Magnetic resonance imaging assessment of proteolytic enzyme concentrations and biologic properties of intraluminal thrombus in abdominal aortic aneurysms

Objective: The aim of the study was to determine whether magnetic resonance imaging (MRI) can be used in assessment of biologic activity of intraluminal thrombus (ILT) and proteolytic processes of the abdominal aortic aneurysm wall. Methods: Using MRI, 50 patients with asymptomatic infrarenal abdominal aortic aneurysm were analyzed at the maximum aneurysm diameter on Tl-weighted images in the arterial phase after administration of contrast material. Relative ILT signal intensity (SI) was determined as the ratio between ILT SI and psoas muscle SI. During surgery, the full thickness of the ILT and the adjacent part of the aneurysm wall were harvested at the maximal diameter for biochemical analysis. The concentrations of matrix metalloproteinase 9 and neutrophil elastase (NE/ELA) were analyzed in harvested thrombi, and the concentrations of collagen type III, elastin, and proteoglycans were analyzed in harvested aneurysm walls. Results: A significant positive correlation was found between the NE/ELA concentration of the ILT and the relative SI (rho = 0.309; P= .029). Furthermore, a negative correlation was observed between the elastin content of the aneurysm wall and the relative SI (rho = -0.300; P = .034). No correlations were found between relative SI and concentration of matrix metalloproteinase 9, NE/ELA, collagen type III, or proteoglycan 4 in the aneurysm wall. Conclusions: These findings indicate a potential novel use of MRI in prediction of thrombus proteolytic enzyme concentrations and the extracellular matrix content of the aneurysm wall, thus providing additional information for the risk of potential aneurysm rupture.