Abstract

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.