Assessment of the Global and Regional Circumferential Strain of Abdominal Aortic Aneurysm with Different Size by Speckle-Tracking Echocardiography

Measurement of Abdominal Aortic Aneurysm Strain Using MR Deformable Image Registration: Accuracy and Relationship to Recent Aneurysm Progression

BACKGROUND

Management of asymptomatic abdominal aortic aneurysm (AAA) based on maximum aneurysm diameter and growth rate fails to preempt many ruptures. Assessment of aortic wall biomechanical properties may improve assessment of progression and rupture risk. This study aimed to assess the accuracy of AAA wall strain measured by cine magnetic resonance imaging (MRI) deformable image registration (MR strain) and investigate its relationship with recent AAA progression.

METHODS

The MR strain accuracy was evaluated in silico against ground truth strain in 54 synthetic MRIs generated from a finite element model simulation of an AAA patient's abdomen for different aortic pulse pressures, tissue motions, signal intensity variations, and image noise. Evaluation included bias with 95% confidence interval (CI) and correlation analysis. Association of MR strain with AAA growth rate was assessed in 25 consecutive patients with >6 months of prior surveillance, for whom cine balanced steady-state free-precession imaging was acquired at the level of the AAA as well as the proximal, normal-caliber aorta. Univariate and multivariate regressions were used to associate growth rate with clinical variables, maximum AAA diameter (D max ), and peak circumferential MR strain through the cardiac cycle. The MR strain interoperator variability was assessed using bias with 95% CI, intraclass correlation coefficient, and coefficient of variation.

RESULTS

In silico experiments revealed an MR strain bias of 0.48% ± 0.42% and a slope of correlation to ground truth strain of 0.963. In vivo, AAA MR strain (1.2% ± 0.6%) was highly reproducible (bias ± 95% CI, 0.03% ± 0.31%; intraclass correlation coefficient, 97.8%; coefficient of variation, 7.14%) and was lower than in the nonaneurysmal aorta (2.4% ± 1.7%). D max ( β = 0.087) and MR strain ( β = -1.563) were both associated with AAA growth rate. The MR strain remained an independent factor associated with growth rate ( β = -0.904) after controlling for D max .

CONCLUSIONS

Deformable image registration analysis can accurately measure the circumferential strain of the AAA wall from standard cine MRI and may offer patient-specific insight regarding AAA progression.

Using averaged models from 4D ultrasound strain imaging allows to significantly differentiate local wall strains in calcified regions of abdominal aortic aneurysms

Abdominal aortic aneurysms are a degenerative disease of the aorta associated with high mortality. To date, in vivo information to characterize the individual elastic properties of the aneurysm wall in terms of rupture risk is lacking. We have used time-resolved 3D ultrasound strain imaging to calculate spatially resolved in-plane strain distributions characterized by mean and local maximum strains, as well as indices of local variations in strains. Likewise, we here present a method to generate averaged models from multiple segmentations. Strains were then calculated for single segmentations and averaged models. After registration with aneurysm geometries based on CT-A imaging, local strains were divided into two groups with and without calcifications and compared. Geometry comparison from both imaging modalities showed good agreement with a root mean squared error of 1.22 ± 0.15 mm and Hausdorff Distance of 5.45 ± 1.56 mm (mean ± sd, respectively). Using averaged models, circumferential strains in areas with calcifications were 23.2 ± 11.7% (mean ± sd) smaller and significantly distinguishable at the 5% level from areas without calcifications. For single segmentations, this was possible only in 50% of cases. The areas without calcifications showed greater heterogeneity, larger maximum strains, and smaller strain ratios when computed by use of the averaged models. Using these averaged models, reliable conclusions can be made about the local elastic properties of individual aneurysm (and long-term observations of their change), rather than just group comparisons. This is an important prerequisite for clinical application and provides qualitatively new information about the change of an abdominal aortic aneurysm in the course of disease progression compared to the diameter criterion.

Fast strain mapping in abdominal aortic aneurysm wall reveals heterogeneous patterns

Abdominal aortic aneurysm patients are regularly monitored to assess aneurysm development and risk of rupture. A preventive surgical procedure is recommended when the maximum aortic antero-posterior diameter, periodically assessed on two-dimensional abdominal ultrasound scans, reaches 5.5 mm. Although the maximum diameter criterion has limited ability to predict aneurysm rupture, no clinically relevant tool that could complement the current guidelines has emerged so far. In vivo cyclic strains in the aneurysm wall are related to the wall response to blood pressure pulse, and therefore, they can be linked to wall mechanical properties, which in turn contribute to determining the risk of rupture. This work aimed to enable biomechanical estimations in the aneurysm wall by providing a fast and semi-automatic method to post-process dynamic clinical ultrasound sequences and by mapping the cross-sectional strains on the B-mode image. Specifically, the Sparse Demons algorithm was employed to track the wall motion throughout multiple cardiac cycles. Then, the cyclic strains were mapped by means of radial basis function interpolation and differentiation. We applied our method to two-dimensional sequences from eight patients. The automatic part of the analysis took under 1.5 min per cardiac cycle. The tracking method was validated against simulated ultrasound sequences, and a maximum root mean square error of 0.22 mm was found. The strain was calculated both with our method and with the established finite-element method, and a very good agreement was found, with mean differences of one order of magnitude smaller than the image spatial resolution. Most patients exhibited a strain pattern that suggests interaction with the spine. To conclude, our method is a promising tool for investigating abdominal aortic aneurysm wall biomechanics as it can provide a fast and accurate measurement of the cyclic wall strains from clinical ultrasound sequences.

Changes in Aortic Diameter and Wall Strain in Progressing Abdominal Aortic Aneurysms

OBJECTIVES

The analysis of wall strain opens new perspectives in the prediction of abdominal aortic aneurysm (AAA) rupture. This study investigates the capability of four-dimensional ultrasound (4D US) to detect and characterize changes in wall strain in the same patients during follow-up observations.

METHODS

Eighteen patients were examined by 64 4D US scans during a median follow-up period of 24.5 months. After performing the 4D US and manual aneurysm segmentation, kinematic analysis was performed using a customized interface and evaluation of the mean and peak circumferential strain, as well as spatial heterogeneity.

RESULTS

All aneurysms showed a continuous diameter growth with a mean rate of 4% per year (P < .001). The mean circumferential strain (MCS) tends to increase from a median 0.89% by 10.49% per year in follow-up independent of the aneurysm diameter (P = .063). The subgroup analysis reveals a cohort with increasing MCS and decreasing spatial heterogeneity, as well as a cohort with nonincreasing MCS and increasing spatial heterogeneity (P < .05).

CONCLUSIONS

The 4D US is able to register the strain changes in AAA follow-up. The MCS tends to increase during the observation time in the entire cohort, but the changes were independent of the maximum aneurysm diameter. The kinematic parameters allow the entire AAA cohort to differentiate into two subgroups and provide additional information about the pathologic behavior of the aneurysm wall.

Does types of atrial fibrillation matter in the impairment of global and regional left ventricular mechanics and intra-ventricular dyssynchrony?

Background

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, which is associated with cardiac dysfunction. This study aimed to compare the impairment severity of left ventricular strain and intra-ventricular dyssynchrony using echocardiography-derived velocity vector imaging in patients with different types of AF without heart failure.

Methods

168 non-valvular AF patients with normal left ventricular ejection fraction (98 paroxysmal AF patients and 70 persistent AF patients) and 86 healthy control subjects were included in this study. Regional and global left ventricular longitudinal and circumferential strain were measured. Time to regional peak longitudinal strain was measured and the standard deviation of all 12 segments (SDT-S) was used as a measure of intra-ventricular dyssynchrony.

Results

Significantly lower GLS (−18.71 ± 3.00% in controls vs. −17.10 ± 3.01% in paroxysmal AF vs. −12.23 ± 3.25% in persistent AF, P &lt; 0.05) and GCS (−28.75 ± 6.34% in controls vs. −24.43 ± 6.86% in paroxysmal AF vs. −18.46 ± 6.42% in persistent AF, P &lt; 0.01) were observed in either persistent AF subjects or paroxysmal AF subjects compared with healthy control subjects (P &lt; 0.05). The impairment was much worse in persistent AF subjects compared with paroxysmal AF subjects (P &lt; 0.001). Intraventricular dyssynchrony was found in both persistent AF patients and paroxysmal AF patients, and it’s worse in persistent AF patients (52 ± 18 ms in controls, 61 ± 17 ms in paroxysmal AF, and 70 ± 28 ms in persistent AF, P &lt; 0.05). Multivariate regression analysis revealed AF types were independent risk factors of GLS, GCS, and intraventricular dyssynchrony.

Conclusion

AF types were not only associated with impaired longitudinal and circumferential left ventricle mechanics but also intra-ventricular mechanical dyssynchrony. Worse systolic mechanics and intra-ventricular dyssynchrony were found in patients with persistent AF compared with these in patients with paroxysmal AF.