Comparison of ultrasound vector flow imaging and CFD simulations with PIV measurements of flow in a left ventricular outflow trackt phantom - Implications for clinical use and in silico studies

In this study we have compared two modalities for flow quantification from measurement data; ultrasound (US) and shadow particle image velocimetry (PIV), and a flow simulation model using computational fluid dynamics (CFD). For the comparison we have used an idealized Quasi-2D phantom of the human left ventricular outflow tract (LVOT). The PIV data will serve as a reference for the true flow field in our setup. Furthermore, the US vector flow imaging (VFI) data has been post processed with model-based regularization developed to both smooth noise and sharpen physical flow features. The US VFI flow reconstruction results in an underestimation of the flow velocity magnitude compared to PIV and CFD. The CFD results coincide very well with the PIV flow field maximum velocities and curl intensity, as well as with the detailed vortex structure, however, this correspondence is subject to exact boundary conditions.publishedVersio

A Scientific Tool for Real-time Acquisition and Analysis of Cardiovascular Measurements : Including ultrasound and other physiological data sources

En programvare for studier av karsystemet, for både eksperimentelle og kliniske forsøk, skal utvikles i denne oppgaven. Data fra både ultralyd og andre fysiologiske kilder, som trykk, blodstrøm og volum, skal kunne mottas i sanntid. Datakildene må synkroniseres for at målingene skal kunne kombineres og sammenlignes. B-mode og Color Flow skal være støttet av det utviklede programmet, slik at data(hovedsakelig hastighet) kan ekstraheres fra områder i bilde.Brukergrensesnittet skal være intuitivt for akkvisisjon og analyse, og sørge for muligheter for funksjonell lagring av data i et format som kan importeres til annen programvare, som Matlab, for ytterligere analyse

In vivo intracardiac vector flow imaging using phased array transducers for pediatric cardiology

Two-dimensional blood speckle tracking (ST) has shown promise for measuring complex flow patterns in neonatal hearts using linear arrays and high-frame-rate plane wave imaging. For general pediatric applications, however, the need for phased array probes emerges due to the limited intercostal acoustic window available. In this paper, a clinically approved real-time duplex imaging setup with phased array probes was used to investigate the potential of blood ST for the 2-D vector flow imaging of children with congenital heart disease. To investigate transmit beam pattern and tracking accuracy, straight tubes with parabolic flow were simulated at three depths (4.5, 7, and 9.5 cm). Due to the small aperture available, diffraction effects could be observed when approaching 10 cm, which limited the number of parallel receive beams that could be utilized. Moving to (slightly) diverging beams was shown to solve this issue at the expense of a loss in signal-to-noise ratio. To achieve consistent estimates, a forward-backward tracking scheme was introduced to avoid measurement bias occurring due to tracking kernel averaging artifacts at flow domain boundaries. Promising results were observed for depths <;10 cm in two pediatric patients, where complex cardiac flow patterns could be estimated and visualized. As a loss in penetration compared with color flow imaging is expected, a larger clinical study is needed to establish the clinical feasibility of this approach

Intraventricular Vector Flow Imaging with Blood Speckle Tracking in Adults: Feasibility, Normal Physiology and Mechanisms in Healthy Volunteers

This study examines the feasibility of blood speckle tracking for vector flow imaging in healthy adults and describes the physiologic flow pattern and vortex formation in relation to the wall motion in the left ventricle. The study included 21 healthy volunteers and quantified and visualized flow patterns with high temporal resolution down to a depth of 10–12 cm without the use of contrast agents. Intraventricular flow seems to originate during the isovolumetric relaxation with a propagation of blood from base to apex. With the E-wave, rapid inflow and vortex formation occurred on both sides of the valve basally. During diastasis the flow gathers in a large vortex before the pattern from the E-wave repeats during the A-wave. In isovolumetric contraction, the flow again gathers in a large vortex that seems to facilitate the flow out in the aorta during systole. No signs of a persistent systolic vortex were visualized. The geometry of the left ventricle and the movement of the AV-plane is important in creating vortices that are favorable for the blood flow and facilitate outflow. The quantitative measurements are in concordance with these findings, but the clinical interpretation must be evaluated in future clinical studies

Blood Speckle-Tracking Based on High–Frame Rate Ultrasound Imaging in Pediatric Cardiology

Background: Flow properties play an important role in cardiac function, remodeling, and morphogenesis but cannot be displayed in detail with today’s echocardiographic techniques. The authors hypothesized that blood speckle-tracking (BST) could visualize and quantify flow patterns. The aim of this study was to determine the feasibility, accuracy, and potential clinical applications of BST in pediatric cardiology. Methods: BST is based on high–frame rate ultrasound, using a combination of plane-wave imaging and parallel receive beamforming. Pattern-matching techniques are used to quantify blood speckle motion. Accuracy of BST velocity measurements was validated using a rotating phantom and by comparing BST-derived inflow velocities with pulsed-wave Doppler obtained in the left ventricles of healthy control subjects. To test clinical feasibility, 102 subjects (21 weeks to 11.5 years of age) were prospectively enrolled, including healthy fetuses (n = 4), healthy control subjects (n = 51), and patients with different cardiac diseases (n = 47). Results: The phantom data showed a good correlation (r = 0.95, with a tracking quality threshold of 0.4) between estimated BST velocities and reference velocities down to a depth of 8 cm. There was a good correlation (r = 0.76) between left ventricular inflow velocity measured using BST and pulsed-wave Doppler. BST displayed lower velocities (mean 6 SD, 0.59 6 0.14 vs 0.82 6 0.21 m/sec for pulsed-wave Doppler). However, the velocity amplitude in BST increases with reduced smoothing. The clinical feasibility of BST was high, as flow patterns in the area of interest could be visualized in all but one case (>99%). Conclusions: BST is highly feasible in fetal and pediatric echocardiography and provides a novel approach for visualizing blood flow patterns. BST provides accurate velocity measurements down to 8 cm, but compared with pulsed-wave Doppler, BST displays lower velocities. Studying blood flow properties may provide novel insights into the pathophysiology of pediatric heart disease and could become an important diagnostic tool

Detailed flow visualization in fetal and neonatal hearts using 2-D speckle tracking

Two-dimensional blood speckle tracking has shown promise for measuring the complex flow patterns in neonatal hearts when based on linear array and high-frame-rate plane wave imaging. For phased array pediatric imaging, additional challenges emerge due to the reduced lateral bandwidth and increased imaging depth and field-of-view. In this work, a clinically approved setup with pediatric phased array probes and unfocused pulses was used to investigate the potential of blood speckle tracking to acquire 2-D vector velocity maps for neonates, infants and children with congenital heart disease.Promising results were observed for depths <; 10 cm, where complex cardiac flow patterns could be visualized. However, due to the small aperture available, diffraction effects could be observed. Further, as the depth dependent lateral resolution and loss in signal-to-noise ratio degrades tracking results for increasing depths, a larger feasibility study is needed to establish clinical viability. Vector velocity maps were also obtained from fetal examinations with the phased array setup as well as with a diverging beam setup on a research scanner, where detailed secondary flows such as the vortex formations in the ventricles of the fetal heart could be observed

Comparison of ultrasound vector flow imaging and CFD simulations with PIV measurements of flow in a left ventricular outflow trackt phantom - Implications for clinical use and in silico studies

In this study we have compared two modalities for flow quantification from measurement data; ultrasound (US) and shadow particle image velocimetry (PIV), and a flow simulation model using computational fluid dynamics (CFD). For the comparison we have used an idealized Quasi-2D phantom of the human left ventricular outflow tract (LVOT). The PIV data will serve as a reference for the true flow field in our setup. Furthermore, the US vector flow imaging (VFI) data has been post processed with model-based regularization developed to both smooth noise and sharpen physical flow features. The US VFI flow reconstruction results in an underestimation of the flow velocity magnitude compared to PIV and CFD. The CFD results coincide very well with the PIV flow field maximum velocities and curl intensity, as well as with the detailed vortex structure, however, this correspondence is subject to exact boundary conditions

Comparison of ultrasound vector flow imaging and CFD simulations with PIV measurements of flow in a left ventricular outflow trackt phantom - Implications for clinical use and in silico studies

In this study we have compared two modalities for flow quantification from measurement data; ultrasound (US) and shadow particle image velocimetry (PIV), and a flow simulation model using computational fluid dynamics (CFD). For the comparison we have used an idealized Quasi-2D phantom of the human left ventricular outflow tract (LVOT). The PIV data will serve as a reference for the true flow field in our setup. Furthermore, the US vector flow imaging (VFI) data has been post processed with model-based regularization developed to both smooth noise and sharpen physical flow features. The US VFI flow reconstruction results in an underestimation of the flow velocity magnitude compared to PIV and CFD. The CFD results coincide very well with the PIV flow field maximum velocities and curl intensity, as well as with the detailed vortex structure, however, this correspondence is subject to exact boundary conditions