Comparison of the strain field of abdominal aortic aneurysm measured by magnetic resonance imaging and stereovision: A feasibility study for prediction of the risk of rupture of aortic abdominal aneurysm

Distensibility of Deformable Aortic Replicas Assessed by an Integrated In-Vitro and In-Silico Approach

The correct estimation of the distensibility of deformable aorta replicas is a challenging issue, in particular when its local characterization is necessary. We propose a combined in-vitro and in-silico approach to face this problem. First, we tested an aortic silicone arch in a pulse-duplicator analyzing its dynamics under physiological working conditions. The aortic flow rate and pressure were measured by a flow meter at the inlet and two probes placed along the arch, respectively. Video imaging analysis allowed us to estimate the outer diameter of the aorta in some sections in time. Second, we replicated the in-vitro experiment through a Fluid-Structure Interaction simulation. Observed and computed values of pressures and variations in aorta diameters, during the cardiac cycle, were compared. Results were considered satisfactory enough to suggest that the estimation of local distensibility from in-silico tests is reliable, thus overcoming intrinsic experimental limitations. The aortic distensibility (AD) is found to vary significantly along the phantom by ranging from 3.0 × 10⁻³ mmHg⁻¹ in the ascending and descending tracts to 4.2 × 10⁻³ mmHg⁻¹ in the middle of the aortic arch. Interestingly, the above values underestimate the AD obtained in preliminary tests carried out on straight cylindrical samples made with the same material of the present phantom. Hence, the current results suggest that AD should be directly evaluated on the replica rather than on the samples of the adopted material. Moreover, tests should be suitably designed to estimate the local rather than only the global distensibility.

Validation of the Strain Assessment of a Phantom of Abdominal Aortic Aneurysm: Comparison of Results Obtained From Magnetic Resonance Imaging and Stereovision Measurements

Predicting aortic aneurysm ruptures is a complex problem that has been investigated by many research teams over several decades. Work on this issue is notably complex and involves both the mechanical behavior of the artery and the blood flow. Magnetic resonance imaging (MRI) can provide measurements concerning the shape of an organ and the blood that flows through it. Measuring local distortion of the artery wall is the first essential factor to evaluate in a ruptured artery. This paper aims to demonstrate the feasibility of this measure using MRI on a phantom of an abdominal aortic aneurysm (AAA) with realistic shape. The aortic geometry is obtained from a series of cine-MR images and reconstructed using Mimics software. From 4D flow and MRI measurements, the field of velocity is determined and introduced into a computational fluid dynamic (CFD) model to determine the mechanical boundaries applied on the wall artery (pressure and ultimately wall shear stress (WSS)). These factors are then converted into a solid model that enables wall deformations to be calculated. This approach was applied to a silicone phantom model of an AAA reconstructed from a patient's computed tomography-scan examination. The calculated deformations were then compared to those obtained in identical conditions by stereovision. The results of both methods were found to be close. Deformations of the studied AAA phantom with complex shape were obtained within a gap of 12% by modeling from MR data.

Limb graft occlusion following endovascular aortic repair: Incidence, causes, treatment and prevention in a study cohort

The present study investigated the incidence, causes, treatment and prevention of limb graft occlusion following endovascular aortic repair (EVAR). A total of 66 cases of abdominal aortic aneurysm receiving EVAR at our department from January 2005 to December 2013 were enrolled. After EVAR, patients received routine antiplatelet therapy of 75 mg PLAVIX for 6 months and then 100 mg Aspirin for another 6 months by oral administration. According to previous clinical experiences, antiplatelet therapy is able to effectively reduce the incidence of iliac occlusion after EVAR. A total of 61 bifurcated grafts and 5 aortauniilac grafts (127 limbs in total) were used. Physical examination, ankle-brachial-index and computer tomographic angiography were performed at 10 days, at 3, 6 and 12 months and annually thereafter. It was found that 7 limbs in 7 patients (10.6% of patients, 5.5% of limbs) were occluded between 20 days and 12 months (average, 7.8±5.3 months) after EVAR. Acute and severe ischemia was found in 2 cases, claudication was in found 3 cases, asthenia in both legs was found in 1 case and 1 case was asymptomatic. Femoral-femoral bypass, femoral-femoral bypass and stenting, aorto-iliac/femoral bypass, thrombectomy and conservative treatment were performed in 1 patient each and thrombectomy together with stenting was performed in 2 cases. Limb graft occlusion was not rare after EVAR. Treatment of this complication included surgery and endovascular therapy such as bypass, thrombectomy and thrombolysis. In conclusion, aggressive pre-emptive treatment including angioplasty and stenting prevented occlusion in certain cases.