Yuan-Qing Xu

Texture analysis and classification of ultrasound liver images

Ultrasound as a noninvasive imaging technique is widely used to diagnose liver diseases. Texture analysis and classification of ultrasound liver images have become an important research topic across the world. In this study, GLGCM (Gray Level Gradient Co-Occurrence Matrix) was implemented for texture analysis of ultrasound liver images first, followed by the use of GLCM (Gray Level Co-occurrence Matrix) at the second stage. Twenty two features were obtained using the two methods, and seven most powerful features were selected for classification using BP (Back Propagation) neural network. Fibrosis was divided into five stages (S0-S4) in this study. The classification accuracies of S0-S4 were 100%, 90%, 70%, 90% and 100%, respectively.

Red blood cell partitioning and blood flux redistribution in microvascular bifurcation

This paper studies red blood cell (RBC) partitioning and blood flux redistribution in microvascular bifurcation by immersed boundary and lattice Boltzmann method. The effects of the initial position of RBC at low Reynolds number regime on the RBC deformation, RBC partitioning, blood flux redistribution and pressure distribution are discussed in detail. It is shown that the blood flux in the daughter branches and the initial position of RBC are important for RBC partitioning. RBC tends to enter the higher-flux-rate branch if the initial position of RBC is near the center of the mother vessel. The RBC may enter the lower-flux-rate branch if it is located near the wall of mother vessel on the lower-flux-rate branch side. Moreover, the blood flux is redistributed when an RBC presents in the daughter branch. Such redistribution is caused by the pressure distribution and reduces the superiority of RBC entering the same branch. The results obtained in the present work may provide a physical insight into the understanding of RBC partitioning and blood flux redistribution in microvascular bifurcation.

IB-LBM simulation on blood cell sorting with a micro-fence structure

A size-based blood cell sorting model with a micro-fence structure is proposed in the frame of immersed boundary and lattice Boltzmann method (IB-LBM). The fluid dynamics is obtained by solving the discrete lattice Boltzmann equation, and the cells motion and deformation are handled by the immersed boundary method. A micro-fence consists of two parallel slope post rows which are adopted to separate red blood cells (RBCs) from white blood cells (WBCs), in which the cells to be separated are transported one after another by the flow into the passageway between the two post rows. Effected by the cross flow, RBCs are schemed to get through the pores of the nether post row since they are smaller and more deformable compared with WBCs. WBCs are required to move along the nether post row till they get out the micro-fence. Simulation results indicate that for a fix width of pores, the slope angle of the post row plays an important role in cell sorting. The cells mixture can not be separated properly in a small slope angle, while obvious blockages by WBCs will take place to disturb the continuous cell sorting in a big slope angle. As an optimal result, an adaptive slope angle is found to sort RBCs form WBCs correctly and continuously.

STUDY ON A SELF-PROPELLED FISH SWIMMING IN VISCOUS FLUID BY A FINITE ELEMENT METHOD

A self-propelled fish swimming in viscous fluid is investigated by solving the incompressible Navier–Stokes equations numerically with the space-time finite element method to understand the mechanisms of aquatic animal locomotion. Two types of propulsion strategies, undulatory body and traveling wave surface (TWS), are considered. Based on the simulations, we find that by performing lateral undulation, the fish is able to move forward with a reverse von Karman vortex street in its wake. In addition, there is no vortex street in the wake of the fish using TWS. In this case, the thrust of the fish is generated by the jets outside the boundary layer and the high pressure on the leeward side of the traveling wave. The results obtained in this paper will be of help in understanding of the propulsive performance of aquatic animal locomotion.

IB-LBM study on cell sorting by pinched flow fractionation.

Separation of two categories of cells in pinched flow fractionation(PFF) device is simulated by employing IB-LBM. The separation performances at low Reynolds number (about 1) under different pinched segment widths, flow ratios, cell features, and distances between neighboring cells are studied and the results are compared with those predicted by the empirical formula. The simulation indicates that the diluent flow rate should approximate to or more than the flow rate of particle solution in order to get a relatively ideal separation performance. The discrepancy of outflow position between numerical simulation and the empirical prediction enlarges, when the cells become more flexible. Too short distance between two neighboring cells could lead to cell banding which would result in incomplete separation, and the relative position of two neighboring cells influences the banding of cells. The present study will probably provide some new applications of PFF, and make some suggestions on the design of PFF devices.

Immersed Boundary-Lattice Boltzmann Method for Biological and Biomedical Flows

In this paper, we describe an immersed boundary (IB)–lattice Boltzmann (LB) method for computing the fluid–structure interaction (FSI) encountered in biological and biomedical flows, such as fish swimming, red blood cell (RBC) dynamics and cell manipulating in micro scope. The approach combines a single relax time LB method for viscous incompressible flow and a delta function IB method for coupling the flexible boundary with the fluid. The IB method handles the effect of the moving boundary by spreading the stress exerted by the boundary on the fluid onto the collocated grid points near the boundary. For the boundary of FSI, the Lagrangian force is calculated by the standard second-order finite difference method, while the Lagrangian force of prescribed boundary is determined by a feedback scheme. The FSI solver has been validated and verified against previous studies. The details of this method and its applications in both fundamental study of biophysics of fish swimming, RBC behavior in micro flow and cell capturing in a micro architecture will be introduced.

A MATHEMATICAL MODEL FOR MICRO- AND NANO-SWIMMERS

In order to explore the kinetic characteristics of planktonic microorganisms and nanometer biological motors, a mathematical model is developed to estimate the hydrodynamic force in the migration of micro- and nano-swimmers by using the Laplace transformation and linear superposition. Based on the model, it is found that a micro- and nano-swimmer will enjoy a positive propulsive force by improving frequencies or generating traveling waves along its body if it is not time reversible. The results obtained in this study provide a physical insight into the behaviors of the micro- and nano-swimmer at low Reynolds numbers, and the corresponding quantitative basis can also be potentially used in the design of nanorobot and nanosized biomaterials.