Sizing for endovascular aneurysm repair: clinical evaluation of a new automated three-dimensional software

Influence of Patient Anatomy on Intraoperative Radiation Exposure and Operation Time during Standard EVAR

Endovascular aortic repair (EVAR) is the primary treatment for abdominal aortic aneurysms (AAAs). To optimise patient safety during the standard EVAR procedure, we aimed to investigate the influence of patient anatomy on intraoperative radiation exposure and surgical time. This retrospective study comprised 90 patients (mean age 73.4 ± 8.2 years; 92.2% male) with an infrarenal aortic aneurysm who underwent a standard EVAR procedure. The relationships between dose area product, operating time, and anatomical conditions were investigated in preoperative computed tomography angiography using open-source software. Logistic regression analysis indicated that only body mass index (BMI) had predictive value for radiation exposure. The accuracy of the model was 98.67%, with an area under the curve of 0.72. The duration of surgery was significantly correlated with an increased BMI (odds ratio (OR) = 1.183; p < 0.05), the tortuosity of AAAs (OR = 1.124; p < 0.05), and the left common iliac artery (OR = 1.028; p < 0.05). Thus, BMI impacts the prediction of intraoperative radiation exposure more significantly than the anatomical characteristics of the infrarenal aorta and iliac arteries, and the duration of surgery significantly correlates with both BMI and the tortuosity of the infrarenal aorta and iliac arteries.

Mature artificial intelligence- and machine learning-enabled medical tools impacting vascular surgical care: A scoping review of late-stage, US Food and Drug Administration-approved or cleared technologies relevant to vascular surgeons

Artificial intelligence and machine learning (AI/ML)-enabled tools are shifting from theoretical or research-only applications to mature, clinically useful tools. The goal of this article was to provide a scoping review of the most mature AI/ML-enabled technologies reviewed and cleared by the US Food and Drug Administration relevant to the field of vascular surgery. Despite decades of slow progress, this landscape is now evolving rapidly, with more than 100 AI/ML-powered tools being approved by the US Food and Drug Administration each year. Within the field of vascular surgery specifically, this review identified 17 companies with mature technologies that have at least one US Food and Drug Administration clearance, all occurring between 2016 and 2022. The maturation of these technologies appears to be accelerating, with improving regulatory clarity and clinical uptake. The early AI/ML-powered devices extend or amplify clinically entrenched platform technologies and tend to be focused on the diagnosis or evaluation of time-sensitive, clinically important pathologies (eg, reading Digital Imaging and Communications in Medicine-compliant computed tomography images to identify pulmonary embolism), or when physician efficiency or time savings is improved (eg, preoperative planning and intraoperative guidance). The majority (>75%) of these technologies are at the intersection of radiology and vascular surgery. It is becoming increasingly important that the contemporary vascular surgeon understands this shifting paradigm, as these once-nascent technologies are finally maturing and will be encountered with increasingly regularity in daily clinical practice.

Deep-learning approach to automate the segmentation of aorta in non-contrast CTs

Purpose

Segmentation of vascular structures in preoperative computed tomography (CT) is a preliminary step for computer-assisted endovascular navigation. It is a challenging issue when contrast medium enhancement is reduced or impossible, as in the case of endovascular abdominal aneurysm repair for patients with severe renal impairment. In non-contrast-enhanced CTs, the segmentation tasks are currently hampered by the problems of low contrast, similar topological form, and size imbalance. To tackle these problems, we propose a novel fully automatic approach based on convolutional neural network.

Approach

The proposed method is implemented by fusing the features from different dimensions by three kinds of mechanisms, i.e., channel concatenation, dense connection, and spatial interpolation. The fusion mechanisms are regarded as the enhancement of features in non-contrast CTs where the boundary of aorta is ambiguous.

Results

All of the networks are validated by three-fold cross-validation on our dataset of non-contrast CTs, which contains 5749 slices in total from 30 individual patients. Our methods achieve a Dice score of 88.7% as the overall performance, which is better than the results reported in the related works.

Conclusions

The analysis indicates that our methods yield a competitive performance by overcoming the above-mentioned problems in most general cases. Further, experiments on our non-contrast CTs demonstrate the superiority of the proposed methods, especially in low-contrast, similar-shaped, and extreme-sized cases.

Rupture risk parameters upon biomechanical analysis independently change from vessel geometry during abdominal aortic aneurysm growth

Objective

The indication for abdominal aortic aneurysm (AAA) repair is based on a diameter threshold. However, mechanical properties, such as peak wall stress (PWS) and peak wall rupture index (PWRI), influence the individual rupture risk. This study aims to correlate biomechanical and geometrical AAA characteristics during aneurysm growth applying a new linear transformation-based comparison of sequential imaging.

Methods

Patients with AAA with two sequential computed tomography angiographies (CTA) were identified from a single-center aortic database. Patient characteristics included age, gender, and comorbidities. Semiautomated segmentation of CTAs was performed using Endosize (Therenva) for geometric variables (diameter, neck configuration, α/β angle, and vessel tortuosity) and for finite element method A4 Clinics Research Edition (Vascops) for additional variables (intraluminal thrombus [ILT]), vessel volume, PWS, PWRI). Maximum point coordinates from at least one CTA 6 to 24 months before their final were predicted for the final preoperative CTA using linear transformation along fix and validation points to estimate spatial motion. Pearson's correlation and the t test were used for comparison.

Results

Thirty-two eligible patients (median age, 70 years) were included. The annual AAA growth rate was 3.7 mm (interquartile range [IQR], 2.25-5.44; P < .001) between CTs. AAA (+17%; P < .001) and ILT (+43%; P < .001) volume, maximum ILT thickness (+35%; P < .001), β angle (+1.96°; P = .017) and iliac tortuosity (+0.009; P = .012) increased significantly. PWS (+12%; P = .0029) and PWRI (+16%; P < .001) differed significantly between both CTAs. Both mechanical parameters correlated most significantly with the AAA volume increase (r = 0.68 [P < .001] and r = 0.6 [P < .001]). Changes in PWS correlated best with the aneurysm neck configuration. The spatial motion of maximum ILT thickness was 14.4 mm (IQR, 7.3-37.2), for PWS 8.4 mm (IQR, 3.8-17.3), and 11.5 mm (IQR, 5.9-31.9) for PWRI. Here, no significant correlation with any of the aforementioned parameters, patient age, or time interval between CTs were observed.

Conclusions

PWS correlates highly significant with vessel volume and aneurysm neck configuration. Spatial motion of maximum ILT thickness, PWS, and PWRI is detectable and predictable and might expose different aneurysm wall segments to maximum stress throughout aneurysm growth. Linear transformation could thus add to patient-specific rupture risk analysis.

Clinical Relevance

Abdominal aortic aneurysm rupture risk assessment is a key feature in future individualized therapy approaches for patients, since more and more data are obtained concluding a heterogeneous disease entity that might not be addressed ideally looking only at diameter enlargement. The approach presented in this pilot study demonstrates the feasibility and importance of measuring peak wall stress and rupture risk indices based on predicted and actual position of maximum stress points including intraluminal thrombus.

Can We Still Teach Open Repair of Abdominal Aortic Aneurysm in The Endovascular Era? Single-Center Analysis on The Evolution of Procedural Characteristics Over 15 Years

OBJECTIVE

In many vascular centers an endovascular first policy for the treatment of abdominal aortic aneurysms (AAA) has resulted in endovascular aortic repair (EVAR) outnumbering open aortic repair (OAR). The declining routine in OAR raises the question whether this might influence procedural outcomes and diminish surgical expertise for current and future vascular surgeons. We aimed to analyze OAR outcomes, AAA morphology and procedural details over the past 15 years while an endovascular first approach was successively implemented.

PARTICICPANTS AND DESIGN

All patients operated for (i)ntact infra-/juxtarenal AAA between January 1, 2005 and December 31, 2019 were identified. Outcome parameters were length of stay (hospital/ICU), in-hospital mortality and medical/surgical complications. Operative details were clamping zone, access and graft configuration. AAA anatomy including neck and iliac parameters was analyzed with Endosize©. Logistic regression, uni- and multivariate analysis were applied.

RESULTS

293 patients received elective OAR for iAAA. Baseline characteristics (age, sex, hypertension, smoking, occlusive disease, coronary disease, hyperlipidemia, diabetes, renal insufficiency and obesity) did not change over time. The number of OAR dropped significantly (-0.5 cases/year p = 0.02). The procedure time (2005-2007: 192.2 ± 87.5min to 2017-2019: 235.6 ± 88.2min; p = 0.0001) and the length of stay (2005-2007: 12.0 ± 7.9 to 2017-2019: 17.0 ± 23.1; p = 0.03) increased significantly, whereas the in-hospital mortality, length of ICU stay and complication rates didn't, nor did AAA anatomy. Upon multivariate analysis, annual number of OAR and any additional anastomosis significantly influenced procedure time, trainee involvement, for example, did not. Hospital length-of-stay depended on patient age (p = 0.002), complication rates (p < 0.0001) and procedure time (p = 0.006).

CONCLUSION

Mortality and complication rates for OAR have remained low and constant. With the increase of EVAR, the absolute number of OARs has decreased significantly. However, the total procedure time has increased and depends significantly on the annual number of OARs in total and per surgeon. This might influence outcome parameters and should be implanted in future surgical education.

Validation of a Whole Heart Segmentation from Computed Tomography Imaging Using a Deep-Learning Approach

The aim of this study is to develop an automated deep-learning-based whole heart segmentation of ECG-gated computed tomography data. After 21 exclusions, CT acquired before transcatheter aortic valve implantation in 71 patients were reviewed and randomly split in a training (n = 55 patients), validation (n = 8 patients), and a test set (n = 8 patients). A fully automatic deep-learning method combining two convolutional neural networks performed segmentation of 10 cardiovascular structures, which was compared with the manually segmented reference by the Dice index. Correlations and agreement between myocardial volumes and mass were assessed. The algorithm demonstrated high accuracy (Dice score = 0.920; interquartile range: 0.906-0.925) and a low computing time (13.4 s, range 11.9-14.9). Correlations and agreement of volumes and mass were satisfactory for most structures. Six of ten structures were well segmented. Deep-learning-based method allowed automated WHS from ECG-gated CT data with a high accuracy. Challenges remain to improve right-sided structures segmentation and achieve daily clinical application.

Deep Learning to Automatically Segment and Analyze Abdominal Aortic Aneurysm from Computed Tomography Angiography

PURPOSE

Although segmentation of Abdominal Aortic Aneurysms (AAA) thrombus is a crucial step for both the planning of endovascular treatment and the monitoring of the intervention's outcome, it is still performed manually implying time consuming operations as well as operator dependency. The present paper proposes a fully automatic pipeline to segment the intraluminal thrombus in AAA from contrast-enhanced Computed Tomography Angiography (CTA) images and to subsequently analyze AAA geometry.

METHODS

A deep-learning-based pipeline is developed to localize and segment the thrombus from the CTA scans. The thrombus is first identified in the whole sub-sampled CTA, then multi-view U-Nets are combined together to segment the thrombus from the identified region of interest. Polygonal models are generated for the thrombus and the lumen. The lumen centerline is automatically extracted from the lumen mesh and used to compute the aneurysm and lumen diameters.

RESULTS

The proposed multi-view integration approach returns an improvement in thrombus segmentation with respect to the single-view prediction. The thrombus segmentation model is trained over a training set of 63 CTA and a validation set of 8 CTA scans. By comparing the thrombus segmentation predicted by the model with the ground truth data, a Dice Similarity Coefficient (DSC) of 0.89 ± 0.04 is achieved. The AAA geometry analysis provided an Intraclass Correlation Coefficient (ICC) of 0.92 and a mean-absolute difference of 3.2 ± 2.4 mm, for the measurements of the total diameter of the aneurysm. Validation of both thrombus segmentation and aneurysm geometry analysis is performed over a test set of 14 CTA scans.

CONCLUSION

The developed deep learning models can effectively segment the thrombus from patients affected by AAA. Moreover, the diameters automatically extracted from the AAA show high correlation with those manually measured by experts.

A new software tool for planning interventional procedures in liver cancer

INTRODUCTION

Intra-arterial therapy is an effective way of performing chemotherapy or radiation therapy in patients with primary liver cancer (i.e. hepatocellular carcinoma). Although this minimally invasive approach is now an established treatment option, support tools for pre-operative planning and intra-operative assistance might be helpful.

MATERIAL AND METHODS

We developed an approach for semi-automatic segmentation of computed tomography angiography images of the main arterial branches (required for access path to the treatment site), automatic segmentation of the liver, arterial and venous tree, and interactive segmentation of the tumors (required for procedure-specific planning). This approach was then integrated into a liver-specific workflow within EndoSize^® solution, a planning software for endovascular procedures. The main branches extraction approach was qualitatively evaluated inside the software, while the automatic segmentation methods were quantitatively assessed.

RESULTS

Main branches extraction provides a success rate of 85% (i.e. all arteries correctly extracted) in a dataset of 172 patients. On public databases, a mean DICE of 0.91, 0.47 and 0.92 was obtained for liver, venous and arterial trees segmentation, respectively.

CONCLUSIONS

This pipeline is suitable for directly accessing the treatment site, giving anatomic measurements, and visualizing the hepatic trees, liver, and surrounding arteries during the pre-operative planning.

ABBREVIATIONS

HCC: hepatocellular carcinoma; TACE: transarterial chemoembolization; SIRT: selective internal radiation therapy; CT: computed tomography; CTA: computed tomography angiography; AMS: superior mesenteric artery; LGA: left gastric artery; RHA: right hepatic artery; LHA: left hepatic artery; rbHA: right branch of the hepatic artery; lbHA: left branch of the hepatic artery; GDA: gastroduodenal artery; VOI: volume of interest; SD: standard deviation; MICCAI: medical image computing and computer assisted interventions; MR: magnetic resonance.

Numerical simulation of fenestrated graft deployment: Anticipation of stent graft and vascular structure adequacy

Fenestrated endovascular aneurism repair (FEVAR) is a minimally invasive technique, and its success depends on the adequacy of the correspondence between the visceral arteries ostia and position of the fenestrations of the stent graft (SG) during its deployment in juxtarenal aneurisms. However, the fenestration position is generally determined from a preoperative computerised tomography (CT) scan, without considering the vascular deformation induced by the insertion of the endovascular tools. Catheterisation difficulties may occur during clinical procedures. Accordingly, the objective of this work is to present an initial proof of concept aimed at anticipating and optimising the position of the fenestrations, while considering the vascular deformation induced by the insertion of the endovascular tools. The proposed method relies on the finite element method to simulate the SG deployment in a vascular structure (VS), and considers the vascular deformation induced by the tools. After determining the optimal simulation parameters for a patient-specific case, the robustness of the method is demonstrated on six other representative anatomies. The simulated SG is also compared with post-deployment CT observations, and demonstrates good adequacy. The results show that the numerically corrected fenestration positions, as determined from the simulated results following the insertion of the endovascular tools, deviate from those of the standard plan (as determined from the preoperative CT scan). This indicates that the SG-VS adequacy could be improved via simulation-based planning, to anticipate potential catheterisation difficulties.

Factors affecting the occurrence of proximal endoleak after endovascular abdominal aortic repair for abdominal aneurysms

Objective

This retrospective study was performed to assess the clinical and radiological variables associated with proximal type IA endoleak (EL) in patients treated with elective endovascular repair for abdominal aortic aneurysms.

Methods

The chi-square test, t-test, and logistic regression analysis were performed as appropriate. A P value of <0.05 was considered statistically significant.

Results

The data of 79 patients were analyzed. No mortality occurred. During follow-up (median, 28.5 months; interquartile range, 12.8–43.0 months), 10 patients developed type IA EL. In the logistic regression analysis, undersizing of the endograft diameter by <10% significantly affected the occurrence of type IA EL. When the diameter was used for measurements, less oversizing was significantly associated with a higher risk of type IA EL. When the area was used for measurements, oversizing of >20% significantly affected the occurrence of type IA EL.

Conclusion

When sizing endografts, a discrepancy was noted between the measurements of the diameter and area of the proximal neck. The area might represent a more accurate measurement than the axial diameter to optimize the proximal sealing and lower the risk of developing type IA EL.

Catheter navigation support for liver radioembolization guidance: feasibility of structure-driven intensity-based registration

PURPOSE

The fusion of pre/intraoperative images may improve catheter manipulation during radioembolization (RE) interventions by adding relevant information. The objective of this work is to propose and evaluate the performance of a RE guidance strategy relying on structure-driven intensity-based registration between preoperative CTA and intraoperative X-ray images.

METHODS

The navigation strategy is decomposed into three image fusion steps, supporting the catheter navigation from the femoral artery till reaching the injection site (IS). During the pretreatment assessment intervention, the aorta and the origins of its side branches are projected on the intraoperative 2D fluoroscopy following a 3D/2D bone-based registration process, to assist the celiac trunk access. Subsequently, a similar approach consisting in projecting the hepatic vasculature on intraoperative DSA through 3D/2D vessel-based registration is performed to assist the IS location. Lastly, the selected IS is reproduced during the treatment intervention by employing 2D/2D image-based registration between pretreatment and treatment fluoroscopic images.

RESULTS

The three fusion steps were independently evaluated on subsets of 20, 19 and 5 patient cases, respectively. Best results were obtained with gradient difference as similarity measure and with a delimited preoperative vascular structure for vessel-based registration. The approach resulted in qualitatively appropriate anatomical correspondences when projecting the preoperative structures on intraoperative images. With the best configuration, the registration steps showed accuracy and feasibility in aligning data, with global mean landmarks errors of 1.59 mm, 2.32 mm and 2.17 mm, respectively, a computation time that never exceeded 5 s, 25 s and 11 s, respectively, and a user interaction limited to manual initialization of the 3D/2D registration.

CONCLUSION

An image fusion-based approach has been specifically proposed for RE procedures guidance. The catheter manipulation strategy based on the fusion of pre- and intraoperative images has the potential to support different steps of the RE clinical workflow and to guide the overall procedure.

Learn EVAR sizing from scratch: The results of a one-day intensive course in EVAR sizing and stent graft selection for vascular trainees

Background and aim

Recognition of structured training in endovascular aortic repair (EVAR) for vascular trainees is increasing. Nevertheless, how trainees can achieve sufficient skills in EVAR sizing and graft selection is sparsely described. The aim of this study was to investigate the effect of systematic training in basic EVAR sizing and graft selection on vascular surgery trainees using a validated assessment tool.

Methods

Sixteen vascular surgery trainees were included in an intensive 6-h hands-on workshop in aortic sizing and stent graft selection for EVAR with a trainer-to-trainee ratio of 1:2. After 1-h lecture, participants did 5 h of supervised training on increasingly complex cases. Finally, the participants were tested using a validated assessment tool.

Results

All participants were able to size the test-case and select a stent graft combination in 24:35 (13:30–48:20) min (median and range). The participants’ overall test scores (lower is better) were in median 17.9 (11.9–28.4). This did not differ from the scores of experienced EVAR operators 14.7 (11.7–25.2) (<200 EVAR’s) ( p = .32) but was inferior to the score of EVAR experts 11.2 (9.8 –18.7) (≥200 EVAR’s) ( p = .01). The sub-score for anatomical measurements was 10.6 (3.9–18.8) and comparable with the experienced group 9.7 (8.1–12.8) ( p = .83) but inferior to the expert operators 6.5 (5.2–10.2) ( p = .04). The sub-score for stent graft selection was 7.5 (4.9–14.1) and comparable with experienced operators scoring 4.5 (3.6–12.3) ( p = .09) but inferior to the expert operators score of 5.0 (3.6–8.4) ( p = .01).

Conclusion

This study presents the results of a standardised one-day basic EVAR sizing and graft selection workshop. Vascular surgery trainees with no prior EVAR experience learned to size and select stent grafts for a simple infra-renal AAA on par with experienced EVAR operators.

Clinical Validation of a Semi-Automated Software for Maximal Diameter Measurements for Endovascular Repair Follow-up

PURPOSE

To compare automated measurements of maximal diameter (D_max) of abdominal aortic aneurysm (AAA) orthogonal to luminal or outer wall envelope centerline for endovascular repair (EVAR) follow-up.

MATERIAL AND METHODS

Eighty-three consecutive patients with AAA treated by EVAR who had at least 1 computed tomography (CT) scan before and 2 CT scans after EVAR with at least 5 months' interval were included. Three-dimensional reconstruction of the AAA was achieved with dedicated segmentation software. Performances of automated calculation algorithms of D_max perpendicular to lumen or outer wall envelope centerlines were then compared to manual measurement of D_max on double-oblique multiplanar reconstruction (gold standard). Accuracy of automated D_max measurements at baseline, follow-up, and progression over time was evaluated by calculation of mean error, Bland-Altman plot, and regression models.

RESULTS

Disagreement in D_max measurements between outer wall envelope algorithm and manual method was insignificant (mean error: baseline, -0.07 ± 1.66 mm, P = .7; first follow-up, 0.24 ± 1.69 mm, P = .2; last follow-up, -0.41 ± 2.74 mm, P = .17); whereas significant discrepancies were found between the luminal algorithm and the manual method (mean error: baseline, -1.24 ± 2.01 mm, P < .01; first follow-up, -1.49 ± 3.30 mm, P < .01; last follow-up, -1.78 ± 3.60 mm, P < .01). D_max progression results were more accurate with AAA outer wall envelope algorithm compared to luminal method (P = .2).

CONCLUSIONS

AAA outer wall envelope segmentation is recommended to enable automated calculation of D_max perpendicular to its centerline during EVAR follow-up.

Validation of a New Methodology to Determine 3-Dimensional Endograft Apposition, Position, and Expansion in the Aortic Neck After Endovascular Aneurysm Repair

Purpose: To validate a novel methodology employing regular postoperative computed tomography angiography (CTA) scans to assess essential factors contributing to durable endovascular aneurysm repair (EVAR), including endograft deployment accuracy, neck adaptation to radial forces, and effective apposition of the fabric within the aortic neck. Methods: Semiautomatic calculation of the apposition surface between the endograft and the infrarenal aortic neck was validated in vitro by comparing the calculated surfaces over a cylindrical silicon model with known dimensions on CTA reconstructions with various slice thicknesses. Interobserver variabilities were assessed for calculating endograft position, apposition, and expansion in a retrospective series of 24 elective EVAR patients using the repeatability coefficient (RC) and the intraclass correlation coefficient (ICC). The variability of these calculations was compared with variability of neck length and diameter measurements on centerline reconstructions of the preoperative and first postoperative CTA scans. Results: In vitro validation showed accurate calculation of apposition, with deviation of 2.8% from the true surface for scans with 1-mm slice thickness. Excellent agreement was achieved for calculation of the endograft dimensions (ICC 0.909 to 0.996). Variability was low for calculation of endograft diameter (RC 2.3 mm), fabric distances (RC 5.2 to 5.7 mm), and shortest apposition length (RC 4.1 mm), which was the same as variability of regular neck diameter (RC 0.9 to 1.1 mm) and length (RC 4.0 to 8.0 mm) measurements. Conclusion: This retrospective validation study showed that apposition surfaces between an endograft and the infrarenal neck can be calculated accurately and with low variability. Determination of the (ap)position of the endograft in the aortic neck and detection of subtle changes during follow-up are crucial to determining eventual failure after EVAR.

Validation of the Gatortail method for accurate sizing of pulmonary vessels from 3D medical images

PURPOSE

Detailed characterization of changes in vessel size is crucial for the diagnosis and management of a variety of vascular diseases. Because clinical measurement of vessel size is typically dependent on the radiologist's subjective interpretation of the vessel borders, it is often prone to high inter- and intra-user variability. Automatic methods of vessel sizing have been developed for two-dimensional images but a fully three-dimensional (3D) method suitable for vessel sizing from volumetric X-ray computed tomography (CT) or magnetic resonance imaging has heretofore not been demonstrated and validated robustly.

METHODS

In this paper, we refined and objectively validated Gatortail, a method that creates a mathematical geometric 3D model of each branch in a vascular tree, simulates the appearance of the virtual vascular tree in a 3D CT image, and uses the similarity of the simulated image to a patient's CT scan to drive the optimization of the model parameters, including vessel size, to match that of the patient. The method was validated with a 2-dimensional virtual tree structure under deformation, and with a realistic 3D-printed vascular phantom in which the diameter of 64 branches were manually measured 3 times each. The phantom was then scanned on a conventional clinical CT imaging system and the images processed with the in-house software to automatically segment and mathematically model the vascular tree, label each branch, and perform the Gatortail optimization of branch size and trajectory. Previously proposed methods of vessel sizing using matched Gaussian filters and tubularity metrics were also tested. The Gatortail method was then demonstrated on the pulmonary arterial tree segmented from a human volunteer's CT scan.

RESULTS

The standard deviation of the difference between the manually measured and Gatortail-based radii in the 3D physical phantom was 0.074 mm (0.087 in-plane pixel units for image voxels of dimension 0.85 × 0.85 × 1.0 mm) over the 64 branches, representing vessel diameters ranging from 1.2 to 7 mm. The linear regression fit gave a slope of 1.056 and an R² value of 0.989. These three metrics reflect superior agreement of the radii estimates relative to previously published results over all sizes tested. Sizing via matched Gaussian filters resulted in size underestimates of >33% over all three test vessels, while the tubularity-metric matching exhibited a sizing uncertainty of >50%. In the human chest CT data set, the vessel voxel intensity profiles with and without branch model optimization showed excellent agreement and improvement in the objective measure of image similarity.

CONCLUSIONS

Gatortail has been demonstrated to be an automated, objective, accurate and robust method for sizing of vessels in 3D non-invasively from chest CT scans. We anticipate that Gatortail, an image-based approach to automatically compute estimates of blood vessel radii and trajectories from 3D medical images, will facilitate future quantitative evaluation of vascular response to disease and environmental insult and improve understanding of the biological mechanisms underlying vascular disease processes.

How Precise Are Preinterventional Measurements Using Centerline Analysis Applications? Objective Ground Truth Evaluation Reveals Software-Specific Centerline Characteristics

PURPOSE

To evaluate different centerline analysis applications using objective ground truth from realistic aortic aneurysm phantoms with precisely defined geometry and centerlines to overcome the lack of unknown true dimensions in previously published in vivo validation studies.

METHODS

Three aortic phantoms were created using computer-aided design (CAD) software and a 3-dimensional (3D) printer. Computed tomography angiograms (CTAs) of phantoms and 3 patients were analyzed with 3 clinically approved and 1 research software application. The 3D centerline coordinates, intraluminal diameters, and lengths were validated against CAD ground truth using a dedicated evaluation software platform.

RESULTS

The 3D centerline position mean error ranged from 0.7±0.8 to 2.9±2.5 mm between tested applications. All applications calculated centerlines significantly different from ground truth. Diameter mean errors varied from 0.5±1.2 to 1.1±1.0 mm among 3 applications, but exceeded 8.0±11.0 mm with one application due to an unsteady distortion of luminal dimensions along the centerline. All tested commercially available software tools systematically underestimated centerline total lengths by -4.6±0.9 mm to -10.4±4.3 mm (maximum error -14.6 mm). Applications with the highest 3D centerline accuracy yielded the most precise diameter and length measurements.

CONCLUSION

One clinically approved application did not provide reproducible centerline-based analysis results, while another approved application showed length errors that might influence stent-graft choice and procedure success. The variety and specific characteristics of endovascular aneurysm repair planning software tools require scientific evaluation and user awareness.

Generic thrombus segmentation from pre- and post-operative CTA

PURPOSE

Abdominal aortic aneurysm (AAA) is a localized, permanent and irreversible enlargement of the artery, with the formation of thrombus into the inner wall of the aneurysm. A precise patient-specific segmentation of the thrombus is useful for both the pre-operative planning to estimate the rupture risk, and for post-operative assessment to monitor the disease evolution. This paper presents a generic approach for 3D segmentation of thrombus from patients suffering from AAA using computed tomography angiography (CTA) scans.

METHODS

A fast and versatile thrombus segmentation approach has been developed. It is composed of initial centerline detection and aorta lumen segmentation, an optimized pre-processing stage and the use of a 3D deformable model. The approach has been designed to be very generic and requires minimal user interaction. The proposed method was tested on different datasets with 145 patients overall, including pre- and post-operative CTAs, abdominal aorta and iliac artery sections, different calcification degrees, aneurysm sizes and contrast enhancement qualities.

RESULTS

The thrombus segmentation approach showed very accurate results with respect to manual delineations for all datasets ([Formula: see text] and [Formula: see text] for abdominal aorta sections on pre-operative CTA, iliac artery sections on pre-operative CTAs and aorta sections on post-operative CTA, respectively). Experiments on the different patient and image conditions showed that the method was highly versatile, with no significant differences in term of precision. Comparison with the level-set algorithm also demonstrated the superiority of the 3D deformable model. Average processing time was [Formula: see text].

CONCLUSION

We presented a near-automatic and generic thrombus segmentation algorithm applicable to a large variability of patient and imaging conditions. When integrated in an endovascular planning system, our segmentation algorithm shows its compatibility with clinical routine and could be used for pre-operative planning and post-operative assessment of endovascular procedures.

Measuring of Abdominal Aortic Aneurysm with Three-Dimensional Computed Tomography Reconstruction before Endovascular Aortic Aneurysm Repair

PURPOSE

Conventional computed tomography (CT) is the gold standard method for case planning for endovascular aortic aneurysm repair (EVAR). However, aortography with a marking catheter is needed for measuring the actual length of an aneurysm. With advances in imaging technology, a 3-dimensional (3D) workstation can obviate the need for the aortography. The objective of this study was to determine whether a 3D workstation could obviate the need for aortography for EVAR.

MATERIALS AND METHODS

One vascular surgeon and 1 interventional radiologist retrospectively assessed axial CT scans and reformatted the 3D CT scans by using the iNtuition workstation (TeraRecon Inc., San Mateo, CA, USA) for 25 patients who underwent EVAR. Four measurements of diameter and length were obtained from each modality. The actual length of an aneurysm for the proper graft was decided by 2 observers by reviewing the aortography with a marking catheter.

RESULTS

The measurements from the 2 modalities were reproducible with intraobserver correlation coefficients of 0.89 to 1.0 for conventional CT and 0.98 to 1.0 for 3D workstation. Interobserver correlation coefficients were 0.29 to 0.95 for conventional CT and 0.85 to 0.99 for the 3D workstation. The length of the aneurysm for proper main graft coincided in 18 and 14 patients according to the conventional CT scan and in 21 and 18 patients according to the 3D workstation, respectively.

CONCLUSION

The interobserver agreement in planning EVAR was significantly better with the iNtuition 3D workstation. But aortography with a marking catheter may still be needed for selecting the proper graft.

Preoperative CT-scan-based sizing and in-stent restenosis in peripheral endovascular revascularizations

Objectives This study evaluates the effect of stent sizing with CT-scan on the incidence of restenosis in peripheral arterial disease. Methods This retrospective study included 59 patients with 66 arterial lesions who underwent a endovascular procedure for peripheral arterial disease between April 2013 and October 2013. All patients had de novo iliac or femoral lesions, were candidates for an endovascular procedure alone and underwent CTA preoperatively. The stent actually implanted, whose dimensions were chosen on the basis of the operator's experience on an intraoperative 2D angiography, was compared to the "ideal" stent chosen retrospectively on the basis of precise lesion sizing by the preoperative CTA. Planning was considered "discordant" if there was a difference in length of more than 20 mm and/or a difference in diameter of more than 1 mm between the ideal stent and the actual stent. Results For iliac lesions, discordance essentially concerned stent diameter (36.1%), whereas stent length was the main reason for discordance for femoral lesions (36.7%). The median length of follow-up was 18 months (range 6-24). For iliac lesions, freedom from restenosis at 24 months was higher for patients with concordant planning (90% vs. 62.5%, p = 0.045). Most restenoses occurred in the external iliac artery, where there was a tendency towards oversizing of the implanted stent. For femoral lesions, the restenosis-free rate at 24 months was higher for patients with concordant planning (77.8% vs. 50%, p = 0.057). A multivariate analysis was conducted on the prediction of restenosis. Among factors, only discordant planning was found to be a significant predictor of restenosis with an odds ratio of 0.115 (95% confidence interval, 0.02-0.674; p = 0.016). Conclusion The absence of sizing for peripheral lesions engenders a tendency to choose the wrong stent, in particular in terms of diameter in iliac arteries and length in femoral arteries.

Experimental validation of more realistic computer models for stent-graft repair of abdominal aortic aneurysms, including pre-load assessment

Although the endovascular repair of abdominal aortic aneurysms is a less invasive alternative than classic open surgery, complications such as endoleak and kinking still need to be addressed. Numerical simulation of endovascular repair is becoming a valuable tool in stent-graft (SG) optimization, patient selection and surgical planning. The experimental and numerical forces required to produce SG deformations were compared in a range of in vivo conditions in the present study. The deformation modes investigated were: bending as well as axial, transversal and radial compressions. In particular, an original method was developed to efficiently account for radial pre-load because of the pre-compression of stents to match the graft dimensions during manufacturing. This is important in order to compute the radial force exerted on the vessel after deployment more accurately. Variations of displacement between the experimental and numerical results ranged from 1.39% for simple leg bending to 5.93% for three-point body bending. Finally, radial pre-load was modeled by increasing Young's modulus of each stent. On average, it was found that Young's modulus had to be augmented by a factor of 2. Copyright © 2016 John Wiley & Sons, Ltd.

Predictive Models of Complications after Endovascular Aortic Aneurysm Repair

BACKGROUND

The risk of long-term complications after endovascular aneurysm repair (EVAR) is still higher than open surgery and is a critical issue. This study aims to make available reliable statistical predictive models of complications after EVAR.

METHODS

Two hundred and thirteen patients who underwent EVAR between 2002 and 2012 were included in this study. The preoperative computed tomography scans were analyzed with a dedicated workstation to provide spatially correct 3-dimensional data. Age, gender, operation-related factors, and 21 morphologic variables were measured and included in the analyses. Five postoperative outcomes were studied. After an initial selection of predictors based on univariate analysis, binomial logistic regression models were proposed for each outcome. The ability to predict each outcome was assessed with receiver operating characteristic curves considering that an area under the curve (AUC) > 0.70 is generally considered sufficiently accurate.

RESULTS

The mean age was 74.8 ± 8.6 years with a mean follow-up of 43.8 ± 22.1 months. Respectively, rates and risk factors of each outcome were 25.3% (n = 51) for abdominal aortic aneurysm (AAA) enlargement (age, number of patent sac branches, iliac calcifications and tortuosity, aneurysmal thrombus), 7% (n = 15) for type IA endoleak (neck calcification and AAA diameter), 3.7% (n = 8) for type IB endoleak (iliac tortuosity, AAA diameter, neck thrombus), 19.8% (n = 40) for type II endoleak (female, number of patent sac branches), and 25.9% (n = 55) for reintervention from any cause (neck calcification). The risk associated to each outcome can be calculated with a combination of these different preoperative variables. AUC for each outcome were 79.6% for AAA enlargement, 70.4% for reintervention, 81.3% for type IA endoleak, 92.3% for type IB endoleak, 70.6% for type II endoleak.

CONCLUSIONS

This study shows that an exhaustive description of the preoperative anatomy before EVAR is a powerful and reliable tool to predict the risk of developing the most common complications after EVAR.

The imaging assessment and specific endograft design for the endovascular repair of ascending aortic dissection

Background

Endovascular option has been proposed for a very limited and selected number of Stanford type A aortic dissection (TAAD) patients. We have performed a computed tomography (CT)-based TAAD study to explore appropriate endograft configurations for the ascending aortic pathology.

Methods

TAAD patients treated with optimal CT scans were retrospectively reviewed, and their entry tears (ETs) were identified using three-dimensional and multiplanar reconstructions in an EndoSize workstation. After generating a centerline of flow, measurements, including numerous morphologic characteristics of anatomy, were evaluated and a selected subset of patients were determined to be suitable for endovascular treatments. Proximal diameter and distal diameter of endograft were selected based on diameters measured at the ET level and at the innominate artery (IA) level, with 10% oversizing with respect to the true lumen, but not exceeding the original aortic diameter. The length of the endograft was determined by the distance from the sinotubular junction to IA.

Results

This study covered 126 TAAD patients with primary ET in ascending aorta, among which, according to the assumed criteria, 48 (38.1%) patients were deemed to be suitable for endovascular treatment. The diameters of ascending aorta from the sinotubular junction to the IA level presented a downward trend, and the proximal diameters differed significantly from distal diameters of the endograft for TAAD (39.9 versus 36.2 mm, P<0.01), implying that the conical endograft might be compatible with the ascending pathology. In the ascending aorta, lengths of the endograft should be 50, 60, 70, 80, and 90 mm in five (10.4%), 22 (45.9%), 13 (27.1%), six (12.5%), and two (4.2%) patients, respectively.

Conclusion

In this selected number of Chinese patients, the suitability of endovascular repair has been demonstrated based on the CT imaging. Shorter, larger, and bare spring-free conical endografts were preferred in the ascending aortic pathology.

Endograft Sizing for Endovascular Aortic Repair and Incidence of Endoleak Type 1A

Objective

In endovascular aortic aneurysm repair (EVAR), proximal type 1A endoleaks can occur as a result of hostile neck anatomy or over- or undersizing of the endograft. As the current standard is based on the diameter or average of the short and long axes in a central lumen reconstruction image, it can falter in irregularly shaped aortic necks. An alternative method is circumference-based, therefore minimizing the measurement error. In this study we aimed to assess the degree of discrepancy between both methods and the association of this discrepancy with the occurrence of endoleak type 1A.

Methods

All patients with early (<30 days post-operative) endoleak type 1A after elective EVAR at our center between 2004 and 2016 were identified for a retrospective case-control study. Control patients were matched based on hostile neck anatomy, such as calcification, thrombus, reverse taper, and β-angulation. The aortic neck diameter was measured using the traditional, diameter-based method as well as an alternative method, based on the circumference of the aortic neck.

Results

In 482 EVAR patients, 18 early endoleak type 1A cases were found (3.9%). After exclusion, 12 cases remained and 48 matching controls were found. No significant differences were found between the two measuring methods at any level below the renal arteries. The inter-observer variability was significant for the D(mean) (0.4 ± 1.69 mm, P = .02) and was larger than the D(circ) method (-0.1 ± 1.03 mm, P = .35). In only four out of 12 cases the endograft size was 10–20% larger than the D(mean) and D(circ) measurements. The differences between the diameter of the D(mean) and D(circ) and the chosen endograft were smaller for the case group (-8 ± 25.6% and -7 ± 24%) than for the control group. (-12.4 ± 12.4% and -11 ± 10.7%).

Conclusion

The difference between the D(mean) and D(circ) methods for aortic neck measurement was not large enough to play a significant role in the incidence of endoleak type 1A. Inadequate oversizing and considerable β-angulation of the aortic neck may have been the cause of endoleak type 1A in this population. Robust and well-investigated sizing methods are paramount for accurate endograft sizing and prevention of endoleak type 1A. Therefore the lack of studies in this field and a sizeable inter-observer variability do not justify the widespread reliance on the traditional diameter-based methods for endograft sizing.

Virtual implantation of a novel LVAD: toward computer-assisted surgery for heart failure

BACKGROUND

Mechanical and hemodynamic factors are among the determinants of patient-device interaction and early-term and long-term outcomes in left ventricular assist device (LVAD) recipients.

MATERIAL AND METHODS

We are currently developing computer simulation tools aimed at (1) analyze the intrathoracic and intracavitary positioning of LVADs after implantation and establish correlation with clinical outcomes; (2) assist surgeons in the choice of device and of left ventricular coring site for optimized intrathoracic placement and function; and (3) facilitate the planning of less-invasive LVAD implantation. A virtual representation of LVAD (mesh device component) was created through cone-beam computed tomography and semiautomatic segmentation. A modular framework software (CamiTK, Grenoble, France) was used to create a three-dimensional representation of patients' computed tomography (CT) scan and incorporate the mesh device component for virtual implantation.

RESULTS

Device reconstruction was included into a dedicated software with the purposes of virtual implantation, based on the preoperative CT scan of surgical candidates.

CONCLUSIONS

We present herein the first digital reconstruction of the novel HeartMate 3 LVAD. Virtual implantation on the basis of preoperative CT scan is feasible within a user-friendly interactive software. Future studies will be focused on correlation with clinical variables.

Sealing zones have a greater influence than iliac anatomy on the occurrence of limb occlusion following endovascular aortic aneurysm repair

Limb occlusion is a well-known complication following endovascular aortic aneurysm repair (EVAR), and it very often leads to reoperation. The aim of this study is to identify predictive factors for limb occlusion following EVAR. Two hundred and twenty-four patients undergoing EVAR between 2004 and 2012 were included in this retrospective study. Demographics, anatomic, and follow-up data were compared between two groups (with or without thrombosis). Preoperative anatomy was analyzed with a dedicated workstation, using the Society of Vascular Surgery reporting standards. Eleven (4.9%) patients presented with a limb occlusion during follow-up (46 ± 12 months). Univariate analyses were first performed to investigate the influence of preoperative variables on limb occlusion. Then, variables with a p value <0.1 were included in the multivariate analysis and showed that in the occlusion group there was a greater rate of chronic renal failure (18.2% vs. 3.8%, p = 0.012), a more frequent occurrence of distal landing zones in the external iliac artery (15.4% vs. 2.1%, p = 0.006), and a smaller aortic neck diameter (21.0 ± 2.9 mm vs. 23.6 ± 3.3 mm, p = 0.014). Although iliac anatomy does not appear to have a significant influence on limb occlusion rate in the multivariate analysis, proximal and distal sealing zones appear to be involved in this complication.

Standard and fenestrated endograft sizing in EVAR planning: Description and validation of a semi-automated 3D software

An abdominal aortic aneurysm (AAA) is a pathological dilation of the abdominal aorta that may lead to a rupture with fatal consequences. Endovascular aneurysm repair (EVAR) is a minimally invasive surgical procedure consisting of the deployment and fixation of a stent-graft that isolates the damaged vessel wall from blood circulation. The technique requires adequate endovascular device sizing, which may be performed by vascular analysis and quantification on Computerized Tomography Angiography (CTA) scans. This paper presents a novel 3D CTA image-based software for AAA inspection and EVAR sizing, eVida Vascular, which allows fast and accurate 3D endograft sizing for standard and fenestrated endografts. We provide a description of the system and its innovations, including the underlying vascular image analysis and visualization technology, functional modules and user interaction. Furthermore, an experimental validation of the tool is described, assessing the degree of agreement with a commercial, clinically validated software, when comparing measurements obtained for standard endograft sizing in a group of 14 patients.

Combined frozen elephant trunk and endovascular repair for extensive thoracic aortic aneurysms

BACKGROUND

We describe a 1-step treatment of extensive arch and descending aortic aneurysm by combination of frozen elephant trunk (FET) (hybrid endoprosthesis) and of conventional endoprosthesis deployment.

METHODS

In a single-center, prospective, treatment-only study, the clinical data of 4 patients receiving combined FET and distal endoprosthesis deployment in the descending aorta were prospectively collected. Thoracic endoprostheses were deployed either retrogradely (off-pump from the femoral arterial access) or antegradely (from the aortic arch during hypothermic arrest). A distal-first approach was used ("trombone" mechanism). Spinal cord protection was achieved by transposition of the left subclavian artery to the left common carotid artery and selective antegrade cerebral perfusion. Preoperative computed tomography scan was performed to identify the collateral circulation. Preoperative planning was assisted by a sizing software (Endosize, Therenva Inc.).

RESULTS

The aortic coverage was extended down to the orifice of the celiac trunk in one case and to the T8 level in the remainders. There was no operative mortality, 1 transient paraparesis, and 1 case of renal insufficiency. Follow-up results were satisfying (no device migration, no endoleak, no endotension, and no late neurologic complications).

CONCLUSIONS

The present strategy may abolish the risks connected with the waiting time between the surgical first step and the later completion (aortic-related adverse events and drop-out) and deserves further investigations to determine its safety and feasibility profile.

Mid-term results of elective repair of extensive thoracic aortic pathology by the Evita Open Plus hybrid endoprosthesis only

OBJECTIVES

To describe the early and mid-term clinical and instrumental results of the frozen elephant trunk (FET) procedure using the recent Evita Open Plus hybrid endoprosthesis for elective one-stage treatment of extensive thoracic aortic disease.

METHODS

We reviewed 16 patients undergoing FET for post-dissection aneurysm (50%), true aneurysm (31%) or other aetiologies (19%), through median sternotomy and hypothermic circulatory arrest. An average 14 ± 7.6-month follow-up with regular contrast-enhanced control computed tomography scans was available. Four patients received preliminary carotid-subclavian bypass to improve spinal cord protection. Distal extension through endovascular deployment of stent-grafts into the descending aorta was performed during the same procedure in 3 patients. Concomitant procedures on the ascending aorta/root were done in 25% of cases.

RESULTS

There were no cases of operative mortality. Cases of neither cerebral stroke nor postoperative paraplegia were observed. Two cases of transient paraparesis and 1 case of Brown-Séquard syndrome occurred. At follow-up, there were no cases of endoleak or endotension. One patient was reoperated for distal completion (thoracoabdominal aortic replacement).

CONCLUSIONS

The FET using the Evita Open Plus device is a reliable and versatile treatment for one-step management of extensive disease of the aortic arch and the descending aorta. This strategy should be reserved for patients having limited preoperative comorbidities and good functional status.

Computer-aided surgery: concepts and applications in vascular surgery

Computer-aided surgery makes use of a variety of technologies and information sources. The challenge over the past 10 years has been to apply these methods to tissues that deform, as do vessels when relatively rigid flexible objects are introduced into them (Lunderquist rigid guide wire, aortic prosthesis, etc) Three stages of computer-aided endovascular surgery are examined: sizing, planning, and intraoperative assistance. The authors' work shows that an approach based on optimized use of the imaging data acquired during the various observation phases (pre- and intraoperative), involving only lightweight computer equipment that is relatively transparent for the user, makes it possible to provide useful (ie, necessary and sufficient) information at the appropriate moment, in order to aid decision making and enhance the security of endovascular procedures.