Conformable Row-Column Ultrasound Arrays for Abdominal Imaging

Fully-addressable two-dimensional (2D) array ultrasound transducers have issues such as a large number of elements, difficult to interconnect with an imaging system, high acoustic impedance of each array element which leads to a low signal-to-noise ratio (SNR), and high cost for medical ultrasound imaging systems, especially, for a 2D array of a size close to 300 mm by 300 mm with more than one million elements for imaging of a large area such as the abdomen of big patients and pregnant women. Despite the issues above, an array of a large size is necessary to reconstruct a large 3D volumetric image for artificial intelligent (AI) assisted medical diagnoses with minimal human interventions, which is especially desirable in countries or areas where there are few highly trained medical professionals to operate ultrasound imaging systems. To address the issues associated with large fully-addressable 2D array transducers, row-column (RC) arrays have been proposed to reduce the number of elements of the 2D arrays and reduce the acoustic impedance of each array element to increase SNR.Although a RC array can address some issues of the fully-addressable 2D arrays and simplify the imaging system greatly, the array must be rigid to avoid introducing phase aberrations due to deformation of the array. To solve the problem, in this paper, 36 sub-arrays of 25.6 mm by 25.6 mm each are proposed to form a large conformable RC array of a size of about 281.6 mm by 281.6 mm. To simplify the imaging system by further reducing the number of elements, a 25.6-mm gap filled with flexible materials between the sub-arrays is introduced. To cover the space between the sub-arrays in imaging, a 2D acoustic lens of 30
^o
divergence is applied to each sub-array. To determine the position of each sub-array in the space for image reconstruction, 3 markers are placed on each sub-array to allow a position-reading camera to determine the position of the sub-array. Computer simulation with limited-diffraction array beam method was performed to calculate the ultrasound fields produced by a sub-array and the results show that the beam width of each sub-array of 2.5-MHz center frequency is about 2.6 mm at a depth of 70 mm and 0° steering angle. Thus, the pulse-echo beam dimension is about 2.6 mm by 2.6 mm in the plane that is perpendicular to the ultrasound wave propagation. This demonstrates that the proposed RC array is capable of 3D imaging of a large volume for AI-assisted medical diagnoses with minimal human intervention. Although, as compared to the fully-addressable 2D arrays, the RC arrays can only focus in one dimension in both transmission and reception, leading to lower image resolution and higher sidelobe (reduced image contrast), the proposed RC array is a good compromise and make it feasible for intelligent imaging of a large area such as the abdomen of big patients or pregnant women.