4-D Echo-Particle Image Velocimetry in a Left Ventricular Phantom
TL;DR: It is demonstrated that 4-D echo-PIV could be performed in just four heart cycles, which would require only a short breath-hold, providing promising results, however, methods for resolving high velocity gradients in regions of poor spatial resolution are required before clinical translation.
Abstract: Left ventricular (LV) blood flow is an inherently complex time-varying 3-D phenomenon, where 2-D quantification often ignores the effect of out-of-plane motion. In this study, we describe high frame rate 4-D echocardiographic particle image velocimetry (echo-PIV) using a prototype matrix transesophageal transducer and a dynamic LV phantom for testing the accuracy of echo-PIV in the presence of complex flow patterns. Optical time-resolved tomographic PIV (tomo-PIV) was used as a reference standard for comparison. Echo-PIV and tomo-PIV agreed on the general profile of the LV flow patterns, but echo-PIV smoothed out the smaller flow structures. Echo-PIV also underestimated the flow rates at greater imaging depths, where the PIV kernel size and transducer point spread function were large relative to the velocity gradients. We demonstrate that 4-D echo-PIV could be performed in just four heart cycles, which would require only a short breath-hold, providing promising results. However, methods for resolving high velocity gradients in regions of poor spatial resolution are required before clinical translation.
Citations
More filters
TL;DR: A review is presented of measurement techniques to characterise dispersed multiphase flows, which are not accessible by means of conventional optical techniques, and X-ray imaging is demonstrated to be an important tool to quantify local gas fractions.
Abstract: A review is presented of measurement techniques to characterise dispersed multiphase flows, which are not accessible by means of conventional optical techniques. The main issues that limit the accuracy and effectiveness of optical techniques are briefly discussed: cross-talk, a reduced signal-to-noise ratio, and (biased) data drop-out. Extensions to the standard optical techniques include the use of fluorescent tracers, refractive index matching, ballistic imaging, structured illumination, and optical coherence tomography. As the first non-optical technique, a brief discussion of electrical capacitance tomography is given. While truly non-invasive, it suffers from a low resolving power. Ultrasound-based techniques have rapidly evolved from Doppler-based profiling to recent 2D approaches using feature tracking. The latter is also suitable for time-resolved flow studies. Magnetic resonance velocimetry can provide time-averaged velocity fields in 3D for the continuous phase. Finally, X-ray imaging is demonstrated to be an important tool to quantify local gas fractions. While potentially very powerful, the impact of the techniques will depend on the development of acquisition and measurement protocols for fluid mechanics, rather than for clinical imaging. This requires systematic development, aided by careful validation experiments. As theoretical predictions for multiphase flows are sparse, it is important to formulate standardised ‘benchmark’ flows to enable this validation.
36 citations
Cites background from "4-D Echo-Particle Image Velocimetry..."
...Recently, even 4D measurements have been reported [104]....
[...]
21 citations
TL;DR: In this paper, an efficient 3D high-frame-rate vector Doppler method, which estimates the displacements in the frequency domain, is proposed, which extends to 3D an approach so far proposed for two-dimensional (2-D) velocity measurements.
Abstract: Ultrasound vector Doppler techniques for three-dimensional (3-D) blood velocity measurements are currently limited by low temporal resolution and high computational cost. In this paper, an efficient 3-D high-frame-rate vector Doppler method, which estimates the displacements in the frequency domain, is proposed. The novel method extends to 3-D an approach so far proposed for two-dimensional (2-D) velocity measurements by approximating the (x, y, z) displacement of a small volume through the displacements estimated for the 2-D regions parallel to the y and x directions, respectively. The new method was tested by simulation and experiments for a 3.7 MHz, 256-element, 2-D piezoelectric sparse spiral array. Simulations were also performed for an equivalent 7 MHz Capacitive Micromachined Ultrasonic Transducer spiral array. The results indicate performance (bias ± standard deviation: 6.5 ± 8.0) comparable to the performance obtained by using a linear array for 2-D velocity measurements. These results are particularly encouraging when considering that sparse arrays were used, which involve a lower signal-to-noise ratio and worse beam characteristics with respect to full 2-D arrays.
15 citations
TL;DR: It is demonstrated that contrast-enhanced UIV is capable of measuring spatiotemporal variation in flow velocity, arterial wall location and hence WSS in vivo with high accuracy over a large field of view.
Abstract: Abnormal blood flow and wall shear stress (WSS) can cause and be caused by cardiovascular disease. To date, however, no standard method has been established for mapping WSS in vivo. Here we demonstrate wide-field assessment of WSS in the rabbit abdominal aorta using contrast-enhanced ultrasound image velocimetry (UIV). Flow and WSS measurements were made independent of beam angle, curvature or branching. Measurements were validated in an in silico model of the rabbit thoracic aorta with moving walls and pulsatile flow. Mean errors over a cardiac cycle for velocity and WSS were 0.34 and 1.69%, respectively. In vivo time average WSS in a straight segment of the suprarenal aorta correlated highly with simulations (PC = 0.99) with a mean deviation of 0.29 Pa or 5.16%. To assess fundamental plausibility of the measurement, UIV WSS was compared to an analytic approximation derived from the Poiseuille equation; the discrepancy was 17%. Mapping of WSS was also demonstrated in regions of arterial branching. High time average WSS (TAWSSxz = 3.4 Pa) and oscillatory flow (OSIxz = 0.3) were observed near the origin of conduit arteries. In conclusion, we have demonstrated that contrast-enhanced UIV is capable of measuring spatiotemporal variation in flow velocity, arterial wall location and hence WSS in vivo with high accuracy over a large field of view.
15 citations
TL;DR: Current advanced ultrasound equipment is technologically ready for use in human contrast-enhanced studies, thus potentially leading to identification of the most clinically relevant flow parameters for quantifying cardiac and vascular function.
Abstract: Cardiac function and vascular function are closely related to the flow of blood within. The flow velocities in these larger cavities easily reach 1 m/s, and generally complex spatiotemporal flow patterns are involved, especially in a non-physiologic state. Visualization of such flow patterns using ultrasound can be greatly enhanced by administration of contrast agents. Tracking the high-velocity complex flows is challenging with current clinical echographic tools, mostly because of limitations in signal-to-noise ratio; estimation of lateral velocities; and/or frame rate of the contrast-enhanced imaging mode. This review addresses the state of the art in 2-D high-frame-rate contrast-enhanced echography of ventricular and deep-vessel flow, from both technological and clinical perspectives. It concludes that current advanced ultrasound equipment is technologically ready for use in human contrast-enhanced studies, thus potentially leading to identification of the most clinically relevant flow parameters for quantifying cardiac and vascular function.
12 citations
References
More filters
01 Jan 2005
TL;DR: This chapter describes the design and features of a visualization tool called ParaView, a tool that allows scientists to visualize and analyze extremely large datasets and discusses key design decisions and tradeoffs.
Abstract: This chapter describes the design and features of a visualization tool called ParaView, a tool that allows scientists to visualize and analyze extremely large datasets. The tool provides a graphical user interface for the creation and dynamic execution of visualization tasks. ParaView transparently supports the visualization and rendering of large datasets by executing these programs in parallel on shared or distributed memory machines. ParaView supports hardware-accelerated parallel rendering and achieves interactive rendering performance via level-of-detail techniques. The design balances and integrates a number of diverse requirements, including the ability to handle large data, ease of use, and extensibility by developers. The chapter describes the requirements that guided the design, identifies the importance of those requirements to scientific users, and discusses key design decisions and tradeoffs.
1,683 citations
TL;DR: In this article, an adaptation of the original median test for the detection of spurious PIV data is proposed that normalizes the median residual with respect to a robust estimate of the local variation of the velocity.
Abstract: An adaptation of the original median test for the detection of spurious PIV data is proposed that normalizes the median residual with respect to a robust estimate of the local variation of the velocity. It is demonstrated that the normalized median test yields a more or less ‘universal’ probability density function for the residual and that a single threshold value can be applied to effectively detect spurious vectors. The generality of the proposed method is verified by the application to a large variety of documented flow cases with values of the Reynolds number ranging from 10−1 to 107.
1,121 citations
Additional excerpts
...Outlier detection Universal outlier detector (Westerweel and Scarano 2005) Gaussian temporal moving average Standard dev....
[...]
TL;DR: An image-processing technique that performs iterative interrogation of particle image velocimetry (PIV) recordings based on cross-correlation enhances the matching performances by means of a relative transformation between the interrogation areas, showing that a remarkable improvement can be obtained in terms of precision and dynamic range.
Abstract: An image-processing technique is proposed, which performs iterative interrogation of particle image velocimetry (PIV) recordings. The method is based on cross-correlation, enhancing the matching performances by means of a relative transformation between the interrogation areas. On the basis of an iterative prediction of the tracers motion, window offset and deformation are applied, accounting for the local deformation of the fluid continuum. In addition, progressive grid refinement is applied in order to maximise the spatial resolution. The performances of the method are analysed and compared with the conventional cross correlation with and without the effect of a window discrete offset. The assessment of performance through synthetic PIV images shows that a remarkable improvement can be obtained in terms of precision and dynamic range. Moreover, peak-locking effects do not affect the method in practice. The velocity gradient range accessed with the application of a relative window deformation (linear approximation) is significantly enlarged, as confirmed in the experimental results.
640 citations
TL;DR: It is described that 4D Flow CMR can be clinically advantageous because placement of a single acquisition volume is straightforward and enables flow through any plane across it to be calculated retrospectively and with good accuracy.
Abstract: Pulsatile blood flow through the cavities of the heart and great vessels is time-varying and multidirectional. Access to all regions, phases and directions of cardiovascular flows has formerly been limited. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has enabled more comprehensive access to such flows, with typical spatial resolution of 1.5×1.5×1.5 – 3×3×3 mm3, typical temporal resolution of 30–40 ms, and acquisition times in the order of 5 to 25 min. This consensus paper is the work of physicists, physicians and biomedical engineers, active in the development and implementation of 4D Flow CMR, who have repeatedly met to share experience and ideas. The paper aims to assist understanding of acquisition and analysis methods, and their potential clinical applications with a focus on the heart and greater vessels. We describe that 4D Flow CMR can be clinically advantageous because placement of a single acquisition volume is straightforward and enables flow through any plane across it to be calculated retrospectively and with good accuracy. We also specify research and development goals that have yet to be satisfactorily achieved. Derived flow parameters, generally needing further development or validation for clinical use, include measurements of wall shear stress, pressure difference, turbulent kinetic energy, and intracardiac flow components. The dependence of measurement accuracy on acquisition parameters is considered, as are the uses of different visualization strategies for appropriate representation of time-varying multidirectional flow fields. Finally, we offer suggestions for more consistent, user-friendly implementation of 4D Flow CMR acquisition and data handling with a view to multicenter studies and more widespread adoption of the approach in routine clinical investigations.
638 citations
TL;DR: An ultrasonic human-blood-flow velocity profile measurement method using time-domain correlation of consecutive echo pairs has been developed and the interdependencies of window length, beam width, vessel diameter, and viewing angle are evaluated.
Abstract: An ultrasonic human-blood-flow velocity profile measurement method using time-domain correlation of consecutive echo pairs has been developed. The time shift between a pair of range gated echoes is estimated by searching for the shift that results in the maximum correlation. The time shift indicates the distance a group of scatterers has moved, from which flow velocity is estimated. The basis for the computer simulations and error analyses of the scheme includes a band-passed white Gaussian noise signal model for an echo from a scattering medium, the estimate of flow velocity from both a single scatterer and multiple scatterers, and a derived precision estimation. The error analysis via computer simulation includes an evaluation of errors associated with the correlation method. For a uniform flow velocity profile, beamwidth modulation represents the greatest error source. However, for a nonuniform flow velocity profile, the jitter caused by a small flow velocity gradient can exceed the other error sources. A detailed computer simulation evaluated the interdependencies of window length, beam width, vessel diameter, and viewing angle on the estimation of flow velocity. >
246 citations
Additional excerpts
...A similar interaction between velocity gradient and spatial resolution was found almost 30 y ago, where Foster et al. (1990) found (using pulsed wave Doppler) that longer range gates and larger beam widths increased underestimation of flow profiles with steep velocity gradients....
[...]