Coronary Artery Segmentation and Motion Modelling

Conventional coronary artery bypass surgery requires invasive sternotomy and the use of a cardiopulmonary bypass, which leads to long recovery period and has high infectious potential. Totally endoscopic coronary artery bypass (TECAB) surgery based on image guided robotic surgical approaches have been developed to allow the clinicians to conduct the bypass surgery off-pump with only three pin holes incisions in the chest cavity, through which two robotic arms and one stereo endoscopic camera are inserted. However, the restricted field of view of the stereo endoscopic images leads to possible vessel misidentification and coronary artery mis-localization. This results in 20-30% conversion rates from TECAB surgery to the conventional approach. We have constructed patient-specific 3D + time coronary artery and left ventricle motion models from preoperative 4D Computed Tomography Angiography (CTA) scans. Through temporally and spatially aligning this model with the intraoperative endoscopic views of the patient's beating heart, this work assists the surgeon to identify and locate the correct coronaries during the TECAB precedures. Thus this work has the prospect of reducing the conversion rate from TECAB to conventional coronary bypass procedures. This thesis mainly focus on designing segmentation and motion tracking methods of the coronary arteries in order to build pre-operative patient-specific motion models. Various vessel centreline extraction and lumen segmentation algorithms are presented, including intensity based approaches, geometric model matching method and morphology-based method. A probabilistic atlas of the coronary arteries is formed from a group of subjects to facilitate the vascular segmentation and registration procedures. Non-rigid registration framework based on a free-form deformation model and multi-level multi-channel large deformation diffeomorphic metric mapping are proposed to track the coronary motion. The methods are applied to 4D CTA images acquired from various groups of patients and quantitatively evaluated

First-principles calculations of phase transition, elasticity, and thermodynamic properties for TiZr alloy

tructural transformation, pressure dependent elasticity behaviors, phonon, and thermodynamic properties of the equiatomic TiZr alloy are investigated by using first-principles density-functional theory. Our calculated lattice parameters and equation of state for $\alpha$ and $\omega$ phases as well as the phase transition sequence of $\alpha$$\mathtt{\rightarrow}$$\omega$$\mathtt{\rightarrow}$$\beta$ are consistent well with experiments. Elastic constants of $\alpha$ and $\omega$ phases indicate that they are mechanically stable. For cubic $\beta$ phase, however, it is mechanically unstable at zero pressure and the critical pressure for its mechanical stability is predicted to equal to 2.19 GPa. We find that the moduli, elastic sound velocities, and Debye temperature all increase with pressure for three phases of TiZr alloy. The relatively large $B/G$ values illustrate that the TiZr alloy is rather ductile and its ductility is more predominant than that of element Zr, especially in $\beta$ phase. Elastic wave velocities and Debye temperature have abrupt increase behaviors upon the $\alpha$$\mathtt{\rightarrow}$$\omega$ transition at around 10 GPa and exhibit abrupt decrease feature upon the $\omega$$\mathtt{\rightarrow}$$\beta$ transition at higher pressure. Through Mulliken population analysis, we illustrate that the increase of the \emph{d}-band occupancy will stabilize the cubic $\beta$ phase. Phonon dispersions for three phases of TiZr alloy are firstly presented and the $\beta$ phase phonons clearly indicate its dynamically unstable nature under ambient condition. Thermodynamics of Gibbs free energy, entropy, and heat capacity are obtained by quasiharmonic approximation and Debye model.Comment: 9 pages, 10 figure

Algebraic Cayley Graphs over Finite Fields

A new algebraic Cayley graph is constructed using finite fields. Its connectedness and diameter bound are studied via Weil's estimate for character sums. These graphs provide a new source of expander graphs, extending classical results of Chung

Passive fault-tolerant control for vehicle active suspension system based on H2/H∞ approach

In this paper, a robust passive fault-tolerant control (RPFTC) strategy based on H2/H∞ approach and an integral sliding mode passive fault tolerant control (ISMPFTC) strategy based on H2/H∞ approach for vehicle active suspension are presented with considering model uncertainties, loss of actuator effectiveness and time-domain hard constraints of the suspension system. H∞ performance index less than γ and H2 performance index is minimized as the design objective, avoid choosing weighting coefficient. The half-car model is taken as an example, the robust passive fault-tolerant controller and the integral sliding mode passive fault tolerant control law is designed respectively. Three different fault modes are selected. And then compare and analyze the control effect of vertical acceleration of the vehicle body and pitch angular acceleration of passive suspension control, robust passive fault tolerant control and integral sliding mode passive fault tolerant control to verify the feasibility and effectiveness of passive fault tolerant control algorithm of active suspension. The studies we have performed indicated that the passive fault tolerant control strategy of the active suspension can improve the ride comfort of the suspension system