Application of vibro-acoustography to tissue elasticity imaging

The image of a tissue deformability is obtained with the vibro-acoustography imaging method using mechanical low frequency (LF) excitation. This ultrasound excitation is locally created by means of a focused annular array emitting two primary beams at two close frequencies, f(1) and f(2) (f(2) = f(1) + f(LF)). The LF acoustic emission resulting from the vibration of the medium is detected by a sensitive hydrophone and then used to form the image. A theoretical model of oscillations in soft biological tissue induced by focused ultrasound is described. In the case of vibro-acoustography, oscillations originate from shear waves induced by an alternative radiation force. This non-invasive imaging method was demonstrated in this study to be suitable for tissue imaging, with x and y transverse resolutions less than 300 mum. A vibro-acoustic image of a calcaneus bone slice is presented and compared with images of the same bone realised with other bone imaging methods.