低辐射剂量下物质间CT值相互影响及CTA图像质量的研究

发布时间：2018-10-24 07:24

【摘要】：目的：1.探讨不同管电压及周围结构对CT值测量的影响。2.评价降低管电压及管电流时下肢动脉CTA检查的可行性及其对图像质量和X射线辐射剂量的影响,并在不影响诊断的前提下找出合理的管电压、管电流组合,以最大限度的降低X线辐射剂量。 材料和方法：1.CT扫描仪的管电压分别设定为120、100、80kV,其它扫描参数不变,分别对浓度为14mgI/ml的碘对比剂、医用硅胶块、乳胶块、生物胶块及由这几种物质制备的模拟动脉硬化血管模型进行扫描,测量不同条件下各单一结构扫描的CT值和模型扫描中相应的同种物质的CT值,评估不同管电压及周围结构对CT值测量的影响。2.采用16层螺旋CT,收集临床诊断为ASO的病人30例,随机分为3组：组Ⅰ管电压为100kV,管电流260mA；组Ⅱ管电压为100kV,管电流210mA；组Ⅲ管电压为80kV,管电流260mA,以上述扫描条件分别行下肢动脉CTA检查。测量动脉管腔内CT值、周围软组织CT值、背景噪声,计算图像信噪比(SNR)、对比噪声比(CNR)、图像优良指数(FOM),并由两名有经验的放射科医生采用双盲法分别对图像质量进行评分。 结果：1.管电压120kV时单独扫描碘对比剂、医用硅胶块、乳胶块、生物胶块及模型中4种物质的CT值分别为(380.63±8.49)HU和(377.03±3.83)HU(P=0.02)、(293.94±17.83)HU和(334.07±5.95)HU(P=0.00)、(-154.64±12.56)HU和(-95.09±26.22)HU(P=0.00)、(-54.66±2.09)HU和(-40.79±6.85)HU(P=0.00)；管电压100kV时其CT值分别为(442.97±6.48)HU和(439.77±4.95)HU(P=0.02)、(332.79±6.78)HU和(383.90±6.14)HU(P=0.00)、(-166.2±12.61)HU和(-122.43±27.71)HU(P=0.00)、(-74.28±4.41)HU和(-64.74±10.65)HU(P=0.00)；管电压80kV时其CT值分别为(557.74±5.61)HU和(556.80±9.70)HU(P=0.62)、(426.71±8.70)HU和(489.90±12.31)HU(P=0.00)、(-202.30±27.10)HU和(-139.57±26.77)HU(P=0.00)、(-87.64±4.77)HU和(-79.81±14.64)HU(P=0.00)。当管电压由高降低时,高密度物质CT值升高,低密度物质CT值降低。周围结构对CT值测量亦有影响,物质之间的密度差别越大,其CT值所受影响越大。2.组Ⅲ动脉管腔内CT值高于组Ⅰ、组Ⅱ,差异有统计学意义(P0.05),组Ⅰ与组Ⅱ间差异无统计学意义(P0.05)。体厚较厚区域组Ⅲ软组织CT值低于组Ⅰ、组Ⅱ,差异有统计学意义(P0.05),组Ⅰ与组Ⅱ间差异无统计学意义(P0.05)；体厚较薄区域三组间软组织CT值差异均无统计学意义(P0.05)。三组间背景噪声差异有统计学意义(P0.05),组Ⅲ背景噪声最大。三组间血管SNR、CNR及图像质量主观评分差异均无统计学意义(P0.05),而体厚较厚区域软组织SNR的差异有统计学意义(P0.05)。三组管电压、管电流组合条件下CTDIvol、 DLP、ED分别为5.41、635.00±11.25、12.07±0.24；4.02、488.89+25.94、9.29±0.55；2.63、304.56±9.50、5.79±0.20,差异均有统计学意义(P=0.00)。三组间FOM差异有统计学意义(P0.05),组Ⅲ(管电压80kV,管电流260mA)时FOM最大。 结论：1.管电压改变时物质的CT值会发生改变,同时周围结构也会影响到CT值,但周围结构对碘对比剂的CT值影响不大。2.在进行CT值的定量研究时要关注管电压的改变以及周围结构对CT值的影响。3.降低管电压可以较明显的降低X线辐射剂量。4.X线辐射剂量的降低对血管SNR无影响,但会影响到腹盆部软组织的SNR。5.推荐80kV和260mA的组合作为下肢动脉CTA检查的常规扫描条件。
[Abstract]:Purpose: 1. To investigate the effect of different tube voltage and surrounding structure on the measurement of CT value. To evaluate the feasibility of CTA examination of lower limb artery and its effect on image quality and X-ray radiation dose in reducing tube voltage and tube current, and to find out reasonable tube voltage and tube current combination without affecting diagnosis, so as to minimize X-ray radiation dose. Materials and Methods: 1. The tube voltage of CT scanner was set to 120, 100, 80kV respectively, and the other scanning parameters remained unchanged. The iodine contrast agent, medical silica gel block, latex block, bio-gel block and the simulated arteriosclerosis vascular model prepared by these substances were respectively applied to the iodine contrast agent with concentration of 14mgI/ ml. scanning, measuring CT value of each single structure scan under different conditions and CT value of corresponding same substance in model scanning, evaluating the effect of different tube voltage and surrounding structure on CT value measurement. 2. 30 patients with ASO were collected by 16-slice spiral CT, and randomly divided into 3 groups: group 鈪，

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