Design of 2D sparse array transducers for anomaly detection associated with a transcranial ultrasound system

Ultrasound imaging is a low cost and non-invasive technique, with many biomedical and industrial applications. In many applications, operator dependency can significantly influence the quality of the acquired information. Transcranial ultrasound is one such application, and this Thesis will investigate both transducer design and image processing techniques inspired by the desire to improve the ability of an ultrasonic system to detect and size anomalies in the blood flow. Aperiodic sparse 2D ultrasonic array configurations, including random array, log spiral array, and sunflower spiral array, have been considered for their potential as a conformable transducer able to image within a focal range of 30-80 mm, at an operating frequency of 2 MHz. Optimisation of the imaging performance of potential array patterns has been undertaken based on their simulated far field directivity functions.;Subsequently, two log spiral array patterns have been selected: one is the overall optimal design; the other is a compromise design to accommodate in-house manufacturing limitations. Both conventional 1-3 (C13) piezocomposite and piezoceramic fibre Composite Element Composite Array Transducer (CECAT) structures have been fabricated and characterised. The CECAT device provides a conformable piezocomposite material and demonstrated reduced mechanical cross-talk between neighbouring array elements and improved the operational bandwidth, while the mechanically stiff C13 devices perform better in terms of sensitivity. Moreover, the C13 device incorporating the overall optimal array pattern performs best in terms of the image background noise level, while for transducers based on the compromise design, the CECAT device offers better axial resolution when imaging multiple reflectors.;Image processing algorithms, such as Hough transform and Morphological Opening, have been implemented to automatically detect and dimension particles located within a fluid-filled tube structure, in a variety of experimental scenarios. This includes bespoke phantoms using tissue mimicking material to simulate a basic transcranial ultrasound arrangement. The image processing algorithms were initially developed using data collected from a commercial 1D linear array transducer. Subsequent experiments using the fabricated CECAT log spiral 2D array transducer demonstrated that this algorithmic approach was able to detect the walls of the tube structure and stationary anomalies within the tube with a precision of ~0.1 mm.Ultrasound imaging is a low cost and non-invasive technique, with many biomedical and industrial applications. In many applications, operator dependency can significantly influence the quality of the acquired information. Transcranial ultrasound is one such application, and this Thesis will investigate both transducer design and image processing techniques inspired by the desire to improve the ability of an ultrasonic system to detect and size anomalies in the blood flow. Aperiodic sparse 2D ultrasonic array configurations, including random array, log spiral array, and sunflower spiral array, have been considered for their potential as a conformable transducer able to image within a focal range of 30-80 mm, at an operating frequency of 2 MHz. Optimisation of the imaging performance of potential array patterns has been undertaken based on their simulated far field directivity functions.;Subsequently, two log spiral array patterns have been selected: one is the overall optimal design; the other is a compromise design to accommodate in-house manufacturing limitations. Both conventional 1-3 (C13) piezocomposite and piezoceramic fibre Composite Element Composite Array Transducer (CECAT) structures have been fabricated and characterised. The CECAT device provides a conformable piezocomposite material and demonstrated reduced mechanical cross-talk between neighbouring array elements and improved the operational bandwidth, while the mechanically stiff C13 devices perform better in terms of sensitivity. Moreover, the C13 device incorporating the overall optimal array pattern performs best in terms of the image background noise level, while for transducers based on the compromise design, the CECAT device offers better axial resolution when imaging multiple reflectors.;Image processing algorithms, such as Hough transform and Morphological Opening, have been implemented to automatically detect and dimension particles located within a fluid-filled tube structure, in a variety of experimental scenarios. This includes bespoke phantoms using tissue mimicking material to simulate a basic transcranial ultrasound arrangement. The image processing algorithms were initially developed using data collected from a commercial 1D linear array transducer. Subsequent experiments using the fabricated CECAT log spiral 2D array transducer demonstrated that this algorithmic approach was able to detect the walls of the tube structure and stationary anomalies within the tube with a precision of ~0.1 mm