1,721,187 research outputs found
Computational Analysis of Self-Expanding and Balloon-Expandable Transcatheter Heart Valves
Full text linkBicuspid aortic valve (BAV) patients are usually excluded from transcatheter aortic valve implantation (TAVI) as this valve anatomy likely leads to oval expansion. This study presents a numerical study of TAVI using both self-expanding and balloon expandable transcatheter heart valve (THV) in bicuspid patients with severe stenosis. The simulation framework included a patient-specific anatomy of the aortic root, calcifications and BAV leaflets extracted from medical imaging analysis as well as a realistic crimping and deployment of the THV. Tissue stress analysis highlighted local maxima in the contact area between the inner aortic lumen and the THV stent frame. Flow analysis based on the smoothed particle hydrodynamics (SPH) technique displayed the area at risk of paravalvular leakage (PVL). These findings provide insights on the TAVI in BAV and thus represents a further step towards the use of in-silico for the virtual planning of TAVI, aiming at improving not only the efficacy of the implantation but also the exploration of borderline anatomy as the case of TAVI in BAVs
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Tumors of the Spine in Children
No full textIn children, tumors of the spine are much rarer than intracranial tumors. They are classified into intramedullary, intradural-extramedullary, and extradural tumors. Magnetic resonance imaging provides crucial information regarding the extent, location, and internal structure of the mass, thus critically narrowing the differential diagnosis and guiding surgery. © 2007 Elsevier Inc. All rights reserved
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Numerical Analysis of the Bicaval Transcatheter System for the Treatment of Severe Tricuspid Regurgitation
No full textTricuspid regurgitation (TR), also called tricuspid insufficiency, is a relatively common valvular diseases that can result from structural abnormalities of any anatomic part of the tricuspid valve apparatus. While trivial and moderate TR are compensated by the right atrial compliance, severe regurgitation conditions can result in congestive heart failure and hemodynamic impairment. We aim to model the non-invasive caval implantation treatment of TR seen in one patient using the novel bicaval transcatheter system (TricValve). Geometric models of TricValve devices were obtained from manufacturing guidelines and photography of devices. Then, the TricValve was simulated in a patient-specific model to assess the device structural performance. Computational fluid dynamics was also used to evaluate the pre- and post-TricValve haemodynamic. Ultimately, this study has the potential to better understanding the biomechanical performance of the novel TricValve system and may improve the way we design the next-generation of transcatheter therapies for severe TR
On the accuracy of the segmentation process and transcatheter heart valve dimensions in TAVI patients
No full textAccurate segmentation of medical images is critical for generating patient-specific models suitable for computational analyses, particularly in the context of transcatheter aortic valve implantation (TAVI). This study aimed to quantify the accuracy of the segmentation process from medical images of TAVI patients to understand the uncertainty in patient-specific geometries. We also quantified discrepancies between actual and CT-related diameter measurements due to artifacts and intra-observer variability. Segmentation accuracy was assessed using both synthetic phantom models and patient-specific data. The impact of voxelization and CT scanner resolution on segmentation accuracy was evaluated, while the intersection over union (IoU) metric was used to compare the consistency of different segmentation methodologies. The voxelization process introduced a marginal error (<1%) in phantom models relative to CAD models. CT scanner resolution impacted segmented model accuracy only after a 7.5-fold increase in voxel size compared to the baseline medical image. IoU analysis revealed higher segmentation accuracy for calcification (93.4 ± 3.1 %) compared to the aortic wall (85.4 ± 8.4 %) and native valve leaflets (75.5 ± 6.3 %). Discrepancies in THV diameter measurements highlighted a ∼5 % error due to metallic artifacts, with variability among observers and at different THV heights. Errors due to voxel size, segmentation methodologies and CT-related artifacts can impact the reliability of patient-specific geometries and ultimately computational predictions used to asses clinical outcomes and enhance decision-making. This study underscores the importance of accurate segmentation and its standardization for patient-specific modeling of TAVI simulations
Evaluating the accuracy of 3D printing and finite element analysis in transcatheter aortic valveimplantation: a comparative study against post-TAVI CT imaging
No full textTranscatheter aortic valve implantation (TAVI) is now the standard treatment for aortic stenosis, offering a less invasive alternative to surgery. While 3D printing and finite element analysis (FEA) show promise for pre-procedural planning, their accuracy in predicting post-TAVI device geometry remains unclear. This study evaluates the agreement between patient-specific FEA models, 3D-printed phantoms, and post-TAVI CT imaging in replicating implanted device geometry. Ten patients treated with the SAPIEN 3 Ultra (S3) device were analysed using pre- and post-TAVI CT scans. Both FEA simulations and 3D-printed models were assessed for stent deformation and anatomical fit. Agreement was quantified using statistical tools including concordance correlation coefficient (CCC), intraclass correlation coefficient (ICC), and Bland-Altman plots. FEA showed stronger agreement with post-TAVI CT (ICC = 0.614, CCC = 0.479) than 3D printing (ICC = 0.363, CCC = 0.165), which had higher variability. While FEA closely approximated device expansion at the annular level, both methods had limitations due to material and computational assumptions. The study supports the greater reliability of FEA in pre-procedural planning, highlighting the need for further validation and standardisation
Biomechanical performance of the Bicaval Transcatheter System for the treatment of severe tricuspid regurgitation
Full text linkIntroduction: Tricuspid regurgitation (TR) is a relatively common valvular disease, which can result from structural abnormalities of any anatomic part of the tricuspid valve. Severe TR is linked to congestive heart failure and hemodynamic impairment, resulting in high mortality when repaired by elective surgery. This study was undertaken to quantify the structural and hemodynamic performance of the novel Transcatheter Bicaval Valves System (TricValve) percutaneously implanted in the superior vena cava (SVC) and inferior vena cava (IVC) of two patients with severe TR and venous congestion. Methods: After developing the SVC and IVC device models, the contact pressure exerted on the vena cava wall was obtained by computational analysis. Both smoothed-particle hydrodynamics (SPH) and computational fluid dynamics were carried out to quantify caval reflux in the right atrium and the pressure field of pre- and post-TricValve scenarios, respectively. Results: Analysis of contact pressure highlighted the main anchoring area of the SVC device occurring near the SVC device belly, while the IVC device exerted pronounced forces in the device’s proximal and distal parts. SPH-related flow velocities revealed the absence of caval reflux, and a decrease in time-averaged pressure was observed near the SVC and IVC after TricValve implantation. Discussion: Findings demonstrated the potential of computational tools for enhancing our understanding of the biomechanical performance of structural tricuspid valve interventions and improving the way we design next-generation transcatheter therapies to treat the tricuspid valve with heterotopic caval valve implantation
- …
