13 research outputs found

    Caractérisation de vortex intraventriculaires par échographie Doppler ultrarapide

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    Les maladies cardiaques sont une cause majeure de mortalitĂ© dans le monde (la premiĂšre cause en AmĂ©rique du nord [192]), et la prise en charge de ses maladies entraĂźne des coĂ»ts Ă©levĂ©s pour la sociĂ©tĂ©. La prĂ©valence de l’insuffisance cardiaque augmente fortement avec l’ñge, et, avec une population vieillissante, elle va demeurer une prĂ©occupation croissante dans le futur, non seulement pour les pays industrialisĂ©s mais aussi pour ceux en dĂ©veloppement. Ainsi il est important d’avoir une bonne comprĂ©hension de son mĂ©canisme pour obtenir des diagnostics prĂ©coces et un meilleur prognostic pour les patients. Parmi les diffĂ©rentes formes d’insuffisance cardiaque, on trouve la dysfonction diastolique qui se traduit par une dĂ©ficience du remplissage du ventricule. Pour une meilleure comprĂ©hension de ce mĂ©canisme, de nombreuses Ă©tudes se sont intĂ©ressĂ©es au mouvement du sang dans le ventricule. On sait notamment qu’au dĂ©but de la diastole le flux entrant prend la forme d’un anneau vortical (ou vortex ring). La formation d’un vortex ring par le flux sanguin aprĂšs le passage d’une valve a Ă©tĂ© dĂ©crite pour la premiĂšre fois en 1513 par LĂ©onard de Vinci (Fig. 0.1). En effet aprĂšs avoir moulĂ© l’aorte dans du verre et ajouter des graines pour observer le flux se dĂ©plaçant dans son fantĂŽme, il a dĂ©crit l’apparition du vortex au passage de la valve aortique. Ces travaux ont pu ĂȘtre confirmĂ©s 500 ans plus tard avec l’apparition de l’IRM [66]. Dans le ventricule, le mĂȘme phĂ©nomĂšne se produit aprĂšs la valve mitrale, c’est ce qu’on appelle le vortex diastolique. Or, le mouvement d’un fluide (ici le sang) est directement reliĂ© a son environnement : la forme du ventricule, la forme de la valve, la rigiditĂ© des parois... L’intĂ©rĂȘt est donc grandissant pour Ă©tudier de maniĂšre plus approfondie ce vortex diastolique qui pourrait apporter de prĂ©cieuses informations sur la fonction diastolique. Les modalitĂ©s d’imagerie permettant de le visualiser sont l’IRM et l’échographie. Cette thĂšse prĂ©sente l’ensemble des travaux effectuĂ©s pour permettre une meilleure caractĂ©risation du vortex diastolique dans le ventricule gauche par imagerie ultrasonore Doppler. Pour suivre la dynamique de ce vortex dans le temps, il est important d’obtenir une bonne rĂ©solution temporelle. En effet, la diastole ventriculaire dure en moyenne 0.5 s pour un coeur humain au repos, une cadence Ă©levĂ©e est donc essentielle pour suivre les diffĂ©rentes Ă©tapes de la diastole. La qualitĂ© des signaux Doppler est Ă©galement primordiale pour obtenir une bonne estimation des vitesses du flux sanguin dans le ventricule. Pour Ă©tudier ce vortex, nous nous sommes intĂ©ressĂ©s Ă  la mesure de sa vorticitĂ© en son centre v et Ă  l’évolution de cette derniĂšre dans le temps. Le travail se divise ainsi en trois parties, pour chaque un article a Ă©tĂ© rĂ©digĂ© : 1. DĂ©veloppement d’une sĂ©quence Doppler ultrarapide : La sĂ©quence se base sur l’utilisation d’ondes divergentes qui permettent d’atteindre une cadence d’image Ă©levĂ©e. AssociĂ©e Ă  la vortographie, une mĂ©thode pour localiser le centre du vortex diastolique et en dĂ©duire sa vorticitĂ©, nous avons pu suivre la dynamique de la vorticitĂ© dans le temps. Cette sĂ©quence a permis d’établir une preuve de concept grĂące Ă  des acquisitions in vitro et in vivo sur des sujets humains volontaires. 2. DĂ©veloppement d’une sĂ©quence triplex : En se basant sur la sĂ©quence ultrarapide Doppler, on cherche ici Ă  ajouter des informations supplĂ©mentaires, notamment sur le mouvement des parois. La sĂ©quence triplex permet non seulement de rĂ©cupĂ©rer le mouvement sanguin avec une haute cadence d’images mais aussi le Doppler tissulaire. Au final, nous avons pu dĂ©duire les Doppler couleur, tissulaire, et spectral, en plus d’un Bmode de qualitĂ© grĂące Ă  la compensation de mouvement. On peut alors observer l’interdĂ©pendance entre la dynamique du vortex et celle des parois, en rĂ©cupĂ©rant tous les indices nĂ©cessaires sur le mĂȘme cycle cardiaque avec une acquisition unique. 3. DĂ©veloppement d’un filtre automatique : La quantification de la vorticitĂ© dĂ©pend directement des vitesses estimĂ©es par le Doppler. Or, en raison de leur faible amplitude, les signaux sanguins doivent ĂȘtre filtrĂ©s. En effet lors de l’acquisition les signaux sont en fait une addition des signaux sanguins et tissulaires. Le filtrage est une Ă©tape essentielle pour une estimation prĂ©cise et non biaisĂ©e de la vitesse. La derniĂšre partie de ce doctorat s’est donc concentrĂ©e sur la mise au point d’un filtre performant qui se base sur les dimensions spatiales et temporelles des acquisitions. On effectue ainsi un filtrage du tissu mais aussi du bruit. Une attention particuliĂšre a Ă©tĂ© portĂ©e Ă  l’automatisation de ce filtre avec l’utilisation de critĂšres d’information qui se basent sur la thĂ©orie de l’information.Heart disease is one of the leading causes of death in the world (first cause in North America [192]), and causes high health care costs for society. The prevalence of heart failure increases dramatically with age and, due to the ageing of the population, will remain a major concern in the future, not only for developed countries, but also for developing countries. It is therefore crucial to have a good understanding of its mechanism to obtain an early diagnosis and a better prognosis for patients. Diastolic dysfunction is one of the variations of heart failure and leads to insufficient filling of the ventricle. To better understand the dysfunction, several studies have examined the blood motion in the ventricle. It is known that at the beginning of diastole, the filling flow creates a vortex pattern known as a vortex ring. This development of the ring by blood flow after passage through a valve was first described in 1513 by Leonardo Da Vinci (Fig. 0.1). After molding a glass phantom in an aorta and adding seeds to visually observe the flow through the phantom, he could describe the vortex ring development of the blood coming out of the aortic valve. His work was confirmed 500 years later with the emergence of MRI [66]. The same pattern can be observed in the left ventricle when the flow emerges from the mitral valve, referred to as the diastolic vortex. The flow motion (in our case the blood) is directly related to its environment : shape of the ventricle, shape of the valve, stiffness of the walls... There is therefore a growing interest in further studies on this diastolic vortex that could lead to valuable information on diastolic function. The imaging modalities which can be used to visualize the vortex are MRI and ultrasound. This thesis presents the work carried out to allow a better characterization of the diastolic vortex in the left ventricle by Doppler ultrasound imaging. For temporal monitoring of vortex dynamics, a high temporal resolution is required, since the ventricular diastole is about 0.5 s on average for a resting human heart. The quality of Doppler signals is also of utmost importance to get an accurate estimate of the blood flow velocity in the ventricle. To study this vortex, we focused on evaluating the core vorticity evaluation and especially on its evolution in time. The work is divided in three parts, and for each of them an article has been written : 1. Ultrafast Doppler sequence : The sequence is based on diverging waves, which resulted in a high frame rate. In combination with vortography, a method to locate the vortex core and derive its vorticity, the vortex dynamics could be tracked over time. This ix sequence could establish a proof of concept based on in vitro and in vivo acquisitions on healthy human volunteers. 2. Triplex sequence : Based on the ultrafast sequence, we were interested in adding information on the wall motion. The triplex sequence is able to recover not only the blood motion with a high framerate but also tissue Doppler. In the end, we could derive color, tissue, and spectral Doppler, along with a high quality Bmode by using motion compensation. The interdependence between vortex and walls dynamics could be highlighted by acquiring all the required parameters over a single cardiac cycle. 3. Automatic clutter filter : Vorticity quantification depends directly on the estimation of Doppler velocity. However, due to their low amplitude, blood signals must be filtered. Indeed, acquired signals are actually an addition of tissue and blood signals. Filtering is a critical step for an unbiased and accurate velocity estimation. The last part of this doctoral thesis has focused on the design of an efficient filter that takes advantage of the temporal and spatial dimensions of the acquisitions. Thus the tissue alongside the noise is removed. Particular care was taken to automatize the filter by applying information criteria based on information theory

    Ultrafast Vector Doppler Using RF Sub-Nyquist Sampling

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    International audienceBackground, Motivation and ObjectiveUltrafast ultrasound has contributed to a renewed interested in vector Doppler. Sampling RF signals at a rate 4 times the carrier frequency is the standard procedure since this rule complies with the Nyquist sampling theorem, regardless of the transducer bandwidth. RF acquisition with a high-performance multi-channel system generates massive datasets,especially in 3-D ultrafast ultrasound. The objective of this in vitro and in vivo study was to demonstrate that sub-Nyquist sampling can lead to substantial lossless data reduction in vector Doppler.Statement of Contribution/MethodsVector Doppler was generated from unsteered plane waves (5-MHz linear array). Two receive sub-apertures were used, with receive angles of ±15°. A staggered dual-PRF sequence (PRF2 = ⅔ PRF1) doubled the Nyquist velocity. The effect of RF data undersampling on vector Doppler was investigated in a rotating disc and in a carotid bifurcation. The RF signalswere sampled at 20 MHz (center frequency × 4), then downsampled to simulate sub-Nyquist sampling. We used downsampling ratios up to 13; a ratio of 13 means that the RF signals were sampled at 20/13 = 1.54 MHz. The ratios were chosen so that the positive and negative frequency components did not overlap within the -10 dB bandwidth. After I/Qdemodulation and beamforming, the Doppler velocities were estimated using an auto-correlator. The Doppler-derived velocity vectors were compared with the actual vector fields. The in vitro phantom rotated at angular velocities up to 15 RPS (maximum outer speed = 1.5 m/s). In vivo vector flow images of the carotid bifurcation were produced in onevolunteer. We used a high-frame-rate duplex sequence (B-mode + color Doppler) based on plane wave imaging. A spatially-adaptive polynomial regression filter was used to remove the clutter components. Since no in vivo reference was available, the velocity vectors produced from the undersampled RF signals were compared with those obtained from thestandard Nyquist sampling.Results/DiscussionThe velocity vector errors due to sub-Nyquist sampling were marginal, which illustrates that vector Doppler can be correctly computed with a drastically reduced amount of RF samples. In our study, a 11-fold data reduction was obtained. Sub-Nyquist sampling can be a method of choice in vector Doppler to avoid information overload and reduce data transfer and storage

    Color and Vector Flow Imaging in Parallel Ultrasound With Sub-Nyquist Sampling

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    International audienceRF acquisition with a high-performance multichannel ultrasound system generates massive data sets in short periods of time, especially in "ultrafast" ultrasound when digital receive beamforming is required. Sampling at a rate four times the carrier frequency is the standard procedure since this rule complies with the Nyquist-Shannon sampling theorem and simplifies quadrature sampling. Bandpass sampling (or undersampling) outputs a bandpass signal at a rate lower than the maximal frequency without harmful aliasing. Advantages over Nyquist sampling are reduced storage volumes and data workflow, and simplified digital signal processing tasks. We used RF undersampling in color flow imaging (CFI) and vector flow imaging (VFI) to decrease data volume significantly (factor of 3 to 13 in our configurations). CFI and VFI with Nyquist and sub-Nyquist samplings were compared in vitro and in vivo. The estimate errors due to undersampling were small or marginal, which illustrates that Doppler and vector Doppler images can be correctly computed with a drastically reduced amount of RF samples. Undersampling can be a method of choice in CFI and VFI to avoid information overload and reduce data transfer and storage. Index Terms— Color Doppler, parallel ultrasound imaging, sub-Nyquist sampling, undersampling, vector Doppler, vector flow imaging (VFI)

    Color and Vector Flow Imaging in Parallel Ultrasound With Sub-Nyquist Sampling

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    Coupling myocardium and vortex dynamics in diverging-wave echocardiography

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    Coupling Myocardium and Vortex Dynamics in Diverging-Wave Echocardiography

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    High-frame-rate speckle-tracking echocardiography

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    International audienceConventional echocardiography is the leading modality for noninvasive 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 this 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 10 volunteers. High-contrast high-resolution B-mode images were constructed at 500 frames/s. The sequences were generated with a Verasonics scanner and a 2.5-MHz phased array. The 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 of the left ventricle was also obtained from STE in 10 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

    Parkinson's disease polygenic risk score is not associated with impulse control disorders: A longitudinal study

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    International audienceObjective: To examine the relationship between a Parkinson's disease (PD) polygenic risk score (PRS) and impulse control disorders (ICDs) in PD. Background: Genome wide association studies (GWAS) have brought forth a PRS associated with increased risk of PD and younger disease onset. ICDs are frequent adverse effects of dopaminergic drugs and are also more frequent in patients with younger disease onset. It is unknown whether ICDs and PD share genetic susceptibility. Methods: We used data from a multicenter longitudinal cohort of PD patients with annual visits up to 6 years (DIG-PD). At each visit ICDs, defined as compulsive gambling, buying, eating, or sexual behavior were evaluated by movement disorders specialists. We genotyped DNAs using the Megachip assay (Illumina) and calculated a weighted PRS based on 90 SNPs associated with PD. We estimated the association between PRS and prevalence of ICDs at each visit using Poisson generalized estimating equations, adjusted for dopaminergic treatment and other known risk factors for ICDs. Results: Of 403 patients, 185 developed ICDs. Patients with younger age at onset had a higher prevalence of ICDs (p < 0.001) as well as higher PRS values (p = 0.06). At baseline, there was no association between the PRS and ICDs (overall, p = 0.84). The prevalence of ICDs increased over time similarly across the quartiles of the PRS (overall, p = 0.88; DA users, p = 0.99). Conclusion: Despite younger disease onset being associated with both higher PRS and ICD prevalence, our findings are not in favor of common susceptibility genes for PD and ICDs
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