Measurement of speed of sound dispersion in soft tissues using a double frequency continuous wave method

We introduce a method for measuring the speed of sound dispersion. It combines a short pulse transmission followed by a long burst comprised of two frequencies, one being double that of the other. The method allows the determination of the speed of sound dispersion using a single transmission. To validate the method, the dispersion was first measured in plastic samples and then in in vitro soft tissues samples. The results obtained for Perspex samples are in excellent agreement with values reported in the literature. The dispersion index in soft tissues ranged for a bovine heart from 0.63 +/- 0.24 (m/s.MHz) at 1.5 MHz to 0.27 +/- 0.05 (m/s.MHz) at 4.5 MHz and for a turkey breast from 1.3 +/- 0.28 (m/s.MHz) at 1.75 MHz to 0.73 +/- 0.1 (m/s.MHz) at 3.8 MHz. The significant difference in the speed of sound dispersion index between the studied materials indicates that dispersion may be used as a new index for soft tissue characterization by ultrasound.