Generation of strain inside objects using dual acoustic radiation force

Many studies have been carried out on the measurement of mechanical properties of tissues by applying an acoustic radiation force induced by ultrasound to an object. However, one acoustic radiation force in a given direction (e.g., vertical direction) does not generate strain in an object effectively because it also causes changes in the object's position, which has zero spatial gradient in displacement (= no strain). Especially when the elastic modulus of the object is much higher than that of the surrounding tissue (such as a tumor in breast tissue), one acoustic radiation force might generate only a change in the position of the object unlike a strain in the object is hardly generated. In such cases, mechanical properties of the object cannot be evaluated. In this study, two cyclic acoustic radiation forces are simultaneously applied to an object in two different directions (e.g., two opposite horizontal directions) to effectively generate strain inside the object, even when the object is much harder than the surrounding tissue.