Quantification of abdominal aortic aneurysm stiffness using magnetic resonance elastography and its comparison to aneurysm diameter

Abstract

Objective Abdominal aortic aneurysm (AAA) wall stiffness has been suggested to be an important factor in the overall rupture risk assessment compared to anatomical measure; we hypothesize that AAA diameter will have no correlation to AAA wall stiffness. The aim of this study is to 1) determine MRE-derived aortic wall stiffness in AAA patients and its correlation to AAA diameter; 2) determine correlation between AAA stiffness and amount of thrombus and calcium; and 3) compare the AAA stiffness measurements against age matched healthy subjects. Methods In-vivo abdominal aortic MRE was performed on 36 subjects (24 patients with AAA measuring 3-10 cm and 12 healthy volunteers) aged 36-78 years old after obtaining written informed consent under the approval of the institutional review board. MRE images were processed to obtain spatial stiffness maps of the aorta. AAA diameter, amount of thrombus and calcium score were reported by experienced interventional radiologists. Spearman correlation, Wilcoxon signed rank test and Mann-Whitney test were performed to determine the correlation between AAA stiffness and diameter, and also to determine significant difference in stiffness measurements between AAA patients and healthy subjects. Results No significant correlation (P>.1) was found between AAA stiffness and diameter or amount of thrombus or calcium score. AAA stiffness (mean:13.97±4.2kPa) is significantly (P≤.02) higher than remote normal aorta in AAA (mean:8.87±2.2kPa) patients and in normal subjects (mean:7.1±1.9kPa). Conclusion Our results suggest that AAA wall stiffness may provide additional information independent of AAA diameter, which may contribute to our understanding of AAA pathophysiology, biomechanics, and risk for rupture.

In vivo quantification of aortic stiffness using MR elastography in hypertensive porcine model

“…The stiffness values reported in this work are in the range of previously published results . However, the stiffness values obtained in this study cannot directly be compared to previous results because those were from both human subjects and ex vivo animal models performed at different mechanical excitation frequencies. Moreover, Young's modulus‐wall thickness product was studied in some of the earlier studies instead of MRE‐derived effective stiffness of the aorta, which was reported in this work.…”

“…This principle provides the opportunity to avoid high spatial‐resolution imaging just to demonstrate the aortic wall. This technique also reported robust stiffness values: 1) with good reproducibility in healthy human subjects ; 2) in evaluating abdominal aortic aneurysms ; 3) in showing significant difference between normotensive and hypertensive human subjects ; and 4) with good correlation against PWV and increase in stiffness as a function of age .…”

“…The effective stiffness of the aorta was evaluated at each cardiac phase in this work, providing a better understanding of temporal variation of aortic stiffness throughout the entire cardiac cycle. The changes in the stiffness during a cardiac cycle are critical in many diseases, such as aneurysm formation, because they provide the information on pressure loading during systolic and diastolic phase, which can eventually lead to aneurysmal rupture . In addition, the changes in compliance of the aorta due to different disease conditions such as atherosclerosis or Marfan syndrome also can alter the pressure within the aorta .…”

Cardiovascular magnetic resonance elastography: A review

“…Aortic MRE was performed on 25 patients with AAA and on 12 age‐matched normal volunteers . It was shown that AAA stiffness (mean stiffness, 13.97 kPa) was significantly higher than age‐matched normal aortic stiffness (mean stiffness, 8.87 kPa).…”

“…No clear relationship can be observed between aortic diameter and stiffness. Reproduced with permission from Kolipaka et al…”