【作者】 李锋坦；

【导师】 张云亭；

【作者基本信息】 天津医科大学 ， 影像医学与核医学， 2010， 硕士

【摘要】 一低剂量CT扫描中管电压和管电流对辐射剂量及CT值的影响目的：通过对不同浓度的含碘溶液样本的CT扫描,探讨管电流和管电压对CT值的影响,及降低管电压和管电流对降低辐射剂量和图像质量的影响程度。材料和方法：在1000ml生理盐水中逐次注入对比剂(优维显,Ultravist,370mgI/ml,拜耳先灵药业公司),每次4ml,每次注入后搅拌均匀,用5ml注射器抽取样本。每25个存有不同浓度对比剂的注射器为一组,将其固定于CT校准专用水模上(直径20cm),进行CT扫描。每组样本扫描模式均为轴扫,机架转速为1s/rot。根据管电压(120kV、100kV和80kV)及管电流(250mA、200mA、150mA、100mA和50mA)不同,共分为15种不同扫描条件。扫描过程中不采用任何其他X线辐射剂量调节技术。将样本的CT图像传至GE AW4.4工作站,进行图像分析和数据测量。在样本轴位图像上,勾画面积为10mm2的圆形感兴趣区(region of interest,ROI),测量每种不同浓度对比剂的样本在不同扫描条件下的CT值。首先测量120kV、250mA的标准条件组图像,选取CT值变化从OHU到450HU,差值不超过5HU的样本,剔除CT值不符合要求的样本,共获得符合要求的样本113个。分别测量和记录15种扫描条件下113个样本的CT值及标准差。将所有数据按管电压不同分为三组：120kV组、100kV组和80kV组,分析管电压固定时,改变管电流对CT值测量的影响；然后再按管电流不同分为五组：250mA组、200mA组、150mA组、100mA组和50mA组,分析管电流固定时,改变管电压对CT值测量的影响。并计算对应关系。每次扫描时由CT机自动生成CT容积剂量指数(CT dose index, CTDIvol,单位：mGy),以CTDI×L (length,扫描长度,本研究统一采用4cm)得出剂量长度乘积(dose length product,DLP,单位：mGy·cm),记录并计算15种扫描条件下的辐射剂量。结果：管电压固定的情况下,不同管电流间的样本CT值比较：120kV下,5种管电流样本CT值比较结果F=0.001,p=1.000；100kV下,5种管电流样本CT值比较结果F=0.008,p=1.000；80kV下,5种管电流样本CT值比较结果F=0.075,p=0.990；测量的差别均不具有统计学意义。管电流固定的条件下,不同管电压间的CT值比较：250mA下,3种管电压样本CT值比较结果H=17.906,p=0.000；200mA下,3种管电压样本CT值比较结果H=17.688,p=0.000；150mA下,3种管电压样本CT值比较结果H=13.527,p=0.000；100mA下,3种管电压样本CT值比较结果H=20.124,p=0.000；50mA下,3种管电压样本CT值比较结果H=23.563,p=0.000；差别均具有显著的统计学意义。计算不同管电压下同一样本CT值的对应关系为公式1和和公式2。利用样本扫描数据分析不同管电压下辐射剂量对图像噪声的影响程度,并确立相关方程。计算出关键点,证明在一般情况下,应用低管电压,高管电流可以降低辐射剂量。结论：管电流对CT值测量没有影响,管电压对CT值测量有直接影响；应用低管电压,高管电流可以在保证图像质量的情况下降低辐射剂量。目的：通过临床病例验证第一部分得出的含有不同碘浓度的物质在管电压改变时其CT值变化规律及对应关系,探讨低管电压CT灌注扫描的可行性。材料和方法：34例行灌注检查患者,排除体重大于75kg的患者12例,符合标准纳入本研究的患者共22例,男性15例,女性7例,年龄32-86岁,身高150-183cm,平均(168±7)cm,体重43-75kg,平均(63±11)kg。随机分成两组：低管电压组(80kV)和标准管电压组(120kV),每组11例。灌注CT检查采用GELightspeed VCT XT 64层螺旋CT机。扫描方式为轴扫描,摇篮式进床。低管电压组采用80kV,500-650 mA,标准管电压组采用120kv,200-280mA。其他扫描参数相同：转速为0.4s/rot,层厚5.0mm,矩阵512×512,FOV 30cm-35cm。扫描次数17次,每次16层图像,每次扫描时间间隔为2.8s,总扫描时间50s。采用高压注射器经前臂静脉以4 ml/s流率注射优维显(Ultravist 370)50ml,于开始注入对比剂后10-12s启动扫描。为确保扫描过程中腹部处于制动状态,除屏住呼吸外,并行腹部肝区绑带加压。将图像传至GE AW4.4工作站,运用CT灌注软件(perfusion 4)进行图像后处理,勾画面积为10mm2的圆形ROI,兴趣区包括腹主动脉、门静脉及正常肝组织,得出两组的CT值,每组正常肝组织各选择33个ROI,再利用公式2,依据低管电压组各兴趣区CT值计算出一组数据为校准后低管电压组。将三组CT值传至个人电脑,输入GE公司提供的专业灌注软件,计算灌注参数血流量(blood flow, BF)、血容量(blood volume, BV)、毛细血管表面通透性(capillary permeability surface area product, PS)及肝动脉灌注量(hepatic arterial perfusion,HAP),进行比较。扫描完成机器自动生成辐射剂量DLP (mGy·cm),再计算患者吸收剂量即有效剂量,进行比较。结果：校准前的低管电压组各参数与标准管电压组相比,BV(t=-2.295,P=0.028),BF(t=-2.784,P=0.009),PS(t=-3.439,P=0.002),HAF(t=-2.115,P=0.048),均具有统计学差异。校准后低管电压组各参数与标准管电压组相比,BV(t=-2.015,P=0.068),BF(t=-1.996,P=0.055),PS(t=-3.039,P=0.132),HAF(t=-1.139,P=0.052),均没有统计学差异。两组患者有效剂量有显著差异,t=-4.21,p=0.001；低管电压组有效剂量降低33%。结论：不同管电压下灌注参数结果存在差异,应用公式2对低管电压下扫描所得数据校正后,所得灌注值与标准管电压结果相一致,且辐射剂量大幅降低。更多还原

【Abstract】 Objective:The purpose was to assess the influence of tube voltage and tube current on CT attenuation measurement, radiation dose, and image quality using serial solutions with different iodine concentrations. Materials and Methods:Infuse 4 ml contrast medium (Ultravist,370mgl/ml, Bayer) for each time into 1000 ml normal sodium, and draw 5ml solutions with a syringe after misce bene. Twenty-five syringes with different solutions were fixed on the CT calibration water phantom with the diameter of 20 cm. Fifteen protocols with different tube voltages (120kV,100kV, and 80kV) and tube currents (250mA,200mA,150mA,100mA, and 50mA) were scanned. The other scan parameters included axial scan mode and 1 s/rot for gantry rotation. No other technique for radiation dose adjustment was adopted. The CT data were transferred to Advantage Workstation 4.4 for GE. Region of interest (ROI) with 10mm2 were drown to measure the CT attenuations of serial solutions under different scan settings. Images with standard setting of 120kV and 250mA were measured first to select the serial solutions, CT attenuations of which were from 0HU to 450HU with increment of 5HU.113 solutions were brought into the study, and CT attenuation under other settings were measured and recorded. The changes of tube voltage and tube current influence on CT attenuation were analyzed, and the relationships were calculated. CT dose indexs (CTDIvol, mGy) were recorded and dose length product (DLP, mGy·cm) were calculated. Results:CT attenuations with fixed tube voltage and different tube current were not different (120kV, F=0.001, p=1.000;100kV, F=0.008,p=1.000;80kV, F=0.075,p=0.990). However, CT attenuations with fixed tube current and different voltage tube were different (250mA, H=17.906,p=0.000;200mA, H=17.688,p=0.000;150mA, H=13.527,p=0.000; 100mA, H=20.124,p=0.000; 50mA, H=23.5635,p=0.000).The relationship of CT attenuations for one solution with different tube voltages was calculated and equations were obtained. The relationship between radiation dose and image noise was also analyzed. The key point was obtained to prove that low tube voltage and high tube current can reduce radiation dose. Conclusions:Tube current had no significant effect on CT attenuation measurement, while tube voltage had effect on CT attenuation measurement. Low tube voltage and high tube current could reduce radiation dose while the image quality would be assuranced.Objective:The purpose was to verified the relationship between tube voltage and CT attenuation obtained in partⅠ, and assess the feasibility of CT perfusion with low tube voltage. Materials and Methods:There were 34 patients accepted CT perfusion examination for liver diseases in our deapartment, and 12 patients were excluded for body weight>75kg.22 patients were included in our study, and 7 were female,at age 32-86 years,at weight 43-75kg (averaged 63±11kg). All the patients were divided into two groups:low tube voltage group(80kV) and standard tube voltage group (120kV). There were 11 patients in each group. GE Lightspeed VCT XT 64-slice spiral CT was used. Low tube voltage group used 80kV and 500-650mA, standard tube voltage used 120kV and 200-280mA. The other parameters included axial scan mode, gantry rotation 0.4s/ro, slice thickness 5.0mm, matrix 512×512, FOV 30cm-35cm.17 scans were performed and 16 images were obtained for each time. The time interval was 2.8s and the total time for scan was 50s. Contrast medium was injected into ulnar vein with velocity of 4ml/s and volume of 50ml. Scan was started 10-12s after injection. The CT data were transferred to Advantage Workstation 4.4 for GE and tool of CT perfusion 4 was used for postprocession. ROI with 10mm2 were drown to measure the CT attenuations of aorta, portal vein, and normal liver for the two groups. According to the relationship of equation 2, the calibrated CT attenuation was calculated for low tube voltage group. CT attenuations of the three sets for two groups were transferred to personal computer to calculate and compare the perfusion parameters with special perfusion tool of GE. The perfusion parameters included blood flow (BF), blood volume (BV), capillary permeability surface area product (PS), and hepatic arterial perfusion (HAP). DLPs and effective radiations were calculated and compared. Results:To compare with standard group, perfusion parameters measured with low tube voltage were different:BV(t=-2.295,P=0.028), BF(t=-2.784,P=0.009), PS (t=-3.439,P= 0.002), HAF(t=-2.115,P=0.048). However, the perfusion parameters calibrated were not different:BV(t=-2.015, P=0.068), BF(t=-1.996, P=0.055), PS(t=-3.039, P=0.132), HAF(t=-1.139, P=0.052). The effective dose of two groups was different (t=-4.21,p=0.001). The effective dose of low tube voltage could be reduced by 33%. Conclusions:The perfusion parameters of different tube voltage were different. After calibration by equation 2, the parameters were according to standard result. Moreover, the radiation dose was reduced significantly.更多还原