Feasibility of wall stress analysis of abdominal aortic aneurysms using three-dimensional ultrasound.

OBJECTIVE: Abdominal aortic aneurysms (AAAs) are local dilations that can lead to a fatal hemorrhage when ruptured. Wall stress analysis of AAAs is a novel tool that has proven high potential to improve risk stratification. Currently, wall stress analysis of AAAs is based on computed tomography (CT) and magnetic resonance imaging; however, three-dimensional (3D) ultrasound (US) has great advantages over CT and magnetic resonance imaging in terms of costs, speed, and lack of radiation. In this study, the feasibility of 3D US as input for wall stress analysis is investigated. Second, 3D US-based wall stress analysis was compared with CT-based results. METHODS: The 3D US and CT data were acquired in 12 patients (diameter, 35-90 mm). US data were segmented manually and compared with automatically acquired CT geometries by calculating the similarity index and Hausdorff distance. Wall stresses were simulated at P = 140 mm Hg and compared between both modalities. RESULTS: The similarity index of US vs CT was 0.75 to 0.91 (n = 12), with a median Hausdorff distance ranging from 4.8 to 13.9 mm, with the higher values found at the proximal and distal sides of the AAA. Wall stresses were in accordance with literature, and a good agreement was found between US- and CT-based median stresses and interquartile stresses, which was confirmed by Bland-Altman and regression analysis (n = 8). Wall stresses based on US were typically higher (+23%), caused by geometric irregularities due to the registration of several 3D volumes and manual segmentation. In future work, an automated US registration and segmentation approach is the essential point of improvement before pursuing large-scale patient studies. CONCLUSIONS: This study is a first step toward US-based wall stress analysis, which would be the modality of choice to monitor wall stress development over time because no ionizing radiation and contrast material are involved.

Quantification of abdominal aortic aneurysm wall enhancement with dynamic contrast-enhanced MRI: feasibility, reproducibility, and initial experience.

PURPOSE: To investigate the feasibility and reproducibility of dynamic contrast-enhanced MRI (DCE-MRI) to quantify abdominal aortic aneurysm (AAA) vessel wall enhancement dynamics which may reflect the amount of wall microvasculature. AAA vessel wall microvasculature has been linked with aneurysm progression and rupture. MATERIALS AND METHODS: Thirty patients with AAA underwent DCE-MRI at 1.5 Tesla. Enhancement dynamics of the aneurysm wall were quantified in regions-of-interest (ROIs) in the vessel wall by calculating the transfer constant (K(trans) ) using pharmacokinetic modeling and the area-under-gadolinium-curve (AUC). To assess reproducibility, 10 patients were imaged twice on different occasions. ROIs were drawn by two independent observers. The intraclass correlation coefficients (ICC) and coefficients of variation (CV) were determined to investigate intra-, interobserver, and interscan variability. RESULTS: Twenty-eight analyzable MR examinations were included for pharmacokinetic analysis after excluding two examinations due to severe motion artifacts. Intra-, interobserver, and interscan variability for K(trans) were small (all ICC > 0.90, CV < 14%) as well as for AUC measurements (all ICC > 0.88, CV < 23%). CONCLUSION: Quantitative analysis of AAA vessel wall enhancement dynamics with DCE-MRI is feasible and reproducible.

Suitability of pharmacokinetic models for dynamic contrast-enhanced MRI of abdominal aortic aneurysm vessel wall: a comparison.

PURPOSE: Increased microvascularization of the abdominal aortic aneurysm (AAA) vessel wall has been related to AAA progression and rupture. The aim of this study was to compare the suitability of three pharmacokinetic models to describe AAA vessel wall enhancement using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). MATERIALS AND METHODS: Patients with AAA underwent DCE-MRI at 1.5 Tesla. The volume transfer constant (K(trans) ), which reflects microvascular flow, permeability and surface area, was calculated by fitting the blood and aneurysm vessel wall gadolinium concentration curves. The relative fit errors, parameter uncertainties and parameter reproducibilities for the Patlak, Tofts and Extended Tofts model were compared to find the most suitable model. Scan-rescan reproducibility was assessed using the interclass correlation coefficient and coefficient of variation (CV). Further, the relationship between K(trans) and AAA size was investigated. RESULTS: DCE-MRI examinations from thirty-nine patients (mean age±SD: 72±6 years; M/F: 35/4) with an mean AAA maximal diameter of 49±6 mm could be included for pharmacokinetic analysis. Relative fit uncertainties for K(trans) based on the Patlak model (17%) were significantly lower compared to the Tofts (37%) and Extended Tofts model (42%) (p<0.001). K(trans) scan-rescan reproducibility for the Patlak model (ICC = 0.61 and CV = 22%) was comparable with the Tofts (ICC = 0.61, CV = 23%) and Extended Tofts model (ICC = 0.76, CV = 22%). K(trans) was positively correlated with maximal AAA diameter (Spearman's ρ = 0.38, p = 0.02) using the Patlak model. CONCLUSION: Using the presented imaging protocol, the Patlak model is most suited to describe DCE-MRI data of the AAA vessel wall with good K(trans) scan-rescan reproducibility.