Standardized 2D ultrasound versus 3D/4D ultrasound and image fusion for measurement of aortic aneurysm diameter in follow-up after EVAR

Deep learning-based segmentation of abdominal aortic aneurysms and intraluminal thrombus in 3D ultrasound images

Ultrasound (US)-based patient-specific rupture risk analysis of abdominal aortic aneurysms (AAAs) has shown promising results. Input for these models is the patient-specific geometry of the AAA. However, segmentation of the intraluminal thrombus (ILT) remains challenging in US images due to the low ILT-blood contrast. This study aims to improve AAA and ILT segmentation in time-resolved three-dimensional (3D + t) US images using a deep learning approach. In this study a "no new net" (nnU-Net) model was trained on 3D + t US data using either US-based or (co-registered) computed tomography (CT)-based annotations. The optimal training strategy for this low-contrast data was determined for a limited dataset. The merit of augmentation was investigated, as well as the inclusion of low-contrast areas. Segmentation results were validated with CT-based geometries as the ground truth. The model trained on CT-based masks showed the best performance in terms of DICE index, Hausdorff distance, and diameter differences, covering a larger part of the AAA. With a higher accuracy and less manual input the model outperforms conventional methods, with a mean Hausdorff distance of 4.4 mm for the vessel and 7.8 mm for the lumen. However, visibility of the lumen-ILT interface remains the limiting factor, necessitating improvements in image acquisition to ensure broader patient inclusion and enable rupture risk assessment of AAAs in the future.

Evaluating the feasibility of contrast-enhanced ultrasound for detecting after preemptive coiling endoleaks in endovascular aortic aneurysm repair: A pilot study

Endovascular aortic aneurysm repair is widely used for the treatment of abdominal aortic aneurysm (AAA), but has a 10% to 40% incidence of type II endoleak during follow-up. There are various techniques to treat these endoleaks in the case of enlarging of the AAA, but the clinical effectiveness is low. In recent years, preemptive AAA sac embolization has shown some encouraging results with significant AAA shrinkage. However, the presence of embolic material can complicate continued endoleak detection making assessment of treatment outcome difficult. We investigate the ability of contrast-enhanced-ultrasound examination to detect endoleaks in patients undergoing preemptive coil embolization of the AAA sac.

Automatic Segmentation and Mechanical Characterisation of the Intraluminal Thrombus and Arterial Wall of Abdominal Aortic Aneurysms Using Time Resolved 3D Ultrasound Images

OBJECTIVE

This study proposed a method for semi-automatic segmentation of abdominal aortic aneurysms (AAAs) and their intraluminal thrombus (ILT), based on time resolved 3D ultrasound (US), and validated results with computed tomography (CT). Mechanical properties of both wall and ILT were determined, and possible correlations with ILT size and blood pressure were investigated.

METHODS

A semi-automatic segmentation algorithm was developed combining a star-Kalman approach with a 3D snake algorithm. The segmented geometries of both lumen and inner vessel wall were validated with both manual US based segmentations and CT based segmentations. Finally, the lumen and vessel wall distensibility and ILT compressibility were estimated and correlated with ILT size and blood pressure.

RESULTS

For the vessel wall and lumen, the median Similarity Index (SI) was 92% (IQR 90, 94%) and 83% (IQR 75, 87%), respectively. The distensibility of the vessel wall could be determined in 37 of 40 cases and had a median value of 0.28 10-5 Pa-1 (IQR 0.18, 0.51 ×10-5). The median systolic to diastolic volume change of the ILT was determined successfully in 21 of 40 patients, and was -0.57% (IQR -1.1, 1.2%). The vessel and lumen distensibility showed a strong correlation with the systolic pressure (p < .010), rather than with the diastolic pressure. Lumen distensibility was strongly correlated with ILT thickness (p = .023). The performance of the semi-automatic segmentation algorithm was shown to be as good as the manual segmentations and highly dependent on the visibility of the ILT (limited contrast in seven patients and clutter in nine patients).

CONCLUSION

This study has shown promising results for mechanical characterisation of the vessel, and ILT, including a correlation between distensibility, ILT size, and blood pressure. For future work, the inclusion rate needs to be increased by improving the image contrast with novel US techniques.

Sonographic 3-D Power Doppler Imaging Enhances Rapid Assessment of Morphologic and Pathologic Arteriovenous Fistula Variations

Early detection of pathologic variations in an arteriovenous fistula (AVF) is essential for preventing fistula dysfunction in individuals undergoing hemodialysis. This study aimed to evaluate the clinical applicability of 3-D tomographic ultrasound (tUS) for rapid and simple visualization of AVF morphology and pathology. We assessed 53 AVFs in 50 consecutive patients using 3-D tUS including secondary, blinded reading. For all examinations, a high-end ultrasound (US) device was used with linear probe, attached to a tUS system to allow freehand 3-D scanning. Participants were examined by 2-D US and 3-D tUS with different raw data (B-mode, power Doppler, B-flow). Additional angiography was available for 15 participants with scheduled interventions. In all participants, 3-D tUS allowed a 3-D representation of AVFs in angiographic-like images with good image quality. The 2-D US assessment took 7.9 ± 4.0 min. A 3-D power Doppler scan required, on average, 1.4 ± 0.6 min. Diagnostic accuracy of blinded reading for pathologies was high (86.8% for aneurysms and 79.2% for stenoses). Bland-Altman plots showed an excellent correlation of 3-D tUS with 2-D US and angiography. 3-D tUS is an easily and rapidly applicable method for visualizing morphologic and pathologic AVF variations. Color-coded 3-D reconstruction of power Doppler data simplifies detection of perfused aneurysms and stenoses.

Evaluation of a novel tomographic ultrasound device for abdominal examinations

Conventional ultrasound (US) is the first-line imaging method for abdominal pathologies, but its diagnostic accuracy is operator-dependent, and data storage is usually limited to two-dimensional images. A novel tomographic US system (Curefab CS, Munich, Germany) processes imaging data combined with three-dimensional spatial information using a magnetic field tracking. This enables standardized image presentation in axial planes and a review of the entire examination. The applicability and diagnostic performance of this tomographic US approach was analyzed in an abdominal setting using conventional US as reference. Tomographic US data were successfully compiled in all subjects of a training cohort (20 healthy volunteers) and in 50 patients with abdominal lesions. Image quality (35% and 79% for training and patient cohort respectively) and completeness of organ visualization (45% and 44%) were frequently impaired in tomographic US compared to conventional US. Conventional and tomographic US showed good agreement for measurement of organ sizes in the training cohort (right liver lobe and both kidneys with a median deviation of 5%). In the patient cohort, tomographic US identified 57 of 74 hepatic or renal lesions detected by conventional ultrasound (sensitivity 77%). In conclusion, this study illustrates the diagnostic potential of abdominal tomographic US, but current significant limitations of the tomographic ultrasound device demand further technical improvements before this and comparable approaches can be implemented in clinical practice.

Contrast-enhanced ultrasound of the abdominal aorta - current status and future perspectives

Ultrasound has been established as an important diagnostic tool in assessing vascular abnormalities. Standard B-mode and Doppler techniques have inherent limitations with regards to detection of slow flow and small vasculature. Contrast-enhanced ultrasound (CEUS) is a complementary tool and is useful in assessing both the macro- and microvascular anatomy of the aorta. CEUS can also provide valuable physiological information in real-time scanning sessions due to the physical and safety profiles of the administered microbubbles. From a macrovascular perspective, CEUS has been used to characterize aortic aneurysm rupture, dissection and endoleaks post-EVAR repair. With regard to microvasculature CEUS enables imaging of adventitial vasa vasorum thereby assessing aortic inflammation processes, such as monitoring treatment response in chronic periaortitis. CEUS may have additional clinical utility since adventitial vasa vasorum has important implications in the pathogenesis of aortic diseases. In recent years, there have been an increasing number of studies comparing CEUS to cross-sectional imaging for aortic applications. For endoleak surveillance CEUS has been shown to be equal or in certain cases superior in comparison to CT angiography. The recent advancement of CEUS software along with the ongoing development of drug-eluting contrast microbubbles has allowed improved targeted detection and real-time ultrasound guided therapy for aortic vasa vasorum inflammation and neovascularization in animal models. Therefore, CEUS is uniquely suited to comprehensively assess and potentially treat aortic vascular diseases in the future.

Late-onset type I endoleak characterized by contrast enhanced ultrasound after endovascular repair of aortic aneurysm

We report in the case of a patient with an intra-abdominal aortic aneurysm treated with endovascular aneurysm repair (EVAR) who developed renal impairment during the period of follow up. The repair was complicated with an early-onset type II endoleak which later evolved into a late-onset type I endoleak. It was treated with proximal extension of stent graft, with treatment success and follow-up documented on contrast enhanced ultrasound (CEUS). This case illustrates the usefulness of CEUS in post-EVAR surveillance and emphasizes the need for life-long monitoring as late-onset complications are not uncommon.

Ultrasound fusion imaging with real-time navigation for the surveillance after endovascular aortic aneurysm repair

Ultrasound can be an effective alternative to computed tomography for surveillance following endovascular aneurysm repair (EVAR). Recently, ultrasound fusion imaging with the real-time navigation system was introduced. Here we described 3 patients who underwent post-EVAR surveillance using this novel technique. Complete coregistration was achieved in all patients. The origin of left renal artery was selected for the target of coregistration. Ultrasound fusion imaging was useful to differentiate the confusing lesion and to evaluate the complete resolution of endoleak and newly developed delayed endoleak. Ultrasound fusion image with real-time navigation system can be a feasible imaging tool for post-EVAR surveillance.

A Review on Real-Time 3D Ultrasound Imaging Technology

Real-time three-dimensional (3D) ultrasound (US) has attracted much more attention in medical researches because it provides interactive feedback to help clinicians acquire high-quality images as well as timely spatial information of the scanned area and hence is necessary in intraoperative ultrasound examinations. Plenty of publications have been declared to complete the real-time or near real-time visualization of 3D ultrasound using volumetric probes or the routinely used two-dimensional (2D) probes. So far, a review on how to design an interactive system with appropriate processing algorithms remains missing, resulting in the lack of systematic understanding of the relevant technology. In this article, previous and the latest work on designing a real-time or near real-time 3D ultrasound imaging system are reviewed. Specifically, the data acquisition techniques, reconstruction algorithms, volume rendering methods, and clinical applications are presented. Moreover, the advantages and disadvantages of state-of-the-art approaches are discussed in detail.

Contrast-enhanced ultrasound to evaluate organ microvascularization after operative versus endovascular treatment of visceral artery aneurysms

PURPOSE

To evaluate the organ microvascularization after operative versus endovascular treatment of visceral artery aneurysms (VAAs) by contrast-enhanced ultrasound (CEUS) and colour-coded duplex sonography (CCDS).

METHOD AND MATERIALS

Between April 1995 to January 2016, 168 patients (78 males, 90 females; median age: 62 years) were diagnosed with VAAs at our hospital site. 60/168 patients (36%) fulfilled treatment criteria and had either open (29/60, 48%) or endovascular (31/60, 52%) aneurysm repair. Patients' characteristics and presentations were consecutively reviewed. Technical success and organ microvascularization were determined by CCDS/CEUS and correlated to computed tomography angiography (CTA) or magnetic resonance imaging (MRI).

RESULTS

18/60 patients (30%) presented with acute bleeding. 16/18 emergency patients (89%) were treated by endovascular means. After emergency treatment, two patients showed segmental liver malperfusion by CEUS and CTA. One small bowel resection had to be performed.42/60 patients (70%) were electively treated. 27/42 patients (64%) had open and 15/42 (36%) endovascular aneurysm repair. There were no liver or bowel infarctions after elective treatment of hepatic or mesenteric artery aneurysms (n = 13) in CCDS/CEUS and in CTA. Treatment of patients with splenic or renal artery aneurysms led to partial or complete organ loss in 42% (8/19) after operative and in 50% (5/10) after endovascular treatment (p < 0.05).

CONCLUSION

The endovascular approach is the preferred therapeutic option in emergency to control bleeding. In contrast to hepatic or mesenteric procedures, patients for elective splenic or renal artery aneurysm repair have to be evaluated very carefully because of a high rate of partial or complete organ loss demonstrated by CEUS - either after open or endovascular aneurysm repair.