Influence of Thoracic Endovascular Aortic Repair on True Lumen Helical Morphology for Stanford Type B Dissections

Objective: Thoracic endovascular aortic repair (TEVAR) can change the morphology of the flow lumen in aortic dissections, which may affect aortic hemodynamics and function. This study characterizes how the helical morphology of the true lumen in type B aortic dissections is altered by TEVAR. Methods: Patients with type B aortic dissection who underwent computed tomography angiography before and after TEVAR were retrospectively reviewed. Images were used to construct three-dimensional stereolithographic surface models of the true lumen and whole aorta using custom software. Stereolithographic models were segmented and co-registered to determine helical morphology of the true lumen with respect to the whole aorta. The true lumen region covered by the endograft was defined based on fiducial markers before and after TEVAR. The helical angle, average helical twist, peak helical twist, and cross-sectional eccentricity, area, and circumference were quantified in this region for pre- and post-TEVAR geometries. Results: Sixteen patients (61.3 \ub1 8.0 years; 12.5% female) were treated successfully for type B dissection (5 acute and 11 chronic) with TEVAR and scans before and after TEVAR were retrospectively obtained (follow-up interval 52 \ub1 91 days). From before to after TEVAR, the true lumen helical angle (–70.0 \ub1 71.1 to –64.9 \ub1 75.4\ub0; P =.782), average helical twist (–4.1 \ub1 4.0 to –3.7 \ub1 3.8\ub0/cm; P =.674), and peak helical twist (–13.2 \ub1 15.2 to –15.4 \ub1 14.2\ub0/cm; P =.629) did not change. However, the true lumen helical radius (1.4 \ub1 0.5 to 1.0 \ub1 0.6 cm; P <.05) and eccentricity (0.9 \ub1 0.1 to 0.7 \ub1 0.1; P <.05) decreased, and the cross-sectional area (3.0 \ub1 1.1 to 5.0 \ub1 2.0 cm2; P <.05) and circumference (7.1 \ub1 1.0 to 8.0 \ub1 1.4 cm; P <.05) increased significantly from before to after TEVAR. The distinct bimodal distribution of chiral and achiral native dissections disappeared after TEVAR, and subgroup analyses showed that the true lumen circumference of acute dissections increased with TEVAR, although it did not for chronic dissections. Conclusions: The unchanged helical angle and average and peak helical twists as a result of TEVAR suggest that the angular positions of the true lumen are constrained and that the endografts were helically conformable in the angular direction. The decrease of helical radius indicated a straightening of the corkscrew shape of the true lumen, and in combination with more circular and expanded lumen cross-sections, TEVAR produced luminal morphology that theoretically allows for lower flow resistance through the endografted portion. The impact of TEVAR on dissection flow lumen morphology and the interaction between endografts and aortic tissue can provide insight for improving device design, implantation technique, and long-term clinical outcomes

Geometric Modeling of Thoracic Aortic Surface Morphology - Implications for Pathophysiology and Clinical Interventions

Vascular disease risk factors such as hypertension, hyperlipidemia and old age are all\ua0results of modern-day lifestyle, and these diseases are getting more and more common. One\ua0treatment option for vascular diseases such as aneurysms and dissections is endovascular\ua0aortic repair introduced in the early 1990s. This treatment uses tubular fabric covered\ua0metallic structures (endografts) that are implanted using a minimally invasive approach\ua0and placed to serve as an articial vessel in a damaged portion of the vasculature. To ensure\ua0that the interventions are successful, the endograft must be placed in the correct location,\ua0and designed to sustain the hostile biological, chemical, and mechanical conditions in the\ua0body for many years. This is an interaction that goes both ways, and keeping in mind\ua0that the endograft is a foreign object placed in the sensitive vascular system, it is also\ua0important that it does not disrupt the native conditions more than necessary.This thesis presents a segmentation and quantication methodology to accurately\ua0describe the complex morphology and motion of diseased blood vessels in vivo through a\ua0natural and intuitive description of their luminal surfaces. After methodology validation,\ua0a series of important clinical applications are performed, all based on non-invasive imaging.\ua0Firstly, it is shown that explicit surface curvature quantication is necessary when\ua0compared to relying solely on centerline curvature and estimation methods. Secondly, it is\ua0shown that endograft malapposition severity can be predicted from preoperative geometric\ua0analysis of thoracic aortic surfaces. Thirdly, a multiaxial dynamics analysis of cardiac\ua0induced thoracic aortic surface motion shows how thoracic endovascular aortic repair\ua0affects the deformations of the dierent portions of the thoracic aorta. Fourthly, the helical\ua0propagation pattern of type B aortic dissection is determined, and two distinct modes of\ua0chirality are revealed, i.e., achiral and right-handed chiral groups. Finally, the effects of\ua0thoracic endovascular aortic repair on helical and cross-sectional morphology of type B\ua0dissections are investigated revealing how acuity and chirality affects the alteration due to\ua0intraluminal lining with endografts. Thus, the work presented in this thesis contributes\ua0by adding knowledge about pathology and pathophysiology through better geometric\ua0description of surface conditions of diseased thoracic aortas. This gives clinicians insights\ua0to use in their treatment planning and provides more nuanced boundary conditions for\ua0endograft manufacturers. Comprehensive knowledge about diseases, better treatment\ua0planning, and better devices are all crucial in order to improve the outcomes of performed\ua0interventions and ultimately the quality of life for the treated patients

Patient-specific virtual stent-graft deployment for Type B aortic dissection: a pilot study of the impact of stent-graft length

Thoracic endovascular aortic repair (TEVAR) has been accepted as a standard treatment option for complicated type B aortic dissection. Distal stent-graft induced new entry (SINE) is recognized as one of the main post-TEVAR complications, which can lead to fatal prognosis. Previous retrospective cohort studies suggested that short stent-graft (SG) length (<165 mm) might correlate with increased risk of distal SINE. However, the influence of SG length on changes in local biomechanical conditions before and after TEVAR is unknown. In this paper, we aim to address this issue using a virtual SG deployment simulation model developed for application in type B aortic dissection. Our model incorporates detailed SG design and hyperelastic behaviour of the aortic wall. By making use of patient-specific geometry reconstructed from pre-TEVAR computed tomography angiography (CTA) scan, our model can predict post-TEVAR SG configuration and wall stress. Virtual SG deployment simulations were performed on a patient who underwent TEVAR with a short SG (158 mm in length), mimicking the actual clinical procedure. Further simulations were carried out on the same patient geometry but with different SG lengths (183 mm and 208 mm) in order to evaluate the effect of SG length on changes in local stress in the treated aorta

The geometric evolution of aortic dissections: Predicting surgical success using fluctuations in integrated Gaussian curvature

Clinical imaging modalities are a mainstay of modern disease management, but the full utilization of imaging-based data remains elusive. Aortic disease is defined by anatomic scalars quantifying aortic size, even though aortic disease progression initiates complex shape changes. We present an imaging-based geometric descriptor, inspired by fundamental ideas from topology and soft-matter physics that captures dynamic shape evolution. The aorta is reduced to a two-dimensional mathematical surface in space whose geometry is fully characterized by the local principal curvatures. Disease causes deviation from the smooth bent cylindrical shape of normal aortas, leading to a family of highly heterogeneous surfaces of varying shapes and sizes. To deconvolute changes in shape from size, the shape is characterized using integrated Gaussian curvature or total curvature. The fluctuation in total curvature (δK) across aortic surfaces captures heterogeneous morphologic evolution by characterizing local shape changes. We discover that aortic morphology evolves with a power-law defined behavior with rapidly increasing δK forming the hallmark of aortic disease. Divergent δK is seen for highly diseased aortas indicative of impending topologic catastrophe or aortic rupture. We also show that aortic size (surface area or enclosed aortic volume) scales as a generalized cylinder for all shapes. Classification accuracy for predicting aortic disease state (normal, diseased with successful surgery, and diseased with failed surgical outcomes) is 92.8±1.7%. The analysis of δK can be applied on any three-dimensional geometric structure and thus may be extended to other clinical problems of characterizing disease through captured anatomic changes

Comparison of diametric and volumetric changes in Stanford type B aortic dissection patients in assessing aortic remodeling post-stent graft treatment

Background: The study aims to analyze the correlation between the maximal diameter (both axial and orthogonal) and volume changes in the true (TL) and false lumens (FL) after stent-grafting for Stanford type B aortic dissection. Method: Computed tomography angiography was performed on 13 type B aortic dissection patients before and after procedure, and at 6 and 12 months follow-up. The lumens were divided into three regions: the stented area (Region 1), distal to the stent graft to the celiac artery (Region 2), and between the celiac artery and the iliac bifurcation (Region 3). Changes in aortic morphology were quantified by the increase or decrease of diametric and volumetric percentages from baseline measurements. Results: At Region 1, the TL diameter and volume increased (pre-treatment: volume =51.4±41.9 mL, maximal axial diameter =22.4±6.8 mm, maximal orthogonal diameter =21.6±7.2 mm; follow-up: volume =130.7±69.2 mL, maximal axial diameter =40.1±8.1 mm, maximal orthogonal diameter =31.9+2.6 mm, P<0.05 for all comparisons), while FL decreased (pre-treatment: volume =129.6±150.5 mL; maximal axial diameter =43.0±15.8 mm; maximal orthogonal diameter =28.3±12.6 mm; follow-up: volume =66.6±95.0 mL, maximal axial diameter =24.5±19.9 mm, maximal orthogonal diameter =16.9±13.7, P<0.05 for all comparisons). Due to the uniformity in size throughout the vessel, high concordance was observed between diametric and volumetric measurements in the stented region with 93% and 92% between maximal axial diameter and volume for the true/false lumens, and 90% and 92% between maximal orthogonal diameter and volume for the true/false lumens. Large discrepancies were observed between the different measurement methods at regions distal to the stent graft, with up to 46% differences between maximal orthogonal diameter and volume. Conclusions: Volume measurement was shown to be a much more sensitive indicator in identifying lumen expansion/shrinkage at the distal stented region

Incidental extravascular findings in computed tomographic angiography for planning or monitoring endovascular aortic aneurysm repair: Smoker patients, increased lung cancer prevalence?

AIMTo validate the feasibility of high resolution computed tomography (HRCT) of the lung prior to computed tomography angiography (CTA) in assessing incidental thoracic findings during endovascular aortic aneurysm repair (EVAR) planning or follow-up.METHODSWe conducted a retrospective study among 181 patients (143 men, mean age 71 years, range 50-94) referred to our centre for CTA EVAR planning or follow-up. HRCT and CTA were performed before or after 1 or 12 mo respectively to EVAR in all patients. All HRCT examinations were reviewed by two radiologists with 15 and 8 years' experience in thoracic imaging. The results were compared with histology, bronchoscopy or follow-up HRCT in 12, 8 and 82 nodules respectively.RESULTSThere were a total of 102 suspected nodules in 92 HRCT examinations, with a mean of 1.79 nodules per patient and an average diameter of 9.2 mm (range 4-56 mm). Eighty-nine out of 181 HRCTs resulted negative for the presence of suspected nodules with a mean smoking history of 10 pack-years (p-y, range 5-18 p-y). Eighty-two out of 102 (76.4%) of the nodules met criteria for computed tomography follow-up, to exclude the malignant evolution. Of the remaining 20 nodules, 10 out of 20 (50%) nodules, suspected for malignancy, underwent biopsy and then surgical intervention that confirmed the neoplastic nature: 4 (20%) adenocarcinomas, 4 (20%) squamous cell carcinomas, 1 (5%) small cell lung cancer and 1 (5%) breast cancer metastasis); 8 out of 20 (40%) underwent bronchoscopy (8 pneumonia) and 2 out of 20 (10%) underwent biopsy with the diagnosis of sarcoidosis.CONCLUSIONHRCT in EVAR planning and follow-up allows to correctly identify patients requiring additional treatments, especially in case of lung cancer

4D flow imaging of the thoracic aorta: is there an added clinical value?

Four-dimensional (4D) flow MRI has emerged as a powerful non-invasive technique in cardiovascular imaging, enabling to analyse in vivo complex flow dynamics models by quantifying flow parameters and derived features. Deep knowledge of aortic flow dynamics is fundamental to better understand how abnormal flow patterns may promote or worsen vascular diseases. In the perspective of an increasingly personalized and preventive medicine, growing interest is focused on identifying those quantitative functional features which are early predictive markers of pathological evolution. The thoracic aorta and its spectrum of diseases, as the first area of application and development of 4D flow MRI and supported by an extensive experimental validation, represents the ideal model to introduce this technique into daily clinical practice. The purpose of this review is to describe the impact of 4D flow MRI in the assessment of the thoracic aorta and its most common affecting diseases, providing an overview of the actual clinical applications and describing the potential role of derived advanced hemodynamic measures in tailoring follow-up and treatment