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Imagerie ultrasonore ultra-rapide dédiée à la quantification 3D du mouvement cardiaque
Abstract
Cette thèse porte sur le développement et l’évaluation de techniques d’imagerie en échocardiographie. L’objectif est de proposer des méthodes d’imagerie ultrasonore ultrarapide pour estimer le mouvement cardiaque 2-D et 3-D.Première modalité d’imagerie du cœur, l’échocardiographie conventionnelle permet la mesure des déformations myocardiques à 80 images/s. Cette cadence d’imagerie est insuffisante pour quantifier les mouvements de la totalité du myocarde lors de tests d’efforts, utiles en évaluation clinique, au cours desquels le rythme cardiaque est augmenté. De plus, la résolution temporelle actuelle en échocardiographie 3-D limite ses applications, pourtant essentielles pour une caractérisation complète du cœur.Les contributions présentées ici sont 1) le développement et l’évaluation, pour l’application cardiaque, d’une méthode originale d’estimation de mouvement 2-D par imagerie ultrarapide et marquage des images, 2) l’étude de faisabilité de la mesure globale des déformations cardiaques avec une méthode innovante d’imagerie ultrasonore ultrarapide 2-D et 3) la généralisation de cette approche en 3-D pour l’imagerie des volumes cardiaques à haute résolution temporelle. Cette technique est basée sur l’émission d’ondes divergentes, et l’intégration d’une compensation de mouvement dans le processus de formation des volumes cardiaques.La méthode proposée permet l’estimation des mouvements cardiaques 2-D et l’échocardiographie ultrarapide 3-D. L’évaluation de notre approche pour la quantification des déformations myocardiques locales 2-D et 3-D pourrait permettre de proposer des pistes innovantes pour poursuivre nos études et améliorer le diagnostic en routine clinique
... An interesting approach for estimating 3D velocity vectors, based on Transverse Oscillations, was proposed in (Pihl & Jensen 2014), . Although applying such a method for cardiac applications had been shown to be challenging (Joos 2017), this technique proved promising results when tested on a flowrig system with steady flow (Pihl et al. 2013), in simulations and on a gelatin phantom . ...
Echocardiography is the most widely used imaging modality for assessing cardiac morphology and function. It does provide a non-invasive tool in diagnosis and assessment of heart diseases and it allows, in addition, monitoring the response to the treatment. However, quantifying fast cardiac events remains a challenge when using the current achievable frame rate, especially in applications such as stress-echocardiography. Moreover, this limitation becomes more pronounced in 3D conventional focused imaging due to the time needed to insonify and acquire a full volume. The fact that only ~20 volumes per second can currently be achieved is one of the reasons restricting its common usage in clinical practice. Improvements in this field would allow exploiting the important potential of 3D imaging in providing a full quantification of cardiac deformation.In this context, the aim of this thesis was to develop high frame rate methods and to test their performance in realistic conditions, aiming decision making regarding an eventual clinical translation. To achieve this objective, both in vitro and in vivo experiments were conducted using 2D and 3D imaging. Our first contribution was a 2D comparison between two high frame rate modalities in terms of image quality and motion estimation performance. Motivated by our 2D results but especially by the challenge of implementing MLT in practice, we extended this approach to 3D. We studied the feasibility of 3D MLT in both static and dynamic conditions. Finally, since testing novel approaches in physiological complex flows conditions is a step forward towards clinical translation, our third contribution was to evaluate the potential of a ring vortex phantom in providing a realistic test object to validate 2D and 3D high frame rate imaging modes.
Conventional echocardiography is the leading modality for non-invasive cardiac imaging. It has been recently illustrated that high-frame rate echocardiography using diverging waves could improve cardiac assessment. The spatial resolution and contrast associated with this method are commonly improved by coherent compounding of steered beams. However, owing to fast tissue velocities in the myocardium, the summation process of successive diverging waves can lead to destructive interferences if motion compensation (MoCo) is not considered. Coherent compounding methods based on MoCo have demonstrated their potential to provide high-contrast B-mode cardiac images. Ultrafast speckle tracking echocardiography (STE) based on common speckle tracking algorithms could substantially benefit from this original approach. In the present paper, we applied STE on high-frame-rate B-mode images obtained with a specific MoCo technique to quantify the 2-D motion and tissue velocities of the left ventricle. The method was first validated in vitro and then evaluated in vivo in the four-chamber view of ten volunteers. High-contrast high-resolution B-mode images were constructed at 500 frames per second. The sequences were generated with a Verasonics scanner and a 2.5 MHz phased array. 2-D motion was estimated with standard cross-correlation combined with three different subpixel adjustment techniques. The estimated in vitro velocity vectors derived from STE were consistent with the expected values, with normalized errors ranging from 4% to 12% in the radial direction, and from 10% to 20% in the cross-range direction. Global longitudinal strain (GLS) of the left ventricle was also obtained from STE in ten subjects and compared to the results provided by a clinical scanner: group means were not statistically different (p-value = 0.33). The in vitro and in vivo results showed that MoCo enables preservation of the myocardial speckles and in turn allows high-frame-rate STE.
The assessment of myocardial fiber disarray is of major interest for the study of the progression of myocardial disease. However, time-resolved imaging of the myocardial structure remains unavailable in clinical practice. In this study, we introduce 3D Backscatter Tensor Imaging (3D-BTI), an entirely novel ultrasound-based imaging technique that can map the myocardial fibers orientation and its dynamics with a temporal resolution of 10 ms during a single cardiac cycle, non-invasively and in vivo in entire volumes. 3D-BTI is based on ultrafast volumetric ultrasound acquisitions, which are used to quantify the spatial coherence of backscattered echoes at each point of the volume. The capability of 3D-BTI to map the fibers orientation was evaluated in vitro in 5 myocardial samples. The helicoidal transmural variation of fiber angles was in good agreement with the one obtained by histological analysis. 3D-BTI was then performed to map the fiber orientation dynamics in vivo in the beating heart of an open-chest sheep at a volume rate of 90 volumes/s. Finally, the clinical feasibility of 3D-BTI was shown on a healthy volunteer. These initial results indicate that 3D-BTI could become a fully non-invasive technique to assess myocardial disarray at the bedside of patients.
High-frame-rate ultrasonography based on coherent compounding of unfocused beams can potentially transform the assessment of cardiac function. As it requires successive waves to be combined coherently, this approach is sensitive to high-velocity tissue motion. We investigated coherent compounding of tilted diverging waves, emitted from a 2.5 MHz clinical phased array transducer. To cope with high myocardial velocities, a triangle transmit sequence of diverging waves is proposed, combined with tissue Doppler imaging to perform motion compensation (MoCo). The compound sequence with integrated MoCo was adjusted from simulations and was tested in vitro and in vivo. Realistic myocardial velocities were analyzed in an in vitro spinning disk with anechoic cysts. While a 8 dB decrease (no motion vs. high motion) was observed without MoCo, the contrast- to-noise ratio of the cysts was preserved with the MoCo approach. With this method, we could provide high-quality in vivo B-mode cardiac images with tissue Doppler at 250 frames per second. Although the septum and the anterior mitral leaflet were poorly apparent without MoCo, they became well perceptible and well contrasted with MoCo. The septal and lateral mitral annulus velocities determined by tissue Doppler were concordant with those measured by pulsed-wave Doppler with a clinical scanner (r2 = 0.7, y = 0.9 x + 0.5, N = 60). To conclude, highcontrast echocardiographic B-mode and tissue Doppler images can be obtained with diverging beams when motion compensation is integrated in the coherent compounding process.
Ultrafast imaging based on plane-wave (PW) has become an intense area of research thanks to its capability of reaching frame rate higher than a thousand of frames per second. Several proposed approaches are based on Fourier-domain reconstruction. In these techniques, the Fourier transform of the received echoes is projected to the k-space corresponding to the Fourier transform of the object function. For one emitted PW, N lines along the kz axis direction are reconstructed in the k-space. We propose in this study a new acquisition scheme which allows acquiring the non-null part of the ultrasound spectrum with finer resolution. We show that this strategy allows obtaining images with slightly better lateral resolution and higher contrast-to-noise ratio (CNR) when compared to other Fourier-based techniques.
We present a new method to estimate 4-D (3-D + time) tissue motion. The method used combines 3-D phase based motion estimation with an unconventional beamforming strategy. The beamforming technique allows us to obtain full 3-D RF volumes with axial, lateral, and elevation modulations. Based on these images, we propose a method to estimate 3-D motion that uses phase images instead of amplitude images. First, volumes featuring 3-D oscillations are created using only a single apodization function, and the 3-D displacement between two consecutive volumes is estimated simultaneously by applying this 3-D estimation. The validity of the method is investigated by conducting simulations and phantom experiments. The results are compared with those obtained with two other conventional estimation methods: block matching and optical flow. The results show that the proposed method outperforms the conventional methods, especially in the transverse directions.
Ultrafast ultrasound is a promising imaging modality that enabled, inter alia, the development of pulse wave imaging and the local velocity estimation of the so-called pulse wave for a quantitative evaluation of arterial stiffness. However, this technique only focuses on the propagation of the axial displacement of the artery wall, and most techniques are not specific to the intima-media complex and do not take into account the longitudinal motion of this complex. Within this perspective, this paper presents a study of two-dimensional tissue motion estimation in ultrafast imaging combining transverse oscillations, which can improve motion estimation in the transverse direction, i.e., perpendicular to the beam axis, and a phase-based motion estimation. First, the method was validated in simulation. Two-dimensional motion, inspired from a real data set acquired on a human carotid artery, was applied to a numerical phantom to produce a simulation data set. The estimated motion showed axial and lateral mean errors of 4.2 ± 3.4 μm and 9.9 ± 7.9 μm, respectively. Afterward, experimental results were obtained on three artery phantoms with different wall stiffnesses. In this study, the vessel phantoms did not contain a pure longitudinal displacement. The longitudinal displacements were induced by the axial force produced by the wall's axial dilatation. This paper shows that the approach presented is able to perform 2-D tissue motion estimation very accurately even if the displacement values are very small and even in the lateral direction, making it possible to estimate the pulse wave velocity in both the axial and longitudinal directions. This demonstrates the method's potential to estimate the velocity of purely longitudinal waves propagating in the longitudinal direction. Finally, the stiffnesses of the three vessel phantom walls investigated were estimated with an average relative error of 2.2%.
This paper demonstrates the fabrication, characterization, and experimental imaging results of a 62+62 element λ/2-pitch row-column-addressed capacitive micromachined ultrasonic transducer (CMUT) array with integrated apodization. A new fabrication process was used to manufacture a 26.3 mm by 26.3 mm array using five lithography steps. The array includes an integrated apodization, presented in detail in Part I of this paper, which is designed to reduce the amplitude of the ghost echoes that are otherwise prominent for row-column-addressed arrays. Custom front-end electronics were produced with the capability of transmitting and receiving on all elements, and the option of disabling the integrated apodization. The center frequency and -6-dB fractional bandwidth of the array elements were 2.77 ± 0.26 MHz and 102 ± 10%, respectively. The surface transmit pressure at 2.5 MHz was 590 ± 73 kPa, and the sensitivity was 0.299 ± 0.090 V/Pa. The nearest neighbor crosstalk level was -23.9 ± 3.7 dB, while the transmit-to-receive-elements crosstalk level was -40.2 ± 3.5 dB. Imaging of a 0.3-mm-diameter steel wire using synthetic transmit focusing with 62 single-element emissions demonstrated axial and lateral FWHMs of 0.71 mm and 1.79 mm (f-number: 1.4), respectively, compared with simulated axial and lateral FWHMs of 0.69 mm and 1.76 mm. The dominant ghost echo was reduced by 15.8 dB in measurements using the integrated apodization compared with the disabled configuration. The effect was reproduced in simulations, showing a ghost echo reduction of 18.9 dB.
Quantification of cardiac deformation and strain with 3D ultrasound takes considerable research efforts. Nevertheless, a widespread use of these techniques in clinical practice is still held back due to the lack of a solid verification process to quantify and compare performance. In this context, the use of fully synthetic sequences has become an established tool for initial in silico evaluation. Nevertheless, the realism of existing simulation techniques is still too limited to represent reliable benchmarking data. Moreover, the fact that different centers typically make use of in-house developed simulation pipelines makes a fair comparison difficult. In this context, this paper introduces a novel pipeline for the generation of synthetic 3D cardiac ultrasound image sequences. State-of-the art solutions in the fields of electromechanical modeling and ultrasound simulation are combined within an original framework that exploits a real ultrasound recording to learn and simulate realistic speckle textures. The simulated images show typical artifacts that make motion tracking in ultrasound challenging. The ground-truth displacement field is available voxelwise and is fully controlled by the electromechanical model. By progressively modifying mechanical and ultrasound parameters, the sensitivity of 3D strain algorithms to pathology and image properties can be evaluated. The proposed pipeline is used to generate an initial library of 8 sequences including healthy and pathological cases, which is made freely accessible to the research community via our project web-page..
Recognizing the critical need for standardization in strain imaging, in 2010, the European Association of Echocardiography (now the European Association of Cardiovascular Imaging, EACVI) and the American Society of Echocardiography (ASE) invited technical representatives from all interested vendors to participate in a concerted effort to reduce intervendor variability of strain measurement. As an initial product of the work of the EACVI/ASE/Industry initiative to standardize deformation imaging, we prepared this technical document which is intended to provide definitions, names, abbreviations, formulas, and procedures for calculation of physical quantities derived from speckle tracking echocardiography and thus create a common standard.
Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.
Conventional hardware for arbitrary waveform formation uses Digital-to-Analog Converters (DAC) and linear amplifiers. Proposed here are methods for encoding a tri-state pulser to approximate arbitrary waveforms. Algorithms are evaluated by simulation and experiment using the Verasonics, Inc. Vantage research ultrasound system, which transmits with 4 ns edge resolution. Two problems were considered: 1) matching the waveform produced by an ideal DAC given a particular transducer, and 2) compensating for the impulse response of a given transducer to reproduce a signal. The problems require the transducer impulse response in one-way and two-way propagation geometries, estimated here in water using a hydrophone and the ATL L7-4 transducer. Within measured nonlinear propagation effects, error in these four scenarios for an LFM waveform was consistent with simulated performance. In another test, a Gaussian pulse is encoded for transducer compensation, and compared to equivalent-bandwidth monopulse excitation in planewave imaging on a phantom. Here, a pin-trailing pedestal artifact is reduced by 3 dB over a span equal to the peak resolution (FWHM).
The Horn-Schunck (HS) method, which amounts to the Jacobi iterative scheme in the interior of the image, was one of the first optical flow algorithms. In this paper, we prove the convergence of the HS method whenever the problem is well-posed. Our result is shown in the framework of a generalization of the HS method in dimension n≥1, with a broad definition of the discrete Laplacian. In this context, the condition for the convergence is that the intensity gradients not all be contained in the same hyperplane. Two other works ([A. Mitiche and A. Mansouri, IEEE Trans. Image Process. 13, 848–852 (2004)] and [Y. Kameda, A. Imiya and N. Ohnishi, “A convergence proof for the Horn-Schunck optical-flow computation scheme using neighborhood decomposition”, in Combinatorial Image Analysis. Berlin: Springer (2008), p. 262–273]) claimed to solve this problem in the case n=2, but it appears that both of these proofs are erroneous. Moreover, we explain why some standard results about the convergence of the Jacobi method do not apply for the HS problem, unless n=1. It is also shown that the convergence of the HS scheme implies the convergence of the Gauss-Seidel and successive overrelaxation schemes for the HS problem.
Very high frame rate ultrasound imaging has recently allowed for the extension of the applications of echography to new fields of study such as the functional imaging of the brain, cardiac electrophysiology, and the quantitative imaging of the intrinsic mechanical properties of tumors, to name a few, non-invasively and in real time. In this study, we present the first implementation of Ultrafast Ultrasound Imaging in 3D based on the use of either diverging or plane waves emanating from a sparse virtual array located behind the probe. It achieves high contrast and resolution while maintaining imaging rates of thousands of volumes per second. A customized portable ultrasound system was developed to sample 1024 independent channels and to drive a 32??×??32 matrix-array probe. Its ability to track in 3D transient phenomena occurring in the millisecond range within a single ultrafast acquisition was demonstrated for 3D Shear-Wave Imaging, 3D Ultrafast Doppler Imaging, and, finally, 3D Ultrafast combined Tissue and Flow Doppler Imaging. The propagation of shear waves was tracked in a phantom and used to characterize its stiffness. 3D Ultrafast Doppler was used to obtain 3D maps of Pulsed Doppler, Color Doppler, and Power Doppler quantities in a single acquisition and revealed, at thousands of volumes per second, the complex 3D flow patterns occurring in the ventricles of the human heart during an entire cardiac cycle, as well as the 3D in vivo interaction of blood flow and wall motion during the pulse wave in the carotid at the bifurcation. This study demonstrates the potential of 3D Ultrafast Ultrasound Imaging for the 3D mapping of stiffness, tissue motion, and flow in humans in vivo and promises new clinical applications of ultrasound with reduced intra?and inter-observer variability.
High frame rate (HFR) echocardiography may be of benefit for functional analysis of the heart. In current clinical equipment, HFR is obtained using multi-line acquisition (MLA) which typically requires broadening of transmit beams. As this may result in a significant degradation of spatial resolution and signal-to-noise ratio (SNR), the capacity of MLA to obtain high quality HFR images remains limited. As an alternative, we have demonstrated by computer simulation that simultaneously transmitting multiple focused beams into different directions [multi-line transmit (MLT)], can increase the frame rate without significantly compromising the spatial resolution or SNR. This study aimed to experimentally verify these theoretical predictions both in vitro and in vivo to demonstrate, for the first time, that cardiac MLT imaging is feasible. Hereto, the ultrasound advanced open platform, equipped with a 2.0 MHz phased array, was programmed to interleave MLT and conventional single line transmit (SLT) beam forming. Using these two beam forming methods, images of phantoms and healthy volunteers were acquired and investigated both qualitatively and quantitatively. The results confirmed our simulations that image quality of a 4MLT imaging system with a Tukey apodization scheme is very competitive to that of SLT while providing a 4 times higher frame rate. It is also demonstrated that MLT can be combined with MLA to provide images at 12- to 16-fold frame rate (about 340–450 Hz) without significantly compromising spatial resolution and SNR. This is thus the first study to demonstrate that this new ultrasound imaging paradigm is viable which could have significant impact on future cardiac ultrasound systems.
Synthetic transmit aperture (STA) imaging is susceptible to tissue motion because it uses summation of low-resolution images to create the displayed high-resolution image. A method for 2-D tissue motion correction in STA imaging is presented. It utilizes the correlation between highresolution images recorded using the same emission sequence. The velocity and direction of the motion are found by cross correlating short high-resolution lines beamformed along selected angles. The motion acquisition is interleaved with the regular B-mode emissions in STA imaging, and the motion compensation is performed by tracking each pixel in the reconstructed image using the estimated velocity and direction. The method is evaluated using simulations, and phantom and in vivo experiments. In phantoms, a tissue velocity of 15 cm/s at a 45° angle was estimated with relative bias and standard deviation of -6.9% and 5.4%; the direction was estimated with relative bias and standard deviation of -8.4% and 6.6%. The contrast resolution in the corrected image was -0.65% lower than the reference image. Abdominal in vivo experiments with induced transducer motion demonstrate that severe tissue motion can be compensated for, and that doing so yields a significant increase in image quality.
Post-processing of PIV (particle image velocimetry) data typically contains three following stages: validation of the raw data, replacement of spurious and missing vectors, and some smoothing. A robust post-processing technique that carries out these steps simultaneously is proposed. The new all-in-one method (DCT-PLS), based on a penalized least squares approach (PLS), combines the use of the discrete cosine transform (DCT) and the generalized cross-validation, thus allowing fast unsupervised smoothing of PIV data. The DCT-PLS was compared with conventional methods, including the normalized median test, for post-processing of simulated and experimental raw PIV velocity fields. The DCT-PLS was shown to be more efficient than the usual methods, especially in the presence of clustered outliers. It was also demonstrated that the DCT-PLS can easily deal with a large amount of missing data. Because the proposed algorithm works in any dimension, the DCT-PLS is also suitable for post-processing of volumetric three-component PIV data.
Quantification of regional myocardial motion and deformation from cardiac ultrasound is fostering considerable research efforts. Despite the tremendous improvements done in the field, all existing approaches still face a common limitation which is intrinsically connected with the formation of the ultrasound images. Specifically, the reduced lateral resolution and the absence of phase information in the lateral direction highly limit the accuracy in the computation of lateral displacements. In this context, this paper introduces a novel setup for the estimation of cardiac motion with ultrasound. The framework includes an unconventional beamforming technique and a dedicated motion estimation algorithm. The beamformer aims at introducing phase information in the lateral direction by producing transverse oscillations. The estimator directly exploits the phase information in the two directions by decomposing the image into two 2-D single-orthant analytic signals. An in silico evaluation of the proposed framework is presented on five ultra-realistic simulated echocardiographic sequences, where the proposed motion estimator is contrasted against other two phase-based solutions exploiting the presence of transverse oscillations and against block-matching on standard images. An implementation of the new beamforming strategy on a research ultrasound platform is also shown along with a preliminary in vivo evaluation on one healthy subject.
Transverse oscillation techniques have shown their high potential for accurate and robust vector motion estimation for both flow and tissue. Unfortunately to form such images, it is necessary to modify the ultrasound scanner's beamformer. This paper proposes alternative strategies to create transverse oscillation images in order to estimate motions in ultrasound images. The proposed methods are based on 1) one dimensional convolution or filtering of the radio frequency images or 2) two dimensional convolution or filtering of the B-mode images. They are first evaluated on a single lateral motion case in simulations and experiments, and then in a quasi-static elastography situation. The results with our filtering/convolution approach are very similar to the ones obtained with TO images obtained by classical beamforming. The mean deviation between the classical TO beamforming and the proposed method is 5.5%, which validates that one direction filtering is an efficient way to simplify the creation of TO images.
Ultrafast ultrasound is an emerging modality that offers new perspectives and opportunities in medical imaging. Plane wave imaging (PWI) allows one to attain very high frame rates by transmission of planar ultrasound wavefronts. As a plane wave reaches a given scatterer, the latter becomes a secondary source emitting upward spherical waves and creating a diffraction hyperbola in the received RF signals. To produce an image of the scatterers, all the hyperbolas must be migrated back to their apexes. To perform beamforming of plane wave echo RFs and return high-quality images at high frame rates, we propose a new migration method carried out in the frequency-wavenumber (f-k) domain. The f-k migration for PWI has been adapted from the Stolt migration for seismic imaging. This migration technique is based on the exploding reflector model (ERM), which consists in assuming that all the scatterers explode in concert and become acoustic sources. The classical ERM model, however, is not appropriate for PWI. We showed that the ERM can be made suitable for PWI by a spatial transformation of the hyperbolic traces present in the RF data. In vitro experiments were performed to outline the advantages of PWI with Stolt's f-k migration over the conventional delay-and-sum (DAS) approach. The Stolt's f-k migration was also compared with the Fourier-based method developed by J.-Y. Lu. Our findings show that multi-angle compounded f-k migrated images are of quality similar to those obtained with a stateof- the-art dynamic focusing mode. This remained true even with a very small number of steering angles, thus ensuring a highly competitive frame rate. In addition, the new FFT-based f-k migration provides comparable or better contrast-to-noise ratio and lateral resolution than the Lu's and DAS migration schemes. Matlab codes for the Stolt's f-k migration for PWI are provided.
We present a registration framework that combines both tissue Doppler and B-mode echocardiographic sequences. The estimated spatiotemporal transform is diffeomorphic, and calculated by modeling its corresponding velocity field using continuous B-splines. A new cost function using both B-mode image voxel intensities and Doppler velocities is also proposed. Registration accuracy was evaluated on synthetic data with known ground truth. Results showed that our method allows quantifying wall motion with higher accuracy than when using a single modality. On patient data, both displacement and velocity curves were compared with the ones obtained from widely used commercial software using either B-mode images or TDI. Our method demonstrated to be more robust to image noise while being independent from the beam angle.
Noninvasive ultrafast imaging of intrinsic waves such as electromechanical waves or remotely induced shear waves in elastography imaging techniques for human cardiac applications remains challenging. In this paper, we propose ultrafast imaging of the heart with adapted sector size by coherently compounding diverging waves emitted from a standard transthoracic cardiac phased-array probe. As in ultrafast imaging with plane wave coherent compounding, diverging waves can be summed coherently to obtain high-quality images of the entire heart at high frame rate in a full field of view. To image the propagation of shear waves with a large SNR, the field of view can be adapted by changing the angular aperture of the transmitted wave. Backscattered echoes from successive circular wave acquisitions are coherently summed at every location in the image to improve the image quality while maintaining very high frame rates. The transmitted diverging waves, angular apertures, and subaperture sizes were tested in simulation, and ultrafast coherent compounding was implemented in a commercial scanner. The improvement of the imaging quality was quantified in phantoms and in one human heart, in vivo. Imaging shear wave propagation at 2500 frames/s using 5 diverging waves provided a large increase of the SNR of the tissue velocity estimates while maintaining a high frame rate. Finally, ultrafast imaging with 1 to 5 diverging waves was used to image the human heart at a frame rate of 4500 to 900 frames/s over an entire cardiac cycle. Spatial coherent compounding provided a strong improvement of the imaging quality, even with a small number of transmitted diverging waves and a high frame rate, which allows imaging of the propagation of electromechanical and shear waves with good image quality.
Contrast echocardiography (CE) ultrasound with microbubble contrast agents have significantly advanced our capability in assessing cardiac function, including myocardium perfusion imaging and quantification. However in conventional CE techniques with line by line scanning, the frame rate is limited to tens of frames per second and image quality is low. Recent research works in high frame-rate (HFR) ultrasound have shown significant improvement of the frame rate in non-contrast cardiac imaging. But with a higher frame rate, the coherent compounding of HFR CE images shows some artifacts due to the motion of the microbubbles. In this work we demonstrate the impact of this motion on compounded HFR CE in simulation and then apply a motion correction algorithm on in-vivo data acquired from the left ventricle (LV) chamber of a sheep. It shows that even if with the fast flow found inside the LV, the contrast is improved at least 100%.
In daily clinical cardiology practice, left ventricle (LV) global and regional function assessment is crucial for disease diagnosis, therapy selection and patient follow-up. Currently, this is still a time-consuming task, spending valuable human resources. In this work, a novel fast methodology for automatic LV tracking is proposed based on localized anatomically constrained affine optical flow. This novel method can be combined to previously proposed segmentation frameworks or manually delineated surfaces at an initial frame to obtain fully delineated datasets and, thus, assess both global and regional myocardial function. Its feasibility and accuracy was investigated in three distinct public databases, namely in realistically simulated 3D ultrasound (US), clinical 3D echocardiography and clinical cine cardiac magnetic resonance (CMR) images. The method showed accurate tracking results in all databases, proving its applicability and accuracy for myocardial function assessment. Moreover, when combined to previous state-of-the-art segmentation frameworks, it outperformed previous tracking strategies in both 3D US and CMR data, automatically computing relevant cardiac indices with smaller biases and narrower limits of agreement compared to reference indices. Simultaneously, the proposed localized tracking method showed to be suitable for online processing, even for 3D motion assessment. Importantly, although here evaluated for LV tracking only, this novel methodology is applicable for tracking of other target structures with minimal adaptations. This article is protected by copyright. All rights reserved.
Today’s three-dimensional (3-D) cardiac ultrasound imaging systems suffer from relatively low spatial and temporal resolution, limiting their applicability in daily clinical practice. To address this problem, 3-D diverging wave imaging with spatial coherent compounding (DWC) as well as 3-D multi-line-transmit (MLT) imaging have recently been proposed. Currently, the former improves the temporal resolution significantly at the expense of image quality and the risk of introducing motion artifacts whereas the latter only provides a moderate gain in volume rate but mostly preserves quality. In this study, a new technique for real-time volumetric cardiac imaging is proposed by combining the strengths of both approaches. Hereto, multiple planar (i.e., 2-D) diverging waves are simultaneously transmitted in order to scan the 3-D volume, i.e., multi-plane-transmit (MPT) beamforming. The performance of a 3MPT imaging system was contrasted to that of a 3-D DWC system and that of a 3-D MLT system by computer simulations during both static and moving conditions of the target structures while operating at similar volume rate. It was demonstrated that for stationary targets, the 3MPT imaging system was competitive with both the 3-D DWC and 3-D MLT systems in terms of spatial resolution and side lobe levels (i.e., image quality). However, for moving targets, the image quality quickly deteriorated for the 3-D DWC systems while it remained stable for the 3MPT system while operating at twice the volume rate of the 3D-MLT system. The proposed MPT beamforming approach was thus demonstrated to be feasible and competitive to state-of-the-art methodologies.
It was previously demonstrated in 2D echocardiography that a proper multi-line transmit (MLT) implementation can be used to increase frame rate while preserving image quality. Initial findings for extending MLT to 3D showed that it might address the low spatiotemporal resolution of current volumetric ultrasound systems. However, to date, it remains unclear how much transmit/receive parallelization would be possible using a 3D MLT system. Therefore, the aim of this study was to contrast different MLT setups for 3D imaging by computer simulation in order to determine an optimal trade-off between the amount of parallelization of a MLT system and the corresponding signal-to-noise ratio of the resulting images. Hereto, the image quality of several MLT setups was estimated by quantifying their cross-talk energy level. The results showed that for the tested setups 4MLT broad beams and 9MLT narrow beams with Tukey (α=0.5) apodization in transmit and receive, give the highest frame rate gain while maintaining an acceptable inter-beam interference level. Moreover, although 16MLT narrow beams with Tukey/Tukey (α=0.5) apodization did show more pronounced inter-beam interference, its gain in frame rate might outweigh its predicted loss in image quality. As such both 9MLT and 16MLT narrow beams were tested experimentally. For both systems, 4 receive lines were reconstructed from each transmit beam. The contrast-to-noise ratio of these imaging strategies was quantified and compared to the image quality obtained with line-by-line scanning. Despite some expected loss in 2 image quality, the resulting images of the parallelized systems were very competitive to the benchmark, while speeding-up the acquisition process by a factor of 36 and 64 respectively.
The study describes a novel algorithm for deriving myocardial strain from an entire cardiac cycle using high-frame-rate ultrasound images. Validation of the tracking algorithm was conducted in vitro prior to the application to patient images. High-frame-rate ultrasound images were acquired in vivo from 10 patients, and strain curves were derived in six myocardial regions around the left ventricle from the apical four-chamber view. Strain curves derived from high-frame-rate images had a higher frequency content than those derived using conventional methods, reflecting improved temporal sampling.
Objectives
To investigate if shear wave imaging (SWI) can detect endoleaks and characterize thrombus organization in abdominal aortic aneurysms (AAAs) after endovascular aneurysm repair. Methods
Stent grafts (SGs) were implanted in 18 dogs after surgical creation of type I endoleaks (four AAAs), type II endoleaks (13 AAAs) and no endoleaks (one AAA). Color flow Doppler ultrasonography (DUS) and SWI were performed before SG implantation (baseline), on days 7, 30 and 90 after SG implantation, and on the day of the sacrifice (day 180). Angiography, CT scans and macroscopic tissue sections obtained on day 180 were evaluated for the presence, size and type of endoleaks, and thrombi were characterized as fresh or organized. Endoleak areas in aneurysm sacs were identified on SWI by two readers and compared with their appearance on DUS, CT scans and macroscopic examination. Elasticity moduli were calculated in different regions (endoleaks, and fresh and organized thrombi). ResultsAll 17 endoleaks (100 %) were identified by reader 1, whereas 16 of 17 (94 %) were detected by reader 2. Elasticity moduli in endoleaks, and in areas of organized thrombi and fresh thrombi were 0.2 ± 0.4, 90.0 ± 48.2 and 13.6 ± 4.5 kPa, respectively (P < 0.001 between groups). SWI detected endoleaks while DUS (three endoleaks) and CT (one endoleak) did not. ConclusionsSWI has the potential to detect endoleaks and evaluate thrombus organization based on the measurement of elasticity. Key points• SWI has the potential to detect endoleaks in post-EVAR follow-up.• SWI has the potential to characterize thrombus organization in post-EVAR follow-up.• SWI may be combined with DUS in post-EVAR surveillance of endoleak.
Full matrix arrays are excellent tools for 3-D ultrasound imaging, but the required number of active elements is too high to be individually controlled by an equal number of scanner channels. The number of active elements is significantly reduced by the sparse array techniques, but the position of the remaining elements must be carefully optimized. This issue is faced here by introducing novel energy functions in the simulated annealing (SA) algorithm. At each iteration step of the optimization process, one element is freely translated and the associated radiated pattern is simulated. To control the pressure field behavior at multiple depths, three energy functions inspired by the pressure field radiated by a Blackman-tapered spiral array are introduced. Such energy functions aim at limiting the main lobe width while lowering the side lobe and grating lobe levels at multiple depths. Numerical optimization results illustrate the influence of the number of iterations, pressure measurement points, and depths, as well as the influence of the energy function definition on the optimized layout. It is also shown that performance close to or even better than the one provided by a spiral array, here assumed as reference, may be obtained. The finite-time convergence properties of SA allow the duration of the optimization process to be set in advance.
Speckle Tracking is one of the most prominent techniques used to estimate the regional movement of the heart based on ultrasound acquisitions. Many different approaches have been proposed, proving their suitability to obtain quantitative and qualitative information regarding myocardial deformation, motion and function assessment. New proposals to improve the basic algorithm usually focus on one of these three steps: (1) the similarity measure between images and the speckle model; (2) the transformation model, i.e. the type of motion considered between images; (3) the optimization strategies, such as the use of different optimization techniques in the transformation step or the inclusion of structural information. While many contributions have shown their good performance independently, it is not always clear how they perform when integrated in a whole pipeline. Every step will have a degree of influence over the following and hence over the final result. Thus, a Speckle Tracking pipeline must be analyzed as a whole when developing novel methods, since improvements in a particular step might be undermined by the choices taken in further steps. This work presents two main contributions: (1) We provide a complete analysis of the influence of the different steps in a Speckle Tracking pipeline over the motion and strain estimation accuracy. (2) The study proposes a methodology for the analysis of Speckle Tracking systems specifically designed to provide an easy and systematic way to include other strategies. We close the analysis with some conclusions and recommendations that can be used as an orientation of the degree of influence of the models for speckle, the transformation models, interpolation schemes and optimization strategies over the estimation of motion features. They can be further use to evaluate and design new strategy into a Speckle Tracking system.
Background:
Cancer chemotherapy increases the risk of heart failure. This cost-effectiveness model compared strain-guided cardioprotection with other protective strategies using a health care payer perspective and five-year time horizon.
Methods:
Three cardioprotection strategies were assessed: 1) usual care (EF-guided cardioprotection, EFGCP) with cardioprotection initiated on diagnosis of LVEF-defined cardiotoxicity (EF-CTX), 2) universal cardioprotection (UCP) for all such patients, and 3) strain-guided cardioprotection (SGCP - treatment of patients with subclinical cardiotoxicity [S-CTX]). A Markov model, informed by the published literature on transitional probabilities, costs and quality-adjusted life years (QALYs) was developed to assess the incremental cost-effectiveness ratio (ICER). Costs, effects and ICER of each specified cardioprotective strategy were assessed over a 5-year range, with sensitivity analyses for significant variables.
Results:
In the reference case of a 49year old woman with stage IIb breast cancer treated with sequential anthracyclines and trastuzumab, strain-guided cardioprotection (3.79 QALYS and $4159 cost over 5years) dominated both UCP (3.64 QALYs and $5967 cost over 5years) and EFGCP (3.53 QALYs and $7033 cost over five years). Model results were dependent on the probabilities of patients developing subclinical LV dysfunction, with UCP dominating alternative strategies at probabilities ≥51%. Variations in the cost of cardioprotective medications and probabilities of cardioprotection side-effects had no effect on model conclusions.
Conclusions:
In patients at risk of chemotherapy-related cardiotoxicity, strain-guided cardioprotection provides more QALYs at lower cost than standard care or uniform cardioprotection.
Color tissue Doppler (TDI) is a well-established methodology to assess local myocardial motion/deformation. Typically, a frame rate of ~200 Hz can be achieved by imaging a narrow sector (~ 30°, which can only cover one cardiac wall) at moderate line density, using a dedicated pulse sequence and multi-line acquisition (MLA). However, a wide angle sector (i.e., wide field-of-view) is required in some clinical applications in order to image the whole left ventricle, which implies a drop in the temporal resolution. Hereto, the aim of this study was to propose a novel imaging sequence using a multi-line transmit (MLT) beamforming approach to achieve high frame rate color tissue Doppler imaging while preserving a wide field-of-view (i.e., 90° sector). To this end, a color MLT-TDI sequence achieving a frame rate of 208 Hz with a 90°-sector was implemented on an ultrasound experimental scanner interleaved with a conventional color TDI sequence achieving the same frame rate but only with a 22.5 °-sector. Using this setup, the septal wall of 9 healthy volunteers was imaged and the corresponding velocity was extracted by means of a standard autocorrelation estimator. The curved M-mode velocity images as well as the velocity profiles obtained from selected sample volumes of MLT-TDI images presented physiologic patterns, very similar to those from conventional TDI. For several typical clinical relevant velocity properties, such as the peak systolic/diastolic velocities, good agreement and strong correlation between color MLT-TDI and conventional color TDI were found by means of Bland-Altman analysis and correlation coefficients. The results thus demonstrate the feasibility of the novel MLT based TDI methodology to achieve high frame rate color TDI without compromising the field-of-view. This may open the opportunity to simultaneously assess regional myocardial function of the whole left ventricle at high temporal resolution.
This study was planned by the EACVI/ASE/Industry Task Force to Standardize Deformation Imaging to (1) test the variability of speckle-tracking global longitudinal strain (GLS) measurements among different vendors and (2) compare GLS measurement variability with conventional echocardiographic parameters.
Sixty-two volunteers were studied using ultrasound systems from seven manufacturers. Each volunteer was examined by the same sonographer on all machines. Inter- and intraobserver variability was determined in a true test-retest setting. Conventional echocardiographic parameters were acquired for comparison. Using the software packages of the respective manufacturer and of two software-only vendors, endocardial GLS was measured because it was the only GLS parameter that could be provided by all manufactures. We compared GLSAV (the average from the three apical views) and GLS4CH (measured in the four-chamber view) measurements among vendors and with the conventional echocardiographic parameters.
Absolute values of GLSAV ranged from 18.0% to 21.5%, while GLS4CH ranged from 17.9% to 21.4%. The absolute difference between vendors for GLSAV was up to 3.7% strain units (P < .001). The interobserver relative mean errors were 5.4% to 8.6% for GLSAV and 6.2% to 11.0% for GLS4CH, while the intraobserver relative mean errors were 4.9% to 7.3% and 7.2% to 11.3%, respectively. These errors were lower than for left ventricular ejection fraction and most other conventional echocardiographic parameters.
Reproducibility of GLS measurements was good and in many cases superior to conventional echocardiographic measurements. The small but statistically significant variation among vendors should be considered in performing serial studies and reflects a reference point for ongoing standardization efforts.
Copyright © 2015 American Society of Echocardiography. Published by Elsevier Inc. All rights reserved.
The aim of this study was to assess the long-term prognostic value of the global longitudinal strain of the right ventricle (GLSRV) in patients with inferior ST-segment elevation myocardial infarction (STEMI) who underwent primary percutaneous coronary intervention (PCI).
RV systolic dysfunction is an important prognostic factor in patients with inferior STEMI.
All consecutive inferior STEMI patients were included from January 2005 to December 2013. RV systolic function was analyzed with GLSRV using velocity vector imaging (Siemens, Mountain View, California), as well as conventional echocardiographic indices, including right ventricular fractional area change (RVFAC) and tricuspid annular plane systolic excursion (TAPSE).
We analyzed a total of 282 consecutive inferior STEMI patients (212 men, age 63 ± 13 years) treated with primary PCI. During the follow-up period (54 ± 35 months), 59 patients (21%) had 1 or more major adverse cardiovascular event (MACE) (43 deaths, 7 nonfatal MI, 4 target vessel revascularization, and 6 heart failure admission). The best cutoff value of GLSRV for the prediction of MACE was ≥-15.5% (area under the curve = 0.742, p < 0.001) with a sensitivity of 73% and a specificity of 65%. GLSRV showed better sensitivity and specificity than RVFAC and TAPSE. After multivariate analysis, GLSRV showed a higher c-statistic value (0.770) than RVFAC (0.749) and TAPSE (0.751) in addition to age, Killip class, troponin-I, left ventricular (LV) ejection fraction and RV infarction. Patients with GLSRV≥-15.5% showed significantly lower 5-year survival rate (74 ± 5% vs. 89 ± 3%, p < 0.001) and lower MACE-free survival rate (64 ± 5% vs. 87 ± 3%, p < 0.001) than the control group.
Because GLSRV showed additive predictive value to age and LV function, it can be the strongest parameter of RV systolic function evaluating the prognosis after PCI for acute inferior STEMI particularly in patients with preserved LV function.
Copyright © 2015 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.
The main requirement of pulsed-echo ultrasound applications such as cardiac imaging, 3-D imaging, or blood flow imaging can be identified as frame rate. Currently, frame rate is limited by the imaging depth range and the number of ultrasonic fires. For example, a 15 cm imaging range gives rise to 200 microsecond(s) lines or to a 2 s acquisition time for 100 planes of 100 lines in 3-D medical applications. The only way to increase frame rate is parallel beam formation in the receive mode. Simultaneous parallel beam forming allows us to divide the acquisition time by a factor proportional to the number of beam formed lines. In the technique developed by S. W. Smith, an increase frame rate of 16 is achieved. However, this technique is limited by a loss in lateral resolution due to the requirement for a wide illumination beam of the explored medium in the transmit mode. We propose an alternate illumination scheme that minimizes the loss in resolution in the transmit mode. In this technique, ultrasonic energy is transmitted simultaneously in several narrow beams. This technique works in pulsed mode and we have built the hardware needed for the simultaneous production of several beams. Each transducer is connected to a transmitter able to generate a sequence of excitation pulses. If n beams are to be transmitted, the excitation signal is the sum of n cylindrical wave fronts. For those, among elements where the n wave fronts are disjoint, the excitation signal is thus the succession of n pulses with specific time positions with respect to the system synchronization. For the others, the excitation signal is more complex since it consists in a (n - 1) level signal (0, 1, 2, ... n - 1 times the basic excitation signal). We show the performances of such a parallel transmit scheme based on beam plots as well as on tissue phantom images. This leads to an evaluation of the maximal number of beams compatible with current medical imaging quality standards. It is shown that a gain of 16 in the acquisition time can be achieved without any loss in lateral resolution.
Despite the availability of multiple ultrasound approaches to left ventricular (LV) flow characterization in two dimensions, this technique remains in its childhood and further developments seem warranted. This article describes a new methodology for tracking the 2-D LV flow field based on ultrasound data. Hereto, a standard speckle tracking algorithm was modified by using a dynamic kernel embedding Navier–Stokes-based regularization in an iterative manner. The performance of the proposed approach was first quantified in synthetic ultrasound data based on a computational fluid dynamics model of LV flow. Next, an experimental flow phantom setup mimicking the normal human heart was used for experimental validation by employing simultaneous optical particle image velocimetry as a standard reference technique. Finally, the applicability of the approach was tested in a clinical setting. On the basis of the simulated data, pointwise evaluation of the estimated velocity vectors correlated well (mean r = 0.84) with the computational fluid dynamics measurement. During the filling period of the left ventricle, the properties of the main vortex obtained from the proposed method were also measured, and their correlations with the reference measurement were also calculated (radius, r = 0.96; circulation, r = 0.85; weighted center, r = 0.81). In vitro results at 60 bpm during one cardiac cycle confirmed that the algorithm properly measures typical characteristics of the vortex (radius, r = 0.60; circulation, r = 0.81; weighted center, r = 0.92). Preliminary qualitative results on clinical data revealed physiologic flow fields.
Full text available until February 18, 2015 via http://authors.elsevier.com/a/1QHmI14aKMNUBk
Background:
We sought to assess the utility of left ventricular global longitudinal strain (LV-GLS) in predicting mortality in moderate to severe and paradoxical severe aortic stenosis (AS) patients with preserved ejection fraction.
Methods and results:
We studied 395 AS patients (70 ± 14 years, 57% men) with aortic valve area <1.3 cm(2) evaluated between January to June 2008 (excluding severe other valve disease and LV ejection fraction <50%). Clinical and echocardiographic data were recorded. LV-GLS was analyzed using Velocity Vector Imaging. AS patients were classified as (a) moderate-severe (n=93; aortic valve area, 1.1-1.3 cm(2)), (b) standard severe (n=161; aortic valve area, ≤1 cm(2); mean gradient ≥40 mm Hg), and (c) paradoxical severe (n=141; aortic valve area, ≤1 cm2 and mean gradient <40 mm Hg). Additive Euroscore was 7 ± 3. The association of LV-GLS with all-cause mortality was assessed after risk-adjustment using Cox proportional hazards models. Median LV-GLS was -14.8% (interquartile range, -17.2%, -12.1%). At 4.4±1.4 years, there were 92 (23%) deaths. On multivariable Cox analysis, additive Euroscore (hazard ratio, 1.19; 1.13-1.27; P<0.001), New York Heart Association class (hazard ratio, 1.44; 1.11-1.87; P<0.001), AV surgery with time-dependent covariate analysis (hazard ratio, 0.29; 0.19-0.45; P<0.001), and LV-GLS (hazard ratio, 1.05; 1.03-1.07; P<0.001) were independent predictors of mortality. LV-GLS <-12.1% (4th quartile) was associated with significantly reduced survival. Addition of LV-GLS to clinical parameters (additive Euroscore+New York Heart Association class) led to significant improvement in prediction of mortality (χ(2) increased from 48 to 58; P<0.01).
Conclusions:
LV-GLS independently predicts mortality in moderate-severe and severe AS patients with preserved LV ejection fraction, providing incremental prognostic utility, in addition to standard clinical and echocardiographic parameters.
Several recent technical advances in cardiac ultrasound allow data to be acquired at a very high frame rate. Retrospective gating, plane/diverging wave imaging, and multiline transmit imaging all improve the temporal resolution of the conventional ultrasound system. The main drawback of such high frame rate data acquisition is that it typically has reduced image quality. However, for given clinical applications, the acquisition of temporally-resolved data might outweigh the reduction in image quality. It is the aim of this paper to provide an overview of the technical principles behind these new ultrasound imaging modalities, to review the current evidence of their potential clinical added value, and to forecast how they might influence daily clinical practice.
Background Global longitudinal strain (GLS) is a robust, well validated and reproducible technique for the measurement of LV longitudinal deformation. We sought to assemble evidence that GLS is an accurate marker in predicting cardiovascular outcomes, compared to LVEF.
Methods We undertook a systematic review of the evidence from observational studies which compared GLS against LVEF in predicting major adverse cardiac events. The primary outcome was all-cause mortality. The secondary outcome was a composite of cardiac death, malignant arrhythmia, hospitalisation due to heart failure, urgent valve surgery or heart transplantation, and acute coronary ischaemic event. A random effects model was used to combine HR and 95% CIs. A meta-regression was undertaken to assess the impact of potential covariates.
Results Data were collated from 16 published articles (n=5721 adults) comprising 15 prospective and 1 retrospective observational studies. The underlying cardiac conditions were heart failure, acute myocardial infarction, valvular heart disease, and miscellaneous cardiac diseases. Mortality was independently associated with each SD change in the absolute value of baseline GLS (HR 0.50, 95% CI 0.36 to 0.69; p<0.002) and less strongly with LVEF (HR 0.81, 95% CI 0.72 to 0.92; p=0.572). The HR per SD change in GLS was associated with a reduction in mortality 1.62 (95% CI 1.13 to 2.33; p=0.009) times greater than the HR per SD change in LVEF.
Conclusions There is strong evidence of the prognostic value of GLS, which appears to have superior prognostic value to EF for predicting major adverse cardiac events.
The quantitative analysis of cardiac motion from echocardiographic images helps clinicians in the diag-nosis and therapy of patients suffering from heart disease. Quantitative analysis is usually based on TDI (Tissue Dop-pler Imaging) or speckle tracking. These methods are based on two techniques which to a large degree are independent - the Doppler phenomenon and image sequence processing, respectively. Herein, to increase the accuracy of the speckle tracking technique and to cope with the angle dependency of TDI, a combined approach dubbed TDIOF (Tissue Doppler Imaging Optical Flow) is proposed. TDIOF is formulated based on the combination of B-mode and Doppler energy terms minimized using algebraic equations and, is validated on simulated images, and in-vivo data. It was observed that the additional Doppler term is able to increase the accuracy of speckle tracking, compared to two popular motion esti-mation and speckle tracking techniques (Horn-Schunck and block matching methods). This observation was more pro-nounced when noise was present. . The magnitude and angu-lar error for TDIOF applied to simulated images, when comparing estimated motion with ground-truth motion, were 15% and 9.2 degrees/frame, respectively. As an addi-tional validation, echocardiography-derived strains were compared to tagged MRI-derived myocardial strains in the same subjects. The correlation coefficient (r) between the TDIOF-derived radial strains and tagged MRI-derived radial strains value were 0.83 (P<0.001). The correlation coefficient (r) for the TDIOF-derived circumferential strains compared to the tagged MRI-derived circumferential strains were 0.86 (P<0.001). The comparison of TDIOF-derived and block matching speckle tracking and Horn-Schunck optical flow strain values using student t-test demonstrated superi-ority of TDIOF (95% confidence interval, P<0.001).
Multi-line transmission (MLT) is a technique in which ultrasound pulses for several directions are transmitted simultaneously. The purpose is increased frame rate, which is especially important in 3-D echocardiography. Compared with techniques purely based on parallel beamformation, MLT avoids the need for reducing the transmit aperture and thus maintains a high harmonic signal level. The main disadvantage is that artifacts are caused by cross-talk between the simultaneous beams. In a conventional MLT implementation, simultaneous transmits would be spaced regularly in the azimuth and elevation planes. However, using rectangular geometry arrays, most of the acoustic side-lobe energy is concentrated along these planes. The results in this work show that the crosstalks can be pushed below the typical display range of 50 dB used in cardiac applications if the parallel transmit directions are aligned along the transverse diagonal of the array. Dispositions with 2 to 5 MLT for a typical cardiac 2-D phased-array were investigated using simulation software. Using the proposed alignment, the maximal crosstalk artifact amplitudes decreased 20 to 30 dB compared with conventional MLT dispositions. In water-tank measurements, side-lobe levels of a commercially available rectangular probe were 15 to 25 dB lower along the transverse diagonal, confirming that similar suppressions can be expected using actual transducers.
Imaging at high temporal resolution is critical for a better understanding of transient cardiac phases with potential diagnostic value. Typically, parallel receive beam forming is used to achieve this. As an alternative, transmitting multiple lines simultaneously [i.e., multi-line transmit (MLT)] has been proposed. However, this approach has received less attention, most likely because of potential cross-talk artifacts between beams. In this study, based on different transducer configurations, the cross-talk level of different MLT systems was investigated and their point spread functions (PSFs) were compared with that of conventional beam forming (single-line transmit, SLT) by computer simulation. To reduce cross-talk artifacts, 7 different windowing functions were tested on transmit and receive: rectangular, Tukey (α = 0.5), Hann, cosine, Hamming, Gaussian (α = 0.4), and Nuttall. The simulation results showed the cross-talk varied inversely with the MLT beam opening angle and apodization could significantly reduce these artifacts at distinct opening angles, which were dependent on the transducer configuration. The optimal settings for an MLT system were highly dependent on the exact transducer configuration and must be deduced based on a given transducer. In particular, for a typical cardiac transducer configuration, a 4MLT imaging system with an opening angle of 22.73° and a Tukey (α = 0.5)-Tukey (α = 0.5) windowing scheme provided very similar image quality to SLT but with a 4 times higher frame rate. In addition, the MLT approach can be combined with (multiple) parallel receive beamforming to increase frame rate further. With these methods, a frame rate of approximately 300 Hz can be achieved to generate a 90° sector image without significant loss in image quality.
We have developed new universal strain software (USS) that can be used to perform speckle tracking of any Digital Imaging and Communications in Medicine (DICOM) image, regardless of the ultrasound system used to obtain it.
Fifty patients prospectively underwent echocardiography immediately prior to cardiac catheterization. Biplane peak global longitudinal strain (GLS), peak systolic longitudinal strain rate (SSR), peak early diastolic longitudinal strain rate (DSR), and peak early diastolic circumferential strain rate (DCSR) were determined using conventional strain software (CSS) that uses raw data, and using the new USS applied to DICOM images.
Universal strain software correlated with CSS for GLS (r = 0.78, P < 0.001), SSR (r = 0.78, P < 0.001), DSR (r = 0.54, P < 0.001), and DCSR (r = 0.43, P = 0.019). GLS and SSR using USS correlated with left ventricular ejection fraction (LVEF) (r = -0.67 and -0.71, respectively) as well as using CSS (r = -0.66 and -0.71). Patients with diastolic dysfunction had significantly lower DSR (0.61 vs. 0.87/sec, P = 0.02) and DCSR (0.89 vs. 1.23/sec, P = 0.03), and less negative GLS (-10.8 vs. -16.1%, P = 0.002) using USS in all patients, as well as among those with LVEF ≥ 50%. Receiver-operating characteristic (ROC) analysis for detection of diastolic dysfunction revealed a sensitivity and specificity of 82% and 83% for DCSR < 1.09/sec (area under the curve [AUC = 0.80]) and 85% and 83% for GLS > -13.7% (AUC = 0.84) using USS.
Universal strain software can be used to accurately assess LV systolic and diastolic function using speckle tracking echocardiography.