MYOCARDIAL TRANSIT-TIME OF THE ECHOCARDIOGRAPHIC CONTRAST-MEDIA

The mean transit time of a tracer through a sample of tissue is a quan titative marker most closely related to regional tissue blood flow. Th erefore, an accurate estimation of the mean time of transit of an ultr asonic tracer through a sample of myocardial tissue, obtained by contr ast echocardiography, may provide a quantitative noninvasive estimate of myocardial perfusion. We hereby present an algorithm for the determ ination of the mean transit time by computerized analysis of a series of contrast-enhanced echocardiographic images. The algorithm comprises the evaluation of the echocardiographic impulse response function of a selected region of interest, using a deconvolution technique based o n a fast Fourier transform and a frequency domain division of the vide ointensities measured in the sample, by that measured in a predetermin ed reference region. An extensive computer simulation study was design ed to facilitate the optimization of the steps of analysis. We present the results of the evaluation study performed in order to assess the accuracy of the procedure in computer-simulated echocardiographic imag es. Within a wide range of parameters chosen to define these functions , the analysis is shown to be essentially independent of the rise and decay times of the impulse response function of the tissue sample as w ell as of the simulated intensities. The effects of random noise intro duced into the simulated intensity curves and of their variable width were investigated. The mean transit time was found to be accurately ev aluated within about 10% of error for the variety of widths and noise levels permitted. The reconvolution error did not correlate with the a ccuracy of the evaluation of the mean transit time, indicating that th e reconvolution error cannot be used as an estimate of the accuracy of the procedure. The numerical methods and the results of the computer study are discussed in detail. The approach is proposed to be used as part of a more general technique for the quantitative measurement of r egional myocardial tissue blood flow.