RESUMO
The velocity fields of turbulent jets can be described using a single formula which includes two empirical constants: k(core) determining the length of the central core and k(turb) the jet widening. Flow models simulating jet adhesion, confinement and noncircular orifices were studied using laser Doppler anemometer and the modifications of the constants were derived from series of velocity profiles. In circular free jets, k(core) was found equal to 4.1 with a variability of 1.4%. In complex configurations, its variability was equal to 15.2%. For k(turb), the value for free circular jets was of 45.2 with a variability of 6.0% and this variability in complex configurations was significantly higher (30. 1%, p=0.025). The correlation between the actual orifice size and the jet extension was poor (r=0.52). However, the almost constant value of k(core) allowed to define a new algorithm calculating the regurgitant orifice diameter with the use of outlines of the jet image (r=0.89). In conclusion, the fluid mechanics of regurgitant jets is modified in complex configurations but, due to the relative independency of the central core, velocity fields could be used to evaluate the dimensions of the effective regurgitant orifice.
Assuntos
Insuficiência da Valva Aórtica/fisiopatologia , Valva Aórtica/patologia , Hemorreologia , Insuficiência da Valva Mitral/fisiopatologia , Valva Mitral/patologia , Modelos Cardiovasculares , Insuficiência da Valva Tricúspide/fisiopatologia , Valva Tricúspide/patologia , Algoritmos , Velocidade do Fluxo Sanguíneo/fisiologia , Humanos , Fluxometria por Laser-DopplerRESUMO
Detection of myocardial borders on sequences of electron beam CT images is carried out using an adaptive segmentation algorithm developed to enhance dynamic analysis of cardiac function. Adaptivity is based on description of the myocardial borders from the mean and standard deviation of the grey level and gradient distributions on each image of the sequence. Comparison of segmentations from five experimentators with automatically determined borders on a set of 416 endocardial and epicardial contours indicated differences between automatic and manual tracing very close to differences due to inter-observer reproducibility.
Assuntos
Algoritmos , Ventrículos do Coração/diagnóstico por imagem , Processamento de Imagem Assistida por Computador/métodos , Tomografia Computadorizada por Raios X , Baixo Débito Cardíaco/diagnóstico por imagem , Baixo Débito Cardíaco/fisiopatologia , Cardiomiopatia Dilatada/diagnóstico por imagem , Cardiomiopatia Dilatada/fisiopatologia , Cardiomiopatia Hipertrófica/diagnóstico por imagem , Cardiomiopatia Hipertrófica/fisiopatologia , Meios de Contraste/administração & dosagem , Endocárdio/diagnóstico por imagem , Humanos , Variações Dependentes do Observador , Pericárdio/diagnóstico por imagem , Intensificação de Imagem Radiográfica , Reprodutibilidade dos Testes , Disfunção Ventricular Esquerda/diagnóstico por imagem , Disfunção Ventricular Esquerda/fisiopatologia , Função Ventricular/fisiologiaRESUMO
The purpose of this study is to minimize errors that occur when using a four vs six landmark superimpositioning method in the cranial base to define the co-ordinate system. Cone beam CT volumetric data from ten patients were used for this study. Co-ordinate system transformations were performed. A co-ordinate system was constructed using two planes defined by four anatomical landmarks located by an orthodontist. A second co-ordinate system was constructed using four anatomical landmarks that are corrected using a numerical optimization algorithm for any landmark location operator error using information from six landmarks. The optimization algorithm minimizes the relative distance and angle between the known fixed points in the two images to find the correction. Measurement errors and co-ordinates in all axes were obtained for each co-ordinate system. Significant improvement is observed after using the landmark correction algorithm to position the final co-ordinate system. The errors found in a previous study are significantly reduced. Errors found were between 1 mm and 2 mm. When analysing real patient data, it was found that the 6-point correction algorithm reduced errors between images and increased intrapoint reliability. A novel method of optimizing the overlay of three-dimensional images using a 6-point correction algorithm was introduced and examined. This method demonstrated greater reliability and reproducibility than the previous 4-point correction algorithm.
Assuntos
Pontos de Referência Anatômicos/diagnóstico por imagem , Cefalometria/métodos , Tomografia Computadorizada de Feixe Cônico/métodos , Ossos Faciais/diagnóstico por imagem , Processamento de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Crânio/diagnóstico por imagem , Algoritmos , Pontos de Referência Anatômicos/anatomia & histologia , Meato Acústico Externo/anatomia & histologia , Meato Acústico Externo/diagnóstico por imagem , Ossos Faciais/anatomia & histologia , Forame Magno/anatomia & histologia , Forame Magno/diagnóstico por imagem , Humanos , Mandíbula/anatomia & histologia , Mandíbula/diagnóstico por imagem , Órbita/anatomia & histologia , Órbita/diagnóstico por imagem , Técnica de Expansão Palatina , Reprodutibilidade dos Testes , Estudos Retrospectivos , Crânio/anatomia & histologia , Base do Crânio/anatomia & histologia , Base do Crânio/diagnóstico por imagem , Osso Esfenoide/anatomia & histologia , Osso Esfenoide/diagnóstico por imagemRESUMO
We improved the three-point phase-contrast method by regularization of MR velocity data after acquisition of a low velocity-to-noise ratio (VNR) velocity image and a high VNR aliased velocity image. The phase unwrapping algorithm is based on the assumed correlation of the velocity of adjacent flow voxels on the low VNR and the unaliased high VNR images. We used Fourier encoding with eight velocity-encoding gradient steps to obtain reference velocity images of the aorta from five subjects (274 images) and compared them with the phase-contrast and three-point phase-contrast images with and without regularization. The VNR of the regularized velocity image was improved by 9.1 dB and the VNR of the three-point phase-contrast velocity image was improved by 0.7 dB with respect to the low first moment velocity image. Corresponding improvements of 9 dB and 3.7 dB were obtained for the estimations of instantaneous flow rate. Magn Reson Med 44:122-128, 2000.