探究单源双能CT螺距对标准水模能谱成像数据的影响

To Explore the Influence of GSI Data of Standard Model in Different Pitch of Single Source-dual Energy CT

目的:探讨单源双能CT不同螺距的能谱成像(GSI)扫描对标准水模的CT值和水碘浓度值的影响。方法:采用GE Discovery 750 HD单源双能CT的GSI扫描模式对GE公司标准水模进行扫描,选择辐射剂量相近(180~192.5 mAs范围)的6个扫描协议,分别对标准水模进行两种螺距(1.375︰1和0.984︰1)扫描,扫描野为M,扫描层厚5 mm,连续扫描6层,共获得12组数据。根据扫描螺距不同分为两组:大螺距组(螺距1.375︰1)、小螺距组(螺距0.984︰1)。获得的图像利用GSI分析软件,以1.25 mm进行无间隔标准算法重建70 keV单能量图像及水(碘)基物质图像,于标准水模中心及3、6、9和12点放置面积为3 000 mm^2圆形感兴趣区(ROI),对两种图像进行测量,记录各ROI的CT值及其SD值、水(碘)值及其SD值,采用SPSS软件配对样本t检验进行统计学分析。结果:大、小螺距组水的CT值分别为(1.39±1.90)HU和(1.97±1.74)HU,SD值分别为(7.21±0.55)HU和(6.47±0.56)HU;大、小螺距组水(碘)基物质图像的水(碘)值分别为1 001.95±1.47和1 002.19±1.34,其SD值分别为4.88±0.36和4.49±0.37。两组间差异均具有统计学意义(P<0.05)。结论:扫描参数螺距对GSI数据获得有影响,使用较小螺距扫描条件可提高诊断可靠性。

Objective： To explore the influence of GSI data in different pitch of single source-dual energy CT. Method： AGE standard water model was imaged by different scanning pitch of single source-dual energy CT （Discovery CT 750 HD）. Scanning parameter： 6 Scan Protocols with tube current form 180 to 192.5 mAs, medium FOV, thickness 5 mm, and two different pitch （1.375 ： 1 and 0.984 ： 1） for scanning. 6 slices of images was acquired in succession for each 12 groups of data and reconstructed 1.25 millimeter-thickness images. Using GSI general MD analysis software for image processing, 5 ROIs （3 000 mm2） were putted in the middle and 3, 6, 9, 12 o＇clock direction. CT value and CT SD value were measured on the 70 keV monochromatic image, water-iodine value and water-iodine SD value were measured on the water-iodine concentration image. Independent-samples t test were used for statistical analysis. Result： The CT value of 1.375 ： 1 group and 0.984 ： 1 group were （1.390± 1.90） HU and （1.969 ±1.74） HU, SD value were （7.21 ±0.55） HU, （6.47 ±0.56） HU; 1.375：1 group were closer to the standard value. The water-iodine value of 1.375mm group were 1001.56 ±1.76, SD value were 4.95 ± 0.43; the water-iodine value of 1.375 ： 1 group and 0.984 ： 1 group were 1001.95 ±1.47, 1002.19 ± 1.34. Differences between the two groups have statistical significance （P 〈 0.05）. Conclusion： Scanning pitch influenced GSI data. Using smaller pitch scanning condition, the reliability of diagnosis can be improved.