Mingzi Zhang

HEMODYNAMIC EFFECTS OF THE ANASTOMOSES IN THE MODIFIED BLALOCK–TAUSSIG SHUNT: A NUMERICAL STUDY USING A 0D/3D COUPLING METHOD

The modified Blalock–Taussig (BT) shunt is a palliative surgery which can help the tetralogy of Fallot (TOF) patient increase the blood oxygen saturation by interposing a systemic-to-pulmonary artery shunt. Two typical anastomotic shapes are frequently used in clinical practice: the end-to-side (ETS) and the side-to-side (STS) anastomosis. This paper examines the hemodynamic influence of the anastomotic shape in the modified BT shunt. Three models with different anastomotic shapes were reconstructed. The ETS anastomoses were applied in the first model. For the innominate artery (IA) and the pulmonary artery (PA) in the second model, the ETS and the STS anastomosis were applied, respectively. Finally, the STS anastomoses were applied in the third model. The 0D/3D coupling method was used to perform a numerical simulation by coupling the three-dimensional (3D) artery model with a zero-dimensional (0D) lumped parameter model for the cardiovascular system. The simulation results showed that the perfusion into the left and right PA in Model 1 was unbalanced. Swirling flow appeared in the shunt in Model 3, but the shunt flow rate in Model 3 was lower. The ETS anastomosis at the PA may cause unbalanced blood perfusion into the left and right PA. Conversely, the STS anastomosis can make the blood perfusion more balanced. Otherwise, the STS anastomosis at the IA could generate a swirling flow in the shunt which may provide a better hemodynamic environment while decreasing the pulmonary perfusion.

Towards the patient-specific design of flow diverters made from helix-like wires: an optimization study

BackgroundFlow diverter (FD) intervention is an emerging endovascular technique for treating intracranial aneurysms. High flow-diversion efficiency is desired to accelerate thrombotic occlusion inside the aneurysm; however, the risk of post-stenting stenosis in the parent artery is posed when flow-diversion efficiency is pursued by simply decreasing device porosity. For improving the prognosis of FD intervention, we develop an optimization method for the design of patient-specific FD devices that maintain high levels of porosity.MethodsAn automated structure optimization method for FDs with helix-like wires was developed by applying a combination of lattice Boltzmann fluid simulation and simulated annealing procedure. Employing intra-aneurysmal average velocity as the objective function, the proposed method tailored the wire structure of an FD to a given vascular geometry by rearranging the starting phase of the helix wires.ResultsFD optimization was applied to two idealized (S and C) vascular models and one realistic (R) model. Without altering the original device porosity of 80%, the flow-reduction rates of optimized FDs were improved by 5, 2, and 28% for the S, C, and R models, respectively. Furthermore, the aneurysmal flow patterns after optimization exhibited marked alterations. We confirmed that the disruption of bundle of inflow is of great help in blocking aneurysmal inflow. Axial displacement tests suggested that the optimal FD implanted in the R model possesses good robustness to tolerate uncertain axial positioning errors.ConclusionsThe optimization method developed in this study can be used to identify the FD wire structure with the optimal flow-diversion efficiency. For a given vascular geometry, custom-designed FD structure can maximally reduce the aneurysmal inflow with its porosity maintained at a high level, thereby lowering the risk of post-stenting stenosis. This method facilitates the study of patient-specific designs for FD devices.

Hemodynamic Influence of Different Pulmonary Stenosis Degree in Glenn Procedure: A Numerical Study

Background. Single ventricle disease is treated by Glenn surgery. It is generally accompanied by stenosis on a pulmonary artery or its branches, which has great effect on hemodynamics. This study investigated the hemodynamic influence of different pulmonary stenosis degree in Glenn procedure. Materials. Four three-dimensional Glenn models with different left pulmonary artery stenosis rates as, respectively, 0% (model 1), 25% (model 2), 50% (model 3), and 75% (model 4) by the diameter were generated. Method. Geometric multiscale analysis method was used in the numerical simulations by coupling the lumped parameter model (LPM) and three-dimensional model. Results. During one cardiac cycle, the flow ratio between left pulmonary artery and superior vena cava was about 0.49 for models 1, 2, and 3, while the ratio decreased to 0.34 for model 4. On the other hand, hemodynamics parameters like power loss and oscillation shear index show complications of the stenosis to the postoperative development. Conclusion. When the stenosis rate is above 75%, it is suggested to treat stenosis before Glenn procedure, while when the stenosis rate is below 50%, there is no necessity to pay attention to it due to the little effect it makes.

Haemodynamic effects of stent diameter and compaction ratio on flow-diversion treatment of intracranial aneurysms: A numerical study of a successful and an unsuccessful case

BACKGROUND Compacting a flow-diverting (FD) stent is an emerging technique to create a denser configuration of wires across the aneurysm ostium. However, quantitative analyses of post-stenting haemodynamics affected by the compaction level of different stent sizes remain inconclusive. OBJECTIVE To compare the aneurysmal haemodynamic alterations after virtual FD treatments with different device diameters at different compaction ratios. METHODS We virtually implanted three sizes of FD stent, with each size deployed at four compaction ratios, into two patient aneurysms previously treated with the Silk+FD-one successful case and the other unsuccessful. Wire configurations of the FD in the 24 treatment scenarios were examined, and aneurysmal haemodynamic alterations were resolved by computational fluid dynamics (CFD) simulations. We investigated the aneurysmal flow patterns, aneurysmal average velocity (AAV), mass flowrate (MF), and energy loss (EL) in each scenario. RESULTS Compactions of the stent in the successful case resulted in a greater metal coverage rate than that achieved in the unsuccessful one. A 25% increment in compaction ratio further decreased the AAV (12%), MF (11%), and EL (9%) in both cases (average values). The averaged maximum differences attributable to device size were 10% (AAV), 8% (MF), and 9% (EL). CONCLUSIONS Both stent size and compaction level could markedly affect the FD treatment outcomes. It is therefore important to individualise the treatment plan by selecting the optimal stent size and deployment procedure. CFD simulation can be used to investigate the treatment outcomes, thereby assisting doctors in choosing a favourable treatment plan.

Sensitivity study on modelling a flow-diverting stent as a porous medium using computational fluid dynamics

The flow-diverting (FD) stent has become a commonly used endovascular device to treat cerebral aneurysms. This discourages blood from entering the aneurysm, thereby reducing the likelihood of aneurysm rupture. Using computational fluid dynamics (CFD) to simulate the aneurysmal haemodynamics after FD treatment could help clinicians predict the stent effectiveness prior to the real procedure in the patient. As an alternative to modelling the stent as a fine wire mesh, modelling the FD stent as a porous medium was established to save computational time, and has also been proved capable of predicting the same haemodynamics as obtained using the real FD stent geometry. The flow resistance effect of a porous-medium stent may differ with respect to its morphology or permeability; however, the flow resistance effect after adjusting these parameters had not been clarified. In this study, we analysed the haemodynamic changes caused by alterations of porous-medium thickness and permeability, thereby providing future porous-medium stent simulations with important information on the respective parametric sensitivities. We found significant sensitivity to permeability. Results were insensitive to thickness when permeability was adjusted beforehand to compensate. We also compared our results with observations from an in-vitro model, and found good agreement. This supports adoption of porous-medium models in future work.

Numerical simulation of aneurysmal haemodynamics with calibrated porous-medium models of flow-diverting stents

Modelling flow-diverting (FD) stents as porous media (PM) markedly improves the efficiency of computational fluid dynamics (CFD) simulations in the study of intracranial aneurysm treatment. Nonetheless, the parameters of PM models adopted for simulations up until now were rarely calibrated to match the represented FD structure. We therefore sought to evaluate the PM parameters for a representative variety of commercially available stents, so characterising the flow-diversion behaviours of different FD devices on the market. We generated fully-resolved geometries for treatments using PED, Silk+, FRED, and dual PED stents. We then correspondingly derived the calibrated PM parameters-permeability (k) and inertial resistance factor (C2)-for each stent design from CFD simulations, to ensure the calibrated PM model has identical flow resistance to the FD stent it represents. With each of the calibrated PM models respectively deployed in two aneurysms, we studied the flow-diversion effects of these stent configurations. This work for the first time reported several sets of parameters for PM models, which is vital to address the current knowledge gap and rectify the errors in PM model simulations, thereby setting right the modelling protocol for future studies using PM models. The flow resistance parameters were strongly affected by porosity and effective thickness of the commercial stents, and thus accounted for in the PM models. Flow simulations using the PM stent models revealed differences in aneurysmal mass flowrate (MFR) and energy loss (EL) between various stent designs. This study improves the practicability of FD simulation by using calibrated PM models, providing an individualised method with improved simulation efficiency and accuracy.

Applying computer simulation to the design of flow-diversion treatment for intracranial aneurysms

Although flow-diversion (FD) treatment has been proven to be able to induce intracranial aneurysm (IA) occlusion, clinical follow-ups reported that a number of patients may still suffer from delayed IA rupture or incomplete aneurysm occlusion post-treatment. Complete aneurysm occlusion is believed to be associated with favourable haemodynamic alteration post-treatment, which may be greatly affected by the selection of device size and quantity, as well as the FD deployment procedure. However, clinicians have to choose and deploy the FD relying on their experience, since no post-stenting haemodynamic information is generally available to them prior to a specific treatment. In this study, using a virtual FD deployment technique and computational fluid dynamics method, we demonstrate and compare the haemodynamic changes after virtual FD treatments using a variety of prospective treating strategies.

Multiscale Study on Hemodynamics in Patient-Specific Thoracic Aortic Coarctation

In this challenge, we intended to mimic the patients cardiovascular system by using 0D-3D connected multiscale model. The purpose of the multiscale analysis is to find out the appropriate boundary conditions of the innominate artery IA, left common carotid artery LCA and left subclavian artery LSA in the local 3D computational fluid dynamics simulation. Firstly, a lumped parameter modelLPM of the patients circulatory system was established which could mimic both the rest and stress conditions by adjusting parameters like elastance function of the heart and the peripheral resistance, since that administering is oprenaline leads to the patients heart beat rate and peripheral resistance changes. Secondly, the values of parameters in the LPM were slightly revised to match the following conditions: 1. provided pressure and flow rate curves, 2. provided blood distribution ratio of the AcsAo, IA, LCA and LSA. Finally, we got the outlet conditions of the IA, LCA and LSA, and then connecting the 0D model and the 3D model at each time step. As the results, we got the streamlines, pressure drop through the coarctation, pressure gradient, and some other parameters by coupled multiscale simuation.