"Abdominal aortic aneurysms: a biomechanical approach "
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Abstract: Abdominal aortic aneurysms (AAA) are characterized by structural remodeling resulting in the gradual weakening and expansion of the aortic wall.  AAA can typically remain stable until the strength of the aortic wall is unable to withstand the forces acting on it as a result of the luminal blood pressure, resulting in AAA rupture.  Since AAAs are often times asymptomatic, impending AAA rupture can be without warning. 

The clinical treatment of AAA patients presents a dilemma for the surgeon: surgery should only be recommended when the risk of rupture of the AAA outweighs the risks associated with the interventional procedure.

Our FEM-based AAA wall stress analysis technique has undergone several stages of improvement since our original report. These have included the inclusion of the commonly found intraluminal thrombus (ILT) and the anisotropic AAA tissue behavior into the computer models of AAA.  Though these changes have lead to improvements of estimations of AAA wall stress over previous techniques, this quantity alone is theoretically insufficient to predict AAA rupture potential.  That is, since AAA rupture occurs when the stress acting on the wall exceeds its strength, the prediction of AAA rupture should include both the wall stress distribution as well as the wall strength distribution.  To facilitate this, we have developed techniques for non-invasively estimating AAA wall strength distribution.  We may then define a rupture potential index (RPI) as the ratio of the acting wall stress to the wall strength.  Therefore, the maximum RPI value for a particular AAA would represent its rupture potential.  When the RPI approaches a value of 1, rupture of that AAA would be imminent.  We believe the RPI to be a more reliable criterion than those previously proposed for assessing patient-specific rupture potential, including the widely accepted maximum transverse diameter criterion.