胸部X射线CT扫描中的放射防护最优化

OPTIMIZATION OF RADIATION PROTECTION IN X-RAY CT SCAN OF CHEST

X射线螺旋CT机不同扫描条件下,用有机玻璃均匀模体测量多层扫描的CT剂量指数值,用均匀水模体测量CT值的均匀性及其噪声。比较了不同扫描条件下,患者肺部肿块影及片状影的CT图像质量。结果表明:曝露量为402、5、7.5 mAs时的CT剂量指数值分别不超过曝露量为115 mAs时的40%、30%和15%。本文用CT扫描“优化因子”作为图像质量、病人所受剂量的综合评价指标,实现了CT扫描条件优化的定量分析。虽然,随X射线曝露量减少,均匀模体断层内CT值噪声增加、正常图像百分率下降,但从图像质量、病人剂量综合考虑,X射线胸部CT扫描的曝露量宜取25 mAs。

Under different scan conditions, CT dose indices of multiple scan were measured using homogeneous PMMA phantom. Homogeneity and noise of CT values were also measured using a water phantom. CT image quality for mass and patch in the lung of patients that were selected randomly was compared. The results indicated： that CT dose indices for 40, 25,7.5 mAs are not more than 40%, 30%, 15 % of that for 115 mAs respectively. Quantitative analysis of scan conditions was carried out by using CT scan optimization factor as a comprehensive index to evaluate image quality and patient dose. The noise of CT values in homogeneous phantom increased and percentage of normal image decreased with reduction of X-ray exposure. Considering image quality and patient dose comprehensively, the optimized exposure for chest scanning is 25 mAs.