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A comparison of modelling techniques for computing wall stress in abdominal aortic aneurysms.

Doyle BJ, Callanan A, McGloughlin TM - Biomed Eng Online (2007)

Bottom Line: It was also noted that wall stress was shown to reduce by 59% when modelled using the most accurate non-linear complex approach, compared to the same model without intraluminal thrombus.The results here show that using more realistic parameters affect resulting wall stress.Care should be taken when examining stress results found using simplified techniques, in particular, if the wall stress results are to have clinical importance.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Applied Biomedical Engineering Research (CABER), Department of Mechanical and Aeronautical Engineering and Materials and Surface Science Institute, University of Limerick, Ireland. barry.doyle@ul.ie

ABSTRACT

Background: Aneurysms, in particular abdominal aortic aneurysms (AAA), form a significant portion of cardiovascular related deaths. There is much debate as to the most suitable tool for rupture prediction and interventional surgery of AAAs, and currently maximum diameter is used clinically as the determining factor for surgical intervention. Stress analysis techniques, such as finite element analysis (FEA) to compute the wall stress in patient-specific AAAs, have been regarded by some authors to be more clinically important than the use of a "one-size-fits-all" maximum diameter criterion, since some small AAAs have been shown to have higher wall stress than larger AAAs and have been known to rupture.

Methods: A patient-specific AAA was selected from our AAA database and 3D reconstruction was performed. The AAA was then modelled in this study using three different approaches, namely, AAA(SIMP), AAA(MOD) and AAA(COMP), with each model examined using linear and non-linear material properties. All models were analysed using the finite element method for wall stress distributions.

Results: Wall stress results show marked differences in peak wall stress results between the three methods. Peak wall stress was shown to reduce when more realistic parameters were utilised. It was also noted that wall stress was shown to reduce by 59% when modelled using the most accurate non-linear complex approach, compared to the same model without intraluminal thrombus.

Conclusion: The results here show that using more realistic parameters affect resulting wall stress. The use of simplified computational modelling methods can lead to inaccurate stress distributions. Care should be taken when examining stress results found using simplified techniques, in particular, if the wall stress results are to have clinical importance.

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Related in: MedlinePlus

Effect of axial smoothing on the polylines constructed from the CT scans. Model 1 consists of 7 control points, Model 2 has 20 control points, Model 3 has 50 control points, and Model 4 has 70 control points per polylines slice. Green line is the original polyline from the CT scan slice, with the red line being the new smoothed polyline.
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Figure 2: Effect of axial smoothing on the polylines constructed from the CT scans. Model 1 consists of 7 control points, Model 2 has 20 control points, Model 3 has 50 control points, and Model 4 has 70 control points per polylines slice. Green line is the original polyline from the CT scan slice, with the red line being the new smoothed polyline.

Mentions: Each of these 3D models were initially quite rough containing sharp edges and surface artefacts, and required smoothing to ensure that the model could be readily meshed and that stress analyses could be performed. The method of reconstruction and smoothing was validated from previous work by our group, [30,31] and it was shown that there are negligible differences between the two methods. In order to determine the optimum level of smoothing for these reconstructions, four degrees of smoothing were examined. These four smoothing levels were based on axial smoothing of individual polyline slices created from the CT scans. Four models were then reconstructed. Model 1 contained 7 control points per polyline slice, model 2 had 20 control points, model 3 had 50 control points, and model 4 had 70 control points per slice. The more control points per polyline decreases the surface smoothness of the resulting AAA. Figure 2 shows the difference in polylines between the various degrees of smoothing. Non-linear stress analyses were then performed on each of the four models. Resulting wall stress distributions are shown in Figure 3, with stress results normalised to the peak stress experienced in the roughest model, namely model 4. Mesh independence was performed on all models. From these results, model 2 was deemed to be the optimum level of smoothing as unwanted surface detail is removed without causing unnecessary over-smoothing. Figure 4 illustrates the difference between the resulting rough and smooth models. These AAA surfaces were then exported in IGES file format for further work.


A comparison of modelling techniques for computing wall stress in abdominal aortic aneurysms.

Doyle BJ, Callanan A, McGloughlin TM - Biomed Eng Online (2007)

Effect of axial smoothing on the polylines constructed from the CT scans. Model 1 consists of 7 control points, Model 2 has 20 control points, Model 3 has 50 control points, and Model 4 has 70 control points per polylines slice. Green line is the original polyline from the CT scan slice, with the red line being the new smoothed polyline.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2169238&req=5

Figure 2: Effect of axial smoothing on the polylines constructed from the CT scans. Model 1 consists of 7 control points, Model 2 has 20 control points, Model 3 has 50 control points, and Model 4 has 70 control points per polylines slice. Green line is the original polyline from the CT scan slice, with the red line being the new smoothed polyline.
Mentions: Each of these 3D models were initially quite rough containing sharp edges and surface artefacts, and required smoothing to ensure that the model could be readily meshed and that stress analyses could be performed. The method of reconstruction and smoothing was validated from previous work by our group, [30,31] and it was shown that there are negligible differences between the two methods. In order to determine the optimum level of smoothing for these reconstructions, four degrees of smoothing were examined. These four smoothing levels were based on axial smoothing of individual polyline slices created from the CT scans. Four models were then reconstructed. Model 1 contained 7 control points per polyline slice, model 2 had 20 control points, model 3 had 50 control points, and model 4 had 70 control points per slice. The more control points per polyline decreases the surface smoothness of the resulting AAA. Figure 2 shows the difference in polylines between the various degrees of smoothing. Non-linear stress analyses were then performed on each of the four models. Resulting wall stress distributions are shown in Figure 3, with stress results normalised to the peak stress experienced in the roughest model, namely model 4. Mesh independence was performed on all models. From these results, model 2 was deemed to be the optimum level of smoothing as unwanted surface detail is removed without causing unnecessary over-smoothing. Figure 4 illustrates the difference between the resulting rough and smooth models. These AAA surfaces were then exported in IGES file format for further work.

Bottom Line: It was also noted that wall stress was shown to reduce by 59% when modelled using the most accurate non-linear complex approach, compared to the same model without intraluminal thrombus.The results here show that using more realistic parameters affect resulting wall stress.Care should be taken when examining stress results found using simplified techniques, in particular, if the wall stress results are to have clinical importance.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Applied Biomedical Engineering Research (CABER), Department of Mechanical and Aeronautical Engineering and Materials and Surface Science Institute, University of Limerick, Ireland. barry.doyle@ul.ie

ABSTRACT

Background: Aneurysms, in particular abdominal aortic aneurysms (AAA), form a significant portion of cardiovascular related deaths. There is much debate as to the most suitable tool for rupture prediction and interventional surgery of AAAs, and currently maximum diameter is used clinically as the determining factor for surgical intervention. Stress analysis techniques, such as finite element analysis (FEA) to compute the wall stress in patient-specific AAAs, have been regarded by some authors to be more clinically important than the use of a "one-size-fits-all" maximum diameter criterion, since some small AAAs have been shown to have higher wall stress than larger AAAs and have been known to rupture.

Methods: A patient-specific AAA was selected from our AAA database and 3D reconstruction was performed. The AAA was then modelled in this study using three different approaches, namely, AAA(SIMP), AAA(MOD) and AAA(COMP), with each model examined using linear and non-linear material properties. All models were analysed using the finite element method for wall stress distributions.

Results: Wall stress results show marked differences in peak wall stress results between the three methods. Peak wall stress was shown to reduce when more realistic parameters were utilised. It was also noted that wall stress was shown to reduce by 59% when modelled using the most accurate non-linear complex approach, compared to the same model without intraluminal thrombus.

Conclusion: The results here show that using more realistic parameters affect resulting wall stress. The use of simplified computational modelling methods can lead to inaccurate stress distributions. Care should be taken when examining stress results found using simplified techniques, in particular, if the wall stress results are to have clinical importance.

Show MeSH
Related in: MedlinePlus