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

Modeling of Intraluminal Surfaces of Thoracic Aortas

Vascular diseases are getting more and more common as a result of modern-day lifestyle and the fact that the population is getting older. One of the newest treatments for vascular diseases such as aneurysms and dissections is endovascular repair with endografting. This treatment uses a fabric covered metallic structure that is implanted using a minimally invasive approach to serve as an artificial vessel in a damaged region. To ensure that the interventions are successful, the endograft must be placed in the correct location, and be designed to sustain the hostile biological, chemical, and mechanical conditions in the body for many years.To accurately describe the complex mechanical conditions of the intraluminal surfaces of diseased blood vessels inside the body, this thesis presented a segmentation and quantification methodology for a natural and intuitive vessel surface description. The thesis also included some important clinical applications, all based on non-invasive temporal imaging. The results emphasized the need for explicit surface curvature quantification, as compared to relying solely on centerline curvature and estimation methods. Methods for preoperative prediction of endograft malapposition severity based on geometric analysis of thoracic aortic surfaces were introduced. Finally, a multiaxial dynamic analysis of cardiac induced thoracic aortic surface deformation showed how a thoracic endovascular aortic repair is a↵ecting the deformations of the thoracic aorta.Thus, the work presented in this thesis contributes by giving surgeons a tool to use in their treatment planning to minimize complications. Moreover, this method provides more nuanced boundary conditions so that endograft manufacturers can improve their designs to improve the quality of life for the treated patients

Adaptive Real-time Control of Nonlinear Throttle Unit

This mastert hesis has been done as a joint project between the Department of Automatic Control in Lund and Volvo Technological Development in Gothenburg. The thesis treats methods to handle nonlinearities in a throttle unit. Theapproach has been to first design a linear controller based on the results from system identification, and then to develop an adaptive updating law estimating uncertain parameters of the throttle. The implementation has been done on a PC using Matlab. The underlaying robust linear controller design was done with two different approaches. A first attempt was pole placement on polynomial form, i.e. an RST-controller. This controller was not easy to tune, and the design of a well behaved closed loop system failed. A second attempt was made using the method of optimal control on state space form. The use of weight functions in the design made it easier to tune the controller. The closed-loop performance of the derived linear controller meets all specifications except the rise time for small steps. For the adaptive update law three methods were tested based on gradient theory, stability theory and a state observer. The task has been to estimate the characteristics of the main nonlinearity of the throttle, the dead-zone. The first two methods cannot estimate all of the required parameters, so they were rejected. By introducing a disturbance driven by white noise as an extra state in the state observer it is possible to estimate all the needed parameters. The closed loop performance through the dead-zone is very fast and meets almost every demand in the specification. The control law fails to meet the specified rise time for small steps and the overshoot is sometimes too large. There are also some oscillations under certain circumstances when controlling close to the dead-zone. </p

Multiaxial pulsatile dynamics of the thoracic aorta and impact of thoracic endovascular repair

Purpose: The thoracic aorta is a highly mobile organ whose dynamics are altered by thoracic endovascular aorta repair (TEVAR). The aim of this study was to quantify cardiac pulsatility-induced multi-axial deformation of the thoracic aorta before and after descending aortic TEVAR. Methods: Eleven TEVAR patients (8 males and 3 females, age 57–89) underwent retrospective cardiac-gated CT angiography before and after TEVAR. 3D geometric models of the thoracic aorta were constructed, and lumen centerlines, inner and outer surface curves, and cross-sections were extracted to measure aortic arclength, centerline, inner surface, and outer surface longitudinal curvatures, as well as cross-sectional effective diameter and eccentricity for the ascending and stented aortic portions. Results: From pre- to post-TEVAR, arclength deformation was increased at the ascending aorta from 5.9 \ub1 3.1 % to 8.8 \ub1 4.4 % (P &lt; 0.05), and decreased at the stented aorta from 7.5 \ub1 5.1 % to 2.7 \ub1 2.5 % (P &lt; 0.05). Longitudinal curvature and diametric deformations were reduced at the stented aorta. Centerline curvature, inner surface curvature, and cross-sectional eccentricity deformations were increased at the distal ascending aorta. Conclusions: Deformations were reduced in the stented thoracic aorta after TEVAR, but increased in the ascending aorta near the aortic arch, possibly as a compensatory mechanism to maintain overall thoracic compliance in the presence of reduced deformation in the stiffened stented aorta

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 &lt;.05) and eccentricity (0.9 \ub1 0.1 to 0.7 \ub1 0.1; P &lt;.05) decreased, and the cross-sectional area (3.0 \ub1 1.1 to 5.0 \ub1 2.0 cm2; P &lt;.05) and circumference (7.1 \ub1 1.0 to 8.0 \ub1 1.4 cm; P &lt;.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

Definition of Tubular Anatomic Structures from Arbitrary Stereo Lithographic Surface

An accurate description of anatomies and dynamics of vessels is crucial to understand their characteristics and improve surgical techniques, thus it is the basis, in addition to surgeon experience, on which stent design and operation procedures rely. The process of producing this description is user intensive, and recent improvement in image processing of medical3D imaging allows for a more automated workflow. However, there is a need to bridge the gap from a processed geometry to a robust mathematical computational grid. By sequentially segmenting a tubular anatomic structure, here defined by a stereo lithographic (STL) surface, an initial centerline is formed by connecting centroids of orthogonal cross-sectional contours along the length of the structure. Relying on the initial centerline, a set of non-overlapping 2D cross sectional contours are defined along the centerline, a centerline which is updated after the 2D contours are produced. After a second iteration of producing 2D contours and updating the centerline, a full description of the structure is created. Our method for describing vessel geometry shows good coherence to existing method. The main advantages of our method include the possibility of having arbitrary triangulated STL surface input, automated centerline definition, safety against intersecting cross-sectional contours and automatic clean-up of local kinks and wrinkles

What successful branding looks like: a managerial perspective

Purpose - The purpose of this paper is to develop an understanding of the ways in which food companies can work with branding to perform better in the market. The authors achieve this purpose by comparing how different managers of food brands prioritise and evaluate their brands, in relation to a theoretical ideal framework. Design/methodology/approach - A survey of 77 managers of domestic and international brands. Findings - Beliefs and priorities are similar between managers. What differs is how they measure and monitor their brands. Managers of high performing brands, for example, in general measure brand equity to a greater extent than other managers, and they focus significantly more on monitoring typical brand equity elements such as brand awareness, uniqueness, and feelings. Also managers of international brands measure and monitor more intensively than those of domestic brands. Practical implications - Weaker and domestic brands could learn from the better-performing brands, by becoming more oriented towards key brand equity elements when performing monitoring, rather than focusing mainly on perceived quality. Originality/value - A comparative and systematic method that suggests an alternative and analytical approach to strengthening domestic and weaker brand

Brand value chain in practise; the relationship between mindset and market performance metrics: A study of the Swedish market for FMCG

For decades, managers have analysed, planned and implemented long-term brand strategies based on customer mindset metrics (MSMs). Typically, such MSMs are customer satisfaction, liking, brand preference and Net Promoter Score (NPS). One of the core pillars, in brand management literature, is the assumed link between certain customer-based brand assets, often operationalized as MSMs, and future long-term market performance. However, few studies have systematically and broadly evaluated how the most common MSMs relate to actual performance data. This study investigates the link between the customer MSMs, most commonly used by practitioners, and their relationships with actual market performance. The paper explores 10 MSMs and 14 market performance metrics, in 10 categories, in the Swedish fast-moving consumer goods (FMCG) market. The study is based on survey data from 2007 that is compared to purchase panel household data from 2007 and 2010. Although MSMs are highly correlated to each other, their relations to brands' long-term market performance differ. A more nuanced approach to the MSM-market performance link is proposed, as there appears to be no single “silver bullet” MSM to rely on. Using a cash flow-oriented framework, the authors recommend opting for different MSMs depending on which of the three generic types of market performance (enhanced, sustained or accelerated) are targeted

Brand Equity and the Brand Value Chain : What it is and How to Use it in Practice

Many brand managers have long since established the desired core values for their brand, but are still not sure whether they differentiate themselves enough from their most daunting competitors, and whether their brand actually helps to boost sales of their products. This chapter describes a basic brand equity framework for understanding how brand management can create customer value and shareholder value. The chapter starts by describing a conceptual framework and ends with four concrete issues and one case to demonstrate how the brand value chain can be used