The objective of this research proposal is the improvement of medical diagnostic ultrasound image quality via the development of a new generation of piezoelectric, two-dimensional array transducers using the technology of multi-layer ceramic (MLC) materials currently applied in the field of microelectronics. In particular, the hypothesis is that more sensitive, higher frequency clinically effective two-dimensional transducer arrays will be developed with MLC materials than with conventional transducer technology. The arrays will consist of as many as 32x32=1024 elements, operating at frequencies up to 5 MHz with individual element sizes as small as 0.2 mm on a side. These new 2-D arrays will be used in medical ultrasound phased array scanning to implement new advanced imaging techniques including phase correction in ultrasound B-scans to overcome effects of tissue inhomogeneities, high speed volumetric scanning to produce real time 3-D ultrasound images, and angle independent flow imaging. The two obstacles which limit the development of 2-D array transducers are (1) fabrication difficulties and (2) low transducer sensitivity due to high impedance array elements. The application of multi-layer ceramic technology to ultrasound transducers will solve both of these problems. Fabrication problems will be ameliorated by multi-layer ceramic connectors. These consist of many thick films of ceramic (e.g., alumina) and metallization with customized interconnections between the layers. Such connectors will expand the tiny spacing between array elements to enable connection to the transducer handle. Transducer sensitivity of 2-D arrays will be radically improved by multi-layer ceramic piezoelectric chips. Multiple PZT layers laminated in parallel electrically but in series acoustically will reduce electrical impedance of array elements to improve sensitivity by as much as a factor of 30. 2-D array transducers fabricated with MLC connectors and MLC piezoelectric chips will be compared to conventional 2-D arrays and linear array transducers via laboratory measurements of vector impedance, sensitivity, bandwidth, angular response and cross-talk. Comparisons of image quality will also be made in tissue mimicking phantoms and in limited patient studies.
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