低管电压腹部CT扫描对图像质量及辐射剂量影响的体模实验

Experiment on the impact of low tube voltage on imaging quality and radiation dose in abdominal multi-detector CT

目的探讨80kV低管电压腹部CT扫描对图像质量及辐射剂量的影响。方法选用Catphan500体模,以其低对比模块中直径20mm、对比度为1.0%的圆柱体为研究对象,模拟腹部CT低对比的特点;在其他扫描参数相同的情况下,分别以低管电压80kV和常规腹部CT扫描标准管电压120kV对体模进行扫描,管电流均设置为150～650mA(以50mA为间隔)。记录每组扫描方案的容积CT剂量指数(CTDIvol)、图像噪声及对比噪声比(CNR),同时由2名医师对图像的低对比可探测能力(LCD)进行独立评分,分析80、120kV时的CNR与CTDIvol的相关性,并比较80kV管电压条件下所得图像噪声、CNR及LCD评分与腹部标准扫描条件120kV、300mA之间的差异。结果 CNR与CTDIvol呈正相关,辐射剂量相同时,80kV条件下所得CNR明显高于120kV。80kV时图像噪声显著增加(t=6.99～15.78,P<0.001),但当管电流增加至550～650mA时,80kV所得图像的CNR及LCD评分与120kV、300mA之间差异无统计学意义(P>0.05)。结论管电流增加至550mA时,在不影响图像质量CNR及LCD的前提下,80kV低管电压CT扫描最多可降低42.23%的辐射剂量。

Objective To investigate the impact of low tube voltage with 80 kV on imaging quality and radiation dose in abdominal CT. Methods A phantom containing low-contrast objects was scanned with a 16-section multi-detector CT scanner at 80 and 120 kV, with tube current-time product settings at 150-650 mA. The image noise （SD, standard deviation of CT number）, contrast-to-noise ratio （CNR） and CT doses index volume （CTDLol） were objectively measured. To assess low-contrast detectability （LCD）, subjective assessment of the visibility was performed by 2 independent observers. The relationship between CNR and CTDLol was analyzed. The differences between image noise, CNR and scores of LCD obtained with 80 kV at 150-650 mA and those obtained with 120 kV at 300 mA were compared. Results There was direct correlation between CNR and CTDLol. With identical dose, using of 80 kV tube voltage resulted in higher CNR compared with CNR at 120 kV. Although the image noise substantially increased with low tube voltage （80 kV）, there was no statistical difference between CNR and scores of LCD obtained with 120 kV at 300 mA and those obtained with 80 kV at 550-650 mA （P〉0. 05）. Conclusion With a reduction of the tube voltage from 1Z0 kV to 80 kV, the amount of reduction in the radiation dose can be achieved mostly by 42.23% without degradation of CNR and LCD.