Large-Pitch Methods for 2D/3D Synthetic Transmit Aperture Ultrasound Imaging

This dissertation describes ultrasound algorithms developed on 2D/3D synthetic transmit aperture (STA) imaging. They demonstrate significant reduction in the hardware complexity of the 2D/3D STA ultrasound imaging system while maintaining the reasonable image quality.

A large-pitch synthetic transmit aperture (LPSTA) method integrated with a spatial response function (SRF) was designed in this dissertation. The LPSTA demonstrated the better lateral resolution (+25%), contrast-to-noise ratio (CNR) (+24.6%) and contrast ratio (CR) (+42.3%) than B-mode with the similar hardware complexity. LPSTA with 15-fold reduction in number measurement channels (the product of number of transmission events and the number of digital receive channels) achieved comparable image contrast to the standard STA with a full array at the cost of a reduced field of view.

We extended the LPSTA method to 2D matrix array for 3D imaging, referred to as 3D-LPSTA system. A new Gaussian approximated SRF (G-SRF) was derived and integrated in the image reconstruction process to significantly improve the image contrast. With approximately 1900-fold reduction in number of measurement channels, 3D-LPSTA can provide image contrast at the specific region of interest (ROI) comparable to the standard 3D-STA with a full array and significantly better than a periodically sparse array with similar complexity. In addition to reducing the system complexity, the 3D-LPSTA achieve 700-fold reduction in computational complexity and 523-fold reduction in data storage.

We proposed to combine the LPSTA with micro-beamforming technique to focus in a ROI: focused transmission and focused receiving (XTXR). The proposed XTXR method showed the image quality comparable to the standard STA a full array at the selected ROI. Moreover, the proposed XTXR method demonstrated significantly superior image quality compared to the conventional B-mode imaging with the similar micro-beamforming configuration. Finally, the beam pattern analysis was used to estimate the lateral FOV of XTXR and demonstrated a good agreement with the experimental measurement.

This dissertation investigates all these proposed advanced ultrasound algorithms, with the goal of implementing these methods to extend its application in clinics.