Abstract The elastic properties of soft tissues depend on their molecular building blocks, and on the microscopic and macroscopic anization of these blocks. The changes in tissues’ elastic properties are correlated with pathological changes as well. So there are some differences in stiffness between the lesion and the surrounding normal tissue. Be imposed on with an incentive, biological soft tissue has a deformation, so we can obtain the pre- and pression RF signals and estimate the displacement distribution of tissue, and then get the strain distribution and elastic modulus distribution of biological soft tissue by means of signal processing and cross-correlation. Based on the reflection-type ultrasound elastography system, the thesis put forward a 1-D axial strain estimation method, which can accurately estimate the elastic modulus (or hardness) distribution of biological soft tissue. The main work of the thesis is as follows: Firstly, it introduces one fundamental mechanics law of biological soft tissue in ultrasound elastography – Hooke’s law, and studies mechanical properties of biological soft tissue and that elastography is applied in the tissue so that simplify it to build the mechanical model of biological tissue in elastography. It introduces the principle of ultrasonic elastography and some mon elastographies and ultrasound elastography system and its classifications based on the principle of ultrasonic elastography of quasi-static or pression, and studies on the imaging principle of reflection-type ultrasonic elastography pared with transmission-type ultrasonic elastography system. Secondly, it studies on cross-correlation algorithm, a classical algorithm for ultrasonic elastography, and traditional time-domain cross-correlation algorithm based on cross-correlation algorithm. Considering the deficiencies of traditional methods, the thesis puts forward a method puting scaling factor for estimating strain of tissue. It designs a method calculating the
