Abstract
Aperiodic sparse 2D ultrasonic array configurations, including random array, log spiral array, and sunflower array, have been considered for their potential as conformable transducers 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. Two evaluation criteria, peak sidelobe level (PSL) and integrated sidelobe ratio (ISLR), are used to access the performance of each array configuration. Subsequently, a log spiral array pattern with −19.33 dB PSL and 2.71 dB ISLR has been selected as the overall optimal design. Two prototype transducers with the selected log spiral array pattern have been fabricated and characterised, one using a fibre composite element composite array transducer (CECAT) structure, the other using a conventional 1–3 composite (C1–3) structure. The CECAT device demonstrates improved coupling coefficient (0.64 to 0.59), reduced mechanical cross-talk between neighbouring array elements (by 10 dB) and improved operational bandwidth (by 16.5%), while the C1–3 device performs better in terms of sensitivity (~50%). 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, including bespoke phantoms using tissue mimicking material. 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.
Highlights
Transcranial ultrasonography has become an important method for stroke diagnosis, as it is a non-invasive, low-cost, and safe test
As results illustrated in the figures, For the random array, samples were simulated for each element number, and the minimum values both random array and sunflower array, peak sidelobe level (PSL) and integrated sidelobe ratio (ISLR) tend to decrease with the increase in element for
This paper describes the design, fabrication and evaluation of a 2D sparse array ultrasonic transducer, whose design specification was developed for the potential to be applied for transcranial ultrasound imaging through the temporal window
Summary
Transcranial ultrasonography has become an important method for stroke diagnosis, as it is a non-invasive, low-cost, and safe test. The experience of the operator could highly affect the diagnostic efficiency and has limited the application of transcranial ultrasound in situations when experienced ultrasound operators are not available This provided the motivation for the work described in this paper, with two technical aspects considered to reduce operator dependency: Design a 2D array transducer to achieve enhanced and flexible imaging capability. Due to the associated half-wavelength criteria for element pitch in dense imaging array designs [4], a full matrix 2D array transducer would require ~5000 array elements for a 30 mm diameter active area. These methods intend to find the set of elements that can achieve a desired beam pattern from a large amount of of periodically arranged grids [8].
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