Simulation and quantitative analysis of fluorescence intensity distribution based on the Monte Carlo method

The Monte Carlo method is a versatile simulation algorithm to model the propagation of photons inside the biological tissues.It has been applied to the reconstruction of the fluorescence molecular tomography(FMT).However,such method suffers from low computational efficiency,and the time consumption is not desirable.One way to solve this problem is to introduce a priori knowledge which will facilitate iterative convergence.We presented an in vivo simulation environment for°uorescence molecular tomography(ISEFMT)using the Monte Carlo method to simulate the photon distribution of fluorescent objects and their sectional view in any direction quantitatively.A series of simulation experiments were carried out on different phantoms each with two fluorescent volumes to investigate the relationship among fluorescence intensity distribution and the excitation photon number,the locations and sizes of the fluorescence volumes,and the anisotropy coefficient.A significant principle was discovered,that along the direction of the excitation light,the fluorescent volume near the excitation point will provide shelter effect so that the energy of the fluorescent volume farther away from the excitation point is relatively lower.Through quantitative analysis,it was discovered that both the photon energy distribution on every cross section and the fluorescence intensity distributed in the two volumes exhibit exponential relationships.The two maximum positions in this distribution correspond to the centers of fluorescent volumes.Finally,we also explored the effect of the phantom coefficients on the exponential rule,and found out that the exponential rule still exists,only the coefficient of the exponential rule changed.Such results can be utilized in locating the positions of multiple fluorescent volumes in complicated FMT reconstruction involving multiple fluorescent volumes.Thus,a priori knowledge can be generalized,which would accelerate the reconstruction of FMT and even other images.

Thixotropy of Aqueous Suspensions Containing Mg-AI Hydrotalcite-like Compound and Low-substituted Cationic Starch： Comparison between Oscillatory Shear and Thixotropic Loop Measurements

The rheological properties of aqueous suspensions consisting of positively charged aluminum magnesium hydrotalcite-like compound （HTlc） and low-substituted cationic starch （LCS） were investigated. Special emphasis was placed on the thixotropic phenomenon. Thixotropic behavior was investigated by two thixotropic methods： thixotropic loop and oscillatory shear measurements. LCS molecules could be adsorbed onto HTlc particles due to the hydrogen bonding between ether groups or hydroxyl groups of LCS and hydroxyl groups of HTlc. The elastic dynamic response of the HTlc/LCS suspension increased with increasing mass ratio （R） of HTlc and a three-dimensional network structure could be formed in the suspension with higher R value. The thixotropic type of the HTlc/LCS suspension transformed from negative to positive and then to complex thixotropy when R changed from 0 to 0.5. By comparing between the thixotropic results obtained by thixotropic loop and oscillatory shear measurements, it was validated that the thixotropic loop for the suspension showing complex thixotropy had a crossover point.