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Multidimensional growth measurements of abdominal aortic aneurysms
KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics. (vascuMECH)
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2013 (English)In: Journal of Vascular Surgery, ISSN 0741-5214, Vol. 58, no 3, 748-755 p.Article in journal (Refereed) Published
Abstract [en]

Background: Monitoring the expansion of abdominal aortic aneurysms (AAAs) is critical to avoid aneurysm rupture in surveillance programs, for instance. However, measuring the change of the maximum diameter over time can only provide limited information about AAA expansion. Specifically, regions of fast diameter growth may be missed, axial growth cannot be quantified, and shape changes of potential interest for decisions related to endovascular aneurysm repair cannot be captured. Methods: This study used multiple centerline-based diameter measurements between the renal arteries and the aortic bifurcation to quantify AAA growth in 51 patients from computed tomography angiography (CTA) data. Criteria for inclusion were at least 1 year of patient follow-up and the availability of at least two sufficiently high-resolution CTA scans that allowed an accurate three-dimensional reconstruction. Consequently, 124 CTA scans were systematically analyzed by using A4clinics diagnostic software (VASCOPS GmbH, Graz, Austria), and aneurysm growth was monitored at 100 cross-sections perpendicular to the centerline. Results: Monitoring diameter development over the entire aneurysm revealed the sites of the fastest diameter growth, quantified the axial growth, and showed the evolution of the neck morphology over time. Monitoring the development of an aneurysm's maximum diameter or its volume over time can assess the mean diameter growth (r = 0.69, r = 0.77) but not the maximum diameter growth (r = 0.43, r = 0.34). The diameter growth measured at the site of maximum expansion was similar to 16%/y, almost four times larger than the mean diameter expansion of 4.4%/y. The sites at which the maximum diameter growth was recorded did not coincide with the position of the maximum baseline diameter (rho = 0.12; P = .31). The overall aneurysm sac length increased from 84 to 89 mm during the follow-up (P < .001), which relates to the median longitudinal growth of 3.5%/y. The neck length shortened, on average, by 6.2% per year and was accompanied by a slight increase in neck angulation. Conclusions: Neither maximum diameter nor volume measurements over time are able to measure the fastest diameter growth of the aneurysm sac. Consequently, expansion-related wall weakening might be inappropriately reflected by this type of surveillance data. In contrast, localized spots of fast diameter growth can be detected through multiple centerline-based diameter measurements over the entire aneurysm sac. This information might further reinforce the quality of aneurysm surveillance programs.

Place, publisher, year, edition, pages
2013. Vol. 58, no 3, 748-755 p.
Keyword [en]
Randomized Controlled-Trial, Early Elective Surgery, Ultrasonographic Surveillance, Endovascular Repair, Expansion Rate, Rupture Risk, Wall Stress, Diameter, Size, Enlargement
National Category
URN: urn:nbn:se:kth:diva-101989DOI: 10.1016/j.jvs.2012.11.070ISI: 000323616800026ScopusID: 2-s2.0-84883176627OAI: diva2:550177

QC 20130930

Available from: 2012-09-06 Created: 2012-09-06 Last updated: 2013-09-30Bibliographically approved
In thesis
1. Biomechanics of abdominal aortic aneurysm:Experimental evidence and multiscale constitutive modeling
Open this publication in new window or tab >>Biomechanics of abdominal aortic aneurysm:Experimental evidence and multiscale constitutive modeling
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The reliable assessment of Abdominal Aortic Aneurysm (AAA) rupture risk is critically important in reducing related mortality without unnecessarily increasing the rate of elective repair. A multi-disciplinary approach including vascular biomechanics and constitutive modeling is needed to better understand and more effectively treat these diseases. AAAs are formed through irreversible pathological remodeling of the vascular wall and integrating this biological process in the constitutive description could improve the current understanding of this disease as well as the predictability of biomechanical simulations.

First in this thesis, multiple centerline-based diameter measurements between renal arteries and aortic bifurcation have been used to monitor aneurysm growth of in total 51 patients from Computer Tomography-Angiography (CT-A) data. Secondly, the thesis proposes a novel multi-scale constitutive model for the vascular wall, where collagen fibers are assembled by proteoglycan cross-linked collagen fibrils and reinforce an otherwise isotropic matrix (elastin). Collagen fibrils are dynamically formed by a continuous stretch-mediated process, deposited in the current configuration and removed by a constant degradation rate. The micro-plane concept is then used for the Finite Element (FE) implementation of the constitutive model. Finally, histological slices from intra-luminal thrombus (ILT) tissue were analyzed using a sequence of automatic image processing steps. Derived microstructural data were used to define Representative Volume Elements (RVEs), which in turn allowed the estimation of microscopic material properties using the non-linear FE.

The thesis showed that localized spots of fast diameter growth can be detected through multiple centerline-based diameter measurements all over the AAA sac. Consequently, this information might further reinforce the quality of aneurysm surveillance programs. The novel constitutive model proposed in the thesis has a strong biological motivation and provides an interface with biochemistry. Apart from modeling the tissue’s passive response, the presented model is helpful to predict saline feature of aneurysm growth and remodeling. Finally, the thesis provided novel microstructural and micromechanical data of ILT tissue, which is critically important to further explore the role of the ILT in aneurysm rupture.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 48 p.
Trita-HFL. Report / Royal Institute of Technology, Solid mechanics, ISSN 1654-1472 ; 0530
National Category
Mechanical Engineering Medical Engineering Materials Engineering Applied Mechanics
urn:nbn:se:kth:diva-101990 (URN)
Public defence
2012-09-20, Sal L1, Drottning Kristinas väg 30, KTH, Stockholm, 10:00 (English)

QC 20120907

Available from: 2012-09-07 Created: 2012-09-06 Last updated: 2013-01-14Bibliographically approved

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