Mon, 20 July, 2009, 14:00-15:00, C1
Palpation has been used for thousands of years to assess the mechanical properties of tissues, and thus detect and characterise disease or injury. It continues to be of value in modern medicine, but is limited to a few accessible tissues and organs, and the interpretation of the information sensed by the fingers is highly subjective. Ultrasound elastography aims to display images that are related to a broad range of tissue viscoelastic parameters, by processing time-varying echo data to extract the spatial and/or temporal variation of a stress-induced tissue displacement or strain. In recent years the method in early form has emerged as a real-time imaging modality available as an option on several commercial ultrasound systems, and is starting to prove clinically valuable, for example in breast cancer diagnosis. Nevertheless, it remains a strongly subjective technique and continues, as with palpation, to require interpretive skills to be learnt. There are good reasons to believe that a more quantitative and objective analysis will lead to clinically more valuable measures of tissue composition, function or state, with images that are easier to interpret. Insufficient knowledge exists to tackle a full multivariate inverse problem, or to know which variables can be ignored or taken advantage of to simplify the problem. We have therefore begun work to gain a better understanding of how to solve specific elastographic problems, at the same time as studying, experimentally and theoretically, the relative importance of a number of mechanical characteristics in various situations. This presentation reviews some of the early work and describes a selection of recent studies, including the use of Young's modulus images for quantitative imaging of radiation dose distribution in gel dosimeters, the detection of changes in the stiffness of breast tissue due to post-treatment radiation fibrosis, the application of poroelastic theory to describe and understand the spatio-temporal distribution of strain in fluid-containing tissues held under a sustained compression, the detection of lymphoedema using poroelastic techniques, the anisotropic, viscoelastic and nonlinear behaviour of skin, the use of stiffness anisotropy in skin for the monitoring lymphoedema, and the estimation of the amount of adhesion at tissue boundaries for disease assessment. Ongoing work includes developing methods for the 3D measurement of time varying displacement and strain, taking advantage of recent developments in 4D ultrasound imaging technology to potentially greatly improve the quality and completeness of the data available for solving the inverse problem.
Presentation slides (pdf, 2.9 MB)
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