Objective Normal estimation is the key step for volume visualization. Commonly used methods for normal estimation are based on interpolation and derivative. A novel normal estimation algorithm based on approximation for visualization of medical images was presented in this paper. Method It approximated the density function in local neighborhood with a second-degree polynomial function. The coefficients of the polynomial function were solved by minimizing the error of the approximation and the gradient vector at arbitrary point was obtained directly from the analytical derivative of the density function without interpolation. Because of symmetry, the solution of this equation was simplified.This method was tested in several volume data sets. The results and the generation time by different methods were obtained and compared. Result The results showed that this algorithm produced satisfactory quality images while the computational complexity was not increased. Conclusion This approach is preferable for most applications, especially for medical images reconstruction.

BACKGROUND:Amniotic cells are mainly composed of amniotic epithelial cells and amniotic mesenchymal cells, which have multi-differentiation potential and can be transformed into neurons as wel as synthesize and release biological y active substances and neurotrophic factors. In preliminary studies, amniotic cells that are transplanted into the brain can significantly promote the regeneration of brain neurons. OBJECTIVE:To explore the role of amniotic cells in mouse brain cells after ischemia-reperfusion injury. METHODS:The model of cerebral ischemia-reperfusion injury was established in Babl/c mice using occlusion of bilateral common carotid arteries, and then brain cells were separated from mice. Amniotic cells were isolated from mouse placenta. Brain cells from Balb/C mice co-cultured with amniotic cells served as experimental group, and brain cells cultured with PBS as control group. RESULTS AND CONCLUSION:The viability of brain cells in the experimental group was significantly higher than that in the control group (P<0.05). There was no difference in necrotic rate of brain cells between the experimental and control groups after 24 and 72 hours co-culture (P>0.05);after 48 hours co-culture, however, the necrotic rate of brain cells was significantly lower in the experimental group than the control group (P<0.05). In cellcycle, the experiment group showed increased S phase cells;while, the control group exhibited increased G 1 phase cells and decreased S phase cells. G 2 phase cells had no changes in number in both two groups. Through the above results, amnion cells can be proved to protect and promote the regeneration of brain cells of Balb/C mice with ischemia-reperfusion injury, and inhibit cellnecrosis and apoptosis.