Ultrasound propagation speed measurement of mimicking soft tissue phantoms based on agarose in the range of 25°C to 50°C

To simulate the real conditions where the ultrasound will be applied, it is necessary the employment of materials to mimic the ultrasound behavior of tissues; these kind of materials are called phantoms. Therefore, it is important to measure the basic characteristics that must be mimicked; one of them is the ultrasound propagation speed. This characteristic could be employed to estimate the soft tissue temperatures in a non-invasive way. Agarose was used, for phantom preparation, in this work because it is an easy material to work with and also because the change of the ultrasound propagation speed in the phantoms only depends on the quantity of agarose concentration; it makes easier the phantom preparation. Ultrasound signals obtained from the phantom, using the pulse-echo transmission technique, were processed by using cross-correlation to calculate the time-of-flight, which is defined as the difference between the time of the first and the last phantom echo signal, with this information, and the phantom thickness, it is possible to calculate the propagation speed. The results are compared with the ultrasound speed obtained from degassed water, in the range from 25degC to 50degC. The phantom propagation speed with 1.5% agarose concentration had a behavior close to that of the water. A non-linear behavior after 43degC was observed.