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A class of adapted mean frequency estimators is proposed for color flow mapping. These estimators can be fitted to the specific characteristics of a given Doppler signal to optimize the compromise between the range of analysable frequencies and the variance of mean frequency estimation. A sub-optimal estimator is derived for real-time applications, and an(More)
The definition of medical ultrasound images is strongly limited by the need for low examination frequencies which is imposed by the high attenuation of acoustic waves in tissues. The filtering effect of imaging systems is described and quantified for echography, transmission tomography and reflection tomography. Improvement of image definition is(More)
The color Doppler estimator (CE1), which is calculated from the phase of the first correlation lag of the Doppler signal, is compared to the general mean frequency estimator (CEn), which is based on a weighted summation of all the available correlation lags, for long and short Doppler data sets (typically 48 and 8 Doppler samples). A new estimator of the(More)
In order to provide physical information supporting the clinical use of flow mapping, an in vitro model was designed to measure the velocity fields in a pulsatile hydraulic turbulent jet. We used a peak velocity ranging from 2.5 to 5.5 m.s-1, an orifice diameter ranging from 5.8 to 11.3 mm and confined the jet in a receiving tube whose diameter ranged from(More)
The present work is aimed at investigating the effects of myocardial infarction and ischemia on induction of ventricular fibrillation. Electrophysiologic effects of global and local ischemia (variation of the dispersion of refractory periods as well as conduction velocity) on initiation of reentry mechanisms was studied by means of computer simulations(More)
BACKGROUND Color Doppler and magnetic resonance imaging give pictures of abnormal jets within which the respective contribution of fluid mechanics and image artifacts are difficult to establish because of current technical limitations of these modalities. We conducted the present study to provide numerical descriptions of the velocity fields within(More)
An adaptive mean frequency estimator is proposed for color flow imaging. It is based on a series expansion of the first derivative of the autocorrelation function of the Doppler signal at origin. Its bias can be reduced by shifting the integration bounds in the series expansion and its variance adjusted by adapting the coefficients of the serial(More)
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(More)
A technique dedicated to spatial regularization of magnetic resonance (MR) velocity data has been implemented to improve flow image quality. It is assumed that neighboring flow-velocity pixels are partially correlated, although large-velocity discontinuities remain possible. Increasing MR signal magnitude due to the in-flow effect also is used to enhance(More)
Principles of high-resolution, ultrasonic imaging using data acquisition by a compound scanning with a sector echograph are presented. The signal processing is based on both deconvolution and reflection mode tomography. Three of the methods that can be derived from these principles are selected due to their lower computation costs. Applications of these(More)