ULTRASONIC-IMAGING OF THE STRESS-DISTRIBUTION IN ELASTIC MEDIA DUE TOAN EXTERNAL COMPRESSOR

We describe an experimental ultrasonic method capable of imaging the t wo-dimensional distribution of longitudinal stress in an elastic, tiss ue-like material due to an external compressor of arbitrary size or sh ape and boundary conditions. The method involves the use of a compress or and an opposing ultrasonic transducer. Local strains are derived fr om the ultrasonic backscatter signals before and after compression usi ng cross correlation analysis. The strain distribution is converted to a stress map by assuming a linear stress-strain relationship. The tec hnique is useful for quantifying the corrections that must be made to images of the elastic modulus of tissue (elastograms) due to the effec ts of compressor size and shape, depth and boundary conditions. It is also useful for experimental modeling of stress distributions in elast ic media.