Ultrasonic imaging of tissue elasticity is useful for the detection of lesions such as cancer in which rigidity changes occur. The viscoelasticity of tissue makes the diagnosis by elasticity imaging difficult because the image quality depends on the rate of deformation, but the differences of viscoelasticity reflect the tissue type and degeneration. In this paper, the ultrasonic imaging of the hysteresis parameter (HP), which characterizes the local viscoelasticity, is presented. Quasi-static and cyclic loading by compression and unloading are applied to the body surface for HP imaging. The ability of HP to distinguish the tissue components and degenerations was confirmed in the results of the direct mechanical test for porcine thigh muscle and kidney. For the porcine kidney and the breast fibroadenoma, the HP images depict different patterns than the conventional B-mode and strain images. From these results, HP imaging has the potential to provide different information from conventional imaging.
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