Abstract 493: Ultrasound-Based Image Registration Algorithm for Measuring Regional Wall Strain Changes Leading to Abdominal Aortic Aneurysm Rupture

Abstract

OBJECTIVES: Size-based assessments of AAA do not accurately identify rupture risk. AAA rupture potential is related to wall failure which is dependent on material properties and compliance. Our hypothesis is that transcutaneous ultrasound (US) regional strain measurements can be used to quantify changes in aortic wall mechanical properties indicative of an increase in rupture risk. METHODS: A patient-specific AAA cryogel phantom was fabricated and mechanical compliance and tested on an in vitro hemodynamic simulator. A Sonix-Touch system imaged the phantom through the maximum axial diameter under physiologic, pulsatile conditions with increasing mean arterial pressure (MAP) of 95, 120, 140, 160, and 180 until rupture (200mmHg). An US image registration algorithm was used to measure the circumferential wall strain from systole to diastole. RESULTS: The spatial mean of the circumferential wall strain (%) in the known location of rupture (solid box) decreased from 2.7, 2.0, 2.4, 1.7, 1.6, and 1.2 for MAP of 95, 120, 141, 160, 180 and 200 mm Hg (rupture) respectively. For comparison the mean strain levels in the adjacent wall of the aneurysm (dashed) were 3.4, 3.4, 3.0, 3.2, 2.1 and 1.8 for the same MAP. The mean diameter of the AAA increased from 5.48cm, 5.83cm, 6.13cm, 6.34cm, 6.54cm, and 6.69cm (rupture) over the range of MAP. CONCLUSIONS: At the location of eventual rupture, the mean regional strain decreased as the diameter of the phantom enlarged and progressed to rupture relative to other regions of the wall. This suggests the possibility of applying regional AAA wall strain as a more accurate method of predicting AAA rupture risk.