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Objective:To evaluate the application value of bismuth shielding combined with organ tube current modulation (X-care) in brain CT scanning by measuring the radiation dose of sensitive organs.Methods:The head and neck phantom was scanned with Siemens dual source CT at the same volume CT dose index (CTDI vol) by X-care, bismuth shielding and x-care combined with bismuth shielding, and by dual energy CT angiography (DE-CTA) with and without bismuth shielding. The CT values of cerebral vessels, adjacent brain tissues and cerebrospinal fluid and image noise were measured, and the contrast noise ratio of cerebral vessels and brain parenchyma was calculated. Organ dose equivalent ( HT) was calculated by placing thermoluminescent personal dosimeter (TLD), and CTDI vol and dose length product (DLP) were recorded after each scan. Results:Under the same CTDI vol, the mean values of HT, lens with X-care, Bi shielding and X-care combined with Bi shielding were(37.89 ± 2.00), (42.20 ± 2.96) and (28.21 ± 1.31) mSv, respectively, significantly lower than those of conventional sequence scanning( F=186.52, P<0.05). The values of HT, thyroid with Bi shielding and X-care combined with Bi shielding were (0.77 ± 0.07) and (0.89 ± 0.08) mSv, lower than those of routine brain scan and X-care( F=103.26, P<0.05). The values of HT, lens and HT, thyroidof DE-CTA with bismuth shielding were (11.56 ± 1.04) and (0.32 ± 0.03) mSv, respectively, significantly lower than those without bismuth shielding( t=5.07, P<0.05). There was no significant difference in noise and CNR in routine brain scan between with and without X-care, bismuth shielding and X-care combined with bismuth shielding. There was no significant difference in noise and CNR in dual energy CTA scanning between with and without Bi shielding. Conclusions:Using bismuth shielding and organ tube current modulation, we can significantly reduce organ dose of lens and thyroid during brain CT scanning without sacrificing the image quality.
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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.