[VARR-12c]
F. Varray, C. Cachard, J. Kybic, A. Novell, A. Bouakaz, and O. Basset,
"A Multi-Frequency Approach to Increase the Native Resolution of Ultrasound Images",
European Signal Processing Conference (EUSIPCO), Bucharest, Romania, pp. 2733-2737, 2012

.