胸部X射线CT扫描中的放射防护最优化

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40、25、7．5mAs时的CT剂量指数值分别不超过曝露量为115mAs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25mAs。

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

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.