Shear Wave Elastography Based on Optical Coherence Tomography
Mechanical properties of biological tissue are involved in a wide range of modern advances of medical science and technology. The mechanical property of biological tissue is directly related to the functionalities of tissue or organ, hence the in-depth knowledge of tissue mechanical property could lead to many benefits in medical research and health care. In clinical practice, accurate estimation of tissue mechanical property may facilitate to predict any possible pathological alterations, or to propose artificial intervention approaches. With the purpose of a quantitative, directly visualized estimation of biological tissue mechanical property, numerous research works in elastography have been conducted and had been successfully applied to countless clinical applications. Elastography techniques had been always rooted in medical imaging technique, classified into a range of scales, based on their imaging depth and resolution performance. In the scale of tissue micro structure, elastography is still a relatively new field, enabled by the recent advances in high-resolution medical imaging techniques e.g. high-frequency ultrasound imaging and Optical Coherence Tomography (OCT). The quantitative elastography technique based on OCT, known as quantitative optical coherence elastography (OCE) is a new research field, promising high-resolution quantitative elastography information with minimal contact that is not achievable by other imaging modalities. The aim of the thesis is to develop a multiple-functional OCT system to image the microstructure of biological tissue, meanwhile quantify localised mechanical property in the region of interest, and further apply it for pre-clinical research applications. Starting from the numerical model of mechanical waves, the behaviours of shear waves and surface waves in biological tissue is studied. Contact mechanical stimulations, as well as non-contact ultrasound and pulsed lasers are utilised to generate transient waves in biological samples. High speed shear wave imaging technique is developed and optimized based on a Phase-sensitive OCT (PhS-OCT) system to capture the transient wave propagation in samples, and the inversion algorithm for mapping localized shear modulus is proposed. The experimental results indicated that the Shear Wave Imaging OCT (SWI-OCT) technique is capable to provide abundant temporal and spatial resolution to capture the shear waves in tissuemimicking phantoms and in vivo biological samples. Quantitative elastography results were obtained from mouse skin and cornea samples, suggesting potential diagnostic and therapeutic clinical applications.
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