Increasing Penetration Depth and Field-of-view in 3D Ultrasound Imaging with a Lensed Row-column Array

Row-column (RC) arrays are a promising alternative to conventional matrix arrays for large volumetric imaging due to their fewer electrical connections. However, RC arrays have a restricted field of view. A diverging lens can be used to increase the FOV, but it also causes a decrease in the signal-to-noise ratio (SNR). Previous studies were restricted by using one-element emissions, which have a low SNR. It is hypothesized that using multi-element emission with convex lenses can compensate for the attenuation created by a lens and increase the penetration depth while preserving the FOV. A Vermon RC array with 128+128 elements at 6 MHz and λ pitch was used on the Verasonics Vantage 256 scanner. A single-element emission sequence was used, while 128 orthogonal elements for reception were employed. Also, a multi-element emission method with 2×96 emissions on the rows and columns and acquiring with all orthogonal elements was used. To extend the FOV, two lenses made of polymethylpentene (TPX) and polystyrene (PS) in a convex spherical shape were investigated. The lenses were assessed and compared in terms of Field of View (FOV) and Signal to Noise Ratio (SNR). PS lens had a FOV of about 11.2 degrees, while TPX had a FOV of 9.7 degrees. PS lens had a 5 dB higher SNR in various depths than TPX lenses due to their materials and attenuation coefficients. While maintaining the increased FOV achieved with lenses, multi-element emission sequences increased the penetration depth by around 30 mm and SNR by 25 dB.