Endovascular Repair of Abdominal Aortic Aneurysm: Follow-up with Noninvasive Vascular Elastography in a Canine Model

Strain Ultrasound Elastography of Aneurysm Sac Content after Randomized Endoleak Embolization with Sclerosing and Non-sclerosing Chitosan-based Hydrogels in a Canine Model

PURPOSE

To compare the mechanical properties of aneurysm content after endoleak embolization with a chitosan hydrogel (CH) versus a chitosan hydrogel with sodium tetradecyl sulphate (CH-STS) using strain ultrasound elastography (SUE).

MATERIALS AND METHODS

Bilateral common iliac artery type Ia endoleaks were created in nine dogs. Per animal, one endoleak was randomized to blinded embolization with CH, and the other, with CH-STS. Brightness mode ultrasound, Doppler ultrasound, SUE radiofrequency ultrasound, and computed tomography were performed for up to six months until sacrifice. Radiological and histopathological studies were co-registered to identify three regions of interest: embolic agent, intraluminal thrombus (ILT), and aneurysm sac. SUE segmentations were performed by two blinded, independent observers. Maximum axial strain (MAS) was the primary outcome. Statistical analysis was performed using Fisher's exact test, multivariable linear mixed-effects models, and intraclass correlation coefficients (ICCs).

RESULTS

Residual endoleaks were identified in 7/9 (78%) and 4/9 (44%) aneurysms embolized with CH and CH-STS, respectively (p=0.3348). CH-STS had 66% lower MAS (p<0.001) than CH. The ILT had 37% lower MAS (p=0.01) than CH and 77% greater MAS (p=0.079) than CH-STS. There was no significant difference in ILT between treatments. Aneurysm sacs embolized with CH-STS had 29% lower MAS (p<0.001) than those embolized with CH. Residual endoleak was associated with 53% greater aneurysm sac MAS (p<0.001). The ICC for MAS was 0.807 (95% confidence interval: 0.754-0.849) between segmentations.

CONCLUSION

CH-STS confers stiffer intraluminal properties to embolized aneurysms. Persistent endoleaks are associated with increased sac strain, an observation which may help guide management.

Deformability of ascending thoracic aorta aneurysms assessed using ultrafast ultrasound and a principal strain estimator: In vitro evaluation and in vivo feasibility

BACKGROUND

Noninvasive vascular strain imaging under conventional line-by-line scanning has a low frame rate and lateral resolution, and depends on the coordinate system. It is thus affected by high deformations due to image decorrelation between frames.

PURPOSE

To develop an ultrafast time-ensemble regularized tissue-Doppler optical-flow principal strain estimator for aorta deformability assessment in a long-axis view.

METHODS

This approach alleviated the impact of lateral resolution using image compounding and that of the coordinate system dependency using principal strain. Accuracy and feasibility were evaluated in two aorta-mimicking phantoms first, and then in four age-matched individuals with either a normal aorta or a pathological ascending thoracic aorta aneurysm (TAA).

RESULTS

Instantaneous aortic maximum and minimum principal strain maps and regional accumulated strains during each cardiac cycle were estimated at systolic and diastolic phases to characterize the normal aorta and TAA. In vitro, principal strain results matched sonomicrometry measurements. In vivo, a significant decrease in maximum and minimum principal strains was observed in TAA cases, whose range was respectively 7.9 ± 6.4% and 8.2 ± 2.6% smaller than in normal aortas.

CONCLUSIONS

The proposed principal strain estimator showed an ability to potentially assess TAA deformability, which may provide an individualized and reliable evaluation method for TAA rupture risk assessment. This article is protected by copyright. All rights reserved.

Feasibility of shear wave sonoelastography to detect endoleak and evaluate thrombus organization after endovascular repair of abdominal aortic aneurysm

PURPOSE

To investigate the feasibility of shear wave sonoelastography (SWS) for endoleak detection and thrombus characterization of abdominal aortic aneurysm (AAA) after endovascular repair (EVAR).

MATERIALS AND METHODS

Participants who underwent EVAR were prospectively recruited between November 2014 and March 2016 and followed until March 2019. Elasticity maps of AAA were computed using SWS and compared to computed tomography angiography (CTA) and color Doppler ultrasound (CDUS). Two readers, blinded to the CTA and CDUS results, reviewed elasticity maps and B-mode images to detect endoleaks. Three or more CTAs per participant were analyzed: pre-EVAR, baseline post-EVAR, and follow-ups. The primary endpoint was endoleak detection. Secondary endpoints included correlation between total thrombus elasticity, proportion of fresh thrombus, and aneurysm growth between baseline and reference CTAs. A 3-year follow-up was made to detect missed endoleaks, EVAR complication, and mortality. Data analyses included Cohen's kappa; sensitivity, specificity, and positive predictive value (PPV); Pearson coefficient; and Student's t tests.

RESULTS

Seven endoleaks in 28 participants were detected by the two SWS readers (k = 0.858). Sensitivity of endoleak detection with SWS was 100%; specificity and PPV averaged 67% and 50%, respectively. CDUS sensitivity was estimated at 43%. Aneurysm growth was significantly greater in the endoleak group compared to sealed AAAs. No correlation between growth and thrombus elasticity or proportion of fresh thrombus in AAAs was found. No new endoleaks were observed in participants with SWS negative studies.

CONCLUSION

SWS has the potential to detect endoleaks in AAA after EVAR with comparable sensitivity to CTA and superior sensitivity to CDUS.

KEY POINTS

• Dynamic elastography with shear wave sonoelastography (SWS) detected 100% of endoleaks in abdominal aortic aneurysm (AAA) follow-up that were identified by a combination of CT angiography (CTA) and color Doppler ultrasound (CDUS). • Based on elasticity maps, SWS differentiated endoleaks from thrombi within the aneurysm sac (p < 0.001). • After 3-year follow-up, no new endoleaks were observed in SWS negative examinations.

Adaptive Pulse Wave Imaging: Automated Spatial Vessel Wall Inhomogeneity Detection in Phantoms and in-Vivo

Imaging arterial mechanical properties may improve vascular disease diagnosis. Pulse wave velocity (PWV) is a marker of arterial stiffness linked to cardio-vascular mortality. Pulse wave imaging (PWI) is a technique for imaging the pulse wave propagation at high spatial and temporal resolution. In this paper, we introduce adaptive PWI, a technique for the automated partition of heterogeneous arteries into individual segments characterized by most homogeneous pulse wave propagation, allowing for more robust PWV estimation. This technique was validated in a silicone phantom with a soft-stiff interface. The mean detection error of the interface was 4.67 ± 0.73 mm and 3.64 ± 0.14 mm in the stiff-to-soft and soft-to-stiff pulse wave transmission direction, respectively. This technique was tested in monitoring the progression of atherosclerosis in mouse aortas in vivo ( n = 11 ). The PWV was found to already increase at the early stage of 10 weeks of high-fat diet (3.17 ± 0.67 m/sec compared to baseline 2.55 ± 0.47 m/sec, ) and further increase after 20 weeks of high-fat diet (3.76±1.20 m/sec). The number of detected segments of the imaged aortas monotonically increased with the duration of high-fat diet indicating an increase in arterial wall property inhomogeneity. The performance of adaptive PWI was also tested in aneurysmal mouse aortas in vivo. Aneurysmal boundaries were detected with a mean error of 0.68±0.44 mm. Finally, initial feasibility was shown in the carotid arteries of healthy and atherosclerotic human subjects in vivo ( n = 3 each). Consequently, adaptive PWI was successful in detecting stiffness inhomogeneity at its early onset and monitoring atherosclerosis progression in vivo.

Abdominal aortic aneurysm follow-up by shear wave elasticity imaging after endovascular repair in a canine model

OBJECTIVES

To investigate if shear wave imaging (SWI) can detect endoleaks and characterize thrombus organization in abdominal aortic aneurysms (AAAs) after endovascular aneurysm repair.

METHODS

Stent grafts (SGs) were implanted in 18 dogs after surgical creation of type I endoleaks (four AAAs), type II endoleaks (13 AAAs) and no endoleaks (one AAA). Color flow Doppler ultrasonography (DUS) and SWI were performed before SG implantation (baseline), on days 7, 30 and 90 after SG implantation, and on the day of the sacrifice (day 180). Angiography, CT scans and macroscopic tissue sections obtained on day 180 were evaluated for the presence, size and type of endoleaks, and thrombi were characterized as fresh or organized. Endoleak areas in aneurysm sacs were identified on SWI by two readers and compared with their appearance on DUS, CT scans and macroscopic examination. Elasticity moduli were calculated in different regions (endoleaks, and fresh and organized thrombi).

RESULTS

All 17 endoleaks (100 %) were identified by reader 1, whereas 16 of 17 (94 %) were detected by reader 2. Elasticity moduli in endoleaks, and in areas of organized thrombi and fresh thrombi were 0.2 ± 0.4, 90.0 ± 48.2 and 13.6 ± 4.5 kPa, respectively (P < 0.001 between groups). SWI detected endoleaks while DUS (three endoleaks) and CT (one endoleak) did not.

CONCLUSIONS

SWI has the potential to detect endoleaks and evaluate thrombus organization based on the measurement of elasticity.

KEY POINTS

• SWI has the potential to detect endoleaks in post-EVAR follow-up. • SWI has the potential to characterize thrombus organization in post-EVAR follow-up. • SWI may be combined with DUS in post-EVAR surveillance of endoleak.