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UBC Theses and Dissertations

Dual-transducer ultrasound for elastography Abeysekera, Jeffrey Michael


Medical imaging techniques provide valuable information about the internal anatomy of the body. Commonly used techniques can render many properties of the anatomy and its function, but they are limited in their ability to measure tissue mechanical properties such as elasticity. Over the past two decades there has been growing interest in developing methods of noninvasively characterizing mechanical properties of tissues; a field commonly referred to as elastography. Tissues are known to exhibit changes in mechanical properties in response to pathology. As a result, elastography has the particular potential to help physicians diagnose and locate cancerous tumors and other malignancies. The principle of operation of elastography systems is to apply an excitation to the tissue, such as a compression, and to measure the resulting tissue motion as it deforms. The tissue elasticity can then be inferred from the motion estimates by solving the inverse problem. Tissue motion is typically measured with ultrasound because it is fast, safe, and relatively inexpensive. The point spread function of an ultrasound beam is anisotropic, resulting in poorer quality motion estimates in two of the three spatial directions. This thesis investigates a new method of estimating tissue motion by employing two ultrasound transducers with different view angles. The goal of using these two transducers is to create a plane of high quality 2D motion estimates. Simulations and experimental results on tissue mimicking phantoms show that the method outperforms other commonly used 2D motion estimation methods. For example, in a tissue deformation simulation, the dual transducer method produced lower root mean square measurement error by a factor of 10 compared to a single transducer technique, and a factor of 3 compared to a single transducer with angular compounding. A simple wire-based method of aligning the transducers into a coincident scan plane is initially developed. Later, a novel wedge-based phantom is designed for aligning the two transducers. Calibration results demonstrate improved alignment with the wedge phantom. Manual alignment is found to be repeatable with mean alignment errors under 1 degree in rotation and 1 mm in translation for all degrees of freedom after six independent trials.

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