Trahey G. Acoustic radiation force impulse imaging of thermallyand chemically-induced lesions in soft tissues: preliminary ex vivo results. Ultrasound Med Biol 2004;30:321–328. [PubMed: 15063514

The clinical viability of a method of acoustic remote palpation, capable of imaging local variations in the mechanical properties of soft tissue using Acoustic Radia-tion Force Impulse (ARFI) imaging, is investigated in vivo. In this method, focused ultrasound is used to apply localized radiation force to small volumes of tissue (2 mm3) for short durations (less than 1 msec) and the resulting tissue displacements are mapped using ultrasonic correlation based methods. The tissue displacements are inversely proportional to the sti®ness of the tissue, and thus a sti®er region of tissue exhibits smaller displacements than a more compliant region. Due to the short duration of the force application, this method provides information about the mechanical impulse response of the tissue, which re°ects variations in tissue visco-elastic characteristics. In this paper, experimental results are presented demonstrat-ing that displacements on the order of ten microns can be generated and detected in soft tissues in vivo using a single transducer on a modi¯ed diagnostic ultrasound scanner. Di®erences in the magnitude of displacement and the transient response of tissue are correlated with tissue structures in matched B-mode images. The results comprise the ¯rst in vivo ARFI images, and support the clinical feasibility of a radiation force based remote palpation imaging system