Showing papers by "Victor Mor-Avi published in 1992"

Digital path-dependent recompensation of contrast-enhanced echocardiographic images.

Abstract: The regional video intensity of two-dimensional (2D) ultrasonographic images is directly affected by energy losses from the ultrasonic beam propagating between the transducer and the specific region of interest (ROI). These losses are mainly dependent on the scattering and absorption properties of the more proximal tissues. The commonly utilized automatic time-gain compensation (TGC) procedures, based on the assumption of uniform scattering and energy conversion throughout the investigated tissues and organs, seem to be largely inadequate in the contrast echocardiographic studies which attempt to quantitate the contrast enhancement of myocardial tissue. We hereby present an algorithm for the non-linear adaptive path-dependent recompensation of the ultrasonographic video intensity for the non-uniform scattering and absorption in images obtained using automatic TGC. The variable energy losses are estimated in our technique according to the reflections from the different points along the acoustic beam. The proposed algorithm is a post-processing function. It was developed considering beam attenuation by scattering and absorption and comparing correction procedures necessary with and without the assumption of uniform attenuation. We hereby present the results obtained by applying this algorithm to contrast enhanced echocardiographic images of canine hearts. The artifacts produced by the inadequate automatic TGC are essentially reduced by the recompensation procedure. The recompensation allows the observation of the changes in video intensity induced in the myocardial tissue by contrast-enhancing media, which are otherwise severely obscured by contrast transit altering the propagation effects.

Quantitation of regional myocardial blood flow by contrast echocardiography

Abstract: A basic theoretical approach is presented for the quantitative measurement of regional myocardial tissue blood flow based on the computer analysis of contrast enhanced echocardiographic images. Blood flow is evaluated as the ratio of the intravascular fraction, and the mean transit time of the contrast agent. Both parameters are obtained by analyzing the variations in mean videointensity in two regions of interest, defined in the left ventricular (LV) cavity and the myocardial tissue. The main transit time is computed using combined time- and frequency-domain processing, applying deconvolution of the response function. Extensive computer simulation showed that the algorithm successfully evaluates the mean transit time within 10% of error for signal-to-noise levels up to 2:1. The intravascular volume fraction is computed as a ratio of the integrated intensities in the two regions of interest. Animal experiments involving radiolabeled microspheres showed high correlation between the two independent measurements of blood flow. >