Shear wave speed measurement using an unfocused ultrasound push beam

Tissue viscoelasticity is related to pathology and therefore has important medical applications. Radiation force from a focused ultrasound beam has been used to produce shear wave in tissues for shear wave speed and tissue elasticity measurements. The feasibility of shear wave speed measurement using radiation force of an unfocused ultrasound beam is demonstrated in this study with a linear and a curved array transducer. Good estimation of shear wave speed was achieved in 3 calibrated phantoms with different shear modulus. Shear wave speed can be measured over a relatively long axial extent (z = 10-40 mm for the linear array, and z = 15-60 mm for the curve array) from a single acquisition with an unfocused push beam. In vivo measurements on the biceps of a healthy volunteer show consistent increase of shear modulus for the biceps under 0, 1, 2, and 3 kg loading. Advantages and limitation of unfocused push are discussed.