Session: 4K

Vibro-acoustography is a method of imaging and measurement that uses ultrasound to produce radiation force to vibrate objects. The radiation force is concentrated laterally by focusing the ultrasound beam. The radiation force is limited in depth by intersecting two beams at different frequencies so that there is interference between the beams at the difference frequency only at their intersection. This results in a radiation stress of limited spatial extent on or within the object of interest. The resulting harmonic displacement of the object is detected by its acoustic emission, with ultrasound Doppler measurement, or with a laser interferometer. The displacement is a complicated function of the object material parameters. However, significant images and measurements can be made with this arrangement. Vibro-acoustography can produce images of biologically relevant objects such as breast micro-calcification and vessel calcifications, heart valves, and normal arteries. Quantitative measurements of the resulting propagating waves within vessels and tubes can be used to estimate the modulus of the tube wall. Vibration of small objects can be used to estimate the modulus of the embedding material. Estimations of pressure within a thin membrane bag are made by measuring propagation speed of waves induced with the radiation pressure. Modes of vibration and their frequencies can be evaluated with this noninvasive imaging and measurement method. Several examples of these results will be described. Supported in part by EB 002640 and EB 002167 from the NIH.