Ultrasound Vector Flow Imaging – could be a new tool in evaluation of arteriovenous fistulas for hemodialysis?

2017 ◽  
Vol 18 (4) ◽  
pp. 284-289 ◽  
Author(s):  
Ilaria Fiorina ◽  
Maria Vittoria Raciti ◽  
Alfredo Goddi ◽  
Vito Cantisani ◽  
Chandra Bortolotto ◽  
...  
Keyword(s):  
Venous Aneurysm ◽  
Flow Imaging ◽  
Angular Deviation ◽  
Complex Flow ◽  
Mean Velocity ◽  
Ultrasound Technique ◽  
Arteriovenous Fistulas ◽  
The Mean ◽  
Vessel Walls ◽  
Ultrasound Scanner

Introduction We report the use of a new ultrasound technique to evaluate the axial and lateral components of a complex flow in the arteriovenous fistula (AVF). Vector Flow Imaging (VFI) allows to identify different components of the flow in every direction, even orthogonal to the flow streamline, represented by many single vectors. VFI could help to identify flow alterations in AVF, probably responsible for its malfunction. Methods From February to June 2016, 14 consecutive patients with upper-limb AVF were examined with a Resona 7 (Mindray, Shenzhen, China) ultrasound scanner equipped with VFI. An analysis of mean velocity, angular direction and mean number of vectors impacting the vessel wall was carried out. We also identified main flow patterns present in the arterial side, into the venous aneurysm and in correspondence of significant stenosis. Results A disturbed flow with the presence of vectors directed against the vessel walls was found in 9/14 patients (64.28%): in correspondence of the iuxta-anastomotic venous side (4/9; 44.4%), into the venous aneurysmal tracts (3/9; 33.3%) and in concomitance of stenosis (2/9; 22.2%). The mean velocity of the vectors was around 20-25 cm/s, except in presence of stenosis, where the velocities were much higher (45-50 cm/s). The vectors directed against the vessel walls presented high angle attack (from 45° to 90°, with a median angular deviation 65°). Conclusions VFI was confirmed to be an innovative and intuitive imaging technology to study the flow complexity in the arteriovenous fistulas.

Stereo-PIV Measurements of Turbulent Swirling Flow Inside a Pipe

2020 ◽  
Author(s):  
Ayesha Almheiri ◽  
Lyes Khezzar ◽  
Mohamed Alshehhi ◽  
Saqib Salam ◽  
Afshin Goharzadeh
Keyword(s):  
Swirling Flow ◽  
Reverse Flow ◽  
Tangential Velocity ◽  
Circular Disk ◽  
Pipe Diameter ◽  
Working Fluid ◽  
Complex Flow ◽  
Mean Velocity ◽  
Radial Profiles ◽  
The Mean

Abstract Stereo-PIV is used to map turbulent strongly swirling flow inside a pipe connected to a closed recirculating system with a transparent test section of 0.6 m in length and a pipe diameter of 0.041 m. The Perspex pipe was immersed inside a water trough to reduce the effects of refraction. The working fluid was water and the Reynolds number based on the bulk average velocity inside the pipe and pipe diameter was equal to 14,450. The turbulent flow proceeds in the downstream direction and interacts with a circular disk. The measurements include instantaneous velocity vector fields and radial profiles of the mean axial, radial and tangential components of the velocity in the regions between the swirler exit and circular disk and around this later. The results for mean axial velocity show a symmetric behavior with a minimum reverse flow velocity along the centerline. As the flow developed along the pipe’s length, the intensity of the reversed flow was reduced and the intensity of the swirl decays. The mean tangential velocity exhibits a Rankine-vortex distribution and reached its maximum around half of the pipe’s radius. As the flow approaches the disk, the flow reaches stagnation and a complex flow pattern of vortices is formed. The PIV results are contrasted with LDV measurements of mean axial and tangential velocity. Good agreement is shown over the mean velocity profiles.

scholarly journals Complex Flow Generation and Development in a Full-Scale Turbofan Inlet

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Tamara Guimarães ◽  
K. Todd Lowe ◽  
Walter F. O'Brien
Keyword(s):  
Secondary Flow ◽  
Full Scale ◽  
Stereoscopic Particle Image Velocimetry ◽  
Complex Flow ◽  
Mean Velocity ◽  
Ground Testing ◽  
Turbofan Engines ◽  
Flow Generation ◽  
Image Velocimetry ◽  
The Mean

The future of aviation relies on the integration of airframe and propulsion systems to improve aerodynamic performance and efficiency of aircraft, bringing design challenges, such as the ingestion of nonuniform flows by turbofan engines. In this work, we describe the behavior of a complex distorted inflow in a full-scale engine rig. The distortion, as in engines on a hybrid wing body (HWB) type of aircraft, is generated by a 21-in diameter StreamVane, an array of vanes that produce prescribed secondary flow distributions. Data are acquired using stereoscopic particle image velocimetry (PIV) at three measurement planes along the inlet of the research engine (Reynolds number of 2.4 × 106). A vortex dynamics-based model, named StreamFlow, is used to predict the mean secondary flow development based on the experimental data. The mean velocity profiles show that, as flow develops axially, the vortex present in the profile migrates clockwise, opposite to the rotation of the fan, and toward the spinner of the engine. The turbulent stresses indicate that the center of the vortex meanders around a preferred location, which tightens as flow gets closer to the fan, yielding a smaller radius mean vortex near the fan. Signature features of the distortion device are observed in the velocity gradients, showing the wakes generated by the distortion screen vanes in the flow. The results obtained shed light onto the aerodynamics of swirling flows representative of distorted turbofan inlets, while further advancing the understanding of the complex vane technology presented herein for advanced ground testing.

The Mean Flow Structure Around and Within a Turbulent Junction or Horseshoe Vortex—Part I: The Upstream and Surrounding Three-Dimensional Boundary Layer

1988 ◽  
Vol 110 (4) ◽  
pp. 406-414 ◽  
Author(s):  
J. D. Menna ◽  
F. J. Pierce
Keyword(s):  
Boundary Layer ◽  
Flow Structure ◽  
Vortex Flow ◽  
Three Dimensional ◽  
Horseshoe Vortex ◽  
Mean Flow ◽  
Complex Flow ◽  
Mean Velocity ◽  
Standard Case ◽  
The Mean

The mean flow structure upstream, around, and in a turbulent junction or horseshoe vortex is reported for an incompressible, subsonic flow. This fully documented, unified, comprehensive, and self-consistent data base is offered as a benchmark or standard case for assessing the predictive capabilities of computational codes developed to predict this kind of complex flow. Part I of these papers defines the total flow being documented. The upstream and surrounding three-dimensional turbulent boundary layer-like flow away from separation has been documented with mean velocity field and turbulent kinetic energy field measurements made with hot film anemometry, and local wall shear stress measurements. Data are provided for an initial condition plane well upstream of the junction vortex flow to initiate a boundary layer calculation, and freestream or edge velocity, as well as floor static pressure, are reported to proceed with the solution. Part II of these papers covers the flow through separation and within the junction vortex flow.

scholarly journals Pediatric Transthoracic Cardiac Vector Flow Imaging – A Preliminary Pictorial Study

2018 ◽  
Vol 05 (01) ◽  
pp. E20-E26 ◽  
Author(s):  
Kristoffer Hansen ◽  
Klaus Juul ◽  
Hasse Møller-Sørensen ◽  
Jens Nilsson ◽  
Jørgen Jensen ◽  
...  
Keyword(s):  
Flow Patterns ◽  
Flow Imaging ◽  
Complex Flow ◽  
Additional Information ◽  
Conventional Ultrasound ◽  
Flow Changes ◽  
Cardiac Vector ◽  
Pediatric Echocardiography ◽  
Ultrasound Scanner ◽  
Conventional Echocardiography

Abstract Purpose Conventional pediatric echocardiography is crucial for diagnosing congenital heart disease (CHD), but the technique is impaired by angle dependency. Vector flow imaging (VFI) is an angle-independent noninvasive ultrasound alternative for blood flow assessment and can assess complex flow patterns not visible on conventional Doppler ultrasound. Materials and Methods 12 healthy newborns and 3 infants with CHD were examined with transthoracic cardiac VFI using a conventional ultrasound scanner and a linear array. Results VFI examinations revealed common cardiac flow patterns among the healthy newborns, and flow changes among the infants with CHD not previously reported with conventional echocardiography. Conclusion For assessment of cardiac flow in the normal and diseased pediatric heart, VFI may provide additional information compared to conventional echocardiography and become a useful diagnostic tool.

The flow of liquid in a stream from the standard turbine impeller

1979 ◽  
Vol 44 (3) ◽  
pp. 700-710 ◽  
Author(s):  
Ivan Fořt ◽  
Hans-Otto Möckel ◽  
Jan Drbohlav ◽  
Miroslav Hrach
Keyword(s):  
Reynolds Number ◽  
Kinematic Viscosity ◽  
Momentum Flux ◽  
Relative Size ◽  
Mean Velocity ◽  
Axial Profile ◽  
The Mean ◽  
Hot Film ◽  
Turbine Impeller

Profiles of the mean velocity have been analyzed in the stream streaking from the region of rotating standard six-blade disc turbine impeller. The profiles were obtained experimentally using a hot film thermoanemometer probe. The results of the analysis is the determination of the effect of relative size of the impeller and vessel and the kinematic viscosity of the charge on three parameters of the axial profile of the mean velocity in the examined stream. No significant change of the parameter of width of the examined stream and the momentum flux in the stream has been found in the range of parameters d/D ##m <0.25; 0.50> and the Reynolds number for mixing ReM ##m <2.90 . 101; 1 . 105>. However, a significant influence has been found of ReM (at negligible effect of d/D) on the size of the hypothetical source of motion - the radius of the tangential cylindrical jet - a. The proposed phenomenological model of the turbulent stream in region of turbine impeller has been found adequate for values of ReM exceeding 1.0 . 103.

scholarly journals The mean velocity of posterior cerebral artery and basilar artery in Parkinson's disease with sleep disorders

2021 ◽  
Vol 4 ◽  
pp. 100207
Author(s):  
Muhammad Iqbal Basri ◽  
Ida Farida ◽  
Yudy Goysal ◽  
Jumraini Tammasse ◽  
Muhammad Akbar
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Sleep Disorders ◽  
Cerebral Artery ◽  
Basilar Artery ◽  
Posterior Cerebral Artery ◽  
Mean Velocity ◽  
The Mean

Effectiveness and safety of repeated percutaneous intervention in an office-based endovascular center in maintaining hemodialysis access

Vascular ◽  
2021 ◽  
pp. 170853812110043
Author(s):  
Jay Patel ◽  
Stephanie Chang ◽  
Shaan Manawar ◽  
John Munn ◽  
Mark C Rummel ◽  
...  
Keyword(s):  
Percutaneous Intervention ◽  
Dialysis Access ◽  
Arteriovenous Graft ◽  
Hemodialysis Access ◽  
Upper Arm ◽  
Access Site ◽  
Arteriovenous Fistulas ◽  
Arteriovenous Grafts ◽  
The Mean

Objectives Percutaneous dialysis access interventions are routinely used to maintain the patency of dialysis access despite the lack of data regarding their long-term effectiveness. This retrospective study was undertaken to study the effectiveness and safety of percutaneous dialysis access interventions in arm fistulas and bridge grafts in an office-based endovascular center. Methods Patients who had a percutaneous dialysis access intervention in their upper extremity access site, performed at a single office-based endovascular center over a nine-year period (2007–2016) were included in this study. The patients’ demographic factors, patency, and complications were analyzed. Patients were entered in the study after first percutaneous dialysis access intervention. Results A total of 298 limbs in 259 patients had 913 procedures carried out over a nine-year period. There were 190 access arteriovenous fistulas and 108 arteriovenous grafts. The two most common arteriovenous fistulas were the brachiocephalic fistula ( n = 74, 39%) and radio cephalic fistula ( n = 69, 36%). Arteriovenous grafts were most commonly placed in the upper arm ( n = 66, 61%) followed by the forearm ( n = 42, 39%). The mean overall patency for all limbs was 50.86 months. Arteriovenous fistulas had a significantly longer patency than arteriovenous grafts (51.65 vs. 42.09 months; P = 0.01). In addition, patients with two or more percutaneous dialysis access intervention in their arteriovenous fistula had significantly greater patency than those with only one percutaneous dialysis access intervention (58.5 vs. 7.6 months; hazard ratio 0.41; P = 0.0008). This was not true for the arteriovenous graft group. Women represented 49% of the patient group. Their accesses had shorter patency than men (39.8 vs. 60 months; P = 0.0007). Conclusions This data support the use of repeated percutaneous dialysis access intervention to maintain long-term patency of dialysis access sites in an office-based endovascular center. Overall, fistulas have longer patency than grafts and women have poorer outcomes as compared to men

scholarly journals Comparison of implant placement accuracy in two different preoperative digital workflows: navigated vs. pilot-drill-guided surgery

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Johannes Spille ◽  
Feilu Jin ◽  
Eleonore Behrens ◽  
Yahya Açil ◽  
Jürgen Lichtenstein ◽  
...  
Keyword(s):  
Navigation System ◽  
Entry Point ◽  
Angular Deviation ◽  
Guided Surgery ◽  
Implant Placement ◽  
Drill Guide ◽  
Navigation Group ◽  
3D Printed ◽  
The Mean ◽  
Master Model

Abstract Background The aim of the study is to evaluate the accuracy of a new implant navigation system on two different digital workflows. Methods A total of 18 phantom jaws consisting of hard and non-warping plastic and resembling edentulous jaws were used to stimulate a clinical circumstance. A conventional pilot-drill guide was conducted by a technician, and a master model was set by using this laboratory-produced guide. After cone beam computed tomography (CBCT) and 3D scanning of the master models, two different digital workflows (marker tray in CBCT and 3D-printed tray) were performed based on the Digital Imaging Communication in Medicine files and standard tessellation language files. Eight Straumann implants (4.1 mm × 10 mm) were placed in each model, six models for each group, resulting in 144 implant placements in total. Postoperative CBCT were taken, and deviations at the entry point and apex as well as angular deviations were measured compared to the master model. Results The mean total deviations at the implant entry point for MTC (marker tray in CBCT), 3dPT (3d-printed tray), and PDG (pilot-drill guide) were 1.024 ± 0.446 mm, 1.027 ± 0.455 mm, and 1.009 ± 0.415 mm, respectively, and the mean total deviations at the implant apex were 1.026 ± 0.383 mm, 1.116 ± 0.530 mm, and 1.068 ± 0.384 mm. The angular deviation for the MTC group was 2.22 ± 1.54°. The 3dPT group revealed an angular deviation of 1.95 ± 1.35°, whereas the PDG group showed a mean angular deviation of 2.67 ± 1.58°. Although there were no significant differences among the three groups (P > 0.05), the navigation groups showed lesser angular deviations compared to the pilot-drill-guide (PDG) group. Implants in the 3D-printed tray navigation group showed higher deviations at both entry point and apex. Conclusions The accuracy of the evaluated navigation system was similar with the accuracy of a pilot-drill guide. Accuracy of both preoperative workflows (marker tray in CBCT or 3D-printed tray) was reliable for clinical use.

scholarly journals Accuracy, Labor-Time and Patient-Reported Outcomes with Partially versus Fully Digital Workflow for Flapless Guided Dental Implants Insertion—A Randomized Clinical Trial with One-Year Follow-Up

2021 ◽  
Vol 10 (5) ◽  
pp. 1102
Author(s):  
Corina Marilena Cristache ◽  
Mihai Burlibasa ◽  
Ioana Tudor ◽  
Eugenia Eftimie Totu ◽  
Fabrizio Di Francesco ◽  
...  
Keyword(s):  
Clinical Trial ◽  
Randomized Clinical Trial ◽  
Dental Implants ◽  
Entry Point ◽  
Angular Deviation ◽  
Digital Workflow ◽  
Position Information ◽  
Patient Reported ◽  
The Mean ◽  
Edentulous Patients

(1) Background: Prosthetically-driven implant positioning is a prerequisite for long-term successful treatment. Transferring the planned implant position information to the clinical setting could be done using either static or dynamic guided techniques. The 3D model of the bone and surrounding structures is obtained via cone beam computed tomography (CBCT) and the patient’s oral condition can be acquired conventionally and then digitalized using a desktop scanner, partially digital workflow (PDW) or digitally with the aid of an intraoral scanner (FDW). The aim of the present randomized clinical trial (RCT) was to compare the accuracy of flapless dental implants insertion in partially edentulous patients with a static surgical template obtained through PDW and FDW. Patient outcome and time spent from data collection to template manufacturing were also compared. (2) Methods: 66 partially edentulous sites (at 49 patients) were randomly assigned to a PDW or FDW for guided implant insertion. Planned and placed implants position were compared by assessing four deviation parameters: 3D error at the entry point, 3D error at the apex, angular deviation, and vertical deviation at entry point. (3) Results: A total of 111 implants were inserted. No implant loss during osseointegration or mechanical and technical complications occurred during the first-year post-implants loading. The mean error at the entry point was 0.44 mm (FDW) and 0.85 (PDW), p ≤ 0.00; at implant apex, 1.03 (FDW) and 1.48 (PDW), p ≤ 0.00; the mean angular deviation, 2.12° (FDW) and 2.48° (PDW), p = 0.03 and the mean depth deviation, 0.45 mm (FDW) and 0.68 mm (PDW), p ≤ 0.00; (4) Conclusions: Despite the statistically significant differences between the groups, and in the limits of the present study, full digital workflow as well as partially digital workflow are predictable methods for accurate prosthetically driven guided implants insertion.

scholarly journals Effect of Mean Velocity-to-Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 883
Author(s):  
Nargess Moghaddassi ◽  
Seyed Habib Musavi-Jahromi ◽  
Mohammad Vaghefi ◽  
Amir Khosrojerdi
Keyword(s):  
Experimental Investigation ◽  
Critical Velocity ◽  
Velocity Ratio ◽  
Scour Depth ◽  
Incipient Motion ◽  
Mean Velocity ◽  
Straight Path ◽  
Meandering Channel ◽  
Bed Topography ◽  
The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity-to-critical velocity ratios have been tested at the upstream straight path to determine the meander’s incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity-to-critical velocity ratios. In addition, the upstream bend’s effect on the downstream bend was investigated. Results indicated that the maximum scour depth at the downstream bend increased as a result of changing the mean velocity-to-critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by, respectively, 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend’s incipient motion was observed for the mean velocity-to-critical velocity ratio of 0.89, while the downstream bend’s incipient motion occurred for the ratio of 0.78.

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