Objective:To compare the efficacy and safety of domestic 16-row and imported 8-row mobile CT in clinics.Methods:A total of 1469 patients accepted domestic 16-row mobile CT head scans (1604 times) from March 2017 to August 2018 in Bayi Brain Hospital Affiliated to 7 th Medical Center of General Hospital of People's Liberation Army and Langfang Aidebao Hospital; and 15510 patients accepted imported 8-row mobile CT head scans (24994 times) from January 2016 to August 2018 in Bayi Brain Hospital Affiliated to 7 th Medical Center of General Hospital of People's Liberation Army. All patients underwent horizontal plain and enhanced head scans, cerebral CT angiography (CTA), and helical 3D imaging; and the imaging quality, operating power consumption, computed tomography dose index volume (CTDIvol) and stability within scanning volume ranges under different scanning modes of the two CT scans were compared. Results:(1) Imaging quality: the horizontal scanning of domestic 16-row mobile CT could clearly display low-density tissues such as the eyeball, optic nerve, brain stem, sulcus and cerebral gyrus; the imaging quality of both CT scans in patients with traumatic subdural hematoma and ischemic stroke completely met the clinical diagnosis and treatment standards. (2) Operating power consumption: the per-hour operating power consumption of domestic 16-row mobile CT ([0.286±0.018] kW·h) was obviously lower than that of imported 8-row mobile CT ([0.485±0.028] kW·h). (3) Radiological hazard: the CTDIvol of the horizontal scanning volume range in domestic 16-row mobile CT ([36.270±0.281] mGy) was significantly lower than that in the imported 8-row mobile CT ([82.520±0.441] mGy, P<0.05); the CTDIvol of enhanced axis scan volume range in the domestic 16-row mobile CT ([36.270±0.335] mGy) was significantly lower than that in the imported 8-row mobile CT ([70.728±0.424] mGy, P<0.05); the CTDIvol in the volume of CTA imaging of domestic 16-row mobile CT ([20.600±0.087] mGy) was significantly lower than that in the imported 8-row mobile CT ([29.300±0.335] mGy, P<0.05). The domestic 16-row mobile CT was designed with shock absorbers and guides; domestic 16-row mobile CT had small load, a low center of gravity, and good stability as compared with imported 8-row mobile CT. Conclusion:In terms of head scanning applications, the imaging quality of domestic 16-row mobile CT and imported 8-row mobile CT is in full compliance with clinical diagnostic standards, but the energy consumption and radiation risk of domestic 16-row mobile CT is significantly lower than imported 8-row mobile CT, enjoying good stability as compared with imported 8-row mobile CT.

Exonuclease Ⅷ (Exo Ⅷ), an ATP-independent dsDNA 5'-3' exonuclease, is a candidate protein with great application value for in vitro DNA recombination. However, the application of Exo Ⅷ in DNA recombination in vitro has not been reported. In this study, the recombinant expression vector of the truncated Exo Ⅷ (tExo Ⅷ) with the full exonuclease activity was built and used to achieve the overexpression of tExo Ⅷ in Escherichia coli. Based on the purified tExo Ⅷ protein with high-purity, the feasibility of tExo Ⅷ applied in vitro DNA recombination and effects of the reaction temperatures, reaction duration, and homology arm lengths were examined. The results showed that tExo Ⅷ was highly expressed in soluble form in E. coli. One liter of bacterial culture yielded 92.40 mg of purified tExo Ⅷ with the specific activity of 1.21×10⁵ U/mg. In a 10 μL recombination system containing 2.5 U tExo Ⅷ, the highest cloning efficiency was achieved in a reaction at 25 °C for 12.5 min and followed by incubation at 50 °C for 50 min. With addition of Pfu DNA polymerase, the homology arm extension strategy can effectively improve the recombination efficiency. Using competent E. coli Mach1 T1 with 2.2×10⁶ cfu/μg transformation efficiency as recipient cell, the recombination of a 1 kb fragment with a 21 bp homology arm and a 5.8 kb linearized vector can form about 1.1×10⁴ recombinant clones per μg vector, and the positive rates was over 80%. The recombination efficiency was increased with the increasing length of homology arm ranged from 8 to 21 bp. Under the optimal reaction condition, only 8 bp homology arm can still achieve valid DNA recombination. This novel in vitro DNA recombination system mediated by tExo Ⅷ was particularly characterized by its easy preparation, no limitation on restriction sites and high recombination cloning efficiency. All results revealed that the new efficient gene cloning system has potential application in the field of molecular biology.
Cloning, Molecular ; Escherichia coli ; genetics ; Exonucleases ; genetics ; Recombinant Proteins ; metabolism ; Recombination, Genetic