the function relationships by means of using the relationships between these coefficients and the concentration of SO2,which can be used to determine the concentration of SO2 directly in DOAS method.Experiments proved this method.For the advantage of eliminating the interference of dust and droplets,reducing the measurement error,the new technique presented in this work is suitable for on-line monitoring emission from utility boilers.
差分吸收光谱法(differential optical absorption spectroscopy,DOAS)用于锅炉排放烟尘烟气直接在线监测时,易受烟尘水汽等的干扰影响,造成测量误差较大。在实验室模拟真实烟道中的烟气监测环境,研究在光源发光强度大幅度衰减、存在高浓度水汽和烟尘情况下不同浓度SO2吸收光谱的特性。在对SO2吸收光谱进行小波分解后,发现即使受到高浓度烟尘颗粒、水汽、光源大幅度衰减等的影响,在某些波长处的小波系数变化仍较小,与未受干扰的SO2吸收光谱的小波系数基本相同。因此,提出一种差分吸收光谱法测量SO2浓度的新算法,即利用这些波长点的小波分解系数与浓度的关系,建立相应的函数关系,由吸收光谱经小波分解后的小波系数直接得到SO2的浓度。实验证明该方法可以消除烟尘水汽等的干扰影响,测量误差较小,可以满足排放监测要求。
