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Noninvasive methods of characterising local regional variations in aortic tissue to advance aneurysm rupture risk prediction

Creator:

Tierney, Áine P.;

Institution: University of Limerick
Subject Keywords: adominal aortic aneurysms (AAAs); biomedical engineering; acoustic radiation force impulse;
Region:
Description:

Abdominal Aortic Aneurysms (AAAs) is a permanent and irreversible dilation of the
infrarenal section of the aorta. AAA’s are generally asymptomatic, until rupture of the
AAA wall occurs. Rupture can lead to large abdominal bleeding and death within a
short period of time. AAA formation affects the integrity of the aortic wall, leading to a
decrease in compliance and tensile strength, increased wall stiffness and a progressive
dilation of the wall. From a biomedical engineering perspective, rupture of an AAA
occurs when, locally, the wall stress surpasses the strength of the wall. This suggests it
is of importance to have wall property information and perform wall stress analysis
which can assess the risk of rupture reliably. Noninvasive assessment of aneurysm wall
properties would improve insight into the vascular changes, preceding rupture. This
thesis aims to explore noninvasive methods of characterising aortic wall properties and
the effectiveness of these techniques to aid in clinical assessment. In this study, the
efficacy of acoustic radiation force impulse (ARFI) imaging for determination of aortic
changes in vitro was reported. The study successfully developed an artificial aneurysm
in excised tissue and the changes induced by aneurysm development were detected
using ARFI. A feasibility case study demonstrated a method for estimation of in vivo
tissue properties using ARFI and exhibited the viability of translation of this modality to
AAA clinical use. Most preoperative imaging protocols use computerised tomography
(CT) angiography with three dimensional (3D) reconstructions for sizing and planning.
The resulting images are static images, despite the fact that the human aorta exists in a
dynamic environment. The elastic properties of the aorta were examined to assess the
changes in the dynamic environment using cardiac gated CT. Different regions of the
aorta were shown to have different mechanical properties. High variation in mechanical
behaviour was found to exist locally. A novel method which allowed these variances to
be reflected in finite element reconstructions was established. This is believed to be an
important step in the improvement and accuracy of finite element studies. The
morphology and the regional variation in mechanical properties were both found to play
a key role in accurate wall stress calculations. An index, described as Regional Prestress
Rupture Index (RPRI), indicates that regional variations are important for accurate
rupture prediction. The knowledge of regional distribution of mechanical behaviour and
accurate wall dynamics has potential to be employed to improve the durability and long
term clinical performance of stent-grafts used for treating AAA. A novel and elegant
approach to compute the damage of the aorta using cardiac gated CT image data is also
presented. This technique can also be applied to analyse image data of patients with
cardiovascular disease and is not limited to the abdominal aorta. The study quantified
tissue damage due to aneurysm formation. Due to the high variations between
individual patients, this technique may represent a method of analysing patient-specific
changes. The results and conclusions presented through this thesis may further
contribute to the understanding of AAA biomechanics and rupture potential, and in the
future may help provide improved clinical guidance on surgical intervention for AAA
treatment.

Suggested citation:

Tierney, Áine P.; . () Noninvasive methods of characterising local regional variations in aortic tissue to advance aneurysm rupture risk prediction [Online]. Available from: http://www.thehealthwell.info/node/815425 [Accessed: 22nd July 2018].

  

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