Optimization-based scatter estimation using semi-transparent beam absorber array.

To correct the scatter in cone beam CT, an optimization-based scatter estimation method (OPMSE) is proposed. Like the previous Fourier-based primary modulation method (FPMSE), semi-transparent beam absorber array (SBAA) is placed between the X-ray source and the imaging target, thus projection data behind the absorber can still be obtained, which is meaningful for dose saving and image quality improving. In the proposed algorithm, scatter is estimated by solving an optimization problem, which makes use of the prior information that primary and scatter are both smooth not only in each frame, but also between adjacent frames. Moreover, an edge-preserving weighting is incorporated to prevent the over-smoothing of structures in the primary signal. The new algorithm is robust that various patterns of modulator can be applied. Simulation and physical experiments demonstrated the good performance of OPMSE in scatter removing.

Study on HBV DNA “a” deteminant mutation in viral carrier children following universal HB vaccination / 中华传染病杂志

Objective To investigate hepatitis B virus mutation rate after the universal immunization in China. Methods DNA sequence analysis of the “a” determinant was performed on sera from 72 viral carrier children after immunoprophylaxis selected through a sampling survery. Results Four mutants were detected, the mutation rate was 5.56%. One strain showed Gly-to-Arg mutation at the 145 codon of surface antigen. Animo acid substitutions at the amino acid 126 and 140 were noted in the other three children. The epidemiological HBV serotype shifted from previous adw infection to more recent adr was also observed. Conclusions These observations indicate that vaccination is probably the cause of mutation, whereas the mutation is low and it will certainly not be a reason for doubting that the vaccination is the method of main choice for preventing hepatitis B infection that still devastates the developing countries.