Shunt quantification in congenital heart disease based on two-dimensional speckle tracking

In this work we investigated how high frame rate speckle tracking based on plane wave imaging could be used to improve the quantification of peak velocities in shunt flows due to septal defects. Simulated jet flow was used to optimize acquisition and tracking parameters. In vivo, a packet based acquisition scheme was used where focused B-mode scans were interleaved high frame rate flow images (100 fps). Results showed that speckle tracking provides calibrated velocities in the shunt flow throughout the cardiac cycle, and improved estimates of peak velocities used for diagnosing shunt severity were acquired

Assessing the performance of ultrafast vector flow imaging in the neonatal heart via multiphysics modeling and In vitro experiments

Ultrafast vector flow imaging would benefit newborn patients with congenital heart disorders, but still requires thorough validation before translation to clinical practice. This paper investigates 2-D speckle tracking (ST) of intraventricular blood flow in neonates when transmitting diverging waves at ultrafast frame rate. Computational and in vitro studies enabled us to quantify the performance and identify artifacts related to the flow and the imaging sequence. First, synthetic ultrasound images of a neonate's left ventricular flow pattern were obtained with the ultrasound simulator Field II by propagating point scatterers according to 3-D intraventricular flow fields obtained with computational fluid dynamics (CFD). Noncompounded diverging waves (opening angle of 60 degrees) were transmitted at a pulse repetition frequency of 9 kHz. ST of the B-mode data provided 2-D flow estimates at 180 Hz, which were compared with the CFD flow field. We demonstrated that the diastolic inflow jet showed a strong bias in the lateral velocity estimates at the edges of the jet, as confirmed by additional in vitro tests on a jet flow phantom. Furthermore, ST performance was highly dependent on the cardiac phase with low flows (< 5 cm/s), high spatial flow gradients, and out-of-plane flow as deteriorating factors. Despite the observed artifacts, a good overall performance of 2-D ST was obtained with a median magnitude underestimation and angular deviation of, respectively, 28% and 13.5 degrees during systole and 16% and 10.5 degrees during diastole

Two-Dimensional Blood Velocity Estimation for Intracardiac Flow Assessment

Måling av blodstrømshastigheter i hjertet Ultralyd (ekkokardiografi) og fargedoppler er viktige verktøy som brukes for å detektere og visualisere medfødt hjertefeil. To av de mest vanlige formene for medfødt hjertefeil er atrie- og ventrikkelseptumdefekter, som er hull i hjerteveggen (septum) mellom forkamrene eller hjertekamrene. Et slikt hull gjør vanligvis at blod kan strømme direkte fra venstre til høyre side av hjertet som igjen kan føre til økt belastning i lungekretsløpet. Hastigheten til blodstrømmen gjennom hullet er et av målene som brukes til å avgjøre defektens alvorlighetsgrad. Denne målingen blir kun nøyaktig med konvensjonelle ultralydmetoder hvis ultralydstrålen har samme retning som blodstrømmen. Dette er på grunn av en fundamental begrensning ved konvensjonell ultralyd; bare den endimensjonale hastighetskomponenten langs ultralydstrålen blir målt. Utvikling av nye ultralydmetoder som kan måle to eller tre hastighetskomponenter av den tredimensjonale blodstrømsvektoren er derfor av klinisk nytteverdi og vil både kunne bedre visualiseringen av den komplekse blodstrømningen gjennom hjertet og gi bedre kvantitative mål på blodstrømshastigheten. Grunnlaget for arbeidet som er presentert i denne avhandlingen er de teknologiske nyvinningene som gjør at vi nå kan avbilde med en mye høyere bilderate enn før. Den høye bilderaten oppnås ved å sende ufokuserte (plane) i stedet for fokuserte lydbølger og ved å bruke parallell stråleforming som gjør at vi kan lage et ultralydbilde etter bare én utsendt lydbølge. I denne avhandlingen brukte vi en metode kalt speckle tracking for å estimere de todimensjonale blodstrømshastighetene. Ekkoet fra blod (og vev) gir et unikt intensitetsmønster i ultralydbildet og en kan derfor spore dette specklemønsteret fra bilde til bilde for å finne forflytningen til blodet og estimere blodstrømshastigheten. I den første studien ble nyfødte med hjertefeil undersøkt med den nye teknikken, og resultatene indikerer at den nye metoden kan brukes til å kvantifisere blodstrømshastigheter gjennom atrie- og ventrikkelseptumdefekter og bedre visualiseringen av blodstrømsretningen i hjertet. En annen begrensing ved ultralydavbildning av blodstrøm er clutterfiltrering som brukes for å skille det svake ekkoet fra blod fra det sterke ekkoet fra vev. Vevsekkoet må filtreres vekk før blodstrømsavbildning er mulig, men filtreringen vil også begrense den laveste blodhastigheten som kan måles. I den andre studien viser vi at en mulig løsning på problematikken rundt clutterfiltrering er å vinkle de utsendte planbølgene og kombinere hastighetsestimatene fra de ulike vinklene. I den tredje studien undersøker vi hvordan clutterfiltreringen påvirker specklemønsteret og hastighetsestimeringen, og hvordan den økte bilderaten kan brukes til å forbedre clutterfiltreringen og øke hastighetsspennet som kan måles

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

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

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

A numerical study of ultrafast vector flow imaging in the neonatal heart

Doppler flow imaging for the visualisation of neonatal intraventricular blood flow currently still has inherent limitations: beam-to-flow angle dependency, aliasing and a too low frame rate. Ultrafast imaging and vector flow estimation may resolve these limitations, yet both still require thorough validation for the pediatric cardiac setting. Hence, a computational modelling approach in the neonatal left ventricle was employed to investigate (i) diverging wave emission to acquire images at very high frame rate and (ii) subsequent speckle tracking algorithms for vector flow estimation. Single non-tilted diverging waves with an opening angle of 60° were transmitted, at a pulse repetition frequency of 9 kHz. Speckle tracking on the acquired ultrasound images provided 2D intraventricular flow estimates at a frame rate of 180 Hz for both the apical four chamber and parasternal short axis view, and this over an entire cardiac cycle. Overall, the blood flow was reasonably accurately tracked throughout the cardiac cycle, yet several imaging artefacts were observed. Zones of low flow proved very difficult to track due to clutter filtering issues, while high spatial flow gradients caused strong underestimation of systolic outflow