Development of Surface Acoustic Wave Optical Coherence Elastography (SAW-OCE) for Soft Tissue Characterisation

Abstract

Mechanical properties of biological soft tissues are closely related to their underlying pathological conditions. In clinical practice, they have been widely recognized as a significant indicator to assist disease diagnosis. There has been enormous technical advancement in imaging modalities such as the magnetic resonance elastography (MRE) and the ultrasound elastography to quantify the mechanical properties. Although the magnetic resonance imaging (MRI) and the ultrasound imaging can penetrate deep inside the human body, the millimetre-scale spatial resolution has limited their applications in the early detection of superficial diseases such as skin abnormalities. This research thesis takes advantage of the surface acoustic wave optical coherence elastography (SAW-OCE) to provide high-resolution microstructure images and quantitative mechanical property estimates of skin tissues for aiding skin disease diagnosis.

In this research project, contact mechanical stimulations and non-contact ultrasound were utilised to induce the SAWs on the specimen surface. Phase-sensitive optical coherence tomography system (PhS-OCT) was employed to image the microstructure of the specimen and to track the transient wave propagation inside the specimen. In a transversely heterogeneous material, the 2D Young’s modulus map was reconstructed based on the SAW group velocity with an improved time-of-flight method, i.e., the multi-kernel-weighted-averaging (MKWA) method. In a vertically heterogeneous material, the elasticity of each layer was evaluated by analysing the SAW phase velocity dispersion using a novel mathematical model, i.e., the weighted average phase velocity (WAPV) inversion model. In a homogeneous viscoelastic material, the complex modulus of the medium was estimated by assessing the SAW phase velocity dispersion with the SAW dispersion model. During the experiments, all the abovementioned techniques were initially validated using tissue-mimicking material (TMM) phantoms and then demonstrated on in-vivo human skin tissues.

The results have shown that the proposed SAW-OCE techniques are capable of imaging the microstructure of biological tissues and quantifying the mechanical properties of homogeneous and heterogeneous TMM phantoms, as well as in-vivo human skin tissues at different sites noninvasively. It has the great clinical potential of utilizing SAW-OCE as an assistant tool for human skin disease diagnosis in the early stage.

Date of Award	2020
Original language	English
Awarding Institution	University of Dundee
Sponsors	China Scholarship Council & SINAPSE (Scottish Imaging Network: A Platform for Scientific Excellence)
Supervisor	Zhihong Huang (Supervisor) & Chunhui Li (Supervisor)