Effects of wall calcifications in patient-specific wall stress analyses of abdominal aortic aneurysms.
ABSTRACT It is generally acknowledged that rupture of an abdominal aortic aneurysm (AAA) occurs when the stress acting on the wall over the cardiac cycle exceeds the strength of the wall. Peak wall stress computations appear to give a more accurate rupture risk assessment than AAA diameter, which is currently used for a diagnosis. Despite the numerous studies utilizing patient-specific wall stress modeling of AAAs, none investigated the effect of wall calcifications on wall stress. The objective of this study was to evaluate the influence of calcifications on patient-specific finite element stress computations. In addition, we assessed whether the effect of calcifications could be predicted directly from the CT-scans by relating the effect to the amount of calcification present in the AAA wall. For 6 AAAs, the location and extent of calcification was identified from CT-scans. A finite element model was created for each AAA and the areas of calcification were defined node-wise in the mesh of the model. Comparisons are made between maximum principal stress distributions, computed without calcifications and with calcifications with varying material properties. Peak stresses are determined from the stress results and related to a calcification index (CI), a quantification of the amount of calcification in the AAA wall. At calcification sites, local stresses increased, leading to a peak stress increase of 22% in the most severe case. Our results displayed a weak correlation between the CI and the increase in peak stress. Additionally, the results showed a marked influence of the calcification elastic modulus on computed stresses. Inclusion of calcifications in finite element analysis of AAAs resulted in a marked alteration of the stress distributions and should therefore be included in rupture risk assessment. The results also suggest that the location and shape of the calcified regions--not only the relative amount--are considerations that influence the effect on AAA wall stress. The dependency of the effect of the wall stress on the calcification elastic modulus points out the importance of determination of the material properties of calcified AAA wall.
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ABSTRACT: Endovascular repair of abdominal aortic aneurysms is a well-established technique throughout the medical and surgical communities. Although increasingly indicated, this technique does have some limitations. Because intervention is commonly performed under fluoroscopic control, 2-D visualization of the aneurysm requires the injection of a contrast agent. The projective nature of this imaging modality inevitably leads to topographic errors, and does not give information on arterial wall quality at the time of deployment. A specially adapted intraoperative navigation interface could increase deployment accuracy and reveal such information, which preoperative 3-D imaging might otherwise provide. One difficulty is the precise matching of preoperative data (images and models) and intraoperative observations affected by anatomical deformations due to tool-tissue interactions. Our proposed solution involves a finite-element-based preoperative simulation of tool-tissue interactions, its adaptive tuning regarding patient specific data, and the matching with intraoperative data. The biomechanical model was first tuned on a group of ten patients and assessed on a second group of eight patients.IEEE Transactions on Biomedical Engineering 05/2013; 60(5):1353-1362. · 2.23 Impact Factor
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ABSTRACT: Abdominal aortic aneurysm (AAA) is a major cause of death in developed countries. The AAA diameter is still the only validated prognostic measure for rupture, and therapeutic interventions are initiated accordingly. This still leads to unnecessary interventions in some cases or unidentified impending ruptures. Vascular calcification has been validated abundantly as a risk factor in the cardiovascular field and may strengthen the rupture risk assessment of the AAA. With this study we aim to assess the correlation between AAA calcification and rupture risk in a retrospective unmatched case-control population. A database of 334 AAA patients was evaluated. Three groups were formed: elective (eAAA; n = 233), ruptured (rAAA; n = 73) and symptomatic non-ruptured (sAAA; n = 28) AAA patients. The Abdominal Aortic Calcification-8 score (AAC-8) was used to measure the severity of vascular calcification. The AAA diameter (61 ± 12 mm vs. 74 ± 21 mm; p < .001) and AAC-8 score (3.4 ± 2 points vs. 4.9 ± 2.3 points; p < .001) of the eAAA and the combined rAAA and sAAA groups, respectively, were significantly different after univariate analysis. Multivariate analysis showed that larger AAA diameter (odds ratio [OR]: 1.048/mm increase; 95% confidence interval [CI]: 1.042-1.082; p < .001) and a higher AAC-8 score (OR: 1.34/point increase; 95% CI: 1.19-1.53; p < .001) were significantly associated with development into a sAAA or rAAA. Peripheral artery disease was significantly correlated to eventual elective treatment (OR: 0.39; 95% CI: .15-1; p = .049). This study suggests a trend of an increased degree of calcification in symptomatic or even ruptured AAA patients compared with elective AAA patients.European journal of vascular and endovascular surgery: the official journal of the European Society for Vascular Surgery 09/2013; · 2.92 Impact Factor
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ABSTRACT: Vascular calcification is a prominent feature of atherosclerosis. The mineral composition and quantity within calcified arterial plaques remains unelucidated; therefore, the aim of this study was to analyze the mineral composition of such plaques. Calcified arterial plaques were obtained from patients with abdominal aortic aneurysms (AAAs) and carotid artery stenoses. Calcified aneurysmal plaques were obtained during the routine open repair of AAAs, while calcified carotid plaques were collected from patients who underwent carotid endarterectomy (CEA). Following the appropriate preparation of each sample, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to analyze the calcium and phosphate levels, while flame atomic absorption spectrometry (FAAS) was used to analyze the levels of iron and zinc. The levels of these mineral components were evaluated. In the aortic and carotid plaques, the mean calcium concentration was 9.83 and 11.94 wt.%, respectively, and the mean phosphate concentration was 4.31 and 6.08 wt.%, respectively. It was not possible to analyze the absolute concentration of iron in the carotid plaques due to the concentration being below the measurement limit. The zinc concentration was variable between samples. In conclusion, the main components of aortic and carotid plaques are calcium and phosphate. The mineral concentrations of the plaques in the present study may be used as reference values for further studies on vascular calcification. More studies are required to elucidate the correlation between the mineral components and vascular calcification.Experimental and therapeutic medicine 01/2014; 7(1):23-26. · 0.94 Impact Factor