胸部CT扫描参数与组织噪声相关性的实验研究

Experiment study of correlation between CT scan parameters and noise of different tissues

目的:探讨胸部CT扫描参数变化与不同组织噪声的相关性及图像质量影响的规律。方法:应用GE BrightSpeed 16层CT机以管电压120 kV,管电流300 mA,螺距0.938为标准,每次扫描改变一种扫描参数,其它扫描参数不变,以不同管电压(80、100、120、140 kV)、管电流(80、100、120、180、240、300 mA)及螺距(0.562、0.938、1.375、1.75)扫描仿真胸部体模,测量、记录体模不同组织噪声值(CT值标准差,SD),并进行统计学分析。结果:肺组织不同管电压组(80、100、120、140 kV)的噪声比较差异无统计学意义(F=0.966,P>0.05),而胸壁软组织、脊柱旁软组织及主动脉噪声80 kV组与常规管电压120 kV组比较差异有统计学意义,P<0.05。肺组织、脊柱旁软组织及主动脉噪声不同管电流组(80、100、120、180、240、300 mA)差异均有统计学意义(肺组织F=3.28,P<0.05、脊柱旁软组织F=11.89,P<0.05及主动脉F=196.67,P<0.05);肺、胸壁软组织、脊柱旁软组织及主动脉噪声80 mA组与常规管电流300 mA组比较差异有统计学意义,P<0.05。肺、胸壁软组织、脊柱旁软组织不同螺距组(0.562、0.938、1.35及1.75)噪声差异无统计学意义(肺组织F=0.23,P>0.05;胸壁软组织F=1.53,P>0.05;脊柱旁软组织F=2.27,P>0.05);主动脉噪声不同螺距组比较差异有统计学意义(F=9.68,P<0.05)。结论:降低管电压、管电流,增加螺距时,不同组织噪声逐渐增高,但肺组织的噪声增加不明显,胸部低剂量扫描时能够在保证肺组织图像噪声变化不大的同时降低辐射剂量。

Objective：To investigate the correlations between CT scan parameters and noises of different tissues and to discuss the factors influencing the image quality.Methods：The anthropomorphic phantom equivalent to human tissue was scanned by 16 slices spiral scanner（GE BrightSpeed） with different voltages（80,100,120 kV and 140 kV）,tube currents（80,100,120,180,240 mA and 300 mA） and pitches（0.562,0.938,1.375 and 1.75）.120 kV,300 mA and 0.938（pitch） were using as the standard.One of the three scanning parameters was changed and other scanning parameters were fixed.The CT value and image noise were recorded and analyzed（Standard derivation,SD）.Results：There was no statistical difference in noises of the lung among groups of 80,100,120,140 kV（F=0.966,P 〉0.05）.There were statistical differences between groups of 80 kV and 120 kV in noises of the chest wall,soft tissue of spine and aorta,P〈0.05.The noises of different tissues were statistically different among groups of 80,100,120,180,240 mA and 300 mA（Lung F=3.28,P〈0.05;soft tissue of spine F=11.89,P〈0.05;aorta F=196.67,P〈0.05）.There were statistical differences between 80 mA group and 300 mA group in noises of the lung,chest wall,soft tissue of spine and aorta,P〈0.05.The noises of the lung,soft tissues of chest wall and spine were not statistically different among groups with different pitches（0.562,0.938,1.35 and 1.75）.（Lung F=0.23,P 〉0.05;chest wall F=1.53,P 〉0.05;soft tissue of spine F=2.27,P 〉0.05）.There were statistical differences in noises of aorta among groups with different pitches,F=9.68,P〈0.05.Conclusions：The noises of different tissues are increasing with the decrease of tube voltage,tube current and increase of pitch,but the increase of noise in the lung is not obviously.The chest scan with low dose can reduce the radiation dose and keep the image quality without obviously increasing the noise in the lung.