Ultrasound Based Soft Tissue Elastic Modulus and Strain Measurement

Conventional B-mode ultrasound provides information on the anatomical features using acoustic impedance differences in the tissues. Ultrasound elastography uses a variety of techniques to map soft tissue elasticity. Tissue stiffness is a novel indicator of the tissue health, as many pathologies can alter the tissue stiffness such as cancer and fibrosis. Accurate and early detection of tissue elasticity can guide towards reliable diagnosis, and prognosis of diseases. The objectives of the research reported in this thesis are to implement strain and shear wave elastography techniques on the locally developed ultrasound systems, along with identifying current challenges in elastography and proposing solutions to develop ultrasound elastography as an accurate, and reliable clinical tool.

In the first study, strain elastography was implemented and novel strain estimation quality assessment approach was proposed to discard noisy strain images. The second study proposed a shear wave generation method, called Dual Push Beam (DPB) to address challenges of the current shear wave elastography techniques, such as to reduce data acquisition events and to improve imaging depth. Further, the thesis includes the study which introduced a new angle-aligned shear wave tracking method, which improved displacement estimation quality for shear compounding. Final study designed seven different elastography schemes and investigated variations in elasticity estimation across the image by changing shear waves generation beam parameters such as aperture size and focal depth and its implication for liver fibrosis and breast cancer diagnosis.