Evaluation of piezo composite based omnidirectional single fibre transducers for 3D USCT

3-D Ultrasound Computer Tomography (USCT) is aimed at early detection of breast cancer. The system uses Synthetic Aperture Focusing Technique (SAFT) for reconstruction of images. 2041 unfocused ultrasound transducers with approx. 2.5MHz center frequency, 1MHz bandwidth and 36 degrees opening angle at -3dB. The system was optimized for highest image quality within a Region Of Interest (ROI). The analysis shows that to increase the size of ROI for the next generation USCT, the opening angle of transducers needs to be increased to 60 degrees while the other characteristics should be preserved or even improved. The approach presented in this paper for fabricating the transducers fulfilled the expectation of reproducible transducer arrays regarding disc thickness and fibre position and size. The mean electrical impedance and phase of the fibres were approx. 10 k Omega and -30. respectively. Though the -3dB opening angle is successfully increased to 61.6 degrees, unexpectedly the characteristics of all the fibres possess great variability and the absolute sound pressure is down by approx. 80%.