Towards A Noninvasive Method for Determination of Patient-Specific Wall Strength Distribution in Abdominal Aortic Aneurysms

Abstract

The spatial distributions of both wall stress and wall strength are required to accurately evaluate the rupture potential for an individual abdominal aortic aneurysm (AAA). The purpose of this study was to develop a statistical model to non-invasively estimate the distribution of AAA wall strength. Seven parameters--namely age, gender, family history of AAA, smoking status, AAA size, local diameter, and local intraluminal thrombus (ILT) thickness--were either directly measured or recorded from the patients hospital chart. Wall strength values corresponding to these predictor variables were calculated from the tensile testing of surgically procured AAA wall specimens. Backwards-stepwise regression techniques were used to identify and eliminate insignificant predictors for wall strength. Linear mixed-effects modeling was used to derive a final statistical model for AAA wall strength, from which 95% confidence intervals on the model parameters were formed. The final statistical model for AAA wall strength consisted of the following variables: sex, family history, ILT thickness, and normalized transverse diameter. Demonstrative application of the model revealed a unique, complex wall strength distribution, with strength values ranging from 56 N/cm2 to 133 N/cm2. A four-parameter statistical model for the noninvasive estimation of patient-specific AAA wall strength distribution has been successfully developed. The currently developed model represents a first attempt towards the noninvasive assessment of AAA wall strength. Coupling this model with our stress analysis technique may provide a more accurate means to estimate patient-specific rupture potential of AAA.

Patient-Based Abdominal Aortic Aneurysm Rupture Risk Prediction with Fluid Structure Interaction Modeling

“…The latter involves information that is not readily available, but can be indirectly estimated by factoring in biomechanical and clinical parameters, as well as the medical history of the specific patient. The RPI 55 that was incorporated in our methodology is a first step toward achieving such an estimate. The strength mapping that we have conducted clearly indicated that wall strength was significantly reduced at the aneurysmal bulge, compromising the integrity of the aortic wall (Fig.…”

“…55 There is a significant reduction in AAAs wall tensile strength as compared to non-aneurysmal tissue. 40 Recent ex-vivo studies of AAA biomechanical properties focused on the extracellular matrix structure and basic properties related to wall stiffness.…”

“…55 It lumps together significant clinical and geometric predictors to yield a local value of the wall strength, Eq. (6): Strength ¼ 71:9 À 37:9 ILT 1=2 À 0:81…”

Computational Growth and Remodeling of Abdominal Aortic Aneurysms Constrained by the Spine

“…The effects of the intraluminal thrombus (ILT) thickness, sex, family history, and smoking on the AAA strength have been well examined in computational models of AAAs [3,50]. In addition, Di Martino et al [51] suggested a weak (but significant) negative correlation (R ¼ À0.42 and P ¼ 0.012) between the AAA wall thickness and its tensile strength.…”

“…We speculate that the inclusion of bending stiffness in our analysis intensifies the effects of spine contact on the morphology, wall stress distribution, and PWS, beyond what we observed in this study. Accurate measures of wall strength are yet to be considered in our analysis for a reliable assessment of rupture [50,51,57,58]. Our simulation cases represent hypothetical models of AAAs initiated by artificial elastin degradation in a healthy aorta instead of the real elastin loss in a patient's AAA wall.…”