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Abstract

In recent years, assessment of aneurysm behavior by means of computational simulation techniques have become a widely accepted field of research and has proven to be a very valuable tool (eg, predicting rupture risk, clinical decision finding, or surgical outcome of aneurysm repair). An elaborative overview of literature can be found in references 5 through 7 in our original article and important and highly respected contributions that demonstrate the importance of computational stress analysis in aneurysm rupture risk assessment are cited in references 8, 9, 12, and 16 in our original article.1Taylor C.A. Humphrey J.D. Open problems in computational vascular biomechanics: hemodynamics and arterial wall mechanics.Comput Methods Appl Mech Eng. 2009; 198: 3514-3523Crossref PubMed Scopus (108) Google Scholar, 2Vande Geest J.P. Wang D.H. Wisniewski S.R. Makaroun M.S. Vorp D.A. Towards a noninvasive method for determination of patient-specific wall strength distribution in abdominal aortic aneurysms.Ann Biomed Eng. 2006; 34: 1098-1106Crossref PubMed Scopus (158) Google Scholar, 3Vande Geest J.P. Di Martino E.S. Bohra A. Makaroun M.S. Vorp D.A. A biomechanics-based rupture potential index for abdominal aortic aneurysm risk assessment: demonstrative application.Ann N Y Acad Sci. 2006; 1085: 11-21Crossref PubMed Scopus (141) Google Scholar Still, there are uncertainties such as wall thickness and strength distributions that one has to be aware of and that currently are considered on a statistical basis2Vande Geest J.P. Wang D.H. Wisniewski S.R. Makaroun M.S. Vorp D.A. Towards a noninvasive method for determination of patient-specific wall strength distribution in abdominal aortic aneurysms.Ann Biomed Eng. 2006; 34: 1098-1106Crossref PubMed Scopus (158) Google Scholar, 3Vande Geest J.P. Di Martino E.S. Bohra A. Makaroun M.S. Vorp D.A. A biomechanics-based rupture potential index for abdominal aortic aneurysm risk assessment: demonstrative application.Ann N Y Acad Sci. 2006; 1085: 11-21Crossref PubMed Scopus (141) Google Scholar and in our contribution.4Maier A. Gee M.W. Reeps C. Pongratz J. Eckstein H.-H. Wall W.A. A comparison of diameter, wall stress, and rupture potential index for abdominal aortic aneurysm rupture risk prediction.Ann Biomed Eng. 2010; ([Epub ahead of print])PubMed Google Scholar Therein, it is clearly demonstrated on a statistically relevant patient group that computational stress analysis in combination with the strength model2 is superior over classical parameters such as abdominal aortic aneurysm diameter in clinical decision finding. However, our contribution on model assumptions in computational mechanics of aneurysms is of a different nature. Therein, no statistical patient group is investigated, but rather four randomly selected cases are utilized to show that the choice of computational model assumptions does greatly influence the quantitative results obtained from computational models to an extent that can exceed that of inter-patient variability. At no point in the contribution was the importance of patient-specific morphological characteristics doubted. We selected seven exemplary model assumptions that have great impact on results and demonstrated the importance of sophisticated complex computational models. Because a lot of researchers have published and will publish computational results on abdominal aortic aneurysms, it is important to see that comparability of such results very much depends on the model assumptions that have been made to obtain them. It is, therefore, a very valuable discussion and demonstration that such results are significantly influenced by not-straightforward and non-obvious factors (eg, pre-stressing or ortho-pressure), as has been pointed out in our contribution, or by the segmentation technique used, as has been previously assessed in reference 11 in our original article. Evolvement of such simulation instruments is undoubtedly important and is widely accepted in the medical and bioengineering community. We, therefore, do not understand at all the comments made by the letter writers about “a dog chasing its tail” but, nonetheless, strongly disagree. Also, we have never questioned the importance of large clinical trials or the clinical evaluation of predictive tools. On the contrary, such trials are extremely important but have to be based on state-of-the-art simulation techniques rather than too simple criteria such as plain aneurysm geometry, as mentioned by the letter writers (a crash engineer in the automotive industry would also rather run a detailed simulation than rely on the judgment of the automobile shape alone to predict crash outcome). As the behavior of the object of interest is highly nonlinear, it is indeed very important to obtain predictions from simulation that are quantitatively as good as possible, otherwise one would intentionally add ignorance to existing uncertainty of the problem at hand. We therefore strongly disagree with the letter writers' point of criticism. Regarding “The impact of model assumptions on results of computational mechanics in abdominal aortic aneurysm”Journal of Vascular SurgeryVol. 52Issue 4PreviewWe read with great interest the recent article by Reeps et al,1 about the impact of model assumptions on the computational mechanics of aneurysms. The authors mention these differences being more important than the differences between patient-specific morphologies and conclude in favor of the pre-stressing computational model. Full-Text PDF Open Archive