鼻窦多层螺旋CT扫描中铋屏蔽对影像质量和晶体辐射剂量的影响

The influence of bismuth shielding on image quality and radiation dose to eye lens in sinus multi-detector CT

目的 探讨鼻窦多层螺旋CT扫描中铋屏蔽对影像质量的影响和对晶体辐射剂量的降低作用.方法 使用16层螺旋CT,选择鼻窦临床扫描条件分别对标准水模、离体头颅标本进行扫描,在无屏蔽、1层、2层和3层铋屏蔽时分别采集影像,对离体头颅标本用热释光剂量片测量每次扫描的晶体辐射剂量.分别采集在屏蔽材料和扫描体表面之间放置厚度为0.5、1.0、1.5和2.0 cm海绵时的影像,并测量晶体接受的辐射剂量.测量模体CT图像中距离屏蔽物分别为2.0、4.0、6.0和8.0 cm处的CT值.评价头颅标本影像中伪影对解剖结构的影响.结果 鼻窦CT扫描时晶体的辐射剂量为20.0 mGy.使用3种铋屏蔽厚度时,晶体的辐射剂量分别下降至13.7、10.9和9.4 mGy,下降趋势随着铋屏蔽物的增加而降低.在使用各种不同厚度的屏蔽物进行扫描时,屏蔽物间隙越大,晶体剂量的降低程度越小,但CT值的增加幅度显著降低.鼻窦CT扫描时,在不影响诊断的前提下,1层屏蔽无间隙或2层屏蔽1.5 cm间隙时图像质量满足诊断要求,辐射剂量分别可降低至13.7和13.1 mGy,降低幅度分别为31.5％和34.5％.结论 铋屏蔽材料的合理应用可在不影响影像质量的前提下,有效降低鼻窦CT扫描中眼晶状体的辐射剂量.

Objective To explore the influence on image quality and the reduction of radiation dose to eye lens when using bismuth shielding in sinus MDCT.Methods The standard water phantom was scanned using clinical scanning protocols of sinus in 16-MDCT,and the images were acquired with none,1 layer,2 layers and 3 layers of bismuth shielding severally.Using the above protocol,the cadaveric head was scanned with no shield,1,2 and 3 layers of bismuth shielding material covered on both eyes,and the organ dose to eye lens in each scanning was measured with thermoluminescence dosimeter （TLD）.The sponge with the thick of 0.5,1.0,1.5,2.0 cm was placed between the shielding material and the surface of subjects separately and the radiation doses to eye lens was measured with sinus scanning conditions in the same way.The CT values of phantom with the distances of 2.0,4.0,6.0 and 8.0 cm to shield material were measured.The influence of bismuth artifacts on anatomic structures was evaluated as well.Results The organ doses to the eye lens in the sinus clinical CT were 20.0 mGy.Doses decreased significantly to 13.7,10.9 and 9.4 mGy separately when using 3 types of bismuth shielding thickness.With different thicknesses of shielding material,the greater the shield gap,the smaller the degree of reduction of organ dose,but the increasment of CT value was significantly reduced.Using 1-layer shield no gap and 2-layer shield with 1.5 cm gap in sinus MDCT,the radiation doses were reduced to 13.7 and 13.1 mGy with the reduction rates of 31.5％ and 34.5％ respectively.Conclusion The reasonable bismuth shielding can effectively reduce the radiation dose to eye lens in sinus CT on the premise of ensuring image-diagnostic quality.