Accurate and Precise Displacement Estimation for Ultrasound Elastography

Accurate and Precise Displacement Estimation for Ultrasound Elastography Morteza Mirzaei, Ph.D. Concordia University, 2021 Elastography is a technique for detecting pathological tissue alterations by extracting mechanical properties of the tissue. It can be performed using different imaging modalities, including magnetic resonance imaging and ultrasound. Unlike biopsy that is invasive and considers a small portion of tissue, elastography is a non-invasive technique that interrogates a larger part of the tissue and reduces the probability of missing abnormalities. UltraSound Elastography (USE) is an approach for detecting mechanical properties of tissue by using ultrasound imaging. Ultrasound as an imaging tool has emerged in the latter half of the 20th century and has become one of the most popular imaging modalities. The main advantages of ultrasound imaging lie in its noninvasive nature, low cost, convenience, and wide availability. USE may help in early diagnosis which substantially increases the success probability of treatment. In recent years, USE has been explored for several clinical applications including ablation guidance and monitoring, differentiating benign thyroid nodules from malignant ones and breast lesion characterization. Surgical treatment of liver cancer, assessment of non-alcoholic fatty liver disease, assessment of fibrosis in chronic liver diseases, detecting prostate cancer, differentiating abnormal lymph nodes in benign conditions and brain tumor surgery are other relevant clinical applications of USE. An important challenging step for USE is Time Delay Estimation (TDE) between pre- and post-deformed tissue. TDE is an ill-posed problem since the 2D displacement of one sample cannot be uniquely calculated based on its intensity. Moreover, presence of noise due to speckles, out-of-plane movement, blood flow and other biological motions affect the accuracy of TDE. The other limiting factors for TDE are low resolution of ultrasound data, low sampling rate and lack of carrier signal in the lateral direction. In this thesis, we propose high level techniques for increasing the accuracy and preciseness of the estimated displacement