铋屏蔽对头颈部多层螺旋CT中眼晶状体辐射剂量的降低作用

目的 探讨扫描平面内铋屏蔽在头颈部多层螺旋CT(MSCT)扫描中对影像质量的影响和眼晶状体辐射剂量的降低作用.方法 分别使用颅脑、颞骨和鼻窦临床扫描条件,在无屏蔽、1层、2层和3层铋屏蔽覆盖眼部区域时,对标准水模和离体头颅标本进行扫描,用热释光剂量片测量头颅标本每次扫描时的眼晶状体器官剂量.在屏蔽材料和被扫描体间放置5、10、15和20 mm厚的海绵时,使用鼻窦扫描条件采集影像,并测量眼晶状体的剂量.测量水模影像中与屏蔽物为2、4、6和8 cm距离处的CT值,主观评价头颅标本影像中伪影对解剖结构的影响.结果 颅脑、颞骨和鼻窦CT临床扫描中眼晶状体的器官剂量分别为24.31、27.60和20.01 mGy.使用铋屏蔽时,均使得眼晶状体剂量有显著下降,但下降幅度随着铋屏蔽物的增加而降低.在各种厚度的屏蔽物时,屏蔽物间隙越大,眼晶状体剂量的降低程度越小,测量兴趣区CT值的增加程度也显著降低.颅脑和颞骨CT扫描分别使用2层和3层铋屏蔽,在不影响诊断的前提下,可有效降低眼晶状体剂量分别为47.1%和59.1%;鼻窦CT扫描时,1层屏蔽无间隙、2层屏蔽1.5 cm间隙不影响诊断,可降低眼晶状体剂量分别为31.5%和34.5%.结论 扫描平面内铋屏蔽材料的合理应用,可有效降低头颈部CT扫描中眼晶状体的辐射剂量.

Radiation dose reduction to the lens of eye with bismuth shielding in head and neck MSCT

Objective To explore the effects on image quality and dose reduction to the lens when using bismuth shielding in head and neck MSCT.Methods The standard phantom and the cadaveric head with none, 1, 2 and 3 layers of bismuth shielding were scanned with protocols of brain, temporal bone and paranasal sinuses using a 16-MDCT scanner. The organ dose to the lens in each scanning was measured with thermoluminescence dosimeters(TLD). The above scanning with sinus protocol was repeated with a sponge with thickness of 5, 10, 15 and 20 mm placed between the shielding and phantom/head. The CT attenuation of phantom with the distance of 2, 4, 6 and 8 cm to shielding were measured. The image quality was subjectively evaluated by 2 physicians.Results The organ doses of the lens with protocols of brain, temporal bone and sinuses were 24.31, 27.60 and 20.01 mGy, respectively. The doses were decreased significantly when using bismuth shielding. With the increase of the shield gap, the degree of dose reduction was reduced, but the increasing degree of CT attenuation significantly reduced. Using 2-layer and 3-layer bismuth shield in brain and temporal bone CT scan, the radiation doses were reduced by 47.1% and 59.1%, respectively while maintaining the diagnostic image quality. Using 1-layer shield without gap and 2-layer shield with 1.5 cm gap in sinus CT, the radiation doses were reduced by 31.5% and 34.5%, respectively.Conclusions Reasonable usage of bismuth shielding can effectively reduce the radiation dose to the lens of eye in head and neck MSCT.