Measurement of shear wave velocity for elastography using conventional B-mode scan of focused ultrasound

A measurement method of shear wave (SW) velocity for elastography by using a conventional B-mode scan with a focused ultrasound system is demonstrated in this paper. In the B-mode scan, there is a scanning time delay among the sequential A-mode measurements. This scanning time delay causes an artificial spatial frequency difference between the induced SW and undesired SWs reflected at tissue boundaries. Therefore, the reflected SW can be removed from the measured SWs using a spatial frequency filter. In our previous study, the SW propagating in the same direction as the B-mode scanning direction was used to measure the SW velocity. In such configuration, a prior knowledge was required whether the values of the SW velocity of a specimen are greater or smaller than the B-mode scanning speed, which may not be known for an arbitrary specimen. In order to address such shortcoming, the measurement configuration was modified in this paper so that such prior knowledge is no longer required. The method was verified by using a soft tissue mimicking phantom with a relatively stiffer cylindrical inclusion. Image contrast between the two different materials was successfully observed in the SW velocity map obtained.