Comparison of Abdominal Aortic Aneurysm Sac and Neck Wall Motion with 4D Ultrasound Imaging

Abstract

WHAT THIS PAPER ADDSAfter developing the wall motion indices (WMIs), based on statistical analysis of 4D ultrasound strain imaging, previous studies have demonstrated the kinematic differences of aortic wall deformation according to age and cardiovascular pathology. In the current study, the pathological wall motion in the abdominal aortic aneurysm (AAA) is described for the first time. The specific kinematic properties of aneurysm neck and degenerated aneurysm bulge are characterised using WMIs and the regions with higher heterogeneity are identified. This is a promising step on the way to making additional individual patient information available for the evaluation of AAA stability.Objective: The rupture of abdominal aortic aneurysms (AAAs) is associated with high mortality despite surgical developments. The determination of aneurysm diameter allows for follow up of aneurysm growth but fails in precisely predicting aneurysm rupture. In this study, time resolved three dimensional ultrasound (4D ultrasound) based wall motion indices (WMIs) are investigated to see if they are capable of distinguishing between uneven affected regions of the aneurysm wall. Methods: In a prospective study, 56 patients with an AAA were examined using 4D ultrasound. Local longitudinal, circumferential, and shear strains were computed using custom methods. The deformation of the neck and sac of each aneurysm was characterised by statistical indices of the obtained distributions of local wall strains (WMIs): mean and peak strain, heterogeneity index, and local strain ratio. The locations of regions with highest local peak strain were determined. Results: Compared with the aneurysm neck, the sac is characterised by low mean strain, but highly heterogeneous deformation, described by high local strain ratio and heterogeneity index. Differences were highly significant (p < .001) for all strain components. The regions with the highest circumferential peak strain were found more often in the posterior part of the aneurysm neck (p < .050) and sac (p < .001) regions, compared with other wall regions. No statistically significant correlation was found between the WMIs and maximum AAA diameter, except for longitudinal mean strain, which decreased with the increasing diameter (rho ¼ À.42, p < .010). Conclusion: Characterisation of wall kinematics by 4D ultrasound based WMIs provides a new and independent criterion for the distinction of diseased tissue in the AAA sac and the less affected neck region. This is a promising step towards the establishment of new biomarkers to differentiate between the mechanical instability of the AAA and rupture risk.

Heterogeneity of Ex Vivo and In Vivo Properties along the Length of the Abdominal Aortic Aneurysm

“…In recent years, different studies highlighted the inadequacy of the diameter criterion by pointing out the high level of heterogeneity in the aneurysmal tissue and its impact on the risk of rupture of individual aortas [1][2][3][4][5]. Aneurysm initiation and progression are multifactorial processes linked to the tissue's heterogeneous remodeling and structural degradation in response to the local environment, including both mechanical (altered hemodynamics) and biological factors (inflammation, presence of intraluminal thrombus) [6][7][8].…”

Intra‐ and Interobserver Variability of 4D Ultrasound Examination of the Infrarenal Aorta

“…The use of 4D‐US provides information about the geometry of the aorta and local deformation of the aortic wall during the heart cycle. Such specific data about diastolic reference geometry and deformation enable biomechanical analyses with the characterization of the deformation pattern, determination of the patient‐individual material properties, 8 and description of the functional and morphological heterogeneity of the aortic wall in the healthy and aneurysmal aorta 6,9 …”

Is It Time to Move Beyond the 5.0/5.5 cm Diameter Thresholds for AAA Repair? Time Resolved Ultrasound Imaging for Assessment of AAA Wall Motion

“…Furthermore, analysis in the study by Derwich et al 1 was mainly based on AAAs with a diameter ranging from 3.0 to 5.5 cm and the absence of a significant correlation between WMI and AAA size is likely to reflect a type II statistical error. However, the management of fusiform degenerative aneurysms 4.0e5.5 cm in diameter has been effectively determined by four randomised controlled trials (including two larger trials of early open elective surgery vs. surveillance, UKSAT and ADAM, and two smaller trials of endovascular repair vs. surveillance, CAESAR and PIVOTAL).…”

“…However, the mechanism of rupture is a complex combination of physiological, biomechanical, histopathological, and genetic factors. In that sense, although the study by Derwich et al 1 was able to detect different biomechanical properties of AAA regions on a population based level, the absence of patient level data makes difficult the automatic extrapolation of the study findings to individual subject.…”

“…The new ultrasound speckle tracking technology, first developed in echocardiography, was applied by Derwich et al 1 to study abdominal aortic aneurysm (AAA) wall motion in 56 patients, using time resolved 3D ultrasound (i.e., 4D ultrasound). The aim of the study was to investigate whether 4D ultrasound based wall motion indices (WMIs) were able to distinguish between AAA regions with different deformation patterns in order to localise areas potentially more vulnerable to rupture.…”