| 1. |
- Gasser, T. Christian, et al.
(författare)
-
A novel strategy to translate the biomechanical rupture risk of abdominal aortic aneurysms to their equivalent diameter risk : Method and retrospective validation
- 2014
-
Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 47:3, s. 288-295
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: To translate the individual abdominal aortic aneurysm (AAA) patient's biomechanical rupture risk profile to risk-equivalent diameters, and to retrospectively test their predictability in ruptured and non-ruptured aneurysms. Methods: Biomechanical parameters of ruptured and non-ruptured AAAs were retrospectively evaluated in a multicenter study. General patient data and high resolution computer tomography angiography (CTA) images from 203 non-ruptured and 40 ruptured aneurysmal infrarenal aortas. Three-dimensional AAA geometries were semi-automatically derived from CTA images. Finite element (FE) models were used to predict peak wall stress (PWS) and peak wall rupture index (PWRI) according to the individual anatomy, gender, blood pressure, intraluminal thrombus (ILT) morphology, and relative aneurysm expansion. Average PWS diameter and PWRI diameter responses were evaluated, which allowed for the PWS equivalent and PWRI equivalent diameters for any individual aneurysm to be defined. Results: PWS increased linearly and PWRI exponentially with respect to maximum AAA diameter. A size-adjusted analysis showed that PWS equivalent and PWRI equivalent diameters were increased by 7.5 mm (p = .013) and 14.0 mm (p < .001) in ruptured cases when compared to non-ruptured controls, respectively. In non-ruptured cases the PWRI equivalent diameters were increased by 13.2 mm (p < .001) in females when compared with males. Conclusions: Biomechanical parameters like PWS and PWRI allow for a highly individualized analysis by integrating factors that influence the risk of AAA rupture like geometry (degree of asymmetry, ILT morphology, etc.) and patient characteristics (gender, family history, blood pressure, etc.). PWRI and the reported annual risk of rupture increase similarly with the diameter. PWRI equivalent diameter expresses the PWRI through the diameter of the average AAA that has the same PWRI, i.e. is at the same biomechanical risk of rupture. Consequently, PWRI equivalent diameter facilitates a straightforward interpretation of biomechanical analysis and connects to diameter-based guidelines for AAA repair indication. PWRI equivalent diameter reflects an additional diagnostic parameter that may provide more accurate clinical data for AAA repair indication.
|
|
| 2. |
- Gasser, T. Christian, et al.
(författare)
-
Biomechanical Rupture Risk Assessment of Abdominal Aortic Aneurysms : Model Complexity versus Predictability of Finite Element Simulations
- 2010
-
Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 40:2, s. 176-185
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: Investigation of the predictability of finite element (FE) models regarding rupture risk assessment of abdominal aortic aneurysms (AAAs). Materials and materials: Peak wall stress (PWS) and peak wall rupture risk (PWRR) of ruptured (n = 20) and non-ruptured (n = 30) AAAs were predicted by four FE models of different complexities derived from computed tomography (CT) data. Two matching sub-groups of ruptured and non-ruptured aneurysms were used to investigate the usability of different FE models to discriminate amongst them. Results: All FE models exhibited a strong positive correlation between PWS and PWRR with the maximum diameter. FE models, which excluded the intra-luminal thrombus (ILT) failed to discriminate between ruptured and non-ruptured aneurysms. The predictability of all applied FE models was strengthened by including wall strength data, that is, computing the PWRR. The most sophisticated FE model applied in this study predicted PWS and PWRR 1.17 (p = 0.021) and 1.43 (p = 0.016) times higher in ruptured than diameter-matched non-ruptured aneurysms, respectively. Conclusions: PWRR reinforces PWS as a biomechanical rupture risk index. The ILT has a major impact on AAA biomechanics and rupture risk, and hence, needs to be considered in meaningful FE simulations. The applied FE models, however, could not explain rupture in all analysed aneurysms.
|
|
| 3. |
- Gasser, T. Christian, et al.
(författare)
-
Failure properties of intraluminal thrombus in abdominal aortic aneurysm under static and pulsating mechanical loads
- 2008
-
Ingår i: Journal of Vascular Surgery. - : Elsevier BV. - 0741-5214 .- 1097-6809. ; 48:1, s. 179-188
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives: It has been suggested that mechanical failure of intraluminal thrombus (ILT) could play a key role in the rupture of abdominal aortic aneurysms (AAAs), and in the present study, this hypothesis has been investigated. An in vitro experimental approach has been proposed, which provides layer-specific failure data of ILT tissue under static and pulsatile mechanical loads. Methods. In total, 112 bone-shaped test specimens are prepared from luminal, medial, and abluminal layers of eight ILTs harvested during open elective AAA repair. Three different types of mechanical experiments, denoted as control test, ultimate strength test, and fatigue test were performed in Dulbecco's modified eagle's medium (DMEM) supplemented with fetal calf serum, L-ascorbic acid, and antibiotics at 37 degrees C and pH 7.0. In detail, fatigue tests, which are experiments, where the ILT tissue is loaded. in pulsatile manner, were carried out at three different load levels with a natural frequency of 1.0 Hz. Results. ILT's ultimate strength (156.5 kPa, 92.0 kPa, and 47.7 kPa for luminal, medial, and abluminal layers, respectively) and referential stiffness (62.88 kPa, 47.52 kPa, and 41.52 kPa, for luminal, medial, and abluminal layers, respectively) continuously decrease from the inside to the outside. ILT tissue failed within less than 1 hour under pulsatile loading at a load level of 60% ultimate strength, while a load level of about 40% ultimate strength did not cause failure within 13.9 hours. Conclusions. ILT tissue is vulnerable against fatigue failure and shows significant decreasing strength with respect to the number of load cycles. Hence, after a reasonable time of pulsating loading ILT's strength is far below its ultimate strength, and when compared with stress predictions from finite element (FE) studies, this indicates the likelihood of fatigue failure in vivo. Failure within the ILT could propagate towards the weakened vessel wall behind it and could initialize AAA failure thereafter.
|
|
| 4. |
- Gasser, T. Christian, et al.
(författare)
-
Micromechanical Characterization of Intra-luminal Thrombus Tissue from Abdominal Aortic Aneurysms
- 2010
-
Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 38:2, s. 371-379
-
Tidskriftsartikel (refereegranskat)abstract
- The reliable assessment of Abdominal Aortic Aneurysm rupture risk is critically important in reducing related mortality without unnecessarily increasing the rate of elective repair. Intra-luminal thrombus (ILT) has multiple biomechanical and biochemical impacts on the underlying aneurysm wall and thrombus failure might be linked to aneurysm rupture. Histological slices from 7 ILTs were analyzed using a sequence of automatic image processing and feature analyzing steps. Derived microstructural data was used to define Representative Volume Elements (RVE), which in turn allowed the estimation of microscopic material properties using the non-linear Finite Element Method. ILT tissue exhibited complex microstructural arrangement with larger pores in the abluminal layer than in the luminal layer. The microstructure was isotropic in the abluminal layer, whereas pores started to orient along the circumferential direction towards the luminal site. ILT's macroscopic (reversible) deformability was supported by large pores in the microstructure and the inhomogeneous structure explains in part the radially changing macroscopic constitutive properties of ILT. Its microscopic properties decreased just slightly from the luminal to the abluminal layer. The present study provided novel microstructural and micromechanical data of ILT tissue, which is critically important to further explore the role of the ILT in aneurysm rupture. Data provided in this study allow an integration of structural information from medical imaging for example, to estimate ILT's macroscopic mechanical properties.
|
|
| 5. |
- Polzer, S., et al.
(författare)
-
The Impact of Intraluminal Thrombus Failure on the Mechanical Stress in the Wall of Abdominal Aortic Aneurysms
- 2011
-
Ingår i: European Journal of Vascular and Endovascular Surgery. - : Elsevier BV. - 1078-5884 .- 1532-2165. ; 41:4, s. 467-473
-
Tidskriftsartikel (refereegranskat)abstract
- Objectives: The role of the intraluminal thrombus (ILT) in abdominal aortic aneurysm (AAA) rupture is controversial, and it is still not clear if an ILT increases or decreases AAA rupture risk. Specifically, signs of bleeding in the ILT are considered to increase AAA rupture risk. to further explore this hypothesis, intact AAAs (n = 4) with clear signs of fissures in the ILT, identified by computed tomography angiography (CTA) were investigated. Methods: Two different cases of ILT fissuring were investigated, where (1) ILT fissures were extracted directly from the CTA data and (2) a hypothetical fissure was introduced in the otherwise-intact ILT tissue. Wall stress distributions were predicted based on detailed Finite Element (FE) models. Results: ILT fissures extracted from CTA data locally increase the mechanical stress in the underlying wall by up to 30%. The largest impact on wall stress was observed if the ILT crack reaches the aneurysm wall, or if it involves large parts of the ILT. By contrast, a concentric failure in the medial ILT, which does not reach the aneurysm wall, has almost no impact on wall stress distribution. Hypothetical ILT fissures that connect the lumen with the wall cause a twofold increase of the stress in the underlying wall. Conclusions: ILT fissures increase the stress in the underlying wall, whereas regions other than that remain unaffected. If ILT fissures reach the wall or involve large parts of the ILT, the resulting increase in wall stress could possibly cause AAA rupture.
|
|
