Design And Optimization Of A Tissue Specific Ultrasonic Transducer Micro-Array For Age-Related Macular Degeneration

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Electrical and Computer Engineering


Doctor of Engineering

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Obtaining quantitative data about tissue has been a goal of ultrasonography since its inception, such data provides invaluable information for diagnosing disease. Traditional ultrasound imaging techniques (B-Mode, C-Mode and M-Mode) have been used to diagnose diseases from images of organs. However, images obtained via these techniques, in some cases, provide limited information about the pathology of the tissues being examined. This is because much of the information that is used for diagnosis depends upon qualitative cues emerging from the echoic profiles of bulk tissue properties. In order to obtain quantitative information about tissue properties, an understanding of the interaction of the ultrasound system proper and tissue is necessary. This requires the creation of detailed models of both the ultrasound imaging system and tissue. These models enable us to obtain quantitative information about tissue, by examining features of backscattered data, generated by the interaction of the ultrasonic imaging system with the tissue under examination. Imaging systems are typically designed with little consideration of the constraints of the imaging environment or the acoustic features of the tissue which include impedance, scatterer size, shape and density. We propose to take into account the physical properties of tissue in designing ultrasonic imaging arrays.\ We develop a framework for designing ultrasonic imaging systems (primarily the transducer and transducer array) with physical parameters that are tuned to detect specific features of tissue. The design methodology obtains the parameters of an NxN transducer array constrained to a size of e.g. 2mm x 2mm (the size required for medical imaging). The physical parameters of the transducer elements are also obtained for capacitive micromachined ultrasonic transducer (cMUT) technology. In addition to the overall size constraints (2 mm x 2 mm), several other constraints put limitation upon the possible system configurations (achievable parameters). A constrained optimization technique is used to generate a set of ultrasound system parameters as a function of operating frequency. A sample set of transducer and transducer array configurations is used to generate associated point spread functions. The effects of the acoustic features of tissue on backscattered ultrasound data are examined through the interaction of the system point spread functions and a tissue phantom model. Tissue characterization experiments are performed on material tissue phantoms in order to obtain information about its acoustic features (sound speed, density, scatterer shape, size and density). From the experimental data finite element models (FEM) of the tissue phantom are created. A simulation of the interaction of the point spread functions (PSF) of the cMUT arrays and the computational tissue phantom (FEM) is then performed and estimates of the statistics of the backscatter are used to estimate scatterer density. In addition frequency dependence of the backscatter is used to estimate scatterer diameter and shape. The ultrasound array that provides the most accurate estimates of scatterer diameter and density is considered to be the array most suited to obtain quantitative information about the tissue under examination.