5,834 research outputs found

    Transthoracic three-dimensional echocardiography for the assessment of straddling tricuspid or mitral valves

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    Background The advent of 3D echocardiography has provided a technique which, potentially, could afford significant additional information over conventional cross-sectional echocardiography in the assessment of patients with straddling atrioventricular valves prior to surgical correction. Methods Eight patients, aged from 1 month to 9˙2 years, were examined with 3D echocardiography. All but three had discordant ventriculoarterial connections or double outlet right ventricle. Data suitable for reconstruction was acquired with transthoracic scanning. Right and left ventricular volumes were calculated in the 3D dataset. Results 3D echocardiography proved capable of defining the exact degree of straddling by imaging theproportion of tension apparatus attached to either side of the ventricular septum. It was able also to display the atrioventricular junction “en face”, thus permitting identification of the precise site of insertion of the muscular ventricular septum relative to the atrioventricular junction. This made it possiblefirst, to calculate the degree of valvar override, and second, to predict the location of the penetrating atrioventricular bundle. End-diastolic volume of the right ventricle in those with straddling tricuspid valves was 73 (61–83)% of normal, and, of the left ventricle in those with mitral valvar straddling 71 (40‐97)% of normal. Conclusions 3D echocardiography can aid in planning the optimal surgical procedure in patients with straddling or overrriding atrioventricular valves, as it provides diagnostic information superiorto standard crosssectional techniques. It also allows for exact measurement of the volumes of the respective ventricles

    Qualitative grading of aortic regurgitation: a pilot study comparing CMR 4D flow and echocardiography.

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    Over the past 10 years there has been intense research in the development of volumetric visualization of intracardiac flow by cardiac magnetic resonance (CMR).This volumetric time resolved technique called CMR 4D flow imaging has several advantages over standard CMR. It offers anatomical, functional and flow information in a single free-breathing, ten-minute acquisition. However, the data obtained is large and its processing requires dedicated software. We evaluated a cloud-based application package that combines volumetric data correction and visualization of CMR 4D flow data, and assessed its accuracy for the detection and grading of aortic valve regurgitation using transthoracic echocardiography as reference. Between June 2014 and January 2015, patients planned for clinical CMR were consecutively approached to undergo the supplementary CMR 4D flow acquisition. Fifty four patients(median age 39 years, 32 males) were included. Detection and grading of the aortic valve regurgitation using CMR4D flow imaging were evaluated against transthoracic echocardiography. The agreement between 4D flow CMR and transthoracic echocardiography for grading of aortic valve regurgitation was good (j = 0.73). To identify relevant,more than mild aortic valve regurgitation, CMR 4D flow imaging had a sensitivity of 100 % and specificity of 98 %. Aortic regurgitation can be well visualized, in a similar manner as transthoracic echocardiography, when using CMR 4D flow imaging

    Three-dimensional echocardiography for the assessment of congenital and acquired heart disease

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    Although conventional two-dimensional and Doppler blood-flow echocardiography are the standard imaging approaches in the assessment of heart disease they do not provide anatomic reconstructions in a form that resembles the cardiac morphology as visualized by the surgeon.The work presented in this thesis has explored the hypotheses that threedimensional echocardiography facilitates spatial recognition of intracardiac structures and therefore enhances the diagnostic confidence of echocardiography in congenital and acquired heart disease. The accuracy of three-dimensional reconstructions has been validated in vitro using two different phantoms and in vivo comparing the results with other established diagnostic techniques or surgical findings. Additionally, as the main limitation of transthoracic three-dimensional echocardiography is poor image quality in a substantial proportion of adult patients, Doppler myocardial imaging has been tested as a potentially superior method to conventional grey-scale imaging for transthoracic three-dimensional image acquisition.In vitro, using a virtual computer-generated phantom and a dynamic tissuemimicking phantom, the accuracy of both linear measurements and volume computation obtained from three-dimensional images was established. For both grey-scale and Doppler myocardial imaging, a detail of 1.0 mm dimension and two details separated from each other by a distance of 1.0 mm were the smallest structures and distances identified from a three-dimensional image. When testing the accuracy of volume measurements it appeared that both techniques marginally underestimated the true phantom volume (by approximately 1.0 ml for Doppler myocardial imaging and 4.0 ml for grey-scale imaging), but the systematic error was smaller and more constant in the case of Doppler myocardial imaging over the range of different true volumes.In vivo, the study was designed to compare the accuracy of grey-scale and Doppler myocardial imaging three-dimensional left ventricular volume measurements and cineventriculography. The differences were significantly smaller for the Doppler technique during both end-diastole and end-systole. A series of congenital heart lesions has also been studied. It has been shown that dynamic surgical reconstruction of the secundum atrial septal defect is feasible from the transthoracic approach in all patients. However, in adults, Doppler myocardial imaging proved more effective than grey-scale imaging in the accuracy of threedimensional defect reconstruction. In patients with sinus venosus atrial septal defect, transthoracic three-dimensional echocardiography was more accurate than standard echocardiography in diagnosing the defect including a detailed description of the abnormal pulmonary venous drainage. Finally, in children with atrio-ventricular septal defects, the 'unroofed' atrial reconstruction of the common valve accurately displayed dynamic valve morphology en face and the mechanism of valve reflux

    Assessment of hemodynamic conditions in the aorta following root replacement with composite valve-conduit graft

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    This paper presents the analysis of detailed hemodynamics in the aortas of four patients following replacement with a composite bio-prosthetic valve-conduit. Magnetic resonance image-based computational models were set up for each patient with boundary conditions comprising subject-specific three-dimensional inflow velocity profiles at the aortic root and central pressure waveform at the model outlet. Two normal subjects were also included for comparison. The purpose of the study was to investigate the effects of the valve-conduit on flow in the proximal and distal aorta. The results suggested that following the composite valve-conduit implantation, the vortical flow structure and hemodynamic parameters in the aorta were altered, with slightly reduced helical flow index, elevated wall shear stress and higher non-uniformity in wall shear compared to normal aortas. Inter-individual analysis revealed different hemodynamic conditions among the patients depending on the conduit configuration in the ascending aorta, which is a key factor in determining post-operative aortic flow. Introducing a natural curvature in the conduit to create a smooth transition between the conduit and native aorta may help prevent the occurrence of retrograde and recirculating flow in the aortic arch, which is particularly important when a large portion or the entire ascending aorta needs to be replaced

    Real-time three-dimensional ultrasound : a valuable new tool in preoperative assessment of complex congenital cardiac disease

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    Evaluating complex cardiac defects in small children preoperatively requires multiple diagnostic procedures including echocardiography, and also invasive methods such as cardiac catheterisation, computer-tomography and magnetic resonance imaging. This article assesses the complex anatomy of the atrioventricular valves in atrioventricular septal defect using bedside real-time three-dimensional echocardiography and comparing these results to the anatomic findings at the time of operative intervention.peer-reviewe

    MR image reconstruction using deep density priors

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    Algorithms for Magnetic Resonance (MR) image reconstruction from undersampled measurements exploit prior information to compensate for missing k-space data. Deep learning (DL) provides a powerful framework for extracting such information from existing image datasets, through learning, and then using it for reconstruction. Leveraging this, recent methods employed DL to learn mappings from undersampled to fully sampled images using paired datasets, including undersampled and corresponding fully sampled images, integrating prior knowledge implicitly. In this article, we propose an alternative approach that learns the probability distribution of fully sampled MR images using unsupervised DL, specifically Variational Autoencoders (VAE), and use this as an explicit prior term in reconstruction, completely decoupling the encoding operation from the prior. The resulting reconstruction algorithm enjoys a powerful image prior to compensate for missing k-space data without requiring paired datasets for training nor being prone to associated sensitivities, such as deviations in undersampling patterns used in training and test time or coil settings. We evaluated the proposed method with T1 weighted images from a publicly available dataset, multi-coil complex images acquired from healthy volunteers (N=8) and images with white matter lesions. The proposed algorithm, using the VAE prior, produced visually high quality reconstructions and achieved low RMSE values, outperforming most of the alternative methods on the same dataset. On multi-coil complex data, the algorithm yielded accurate magnitude and phase reconstruction results. In the experiments on images with white matter lesions, the method faithfully reconstructed the lesions. Keywords: Reconstruction, MRI, prior probability, machine learning, deep learning, unsupervised learning, density estimationComment: Published in IEEE TMI. Main text and supplementary material, 19 pages tota

    Structure-based finite strain modelling of the human left ventricle in diastole

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    Finite strain analyses of the left ventricle provide important information on heart function and have the potential to provide insights into the biomechanics of myocardial contractility in health and disease. Systolic dysfunction is the most common cause of heart failure; however, abnormalities of diastolic function also contribute to heart failure, and are associated with conditions including left ventricular hypertrophy and diabetes. The clinical significance of diastolic abnormalities is less well understood than systolic dysfunction, and specific treatments are presently lacking. To obtain qualitative and quantitative information on heart function in diastole, we develop a three-dimensional computational model of the human left ventricle that is derived from noninvasive imaging data. This anatomically realistic model has a rule-based fibre structure and a structure-based constitutive model. We investigate the sensitivity of this comprehensive model to small changes in the constitutive parameters and to changes in the fibre distribution. We make extensive comparisons between this model and similar models that employ different constitutive models, and we demonstrate qualitative and quantitative differences in stress and strain distributions for the different constitutive models. We also provide an initial validation of our model through comparisons to experimental data on stress and strain distributions in the left ventricle
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