Increasing ultrasound field-of-view with reduced element count arrays containing large elements

Several applications of medical ultrasound can benefit from a larger imaging field of view (FOV). This study is aimed at increasing the FOV of linear array probes by increasing the element size rather than the element count. To investigate larger FOV, this study used coupled elements to imitate a larger element size. The effects of coupling on array beam patterns are examined with Fourier transforms of elements. The effects of coupling on resolution, contrast, and speckle signal-to-noise ratio are examined through phantom images and in-vivo images of a rabbit tumor reconstructed with plane-wave compounding. Furthermore, a positioning system was used to acquire data from a virtual large aperture with 120 mm FOV and 128 elements, collected in sections with a single probe. This study also investigates the Null Subtraction Imaging (NSI), Sign Coherence Factor (SCF), and Minimum Variance (MV) beamformers for regaining resolution lost by an increased F-number with large elements. The MV beamformer, while the most computationally expensive, was best for improving resolution without increasing speckle variance, decreasing Full-Width at Half-Max (FWHM) estimates of wire targets from 0.78 mm with DAS on a 2.5 wavelength element size to 0.54 mm with MV on a 5 wavelength element size.