ABSTRACT
The dynamic behaviour of a microbubble confined within a rigid micro-tube was studied using finite element method. The results indicated that the microbubble oscillation was limited when constrained within the micro-tube. Both the expansion ratio of its effective radius and natural frequency decreased with the decrease of the tube radius. Meanwhile, the deformation of the microbubble was non-spherical and became more significant when the ultrasound pressure amplitude increased. The dynamic behaviour in micro-tube was different from that in infinite liquid.
Subject(s)
Blood Vessels , Physiology , Contrast Media , Finite Element Analysis , Microbubbles , Microtubules , Molecular Dynamics SimulationABSTRACT
Water-fat separation is a particularly important problem for magnetic resonance imaging. Although many methods have been proposed, the reliability is still challenging. In this work, we have presented a method based on the combination of the branch-cut method and multigrid algorithm to get a more robust performance of water-fat separation. First, the branch-cut method is applied to identify residues, which violates the requirement that the interacting phase gradient around a closed path be zero. Residues and branches are marked to be zeros and filled to the weighting factor array. Then, the unwrapped phase array can be given by the multigrid algorithm. Finally, the Dixon method for water-fat separation is applied to the unwrapped phase array. Experiments for brain scanning on the 0.3T low field MRI system demonstrate the successful application of the proposed method.
ABSTRACT
Segmentation is a precondition step for modeling and analysis of the cochlea. In this paper, an interactive segmentation approach with a combination of 3D (three-dimensional) narrow-band level set algorithm and visualization technology was adopted to separate the cochlea. The 3D narrow-band level set algorithm was used to separate the objective of interest from volume data, and the visualization technology was used to display the segmented result. Users could modify intermediate parameters based on the direct 3D visual feedback until getting satisfying result. The basic principle and characteristics of level set and narrow-band level set algorithms were described in detail. The 3D narrow-band level set algorithm was successfully used to separate the cochlea from spiral CT images of the temporal bone. The experimental results show that the interactive method combining the narrow-band level set algorithm with visualization technique is capable of segmenting the cochlea from the medical volume data. Compared with the method of segmenting object from image volume slice by slice, our method can save much time.