Elasticity imaging with time-resolved pulsed elastography

Abstract

Time-resolved pulsed elastography is a promising technique for imaging the shear modulus of soft tissues. It is based on the investigation of a low-frequency transient shear wave using an ultrafast ultrasonic imaging system (up to 10<th>000 frames/s) composed of 128 channels sampled at 50 MHz and having 2 Mbytes. The system is connected to a linear array of transducers. Displacements induced by the propagating shear wave are measured using cross correlation of the ultrasonic signals. A low-frequency vibrating device was designed. The linear array of transducers is placed between two rods fixed to electromagnetic vibrators. The rods are either orthogonal or parallel to the active surface of the transducer array. The low-frequency shear waves are sent using the rods which are placed in such a way that the lobes of the induced shear waves superimpose in front of the transducer array. Large displacements are observed in the tissues which makes deeper investigations possible. Movies of the low-frequency (50–200 Hz) shear wave propagation through soft tissues can be used either to estimate the shear modulus distribution in the medium by direct local inversion, or to localize visually lesions of unexpected elasticity. In vivo measurements in human breast will be presented and discussed.