Impact of aortic repair based on flow field computer simulation within the thoracic aorta

Purpose of this computational study is to examine the hemodynamic parameters of velocity fields and shear stress in the thoracic aorta with and without aneurysm, based on an individual patient case and virtual surgical intervention. These two cases, case I (with aneurysm) and II (without aneurysm), are analyzed by computational fluid dynamics. The 3D Navier-Stokes equations and the continuity equation are solved with an unsteady stabilized finite element method. The vascular geometries are reconstructed based on computed tomography angiography images to generate a patient-specific 3D finite element mesh. The input data for the flow waveforms are derived from MR phase contrast flow measurements of a patient before surgical intervention.The computed results show velocity profiles skewed towards the inner aortic wall for both cases in the ascending aorta and in the aortic arch, while in the descending aorta these velocity profiles are skewed towards the outer aortic wall. Computed streamlines indicate that flow separation occurs at the proximal edge of the aneurysm, i.e. computed flow enters the aneurysm in the distal region, and that there is essentially a single, slowly rotating, vortex within the aneurysm during most of the systole.In summary, after virtual surgical intervention in case II higher shear stress distribution along the descending aorta could be found, which may produce more healthy reactions in the endothelium and benefit of vascular reconstruction of an aortic aneurysm at this particular location.     

Rapid vessel prototyping: vascular modeling using 3t magnetic resonance angiography and rapid prototyping technology

Object Conversion of thoracic aortic vasculature as measured by Magnetic Resonance Imaging into a real physical replica. Materials and methods Several procedural steps including data acquisition with contrast enhanced MR Angiography at 3T, data visualization and 3D computer model generation, as well as rapid prototyping were used to construct an in-vitro model of the vessel geometry. Results A rapid vessel prototyping process was implemented and used to convert complex vascular geometry of the entire thoracic aorta and major branching arteries into a real physical replica with large anatomical coverage and high spatial resolution. Conclusion Rapid vessel prototyping permits the creation of a concrete solid replica of a patient’s vascular anatomy Parts of this work were presented at the ESMRMB 2005     

Design,optimization and numerical simulation of a MicroFlow sensor in the realistic model of human aorta

Among all arterial diseases, aneurysm and atherosclerosis are of great importance. In these diseases the cross-section area of the artery and therefore the blood flow velocity changes. Therefore, it is a good idea to use a micro flow sensor for measuring the blood flow velocity to diagnosing these diseases. In this study, design, geometric optimization and numerical simulation of a hotfilm microsensor in the realistic model of human's aorta are investigated. A normal aorta geometry is extracted from CT Angiography images, and after applying oscillating boundary conditions on the inlet and outlet arteries, blood flow parameters are investigated by computational fluid dynamics (CFD) simulation. After designing the microsensor, the effects of its location in different aorta regions on the blood flow characteristics are numerically investigated. The results show that in the presence of microsensor, streamlines patterns almost remain unchanged while the maximum blood flow velocity in the aorta cross section where the microsensor is located, increases up to 10%. It is also found that the secondary flow weakens when the microsensor enters the artery causing a reduction in velocity measurement error. Furthermore, because of the presence of a catheter, the pressure drop increases up to 768 Pa. Results show that less than 30% of the arterial cross-sectional area where the microsensor is located, senses an increase in temperature.     

Aortic injuries in newer vehicles

The occurrence of AI was studied in relation to vehicle model year (MY) among front seat vehicular occupants, age ≥ 16 in vehicles MY ≥ 1994, entered in the National Automotive Sampling System Crashworthiness Data System between 1997 and 2010 to determine whether newer vehicles, due to their crashworthiness improvements, are linked to a lower risk of aortic injuries (AI). MY was categorized as 1994–1997, 1998–2004, or 2005–2010 reflecting the introduction of newer occupant protection technology. Logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals for the association between AI and MY independent of possible confounders. Analysis was repeated, stratified by frontal and near lateral impacts. AI occurred in 19,187 (0.06%) of the 31,221,007 (weighted) cases, and contributed to 11% of all deaths. AIs were associated with advanced age, male gender, high BMI, near-side impact, rollover, ejection, collision against a fixed object, high ΔV, vehicle mismatch, unrestrained status, and forward track position. Among frontal crashes, MY 98–04 and MY 05–10 showed increased adjusted odds of AI when compared to MY 94–97 [OR 1.84 (1.02–3.32) and 1.99 (0.93–4.26), respectively]. In contrast, among near-side impact crashes, MY 98–04 and MY 05–10 showed decreased adjusted odds of AI [OR 0.50 (0.25–0.99) and 0.27 (0.06–1.31), respectively]. While occupants of newer vehicles experience lower odds of AI in near side impact crashes, a higher AI risk is present in frontal crashes.     

Endovascular Stent‐Grafts for Thoracic Aortic Disease

Diseases of the descending thoracic aorta pose a significant therapeutic challenge. The standard therapy for thoracic aneurysms or dissection is open surgical repair with prosthetic graft replacement of the diseased segment, requiring major thoracotomy. Despite important advances in surgical techniques, mortality and morbidity rates remain high. Endovascular stent‐graft placement which is performed via the femoral route provides an attractive treatment alternative for thoracic aortic diseases. Due to its minimal‐invasive approach, endovascular repair is also applicable for patients with contraindication to major surgery. Early results are encouraging, documenting low mortality and complication rates. However, long‐term results, particularly concerning the long‐term durability of the endoprostheses, are lacking, so far. Results of prospective randomized trials that compare the outcomes of endovascular repair with those of standard therapy are required before a widespread use of stent‐grafts can be recommended.