FILIPCZYŃSKI, L., et al. “Application of the Stationary Echo Cancellation Technique (SEC) in Ultrasonic Doppler Measurements of Blood Flow in children’s Hearts”. Archives of Acoustics, vol. 7, no. 3-4, Mar. 2016, pp. 247-52, https://acoustics3.ippt.pan.pl/index.php/aa/article/view/3285.