Constitutive law of healthy gallbladder walls in passive state with damage effect

Biomechanical properties of human gallbladder (GB) wall in passive state can be valuable to diagnosis of GB diseases. In the article, an approach for identifying damage effect in GB walls during uniaxial tensile test was proposed and a strain energy function with the damage effect was devised as a constitutive law phenomenologically. Scalar damage variables were introduced respectively into the matrix and two families of fibres to assess the damage degree in GB walls. The parameters in the constitutive law with the damage effect were determined with a custom MATLAB code based on two sets of existing uniaxial tensile test data on human and porcine GB walls in passive state. It turned out that the uniaxial tensile test data for GB walls could not be fitted properly by using the existing strain energy function without the damage effect, but could be done by means of the proposed strain energy function with the damage effect involved. The stresses and Young moduli developed in two families of fibres were more than thousands higher than the stresses and Young's moduli in the matrix. According to the damage variables estimated, the damage effect occurred in two families of fibres only. Once the damage occurs, the value of the strain energy function will decrease. The proposed constitutive laws are meaningful for finite element analysis on human GB walls.

Automatic error correction using adaptive weighting for vessel-based deformable image registration

In this paper, we extend our previous work on deformable image registration to inhomogenous tissues. Inhomogenous tissues include the tissues with embedded tumors, which is common in clinical applications. It is a very challenging task since the registration method that works for homogenous tissues may not work well with inhomogenous tissues. The maximum error normally occurs in the regions with tumors and often exceeds the acceptable error threshold. In this paper, we propose a new error correction method with adaptive weighting to reduce the maximum registration error. Our previous fast deformable registration method is used in the inner loop. We have also proposed a new evaluation metric average error of deformation field (AEDF) to evaluate the registration accuracy in regions between vessels and bifurcation points. We have validated the proposed method using liver MR images from human subjects. AEDF results show that the proposed method can greatly reduce the maximum registration errors when compared with the previous method with no adaptive weighting. The proposed method has the potential to be used in clinical applications to reduce registration errors in regions with tumors.

Determining the number of preconditioning cycles by calculating the decay rate of strain energy in uniaxial tensile test on soft tissue / 医用生物力学

Objective To investigate a method determining the number of preconditioning cycles in uniaxial tensile test on soft tissues by calculating the decay rate of strain energy. Methods The abdominal skin of healthy New Zealand rabbits was selected as study object, from which strip specimens were obtained in directions parallel to linea alba (0°)and perpendicular to linea alba(90°). Then the uniaxial preconditioning tests with 15% preconditioning strain were performed on these specimens. Load displacement preconditioning data were obtained, and transformed into the stress strain data correspondingly. The preconditioning cycles (n values), at the decay rate of strain energy being 5% and 10%, respectively, were then calculated by MATLAB programme when n values satisfy the inequality η=Wn－Wn－1Wn－1×100%≤5% or≤10%（Wn signifies the strain energy loss in the nth preconditioning cycle）. Results When the decay rate of strain energy was 5%, the number of preconditioning cycles in 0° and 90° direction was 11.11 and 13.67, respectively. When the decay rate of strain energy was 10%, the number of preconditioning cycles in 0° and 90° direction was 6.67 and 7.78, respectively. Conclusions By calculating the decay rate of strain energy, the number of preconditioning cycles in uniaxial tensile on soft tissues can be quantified, which could help provide the research basis for standardization of biomechanical testing on soft tissues.

Compare the influence of two explorers on the enamel of artificial initial caries / 实用口腔医学杂志

Objective: To compare the influence of two explorers on the enamel of artificial initial caries. Methods: Built an artificial initial caries model in vitro. Compared the influence of two explorers on the enamel of artificial initial caries. Results: 1.The holes probed by sharp explorer were deep and narrow. The holes probed by CPI explorer were shallow and wide. 2. The average strain energy produced by CPI explorer was larger than sharp explorer(Z=-2.021,P=0.043), But there was no significant difference because the strain energy produced by two explorers were in the same rate range. Conclusion: The damage on the enamel of artificial initial caries caused by sharp explorer is not larger than that caused by CPI explorer. So we suggest that the sharp explorer can still be used in sampling survey and clinical examination. But a gentle probing action is strongly recommended.