Editorial

Automatic Segmentation, Detection, and Diagnosis of Abdominal Aortic Aneurysm (AAA) Using Convolutional Neural Networks and Hough Circles Algorithm Abstract Purpose An abdominal aortic aneurysm (AAA) is known as a cardiovascular disease involving localized deformation (swelling or enlargement) of aorta occurring between the renal and iliac arteries. AAA would jeopardize patients’ lives due to its rupturing risk, so prompt recognition and diagnosis of this disorder is vital. Although computed tomography angiography (CTA) is the preferred imaging modality used by radiologist for diagnosing AAA, computed tomography (CT) images can be used too. In the recent decade, there has been several methods suggested by experts in order to find a precise automated way to diagnose AAA without human intervention base on CT and CTA images. Despite great approaches in some methods, most of them need human intervention and they are not fully automated. Also, the error rate needs to decrease in other methods. Therefore, finding a novel fully automated with lower error rate algorithm using CTA and CT images for Abdominal region segmentation, AAA detection, and disease severity classification is the main goal of this paper. Methods The proposed method in this article will be performed in three steps: (1) designing a classifier based on Convolutional Neural Network (CNN) for classifying different parts of abdominal into four different classes such as: abdominal inside region, aorta, body border, and bone. (2) After correct aorta detection, defining its edge and measuring its diameter with the use of Hough Circle Algorithm (which is an algorithm for finding an arbitrary shape in images and measuring its diameter in pixel) is the second step. (3) Ultimately, the detected aorta, depending on its diameter, will be categorized in one of these groups: (a) there is no risk of AAA, (b) there is a medium risk of AAA, and (c) there is a high risk of AAA. Results The designed CNN classifier classifies different parts of abdominal into four different classes such as: abdominal inside region, aorta, body border, and bone with the accuracy, precision, and sensitivity of 97.93, 97.94, and 97.93% respectively. The accuracy of the proposed classifier for aorta region detection is 98.62% and Hough Circles algorithm can classify 120 aorta patches according to their diameter with accuracy of 98.33%. Conclusions As a whole, a classifier using Convolutional Neural Network is designed and applied in order to detect AAA region among other abdominal regions. Then Hough Circles algorithm is applied to aorta patches for finding aorta border and measuring its diameter. Ultimately, the detected aortas will be categorized according to their diameters. All steps meet the expected results.

Fabrication of Low-Cost Patient-Specific Vascular Models for Particle Image Velocimetry Abstract Purpose Particle image velocimetry (PIV), an in vitro experimentation technique that optically measures velocity components to analyze fluid velocity fields, has become increasingly popular to study flow dynamics in various vascular territories. However, it can be difficult and expensive to create patient-specific clear models for PIV due to the importance of refractive index matching of the model and the fluid. We aim to implement and test the use of poly-vinyl alcohol (PVA) in a lost-core casting technique to create low-cost, patient-specific models for PIV. Methods Anonymized patient vascular anatomies were segmented and processed in Mimics/3Matic to create patient-specific cores from 3D digital subtraction angiographies. The cores were 3D-printed with PVA and post-processed with a 80:20 water:glue mixture to smooth the surface. Two silicones, Sylgard 184 and Solaris, were used to encapsulate the model and the PVA core was dissolved using warm water. Computed tomography scans were used to evaluate geometric accuracy using circumferences and surface differences in the model. Results Mean geometric differences in circumference along the inlet centerline and the mean surface difference in the aneurysm between the final Silicone Model and the desired STL Print geometry were statistically insignificant (0.6 mm, 95% CI [− 1.4, 2.8] and 0.3 mm 95% CI [− 0.1, 0.7], respectively). Particle illumination within each model was successful. The cost of one 10 cm × 10 cm × 5 cm model was $69. Conclusion This technique was successful to implement and test the use of PVA in a lost-core casting technique to create low-cost, patient-specific in vitro models for PIV experimentation.

A Virtual Comparison of the eCLIPs Device and Conventional Flow-Diverters as Treatment for Cerebral Bifurcation Aneurysms Abstract Purpose Effective, consistent, and complication-free treatment of cerebral bifurcation aneurysms remains elusive despite a pressing need, with the majority of lesions presenting in such locations. Current treatment options focus either on aneurysm coil retention, supported by a stent-like device positioned in the parent vessel lumen, or intrasaccular devices that disrupt flow within the aneurysm dome. A third alternative, i.e., the use of conventional (intraluminal) flow-diverters to treat such bifurcation aneurysms raises the problem that at least one daughter vessel needs to be jailed in such a deployment. The eCLIPs is a stent-like device that offers the possibility of flow-diversion at the aneurysm neck, without the drawbacks of daughter vessel occlusion or those of intrasaccular deployment. Methods In this study the eCLIPs device was virtually deployed in five cerebral bifurcation aneurysms and compared with a conventional tubular flow-diverter device. Computational fluid dynamics (CFD) simulations of the aneurysm haemodynamic environment pre- and post-implantation were conducted, and focussed on metrics associated with successful aneurysm occlusion. Absolute and relative reductions in aneurysm inflow rate (Q) and time-averaged wall shear stress (TAWSS) were recorded. Results The eCLIPs device was found to perform in a similar qualitative fashion to tubular flow-diverters, with overall reduction of metrics being somewhat more modest however, when compared to such devices. Aneurysm inflow reduction and TAWSS reduction were typically 10–20% lower for the eCLIPs, when compared to a generic flow diverter (FDBRAIDED) similar to devices currently in clinical use. The eCLIPs was less effective at diffusing inflow jets and at reducing the overall velocity of the flow, when compared to these devices. This result is likely due to the larger device pore size in the eCLIPs. Notably, it was found that the eCLIPs provided approximately equal resistance to flow entering and exiting the aneurysm, which was not true for the FDBRAIDED device, where high-speed concentrations of outflow were seen at the aneurysm neck along with local TAWSS elevation. The clinical implications of such behaviour are not examined in detail here but could be significant. Conclusions Our findings indicate that the eCLIPs device acts as a flow-diverter for bifurcation aneurysms, with somewhat diminished occlusion properties comparing to tubular flow diverters but without the jailing and diminished flow evident in a daughter vessel associated with use of conventional devices.

On the Modeling of Patient-Specific Transcatheter Aortic Valve Replacement: A Fluid–Structure Interaction Approach Abstract Purpose Transcatheter aortic valve replacement (TAVR) is a minimally invasive treatment for high-risk patients with aortic diseases. Despite its increasing use, many influential factors are still to be understood and require continuous investigation. The best numerical approach capable of reproducing both the valves mechanics and the hemodynamics is the fluid–structure interaction (FSI) modeling. The aim of this work is the development of a patient-specific FSI methodology able to model the implantation phase as well as the valve working conditions during cardiac cycles. Methods The patient-specific domain, which included the aortic root, native valve and calcifications, was reconstructed from CT images, while the CAD model of the device, metallic frame and pericardium, was drawn from literature data. Ventricular and aortic pressure waveforms, derived from the patient’s data, were used as boundary conditions. The proposed method was applied to two real clinical cases, which presented different outcomes in terms of paravalvular leakage (PVL), the main complication after TAVR. Results The results confirmed the clinical prognosis of mild and moderate PVL with coherent values of regurgitant volume and effective regurgitant orifice area. Moreover, the final release configuration of the device and the velocity field were compared with postoperative CT scans and Doppler traces showing a good qualitative and quantitative matching. Conclusion In conclusion, the development of realistic and accurate FSI patient-specific models can be used as a support for clinical decisions before the implantation.

In-Vitro Pulsatile Flow Testing of Prosthetic Heart Valves: A Round-Robin Study by the ISO Cardiac Valves Working Group Abstract Purpose Hydrodynamic performance testing is one of the core in vitro assessments required by the ISO 5840 series of standards for all prosthetic heart valves. A round-robin study carried out in 2005 in accordance with ISO 5840:2005 revealed significant variabilities in prosthetic heart valve hydrodynamic performance measurements among the participating laboratories. In order to re-examine the inter-laboratory variability based on the “state-of-the-art” under ISO 5840-1 and 5840-2:2015, the ISO Cardiac Valve Working Groups decided in 2016 to repeat the round-robin study. Methods A total of 13 international laboratories participated in the study. The test valves were chosen to be the St. Jude Medical Masters Series mechanical valves (19 mm aortic, 25 mm aortic, 25 mm mitral, and 31 mm mitral), which were circulated among the laboratories. The testing was conducted according to a common test run sequence, with prespecified flow conditions. Results The study revealed improved, yet still significant variability among different laboratories as compared to the 2005 study. The coefficient of variation ranged from 7.7 to 21.6% for the effective orifice area, from 10.1 to 32.8% for the total regurgitant fraction, and from 14.7 to 45.5% for the mean transvalvular pressure gradient. Conclusions The study revealed the ambiguities in the current versions of the ISO 5840 series of standards and the shortcomings of some participating laboratories. This information has allowed the ISO Working Group to incorporate additional clarifying language into the ISO 5840-1, -2, and -3 standards that are currently under revision to improve in vitro assessments. The results presented here can also be used by the testing laboratories to benchmark pulse duplicator systems and to train and certify testing personnel.

Asymmetric Dynamics of the Native Aortic Annulus Evaluated by Force Transducer and Sonomicrometry in a Porcine Model Abstract Purpose With new repair techniques of the aortic root and valve emerging, a detailed understanding of the dynamics of the aortic annulus and valve is required for optimal results. The objective of this study was to characterize geometrical changes and force distribution of the native porcine aortic annulus throughout the cardiac cycle. Methods Measurements were performed in an acute 80 kg porcine model (n = 7) using sonomicrometry crystals in the aortic annulus for evaluation of geometry and dynamics, annular force transducer evaluating force distribution, and pressure measurements and echocardiography evaluating valve performance. Results Overall, segmental force distribution and geometrical changes differed between different segments of the aortic annulus. The highest force development was found at the left/right interleaflet triangle (2.87 ± 2.1 N) and the largest segmental expansion was observed at the right-coronary and left-coronary sinus. The aortic annulus changed configuration throughout the cardiac cycle and became more oval in systole. Conclusions This study is the first to describe detailed segmental dynamics and force distribution of the native aortic annulus in a porcine model in vivo. The heterogenous behavior of the aortic annulus suggests that different segments demand different support for repair of the aortic root and valve.

Optimization of a Transcatheter Heart Valve Frame Using Patient-Specific Computer Simulation Abstract Purpose This study proposes a new framework to optimize the design of a transcatheter aortic valve through patient-specific finite element and fluid dynamics simulation. Methods Two geometrical parameters of the frame, the diameter at ventricular inflow and the height of the first row of cells, were examined using the central composite design. The effect of those parameters on postoperative complications was investigated by response surface methodology, and a Nonlinear Programming by Quadratic Lagrangian algorithm was used in the optimization. Optimal and initial devices were then compared in 12 patients. The comparison was made in terms of device performance [i.e., reduced contact pressure on the atrioventricular conduction system and paravalvular aortic regurgitation (AR)]. Results Results suggest that large diameters and high cells favor higher anchoring of the device within the aortic root reducing the contact pressure and favor a better apposition of the device to the aortic root preventing AR. Compared to the initial device, the optimal device resulted in almost threefold lower predicted contact pressure and limited AR in all patients. Conclusions In conclusion, patient-specific modelling and simulation could help to evaluate device performance prior to the actual first-in-human clinical study and, combined with device optimization, could help to develop better devices in a shorter period.

Evaluating the Performance of Cardiac Pulse Duplicators Through the Concept of Fidelity Abstract Introduction The advanced design techniques used in modern prosthetic heart valve (PHV) development require accurate replication of the entire cardiac cycle. While cardiac pulse duplicator (CPD) design has a direct impact on the PHV test data generated, no clear guidelines exist to evaluate the CPD’s performance. In response to this, we present a method to quantitatively assess CPD performance. Materials and Methods A method to establish the fidelity of CPDs was formulated based on the pressure/time relationship and the error related to this relationship’s target. This method was applied to assess the performance of a custom-made CPD. The performance evaluation included the assessment of the motion control system and overall repeatability of pressure measurements using a St Jude Epic 21 mm aortic valve. Results The CPD’s motion control system had an average root mean square error (RMSE) beat-to-beat tracking accuracy of 0.046 ± 0.008 mm. Assessment of the pressure measurements yielded a repeatability of < 2.4 ± 0.9 mmHg RMSE beat-to-beat differential pressure. The combination of pressure and its location within a heartbeat (fidelity) was within 5.0% of the individual targets for at least 95% of heartbeats. Conclusion Fidelity can be used to objectively quantify the performance of various aspects of CPDs and to identify the cause of unexpected PHV or CPD behaviour. It also enables comparisons to be made among various CPDs in terms of overall performance. This approach may enable standardization of the assessment of CPD performance in the future.

High-Resolution Measurements of Leakage Flow Inside the Hinge of a Large-scale Bileaflet Mechanical Heart Valve Hinge Model Abstract Purpose It is believed that non-physiological leakage flow through hinge gaps during diastole contributes to thrombus formation in Bileaflet Mechanical Heart Valves (BMHVs). Because of the small scale and difficulty of experimental access, fluid dynamics inside the hinge cavity has not yet been characterised in detail. The objective is to investigate small-scale structure inside the hinge experimentally, and gain insight into its role in stimulating cellular responses. Methods An optically accessible scaled-up model of a BMHV hinge was designed and built, preserving dynamic similarity to a clinical BMHV. Particle Image Velocimetry (PIV) was used to visualize and quantify the flow fields inside the hinge at physiological Reynolds number and dimensionless pressure drop. The flow was measured at in-plane and out-of-plane spatial resolution of 32 and 86 μm, respectively, and temporal resolution of \(297\,\mu\hbox{s}.\) Results Likely flow separation on the ventricular surface of the cavity has been observed for the first time, and is a source of unsteadiness and perhaps turbulence. The shear stress found in all planes exceeds the threshold of platelet activation, ranging up to 168 Pa. Conclusions The scale-up approach provided new insight into the nature of the hinge flow and enhanced understanding of its complexity. This study revealed flow features that may induce blood element damage.