Improving the Efficiency of Abdominal Aortic Aneurysm Wall Stress Computations

An abdominal aortic aneurysm is a pathological dilation of the abdominal aorta, which carries a high mortality rate if ruptured. The most commonly used surrogate marker of rupture risk is the maximal transverse diameter of the aneurysm. More recent studies suggest that wall stress from models of patient-specific aneurysm geometries extracted, for instance, from computed tomography images may be a more accurate predictor of rupture risk and an important factor in AAA size progression. However, quantification of wall stress is typically computationally intensive and time-consuming, mainly due to the nonlinear mechanical behavior of the abdominal aortic aneurysm walls. These difficulties have limited the potential of computational models in clinical practice. To facilitate computation of wall stresses, we propose to use a linear approach that ensures equilibrium of wall stresses in the aneurysms. This proposed linear model approach is easy to implement and eliminates the burden of nonlinear computations. To assess the accuracy of our proposed approach to compute wall stresses, results from idealized and patient-specific model simulations were compared to those obtained using conventional approaches and to those of a hypothetical, reference abdominal aortic aneurysm model. For the reference model, wall mechanical properties and the initial unloaded and unstressed configuration were assumed to be known, and the resulting wall stresses were used as reference for comparison. Our proposed linear approach accurately approximates wall stresses for varying model geometries and wall material properties. Our findings suggest that the proposed linear approach could be used as an effective, efficient, easy-to-use clinical tool to estimate patient-specific wall stresses.     

Different Long-Term Outcomes of Abdominal Aortic Aneurysm and Intracranial Aneurysm Models: Hemodynamic Change may also Play an Essential Role in the Initiation and Progression of Abdominal Aortic Aneurysm in Rabbits

Self-healing phenomenon was found in the periarterial elastase-induced abdominal aortic aneurysm (AAA) in rabbit. This kind of aneurysm model does not progress and heals spontaneously in the long term, which is quite different from the performance of AAA disease in human. In order to better mimic human AAA and overcome this shortcoming of traditional AAA model in rabbit, we studied the pathogenesis of cerebral aneurysm (CA) model in small animal, which shows an excellent long-term patency and progressive enlargement. We found that hemodynamic conditions, such as turbulence flow, high blood flow, and shear stress, play an important role in the formation and progression of CA. So, we hypothesize that hemodynamic change may also play an essential role in the initiation and progression of rabbit AAA, and self-healing will be overcome if hemodynamic condition changes by coarctation of infra-renal aorta after elastase incubation.     

Homocysteine Level and Risk of Abdominal Aortic Aneurysm: A Meta-Analysis

Objectives

Previous studies have reported inconsistent findings regarding the association between elevated plasma homocysteine (Hcy) levels and abdominal aortic aneurysm (AAA). We investigated this association between Hcy levels in patients with AAA and unaffected controls by conducting a meta-analysis and systematic review.

Methods

We conducted a systematic literature search (up to August 2013) of the PubMed database and Embase. We selected observational studies that evaluated Hcy levels in subjects with AAA compared to unaffected controls. Criteria for inclusion were the assessment of baseline Hcy and risk of AAA as an outcome. The results were presented as odd ratio (OR) and corresponding 95% confidence intervals (CI) comparing AAA patients to the control subjects.

Results

7 studies with 6,445 participants were identified and analyzed. Overall, elevated plasma Hcy was associated with an increased risk of AAA (3.29; 95% CI 1.66–6.51). The pooled adjusted OR from a random effect model of only men participants in the AAA compared with the control group was 2.36 (95% CI 0.63–8.82).

Conclusion

This meta-analysis and systematic review suggested that Hcy significantly increased the risk of AAA.     

An Aortic Tampon for Emergency Control of Ruptured Abdominal Aneurysm

Ruptured abdominal aneurysm has now become a common surgical emergency, frequently amenable to successful resection and cure. The final result is often marred, however, by the effects of renal, coronary or cerebral ischemia resulting from dangerous hypotension during transportation of the patient to a vascular centre.An aortic catheter has been developed which is passed by way of a brachial artery cut-down so that it rests in the abdominal aorta. The balloon at its tip is then filled with sodium diatrizoate (Hypaque) so that it completely obstructs the aortic lumen just above the level of the aneurysm. Accurate positioning of the balloon to carefully preserve renal blood flow is facilitated by fluoroscopic control. The use of this procedure in three patients has been very satisfactory, with a dramatic return of consciousness and of normal blood pressure, without the need for further blood replacement. Subsequent surgery with dissection of the aneurysm was aided by the presence of the palpable inflated balloon.     

Dynamic simulation and Doppler Ultrasonography validation of blood flow behavior in Abdominal Aortic Aneurysm

Criteria for rupture prediction of Abdominal Aortic Aneurysm (AAA) are based only on the diameter of AAA. This method does not consider complex hemodynamic forces exerted on AAA wall. The methodology used in our study combines Computer-Aided Design (CAD) with Computational Fluid Dynamics (CFD). Three-dimensional vascular structures reconstructions were based on Computed Tomography (CT) images and CAD. CFD theory was used for mathematical modeling and simulations. In this way, dynamic behavior of blood flow in bounded three-dimensional space was described. Doppler Ultrasonography (US) was used for model results validation. All simulations were based on medical investigation of 4 patients (male older than 65 years) with diagnosed AAA. Good correspondence between computed velocities in AAA and measured values with Doppler US (Patient 1 0.60 m·s⁻¹ versus 0.61 m·s⁻¹, Patient 2 0.80 m·s⁻¹ versus 0.80 m·s⁻¹, Patient 3 0.75 m·s⁻¹ versus 0.78 m·s⁻¹, Patient 4 0.50 m·s⁻¹ versus 0.49 m·s⁻¹) was noticed. The good agreement between measured and simulated velocities validates our methodology and the other data available from simulations (eg. von Misses stress) could be used to provide useful information about the possibility of AAA rupture.     

腹主动脉瘤生长过程的蠕变力学模型

基于增强对腹主动脉瘤生长过程的理解、为腹主动脉瘤临床手术提供参考的目的,本文根据腹主动脉瘤的生长物理机制,提出了以蠕变力学为基础模拟腹主动脉瘤生长过程的模型.建立了腹主动脉瘤简化模型,利用有限元方法进行模拟计算.结果显示蠕变模型能够有效模拟腹主动脉瘤生长过程中的形态变化.参数优化模型模拟结果符合临床统计数据所示的腹主动脉瘤生长过程.本文还讨论了腹主动脉材料力学参数对模型的影响.     

Possible Dual Role of Decorin in Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is characterized by chronic inflammation, which leads to pathological remodeling of the extracellular matrix. Decorin, a small leucine-rich repeat proteoglycan, has been suggested to regulate inflammation and stabilize the extracellular matrix. Therefore, the present study investigated the role of decorin in the pathogenesis of AAA. Decorin was localized in the aortic adventitia under normal conditions in both mice and humans. AAA was induced in mice using CaCl₂ treatment. Initially, decorin protein levels decreased, but as AAA progressed decorin levels increased in all layers. Local administration of exogenous decorin prevented the development of CaCl₂-induced AAA. However, decorin was highly expressed in the degenerative lesions of human AAA walls, and this expression positively correlated with matrix metalloproteinase (MMP)-9 expression. In cell culture experiments, the addition of decorin inhibited secretion of MMP-9 in vascular smooth muscle cells, but had the opposite effect in macrophages. The results suggest that decorin plays a dual role in AAA. Adventitial decorin in normal aorta may protect against the development of AAA, but macrophages expressing decorin in AAA walls may facilitate the progression of AAA by up-regulating MMP-9 secretion.     

腹主动脉瘤的流固耦合分析方法研究

目的:将流固耦合分析方法运用于血流动力学的研究,可以获得更加准确的结果,为临床诊断和治疗提供有效的指导.方法:本文运用ANSYS和CFX对腹主动脉瘤(Abdominal Aortic Aneurysm,AAA)进行流固耦合模拟分析,以便获得动脉瘤的血流速度和瘤壁的应力分布,判断易破裂危险区域.结果:实验结果表明,本例的腹部主动脉瘤应力峰值位于瘤体颈部.结论:流动和壁面切应力分布揭示动脉瘤颈部为破裂的危险区域.     

Comparison of Dynamic and Liver-Specific Gadoxetic Acid Contrast-Enhanced MRI versus Apparent Diffusion Coefficients

Background

Hepatic lesions often present diagnostic connundrums with conventional MR techniques. Hepatobiliary phase contrast-enhanced imaging with gadoxetic acid can aid in the characterization of such lesions. However, quantitative measures describing late-phase enhancement must be assessed relative to their accuracy of hepatic lesion classification.Purpose: To compare quantitative parameters in gadoxetic acid contrast-enhanced dynamic and hepatobiliary phase imaging versus apparent diffusion coefficients in hepatic lesion characterization.

Material and Methods

57 patients with focal hepatic lesions on gadoxetic acid MR were included. Lesion enhancement at standard post-contrast time points and in the hepatobiliary phase (HB; 15 and 25 minutes post-contrast) was assessed via calculation of contrast (CR) and enhancement ratios (ER). Apparent diffusion coefficient (ADC) values were also obtained. Values for these parameters were compared among lesions and ROC analyses performed.Results: HB enhancement was greatest with FNH and adenomas. HB ER parameters but not HB CR could distinguish HCC from benign entities (0.9 ER ROC AUC versus 0.5 CR ROC AUC). There was no statistically significant difference found between the 15 and 25 minutes HB time points in detection of any lesion (p>0.4). ADC values were statistically significantly higher with hemangiomas (p<0.05) without greater accuracy in lesion detection relative to HB phase parameters.

Conclusion

Hepatobiliary phase gadoxetic acid contrast-enhanced MR characterizes focal hepatic lesions more accurately than ADC and conventional dynamic post-contrast time point enhancement parameters. ER values are generally superior to CR. No discernible benefit of 25 minute versus 15 minute delayed imaging is demonstrated.     

Hypoperfusion of the Adventitial Vasa Vasorum Develops an Abdominal Aortic Aneurysm

The aortic wall is perfused by the adventitial vasa vasorum (VV). Tissue hypoxia has previously been observed as a manifestation of enlarged abdominal aortic aneurysms (AAAs). We sought to determine whether hypoperfusion of the adventitial VV could develop AAAs. We created a novel animal model of adventitial VV hypoperfusion with a combination of a polyurethane catheter insertion and a suture ligation of the infrarenal abdominal aorta in rats. VV hypoperfusion caused tissue hypoxia and developed infrarenal AAA, which had similar morphological and pathological characteristics to human AAA. In human AAA tissue, the adventitial VV were stenotic in both small AAAs (30–49 mm in diameter) and in large AAAs (> 50 mm in diameter), with the sac tissue in these AAAs being ischemic and hypoxic. These results indicate that hypoperfusion of adventitial VV has critical effects on the development of infrarenal AAA.     

腔内修复术治疗腹主动脉瘤的临床疗效分析

目的:评价腔内修复术(EVAR)治疗腹主动脉瘤(AAA)的临床疗效及安全性。方法:选择2008年12月至2013年12月收治的29例AAA患者,给予EVAR治疗,观察其围术期的疗效及血管破裂死亡、伤口愈合情况、截瘫、腔内隔绝术后并发症的发生情况和随访期疗效及血管破裂死亡、截瘫及内漏的发生情况。结果:29例手术均成功,1例术后3天出现右髂动脉支架内血栓、消化道出血及肝肾功能衰竭,行持续性血液净化好转出院。2例术区切口愈合延迟,9例术后发热,无在院死亡及截瘫病患。随访期间,1例术后30天死亡,死于肝肾功能衰竭;1例3个月出现肾功能不全;1例双下肢乏力,无截瘫发生。存活的28例患者复查增强CT见支架位置、形态良好,无移位及内漏发生。结论:EVAR具有成功率高、创伤小、恢复快等特点,且并发症少,治疗AAA安全有效。     

Delayed Contrast-Enhanced MRI of the Coronary Artery Wall in Takayasu Arteritis

Background

Takayasu arteritis (TA) is a rare form of chronic inflammatory granulomatous arteritis of the aorta and its major branches. Late gadolinium enhancement (LGE) with magnetic resonance imaging (MRI) has demonstrated its value for the detection of vessel wall alterations in TA. The aim of this study was to assess LGE of the coronary artery wall in patients with TA compared to patients with stable CAD.

Methods

We enrolled 9 patients (8 female, average age 46±13 years) with proven TA. In the CAD group 9 patients participated (8 male, average age 65±10 years). Studies were performed on a commercial 3T whole-body MR imaging system (Achieva; Philips, Best, The Netherlands) using a 3D inversion prepared navigator gated spoiled gradient-echo sequence, which was repeated 34–45 minutes after low-dose gadolinium administration.

Results

No coronary vessel wall enhancement was observed prior to contrast in either group. Post contrast, coronary LGE on IR scans was detected in 28 of 50 segments (56%) seen on T2-Prep scans in TA and in 25 of 57 segments (44%) in CAD patients. LGE quantitative assessment of coronary artery vessel wall CNR post contrast revealed no significant differences between the two groups (CNR in TA: 6.0±2.4 and 7.3±2.5 in CAD; p = 0.474).

Conclusion

Our findings suggest that LGE of the coronary artery wall seems to be common in patients with TA and similarly pronounced as in CAD patients. The observed coronary LGE seems to be rather unspecific, and differentiation between coronary vessel wall fibrosis and inflammation still remains unclear.     

Cerebral Blood Volume Analysis in Glioblastomas Using Dynamic Susceptibility Contrast-Enhanced Perfusion MRI: A Comparison of Manual and Semiautomatic Segmentation Methods

Purpose

To compare the reproducibilities of manual and semiautomatic segmentation method for the measurement of normalized cerebral blood volume (nCBV) using dynamic susceptibility contrast-enhanced (DSC) perfusion MR imaging in glioblastomas.

Materials and Methods

Twenty-two patients (11 male, 11 female; 27 tumors) with histologically confirmed glioblastoma (WHO grade IV) were examined with conventional MR imaging and DSC imaging at 3T before surgery or biopsy. Then nCBV (means and standard deviations) in each mass was measured using two DSC MR perfusion analysis methods including manual and semiautomatic segmentation method, in which contrast-enhanced (CE)-T1WI and T2WI were used as structural imaging. Intraobserver and interobserver reproducibility were assessed according to each perfusion analysis method or each structural imaging. Interclass correlation coefficient (ICC), Bland-Altman plot, and coefficient of variation (CV) were used to evaluate reproducibility.

Results

Intraobserver reproducibilities on CE-T1WI and T2WI were ICC of 0.74–0.89 and CV of 20.39–36.83% in manual segmentation method, and ICC of 0.95–0.99 and CV of 8.53–16.19% in semiautomatic segmentation method, repectively. Interobserver reproducibilites on CE-T1WI and T2WI were ICC of 0.86–0.94 and CV of 19.67–35.15% in manual segmentation method, and ICC of 0.74–1.0 and CV of 5.48–49.38% in semiautomatic segmentation method, respectively. Bland-Altman plots showed a good correlation with ICC or CV in each method. The semiautomatic segmentation method showed higher intraobserver and interobserver reproducibilities at CE-T1WI-based study than other methods.

Conclusion

The best reproducibility was found using the semiautomatic segmentation method based on CE-T1WI for structural imaging in the measurement of the nCBV of glioblastomas.     

Toll-Like Receptor 4 Is Essential in the Development of Abdominal Aortic Aneurysm

Toll-like receptor (TLR) family plays a key role in innate immunity and various inflammatory responses. TLR4, one of the well-characterized pattern-recognition receptors, can be activated by endogenous damage-associated molecular pattern molecules such as high mobility group box 1 (HMGB1) to sustain sterile inflammation. Evidence suggested that blockade of TLR4 signaling may confer protection against abdominal aortic aneurysm (AAA). Herein we aimed to obtain further insight into the mechanism by which TLR4 might promote aneurysm formation. Characterization of the CaCl₂-induced AAA model in mice revealed that upregulation of TLR4 expression, localized predominantly to vascular smooth muscle cells (VSMCs), was followed by a late decline during a 28-day period of AAA development. In vitro, TLR4 expression was increased in VSMCs treated with HMGB1. Knockdown of TLR4 by siRNA attenuated HMGB1-enhanced production of proinflammatory cytokines, specifically interleukin-6 and monocyte chemoattractant protein-1 (MCP-1), and matrix-degrading matrix metalloproteinase (MMP)-2 from VSMCs. In vivo, two different strains of TLR4-deficient (C57BL/10ScNJ and C3H/HeJ) mice were resistant to CaCl₂-induced AAA formation compared to their respective controls (C57BL/10ScSnJ and C3H/HeN). Knockout of TLR4 reduced interleukin-6 and MCP-1 levels and HMGB1 expression, attenuated macrophage accumulation, and eventually suppressed MMP production, elastin destruction and VSMC loss. Finally, human AAA exhibited higher TLR4 expression that was localized to VSMCs. These data suggest that TLR4 signaling contributes to AAA formation by promoting a proinflammatory status of VSMCs and by inducing proteinase release from VSMCs during aneurysm initiation and development.     

Fibulin-5在主动脉夹层血管壁中表达异常

目的:研究Stanford A型主动脉夹层(aortic dissection,AD)升主动脉和正常升主动脉血管组织中Fibulin-5表达的差异。方法:收集Stanford A型AD患者手术中切除的升主动脉血管组织标本12例(AD组),多器官捐献患者升主动脉血管12例(对照组)。采用EVG染色观察主动脉中膜弹性纤维形态结构;应用SP免疫组织化学法及Western blot法对标本组织中的Fibulin-5进行检测分析。结果:AD组主动脉中膜弹性纤维形态和排列不规则、破碎、丢失,结构紊乱。免疫组织化学显示Fibulin-5阳性表达见于主动脉壁平滑肌细胞胞质中,AD组与对照组比较,Fibulin-5表达明显较少。Western blot蛋白印迹示AD组Fibulin-5表达明显减少,差异有统计学意义(P0.05)。结论:Fibulin-5在AD主动脉中膜中表达下调,可能在AD的发生中发挥作用。     

Risk Stratification of Patients with Peripheral Arterial Disease and Abdominal Aortic Aneurysm Using Aortic Augmentation Index

BackgroundCentral augmentation index (cAIx) is an indicator for vascular stiffness. Obstructive and aneurysmatic vascular disease can affect pulse wave propagation and reflection, causing changes in central aortic pressures.AimTo assess and compare cAIx in patients with peripheral arterial disease (PAD) and / or abdominal aortic aneurysm (AAA).MethodscAIx was assessed by radial applanation tonometry (Sphygmocor) in a total of 184 patients at a tertiary referral centre. Patients were grouped as having PAD only, AAA only, or both AAA and PAD. Differences in cAIx measurements between the three patient groups were tested by non-parametric tests and stepwise multivariate linear regression analysis to investigate associations with obstructive or aneurysmatic patterns of vascular disease.ResultsIn the study sample of 184 patients, 130 had PAD only, 20 had AAA only, and 34 patients had both AAA and PAD. Mean cAIx (%) was 30.5 ± 8.2 across all patients. It was significantly higher in females (35.2 ± 6.1, n = 55) than males (28.4 ± 8.2, n = 129), and significantly higher in patients over 80 years of age (34.4 ± 6.9, n = 22) than in those under 80 years (30.0 ± 8.2, n = 162). Intergroup comparison revealed a significant difference in cAIx between the three patient groups (AAA: 27.3 ± 9.5; PAD: 31.4 ± 7.8; AAA & PAD: 28.8 ± 8.5). cAIx was significantly lower in patients with AAA, higher in patients with both AAA and PAD, and highest in patients with PAD only (beta = 0.21, p = 0.006).ConclusionNon-invasive assessment of arterial stiffness in high-risk patients indicates that cAIx differs according to the pattern of vascular disease. Measurements revealed significantly higher cAIx values for patients with obstructive peripheral arterial disease than for patients with aneurysmatic disease.     

Self-Gated CINE MRI for Combined Contrast-Enhanced Imaging and Wall-Stiffness Measurements of Murine Aortic Atherosclerotic Lesions

Background

High-resolution contrast-enhanced imaging of the murine atherosclerotic vessel wall is difficult due to unpredictable flow artifacts, motion of the thin artery wall and problems with flow suppression in the presence of a circulating contrast agent.

Methods and Results

We applied a 2D-FLASH retrospective-gated CINE MRI method at 9.4T to characterize atherosclerotic plaques and vessel wall distensibility in the aortic arch of aged ApoE^−/− mice after injection of a contrast agent. The method enabled detection of contrast enhancement in atherosclerotic plaques in the aortic arch after I.V. injection of micelles and iron oxides resulting in reproducible plaque enhancement. Both contrast agents were taken up in the plaque, which was confirmed by histology. Additionally, the retrospective-gated CINE method provided images of the aortic wall throughout the cardiac cycle, from which the vessel wall distensibility could be calculated. Reduction in plaque size by statin treatment resulted in lower contrast enhancement and reduced wall stiffness.

Conclusions

The retrospective-gated CINE MRI provides a robust and simple way to detect and quantify contrast enhancement in atherosclerotic plaques in the aortic wall of ApoE^−/− mice. From the same scan, plaque-related changes in stiffness of the aortic wall can be determined. In this mouse model, a correlation between vessel wall stiffness and atherosclerotic lesions was found.