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Objective To provide a reference for avoiding the harm to critical target organs following considerable inhalation exposure to the transuranium element americium (Am) as well as post-accident decorporation or other radiation protection measures. Methods We established calculation programs based on the generic criteria for internal radiation emergency preparedness and response in the IAEA Safety Guide No.GSG-2 and current new ICRP biokinetic models and parameters, taking an inhalation of 241Am (activity mean aerodynamic diameter of 5 μm, σ = 2.5) by an adult worker as an example; and determined that the critical target organs were the lung AI region, red bone marrow, and the main source organs leading to acute doses to the critical target organs were the lung AI region, blood, and trabecular bone surface. Results The retention fractions in the main source organs over time after 241Am inhalation were calculated. Conclusion After being absorbed into blood, Am moves quickly to other parts, and Am of different absorption types shows similar early changes in retention fractions in blood: the retention fractions of Am of S, M, and F types in blood peak around 0.03 d, and then halve around 1.7 d. Inhaled Am shows different changes over time in retention fractions in the lung AI region and trabecular bone surface in the early stage: the retention fractions of S- and M-type Am in the lung AI region change little with time, while F-type Am transfers quickly from the lung to blood; In trabecular bone surface, S-type Am increases quickly in the first 7 d, M-type Am gradually increases mainly in the first 2 weeks, and F-type Am increases quickly in the first 2 d.
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Objective:To explore the oxidative stress of cerebral white matter lesion (WML) and normal-appearing white matter (NAWM) with in vivo proton exchange rate (k ex) MRI on relapse-remitting multiple sclerosis (RRMS) patients. Methods:Clinical and imaging data of 37 patients (case group) with RRMS patients of Tongji Hospital of Tongji Medical College of Huazhong University of Science and Technology were analyzed retrospectively from November 2018 to November 2021, including 11 males and 26 females aged 18-41 (29±7) years. Another 22 age-matched healthy volunteers (control group) were recruited for the same period, including 4 males and 18 females aged 23-44 years with a median age of 25 (24, 28.25) years. All subjects received conventional MR protocols and chemical exchange saturation transfer imaging. The manifestation of WML on the k ex map and T 1WI images were assessed while the k ex values of WML, NAWM and normal white matter (NWM) of control group were quantitatively evaluated. Student′s t test was used to compare the k ex difference of WML and NAWM in the case group, NAWM in the case group and NWM in the control group, low-signal and isosignal WML in T 1WI. Spearman rank correlation was used to analyze the correlation of the k ex values of WML with patients′ expanded disability status scale (EDSS) score. Results:A total of 272 WML were found in the 37 RRMS patients, and 25.4% (69/272) were T 1-hypointense. The k ex value of WML in the case group [(932±108) s -1] was higher than that of NAWM [(771±26) s -1], and the difference was statistically significant ( t=8.95, P<0.001); the k ex value of NAWM in the case group [(771±26) s -1 ] was higher than that of NWM [(745±26) s -1] in the control group, and the difference was statistically significant ( t=3.96, P<0.001). The k ex value [(1 039±110) s -1] of WML with low signal at T 1WI was higher than that of WML with equal signal [(895±79) s -1], with a statistically significant difference ( t=9.78, P<0.001). Correlation analysis showed that the k ex value of WML in the case group was positively correlated with the EDSS score ( r=0.54, P<0.001). Conclusions:The elevated k ex values of WML and NAWM reflect the cerebral oxidative stress of RRMS patients and are positively correlated to the severity of tissue damage, which suggests the role of oxidative stress in RRMS lesion formation and brain atrophy.