Ultrasonic imaging of the stress distribution in elastic media due to an external compressor

We describe an experimental ultrasonic method capable of imaging the two-dimensional distribution of longitudinal stress in an elastic, tissue-like material due to an external compressor of arbitrary size or shape and boundary conditions. The method involves the use of a compressor and an opposing ultrasonic transducer. Local strains are derived from the ultrasonic backscatter signals before and after compression using cross correlation analysis. The strain distribution is converted to a stress map by assuming a linear stress-strain relationship. The technique is useful for quantifying the corrections that must be made to images of the elastic modulus of tissue (elastograms) due to the effects of compressor size and shape, depth and boundary conditions. It is also useful for experimental modeling of stress distributions in elastic media.