螺旋CT不同参数与辐射剂量相关性的实验研究

目的:使用不同参数对水模进行CT扫描,探讨不同参数与辐射剂量的相关性。方法:螺距:0.526和1.375,管电流分组选择:20、40、60、80、100、140、180、220、250、300 m A,分别对水模进行扫描,对所有图像进行测量,记录CT值与CT值标准差(SD),分别记录CT机自动计算出来的单次容积CT剂量指数和剂量长度乘积。对水模的CT值和CT值标准差进行方差检验,P<0.05为有统计学意义。结果:螺距0.516∶1约在220 m A相交,相交后,噪声、信噪比曲线走行变缓,略变直;螺距1.375∶1在220 m A后,随着管电流的增加,噪声曲线走行变缓,信噪比增加不多。同等管电流下,螺距大,噪声值大。螺距1.375∶1的图像颗粒感较大,螺距0.516∶1图像较为细腻。结论:2组螺距0.516和1.375,扫描同一范围时,螺距小,采集图像时间较长,辐射剂量也较大;相反,螺距大,图像采集时间短,辐射剂量较小,但是密度分辨率低于小螺距,相同管电流下,图像质量的目测评分也较低。

Experimental study on correlation between spiral CT parameters and radiation dose

Objective To carry out CT scanning for water phantom with different parameters in order to explore the correlation between the parameters and radiation dose. Methods The parameters involved in the pitch of 0.526 and 1.375 as well as the tube current of 20, 40, 60, 80, 100, 140, 180, 220, 250 and 300 m A. All the images were measured, and CT values and standard deviations（SD） were calculated. Single volume CT dose index and dose-length product from CT machine were recorded respectively. Variance tests were performed for CT values and SDs of the water phantom, with P 0.05. Results When the pitch was 0.516：1, intersection occurred at 220 m A, and then the curve of noise and signal noise ratio（SNR） slowed down and straightened slightly; with the pitch 1.375∶1 and after 220 m A, noise curve slowed down with the tube current increased, while the curve of SNR hardly rose. With the same tube current, the pitch was raised with the increase of the noise. The image felt grainy with the pitch of 1.375 ∶1, while exquisite with the pitch of 0.516∶1. Conclusion With the pitches of 0.516 and 1.375 and for the same scope, the pitch positively correlates with the image acquisition time and radiation dose. With the same tube current, the image quality has low visual scores.