Estimation of Blood Flow Velocity in the Heart of Fish Larvae Using Autocorrelation of Echocardiographic Signals

The paper is devoted to the estimation of blood flow velocity in the heart of a fish larva using a high-frequency ultrasonic scanner with a highly focused single-element ultrasonic transducer. The two-dimensional echocardiographic signal, recorded at a given probe position as a function of the delay of the reflected wave and time, is a superposition of randomly distributed responses reflected from moving blood cells. It is shown that a single value of flow velocity can be estimated by calculating the autocorrelation function of the echocardiographic signal, cropped by a two-dimensional data window. Moreover, for this purpose it is sufficient to calculate only the phase of the autocorrelation function at two adjacent points shifted by sampling intervals. The developed processing algorithm was verified using echocardiographic data measured on sturgeon larva aged 3 days after hatching. An ultrasonic transducer with a central frequency of 75 MHz, a bandwidth of 65%, and an angular aperture of 40° was used in the experiment. The velocity calculated in the ventricle area during one cardiac period varied in the range of ±10 mm/s depending on the contraction phase.