眼眶部低剂量螺旋CT扫描参数的优化

The research of the relativity between the scan parameters optimization and radiation dose at orbital helical CT

目的:探讨眼眶部低剂量螺旋CT扫描参数的优化。方法:320例被检者分成16组(每组20例),将管电流140、110、80、60mA,层厚2和3mm,螺距0.75和1.5,设计成16组螺旋CT扫描参数。记录每组容积CT剂量指数(CTD-Iovl)和剂量长度乘积(DLP)平均值,分析管电流、层厚、螺距与辐射量的关系。图像质量从影像层次、背景噪声、解剖结构及能否满足诊断要求等方面进行综合评价,图像质量等级采用秩和检验分析。结果:X线辐射量与管电流呈正相关,当管电流从140mA降至80mA时,CTDIovl和DLP分别下降42.84%、42.86%,图像质量均符合诊断要求,且差异无统计学意义(P>0.05);降至60mA时,图像质量差异有统计学意义(P<0.05)。X线辐射量与螺距呈负相关,当螺距从0.75增至1.5时,CTDIovl和DLP分别下降49.98%、47.37%,图像质量差异无统计学意义(P>0.05)。X线辐射量与层厚关系不大,当层厚由3mm降至2mm时,CTDIovl和DLP分别降低9.90%、12.23%;图像质量差异无统计学意义(P>0.05),但2mm层厚的图像噪声较3mm大。结论:降低管电流,加大螺距是降低辐射量的有效途径;眼眶部螺旋CT扫描参数设置为管电流80mA、螺距1.5时,能兼顾图像质量和辐射量,扫描层厚根据检查要求选择。

Objective：To explore the scanning parameters optimization with low-dose for orbital spiral CT. Methods： 320 cases were divided into 16 groups （n= 20 cases）, mA was respectively 140mA, ll0mA,80mA,60mA;slice thickness： 2mm,3mm;pitch：0. 75,1. 5; spiral CT scanning parameters designed for the 16 groups： mA, slice thickness, pitch 140,2, 0.75;140,2,1.5;140,3,0.75;140,3,~.5;110,2,0.75;110,2,1.5;110,3,0.75;110,3,1.5;80,2,0.75;80,2,1.5;80,3, 0.75;80,3,1.5;60,2,0.75;60,2,1. 5;60,3,0. 75;60,3,1. 5. CT dose index （CTDIovl） and dose length product （DLP） were recorded to analyze relativity among mA, slice thickness, pitch and radiation dose. Image quality was evaluated according to its low-density resolution, background noise, anatomic structure and whether it can meet the diagnostic requirements. The image data were analyzed by Rank sum test. Results：There was a positive relationship between X-ray radiation dose and tube current. When the tube current decreased from 140mA to 80mA,CTDIovl and DLP decreased 42.84% and 42.86%, the image quality had no significant difference （P〈0. 05）, and it met the diagnostic requirements. When decreasing to 60mA,the difference of image quality was statistically significant （P〈0.05）. there was a negative relationship between X-ray radiation dose and the pitch. When the pitch increased from 0. 75 to 1. 5,CTDIovl and DLP decreased 49. 98% and 47.37% ,there was no significant difference （P〈0.05）. When slice thickness reduced from 3mm to 2mm,CTDIvol and DLP decreased 9.90% and 12.23% respectively;there was no statistical difference （P〈0.05） ,and image noise increased more in 2ram slice thickness than 3mm. Conclusion： Reducing the tube current and increasing the pitch are an effective way to reduce radiation dose. When the orbital spiral CT scan parameter is set to 80 mA and pitch 1.5, there will be good image quality and low radiation dose. Slice thickness should be chosen according to the diagnostic requirements.