Virtual Ring Research Articles

Finite element analysis of annuloplasty and papillary muscle relocation on a patient-specific mitral regurgitation model.

ObjectivesFunctional mitral regurgitation (FMR) is a significant complication of left ventricle (LV) dysfunction associated with poor prognosis and commonly treated by undersized ring annuloplasty. This study aimed to quantitatively simulate the treatment outcomes and mitral valve (MV) biomechanics following ring annulopalsty and papillary muscle relocation (PMR) procedures for a FMR patient.MethodsWe utilized a validated finite element model of the left heart for a patient with severe FMR and LV dilation from our previous study and simulated virtual ring annuloplasty procedures with various sizes of Edwards Classic and GeoForm annuloplasty rings. The model included detailed geometries of the left ventricle, mitral valve, and chordae tendineae, and incorporated age- and gender- matched nonlinear, anisotropic hyperelastic tissue material properties, and simulated chordal tethering at diastole due to LV dilation.ResultsRing annuloplasty with either the Classic or GeoForm ring improved leaflet coaptation and increased the total leaflet closing force while increased posterior mitral leaflet (PML) stresses and strains. Classic rings resulted in larger coaptation forces and areas compared to GeoForm rings. The PMR procedure further improved the leaflet coaptation, decreased the PML stress and strain for both ring shapes and all sizes in this patient model.ConclusionsThis study demonstrated that a rigorously developed patient-specific computational model can provide useful insights into annuloplasty repair techniques for the treatment of FMR patients and could potentially serve as a tool to assist in pre-operative planning for MV repair surgical or interventional procedures.

The Virtual Ring Shear-Slip Mesh Update Method

A novel method – the Virtual Ring Shear-Slip Mesh Update Method (VR-SSMUM) – for the efficient and accurate modeling of moving boundary or interface problems in the context of the numerical analysis of fluid flow is presented. We focus on cases with periodic straight-line translation including object entry and exit. The periodic character of the motion is reflected in the method via a mapping of the physical domain onto a closed virtual ring. Therefore, we use an extended mesh, where unneeded portions are deactivated to control the computational overhead. We provide a validation case as well as examples for the applicability of the method to 2D and 3D models of packaging machines.

Relationship between the membranous septum and the virtual basal ring of the aortic root in candidates for transcatheter implantation of the aortic valve.

Knowledge of the anatomy of the membranous septum, as a surrogate to the location of the atrioventricular conduction axis, is a prerequisite for those undertaking transcatheter implantation of the aortic valve (TAVI). Equally important is its relationship of the virtual basal ring. This feature, however, has yet to be adequately described in the living heart. We analyzed computed tomographic angiographic datasets from 107 candidates (84.1 ± 5.2 years, 68% women) for TAVI. Using multiplanar reconstructions, we measured the height and width of the membranous septum, and the distances of its superior and inferior margins from the virtual basal ring plane. We also assessed the extent of wedging of the aortic root between the mitral valve and the ventricular septum. Mean heights and widths of the membranous septum were 6.6 ± 2.0, and 10.2 ± 3.1 mm, respectively, with its size significantly associated with that of the aortic root (P < 0.05). Its superior and inferior margins were 4.5 ± 2.3 and 2.1 ± 2.1 mm, respectively, from the plane of the basal ring. The inferior distance, the surrogate for the adjacency of the atrioventricular conduction axis, was ≤ 5mm in 91% of the patients. Deeper wedging of the aortic root was independently correlated with a shorter inferior distance (β = 0.0569, P = 0.0258). The membranous septum is appreciably closer to the virtual basal ring than previously appreciated. These findings impact on estimations of the risk of damage to the atrioventricular conduction axis during TAVI. Clin. Anat. 31:525-534, 2018. © 2018 Wiley Periodicals, Inc.

Efficient design and extensive hardware evaluation of an anonymous data aggregation scheme for smart grid

In smart grid, consumption reports are sent to the energy supplier at regular intervals through some data collectors. This high‐frequent usage reports' collection may divulge the privacy of smart grid users. Recently, Badra and Zeadally have proposed an interesting virtual ring architecture that is used to collect the smart meters' requests while keeping the privacy of smart grid users. However, their proposed scheme suffers from the false data pollution attack. Several other data collection schemes have been proposed in the last decade. Nevertheless, most of them only have considered the external attackers, some of them rely on a third‐trusted party, some are not anonymous, and none of them has examined suitable hardware to be employed by each entity in smart grid. Thus, in this paper, we propose a lightweight and anonymous data collection scheme that can both provide the required privacy of consumers and resist the attacks performed by both external and internal adversaries. More importantly, we have implemented the cryptographic elements on three state‐of‐the‐art hardware. Detailed comparative performance analysis demonstrates the efficiency of the proposed scheme in terms of both communication and computational costs. We hope that the achieved results be useful for other future researches in this field.

Large radius of curvature measurement based on the evaluation of interferogram-quality metric in non-null interferometry

Non-null interferometry could use to measure the radius of curvature (ROC), we have presented a virtual quadratic Newton rings phase-shifting moiré-fringes measurement method for large ROC measurement (Yang et al., 2016). In this paper, we propose a large ROC measurement method based on the evaluation of the interferogram-quality metric by the non-null interferometer. With the multi-configuration model of the non-null interferometric system in ZEMAX, the retrace errors and the phase introduced by the test surface are reconstructed. The interferogram-quality metric is obtained by the normalized phase-shifted testing Newton rings with the spherical surface model in the non-null interferometric system. The radius curvature of the test spherical surface can be obtained until the minimum of the interferogram-quality metric is found. Simulations and experimental results are verified the feasibility of our proposed method. For a spherical mirror with a ROC of 41,400 mm, the measurement accuracy is better than 0.13%.

A failure detector for HPC platforms

Building an infrastructure for exascale applications requires, in addition to many other key components, a stable and efficient failure detector. This article describes the design and evaluation of a robust failure detector that can maintain and distribute the correct list of alive resources within proven and scalable bounds. The detection and distribution of the fault information follow different overlay topologies that together guarantee minimal disturbance to the applications. A virtual observation ring minimizes the overhead by allowing each node to be observed by another single node, providing an unobtrusive behavior. The propagation stage uses a nonuniform variant of a reliable broadcast over a circulant graph overlay network and guarantees a logarithmic fault propagation. Extensive simulations, together with experiments on the Titan Oak Ridge National Laboratory supercomputer, show that the algorithm performs extremely well and exhibits all the desired properties of an exascale-ready algorithm.

The differences between bisecting and off-center cuts of the aortic root: The three-dimensional anatomy of the aortic root reconstructed from the living heart.

It is axiomatic that the diameter of the virtual basal ring of the aortic root, which is elliptical rather than circular, will differ when assessed using between bisecting as opposed to off-center cuts. Such differences, however, which pertain directly to echocardiographic assessments of the so-called valvar annulus, have yet to be systematically explored. We retrospectively analyzed 30 patients undergoing coronary computed tomographic angiography, measuring the virtual basal ring diameter using routine multiplanar reconstructions. We made orthogonal bisecting cuts from the nadir of the hinge of the right coronary aortic leaflet to the center of the opposite inter-leaflet fibrous triangle between the noncoronary and left coronary aortic leaflets. We compared these measurements with orthogonal off-center cuts made through the nadirs of the hinges of the adjacent leaflets. The measured diameter of the virtual basal ring was significantly longer when measured using the bisecting cut as opposed to all off-center cuts (mean difference: 1.35±1.34mm, P<.0001; 0.77±0.95mm, P=.0001, respectively). The measured diameters of the sinuses of Valsalva, in contrast, were significantly shorter when measured using the bisecting cut (mean difference: -3.24±1.38mm, P<.0001; -2.86±1.61mm, P<.0001). There are significant differences in the diameters of the aortic root, which represent the echocardiographic annulus, when measured using bisecting as opposed to off-center cuts. Account should be taken of these differences when using cross-sectional echocardiographic measurements to assess the dimensions of the aortic root.

A New Technique of Defining a Crossing Angle in Bicuspid Aortic Valve Stenosis

Introduction: Crossing bicuspid aortic valve (BAV) stenosis is challenging given the very eccentric opening of the valve. We describe a novel algorithm to define the plane of this eccentric orifice and our initial experience in aiding crossing the valve with a catheter and J-wire. Methods: Between 1st July 2015 and 28th Feb 2017, all BAV stenosis cases requiring transcatheter aortic valve implantation (TAVI) at St Andrew's War Memorial Hospital had a novel algorithm applied to their CT TAVI data with the aid of OsiriX MD medical software to determine a crossing angle pre TAVI. The plane of the virtual ring was determined by annular segmentation on multiplanar reformats and then points of interests (POI) placed along the circumference of the virtual ring. Immediately superior to this plane, POI were allocated along the commissural line. A three dimensional maximum intensity projection was then reconstructed to define the exact angle where the POI along the commissural line formed one point and the POI along the virtual ring plane formed a straight line. This angle showed both cusps in profile with the opening of the valves in the middle. Crossing times in this angle were then recorded at the time of TAVI. Results: 4 patients were included. A steep RAO Caudal view was always best for crossing. Using a catheter and straight wire, all valves were crossed in < 60 seconds. Conclusions: This unique technique for crossing BAV stenosis with the aid of CT reconstruction is feasible and may decrease xray and procedural time.

Computational virtual evaluation of the effect of annuloplasty ring shape.

Mitral regurgitation (MR) is a result of mitral valve (MV) pathology. Its etiology can be categorized as degenerative or functional MR. Ring annuloplasty aims to reconfigure a dilated mitral annulus to its normal size and shape. We investigated the effect of annuloplasty ring shape on MR outcome using our established 3-dimensional (3-D) echocardiography-based computational MV evaluation protocols. Virtual patient MV models were created from 3-D transesophageal echocardiographic data in patients with MR because of mitral annular dilation. Two distinct annuloplasty rings (Physio II and GeoForm) were designed and virtually implanted to the patient MVs. Dynamic finite element simulations of MV function were performed for each MV after virtual ring annuloplasty of either ring, and physiologic and biomechanical characteristics of MV function were compared. Excessive stress values appeared primarily in the midanterior and midposterior regions, and lack of leaflet coaptation was found in pre-annuloplasty patient MVs. Both rings demonstrated marked reduction of stresses and efficient leaflet coaptation. The Physio II ring demonstrated more evenly distributed stress reduction across the leaflets and annulus compared with the GeoForm ring. Conversely, the highly nonplanar curvature of the GeoForm ring more effectively increased leaflet coaptation compared with the Physio II ring. This indicates that the shape of annuloplasty ring affects post-annuloplasty physiologic and biomechanical conditions, which can lead to tissue alteration over a longer period after ring annuloplasty. This virtual ring annuloplasty simulation strategy provides detailed physiologic and biomechanical information and may help better plan the optimal ring selection and improved patient-specific MV repairs.

Performance Analysis and Comparison of Multi Hop Token Ring and Token Bus LAN Technologies

Token ring and token bus networks are two of the most commonly used type of local-area network (LAN). Token ring is designed in such a way that it can provide high throughput under heavy loads. Token bus is implemented using the token ring protocol over a virtual ring on a coaxial cable. The names, token ring and token bus, are applied to LANs which support a multiple access system using a token passing scheme. It is possible to define the maximum access delay experienced by a packet and thus to define the end-to-end delay across the network. In this paper after simulating the token ring and token bus technologies we have focused on the performance issues like throughput, mean delay, normalized throughput and response time of both the techniques. Lastly using some graphs and the data deduced from our simulation we have compared and concluded that token ring performs better than token bus for multi hop network design.

Adams operations on the virtual K-theory of ℙ(1,n)

We analyze the structure of the virtual (orbifold) [Formula: see text]-theory ring of the complex orbifold [Formula: see text] and its virtual Adams (or power) operations, by using the non-Abelian localization theorem of Edidin–Graham [D. Edidin and W. Graham, Nonabelian localization in equivariant [Formula: see text]-theory and Riemann–Roch for quotients, Adv. Math. 198(2) (2005) 547–582]. In particular, we identify the group of virtual line elements and obtain a natural presentation for the virtual [Formula: see text]-theory ring in terms of these virtual line elements. This yields a surjective homomorphism from the virtual [Formula: see text]-theory ring of [Formula: see text] to the ordinary [Formula: see text]-theory ring of a crepant resolution of the cotangent bundle of [Formula: see text] which respects the Adams operations. Furthermore, there is a natural subring of the virtual K-theory ring of [Formula: see text] which is isomorphic to the ordinary K-theory ring of the resolution. This generalizes the results of Edidin–Jarvis–Kimura [D. Edidin, T. J. Jarvis and T. Kimura, Chern classes and compatible power operation in inertial [Formula: see text]-theory, Ann. K-Theory (2016)], who proved the latter for [Formula: see text].

Virtual ring and quantum elements of a classical particle

The fractal equations of mechanics (quantum and classical) are clearly demonstrated to be definitions of an arbitrary potential on a fractal complex number valued surface. The developed approach helps us to show that a translational motion of any rotating compact object (point-like particle) can be equivalently represented by a specific rotation of a virtual ring described in terms of a fractal “wave function”, the model endowing the particle with a set of quantum characteristics including quantization of the ring’s space translation.

Effective Network Quarantine with Minimal Restrictions on Communication Activities

This paper studies a network structure design problem constrained by the epidemic outbreaks. In our model, geographic locations (nodes) and their connections (edges) are modeled as a ring graph. The movement of a person is represented as a flow from one location to another. A person can be infected at a location (node), depending on the number of infected flows (persons) going through that location. In our paper, diseases are not limited to real human diseases; they can also refer to the general epidemic information propagations. Given desired interaction traffic from a node to other nodes in terms of flows, and a greedy shortest path routing scheme that is analogous to the greedy coin change, we focus on the structure design (representing quarantine rules) that determines the number and distribution of chords on the virtual ring network for remote connections. Our objective is to minimize the average number of routing hops, while the epidemic outbreaks are controlled under given infection and recovery rates. We provide a systematic isomorphic structure design on nine different cases, based on three traffic distribution and three infection rate models. Two hypercube-based structures are proposed. We also provide a greedy solution for constructing polymorphic structures. Our study reveals some intriguing theoretical results, validated through experiments, on tradeoffs between local and global infections. Our work casts new light on the effective network quarantine that places minimal restrictions on connections, i.e., maximal preservation of normal communication activities, while controlling epidemic outbreaks.

Large radius of curvature measurement based on virtual quadratic Newton rings phase-shifting moiré-fringes measurement method in a nonnull interferometer.

We have proposed a virtual quadratic Newton rings phase-shifting moiré-fringes measurement method in a nonnull interferometer to measure the large radius of curvature for a spherical surface. In a quadratic polar coordinate system, linear carrier testing Newton rings interferogram and virtual Newton rings interferogram form the moiré fringes. It is possible to retrieve the wavefront difference data between the testing and standard spherical surface from the moiré fringes after low-pass filtering. Based on the wavefront difference data, we deduced a precise formula to calculate the radius of curvature in the quadratic polar coordinate system. We calculated the retrace error in the nonnull interferometer using the multi-configuration model of the nonnull interferometric system in ZEMAX. Our experimental results indicate that the measurement accuracy is better than 0.18% for a spherical mirror with a radius of curvature of 41,400 mm.

Correlation Between Arthroscopy Simulator and Video Game Performance: A Cross-Sectional Study of 30 Volunteers Comparing 2- and 3-Dimensional Video Games

To investigate the association between arthroscopy simulator performance and video game skills. This study compared the performances of 30 volunteers without experience performing arthroscopies in 3 different tasks of a validated virtual reality knee arthroscopy simulator with the video game experience using a questionnaire and actual performances in 5 different 2- and 3-dimensional (D) video games of varying genres on 2 different platforms. Positive correlations between knee arthroscopy simulator and video game performances (ρ= 0.63, P< .001) as well as experiences (ρ= 0.50, P= .005) were found. The strongest correlations were found for the task of catching (hooking) 6 foreign bodies (virtual rings; "triangulation") and the dribbling performance in a sports game and a first-person shooter game, as well as the meniscus resection and a tile-matching puzzle game (all ρ ≥ 0.60, P < .001). No correlations were found for any of the knee arthroscopy simulator tasks and a strategy game. Although knee arthroscopy performances do not correlate with 2-D strategy video game skills, they show a correlation with 2-D tile-matching puzzle games only for easier tasks with a rather limited focus, and highly correlate with 3-D sports and first-person shooter video games. These findings show that experienced and good 3-D gamers are better arthroscopists than nonexperienced and poor 3-D gamers. Level II, observational cross-sectional study.

Optimization of a guard ring structure in Geiger-mode avalanche photodiodes fabricated at National NanoFab Center

A typical Geiger-mode avalanche photodiode (G-APD) contains a guard ring that protects the structure from having an edge breakdown due to the lowering of electric fields at junction curvatures. In this contribution, G-APDs with a virtual guard ring (vGR) merged with n-type diffused guard ring (nGR) in various sizes were studied to find the optimal design for G-APDs fabricated at National NanoFab Center (NNFC) . The sensors were fabricated via a customized CMOS process with a micro-cell size of 65× 65 μm2 on a 200 mm p-type epitaxial layer wafer. I-V characteristic curves for proposed structures were measured on a wafer-level with an auto probing system and plotted together to compare their performance. A vGR width of 1.5 μm and a nGR width of 1.5 μm with an overlapping between vGR and nGR of 1.5 μm showed the lowest leakage current before the breakdown voltage while suppressing the edge breakdown. Furthermore, the current level of the lowest-leakage-current structure was as low as that of only vGR with a width of 2.0 μm, indicating that the structure is also area efficient. Based on these results, the design with vGR, nGR, and OL with width of 1.5 μm is determined to be the optimal structure for G-APDs fabricated at NNFC.

The Role of Distinctiveness of Stimulus in Memory Distrust as a Function of Repeated Checking

Recent literature proposes that repeated checking increases familiarity with the material, making recollections less vivid and detailed and promoting distrust in memory. The aim of the current study is to investigate the possible underlying mechanisms of low confidence in memory. The Padua Inventory-Washington State University Revision (PI-WSUR) was applied in a cohort of university students. Among the students who completed the PI-WSUR, 84 participants were selected and assigned to low Obsessive-Compulsive Symptomatology (OCS) group or high OCS group according to their PI-WSUR scores. An interactive computer animation was developed to test repeated checking behavior. Participants were randomly assigned to two experimental conditions: "Feedback condition" and "no feedback condition". The participants were all asked to carry out checking rituals on a virtual gas ring. However, half of the participants were given feedback indicating that checking activity was successful and complete and half of the participants were not. While there was no significant difference in terms of memory accuracy, memory detail and memory vividness between feedback condition and no feedback condition, there was a significant difference in terms of memory confidence between two experimental groups. Results are discussed in the light of a different explanation offering that the level of distinctiveness of recollections plays crucial role in memory distrust rather than the explanation of low confidence hypothesis.

A new virtual ring-based system matrix generator for iterative image reconstruction in high resolution small volume PET systems

A common approach to improving the spatial resolution of small animal PET scanners is to reduce the size of scintillation crystals and/or employ high resolution pixellated semiconductor detectors. The large number of detector elements results in the system matrix—an essential part of statistical iterative reconstruction algorithms—becoming impractically large. In this paper, we propose a methodology for system matrix modelling which utilises a virtual single-layer detector ring to greatly reduce the size of the system matrix without sacrificing precision. Two methods for populating the system matrix are compared; the first utilises a geometrically-derived system matrix based on Siddon’s ray tracer method with the addition of an accurate detector response function, while the second uses Monte Carlo simulation to populate the system matrix. The effectiveness of both variations of the proposed technique is demonstrated via simulations of PETiPIX, an ultra high spatial resolution small animal PET scanner featuring high-resolution DoI capabilities, which has previously been simulated and characterised using classical image reconstruction methods. Compression factors of and are achieved using this methodology for the system matrices produced using the geometric and Monte Carlo-based approaches, respectively, requiring a total of 0.5–1.2 GB of memory-resident storage. Images reconstructed from Monte Carlo simulations of various point source and phantom models, produced using system matrices generated via both geometric and simulation methods, are used to evaluate the quality of the resulting system matrix in terms of achievable spatial resolution and the CRC, CoV and CW-SSIM index image quality metrics. The Monte Carlo-based system matrix is shown to provide the best image quality at the cost of substantial one-off computational effort and a lower (but still practical) compression factor. Finally, a straightforward extension of the virtual ring method to a three dimensional virtual cylinder is demonstrated using a 3D DoI PET scanner.

大動脈弁輪評価におけるMDCTの臨床応用 : virtual basal ringレベルの弁輪面積から求めた平均弁輪径の有用性

大動脈弁輪評価におけるMDCTの臨床応用 : virtual basal ringレベルの弁輪面積から求めた平均弁輪径の有用性

Sutureless Aortic Valve Prosthesis Sizing: Estimation and Prediction Using Multidetector-Row Computed Tomography.

The sutureless prostheses may facilitate minimally invasive aortic valve replacement because of easy and fast deployment. However, correct device sizing remains a crucial step of this procedure, which may be difficult and time consuming in minimal invasive approaches. We sought to analyze the accuracy of contrast-enhanced preoperative multidetector-row computed tomography (MDCT) in predicting the size of the prosthesis to be implanted in patients undergoing aortic valve replacement through a right anterior minithoracotomy (RAMT). From January 2011 to September 2013, 235 patients underwent aortic valve surgery as sole procedure with implantation (Sorin Perceval S) in RAMT. Inclusion criterion for this study was presence of preoperative multidetector-row computed tomography (MDCT) with contrast enhancement and Doppler echocardiography. A preoperative MDCT was used to measure the aortic annulus as the diameter derived from either the area (aD) or the circumference (cD) of the virtual basal ring, left ventricular outflow tract (LVOT) diameter derived either from the area (aLVOT) or the circumference (cLVOT). Multidetector-row CT was reviewed by a single operator who was blind to implanted valve size. The operator measured the aortic annulus and LVOT in multiplanar reconstruction modality. Aortic annular diameter and LVOT diameter were retrieved from echocardiographic records. Predictive models were built based on logistic regression; outcome variable was the sutureless valve size, and covariates (annular and LVOT measurements) were used as single and multivariate predictors. A classification tree was built and then pruned with limited nodes to be able to obtain better predictive performance. We identified 54 patients who had preoperative contrast-enhanced MDCT. Seven patients received a size S, 21 received a size M, and 26 received a size L prosthesis. The mean age of the patients at the time of intervention was 76.3 ± 6.8 years, and the mean logistic EuroSCORE was 10.4% ± 8.7%. Echocardiographic measurements showed lower accuracy compared to MDCT measurements. Echocardiographic LVOT measurement was 61.11% to predict the valve size, whereas annulus measurement was 53.7%. The aLVOT from MDCT had an accuracy of approximately 62.96%, and cLVOT had 64.81% predictive accuracy. Aortic annulus perimeter cD had the highest accuracy to predict the valve size [62.96%, under the curve, 0.61] followed by aortic annular surface aD having an accuracy of approximately 70.37% (under the curve, 0.75). Classification tree models, after pruning with 4 nodes, increased their accuracy (83.33%), and it was easy to interpret and possibly to implement for clinical use. Multidetector-row CT-derived estimates seem to have higher predictive value for valve size determination in patients undergoing RAMT with the Perceval S prosthesis, thus facilitating this delicate procedure and preventing the selection of wrong candidates. Possibly for precise aortic annulus measurement, contrast-enhanced MDCT is preferable.